/*!
 * Minimal MIR Interpreter
 *
 * Executes a subset of MIR instructions for fast iteration without LLVM/JIT.
 * Supported: Const, BinOp(Add/Sub/Mul/Div/Mod), Compare, Load/Store, Branch, Jump, Return,
 * Print/Debug (best-effort), Barrier/Safepoint (no-op).
 */

use std::collections::HashMap;

use crate::box_trait::NyashBox;

pub(super) use crate::backend::abi_util::{eq_vm, to_bool_vm};
pub(super) use crate::backend::vm::{VMError, VMValue};
pub(super) use crate::mir::{
    BasicBlockId, BinaryOp, Callee, CompareOp, ConstValue, MirFunction, MirInstruction, MirModule,
    ValueId,
};

mod exec;
mod handlers;
mod helpers;
mod method_router;
mod utils;

pub struct MirInterpreter {
    pub(super) regs: HashMap<ValueId, VMValue>,
    pub(super) mem: HashMap<ValueId, VMValue>,
    // Object field storage keyed by stable object identity (Arc ptr addr fallback)
    pub(super) obj_fields: HashMap<u64, HashMap<String, VMValue>>,
    pub(super) functions: HashMap<String, MirFunction>,
    pub(super) cur_fn: Option<String>,
    // Trace context (dev-only; enabled with NYASH_VM_TRACE=1)
    pub(super) last_block: Option<BasicBlockId>,
    pub(super) last_inst: Option<MirInstruction>,
    // Static box singleton instances (persistent across method calls)
    pub(super) static_boxes: HashMap<String, crate::instance_v2::InstanceBox>,
    // Static box declarations (metadata for creating instances)
    pub(super) static_box_decls: HashMap<String, crate::core::model::BoxDeclaration>,
}

impl MirInterpreter {
    pub fn new() -> Self {
        Self {
            regs: HashMap::new(),
            mem: HashMap::new(),
            obj_fields: HashMap::new(),
            functions: HashMap::new(),
            cur_fn: None,
            last_block: None,
            last_inst: None,
            static_boxes: HashMap::new(),
            static_box_decls: HashMap::new(),
        }
    }

    /// Register static box declarations (called from vm.rs during setup)
    pub fn register_static_box_decl(&mut self, name: String, decl: crate::core::model::BoxDeclaration) {
        self.static_box_decls.insert(name, decl);
    }

    /// Ensure static box singleton instance exists, create if not
    /// Returns mutable reference to the singleton instance
    fn ensure_static_box_instance(&mut self, box_name: &str) -> Result<&mut crate::instance_v2::InstanceBox, VMError> {
        // Check if instance already exists
        if !self.static_boxes.contains_key(box_name) {
            // Get declaration
            let decl = self.static_box_decls.get(box_name)
                .ok_or_else(|| VMError::InvalidInstruction(
                    format!("static box declaration not found: {}", box_name)
                ))?
                .clone();

            // Create instance from declaration
            let instance = crate::instance_v2::InstanceBox::from_declaration(
                box_name.to_string(),
                decl.fields.clone(),
                decl.methods.clone(),
            );

            self.static_boxes.insert(box_name.to_string(), instance);

            if std::env::var("NYASH_VM_STATIC_TRACE").ok().as_deref() == Some("1") {
                eprintln!("[vm-static] created singleton instance for static box: {}", box_name);
            }
        }

        // Return mutable reference
        self.static_boxes.get_mut(box_name)
            .ok_or_else(|| VMError::InvalidInstruction(
                format!("static box instance not found after creation: {}", box_name)
            ))
    }

    /// Check if a function name represents a static box method
    /// Format: "BoxName.method/Arity"
    fn is_static_box_method(&self, func_name: &str) -> Option<String> {
        if let Some((box_name, _rest)) = func_name.split_once('.') {
            if self.static_box_decls.contains_key(box_name) {
                return Some(box_name.to_string());
            }
        }
        None
    }

    /// Execute module entry (main) and return boxed result
    pub fn execute_module(&mut self, module: &MirModule) -> Result<Box<dyn NyashBox>, VMError> {
        // Snapshot functions for call resolution
        self.functions = module.functions.clone();

        // Determine entry function with sensible fallbacks
        // Priority:
        //   1) NYASH_ENTRY env (exact), then basename before '/' if provided (e.g., "Main.main/0" → "Main.main")
        //   2) "Main.main" if present
        //   3) "main" (legacy/simple scripts)
        let mut candidates: Vec<String> = Vec::new();
        if let Ok(e) = std::env::var("NYASH_ENTRY") {
            if !e.trim().is_empty() {
                candidates.push(e.trim().to_string());
            }
        }
        candidates.push("Main.main".to_string());
        candidates.push("main".to_string());

