package maps

import (
	"bytes"
	"compress/gzip"
	"encoding/binary"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"strings"
)

var (
	expectedMagic         = []byte("\x08\x00WHMAP\x00")
	expectedSetNameOffset = uint32(0x34)
	notImplemented        = fmt.Errorf("Not implemented")
)

const (
	MaxHeight = 7   // Z coordinate
	MaxLength = 100 // Y coordinate
	MaxWidth  = 130 // X coordinate

	CellSize = 16 // seems to be

	cellDataOffset = 0x100 // tentatively
	cellDataSize   = MaxHeight * MaxLength * MaxWidth * CellSize
)

type Header struct {
	IsCampaignMap uint32 // Tentatively: 0 = no, 1 = yes
	MinWidth      uint32
	MinLength     uint32
	MaxWidth      uint32
	MaxLength     uint32
	Unknown1      uint32
	Unknown2      uint32
	Unknown3      uint32
	Unknown4      uint32
	Magic         [8]byte // "\x08\x00WHMAP\x00"
	Unknown5      uint32
	Unknown6      uint32
	SetName       [8]byte // Links to a filename in `/Sets/*.set`
	// Need to investigate the rest of the header too
}

func (h Header) Width() int {
	return int(h.MaxWidth - h.MinWidth)
}

func (h Header) Length() int {
	return int(h.MaxLength - h.MinLength)
}

func (h Header) Height() int {
	return MaxHeight
}

type Cell []byte // FIXME: need to deconstruct this into the various fields

// Cells is always a fixed size; use At to get a cell according to x,y,z
type Cells []byte

// FIXME: Ordering may be incorrect? I assume z,y,x for now...
func (c Cells) At(x, y, z int) Cell {
	start :=
		(z * MaxLength * MaxWidth * CellSize) +
			(y * MaxWidth * CellSize) +
			(x * CellSize)

	end := start + CellSize

	return Cell(c[start:end:end])
}

func (h Header) Check() []error {
	var out []error
	if h.IsCampaignMap > 1 {
		out = append(out, fmt.Errorf("Expected 0 or 1 for IsCampaignMap, got %v", h.IsCampaignMap))
	}

	if bytes.Compare(expectedMagic, h.Magic[:]) != 0 {
		out = append(out, fmt.Errorf("Unexpected magic value: %v", h.Magic))
	}

	return out
}

type GameMap struct {
	Header
	Cells
	// TODO: parse this into sections
	Text string
}

// A game map contains a .txt and a .map. If they're in the same directory,
// just pass the directory + basename to load both
func LoadGameMap(prefix string) (*GameMap, error) {
	for _, txtExt := range []string{".TXT", ".txt"} {
		for _, mapExt := range []string{".MAP", ".map"} {
			out, err := LoadGameMapByFiles(prefix+mapExt, prefix+txtExt)
			if err != nil && !os.IsNotExist(err) {
				return nil, err
			}

			if err == nil {
				return out, nil
			}
		}
	}

	return nil, fmt.Errorf("Couldn't find %s.{map,txt}, even ignoring case", prefix)
}

// A game map is composed of two files: .map and .txt
func LoadGameMapByFiles(mapFile, txtFile string) (*GameMap, error) {
	out, err := loadMapFile(mapFile)
	if err != nil {
		return nil, err
	}

	// TODO: load text and parse into sections
	txt, err := ioutil.ReadFile(txtFile)
	if err != nil {
		return nil, err
	}
	out.Text = string(txt)

	for _, err := range out.Check() {
		log.Printf("%s: %v", mapFile, err)
	}

	return out, nil
}

func LoadGameMaps(dir string) (map[string]*GameMap, error) {
	fis, err := ioutil.ReadDir(dir)
	if err != nil {
		return nil, err
	}

	out := make(map[string]*GameMap)

	for _, fi := range fis {
		filename := filepath.Join(dir, fi.Name())
		basename := filepath.Base(filename)
		extname := filepath.Ext(filename)

		// Only pay attention to .MAP files. Assume they will have a .txt too
		if !strings.EqualFold(extname, ".MAP") {
			continue
		}

		prefix := filename[0 : len(filename)-4]

		gameMap, err := LoadGameMap(prefix)
		if err != nil {
			return nil, fmt.Errorf("Error processing %v: %s", filename, err)
		}

		out[basename] = gameMap
	}

	return out, nil
}

func loadMapFile(filename string) (*GameMap, error) {
	var out GameMap

	mf, err := os.Open(filename)
	if err != nil {
		return nil, err
	}

	defer mf.Close()

	zr, err := gzip.NewReader(mf)
	if err != nil {
		return nil, err
	}

	defer zr.Close()

	if err := binary.Read(zr, binary.LittleEndian, &out.Header); err != nil {
		return nil, fmt.Errorf("Error parsing %s: %v", filename, err)
	}

	// no gzip.SeekReader, so discard unread header bytes for now
	discardSize := int64(cellDataOffset - binary.Size(&out.Header))
	if _, err := io.CopyN(ioutil.Discard, zr, discardSize); err != nil {
		return nil, err
	}

	out.Cells = make(Cells, cellDataSize)
	if err := binary.Read(zr, binary.LittleEndian, &out.Cells); err != nil {
		return nil, fmt.Errorf("Error parsing %s: %v", filename, err)
	}

	return &out, nil
}