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"
import { BasicBlock } from "../ir/block"

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

export const realizeInsn = (insn: AbsInsn2): Array<SM83Insn> => insnReduce2(
    realizeCopy,
    realizeLabel,
    realizeGoto,
    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 realizeLabel = (name: string): Array<SM83Insn> => [
    `${name}:`,
]

export const realizeGoto = (name: string): Array<SM83Insn> => [
    `JR ${name}`,
]

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

    let output: Array<SM83Insn> = []

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

        case "subtract":
            return [`SUB ${getSourceName(source)}`]

        case "bit_and":
            return [`AND ${getSourceName(source)}`]

        case "bit_or":
            return [`OR ${getSourceName(source)}`]

        case "bit_xor":
            return [`XOR ${getSourceName(source)}`]

        case "shift_left":
            for (let i = 0; i < source; ++i) {
                output.push("SLA A")
            }
            return output

        case "shift_right":
            for (let i = 0; i < source; ++i) {
                output.push("SRL A")
            }
            return output

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

        case "bit_negate":
            return ["CPL"]
    }
}

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