//! Phase 273 P3: PlanLowerer - CorePlan → MIR 生成 (SSOT)
//!
//! # Responsibilities
//!
//! - Receive CorePlan from PlanNormalizer
//! - Emit MIR instructions using pre-allocated ValueIds
//! - No pattern-specific knowledge (pattern-agnostic)
//!
//! # Key Design Decision
//!
//! Lowerer processes CorePlan ONLY. It does not know about scan, split, or
//! any other pattern-specific semantics. All pattern knowledge is in Normalizer.
//!
//! # Phase 273 P3: SSOT Finalization
//!
//! - Generalized fields (block_effects/phis/frag/final_values) are now REQUIRED
//! - Legacy fallback has been removed (Fail-Fast on missing fields)
//! - Pattern-specific emission functions (emit_scan_with_init_edgecfg) no longer used

use super::{CoreEffectPlan, CoreLoopPlan, CorePlan};
use crate::mir::builder::control_flow::joinir::patterns::router::LoopPatternContext;
use crate::mir::builder::MirBuilder;
use crate::mir::{MirInstruction, ValueId};

/// Phase 273 P1: PlanLowerer - CorePlan → MIR 生成 (SSOT)
pub(in crate::mir::builder) struct PlanLowerer;

impl PlanLowerer {
    /// CorePlan を受け取り、MIR を生成
    ///
    /// # Arguments
    ///
    /// * `builder` - MIR builder (mutable access for instruction emission)
    /// * `plan` - CorePlan from Normalizer (pre-allocated ValueIds)
    /// * `ctx` - Loop pattern context for debug/func_name
    pub(in crate::mir::builder) fn lower(
        builder: &mut MirBuilder,
        plan: CorePlan,
        ctx: &LoopPatternContext,
    ) -> Result<Option<ValueId>, String> {
        match plan {
            CorePlan::Seq(plans) => Self::lower_seq(builder, plans, ctx),
            CorePlan::Loop(loop_plan) => Self::lower_loop(builder, loop_plan, ctx),
            CorePlan::If(_if_plan) => {
                // P1: If is handled inline in Loop body
                Err("[lowerer] Standalone CorePlan::If not yet supported".to_string())
            }
            CorePlan::Effect(effect) => {
                Self::emit_effect(builder, &effect)?;
                Ok(None)
            }
            CorePlan::Exit(_exit) => {
                // P1: Exit is handled by edge CFG in Loop
                Err("[lowerer] Standalone CorePlan::Exit not yet supported".to_string())
            }
        }
    }

    /// Seq: process plans in order
    fn lower_seq(
        builder: &mut MirBuilder,
        plans: Vec<CorePlan>,
        ctx: &LoopPatternContext,
    ) -> Result<Option<ValueId>, String> {
        let mut result = None;
        for plan in plans {
            result = Self::lower(builder, plan, ctx)?;
        }
        Ok(result)
    }

    /// Loop: emit blocks, effects, PHI, and edge CFG
    ///
    /// This is pattern-agnostic. All pattern knowledge is in Normalizer.
    /// Phase 273 P3: Generalized fields are now REQUIRED (Fail-Fast).
    fn lower_loop(
        builder: &mut MirBuilder,
        loop_plan: CoreLoopPlan,
        ctx: &LoopPatternContext,
    ) -> Result<Option<ValueId>, String> {
        use crate::mir::builder::control_flow::joinir::trace;

        let trace_logger = trace::trace();
        let debug = ctx.debug;

        if debug {
            trace_logger.debug(
                "lowerer/loop",
                &format!(
                    "Phase 273 P3: Lowering CoreLoopPlan for {}",
                    ctx.func_name
                ),
            );
        }

        // Phase 273 P3: Generalized fields are now struct fields (not Option)
        // No validation needed - type system guarantees presence

        if debug {
            trace_logger.debug("lowerer/loop", "Processing generalized fields (SSOT)");
        }

        Self::lower_loop_generalized(builder, loop_plan, ctx)
    }

    /// Phase 273 P3: Generalized loop lowering (SSOT)
    fn lower_loop_generalized(
        builder: &mut MirBuilder,
        loop_plan: CoreLoopPlan,
        ctx: &LoopPatternContext,
    ) -> Result<Option<ValueId>, String> {
        use crate::mir::builder::control_flow::joinir::trace;
        use crate::mir::builder::control_flow::edgecfg::api::emit_frag;

        let trace_logger = trace::trace();
        let debug = ctx.debug;

