/*!
 * MIR Builder - Converts AST to MIR/SSA form
 * 
 * Implements AST → MIR conversion with SSA construction
 */

use super::{
    MirInstruction, BasicBlock, BasicBlockId, MirFunction, MirModule, 
    FunctionSignature, ValueId, ConstValue, BinaryOp, UnaryOp, CompareOp,
    MirType, EffectMask, Effect, BasicBlockIdGenerator, ValueIdGenerator
};
use crate::ast::{ASTNode, LiteralValue, BinaryOperator};
use std::collections::HashMap;
use std::collections::HashSet;

fn builder_debug_enabled() -> bool {
    std::env::var("NYASH_BUILDER_DEBUG").is_ok()
}

fn builder_debug_log(msg: &str) {
    if builder_debug_enabled() {
        eprintln!("[BUILDER] {}", msg);
    }
}

/// MIR builder for converting AST to SSA form
pub struct MirBuilder {
    /// Current module being built
    pub(super) current_module: Option<MirModule>,
    
    /// Current function being built
    pub(super) current_function: Option<MirFunction>,
    
    /// Current basic block being built
    pub(super) current_block: Option<BasicBlockId>,
    
    /// Value ID generator
    pub(super) value_gen: ValueIdGenerator,
    
    /// Basic block ID generator
    pub(super) block_gen: BasicBlockIdGenerator,
    
    /// Variable name to ValueId mapping (for SSA conversion)
    pub(super) variable_map: HashMap<String, ValueId>,
    
    /// Pending phi functions to be inserted
    #[allow(dead_code)]
    pub(super) pending_phis: Vec<(BasicBlockId, ValueId, String)>,

    /// Origin tracking for simple optimizations (e.g., object.method after new)
    /// Maps a ValueId to the class name if it was produced by NewBox of that class
    pub(super) value_origin_newbox: HashMap<ValueId, String>,

    /// Names of user-defined boxes declared in the current module
    pub(super) user_defined_boxes: HashSet<String>,

    /// Weak field registry: BoxName -> {weak field names}
    pub(super) weak_fields_by_box: HashMap<String, HashSet<String>>,

    /// Remember class of object fields after assignments: (base_id, field) -> class_name
    pub(super) field_origin_class: HashMap<(ValueId, String), String>,
}

impl MirBuilder {
    /// Create a new MIR builder
    pub fn new() -> Self {
        Self {
            current_module: None,
            current_function: None,
            current_block: None,
            value_gen: ValueIdGenerator::new(),
            block_gen: BasicBlockIdGenerator::new(),
            variable_map: HashMap::new(),
            pending_phis: Vec::new(),
            value_origin_newbox: HashMap::new(),
            user_defined_boxes: HashSet::new(),
            weak_fields_by_box: HashMap::new(),
            field_origin_class: HashMap::new(),
        }
    }

    /// Emit a type check instruction (flagged to TypeOp in PoC)
    #[allow(dead_code)]
    pub(super) fn emit_type_check(&mut self, value: ValueId, expected_type: String) -> Result<ValueId, String> {
        let dst = self.value_gen.next();
        #[cfg(feature = "mir_typeop_poc")]
        {
            self.emit_instruction(MirInstruction::TypeOp { dst, op: super::TypeOpKind::Check, value, ty: super::MirType::Box(expected_type) })?;
            return Ok(dst);
        }
        #[cfg(not(feature = "mir_typeop_poc"))]
        {
            self.emit_instruction(MirInstruction::TypeCheck { dst, value, expected_type })?;
            Ok(dst)
        }
    }

    /// Emit a cast instruction (flagged to TypeOp in PoC)
    #[allow(dead_code)]
    pub(super) fn emit_cast(&mut self, value: ValueId, target_type: super::MirType) -> Result<ValueId, String> {
        let dst = self.value_gen.next();
        #[cfg(feature = "mir_typeop_poc")]
        {
            self.emit_instruction(MirInstruction::TypeOp { dst, op: super::TypeOpKind::Cast, value, ty: target_type.clone() })?;
            return Ok(dst);
        }
        #[cfg(not(feature = "mir_typeop_poc"))]
        {
            self.emit_instruction(MirInstruction::Cast { dst, value, target_type })?;
            Ok(dst)
        }
    }

    /// Emit a weak reference creation (flagged to WeakRef(New) in PoC)
    #[allow(dead_code)]
    pub(super) fn emit_weak_new(&mut self, box_val: ValueId) -> Result<ValueId, String> {
        let dst = self.value_gen.next();
        #[cfg(feature = "mir_refbarrier_unify_poc")]
        {
            self.emit_instruction(MirInstruction::WeakRef { dst, op: super::WeakRefOp::New, value: box_val })?;
            return Ok(dst);
        }
        #[cfg(not(feature = "mir_refbarrier_unify_poc"))]
        {
            self.emit_instruction(MirInstruction::WeakNew { dst, box_val })?;
            Ok(dst)
        }
    }

    /// Emit a weak reference load (flagged to WeakRef(Load) in PoC)
    #[allow(dead_code)]
    pub(super) fn emit_weak_load(&mut self, weak_ref: ValueId) -> Result<ValueId, String> {
        let dst = self.value_gen.next();
        #[cfg(feature = "mir_refbarrier_unify_poc")]
        {
            self.emit_instruction(MirInstruction::WeakRef { dst, op: super::WeakRefOp::Load, value: weak_ref })?;
            return Ok(dst);
        }
        #[cfg(not(feature = "mir_refbarrier_unify_poc"))]
        {
            self.emit_instruction(MirInstruction::WeakLoad { dst, weak_ref })?;
            Ok(dst)
        }
    }

    /// Emit a barrier read (flagged to Barrier(Read) in PoC)
    #[allow(dead_code)]
    pub(super) fn emit_barrier_read(&mut self, ptr: ValueId) -> Result<(), String> {
        #[cfg(feature = "mir_refbarrier_unify_poc")]
        {
            self.emit_instruction(MirInstruction::Barrier { op: super::BarrierOp::Read, ptr })
        }
        #[cfg(not(feature = "mir_refbarrier_unify_poc"))]
        {
            self.emit_instruction(MirInstruction::BarrierRead { ptr })
        }
    }

    /// Emit a barrier write (flagged to Barrier(Write) in PoC)
    #[allow(dead_code)]
    pub(super) fn emit_barrier_write(&mut self, ptr: ValueId) -> Result<(), String> {
        #[cfg(feature = "mir_refbarrier_unify_poc")]
        {
            self.emit_instruction(MirInstruction::Barrier { op: super::BarrierOp::Write, ptr })
        }
        #[cfg(not(feature = "mir_refbarrier_unify_poc"))]
        {
            self.emit_instruction(MirInstruction::BarrierWrite { ptr })
        }
    }

