//! JoinIR MIR Block Merging Coordinator
//!
//! This module coordinates the merging of JoinIR-generated MIR functions
//! into the host MIR builder. The process is broken into 6 phases:
//!
//! 1. Block ID allocation (block_allocator.rs)
//! 2. Value collection (value_collector.rs)
//! 3. ValueId remapping (uses JoinIrIdRemapper)
//! 4. Instruction rewriting (instruction_rewriter.rs)
//! 5. Exit PHI construction (exit_phi_builder.rs)
//! 6. Boundary reconnection (inline in this file)
//!
//! Phase 4 Refactoring: Breaking down 714-line merge_joinir_mir_blocks() into focused modules

mod block_allocator;
mod value_collector;
mod instruction_rewriter;
mod exit_phi_builder;
pub mod exit_line;
pub mod loop_header_phi_builder;

use crate::mir::{BasicBlockId, MirModule, ValueId};
use crate::mir::join_ir::lowering::inline_boundary::JoinInlineBoundary;

/// Phase 49-3.2: Merge JoinIR-generated MIR blocks into current_function
///
/// # Phase 189: Multi-Function MIR Merge
///
/// This merges JoinIR-generated blocks by:
/// 1. Remapping all block IDs across ALL functions to avoid conflicts
/// 2. Remapping all value IDs across ALL functions to avoid conflicts
/// 3. Adding all blocks from all functions to current_function
/// 4. Jumping from current_block to the entry block
/// 5. Converting Return → Jump to exit block for all functions
///
/// **Multi-Function Support** (Phase 189):
/// - Pattern 1 (Simple While) generates 3 functions: entry + loop_step + k_exit
/// - All functions are flattened into current_function with global ID remapping
/// - Single exit block receives all Return instructions from all functions
///
/// # Phase 188-Impl-3: JoinInlineBoundary Support
///
/// When `boundary` is provided, injects Copy instructions at the entry block
/// to connect host ValueIds to JoinIR local ValueIds:
///
/// ```text
/// entry_block:
///   // Injected by boundary
///   ValueId(100) = Copy ValueId(4)  // join_input → host_input
///   // Original JoinIR instructions follow...
/// ```
///
/// This enables clean separation: JoinIR uses local IDs (0,1,2...),
/// host uses its own IDs, and Copy instructions bridge the gap.
///
/// # Returns
///
/// Returns `Ok(Some(exit_phi_id))` if the merged JoinIR functions have return values
/// that were collected into an exit block PHI. さらに、`boundary` に
/// host_outputs が指定されている場合は、exit PHI の結果をホスト側の
/// SSA スロットへ再接続する（variable_map 内の ValueId を更新する）。
pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
    builder: &mut crate::mir::builder::MirBuilder,
    mir_module: &MirModule,
    boundary: Option<&JoinInlineBoundary>,
    debug: bool,
) -> Result<Option<ValueId>, String> {
    if debug {
        eprintln!(
            "[cf_loop/joinir] merge_joinir_mir_blocks called with {} functions",
            mir_module.functions.len()
        );
    }

    // Phase 1: Allocate block IDs for all functions
    let mut remapper = block_allocator::allocate_blocks(builder, mir_module, debug)?;

    // Phase 2: Collect values from all functions
    let (mut used_values, value_to_func_name, function_params) =
        value_collector::collect_values(mir_module, &remapper, debug)?;

    // Phase 171-fix: Add condition_bindings' join_values to used_values for remapping
    if let Some(boundary) = boundary {
        for binding in &boundary.condition_bindings {
            if debug {
                eprintln!(
                    "[cf_loop/joinir] Phase 171-fix: Adding condition binding '{}' JoinIR {:?} to used_values",
                    binding.name, binding.join_value
                );
            }
            used_values.insert(binding.join_value);
        }

