// 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 (
	"bufio"
	"fmt"
	"image"
	"image/draw"
	"image/png"
	"io/ioutil"
	"log"
	"math"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"

	"github.com/nfnt/resize"
)

func findMaxDir(files []os.FileInfo) (min, max int) {
	min, max = math.MaxInt32, math.MinInt32
	for _, file := range files {
		if !file.Mode().IsDir() {
			continue
		}
		if x, err := strconv.Atoi(file.Name()); err == nil {
			if x > max {
				max = x
			}
			if x < min {
				min = x
			}
		}
	}
	return
}

func findMaxFile(files []os.FileInfo) (min, max int) {
	min, max = math.MaxInt32, math.MinInt32
	for _, file := range files {
		if !file.Mode().IsRegular() {
			continue
		}
		name := file.Name()
		name = strings.TrimSuffix(name, filepath.Ext(name))
		if x, err := strconv.Atoi(name); err == nil {
			if x > max {
				max = x
			}
			if x < min {
				min = x
			}
		}
	}
	return
}

type pyramidJob struct {
	src [4]string
	dst string
}

func createParentLevel(oldDir string, jobs chan pyramidJob) (newDir string, err error) {
	oldName := filepath.Base(oldDir)

	var oldLevel int
	if oldLevel, err = strconv.Atoi(oldName); err != nil {
		return
	}

	if oldLevel <= 0 {
		return
	}

	var files []os.FileInfo
	if files, err = ioutil.ReadDir(oldDir); err != nil {
		return
	}

	xMin, xMax := findMaxDir(files)
	if xMax == math.MinInt32 {
		return
	}

	newLevel := oldLevel - 1

	log.Printf("Generating tiles of level %d", newLevel)

	parentDir := filepath.Dir(oldDir)
	newDir = filepath.Join(parentDir, strconv.Itoa(newLevel))

	if err = os.MkdirAll(newDir, os.ModePerm); err != nil {
		return
	}

	for ox, nx := xMin, xMin; ox <= xMax; ox += 2 {

		ox1Dir := filepath.Join(oldDir, strconv.Itoa(ox))
		ox2Dir := filepath.Join(oldDir, strconv.Itoa(ox+1))

		if files, err = ioutil.ReadDir(ox1Dir); err != nil {
			return
		}
		zMin, zMax := findMaxFile(files)
		if zMax == math.MinInt32 {
			nx++
			continue
		}

		nxDir := filepath.Join(newDir, strconv.Itoa(nx))
		if err = os.MkdirAll(nxDir, os.ModePerm); err != nil {
			return
		}

		for oz, nz := zMin, zMin; oz <= zMax; oz += 2 {
			oz1 := fmt.Sprintf("%d.png", oz)
			oz2 := fmt.Sprintf("%d.png", oz+1)
			s1 := filepath.Join(ox1Dir, oz1)
			s2 := filepath.Join(ox1Dir, oz2)
			s3 := filepath.Join(ox2Dir, oz1)
			s4 := filepath.Join(ox2Dir, oz2)
			d := filepath.Join(nxDir, fmt.Sprintf("%d.png", nz))
			jobs <- pyramidJob{src: [4]string{s1, s2, s3, s4}, dst: d}
			nz++
		}

		nx++
	}
	return
}

func loadImage(path string) image.Image {
	var err error
	var file *os.File
	if file, err = os.Open(path); err != nil {
		//log.Printf("WARN: %s", err)
		return image.White
	}
	defer file.Close()
	reader := bufio.NewReader(file)
	var img image.Image
	if img, err = png.Decode(reader); err != nil {
		log.Printf("WARN: %s", err)
		return image.White
	}
	return img
}

func fuseTile(scratch *image.RGBA, job *pyramidJob) (err error) {

	var ofs = [4][2]int{
		{0, 0},
		{0, 256},
		{256, 0},
		{256, 256}}

	for i, path := range job.src {

		img := loadImage(path)

		draw.Draw(scratch,
			image.Rect(ofs[i][0], ofs[i][1], 256, 256),
			img, image.ZP, draw.Src)
	}

	resized := resize.Resize(256, 256, scratch, resize.Bicubic)

	var outFile *os.File
	if outFile, err = os.Create(job.dst); err != nil {
		return
	}

	out := bufio.NewWriter(outFile)

	if err = png.Encode(out, resized); err != nil {
		outFile.Close()
		return
	}

	out.Flush()
	err = outFile.Close()

	return
}

func fuseTiles(jobs chan pyramidJob, done *sync.WaitGroup) {
	defer done.Done()
	scratch := image.NewRGBA(image.Rect(0, 0, 512, 512))

	for job := range jobs {
		if err := fuseTile(scratch, &job); err != nil {
			log.Printf("WARN: Writing image failed: %s", err)
		}
	}
}

func createPyramid(outDir string, numWorker int) (err error) {

	for oldDir := filepath.Join(outDir, baseLevelDir); oldDir != ""; {
		if oldDir, err = createLevel(oldDir, numWorker); err != nil {
			return
		}
	}
	return
}

func createLevel(oldDir string, numWorker int) (newDir string, err error) {

	jobs := make(chan pyramidJob)

	var done sync.WaitGroup

	for i := 0; i < numWorker; i++ {
		done.Add(1)
		go fuseTiles(jobs, &done)
	}

	newDir, err = createParentLevel(oldDir, jobs)
	close(jobs)

	if err != nil {
		return
	}

	done.Wait()

	return
}