    /// Lower a box method (e.g., birth) into a standalone MIR function
    /// func_name: Fully-qualified name like "Person.birth/1"
    /// box_name: Owning box type name (used for 'me' param type)
    fn lower_method_as_function(
        &mut self,
        func_name: String,
        box_name: String,
        params: Vec<String>,
        body: Vec<ASTNode>,
    ) -> Result<(), String> {
        // Prepare function signature: (me: Box(box_name), args: Unknown...)-> Void
        let mut param_types = Vec::new();
        param_types.push(MirType::Box(box_name.clone())); // me
        for _ in &params {
            param_types.push(MirType::Unknown);
        }
        // Lightweight return type inference: if there is an explicit `return <expr>`
        // in the top-level body, mark return type as Unknown; otherwise Void.
        let mut returns_value = false;
        for st in &body {
            if let ASTNode::Return { value: Some(_), .. } = st { returns_value = true; break; }
        }
        let ret_ty = if returns_value { MirType::Unknown } else { MirType::Void };

        let signature = FunctionSignature {
            name: func_name,
            params: param_types,
            return_type: ret_ty,
            effects: EffectMask::READ.add(Effect::ReadHeap), // conservative
        };
        let entry = self.block_gen.next();
        let function = MirFunction::new(signature, entry);

        // Save current builder state
        let saved_function = self.current_function.take();
        let saved_block = self.current_block.take();
        let saved_var_map = std::mem::take(&mut self.variable_map);
        let saved_value_gen = self.value_gen.clone();
        // Reset value id generator so that params start from %0, %1, ...
        self.value_gen.reset();

        // Switch context to new function
        self.current_function = Some(function);
        self.current_block = Some(entry);
        self.ensure_block_exists(entry)?;

        // Create parameter value ids and bind variable names
        if let Some(ref mut f) = self.current_function {
            // 'me' parameter will be %0
            let me_id = self.value_gen.next();
            f.params.push(me_id);
            self.variable_map.insert("me".to_string(), me_id);
            // Record origin: 'me' belongs to this box type (enables weak field wiring)
            self.value_origin_newbox.insert(me_id, box_name.clone());
            // user parameters continue as %1..N
            for p in &params {
                let pid = self.value_gen.next();
                f.params.push(pid);
                self.variable_map.insert(p.clone(), pid);
            }
        }

        // Lower body as a Program block
        let program_ast = ASTNode::Program { statements: body, span: crate::ast::Span::unknown() };
        let _last = self.build_expression(program_ast)?;

        // Ensure function is properly terminated
        if let Some(ref mut f) = self.current_function {
            if let Some(block) = f.get_block(self.current_block.unwrap()) {
                if !block.is_terminated() {
                    let void_val = self.value_gen.next();
                    self.emit_instruction(MirInstruction::Const { dst: void_val, value: ConstValue::Void })?;
                    self.emit_instruction(MirInstruction::Return { value: Some(void_val) })?;
                }
            }
        }

        // Take the function out and add to module
        let finalized_function = self.current_function.take().unwrap();
        if let Some(ref mut module) = self.current_module {
            module.add_function(finalized_function);
        }

        // Restore builder state
        self.current_function = saved_function;
        self.current_block = saved_block;
        self.variable_map = saved_var_map;
        self.value_gen = saved_value_gen;

        Ok(())
    }
    
    /// Build a complete MIR module from AST
    pub fn build_module(&mut self, ast: ASTNode) -> Result<MirModule, String> {
        // Create a new module
        let module = MirModule::new("main".to_string());
        
        // Create a main function to contain the AST
        let main_signature = FunctionSignature {
            name: "main".to_string(),
            params: vec![],
            return_type: MirType::Void,
            effects: EffectMask::PURE,
        };
        
        let entry_block = self.block_gen.next();
        let mut main_function = MirFunction::new(main_signature, entry_block);
        main_function.metadata.is_entry_point = true;
        
        // Set up building context
        self.current_module = Some(module);
        self.current_function = Some(main_function);
        self.current_block = Some(entry_block);
        
        // Add safepoint at function entry
        self.emit_instruction(MirInstruction::Safepoint)?;
        
        // Convert AST to MIR
        let result_value = self.build_expression(ast)?;
        
        // Add return instruction if needed
        if let Some(block_id) = self.current_block {
            if let Some(ref mut function) = self.current_function {
                if let Some(block) = function.get_block_mut(block_id) {
                    if !block.is_terminated() {
                        block.add_instruction(MirInstruction::Return {
                            value: Some(result_value),
                        });
                    }
                }
            }
        }
        
        // Finalize and return module
        let mut module = self.current_module.take().unwrap();
        let function = self.current_function.take().unwrap();
        module.add_function(function);
        
        Ok(module)
    }
    
    /// Build an expression and return its value ID
    pub(super) fn build_expression(&mut self, ast: ASTNode) -> Result<ValueId, String> {
        match ast {
            ASTNode::Literal { value, .. } => {
                self.build_literal(value)
            },
            
            ASTNode::BinaryOp { left, operator, right, .. } => {
                self.build_binary_op(*left, operator, *right)
            },
            
            ASTNode::UnaryOp { operator, operand, .. } => {
                let op_string = match operator {
                    crate::ast::UnaryOperator::Minus => "-".to_string(),
                    crate::ast::UnaryOperator::Not => "not".to_string(),
                };
                self.build_unary_op(op_string, *operand)
            },
            
            ASTNode::Variable { name, .. } => {
                self.build_variable_access(name.clone())
            },
            
            ASTNode::Me { .. } => {
                self.build_me_expression()
            },
            
            ASTNode::MethodCall { object, method, arguments, .. } => {
                // Early TypeOp lowering for method-style is()/as()
                if (method == "is" || method == "as") && arguments.len() == 1 {
                    if let Some(type_name) = Self::extract_string_literal(&arguments[0]) {
                        let obj_val = self.build_expression(*object.clone())?;
                        let ty = Self::parse_type_name_to_mir(&type_name);
                        let dst = self.value_gen.next();
                        let op = if method == "is" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                        self.emit_instruction(MirInstruction::TypeOp { dst, op, value: obj_val, ty })?;
                        return Ok(dst);
                    }
                }
                self.build_method_call(*object.clone(), method.clone(), arguments.clone())
            },
            
            ASTNode::FromCall { parent, method, arguments, .. } => {
                self.build_from_expression(parent.clone(), method.clone(), arguments.clone())
            },
            
            ASTNode::Assignment { target, value, .. } => {
                // Check if target is a field access for RefSet
                if let ASTNode::FieldAccess { object, field, .. } = target.as_ref() {
                    self.build_field_assignment(*object.clone(), field.clone(), *value.clone())
                } else if let ASTNode::Variable { name, .. } = target.as_ref() {
                    // Plain variable assignment - existing behavior
                    self.build_assignment(name.clone(), *value.clone())
                } else {
                    Err("Complex assignment targets not yet supported in MIR".to_string())
                }
            },
            
            ASTNode::FunctionCall { name, arguments, .. } => {
                // Early TypeOp lowering for function-style isType()/asType()
                if (name == "isType" || name == "asType") && arguments.len() == 2 {
                    if let Some(type_name) = Self::extract_string_literal(&arguments[1]) {
                        let val = self.build_expression(arguments[0].clone())?;
                        let ty = Self::parse_type_name_to_mir(&type_name);
                        let dst = self.value_gen.next();
                        let op = if name == "isType" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                        self.emit_instruction(MirInstruction::TypeOp { dst, op, value: val, ty })?;
                        return Ok(dst);
                    }
                }
                self.build_function_call(name.clone(), arguments.clone())
            },
            
