package mcmap

import (
	"errors"
	"fmt"
	"math"
	"os"
	"regexp"
	"strconv"
)

var (
	NotAvailable = errors.New("Chunk or Superchunk not available")
)

type superchunk struct {
	preChunks map[XZPos]*preChunk
	chunks    map[XZPos]*Chunk
	modified  bool
}

type Region struct {
	path             string
	autosave         bool
	superchunksAvail map[XZPos]bool
	superchunks      map[XZPos]*superchunk
}

var mcaRegex = regexp.MustCompile(`^r\.([0-9-]+)\.([0-9-]+)\.mca$`)

// OpenRegion opens a region directory. If autosave is true, mcmap will save modified and unloaded chunks automatically to reduce memory usage. You still have to call Save at the end.
func OpenRegion(path string, autosave bool) (*Region, error) {
	rv := &Region{
		path:             path,
		superchunksAvail: make(map[XZPos]bool),
		superchunks:      make(map[XZPos]*superchunk),
	}

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

	fi, err := f.Stat()
	if err != nil {
		return nil, err
	}

	if !fi.IsDir() {
		return nil, fmt.Errorf("%s is not a directory", path)
	}

	names, err := f.Readdirnames(-1)
	if err != nil {
		return nil, err
	}
	for _, name := range names {
		match := mcaRegex.FindStringSubmatch(name)
		if len(match) == 3 {
			// We ignore the error here. The Regexp already ensures that the inputs are numbers.
			x, _ := strconv.ParseInt(match[1], 10, 32)
			z, _ := strconv.ParseInt(match[2], 10, 32)

			rv.superchunksAvail[XZPos{int(x), int(z)}] = true
		}
	}

	return rv, nil
}

// MaxDims calculates the approximate maximum x, z dimensions of this region in number of chunks. The actual maximum dimensions might be a bit smaller.
func (reg *Region) MaxDims() (xmin, xmax, zmin, zmax int) {
	if len(reg.superchunksAvail) == 0 {
		return 0, 0, 0, 0
	}

	xmin = math.MaxInt32
	zmin = math.MaxInt32
	xmax = math.MinInt32
	zmax = math.MinInt32

	for pos := range reg.superchunksAvail {
		if pos.X < xmin {
			xmin = pos.X
		}
		if pos.Z < zmin {
			zmin = pos.Z
		}
		if pos.X > xmax {
			xmax = pos.X
		}
		if pos.Z > zmax {
			zmax = pos.Z
		}
	}

	xmax++
	zmax++
	xmin *= 32
	xmax *= 32
	zmin *= 32
	zmax *= 32
	return
}

func chunkToSuperchunk(cx, cz int) (scx, scz, rx, rz int) {
	scx = cx >> 5
	scz = cz >> 5
	rx = ((cx % 32) + 32) % 32
	rz = ((cz % 32) + 32) % 32
	return
}

func superchunkToChunk(scx, scz, rx, rz int) (cx, cz int) {
	cx = scx*32 + rx
	cz = scz*32 + rz
	return
}

func (reg *Region) loadSuperchunk(pos XZPos) error {
	if !reg.superchunksAvail[pos] {
		return NotAvailable
	}
	fname := fmt.Sprintf("%s%cr.%d.%d.mca", reg.path, os.PathSeparator, pos.X, pos.Z)

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

	pcs, err := readRegionFile(f)
	if err != nil {
		return err
	}

	reg.superchunks[pos] = &superchunk{
		preChunks: pcs,
		chunks:    make(map[XZPos]*Chunk),
	}
	return nil
}

func (reg *Region) cleanSuperchunks(forceSave bool) error {
	del := make(map[XZPos]bool)

	for scPos, sc := range reg.superchunks {
		if len(sc.chunks) > 0 {
			continue
		}

		if sc.modified {
			if !(reg.autosave || forceSave) {
				continue
			}
			fn := fmt.Sprintf("%s%cr.%d.%d.mca", reg.path, os.PathSeparator, scPos.X, scPos.Z)
			f, err := os.Create(fn)
			if err != nil {
				return err
			}
			defer f.Close()

			if err := writeRegionFile(f, sc.preChunks); err != nil {
				return err
			}
		}

		del[scPos] = true
	}

	for scPos, _ := range del {
		delete(reg.superchunks, scPos)
	}

	return nil
}

func (reg *Region) Chunk(x, z int) (*Chunk, error) {
	scx, scz, cx, cz := chunkToSuperchunk(x, z)
	scPos := XZPos{scx, scz}
	cPos := XZPos{cx, cz}

	sc, ok := reg.superchunks[scPos]
	if !ok {
		if err := reg.loadSuperchunk(scPos); err != nil {
			return nil, err
		}
		sc = reg.superchunks[scPos]
	}

	chunk, ok := sc.chunks[cPos]
	if !ok {
		pc, ok := sc.preChunks[cPos]
		if !ok {
			return nil, NotAvailable
		}

		var err error
		if chunk, err = pc.toChunk(); err != nil {
			return nil, err
		}
		sc.chunks[cPos] = chunk
	}

	if err := reg.cleanSuperchunks(false); err != nil {
		return nil, err
	}

	return chunk, nil
}

// UnloadChunk marks a chunk as unused. If all chunks of a superchunk are marked as unused, the superchunk will be unloaded and saved (if needed).
func (reg *Region) UnloadChunk(x, z int) error {
	scx, scz, cx, cz := chunkToSuperchunk(x, z)
	scPos := XZPos{scx, scz}
	cPos := XZPos{cx, cz}

	sc, ok := reg.superchunks[scPos]
	if !ok {
		return nil
	}

	chunk, ok := sc.chunks[cPos]
	if !ok {
		return nil
	}

	if chunk.modified {
		pc, err := chunk.toPreChunk()
		if err != nil {
			return err
		}
		sc.preChunks[cPos] = pc

		chunk.modified = false
		sc.modified = true
	}

	delete(sc.chunks, cPos)

	return nil
}

// AllChunks returns a channel that will give you the positions of all possibly available chunks in an efficient order.
//
// Note the "possibly available", you still have to check, if the chunk could actually be loaded.
func (reg *Region) AllChunks() <-chan XZPos {
	ch := make(chan XZPos)
	go func(ch chan<- XZPos) {
		for spos, _ := range reg.superchunksAvail {
			scx, scz := spos.X, spos.Z
			for rx := 0; rx < 32; rx++ {
				for rz := 0; rz < 32; rz++ {
					cx, cz := superchunkToChunk(scx, scz, rx, rz)
					ch <- XZPos{cx, cz}
				}
			}
		}
		close(ch)
	}(ch)

	return ch
}

// Save saves modified and unloaded chunks.
func (reg *Region) Save() error {
	return reg.cleanSuperchunks(true)
}