package stfw

import (
	"encoding/binary"
	//"fmt"
	"os"
)

type Record struct {
	Addr        uint32
	Data        []byte
	Sum         uint8
	ComputedSum uint8
	Good        bool
}

func ReadRecord(f *os.File) (*Record, error) {

	r := struct {
		Data [36]byte
		Sum  uint8
	}{}

	err := binary.Read(f, binary.BigEndian, &r)
	if err != nil {
		return nil, err
	}

	var t uint8
	for _, b := range r.Data {
		t += uint8(b)
	}
	t = ^t

	record := &Record{
		Addr:        uint32(r.Data[0])<<24 | uint32(r.Data[1])<<16 | uint32(r.Data[2])<<8 | uint32(r.Data[3]),
		Data:        r.Data[4:],
		Sum:         r.Sum,
		ComputedSum: t,
		Good:        r.Sum == t,
	}

	return record, nil
}

func WriteRecord(f *os.File, rec *Record) error {

	r := struct {
		Data [36]byte
		Sum  uint8
	}{}

	r.Data[0] = byte(rec.Addr >> 24)
	r.Data[1] = byte(rec.Addr >> 16)
	r.Data[2] = byte(rec.Addr >> 8)
	r.Data[3] = byte(rec.Addr)

	copy(r.Data[4:], rec.Data[:])

	for _, b := range r.Data {
		r.Sum += uint8(b)
	}
	r.Sum = ^r.Sum

	err := binary.Write(f, binary.BigEndian, r)
	if err != nil {
		return err
	}

	return nil
}

func SplitBin(mem []byte) ([]byte, []byte) {
	low := make([]byte, len(mem)>>1)
	high := make([]byte, len(mem)>>1)
	for i := 0; i < len(mem); i += 2 {
		low[i/2] = mem[i]
		high[i/2] = mem[i+1]
	}
	return low, high
}

func MergeBin(low []byte, high []byte) []byte {
	mem := make([]byte, len(low)*2)
	for i := 0; i < len(low); i++ {
		mem[i*2] = low[i]
		mem[i*2+1] = high[i]
	}
	return mem
}

type MemoryMode int

func (m MemoryMode) physAddr(addr int) int {
	switch m {
	case MemoryModeCombinedLow:
		return addr * 2
	case MemoryModeCombinedHigh:
		return addr*2 + 1
	}
	return addr
}

const (
	MemoryModeLinear MemoryMode = iota
	MemoryModeCombinedLow
	MemoryModeCombinedHigh
)

func GetChecksum(mem []byte, mm MemoryMode) uint16 {
	return uint16(mem[mm.physAddr(0xfffe)])*256 + uint16(mem[mm.physAddr(0xffff)])
}

func GetChecksums(mem []byte) (uint16, uint16) {
	return GetChecksum(mem, MemoryModeCombinedLow), GetChecksum(mem, MemoryModeCombinedHigh)
}

func CalcChecksum(mem []byte, mm MemoryMode, start int) uint16 {
	var cs uint16
	for i := 0; i <= 0xFFFB; i++ {
		cs = addx(uint16(mem[mm.physAddr(i)]), cs)
	}
	cs = ^cs
	return cs
}

func CalcChecksums(mem []byte, start int) (uint16, uint16) {
	return CalcChecksum(mem, MemoryModeCombinedLow, start), CalcChecksum(mem, MemoryModeCombinedHigh, start)
}

func UpdateChecksum(mem []byte, mm MemoryMode, cs uint16) {
	mem[mm.physAddr(0xfffe)] = byte(cs >> 8)
	mem[mm.physAddr(0xffff)] = byte(cs)
}

var xFlag bool

func addx(x, y uint16) uint16 {
	if x+y < y {
		xFlag = true
		return x + y
	}
	if xFlag {
		xFlag = false
		return x + y + 1
	}
	return x + y
}