            ASTNode::Print { expression, .. } => {
                self.build_print_statement(*expression.clone())
            },
            
            ASTNode::Program { statements, .. } => {
                self.build_block(statements.clone())
            },
            
            ASTNode::If { condition, then_body, else_body, .. } => {
                let else_ast = if let Some(else_statements) = else_body {
                    Some(ASTNode::Program {
                        statements: else_statements.clone(),
                        span: crate::ast::Span::unknown(),
                    })
                } else {
                    None
                };
                
                self.build_if_statement(
                    *condition.clone(), 
                    ASTNode::Program {
                        statements: then_body.clone(),
                        span: crate::ast::Span::unknown(),
                    },
                    else_ast
                )
            },
            
            ASTNode::Loop { condition, body, .. } => {
                self.build_loop_statement(*condition.clone(), body.clone())
            },
            
            ASTNode::TryCatch { try_body, catch_clauses, finally_body, .. } => {
                self.build_try_catch_statement(try_body.clone(), catch_clauses.clone(), finally_body.clone())
            },
            
            ASTNode::Throw { expression, .. } => {
                self.build_throw_statement(*expression.clone())
            },
            
            ASTNode::Return { value, .. } => {
                self.build_return_statement(value.clone())
            },
            
            ASTNode::Local { variables, initial_values, .. } => {
                self.build_local_statement(variables.clone(), initial_values.clone())
            },
            
            ASTNode::BoxDeclaration { name, methods, is_static, fields, constructors, weak_fields, .. } => {
                if is_static && name == "Main" {
                    self.build_static_main_box(methods.clone())
                } else {
                    // Support user-defined boxes - handle as statement, return void
                    // Track as user-defined (eligible for method lowering)
                    self.user_defined_boxes.insert(name.clone());
                    self.build_box_declaration(name.clone(), methods.clone(), fields.clone(), weak_fields.clone())?;

                    // Phase 2: Lower constructors (birth/N) into MIR functions
                    // Function name pattern: "{BoxName}.{constructor_key}" (e.g., "Person.birth/1")
                    for (ctor_key, ctor_ast) in constructors.clone() {
                        if let ASTNode::FunctionDeclaration { params, body, .. } = ctor_ast {
                            let func_name = format!("{}.{}", name, ctor_key);
                            self.lower_method_as_function(func_name, name.clone(), params.clone(), body.clone())?;
                        }
                    }

                    // Phase 3: Lower instance methods into MIR functions
                    // Function name pattern: "{BoxName}.{method}/{N}"
                    for (method_name, method_ast) in methods.clone() {
                        if let ASTNode::FunctionDeclaration { params, body, is_static, .. } = method_ast {
                            if !is_static {
                                let func_name = format!("{}.{}{}", name, method_name, format!("/{}", params.len()));
                                self.lower_method_as_function(func_name, name.clone(), params.clone(), body.clone())?;
                            }
                        }
                    }
                    
                    // Return a void value since this is a statement
                    let void_val = self.value_gen.next();
                    self.emit_instruction(MirInstruction::Const {
                        dst: void_val,
                        value: ConstValue::Void,
                    })?;
                    Ok(void_val)
                }
            },
            
            ASTNode::FieldAccess { object, field, .. } => {
                self.build_field_access(*object.clone(), field.clone())
            },
            
            ASTNode::New { class, arguments, .. } => {
                self.build_new_expression(class.clone(), arguments.clone())
            },
            
            // Phase 7: Async operations
            ASTNode::Nowait { variable, expression, .. } => {
                self.build_nowait_statement(variable.clone(), *expression.clone())
            },
            
            ASTNode::AwaitExpression { expression, .. } => {
                self.build_await_expression(*expression.clone())
            },
            
            _ => {
                Err(format!("Unsupported AST node type: {:?}", ast))
            }
        }
    }
    
    /// Build a literal value
    fn build_literal(&mut self, literal: LiteralValue) -> Result<ValueId, String> {
        let const_value = match literal {
            LiteralValue::Integer(n) => ConstValue::Integer(n),
            LiteralValue::Float(f) => ConstValue::Float(f),
            LiteralValue::String(s) => ConstValue::String(s),
            LiteralValue::Bool(b) => ConstValue::Bool(b),
            LiteralValue::Null => ConstValue::Null,
            LiteralValue::Void => ConstValue::Void,
        };
        
        let dst = self.value_gen.next();
        self.emit_instruction(MirInstruction::Const {
            dst,
            value: const_value,
        })?;
        
        Ok(dst)
    }
    
    /// Build a binary operation
    fn build_binary_op(&mut self, left: ASTNode, operator: BinaryOperator, right: ASTNode) -> Result<ValueId, String> {
        let lhs = self.build_expression(left)?;
        let rhs = self.build_expression(right)?;
        let dst = self.value_gen.next();
        
        let mir_op = self.convert_binary_operator(operator)?;
        
        match mir_op {
            // Arithmetic operations
            BinaryOpType::Arithmetic(op) => {
                self.emit_instruction(MirInstruction::BinOp {
                    dst, op, lhs, rhs
                })?;
            },
            
            // Comparison operations
            BinaryOpType::Comparison(op) => {
                self.emit_instruction(MirInstruction::Compare {
                    dst, op, lhs, rhs
                })?;
            },
        }
        
        Ok(dst)
    }
    
    /// Build a unary operation
    fn build_unary_op(&mut self, operator: String, operand: ASTNode) -> Result<ValueId, String> {
        let operand_val = self.build_expression(operand)?;
        let dst = self.value_gen.next();
        
        let mir_op = self.convert_unary_operator(operator)?;
        
        self.emit_instruction(MirInstruction::UnaryOp {
            dst,
            op: mir_op,
            operand: operand_val,
        })?;
        
        Ok(dst)
    }
    
    /// Build variable access
    fn build_variable_access(&mut self, name: String) -> Result<ValueId, String> {
        if let Some(&value_id) = self.variable_map.get(&name) {
            Ok(value_id)
        } else {
            Err(format!("Undefined variable: {}", name))
        }
    }
    
    /// Build assignment
    fn build_assignment(&mut self, var_name: String, value: ASTNode) -> Result<ValueId, String> {
        let value_id = self.build_expression(value)?;
        
        // In SSA form, each assignment creates a new value
        self.variable_map.insert(var_name.clone(), value_id);
        
        Ok(value_id)
    }
    
    /// Build function call
    fn build_function_call(&mut self, name: String, args: Vec<ASTNode>) -> Result<ValueId, String> {
        // Minimal TypeOp wiring via function-style: isType(value, "Type"), asType(value, "Type")
        if (name == "isType" || name == "asType") && args.len() == 2 {
            if let Some(type_name) = Self::extract_string_literal(&args[1]) {
                let val = self.build_expression(args[0].clone())?;
                let ty = Self::parse_type_name_to_mir(&type_name);
                let dst = self.value_gen.next();
                let op = if name == "isType" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                self.emit_instruction(MirInstruction::TypeOp { dst, op, value: val, ty })?;
                return Ok(dst);
            }
        }
        // Build argument values
        let mut arg_values = Vec::new();
        for arg in args {
            arg_values.push(self.build_expression(arg)?);
        }
        
        let dst = self.value_gen.next();
        
