/*!
 * Minimal MIR Interpreter
 *
 * Executes a subset of MIR instructions for fast iteration without LLVM/JIT.
 * Supported: Const, BinOp(Add/Sub/Mul/Div/Mod), Compare, Load/Store, Branch, Jump, Return,
 * Print/Debug (best-effort), Barrier/Safepoint (no-op).
 */

use std::collections::HashMap;

use crate::box_trait::NyashBox;

pub(super) use crate::backend::abi_util::{eq_vm, to_bool_vm};
pub(super) use crate::backend::vm::{VMError, VMValue};
pub(super) use crate::mir::{
    BasicBlockId, BinaryOp, Callee, CompareOp, ConstValue, MirFunction, MirInstruction, MirModule,
    ValueId,
};

mod exec;
mod handlers;
mod helpers;
mod method_router;
mod utils;

pub struct MirInterpreter {
    pub(super) regs: HashMap<ValueId, VMValue>,
    pub(super) mem: HashMap<ValueId, VMValue>,
    // Object field storage keyed by stable object identity (Arc ptr addr fallback)
    pub(super) obj_fields: HashMap<u64, HashMap<String, VMValue>>,
    pub(super) functions: HashMap<String, MirFunction>,
    pub(super) cur_fn: Option<String>,
    // Trace context (dev-only; enabled with NYASH_VM_TRACE=1)
    pub(super) last_block: Option<BasicBlockId>,
    pub(super) last_inst: Option<MirInstruction>,
    // Static box singleton instances (persistent across method calls)
    pub(super) static_boxes: HashMap<String, crate::instance_v2::InstanceBox>,
    // Static box declarations (metadata for creating instances)
    pub(super) static_box_decls: HashMap<String, crate::core::model::BoxDeclaration>,
}

impl MirInterpreter {
    pub fn new() -> Self {
        Self {
            regs: HashMap::new(),
            mem: HashMap::new(),
            obj_fields: HashMap::new(),
            functions: HashMap::new(),
            cur_fn: None,
            last_block: None,
            last_inst: None,
            static_boxes: HashMap::new(),
            static_box_decls: HashMap::new(),
        }
    }

    /// Register static box declarations (called from vm.rs during setup)
    pub fn register_static_box_decl(&mut self, name: String, decl: crate::core::model::BoxDeclaration) {
        self.static_box_decls.insert(name, decl);
    }

    /// Ensure static box singleton instance exists, create if not
    /// Returns mutable reference to the singleton instance
    fn ensure_static_box_instance(&mut self, box_name: &str) -> Result<&mut crate::instance_v2::InstanceBox, VMError> {
        // Check if instance already exists
        if !self.static_boxes.contains_key(box_name) {
            // Get declaration
            let decl = self.static_box_decls.get(box_name)
                .ok_or_else(|| VMError::InvalidInstruction(
                    format!("static box declaration not found: {}", box_name)
                ))?
                .clone();

            // Create instance from declaration
            let instance = crate::instance_v2::InstanceBox::from_declaration(
                box_name.to_string(),
                decl.fields.clone(),
                decl.methods.clone(),
            );

            self.static_boxes.insert(box_name.to_string(), instance);

            if std::env::var("NYASH_VM_STATIC_TRACE").ok().as_deref() == Some("1") {
                eprintln!("[vm-static] created singleton instance for static box: {}", box_name);
            }
        }

        // Return mutable reference
        self.static_boxes.get_mut(box_name)
            .ok_or_else(|| VMError::InvalidInstruction(
                format!("static box instance not found after creation: {}", box_name)
            ))
    }

    /// Check if a function name represents a static box method
    /// Format: "BoxName.method/Arity"
    fn is_static_box_method(&self, func_name: &str) -> Option<String> {
        if let Some((box_name, _rest)) = func_name.split_once('.') {
            if self.static_box_decls.contains_key(box_name) {
                return Some(box_name.to_string());
            }
        }
        None
    }

    /// Execute module entry (main) and return boxed result
    pub fn execute_module(&mut self, module: &MirModule) -> Result<Box<dyn NyashBox>, VMError> {
        // Snapshot functions for call resolution
        self.functions = module.functions.clone();
        let func = module
            .functions
            .get("main")
            .ok_or_else(|| VMError::InvalidInstruction("missing main".into()))?;
        let ret = self.execute_function(func)?;
        Ok(ret.to_nyash_box())
    }

    fn execute_function(&mut self, func: &MirFunction) -> Result<VMValue, VMError> {
        self.exec_function_inner(func, None)
    }
}