use std::collections::HashMap;

use crate::mir::{ValueId, BasicBlockId};
use crate::backend::vm::VMValue;

use super::Semantics;

/// Minimal VM-backed Semantics implementation used for parity checks.
/// This is not a full VM; it only materializes constants/binary ops and records last return.
pub struct VmSemantics {
    pub vals: HashMap<ValueId, VMValue>,
    pub last_ret: Option<VMValue>,
}

impl VmSemantics {
    pub fn new() -> Self { Self { vals: HashMap::new(), last_ret: None } }
}

impl Semantics for VmSemantics {
    type Val = VMValue;
    type Ptr = ValueId; // address by MIR value id (local slot semantics)
    type BB = BasicBlockId;

    fn const_i64(&mut self, v: i64) -> Self::Val { VMValue::Integer(v) }
    fn const_f64(&mut self, v: f64) -> Self::Val { VMValue::Float(v) }
    fn const_bool(&mut self, v: bool) -> Self::Val { VMValue::Bool(v) }
    fn const_null(&mut self) -> Self::Val { VMValue::Void }
    fn const_str(&mut self, s: &str) -> Self::Val { VMValue::String(s.to_string()) }

    fn neg(&mut self, x: Self::Val) -> Self::Val {
        match x { VMValue::Integer(i) => VMValue::Integer(-i), VMValue::Float(f) => VMValue::Float(-f), _ => VMValue::Integer(0) }
    }
    fn not(&mut self, x: Self::Val) -> Self::Val {
        match x { VMValue::Bool(b) => VMValue::Bool(!b), VMValue::Integer(i) => VMValue::Bool(i==0), _ => VMValue::Bool(false) }
    }
    fn bit_not(&mut self, x: Self::Val) -> Self::Val {
        match x { VMValue::Integer(i) => VMValue::Integer(!i), _ => VMValue::Integer(0) }
    }
    fn add(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Integer(x+y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Float(x+y), _ => VMValue::Integer(0) }
    }
    fn sub(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Integer(x-y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Float(x-y), _ => VMValue::Integer(0) }
    }
    fn mul(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Integer(x*y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Float(x*y), _ => VMValue::Integer(0) }
    }
    fn div(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) if y!=0 => VMValue::Integer(x/y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Float(x/y), _ => VMValue::Integer(0) }
    }
    fn modulo(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) if y!=0 => VMValue::Integer(x%y), _ => VMValue::Integer(0) }
    }
    fn cmp_eq(&mut self, a: Self::Val, b: Self::Val) -> Self::Val { VMValue::Bool(a==b) }
    fn cmp_ne(&mut self, a: Self::Val, b: Self::Val) -> Self::Val { VMValue::Bool(a!=b) }
    fn cmp_lt(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Bool(x<y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Bool(x<y), _ => VMValue::Bool(false) }
    }
    fn cmp_le(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Bool(x<=y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Bool(x<=y), _ => VMValue::Bool(false) }
    }
    fn cmp_gt(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Bool(x>y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Bool(x>y), _ => VMValue::Bool(false) }
    }
    fn cmp_ge(&mut self, a: Self::Val, b: Self::Val) -> Self::Val {
        match (a,b) { (VMValue::Integer(x), VMValue::Integer(y)) => VMValue::Bool(x>=y), (VMValue::Float(x), VMValue::Float(y)) => VMValue::Bool(x>=y), _ => VMValue::Bool(false) }
    }

    fn alloca_ptr(&mut self, vid: ValueId) -> Self::Ptr { vid }
    fn load(&mut self, ptr: &Self::Ptr) -> Self::Val { self.vals.get(ptr).cloned().unwrap_or(VMValue::Integer(0)) }
    fn store(&mut self, ptr: &Self::Ptr, v: Self::Val) { self.vals.insert(*ptr, v); }
    fn jump(&mut self, _target: BasicBlockId) {}
    fn branch(&mut self, _cond: Self::Val, _then_bb: BasicBlockId, _else_bb: BasicBlockId) {}
    fn phi_select(&mut self, incoming: &[(BasicBlockId, Self::Val)]) -> Self::Val { incoming.last().map(|(_,v)| v.clone()).unwrap_or(VMValue::Integer(0)) }
    fn ret(&mut self, v: Option<Self::Val>) { self.last_ret = v; }

    fn new_box(&mut self, _type_id: i64, _args: &[Self::Val]) -> Self::Val { VMValue::Integer(0) }
    fn box_call_tagged(&mut self, _type_id: i64, _method_id: i64, _recv: Self::Val, _argv: &[Self::Val], _tags: &[i64]) -> Self::Val { VMValue::Integer(0) }
    fn extern_call(&mut self, _iface: &str, _method: &str, _args: &[Self::Val]) -> Self::Val { VMValue::Integer(0) }
}