        // Phase 273 P3: Direct access (not Option - type system guarantees presence)
        let block_effects = &loop_plan.block_effects;
        let phis = &loop_plan.phis;
        let frag = &loop_plan.frag;
        let final_values = &loop_plan.final_values;

        // Step 1: Emit Jump from current block to loop entry
        if builder.current_block.is_some() {
            builder.emit_instruction(MirInstruction::Jump {
                target: frag.entry,
                edge_args: None,
            })?;
        }

        // Step 2: Emit block effects in SSOT order (preheader, header, body, step)
        // Note: Body effects are handled separately via body CorePlan
        for (block_id, effects) in block_effects {
            builder.start_new_block(*block_id)?;

            // Special handling for body block: emit body CorePlan instead of effects
            if *block_id == loop_plan.body_bb {
                for plan in &loop_plan.body {
                    match plan {
                        CorePlan::Effect(effect) => {
                            Self::emit_effect(builder, effect)?;
                        }
                        _ => {
                            return Err("[lowerer] Non-Effect plan in Loop body not yet supported".to_string());
                        }
                    }
                }
            } else {
                // Normal block: emit effects
                for effect in effects {
                    Self::emit_effect(builder, effect)?;
                }
            }
        }

        if debug {
            trace_logger.debug(
                "lowerer/loop_generalized",
                &format!("Block effects emitted: {} blocks", block_effects.len()),
            );
        }

        // Step 3: Ensure non-effect blocks exist (after_bb, found_bb, etc.)
        builder.ensure_block_exists(loop_plan.after_bb)?;
        builder.ensure_block_exists(loop_plan.found_bb)?;

        // Step 4: Insert PHIs
        use crate::mir::builder::emission::phi::insert_loop_phi;

        for phi in phis {
            insert_loop_phi(
                builder,
                phi.block,
                phi.dst,
                phi.inputs.clone(),
                &phi.tag,
            )?;
        }

        if debug {
            trace_logger.debug(
                "lowerer/loop_generalized",
                &format!("PHI inserted: {} PHIs", phis.len()),
            );
        }

        // Step 5: Emit Frag (terminators)
        if let Some(ref mut func) = builder.scope_ctx.current_function {
            emit_frag(func, frag)?;
        } else {
            return Err("[lowerer] current_function is None".to_string());
        }

        if debug {
            trace_logger.debug("lowerer/loop_generalized", "Frag emitted");
        }

        // Step 6: Update variable_map for final values
        for (name, value_id) in final_values {
            builder
                .variable_ctx
                .variable_map
                .insert(name.clone(), *value_id);
        }

        // Step 7: Setup after_bb for subsequent AST lowering
        builder.start_new_block(loop_plan.after_bb)?;

        // Step 8: Return Void (pattern applied successfully)
        use crate::mir::builder::emission::constant::emit_void;
        let void_val = emit_void(builder);

        if debug {
            trace_logger.debug(
                "lowerer/loop_generalized",
                &format!("Loop complete, returning Void {:?}", void_val),
            );
        }

        Ok(Some(void_val))
    }

    // Phase 273 P3: lower_loop_legacy() has been REMOVED
    // All patterns must use generalized fields (block_effects/phis/frag/final_values)
    // Pattern-specific emission functions (emit_scan_with_init_edgecfg) are no longer used

    /// Emit a single CoreEffectPlan as MirInstruction
    fn emit_effect(builder: &mut MirBuilder, effect: &CoreEffectPlan) -> Result<(), String> {
        match effect {
            CoreEffectPlan::Const { dst, value } => {
                builder.emit_instruction(MirInstruction::Const {
                    dst: *dst,
                    value: value.clone(),
                })?;
            }
            CoreEffectPlan::MethodCall { dst, object, method, args, effects } => {
                // P2: dst and effects are now specified by Normalizer
                builder.emit_instruction(MirInstruction::BoxCall {
                    dst: *dst,
                    box_val: *object,
                    method: method.clone(),
                    method_id: None,
                    args: args.clone(),
                    effects: *effects,
                })?;
            }
            CoreEffectPlan::BinOp { dst, lhs, op, rhs } => {
                builder.emit_instruction(MirInstruction::BinOp {
                    dst: *dst,
                    lhs: *lhs,
                    op: *op,
                    rhs: *rhs,
                })?;
            }
            CoreEffectPlan::Compare { dst, lhs, op, rhs } => {
                builder.emit_instruction(MirInstruction::Compare {
                    dst: *dst,
                    lhs: *lhs,
                    op: *op,
                    rhs: *rhs,
                })?;
            }
        }
        Ok(())
    }
}