//! 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)
    ///
    /// ## 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)
    ///
    /// ## 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 P1: 最小実装 - main関数1つ + Ret のみ
        // env レイアウト: writes から決定的に決める
        let env_fields: Vec<String> = step_tree.contract.writes.iter().cloned().collect();

        // 関数ID生成（Phase 122では固定ID使用）
        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（最小: Ret のみ）
        let mut main_func = JoinFunction::new(
            main_func_id,
            "main".to_string(),
            env_params.clone(),
        );

        // Phase 122 P1: 最小実装 - Return void のみ
        // TODO Phase 122 P2-P4: If/Assign/条件式の lowering 実装
        main_func.body.push(JoinInst::Ret { value: None });

        // 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))
    }

    /// 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, 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"));
    }
}