        // For now, treat all function calls as Box method calls
        if arg_values.is_empty() {
            return Err("Function calls require at least one argument (the object)".to_string());
        }
        
        let box_val = arg_values.remove(0);
        
        self.emit_instruction(MirInstruction::BoxCall {
            dst: Some(dst),
            box_val,
            method: name,
            args: arg_values,
            effects: EffectMask::PURE.add(Effect::ReadHeap), // Conservative default
        })?;
        
        Ok(dst)
    }
    
    /// Build print statement - converts to console output
    fn build_print_statement(&mut self, expression: ASTNode) -> Result<ValueId, String> {
        builder_debug_log("enter build_print_statement");
        // 根治: print(isType(...)) / print(asType(...)) / print(obj.is(...)) / print(obj.as(...)) は必ずTypeOpを先に生成してからprintする
        match &expression {
            ASTNode::FunctionCall { name, arguments, .. } if (name == "isType" || name == "asType") && arguments.len() == 2 => {
                builder_debug_log("pattern: print(FunctionCall isType|asType)");
                if let Some(type_name) = Self::extract_string_literal(&arguments[1]) {
                    builder_debug_log(&format!("extract_string_literal OK: {}", type_name));
                    let val = self.build_expression(arguments[0].clone())?;
                    let ty = Self::parse_type_name_to_mir(&type_name);
                    let dst = self.value_gen.next();
                    let op = if name == "isType" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                    builder_debug_log(&format!("emit TypeOp {:?} value={} dst= {}", op, val, dst));
                    self.emit_instruction(MirInstruction::TypeOp { dst, op, value: val, ty })?;
                    self.emit_instruction(MirInstruction::Print { value: dst, effects: EffectMask::PURE.add(Effect::Io) })?;
                    return Ok(dst);
                } else {
                    builder_debug_log("extract_string_literal FAIL");
                }
            }
            ASTNode::MethodCall { object, method, arguments, .. } if (method == "is" || method == "as") && arguments.len() == 1 => {
                builder_debug_log("pattern: print(MethodCall is|as)");
                if let Some(type_name) = Self::extract_string_literal(&arguments[0]) {
                    builder_debug_log(&format!("extract_string_literal OK: {}", type_name));
                    let obj_val = self.build_expression(*object.clone())?;
                    let ty = Self::parse_type_name_to_mir(&type_name);
                    let dst = self.value_gen.next();
                    let op = if method == "is" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                    builder_debug_log(&format!("emit TypeOp {:?} obj={} dst= {}", op, obj_val, dst));
                    self.emit_instruction(MirInstruction::TypeOp { dst, op, value: obj_val, ty })?;
                    self.emit_instruction(MirInstruction::Print { value: dst, effects: EffectMask::PURE.add(Effect::Io) })?;
                    return Ok(dst);
                } else {
                    builder_debug_log("extract_string_literal FAIL");
                }
            }
            _ => {}
        }

        let value = self.build_expression(expression)?;
        builder_debug_log(&format!("fallback print value={}", value));
        
        // For now, use a special Print instruction (minimal scope)
        self.emit_instruction(MirInstruction::Print {
            value,
            effects: EffectMask::PURE.add(Effect::Io),
        })?;
        
        // Return the value that was printed
        Ok(value)
    }
    
    /// Build a block of statements
    fn build_block(&mut self, statements: Vec<ASTNode>) -> Result<ValueId, String> {
        let mut last_value = None;
        
        for statement in statements {
            last_value = Some(self.build_expression(statement)?);
        }
        
        // Return last value or void
        Ok(last_value.unwrap_or_else(|| {
            let void_val = self.value_gen.next();
            self.emit_instruction(MirInstruction::Const {
                dst: void_val,
                value: ConstValue::Void,
            }).unwrap();
            void_val
        }))
    }
    
    /// Build if statement with conditional branches
    fn build_if_statement(&mut self, condition: ASTNode, then_branch: ASTNode, else_branch: Option<ASTNode>) -> Result<ValueId, String> {
        let condition_val = self.build_expression(condition)?;
        
        // Create basic blocks for then/else/merge
        let then_block = self.block_gen.next();
        let else_block = self.block_gen.next();
        let merge_block = self.block_gen.next();
        
        // Emit branch instruction in current block
        self.emit_instruction(MirInstruction::Branch {
            condition: condition_val,
            then_bb: then_block,
            else_bb: else_block,
        })?;
        
        // Build then branch
        self.current_block = Some(then_block);
        self.ensure_block_exists(then_block)?;
        // Keep a copy of AST for analysis (phi for variable reassignment)
        let then_ast_for_analysis = then_branch.clone();
        let then_value = self.build_expression(then_branch)?;
        if !self.is_current_block_terminated() {
            self.emit_instruction(MirInstruction::Jump { target: merge_block })?;
        }
        
        // Build else branch
        self.current_block = Some(else_block);
        self.ensure_block_exists(else_block)?;
        let (else_value, else_ast_for_analysis) = if let Some(else_ast) = else_branch {
            let val = self.build_expression(else_ast.clone())?;
            (val, Some(else_ast))
        } else {
            // No else branch, use void
            let void_val = self.value_gen.next();
            self.emit_instruction(MirInstruction::Const {
                dst: void_val,
                value: ConstValue::Void,
            })?;
            (void_val, None)
        };
        if !self.is_current_block_terminated() {
            self.emit_instruction(MirInstruction::Jump { target: merge_block })?;
        }
        
        // Create merge block with phi function
        self.current_block = Some(merge_block);
        self.ensure_block_exists(merge_block)?;
        let result_val = self.value_gen.next();
        
        self.emit_instruction(MirInstruction::Phi {
            dst: result_val,
            inputs: vec![
                (then_block, then_value),
                (else_block, else_value),
            ],
        })?;

        // Heuristic: If both branches assign the same variable name, bind that variable to the phi result
        let assigned_var_then = Self::extract_assigned_var(&then_ast_for_analysis);
        let assigned_var_else = else_ast_for_analysis.as_ref().and_then(|a| Self::extract_assigned_var(a));
        if let (Some(a), Some(b)) = (assigned_var_then, assigned_var_else) {
            if a == b {
                self.variable_map.insert(a, result_val);
            }
        }

        Ok(result_val)
    }

    /// Extract assigned variable name from an AST node if it represents an assignment to a variable.
    /// Handles direct Assignment and Program with trailing single-statement Assignment.
    fn extract_assigned_var(ast: &ASTNode) -> Option<String> {
        match ast {
            ASTNode::Assignment { target, .. } => {
                if let ASTNode::Variable { name, .. } = target.as_ref() { Some(name.clone()) } else { None }
            }
            ASTNode::Program { statements, .. } => {
                // Inspect the last statement as the resulting value of the block
                statements.last().and_then(|st| Self::extract_assigned_var(st))
            }
            _ => None,
        }
    }
    
