//! Phase 121: StepTree → JoinModule shadow lowering (if-only)
//!
//! ## Responsibility
//!
//! - Convert StepTree to JoinModule (Normalized dialect)
//! - Only for if-only patterns (no loops)
//! - Returns None for out-of-scope patterns
//! - Returns Err for patterns that should be supported but conversion failed
//!
//! ## Design
//!
//! - Input: `&StepTree` with pre-computed contract
//! - No AST re-analysis (contract-only decisions)
//! - Single responsibility: structure → JoinIR conversion

use crate::mir::control_tree::step_tree::StepTree;
use crate::mir::join_ir::lowering::carrier_info::{ExitMeta, JoinFragmentMeta};
use crate::mir::join_ir::JoinModule;

use super::contracts::{check_if_only, CapabilityCheckResult};

/// Box-First: StepTree → Normalized shadow lowering
pub struct StepTreeNormalizedShadowLowererBox;

impl StepTreeNormalizedShadowLowererBox {
    /// Try to lower an if-only StepTree to normalized form
    ///
    /// ## Returns
    ///
    /// - `Ok(None)`: Out of scope (e.g., contains loops)
    /// - `Ok(Some(...))`: Shadow generation succeeded
    /// - `Err(...)`: Should be supported but conversion failed (internal error)
    ///
    /// ## Contract
    ///
    /// - Only processes if-only patterns (no loops/breaks/continues)
    /// - Uses contract information only (no AST re-analysis)
    /// - Dev-only: caller must check `joinir_dev_enabled()` before calling
    ///
    /// ## Phase 122 Implementation
    ///
    /// - Generates Normalized JoinIR (env + continuation)
    /// - env layout: writes only (SSOT)
    /// - merge = join_k(env) tail-call (no PHI)
    /// - Minimal node support: If/Return/Assign(Const/Variable/BinOp(Add))
    pub fn try_lower_if_only(
        step_tree: &StepTree,
    ) -> Result<Option<(JoinModule, JoinFragmentMeta)>, String> {
        // Phase 121 P1: Capability check (if-only scope)
        let capability = check_if_only(step_tree);
        match capability {
            CapabilityCheckResult::Supported => {
                // Phase 122 P1: Generate Normalized JoinModule
                Self::lower_if_only_to_normalized(step_tree)
                    .map(Some)
            }
            CapabilityCheckResult::Unsupported(_reason) => {
                // Out of scope for Phase 121/122
                Ok(None)
            }
        }
    }

    /// Lower if-only StepTree to Normalized JoinModule (Phase 122-123)
    ///
    /// ## Design
    ///
    /// - env レイアウト: `writes` に含まれる変数だけ（決定的順序）
    /// - merge 形式: `join_k(env)` への tail-call（PHI 禁止）
    /// - 対応ノード: If/Return/Assign(最小セット)
    ///
    /// ## Phase 123 Node Support
    ///
    /// - Return(Integer literal): `Const + Ret(Some(vid))`
    /// - Return(Variable): Fail-Fast (needs reads fact)
    /// - Return(void): `Ret(None)`
    ///
    /// ## Returns
    ///
    /// - `Ok((module, meta))`: Normalized JoinModule生成成功
    /// - `Err(msg)`: 生成できるはずなのに失敗（内部エラー）
    fn lower_if_only_to_normalized(
        step_tree: &StepTree,
    ) -> Result<(JoinModule, JoinFragmentMeta), String> {
        use crate::mir::join_ir::{JoinFunction, JoinFuncId, JoinInst};
        use crate::mir::ValueId;
        use std::collections::BTreeMap;

        // Phase 122: env レイアウト
        let env_fields: Vec<String> = step_tree.contract.writes.iter().cloned().collect();
        let main_func_id = JoinFuncId::new(0);

        // env フィールドに対応する引数ValueIdを生成
        let mut next_value_id = 1;
        let env_params: Vec<ValueId> = env_fields
            .iter()
            .map(|_| {
                let vid = ValueId(next_value_id);
                next_value_id += 1;
                vid
            })
            .collect();

        // main 関数生成
        let mut main_func = JoinFunction::new(
            main_func_id,
            "main".to_string(),
            env_params.clone(),
        );

        // Phase 123: Return node lowering
        Self::lower_return_from_tree(
            &step_tree.root,
            &mut main_func.body,
            &mut next_value_id,
        )?;

        // JoinModule 構築
        let mut module = JoinModule::new();
        module.add_function(main_func);
        module.entry = Some(main_func_id);
        module.mark_normalized();

        // JoinFragmentMeta 生成（最小）
        let meta = JoinFragmentMeta::empty();