        // Phase 172-3: Add exit_bindings' join_exit_values to used_values for remapping
        for binding in &boundary.exit_bindings {
            if debug {
                eprintln!(
                    "[cf_loop/joinir] Phase 172-3: Adding exit binding '{}' JoinIR {:?} to used_values",
                    binding.carrier_name, binding.join_exit_value
                );
            }
            used_values.insert(binding.join_exit_value);
        }
    }

    // Phase 3: Remap ValueIds
    remap_values(builder, &used_values, &mut remapper, debug)?;

    // Phase 3.5: Build loop header PHIs (if loop pattern with loop_var_name)
    //
    // We need to know PHI dsts before instruction_rewriter runs, so that:
    // 1. Tail call handling can set latch_incoming
    // 2. Return handling can use PHI dsts for exit values
    let (entry_func_name, entry_func) = mir_module
        .functions
        .iter()
        .next()
        .ok_or("JoinIR module has no functions (Phase 3.5)")?;
    let entry_block_remapped = remapper
        .get_block(entry_func_name, entry_func.entry_block)
        .ok_or_else(|| format!("Entry block not found for {} (Phase 3.5)", entry_func_name))?;

    // Phase 33-16: Get host's current block as the entry edge (the block that jumps INTO the loop)
    let host_entry_block = builder.current_block.ok_or(
        "Phase 33-16: No current block when building header PHIs"
    )?;

    let mut loop_header_phi_info = if let Some(boundary) = boundary {
        if let Some(loop_var_name) = &boundary.loop_var_name {
            // Phase 33-16: Get loop variable's initial value from HOST (not JoinIR's ValueId(0))
            // boundary.host_inputs[0] is the host ValueId that holds the initial loop var value
            let loop_var_init = boundary.host_inputs.first().copied().ok_or(
                "Phase 33-16: No host_inputs in boundary for loop_var_init"
            )?;

            if debug {
                eprintln!(
                    "[cf_loop/joinir] Phase 3.5: Building header PHIs for loop_var='{}' at {:?}",
                    loop_var_name, entry_block_remapped
                );
                eprintln!(
                    "[cf_loop/joinir]   loop_var_init={:?} (from boundary.host_inputs[0])",
                    loop_var_init
                );
                eprintln!(
                    "[cf_loop/joinir]   host_entry_block={:?} (where initial value comes from)",
                    host_entry_block
                );
            }

            let phi_info = loop_header_phi_builder::LoopHeaderPhiBuilder::build(
                builder,
                entry_block_remapped,  // header_block (JoinIR's entry block = loop header)
                host_entry_block,      // entry_block (host's block that jumps to loop header)
                loop_var_name,
                loop_var_init,
                &[],  // No other carriers for Pattern 2 (loop var is the only carrier)
                boundary.expr_result.is_some(),  // expr_result_is_loop_var
                debug,
            )?;

            // Phase 33-16: Override remapper so that JoinIR's loop var parameter (ValueId(0))
            // references the PHI dst instead of a separate remapped value.
            // This ensures all uses of the loop variable in the loop body use the PHI result.
            if let Some(phi_dst) = phi_info.get_carrier_phi(loop_var_name) {
                // JoinIR uses ValueId(0) for loop var in loop_step's first parameter
                // After remapping, we want those uses to refer to the header PHI dst
                remapper.set_value(ValueId(0), phi_dst);
                if debug {
                    eprintln!(
                        "[cf_loop/joinir] Phase 33-16: Override remap ValueId(0) → {:?} (PHI dst)",
                        phi_dst
                    );
                }
            }

            phi_info
        } else {
            loop_header_phi_builder::LoopHeaderPhiInfo::empty(entry_block_remapped)
        }
    } else {
        loop_header_phi_builder::LoopHeaderPhiInfo::empty(entry_block_remapped)
    };