    /// Emit an instruction to the current basic block
    pub(super) fn emit_instruction(&mut self, instruction: MirInstruction) -> Result<(), String> {
        let block_id = self.current_block.ok_or("No current basic block")?;
        
        if let Some(ref mut function) = self.current_function {
            if let Some(block) = function.get_block_mut(block_id) {
                if builder_debug_enabled() {
                    eprintln!("[BUILDER] emit @bb{} -> {}", block_id, match &instruction {
                        MirInstruction::TypeOp { dst, op, value, ty } => format!("typeop {:?} {} {:?} -> {}", op, value, ty, dst),
                        MirInstruction::Print { value, .. } => format!("print {}", value),
                        MirInstruction::BoxCall { box_val, method, args, dst, .. } => format!("boxcall {}.{}({:?}) -> {:?}", box_val, method, args, dst),
                        MirInstruction::Call { func, args, dst, .. } => format!("call {}({:?}) -> {:?}", func, args, dst),
                        MirInstruction::NewBox { dst, box_type, args } => format!("new {}({:?}) -> {}", box_type, args, dst),
                        MirInstruction::Const { dst, value } => format!("const {:?} -> {}", value, dst),
                        MirInstruction::Branch { condition, then_bb, else_bb } => format!("br {}, {}, {}", condition, then_bb, else_bb),
                        MirInstruction::Jump { target } => format!("br {}", target),
                        _ => format!("{:?}", instruction),
                    });
                }
                block.add_instruction(instruction);
                Ok(())
            } else {
                Err(format!("Basic block {} does not exist", block_id))
            }
        } else {
            Err("No current function".to_string())
        }
    }
    
    /// Ensure a basic block exists in the current function
    pub(super) fn ensure_block_exists(&mut self, block_id: BasicBlockId) -> Result<(), String> {
        if let Some(ref mut function) = self.current_function {
            if !function.blocks.contains_key(&block_id) {
                let block = BasicBlock::new(block_id);
                function.add_block(block);
            }
            Ok(())
        } else {
            Err("No current function".to_string())
        }
    }
    
    /// Build a loop statement: loop(condition) { body }
    fn build_loop_statement(&mut self, condition: ASTNode, body: Vec<ASTNode>) -> Result<ValueId, String> {
        // Use the specialized LoopBuilder for proper SSA loop construction
        let mut loop_builder = super::loop_builder::LoopBuilder::new(self);
        loop_builder.build_loop(condition, body)
    }
    
    /// Build a try/catch statement
    fn build_try_catch_statement(&mut self, try_body: Vec<ASTNode>, catch_clauses: Vec<crate::ast::CatchClause>, finally_body: Option<Vec<ASTNode>>) -> Result<ValueId, String> {
        let try_block = self.block_gen.next();
        let catch_block = self.block_gen.next();
        let finally_block = if finally_body.is_some() { Some(self.block_gen.next()) } else { None };
        let exit_block = self.block_gen.next();
        
        // Set up exception handler for the try block (before we enter it)
        if let Some(catch_clause) = catch_clauses.first() {
            let exception_value = self.value_gen.next();
            
            // Register catch handler for exceptions that may occur in try block
            self.emit_instruction(MirInstruction::Catch {
                exception_type: catch_clause.exception_type.clone(),
                exception_value,
                handler_bb: catch_block,
            })?;
        }
        
        // Jump to try block
        self.emit_instruction(MirInstruction::Jump { target: try_block })?;
        
        // Build try block
        self.start_new_block(try_block)?;
        
        let try_ast = ASTNode::Program {
            statements: try_body,
            span: crate::ast::Span::unknown(),
        };
        let _try_result = self.build_expression(try_ast)?;
        
        // Normal completion of try block - jump to finally or exit (if not already terminated)
        if !self.is_current_block_terminated() {
            let next_target = finally_block.unwrap_or(exit_block);
            self.emit_instruction(MirInstruction::Jump { target: next_target })?;
        }
        
        // Build catch block (reachable via exception handling)
        self.start_new_block(catch_block)?;
        
        // Handle catch clause
        if let Some(catch_clause) = catch_clauses.first() {
            // Build catch body
            let catch_ast = ASTNode::Program {
                statements: catch_clause.body.clone(),
                span: crate::ast::Span::unknown(),
            };
            self.build_expression(catch_ast)?;
        }
        
        // Catch completion - jump to finally or exit (if not already terminated)
        if !self.is_current_block_terminated() {
            let next_target = finally_block.unwrap_or(exit_block);
            self.emit_instruction(MirInstruction::Jump { target: next_target })?;
        }
        
        // Build finally block if present
        if let (Some(finally_block_id), Some(finally_statements)) = (finally_block, finally_body) {
            self.start_new_block(finally_block_id)?;
            
            let finally_ast = ASTNode::Program {
                statements: finally_statements,
                span: crate::ast::Span::unknown(),
            };
            self.build_expression(finally_ast)?;
            
            self.emit_instruction(MirInstruction::Jump { target: exit_block })?;
        }
        
        // Create exit block
        self.start_new_block(exit_block)?;
        
        // Return void for now (in a complete implementation, would use phi for try/catch values)
        let result = self.value_gen.next();
        self.emit_instruction(MirInstruction::Const {
            dst: result,
            value: ConstValue::Void,
        })?;
        
        Ok(result)
    }
    
    /// Build a throw statement
    fn build_throw_statement(&mut self, expression: ASTNode) -> Result<ValueId, String> {
        let exception_value = self.build_expression(expression)?;
        
        // Emit throw instruction with PANIC effect (this is a terminator)
        self.emit_instruction(MirInstruction::Throw {
            exception: exception_value,
            effects: EffectMask::PANIC,
        })?;
        
        // Throw doesn't return normally, but we need to return a value for the type system
        // We can't add more instructions after throw, so just return the exception value
        Ok(exception_value)
    }
    
    /// Build local variable declarations with optional initial values
    fn build_local_statement(&mut self, variables: Vec<String>, initial_values: Vec<Option<Box<ASTNode>>>) -> Result<ValueId, String> {
        let mut last_value = None;
        
        // Process each variable declaration
        for (i, var_name) in variables.iter().enumerate() {
            let value_id = if i < initial_values.len() && initial_values[i].is_some() {
                // Variable has initial value - evaluate it
                let init_expr = initial_values[i].as_ref().unwrap();
                self.build_expression(*init_expr.clone())?
            } else {
                // No initial value - do not emit a const; leave uninitialized until assigned
                // Use a fresh SSA id only for name binding; consumers should not use it before assignment
                self.value_gen.next()
            };
            
            // Register variable in SSA form
            self.variable_map.insert(var_name.clone(), value_id);
            last_value = Some(value_id);
        }
        
        // Return the last bound value id (no emission); callers shouldn't rely on this value
        Ok(last_value.unwrap_or_else(|| {
            // create a dummy id without emission
            self.value_gen.next()
        }))
    }
    
    /// Build return statement
    fn build_return_statement(&mut self, value: Option<Box<ASTNode>>) -> Result<ValueId, String> {
        let return_value = if let Some(expr) = value {
            self.build_expression(*expr)?
        } else {
            // Return void if no value specified
            let void_dst = self.value_gen.next();
            self.emit_instruction(MirInstruction::Const {
                dst: void_dst,
                value: ConstValue::Void,
            })?;
            void_dst
        };
        
