//! Process instrs that are a simple sequence of other instrs
//!
//! Useless instrs are replaced with `nop` since simply dropping instrs can break jump targets

use super::{ENV_ARG, PROTO_FIELD};

use crate::{
    libqjs::parse::{Atom, ImmOperand as Imm, Instr, JsValue, opcodes::OpCode},
    native,
};

#[allow(non_snake_case)]
pub fn try_replace_expansion(instr: &Instr, out: &mut Vec<Instr>) -> bool {
    use OpCode::*;

    let seq = match (instr.op, instr.imm) {
        (Call0, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Undefined, Imm::None),
            (Call, Imm::Npop(1)),
        ],
        (Call1, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Undefined, Imm::None),
            (Call, Imm::Npop(2)),
        ],
        (Call2, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Undefined, Imm::None),
            (Call, Imm::Npop(3)),
        ],
        (Call3, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Undefined, Imm::None),
            (Call, Imm::Npop(4)),
        ],
        (Call, Imm::Npop(n)) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Undefined, Imm::None),
            (Call, Imm::Npop(n + 1)),
        ],
        (TailCall, Imm::Npop(n)) => [
            (Nop, Imm::None),
            (Undefined, Imm::None),
            (Call, Imm::Npop(n + 1)),
            (Return, Imm::None),
        ],
        (TailCallMethod, imm) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (CallMethod, imm),
            (Return, Imm::None),
        ],
        (GetField2, imm) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Dup, Imm::None),
            (GetField, imm),
        ],
        (GetLoc0Loc1, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (GetLoc0, Imm::None),
            (GetLoc1, Imm::None),
        ],
        (IncLoc, imm) => [
            (Nop, Imm::None),
            (GetLoc, imm),
            (Inc, Imm::None),
            (PutLoc, imm),
        ],
        (DecLoc, imm) => [
            (Nop, Imm::None),
            (GetLoc, imm),
            (Dec, Imm::None),
            (PutLoc, imm),
        ],
        // The added value is on the stack, the local is the left operand
        (AddLoc, imm) => [
            (GetLoc, imm),
            (Swap, Imm::None),
            (Add, Imm::None),
            (PutLoc, imm),
        ],
        (SetProto, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Nop, Imm::None),
            (DefineField, Imm::Atom(PROTO_FIELD)),
        ],
        (DefineMethod, Imm::AtomU8 { atom, arg }) => {
            assert!(arg & 3 == 0, "getters and setters are not supported");
            [
                (Nop, Imm::None),
                (Nop, Imm::None),
                (Nop, Imm::None),
                (DefineField, Imm::Atom(atom)),
            ]
        }
        // The fn itself, which is its env
        (SpecialObject, Imm::U8(2)) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Nop, Imm::None),
            (GetArg, Imm::Arg(ENV_ARG)),
        ],
        // [[HomeObject]], which only `super` reads. `super` is not supported
        (SpecialObject, Imm::U8(4)) => unimplemented!(),
        // A class constructor called without `new` throws. That is not checked for the moment
        (CheckCtor, _) => [
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Nop, Imm::None),
            (Nop, Imm::None),
        ],
        // arguments, new.target, import.meta
        (SpecialObject, _) => unimplemented!(),
        _ => return false,
    };

    for (op, imm) in seq {
        out.push(Instr {
            pc: instr.pc,
            op,
            imm,
        });
    }

    true
}

/// Replace a read of a global with the constant it is (see `native`)
pub fn replace_get_var(
    instr: &Instr,
    atoms: &[Atom],
    cpool: &mut Vec<JsValue>,
    out: &mut Vec<Instr>,
) -> bool {
    if instr.op != OpCode::GetVar {
        return false;
    }

    cpool.push(native::global(instr.imm.atom(), atoms));

    out.push(Instr {
        pc: instr.pc,
        op: OpCode::PushConst,
        imm: Imm::Const(cpool.len() as u32 - 1),
    });

    true
}