        // Try candidates in order
        let mut chosen: Option<&nyash_rust::mir::MirFunction> = None;
        for c in &candidates {
            // exact
            if let Some(f) = module.functions.get(c) {
                chosen = Some(f);
                break;
            }
            // if contains '/': try name before '/'
            if let Some((head, _)) = c.split_once('/') {
                if let Some(f) = module.functions.get(head) {
                    chosen = Some(f);
                    break;
                }
            }
            // if looks like "Box.method": try plain "main" as last resort only when c endswith .main
            if c.ends_with(".main") {
                if let Some(f) = module.functions.get("main") {
                    chosen = Some(f);
                    break;
                }
            }
        }

        let func = match chosen {
            Some(f) => f,
            None => {
                // Build helpful error message
                let mut names: Vec<&String> = module.functions.keys().collect();
                names.sort();
                let avail = names.into_iter().take(12).cloned().collect::<Vec<_>>().join(", ");
                let tried = candidates.join(", ");
                let msg = format!(
                    "entry function not found. searched: [{}]. available: [{}]. hint: define 'static box Main {{ method main(args){{ ... }} }}' or set NYASH_ENTRY=Name",
                    tried, avail
                );
                return Err(VMError::InvalidInstruction(msg));
            }
        };

        // Prepare arguments if the entry takes parameters (pass script args as ArrayBox)
        let ret = if func.signature.params.len() == 0 {
            self.execute_function(func)?
        } else {
            // Build argv from (priority) HEX JSON, normal JSON, or NYASH_ARGV
            // 1) NYASH_SCRIPT_ARGS_HEX_JSON: JSON array of hex-encoded UTF-8 strings
            // 2) NYASH_SCRIPT_ARGS_JSON: JSON array of strings
            // 3) NYASH_ARGV: JSON array (legacy)
            let mut argv_list: Vec<String> = Vec::new();
            if let Ok(s) = std::env::var("NYASH_SCRIPT_ARGS_HEX_JSON") {
                if let Ok(v) = serde_json::from_str::<Vec<String>>(&s) {
                    let mut out = Vec::with_capacity(v.len());
                    for hx in v.into_iter() {
                        match hex_decode_to_string(&hx) {
                            Ok(ss) => out.push(ss),
                            Err(_) => out.push(String::new()),
                        }
                    }
                    argv_list = out;
                }
            } else if let Ok(s) = std::env::var("NYASH_SCRIPT_ARGS_JSON") {
                if let Ok(v) = serde_json::from_str::<Vec<String>>(&s) { argv_list = v; }
            } else if let Ok(s) = std::env::var("NYASH_ARGV") {
                if let Ok(v) = serde_json::from_str::<Vec<String>>(&s) { argv_list = v; }
            }
            // Construct ArrayBox of StringBox
            let array = crate::boxes::array::ArrayBox::new();
            for a in argv_list.iter() {
                let sb = crate::boxes::basic::StringBox::new(a);
                let _ = array.push(Box::new(sb));
            }
            let boxed: Box<dyn crate::box_trait::NyashBox> = Box::new(array);
            let arg0 = super::vm_types::VMValue::from_nyash_box(boxed);
            // Fill remaining params with Void
            let mut vm_args: Vec<super::vm_types::VMValue> = Vec::new();
            vm_args.push(arg0);
            for _ in 1..func.signature.params.len() {
                vm_args.push(super::vm_types::VMValue::Void);
            }
            self.exec_function_inner(func, Some(&vm_args))?
        };
        Ok(ret.to_nyash_box())
    }

    fn execute_function(&mut self, func: &MirFunction) -> Result<VMValue, VMError> {
        self.exec_function_inner(func, None)
    }
}

fn hex_decode_to_string(hex: &str) -> Result<String, ()> {
    let mut bytes: Vec<u8> = Vec::with_capacity(hex.len() / 2);
    let mut it = hex.as_bytes().iter().cloned();
    while let (Some(h), Some(l)) = (it.next(), it.next()) {
        let hi = from_hex(h).ok_or(())?;
        let lo = from_hex(l).ok_or(())?;
        bytes.push((hi << 4) | lo);
    }
    match String::from_utf8(bytes) {
        Ok(s) => Ok(s),
        Err(e) => Ok(String::from_utf8_lossy(e.as_bytes()).into_owned()),
    }
}

fn from_hex(b: u8) -> Option<u8> {
    match b {
        b'0'..=b'9' => Some(b - b'0'),
        b'a'..=b'f' => Some(b - b'a' + 10),
        b'A'..=b'F' => Some(b - b'A' + 10),
        _ => None,
    }
}