        // Emit return instruction
        self.emit_instruction(MirInstruction::Return {
            value: Some(return_value),
        })?;
        
        Ok(return_value)
    }
    
    /// Build static box Main - extracts main() method body and converts to Program
    fn build_static_main_box(&mut self, methods: std::collections::HashMap<String, ASTNode>) -> Result<ValueId, String> {
        // Look for the main() method
        if let Some(main_method) = methods.get("main") {
            if let ASTNode::FunctionDeclaration { body, .. } = main_method {
                // Convert the method body to a Program AST node and lower it
                let program_ast = ASTNode::Program {
                    statements: body.clone(),
                    span: crate::ast::Span::unknown(),
                };
                
                // Use existing Program lowering logic
                self.build_expression(program_ast)
            } else {
                Err("main method in static box Main is not a FunctionDeclaration".to_string())
            }
        } else {
            Err("static box Main must contain a main() method".to_string())
        }
    }
    
    /// Build field access: object.field
    fn build_field_access(&mut self, object: ASTNode, field: String) -> Result<ValueId, String> {
        // Clone the object before building expression if we need to check it later
        let object_clone = object.clone();
        
        // First, build the object expression to get its ValueId
        let object_value = self.build_expression(object)?;

        // Get the field from the object using RefGet
        let field_val = self.value_gen.next();
        self.emit_instruction(MirInstruction::RefGet {
            dst: field_val,
            reference: object_value,
            field: field.clone(),
        })?;

        // If we recorded origin class for this field on this base object, propagate it to this value id
        if let Some(class_name) = self.field_origin_class.get(&(object_value, field.clone())).cloned() {
            self.value_origin_newbox.insert(field_val, class_name);
        }

        // If we can infer the box type and the field is weak, emit WeakLoad (+ optional barrier)
        let mut inferred_class: Option<String> = self.value_origin_newbox.get(&object_value).cloned();
        // Fallback: if the object is a nested field access like (X.Y).Z, consult recorded field origins for X.Y
        if inferred_class.is_none() {
            if let ASTNode::FieldAccess { object: inner_obj, field: ref parent_field, .. } = object_clone {
                // Build inner base to get a stable id and consult mapping
                if let Ok(base_id) = self.build_expression(*inner_obj.clone()) {
                    if let Some(cls) = self.field_origin_class.get(&(base_id, parent_field.clone())) {
                        inferred_class = Some(cls.clone());
                    }
                }
            }
        }
        if let Some(class_name) = inferred_class {
            if let Some(weak_set) = self.weak_fields_by_box.get(&class_name) {
                if weak_set.contains(&field) {
                    // Barrier (read) PoC
                    let _ = self.emit_barrier_read(field_val);
                    // WeakLoad
                    let loaded = self.emit_weak_load(field_val)?;
                    return Ok(loaded);
                }
            }
        }

        Ok(field_val)
    }
    
    /// Build new expression: new ClassName(arguments)
    fn build_new_expression(&mut self, class: String, arguments: Vec<ASTNode>) -> Result<ValueId, String> {
        // Phase 9.78a: Unified Box creation using NewBox instruction
        
        // First, evaluate all arguments to get their ValueIds
        let mut arg_values = Vec::new();
        for arg in arguments {
            let arg_value = self.build_expression(arg)?;
            arg_values.push(arg_value);
        }
        
        // Generate the destination ValueId
        let dst = self.value_gen.next();
        
        // Emit NewBox instruction for all Box types
        // VM will handle optimization for basic types internally
        self.emit_instruction(MirInstruction::NewBox {
            dst,
            box_type: class.clone(),
            args: arg_values.clone(),
        })?;

        // Record origin for optimization: dst was created by NewBox of class
        self.value_origin_newbox.insert(dst, class);

        // Immediately call birth(...) on the created instance to run constructor semantics.
        // birth typically returns void; we don't capture the result here (dst: None)
        self.emit_instruction(MirInstruction::BoxCall {
            dst: None,
            box_val: dst,
            method: "birth".to_string(),
            args: arg_values,
            effects: EffectMask::READ.add(Effect::ReadHeap),
        })?;
        
        Ok(dst)
    }
    
    /// Build field assignment: object.field = value
    fn build_field_assignment(&mut self, object: ASTNode, field: String, value: ASTNode) -> Result<ValueId, String> {
        // Build the object and value expressions
        let object_value = self.build_expression(object)?;
        let mut value_result = self.build_expression(value)?;

        // If we can infer the box type and the field is weak, create WeakRef before store
        if let Some(class_name) = self.value_origin_newbox.get(&object_value).cloned() {
            if let Some(weak_set) = self.weak_fields_by_box.get(&class_name) {
                if weak_set.contains(&field) {
                    value_result = self.emit_weak_new(value_result)?;
                }
            }
        }

        // Set the field using RefSet
        self.emit_instruction(MirInstruction::RefSet {
            reference: object_value,
            field: field.clone(),
            value: value_result,
        })?;

        // Emit a write barrier for weak fields (PoC)
        if let Some(class_name) = self.value_origin_newbox.get(&object_value).cloned() {
            if let Some(weak_set) = self.weak_fields_by_box.get(&class_name) {
                if weak_set.contains(&field) {
                    let _ = self.emit_barrier_write(value_result);
                }
            }
        }

        // Record origin class for this field (if the value originates from NewBox of a known class)
        if let Some(class_name) = self.value_origin_newbox.get(&value_result).cloned() {
            self.field_origin_class.insert((object_value, field.clone()), class_name);
        }

        // Return the assigned value
        Ok(value_result)
    }
    
    /// Start a new basic block
    pub(super) fn start_new_block(&mut self, block_id: BasicBlockId) -> Result<(), String> {
        if let Some(ref mut function) = self.current_function {
            function.add_block(BasicBlock::new(block_id));
            self.current_block = Some(block_id);
            Ok(())
        } else {
            Err("No current function".to_string())
        }
    }
    
    /// Check if the current basic block is terminated
    fn is_current_block_terminated(&self) -> bool {
        if let (Some(block_id), Some(ref function)) = (self.current_block, &self.current_function) {
            if let Some(block) = function.get_block(block_id) {
                return block.is_terminated();
            }
        }
        false
    }
    
    /// Convert AST binary operator to MIR operator
    fn convert_binary_operator(&self, op: BinaryOperator) -> Result<BinaryOpType, String> {
        match op {
            BinaryOperator::Add => Ok(BinaryOpType::Arithmetic(BinaryOp::Add)),
            BinaryOperator::Subtract => Ok(BinaryOpType::Arithmetic(BinaryOp::Sub)),
            BinaryOperator::Multiply => Ok(BinaryOpType::Arithmetic(BinaryOp::Mul)),
            BinaryOperator::Divide => Ok(BinaryOpType::Arithmetic(BinaryOp::Div)),
            BinaryOperator::Modulo => Ok(BinaryOpType::Arithmetic(BinaryOp::Mod)),
            BinaryOperator::Equal => Ok(BinaryOpType::Comparison(CompareOp::Eq)),
            BinaryOperator::NotEqual => Ok(BinaryOpType::Comparison(CompareOp::Ne)),
            BinaryOperator::Less => Ok(BinaryOpType::Comparison(CompareOp::Lt)),
            BinaryOperator::LessEqual => Ok(BinaryOpType::Comparison(CompareOp::Le)),
            BinaryOperator::Greater => Ok(BinaryOpType::Comparison(CompareOp::Gt)),
            BinaryOperator::GreaterEqual => Ok(BinaryOpType::Comparison(CompareOp::Ge)),
            BinaryOperator::And => Ok(BinaryOpType::Arithmetic(BinaryOp::And)),
            BinaryOperator::Or => Ok(BinaryOpType::Arithmetic(BinaryOp::Or)),
        }
    }
    