    // Phase 4: Merge blocks and rewrite instructions
    // Phase 33-16: Pass mutable loop_header_phi_info for latch_incoming tracking
    let merge_result = instruction_rewriter::merge_and_rewrite(
        builder,
        mir_module,
        &mut remapper,
        &value_to_func_name,
        &function_params,
        boundary,
        &mut loop_header_phi_info,
        debug,
    )?;

    // Phase 4.5: Finalize loop header PHIs (insert into header block)
    //
    // By now, instruction_rewriter has set latch_incoming for all carriers.
    // We can finalize the PHIs and insert them into the header block.
    if !loop_header_phi_info.carrier_phis.is_empty() {
        if debug {
            eprintln!(
                "[cf_loop/joinir] Phase 4.5: Finalizing {} header PHIs",
                loop_header_phi_info.carrier_phis.len()
            );
        }
        loop_header_phi_builder::LoopHeaderPhiBuilder::finalize(
            builder,
            &loop_header_phi_info,
            debug,
        )?;
    }

    // Phase 5: Build exit PHI (expr result and carrier PHIs)
    // Phase 33-13: Now also builds carrier PHIs and returns their mapping
    let (exit_phi_result_id, carrier_phis) = exit_phi_builder::build_exit_phi(
        builder,
        merge_result.exit_block_id,
        &merge_result.exit_phi_inputs,
        &merge_result.carrier_inputs,
        debug,
    )?;

    // Phase 6: Reconnect boundary (if specified)
    // Phase 197-B: Pass remapper to enable per-carrier exit value lookup
    // Phase 33-10-Refactor-P3: Delegate to ExitLineOrchestrator
    // Phase 33-13: Pass carrier_phis for proper variable_map update
    if let Some(boundary) = boundary {
        exit_line::ExitLineOrchestrator::execute(builder, boundary, &carrier_phis, debug)?;
    }

    let exit_block_id = merge_result.exit_block_id;

    // Jump from current block to entry function's entry block
    // (Reuse entry_func_name and entry_block_remapped from Phase 3.5)
    let entry_block = entry_block_remapped;

    if debug {
        eprintln!("[cf_loop/joinir]   Entry function name: {}", entry_func_name);
        eprintln!(
            "[cf_loop/joinir]   Entry function's entry_block (JoinIR local): {:?}",
            entry_func.entry_block
        );
        eprintln!("[cf_loop/joinir]   Entry block (remapped): {:?}", entry_block);
        eprintln!(
            "[cf_loop/joinir]   Current block before emit_jump: {:?}",
            builder.current_block
        );
        eprintln!("[cf_loop/joinir]   Jumping to entry block: {:?}", entry_block);
    }

    crate::mir::builder::emission::branch::emit_jump(builder, entry_block)?;

    if debug {
        eprintln!(
            "[cf_loop/joinir]   After emit_jump, current_block: {:?}",
            builder.current_block
        );
    }

    // Switch to exit block for subsequent code
    builder.start_new_block(exit_block_id)?;

    if debug {
        eprintln!(
            "[cf_loop/joinir] Phase 189: Merge complete: {} functions merged, continuing from {:?}",
            mir_module.functions.len(),
            exit_block_id
        );
    }

    Ok(exit_phi_result_id)
}

/// Phase 3: Allocate new ValueIds for all collected values
fn remap_values(
    builder: &mut crate::mir::builder::MirBuilder,
    used_values: &std::collections::BTreeSet<ValueId>,
    remapper: &mut crate::mir::builder::joinir_id_remapper::JoinIrIdRemapper,
    debug: bool,
) -> Result<(), String> {
    if debug {
        eprintln!("[cf_loop/joinir] Phase 3: Remapping {} ValueIds", used_values.len());
    }

    for old_value in used_values {
        let new_value = builder.next_value_id();
        remapper.set_value(*old_value, new_value);
        if debug {
            eprintln!(
                "[cf_loop/joinir]   Value remap: {:?} → {:?}",
                old_value, new_value
            );
        }
    }

    Ok(())
}