// 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 common

import (
	"image/color"
	"io/ioutil"
	"log"
	"path/filepath"
	"strconv"
)

const (
	tileWidth      = 18
	tileHeight     = 18
	yOrderCapacity = 512
)

const (
	MaxHeight = 1934
	MinHeight = -1934
)

// To scan the whole height in terms of the y coordinate
// the database is queried in height units defined in the tileDepths table.
var tileDepths = [...][2]int16{
	{1024, MaxHeight},
	{256, 1023},
	{128, 255},
	{64, 127},
	{32, 63},
	{16, 31},
	{8, 15},
	{4, 7},
	{2, 3},
	{0, 1},
	{-1, 0},
	{-4, -2},
	{-8, -5},
	{-16, -9},
	{-32, -17},
	{-64, -33},
	{-128, -65},
	{-256, -129},
	{-1024, -257},
	{MinHeight, -1025}}

var BackgroundColor = color.RGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff}

type BaseTileUpdateFunc func(x, y int, hash []byte) bool

type BaseTileCreator struct {
	client     *RedisClient
	colors     *Colors
	renderer   *Renderer
	yOrder     *YOrder
	yMin       int16
	yMax       int16
	baseDir    string
	emptyImage []byte
	bg         color.RGBA
}

func NewBaseTileCreator(
	client *RedisClient,
	colors *Colors,
	bg color.RGBA,
	yMin, yMax int16,
	transparent bool,
	baseDir string) *BaseTileCreator {

	renderer := NewRenderer(tileWidth, tileHeight, transparent)
	yMin, yMax = Order16(yMin, yMax)
	btc := &BaseTileCreator{
		client:   client,
		colors:   colors,
		bg:       bg,
		renderer: renderer,
		yMin:     yMin,
		yMax:     yMax,
		baseDir:  baseDir,
	}
	btc.yOrder = NewYOrder(btc.renderBlock, yOrderCapacity)
	return btc
}

func (btc *BaseTileCreator) Close() error {
	return btc.client.Close()
}

// renderBlock is a callback to draw a block with a YOrder.
func (btc *BaseTileCreator) renderBlock(block *Block) error {
	return btc.renderer.RenderBlock(block, btc.colors)
}

// blockLoaded is a callback for RedisClient.QueryCuboid.
func (btc *BaseTileCreator) blockLoaded(block *Block) *Block {
	block, err := btc.yOrder.RenderBlock(block)
	if err != nil {
		log.Printf("WARN: rendering block failed: %s\n", err)
	}
	return block
}

func (btc *BaseTileCreator) RenderArea(x, z int16) error {
	btc.renderer.Reset()
	btc.renderer.SetPos(x, z)
	btc.yOrder.Reset()

	var c1, c2 Coord

	nareas := make([]Area, 0, tileWidth*tileHeight/2)
	areas := make([]Area, 1, tileWidth*tileHeight/2)

	areas[0] = Area{
		X1: 0, Z1: 0,
		X2: int16(tileWidth) - 1, Z2: int16(tileHeight) - 1}

	for _, yRange := range tileDepths {
		if yRange[0] > btc.yMax || yRange[1] < btc.yMin {
			continue
		}

		c1.Y = max16(yRange[0], btc.yMin)
		c2.Y = min16(yRange[1], btc.yMax)

		for _, area := range areas {
			c1.X = area.X1 + x
			c1.Z = area.Z1 + z
			c2.X = area.X2 + x
			c2.Z = area.Z2 + z
			query := Cuboid{P1: c1, P2: c2}
			var count int
			var err error
			if count, err = btc.client.QueryCuboid(query, btc.blockLoaded); err != nil {
				return err
			}
			if err = btc.yOrder.Drain(); err != nil {
				log.Printf("WARN: rendering block failed: %s\n", err)
			}

			// If there where loaded blocks in this area recalculate coverage.
			if count > 0 {
				nareas = area.recalculate(btc.renderer, nareas)
			} else {
				nareas = append(nareas, area)
			}
		}

		if len(nareas) == 0 {
			break
		}
		areas, nareas = nareas, areas[:0]
	}
	return nil
}

func (btc *BaseTileCreator) blankImage() []byte {
	// To avoid redundant encoding cache the resulting empty image.
	if btc.emptyImage == nil {
		m := BackgroundImage((tileWidth-2)*16, (tileHeight-2)*16, btc.bg)
		btc.emptyImage = EncodeToMem(m)
	}
	return btc.emptyImage
}

// WriteFunc returns a function intended to be run in background so
// the creation of the next tile with this creator can be done
// concurrently.
func (btc *BaseTileCreator) WriteFunc(i, j int, update BaseTileUpdateFunc) func() (bool, error) {

	path := filepath.Join(btc.baseDir, strconv.Itoa(i), strconv.Itoa(j)+".png")

	// Empty images are likely to be produced during seeding.
	if update == nil && btc.renderer.IsEmpty() {
		return func() (bool, error) {
			//log.Printf("Writing empty (%d, %d) to file %s\n", x, z, path)
			return true, ioutil.WriteFile(path, btc.blankImage(), 0666)
		}
	}

	image := btc.renderer.CreateShadedImage(
		16, 16, (tileWidth-2)*16, (tileHeight-2)*16,
		btc.colors, btc.bg)

	x, z := btc.renderer.GetPos()

	if update == nil {
		return func() (bool, error) {
			log.Printf("Writing (%d, %d) to file %s.\n", x, z, path)
			return true, SaveAsPNG(path, image)
		}
	}

	return func() (bool, error) {
		if update(i, j, HashImage(image)) {
			log.Printf("Writing (%d, %d) to file %s.\n", x, z, path)
			return true, SaveAsPNGAtomic(path, image)
		}

		log.Printf("(%d, %d) is unchanged.\n", x, z)
		return false, nil
	}
}