        Ok((module, meta))
    }

    /// Phase 123 P1: Lower Return node from StepTree
    ///
    /// ## Support (Phase 123)
    ///
    /// - Return(Integer literal): Generate Const + Ret(Some(vid))
    /// - Return(void): Ret(None)
    /// - Return(other): Fail-Fast with structured error
    fn lower_return_from_tree(
        node: &crate::mir::control_tree::step_tree::StepNode,
        body: &mut Vec<crate::mir::join_ir::JoinInst>,
        next_value_id: &mut u32,
    ) -> Result<(), String> {
        use crate::ast::{ASTNode, LiteralValue};
        use crate::mir::control_tree::step_tree::{StepNode, StepStmtKind};
        use crate::mir::join_ir::JoinInst;
        use crate::mir::ValueId;

        match node {
            StepNode::Block(nodes) => {
                // Find first Return in block (Phase 123 minimal: single return only)
                for n in nodes {
                    if let StepNode::Stmt {
                        kind: StepStmtKind::Return { value_ast },
                        ..
                    } = n
                    {
                        return Self::lower_return_value(value_ast, body, next_value_id);
                    }
                }
                // No return found - default to void
                body.push(JoinInst::Ret { value: None });
                Ok(())
            }
            StepNode::Stmt {
                kind: StepStmtKind::Return { value_ast },
                ..
            } => Self::lower_return_value(value_ast, body, next_value_id),
            _ => {
                // No return in tree - default to void
                body.push(JoinInst::Ret { value: None });
                Ok(())
            }
        }
    }

    /// Phase 123 P1-P2: Lower return value
    ///
    /// ## Support
    ///
    /// - Integer literal: Generate Const + Ret(Some(vid))
    /// - None: Ret(None)
    /// - Variable: Fail-Fast (needs reads fact - Phase 124)
    /// - Other: Fail-Fast (out of scope)
    fn lower_return_value(
        value_ast: &Option<crate::mir::control_tree::step_tree::AstNodeHandle>,
        body: &mut Vec<crate::mir::join_ir::JoinInst>,
        next_value_id: &mut u32,
    ) -> Result<(), String> {
        use crate::ast::{ASTNode, LiteralValue};
        use crate::mir::join_ir::{ConstValue, JoinInst, MirLikeInst};
        use crate::mir::ValueId;

        match value_ast {
            None => {
                body.push(JoinInst::Ret { value: None });
                Ok(())
            }
            Some(ast_handle) => {
                let ast = &ast_handle.0;
                match &**ast {
                    ASTNode::Literal { value, .. } => match value {
                        LiteralValue::Integer(i) => {
                            // Phase 123 P1: Integer literal → Const + Ret(Some(vid))
                            let const_vid = ValueId(*next_value_id);
                            *next_value_id += 1;

                            // Generate Const instruction (wrapped in Compute)
                            body.push(JoinInst::Compute(MirLikeInst::Const {
                                dst: const_vid,
                                value: ConstValue::Integer(*i),
                            }));

                            // Generate Ret instruction
                            body.push(JoinInst::Ret {
                                value: Some(const_vid),
                            });

                            Ok(())
                        }
                        _ => {
                            // Phase 123: Other literals not supported
                            Err(format!(
                                "[phase123/return/literal_unsupported] Phase 123 only supports integer literals. Hint: Use integer literal or wait for Phase 124"
                            ))
                        }
                    },
                    ASTNode::Variable { name, .. } => {
                        // Phase 123 P2: Variable not supported (needs reads fact)
                        Err(format!(
                            "[phase123/return/var_unsupported] Phase 123 only supports return with integer literals (found variable: {}). Hint: Add reads fact (Phase 124) or return literal only",
                            name
                        ))
                    }
                    _ => {
                        // Phase 123: Other expressions not supported
                        Err(format!(
                            "[phase123/return/expr_unsupported] Phase 123 only supports integer literals. Hint: Simplify to literal or wait for Phase 124"
                        ))
                    }
                }
            }
        }
    }

    /// Get shadow lowering status string for dev logging
    ///
    /// ## Contract
    ///
    /// - Returns 1-line summary: "shadow_lowered=true/false reason=..."
    /// - Does not perform actual lowering (use `try_lower_if_only` for that)
    pub fn get_status_string(step_tree: &StepTree) -> String {
        let capability = check_if_only(step_tree);
        match capability {
            CapabilityCheckResult::Supported => {
                format!(
                    "shadow_lowered=true step_tree_sig={} exits={:?} writes={:?}",
                    step_tree.signature_basis_string(),
                    step_tree.contract.exits,
                    step_tree.contract.writes
                )
            }
            CapabilityCheckResult::Unsupported(reason) => {
                format!(
                    "shadow_lowered=false reason=\"{}\" step_tree_sig={}",
                    reason.reason(),
                    step_tree.signature_basis_string()
                )
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::mir::control_tree::step_tree::{
        StepNode, StepStmtKind, StepTreeFeatures, StepTreeSignature,
    };
    use crate::mir::control_tree::step_tree_contract_box::StepTreeContract;

    fn make_if_only_tree() -> StepTree {
        StepTree {
            root: StepNode::Block(vec![]),
            features: StepTreeFeatures {
                has_if: true,
                has_loop: false,
                has_break: false,
                has_continue: false,
                has_return: false,
                max_if_depth: 1,
                max_loop_depth: 0,
            },
            contract: StepTreeContract {
                exits: Default::default(),
                writes: Default::default(),
                required_caps: Default::default(),
                cond_sig: Default::default(),
            },
            signature: StepTreeSignature(0),
        }
    }

