//! JoinIR 実験用のミニ実行器（Phase 27.2）
//!
//! 目的: hand-written / minimal JoinIR を VM と A/B 比較するための軽量ランナー。
//! - 対応値: i64 / bool / String / Unit
//! - 対応命令: Const / BinOp / Compare / BoxCall(StringBox: length, substring) /
//!              Call / Jump / Ret
//!
//! Phase 27.8: ops box 統合
//! - JoinValue / JoinIrOpError は join_ir_ops から再エクスポート
//! - eval_binop() / eval_compare() を使用（実装を一箇所に集約）

use std::collections::HashMap;

use crate::mir::join_ir::{
    ConstValue, JoinFuncId, JoinInst, JoinModule, MirLikeInst, VarId,
};

// Phase 27.8: ops box からの再エクスポート
pub use crate::mir::join_ir_ops::{JoinIrOpError, JoinValue};

// Phase 27.8: 互換性のため JoinRuntimeError を JoinIrOpError の別名として保持
pub type JoinRuntimeError = JoinIrOpError;

pub fn run_joinir_function(
    module: &JoinModule,
    entry: JoinFuncId,
    args: &[JoinValue],
) -> Result<JoinValue, JoinRuntimeError> {
    execute_function(module, entry, args.to_vec())
}

fn execute_function(
    module: &JoinModule,
    mut current_func: JoinFuncId,
    mut current_args: Vec<JoinValue>,
) -> Result<JoinValue, JoinRuntimeError> {
    'exec: loop {
        let func = module
            .functions
            .get(&current_func)
            .ok_or_else(|| JoinRuntimeError::new(format!("Function {:?} not found", current_func)))?;

        if func.params.len() != current_args.len() {
            return Err(JoinRuntimeError::new(format!(
                "Arity mismatch for {:?}: expected {}, got {}",
                func.id,
                func.params.len(),
                current_args.len()
            )));
        }

        let mut locals: HashMap<VarId, JoinValue> = HashMap::new();
        for (param, arg) in func.params.iter().zip(current_args.iter()) {
            locals.insert(*param, arg.clone());
        }

        let mut ip = 0usize;
        while ip < func.body.len() {
            match &func.body[ip] {
                JoinInst::Compute(inst) => {
                    eval_compute(inst, &mut locals)?;
                    ip += 1;
                }
                JoinInst::Call {
                    func: target,
                    args,
                    k_next,
                    dst,
                } => {
                    if k_next.is_some() {
                        return Err(JoinRuntimeError::new(
                            "Join continuation (k_next) is not supported in the experimental runner",
                        ));
                    }
                    let resolved_args = materialize_args(args, &locals)?;
                    if let Some(dst_var) = dst {
                        let value = execute_function(module, *target, resolved_args)?;
                        locals.insert(*dst_var, value);
                        ip += 1;
                    } else {
                        current_func = *target;
                        current_args = resolved_args;
                        continue 'exec;
                    }
                }
                JoinInst::Jump { cont: _, args, cond } => {
                    let should_jump = match cond {
                        Some(var) => as_bool(&read_var(&locals, *var)?)?,
                        None => true,
                    };
                    if should_jump {
                        let ret = if let Some(first) = args.first() {
                            read_var(&locals, *first)?
                        } else {
                            JoinValue::Unit
                        };
                        return Ok(ret);
                    }
                    ip += 1;
                }
                JoinInst::Ret { value } => {
                    let ret = match value {
                        Some(var) => read_var(&locals, *var)?,
                        None => JoinValue::Unit,
                    };
                    return Ok(ret);
                }
            }
        }

        // fallthrough without explicit return
        return Ok(JoinValue::Unit);
    }
}

