package fmp

import (
	"bytes"
	"io"
	"os"
	"time"
)

const (
	sectorSize        = 4096
	sectorHeaderSize  = 20
	sectorPayloadSize = sectorSize - sectorHeaderSize

	magicSequence = "\x00\x01\x00\x00\x00\x02\x00\x01\x00\x05\x00\x02\x00\x02\xC0"
	hbamSequence  = "HBAM7"

	headerSize = sectorSize
	magicSize  = len(magicSequence)
	hbamSize   = len(hbamSequence)
)

func OpenFile(path string) (*FmpFile, error) {
	info, err := os.Stat(path)
	if err != nil {
		return nil, err
	}

	stream, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer stream.Close()

	ctx := &FmpFile{stream: stream, Dictionary: &FmpDict{}}
	if err := ctx.readHeader(); err != nil {
		return nil, err
	}

	ctx.FileSize = uint(info.Size())
	ctx.numSectors = uint64((ctx.FileSize / sectorSize) - 1)
	ctx.Sectors = make([]*FmpSector, 0)
	currentPath := make([]uint64, 0)

	for {
		sector, err := ctx.readSector()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, err
		}

		ctx.Sectors = append(ctx.Sectors, sector)

		if sector.ID != 0 {
			err = sector.processChunks(ctx.Dictionary, &currentPath)
			if err != nil {
				return nil, err
			}
			ctx.Chunks = append(ctx.Chunks, sector.Chunks...)
		}

		ctx.currentSectorID = sector.NextID
		if sector.NextID == 0 {
			break
		} else if sector.NextID > ctx.numSectors {
			return nil, ErrBadHeader
		} else {
			ctx.stream.Seek(int64(sector.NextID*sectorSize), 0)
		}
	}

	return ctx, nil
}

func (ctx *FmpFile) readHeader() error {
	buf := make([]byte, headerSize)
	_, err := ctx.stream.Read(buf)
	if err != nil {
		return err
	}
	if !bytes.Equal(buf[:magicSize], []byte(magicSequence)) {
		return ErrBadMagic
	}
	if !bytes.Equal(buf[magicSize:magicSize+hbamSize], []byte(hbamSequence)) {
		return ErrBadMagic
	}

	ctx.VersionDate, err = time.Parse("06JAN02", string(buf[531:538]))
	if err != nil {
		return ErrBadHeader
	}

	appNameLength := int(buf[541])
	ctx.CreatorName = string(buf[542 : 542+appNameLength])

	return nil
}

func (ctx *FmpFile) readSector() (*FmpSector, error) {
	println("------- Reading sector", ctx.currentSectorID)
	buf := make([]byte, sectorHeaderSize)
	n, err := ctx.stream.Read(buf)

	if n == 0 {
		return nil, io.EOF
	}
	if err != nil {
		return nil, ErrRead
	}

	sector := &FmpSector{
		ID:      ctx.currentSectorID,
		Deleted: buf[0] > 0,
		Level:   uint8(buf[1]),
		PrevID:  parseVarUint64(buf[4 : 4+4]),
		NextID:  parseVarUint64(buf[8 : 8+4]),
		Chunks:  make([]*FmpChunk, 0),
	}

	if ctx.currentSectorID == 0 && sector.PrevID > 0 {
		return nil, ErrBadSectorHeader
	}

	sector.Payload = make([]byte, sectorPayloadSize)
	n, err = ctx.stream.Read(sector.Payload)

	if n != sectorPayloadSize {
		return nil, ErrRead
	}
	if err != nil {
		return nil, ErrRead
	}
	return sector, nil
}