    /// Convert AST unary operator to MIR operator
    fn convert_unary_operator(&self, op: String) -> Result<UnaryOp, String> {
        match op.as_str() {
            "-" => Ok(UnaryOp::Neg),
            "!" | "not" => Ok(UnaryOp::Not),
            "~" => Ok(UnaryOp::BitNot),
            _ => Err(format!("Unsupported unary operator: {}", op)),
        }
    }
    
    /// Build nowait statement: nowait variable = expression
    fn build_nowait_statement(&mut self, variable: String, expression: ASTNode) -> Result<ValueId, String> {
        // Evaluate the expression
        let expression_value = self.build_expression(expression)?;
        
        // Create a new Future with the evaluated expression as the initial value
        let future_id = self.value_gen.next();
        self.emit_instruction(MirInstruction::FutureNew {
            dst: future_id,
            value: expression_value,
        })?;
        
        // Store the future in the variable
        self.variable_map.insert(variable.clone(), future_id);
        
        Ok(future_id)
    }
    
    /// Build await expression: await expression
    fn build_await_expression(&mut self, expression: ASTNode) -> Result<ValueId, String> {
        // Evaluate the expression (should be a Future)
        let future_value = self.build_expression(expression)?;
        
        // Create destination for await result
        let result_id = self.value_gen.next();
        
        // Emit await instruction
        self.emit_instruction(MirInstruction::Await {
            dst: result_id,
            future: future_value,
        })?;
        
        Ok(result_id)
    }
    
    /// Build me expression: me
    fn build_me_expression(&mut self) -> Result<ValueId, String> {
        // If lowering a method/birth function, "me" should be a parameter
        if let Some(id) = self.variable_map.get("me").cloned() {
            return Ok(id);
        }

        // Fallback: use a symbolic constant (legacy behavior)
        let me_value = self.value_gen.next();
        self.emit_instruction(MirInstruction::Const {
            dst: me_value,
            value: ConstValue::String("__me__".to_string()),
        })?;
        // Register a stable mapping so subsequent 'me' resolves to the same ValueId
        self.variable_map.insert("me".to_string(), me_value);
        Ok(me_value)
    }
    
    /// Build method call: object.method(arguments)
    fn build_method_call(&mut self, object: ASTNode, method: String, arguments: Vec<ASTNode>) -> Result<ValueId, String> {
        // Minimal TypeOp wiring via method-style syntax: value.is("Type") / value.as("Type")
        if (method == "is" || method == "as") && arguments.len() == 1 {
            if let Some(type_name) = Self::extract_string_literal(&arguments[0]) {
                // Build the object expression
                let object_value = self.build_expression(object.clone())?;
                // Map string to MIR type
                let mir_ty = Self::parse_type_name_to_mir(&type_name);
                let dst = self.value_gen.next();
                let op = if method == "is" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                self.emit_instruction(MirInstruction::TypeOp { dst, op, value: object_value, ty: mir_ty })?;
                return Ok(dst);
            }
        }
        // ExternCall判定はobjectの変数解決より先に行う（未定義変数で落とさない）
        if let ASTNode::Variable { name: object_name, .. } = object.clone() {
            // Build argument expressions first (externはobject自体を使わない)
            let mut arg_values = Vec::new();
            for arg in &arguments {
                arg_values.push(self.build_expression(arg.clone())?);
            }
            match (object_name.as_str(), method.as_str()) {
                ("console", "log") => {
                    self.emit_instruction(MirInstruction::ExternCall {
                        dst: None,
                        iface_name: "env.console".to_string(),
                        method_name: "log".to_string(),
                        args: arg_values,
                        effects: EffectMask::IO,
                    })?;
                    let void_id = self.value_gen.next();
                    self.emit_instruction(MirInstruction::Const { dst: void_id, value: ConstValue::Void })?;
                    return Ok(void_id);
                },
                ("canvas", "fillRect") | ("canvas", "fillText") => {
                    self.emit_instruction(MirInstruction::ExternCall {
                        dst: None,
                        iface_name: "env.canvas".to_string(),
                        method_name: method,
                        args: arg_values,
                        effects: EffectMask::IO,
                    })?;
                    let void_id = self.value_gen.next();
                    self.emit_instruction(MirInstruction::Const { dst: void_id, value: ConstValue::Void })?;
                    return Ok(void_id);
                },
                _ => {}
            }
        }

        // Build the object expression
        let object_value = self.build_expression(object.clone())?;

        // Secondary interception for is/as in case early path did not trigger
        if (method == "is" || method == "as") && arguments.len() == 1 {
            if let Some(type_name) = Self::extract_string_literal(&arguments[0]) {
                let mir_ty = Self::parse_type_name_to_mir(&type_name);
                let dst = self.value_gen.next();
                let op = if method == "is" { super::TypeOpKind::Check } else { super::TypeOpKind::Cast };
                self.emit_instruction(MirInstruction::TypeOp { dst, op, value: object_value, ty: mir_ty })?;
                return Ok(dst);
            }
        }

        // Build argument expressions
        let mut arg_values = Vec::new();
        for arg in &arguments {
            arg_values.push(self.build_expression(arg.clone())?);
        }

        // Create result value
        let result_id = self.value_gen.next();
        
        // Optimization: If the object is a direct `new ClassName(...)`, lower to a direct Call
        if let ASTNode::New { class, .. } = object {
            // Build function name and only lower to Call if the function exists (user-defined)
            let func_name = format!("{}.{}{}", class, method, format!("/{}", arg_values.len()));
            let can_lower = self.user_defined_boxes.contains(&class)
                && if let Some(ref module) = self.current_module { module.functions.contains_key(&func_name) } else { false };
            if can_lower {
                let func_val = self.value_gen.next();
                self.emit_instruction(MirInstruction::Const { dst: func_val, value: ConstValue::String(func_name) })?;
                let mut call_args = Vec::with_capacity(arg_values.len() + 1);
                call_args.push(object_value);
                call_args.extend(arg_values);
                self.emit_instruction(MirInstruction::Call {
                    dst: Some(result_id),
                    func: func_val,
                    args: call_args,
                    effects: EffectMask::READ.add(Effect::ReadHeap),
                })?;
                return Ok(result_id);
            }
            // else fall through to BoxCall below
        } else {
            // If the object originates from a NewBox in this function, we can lower to Call as well
            if let Some(class_name) = self.value_origin_newbox.get(&object_value).cloned() {
                let func_name = format!("{}.{}{}", class_name, method, format!("/{}", arg_values.len()));
                let can_lower = self.user_defined_boxes.contains(&class_name)
                    && if let Some(ref module) = self.current_module { module.functions.contains_key(&func_name) } else { false };
                if can_lower {
                    let func_val = self.value_gen.next();
                    self.emit_instruction(MirInstruction::Const { dst: func_val, value: ConstValue::String(func_name) })?;
                    let mut call_args = Vec::with_capacity(arg_values.len() + 1);
                    call_args.push(object_value);
                    call_args.extend(arg_values);
                    self.emit_instruction(MirInstruction::Call {
                        dst: Some(result_id),
                        func: func_val,
                        args: call_args,
                        effects: EffectMask::READ.add(Effect::ReadHeap),
                    })?;
                    return Ok(result_id);
                }
            }
        }

