import { R8 } from "./cpu"
import { Loc, LocType } from "../ir/loc"
import { Operand, AbsInsn2, insnReduce2 } from "../ir/insn"
import { BinaryOp, UnaryOp } from "../ast"
import type { SM83Insn } from "./insn"

export const realizeBlock = (block: Array<AbsInsn2>): Array<SM83Insn> => block.flatMap(realizeInsn)

export const realizeInsn = (insn: AbsInsn2): Array<SM83Insn> => insnReduce2(realizeCopy, realizeUnary, insn)

const getSourceName = (source: Operand): string => typeof source === "number"
    ? source.toString()
    : source.asmName()

export const realizeCopy = (dest: Loc, source: Operand): Array<SM83Insn> => [
    `LD ${dest.asmName()}, ${getSourceName(source)}`
]

export const realizeUnary = (dest: Loc, op: UnaryOp | BinaryOp, source: Operand): Array<SM83Insn> => {
    if (!isA(dest)) {
        throw new Error("unexpected form for unary operation")
    }

    switch (op) {
        case "add":
            return [`ADD ${getSourceName(source)}`]

        case "arith_negate":
            return ["CPL", "INC A"]

        case "bit_negate":
            return ["CPL"]

        default:
            throw new Error(`unsupported unary op \`${op}'`)
    }
}

const isA = (loc: Operand): boolean =>
    typeof loc === "object" && loc.type === LocType.REGISTER && loc.name === R8.A