    fn make_loop_tree() -> StepTree {
        StepTree {
            root: StepNode::Block(vec![]),
            features: StepTreeFeatures {
                has_if: false,
                has_loop: true,
                has_break: false,
                has_continue: false,
                has_return: false,
                max_if_depth: 0,
                max_loop_depth: 1,
            },
            contract: StepTreeContract {
                exits: Default::default(),
                writes: Default::default(),
                required_caps: Default::default(),
                cond_sig: Default::default(),
            },
            signature: StepTreeSignature(0),
        }
    }

    #[test]
    fn test_if_only_supported() {
        let tree = make_if_only_tree();
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_ok());
        assert!(result.unwrap().is_some());
    }

    #[test]
    fn test_loop_rejected() {
        let tree = make_loop_tree();
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_ok());
        assert!(result.unwrap().is_none());
    }

    #[test]
    fn test_status_string_if_only() {
        let tree = make_if_only_tree();
        let status = StepTreeNormalizedShadowLowererBox::get_status_string(&tree);
        assert!(status.contains("shadow_lowered=true"));
        assert!(status.contains("step_tree_sig="));
    }

    #[test]
    fn test_status_string_loop() {
        let tree = make_loop_tree();
        let status = StepTreeNormalizedShadowLowererBox::get_status_string(&tree);
        assert!(status.contains("shadow_lowered=false"));
        assert!(status.contains("reason=\"contains loop"));
    }

    #[test]
    fn test_return_integer_literal() {
        use crate::ast::{ASTNode, LiteralValue, Span};
        use crate::mir::control_tree::step_tree::AstNodeHandle;

        // Create StepTree with "return 7"
        let return_ast = Box::new(ASTNode::Literal {
            value: LiteralValue::Integer(7),
            span: Span::unknown(),
        });

        let mut tree = make_if_only_tree();
        tree.root = StepNode::Stmt {
            kind: StepStmtKind::Return {
                value_ast: Some(AstNodeHandle(return_ast)),
            },
            span: Span::unknown(),
        };

        // Lower to JoinModule
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_ok());

        let (module, _meta) = result.unwrap().expect("Should generate JoinModule");

        // Verify Const + Ret instructions
        assert_eq!(module.functions.len(), 1);
        let func = &module.functions.values().next().unwrap();
        assert_eq!(func.body.len(), 2, "Should have Const + Ret");

        // Check Const instruction
        use crate::mir::join_ir::{ConstValue, JoinInst, MirLikeInst};
        use crate::mir::ValueId;
        if let JoinInst::Compute(MirLikeInst::Const { dst, value }) = &func.body[0] {
            assert_eq!(*dst, ValueId(1));
            if let ConstValue::Integer(i) = value {
                assert_eq!(*i, 7);
            } else {
                panic!("Expected Integer const");
            }
        } else {
            panic!("Expected Const instruction");
        }

        // Check Ret instruction
        if let JoinInst::Ret { value } = &func.body[1] {
            assert_eq!(value, &Some(ValueId(1)));
        } else {
            panic!("Expected Ret instruction");
        }
    }

    #[test]
    fn test_return_void() {
        use crate::ast::Span;

        // Create StepTree with "return" (no value)
        let mut tree = make_if_only_tree();
        tree.root = StepNode::Stmt {
            kind: StepStmtKind::Return { value_ast: None },
            span: Span::unknown(),
        };

        // Lower to JoinModule
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_ok());

        let (module, _meta) = result.unwrap().expect("Should generate JoinModule");

        // Verify Ret(None) instruction
        assert_eq!(module.functions.len(), 1);
        let func = &module.functions.values().next().unwrap();
        assert_eq!(func.body.len(), 1, "Should have only Ret");

        // Check Ret instruction
        use crate::mir::join_ir::JoinInst;
        if let JoinInst::Ret { value } = &func.body[0] {
            assert_eq!(value, &None);
        } else {
            panic!("Expected Ret instruction");
        }
    }

    #[test]
    fn test_return_variable_fails() {
        use crate::ast::{ASTNode, Span};
        use crate::mir::control_tree::step_tree::AstNodeHandle;

        // Create StepTree with "return x" (variable)
        let return_ast = Box::new(ASTNode::Variable {
            name: "x".to_string(),
            span: Span::unknown(),
        });

        let mut tree = make_if_only_tree();
        tree.root = StepNode::Stmt {
            kind: StepStmtKind::Return {
                value_ast: Some(AstNodeHandle(return_ast)),
            },
            span: Span::unknown(),
        };

        // Lower to JoinModule - should fail
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_err());

        let err = result.unwrap_err();
        assert!(err.contains("phase123/return/var_unsupported"));
        assert!(err.contains("Phase 124"));
    }
}