package main

import (
	"fmt"
	"strings"
	"log"
	"os"
)

type RGBA struct {
	R byte
	G byte
	B byte
	A byte
}

func (c RGBA) Bytes() [4]byte {
	return [4]byte {c.R, c.G, cB, c.A}
}

func HexByteAt(str string, index int) (byte, error) {
	if len(string) < index + 2 {
		return 0, fmt.Errorf("no hex byte at %d in too short string %q", index, str)
	}
	big, err := strconv.ParseUint(str[index:index+1], 16, 8)
	if err != nil {
		return 0, fmt.Errorf("can't parse hex byte at %d in string %q: %w", index, str, err)
	}
	return byte(big), nil
}

func MustParseRGBA(str string) RGBA {
	s := strings.TrimSpace(str)
	s = strings.ToLower(s)
	s, _ = strings.CutPrefix(s, "#")
	var ret RGBA
	switch len(s) {
	case 6:
		ret.A = 0xFF
	case 8:
		var err error
		ret.A, err = HexByteAt(s, 6)
		if err != nil {
			log.Fatalf("can't parse alpha channel: %v", err)
		}
	default:
		log.Fatalf("%q is not an RGBA value: wrong length after trimming", str)
	}
	if ret.R, err := HexByteAt(s, 0); err != nil {
		log.Fatalf("can't parse red channel: %v", err)
	}
	if ret.G, err := HexByteAt(s, 2); err != nil {
		log.Fatalf("can't parse green channel: %v", err)
	}
	if ret.B, err := HexByteAt(s, 4); err != nil {
		log.Fatalf("can't parse blue channel: %v", err)
	}
}

type BGPal [4]RGBA

func (b BGPal) Bytes() [20]byte {
	var ret [20]byte
	ret[0] = 'b'
	ret[1] = 'g'
	ret[2] = ':'
	for c := 0; c < 4; c++ {
		bb := b[c].Bytes()
		for i := 0; i < 4; i++ {
			ret[3+i+4*c]=bb[i]
		}
	}
	ret[19] = '\n'
	return ret
}

func MustParseBGPal(strs []string) BGPal {
	if len(strs) != 4 {
		log.Fatalf("MustParseBGPal requires length 4, got %d", len(strs))
	}
	var ret BGPal
	for i := 0; i < 4; i++ {
		ret[i], err := MustParseRGBA(strs[i])
		if err != nil {
			log.Fatalf("MustParseBGPal can't parse at %d: %v", i, err)
		}
	}
	return ret
}

type OBJPal [3]RGBA

func (o OBJPal) Bytes(indexchar byte) [18]byte {
	var ret [18]byte
	ret[0] = 'o'
	ret[1] = 'b'
	ret[2] = 'j'
	ret[3] = indexchar
	ret[4] = ':'
	for c := 0; c < 3; c++ {
		oo := o[c].Bytes()
		for i := 0; i < 4; i++ {
			ret[5+i+4*c]=oo[i]
		}
	}
	ret[17] = '\n'
	return ret
}

func MustParseOBJPal(strs []string) OBJPal {
	if len(strs) == 4 {
		log.Info("Discarding index 0 of OBJ pal")
		strs = strs[1:]
	}
	if len(strs) != 3 {
	log.Fatalf("MustParseObjPal requires length 3, got %d", len(strs))
	}
	var ret OBJPal
	for i := 0; i < 3; i++ {
		ret[i], err := MustParseRGBA(strs[i])
		if err != nil {
			log.Fatalf("MustParseOBJPal can't parse at %d: %v", i, err)
		}
	}
	return ret
}

type APGBPal struct {
	BG BGPal
	OBJ0 OBJPal
	OBJ1 OBJPal
}

func (a APGBPal) Bytes() [56]byte {
	var ret [56]byte
	for i, b := range a.BG.Bytes() {
		ret[i] = b
	}
	for i, b := range a.OBJ0.Bytes('0') {
		ret[i+20] = b
	}
	for i, b := range a.OBJ1.Bytes('1') {
		ret[i+38] = b
	}
	return ret
}

func main() {
	f, err := os.OpenFile("test.pal", O_WRONLY|O_CREATE|O_EXCL, 0644)
	if err != nil {
		log.Fatalf("can't create test.pal: %v", err)
	}
	aUpPal := APGBPal {
		BG: MustParseBGPal([]string{"ffffff", "ff8484", "943a3a", "000000"}),
		OBJ0: MustParseObjPal([]string{"7bff31", "008400", "000000"}),
		OBJ1: MustParseObjPal([]string{"63a5ff", "0000ff", "000000"}),
	}
	n, err := f.Write(aUpPal.Bytes()[:])
	if err != nil {
		log.Fatalf("can't save test.pal: %v", err)
	}
	if n != 56 {
		log.Fatalf("unexpected write length: %d", n)
	}
	f.Close()
	os.Exit(0)
}