fn eval_compute(inst: &MirLikeInst, locals: &mut HashMap<VarId, JoinValue>) -> Result<(), JoinRuntimeError> {
    match inst {
        MirLikeInst::Const { dst, value } => {
            let v = match value {
                ConstValue::Integer(i) => JoinValue::Int(*i),
                ConstValue::Bool(b) => JoinValue::Bool(*b),
                ConstValue::String(s) => JoinValue::Str(s.clone()),
                ConstValue::Null => JoinValue::Unit,
            };
            locals.insert(*dst, v);
        }
        MirLikeInst::BinOp { dst, op, lhs, rhs } => {
            // Phase 27.8: ops box の eval_binop() を使用
            let l = read_var(locals, *lhs)?;
            let r = read_var(locals, *rhs)?;
            let v = crate::mir::join_ir_ops::eval_binop(*op, &l, &r)?;
            locals.insert(*dst, v);
        }
        MirLikeInst::Compare { dst, op, lhs, rhs } => {
            // Phase 27.8: ops box の eval_compare() を使用
            let l = read_var(locals, *lhs)?;
            let r = read_var(locals, *rhs)?;
            let v = crate::mir::join_ir_ops::eval_compare(*op, &l, &r)?;
            locals.insert(*dst, v);
        }
        // S-5.2: BoxCall → VM method_router 経由（ガードレール設計）
        // - 制御フロー: JoinIR Runner が担当
        // - Box/Plugin 実装: Rust VM に委譲（VM 2号機を避ける）
        MirLikeInst::BoxCall {
            dst,
            box_name,
            method,
            args,
        } => {
            if box_name != "StringBox" {
                return Err(JoinRuntimeError::new(format!(
                    "Unsupported box call target: {}",
                    box_name
                )));
            }
            match method.as_str() {
                "length" => {
                    let arg = expect_str(&read_var(locals, args[0])?)?;
                    // S-5.2: VM の StringBox.length() 実装を使用（hardcoded 削除）
                    let string_box = crate::boxes::basic::StringBox::new(arg);
                    let result_box = string_box.length();
                    let result_value = box_to_join_value(result_box)?;
                    let dst_var = dst.ok_or_else(|| {
                        JoinRuntimeError::new("length call requires destination")
                    })?;
                    locals.insert(dst_var, result_value);
                }
                "substring" => {
                    if args.len() != 3 {
                        return Err(JoinRuntimeError::new(
                            "substring expects 3 arguments (s, start, end)",
                        ));
                    }
                    let s = expect_str(&read_var(locals, args[0])?)?;
                    let start = expect_int(&read_var(locals, args[1])?)? as usize;
                    let end = expect_int(&read_var(locals, args[2])?)? as usize;
                    // S-5.2: VM の StringBox.substring() 実装を使用（hardcoded 削除）
                    let string_box = crate::boxes::basic::StringBox::new(s);
                    let result_box = string_box.substring(start, end);
                    let result_value = box_to_join_value(result_box)?;
                    let dst_var = dst.ok_or_else(|| {
                        JoinRuntimeError::new("substring call requires destination")
                    })?;
                    locals.insert(dst_var, result_value);
                }
                _ => {
                    return Err(JoinRuntimeError::new(format!(
                        "Unsupported StringBox method: {}",
                        method
                    )))
                }
            }
        }
    }
    Ok(())
}

fn read_var(locals: &HashMap<VarId, JoinValue>, var: VarId) -> Result<JoinValue, JoinRuntimeError> {
    locals
        .get(&var)
        .cloned()
        .ok_or_else(|| JoinRuntimeError::new(format!("Variable {:?} not bound", var)))
}

fn materialize_args(
    args: &[VarId],
    locals: &HashMap<VarId, JoinValue>,
) -> Result<Vec<JoinValue>, JoinRuntimeError> {
    args.iter().map(|v| read_var(locals, *v)).collect()
}

fn as_bool(value: &JoinValue) -> Result<bool, JoinRuntimeError> {
    match value {
        JoinValue::Bool(b) => Ok(*b),
        JoinValue::Int(i) => Ok(*i != 0),
        JoinValue::Unit => Ok(false),
        other => Err(JoinRuntimeError::new(format!(
            "Expected bool-compatible value, got {:?}",
            other
        ))),
    }
}

fn expect_int(value: &JoinValue) -> Result<i64, JoinRuntimeError> {
    match value {
        JoinValue::Int(i) => Ok(*i),
        other => Err(JoinRuntimeError::new(format!(
            "Expected int, got {:?}",
            other
        ))),
    }
}

fn expect_str(value: &JoinValue) -> Result<String, JoinRuntimeError> {
    match value {
        JoinValue::Str(s) => Ok(s.clone()),
        other => Err(JoinRuntimeError::new(format!(
            "Expected string, got {:?}",
            other
        ))),
    }
}

/// S-5.2: Convert Box<dyn NyashBox> from VM to JoinValue
///
/// Tries to downcast to known primitive types first (IntegerBox, BoolBox, StringBox),
/// otherwise wraps as BoxRef for future use.
fn box_to_join_value(nyash_box: Box<dyn crate::box_trait::NyashBox>) -> Result<JoinValue, JoinRuntimeError> {
    use std::sync::Arc;

    // Try to downcast to known primitive types first
    if let Some(int_box) = nyash_box.as_any().downcast_ref::<crate::boxes::basic::IntegerBox>() {
        return Ok(JoinValue::Int(int_box.value));
    }
    if let Some(bool_box) = nyash_box.as_any().downcast_ref::<crate::boxes::basic::BoolBox>() {
        return Ok(JoinValue::Bool(bool_box.value));
    }
    if let Some(str_box) = nyash_box.as_any().downcast_ref::<crate::boxes::basic::StringBox>() {
        return Ok(JoinValue::Str(str_box.value.clone()));
    }

    // Otherwise, wrap as BoxRef (for S-5.3/S-5.4 future use)
    Ok(JoinValue::BoxRef(Arc::from(nyash_box)))
}