mtsatellite/tilemapper/blockdecoder.go

// Copyright 2014 by Sascha L. Teichmann
// Use of this source code is governed by the MIT license
// that can be found in the LICENSE file.

package main

import (
	"compress/zlib"
	"encoding/binary"
	"errors"
	"io"
	"io/ioutil"
)

var (
	ErrMapContentSizeMismatch = errors.New("Content size does not match.")
)

const (
	mapBlockSize = 16
	nodeCount    = mapBlockSize * mapBlockSize * mapBlockSize
)

type DecodedBlock struct {
	Version    byte
	MapContent []byte
	AirId      int
	IgnoreId   int
	NameMap    map[int]string
}

type PosBuf struct {
	Data []byte
	Pos  int
}

func NewDecodedBlock(data []byte) (db *DecodedBlock, err error) {
	version := data[0]

	contentWidth := int(data[2])
	paramsWidth := int(data[3])

	uncompressedLen := nodeCount * (contentWidth + paramsWidth)

	offset := 2
	if version >= 22 {
		offset = 4
	}

	buf := NewPosBuf(data[offset:])
	var zr io.ReadCloser
	if zr, err = zlib.NewReader(buf); err != nil {
		return
	}

	var mapContent []byte
	if mapContent, err = ioutil.ReadAll(zr); err != nil {
		return
	}
	zr.Close()

	if uncompressedLen != len(mapContent) {
		err = ErrMapContentSizeMismatch
		return
	}

	offset += buf.Pos
	buf.Pos = 0
	buf.Data = data[offset:]

	if zr, err = zlib.NewReader(buf); err != nil {
		return
	}

	// Discard the meta data.
	_, err = io.Copy(ioutil.Discard, zr)
	zr.Close()
	if err != nil {
		return
	}

	offset += buf.Pos

	switch {
	case version <= 21:
		offset += 2
	case version == 23:
		offset++
	case version == 24:
		ver := data[offset]
		offset++
		if ver == 1 {
			num := int(binary.BigEndian.Uint16(data[offset:]))
			offset += 2 + 10*num
		}
	}

	offset++
	numStaticObjects := int(binary.BigEndian.Uint16(data[offset:]))
	offset += 2
	for i := 0; i < numStaticObjects; i++ {
		offset += 13
		dataSize := int(binary.BigEndian.Uint16(data[offset:]))
		offset += dataSize + 2
	}
	offset += 4

	airId, ignoreId := -1, -1
	nameMap := make(map[int]string)
	if version >= 22 {
		offset++
		numMappings := int(binary.BigEndian.Uint16(data[offset:]))
		offset += 2
		for i := 0; i < numMappings; i++ {
			nodeId := int(binary.BigEndian.Uint16(data[offset:]))
			offset += 2
			nameLen := int(binary.BigEndian.Uint16(data[offset:]))
			offset += 2
			name := string(data[offset : offset+nameLen])
			offset += nameLen
			switch name {
			case "air":
				airId = nodeId
			case "ignore":
				ignoreId = nodeId
			default:
				nameMap[nodeId] = name
			}
		}
	}

	db = &DecodedBlock{
		Version:    version,
		MapContent: mapContent,
		AirId:      airId,
		IgnoreId:   ignoreId,
		NameMap:    nameMap}

	return
}

func NewPosBuf(data []byte) *PosBuf {
	return &PosBuf{Data: data}
}

func (pb *PosBuf) Read(p []byte) (int, error) {
	pl := len(p)
	ml := len(pb.Data)
	if pb.Pos >= ml {
		return 0, io.EOF
	}
	rest := ml - pb.Pos
	if pl > rest {
		copy(p, pb.Data[pb.Pos:])
		pb.Pos = ml
		return rest, io.EOF
	}
	copy(p, pb.Data[pb.Pos:pb.Pos+pl])
	pb.Pos += pl
	return pl, nil
}

func (pb *PosBuf) ReadByte() (byte, error) {
	if pb.Pos >= len(pb.Data) {
		return 0, io.EOF
	}
	c := pb.Data[pb.Pos]
	pb.Pos++
	return c, nil
}