        // Fallback: Emit a BoxCall instruction for regular or plugin/builtin method calls
        self.emit_instruction(MirInstruction::BoxCall {
            dst: Some(result_id),
            box_val: object_value,
            method,
            args: arg_values,
            effects: EffectMask::READ.add(Effect::ReadHeap), // Method calls may have side effects
        })?;
        Ok(result_id)
    }

    /// Map a user-facing type name to MIR type
    fn parse_type_name_to_mir(name: &str) -> super::MirType {
        match name {
            "Integer" | "Int" | "I64" => super::MirType::Integer,
            "Float" | "F64" => super::MirType::Float,
            "Bool" | "Boolean" => super::MirType::Bool,
            "String" => super::MirType::String,
            "Void" | "Unit" => super::MirType::Void,
            other => super::MirType::Box(other.to_string()),
        }
    }
    
    /// Extract string literal from AST node if possible
    /// Supports: Literal("Type") and new StringBox("Type")
    fn extract_string_literal(node: &ASTNode) -> Option<String> {
        let mut cur = node;
        loop {
            match cur {
                ASTNode::Literal { value: crate::ast::LiteralValue::String(s), .. } => return Some(s.clone()),
                ASTNode::New { class, arguments, .. } if class == "StringBox" && arguments.len() == 1 => {
                    cur = &arguments[0];
                    continue;
                }
                _ => return None,
            }
        }
    }
    
    /// Build from expression: from Parent.method(arguments)
    fn build_from_expression(&mut self, parent: String, method: String, arguments: Vec<ASTNode>) -> Result<ValueId, String> {
        // Build argument expressions
        let mut arg_values = Vec::new();
        for arg in arguments {
            arg_values.push(self.build_expression(arg)?);
        }
        
        // Create a synthetic "parent reference" value
        let parent_value = self.value_gen.next();
        self.emit_instruction(MirInstruction::Const {
            dst: parent_value,
            value: ConstValue::String(parent),
        })?;
        
        // Create result value
        let result_id = self.value_gen.next();
        
        // Emit a BoxCall instruction for delegation
        self.emit_instruction(MirInstruction::BoxCall {
            dst: Some(result_id),
            box_val: parent_value,
            method,
            args: arg_values,
            effects: EffectMask::READ.add(Effect::ReadHeap),
        })?;
        
        Ok(result_id)
    }
    
    /// Build box declaration: box Name { fields... methods... }
    fn build_box_declaration(&mut self, name: String, methods: std::collections::HashMap<String, ASTNode>, fields: Vec<String>, weak_fields: Vec<String>) -> Result<(), String> {
        // For Phase 8.4, we'll emit metadata instructions to register the box type
        // In a full implementation, this would register type information for later use
        
        // Create a type registration constant
        let type_id = self.value_gen.next();
        self.emit_instruction(MirInstruction::Const {
            dst: type_id,
            value: ConstValue::String(format!("__box_type_{}", name)),
        })?;
        
        // For each field, emit metadata about the field
        for field in fields {
            let field_id = self.value_gen.next();
            self.emit_instruction(MirInstruction::Const {
                dst: field_id,
                value: ConstValue::String(format!("__field_{}_{}", name, field)),
            })?;
        }

        // Record weak fields for this box
        if !weak_fields.is_empty() {
            let set: HashSet<String> = weak_fields.into_iter().collect();
            self.weak_fields_by_box.insert(name.clone(), set);
        }
        
        // Process methods - now methods is a HashMap
        for (method_name, method_ast) in methods {
            if let ASTNode::FunctionDeclaration { .. } = method_ast {
                let method_id = self.value_gen.next();
                self.emit_instruction(MirInstruction::Const {
                    dst: method_id,
                    value: ConstValue::String(format!("__method_{}_{}", name, method_name)),
                })?;
            }
        }
        
        Ok(())
    }
}

/// Helper enum for binary operator classification
#[derive(Debug)]
enum BinaryOpType {
    Arithmetic(BinaryOp),
    Comparison(CompareOp),
}

impl Default for MirBuilder {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::ast::{ASTNode, LiteralValue, Span};
    
    #[test]
    fn test_literal_building() {
        let mut builder = MirBuilder::new();
        
        let ast = ASTNode::Literal {
            value: LiteralValue::Integer(42),
            span: Span::unknown(),
        };
        
        let result = builder.build_module(ast);
        assert!(result.is_ok());
        
        let module = result.unwrap();
        assert_eq!(module.function_names().len(), 1);
        assert!(module.get_function("main").is_some());
    }
    
    #[test]
    fn test_binary_op_building() {
        let mut builder = MirBuilder::new();
        
        let ast = ASTNode::BinaryOp {
            left: Box::new(ASTNode::Literal {
                value: LiteralValue::Integer(10),
                span: Span::unknown(),
            }),
            operator: BinaryOperator::Add,
            right: Box::new(ASTNode::Literal {
                value: LiteralValue::Integer(32),
                span: Span::unknown(),
            }),
            span: Span::unknown(),
        };
        
        let result = builder.build_module(ast);
        assert!(result.is_ok());
        
        let module = result.unwrap();
        let function = module.get_function("main").unwrap();
        
        // Should have constants and binary operation
        let stats = function.stats();
        assert!(stats.instruction_count >= 3); // 2 constants + 1 binop + 1 return
    }
    
    #[test]
    fn test_if_statement_building() {
        let mut builder = MirBuilder::new();
        
        // Adapt test to current AST: If with statement bodies
        let ast = ASTNode::If {
            condition: Box::new(ASTNode::Literal {
                value: LiteralValue::Bool(true),
                span: Span::unknown(),
            }),
            then_body: vec![ASTNode::Literal {
                value: LiteralValue::Integer(1),
                span: Span::unknown(),
            }],
            else_body: Some(vec![ASTNode::Literal {
                value: LiteralValue::Integer(2),
                span: Span::unknown(),
            }]),
            span: Span::unknown(),
        };
        
        let result = builder.build_module(ast);
        assert!(result.is_ok());
        
        let module = result.unwrap();
        let function = module.get_function("main").unwrap();
        
        // Should have multiple blocks for if/then/else/merge
        assert!(function.blocks.len() >= 3);
        
        // Should have phi function in merge block
        let stats = function.stats();
        assert!(stats.phi_count >= 1);
    }
}