// Copyright 2014, 2015 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 (
	"encoding/json"
	"image"
	"image/color"
	"image/draw"
	"log"
	"net"
	"net/http"
	"path/filepath"
	"strconv"
	"strings"
	"sync"

	"github.com/bamiaux/rez"

	"bytes"

	"bitbucket.org/s_l_teichmann/mtsatellite/common"
)

// Number of check sums to keep in memory.
const maxHashedTiles = 256

type baseTilesUpdates interface {
	BaseTilesUpdated([]xz)
}

type tileUpdater struct {
	changes      map[xz]struct{}
	btu          baseTilesUpdates
	mapDir       string
	redisAddress string
	ips          []net.IP
	colors       *common.Colors
	bg           color.RGBA
	yMin, yMax   int16
	workers      int
	transparent  bool
	cond         *sync.Cond
	mu           sync.Mutex
}

type xz struct {
	X int16
	Z int16
}

type xzc struct {
	xz
	canceled bool
}

type xzm struct {
	xz
	Mask uint16
}

func (c xz) quantize() xz {
	return xz{X: (c.X - -1933) / 16, Z: (c.Z - -1933) / 16}
}

func (c xz) dequantize() xz {
	return xz{X: c.X*16 + -1933, Z: c.Z*16 + -1933}
}

func (c xz) parent() xzm {
	xp, xr := c.X>>1, uint16(c.X&1)
	zp, zr := c.Z>>1, uint16(c.Z&1)
	return xzm{
		xz{X: xp, Z: zp},
		1 << (zr<<1 | xr)}
}

func newTileUpdater(
	mapDir, redisAddress string,
	ips []net.IP,
	colors *common.Colors,
	bg color.RGBA,
	yMin, yMax int,
	transparent bool,
	workers int,
	btu baseTilesUpdates) *tileUpdater {

	tu := tileUpdater{
		btu:          btu,
		mapDir:       mapDir,
		redisAddress: redisAddress,
		ips:          ips,
		changes:      map[xz]struct{}{},
		colors:       colors,
		bg:           bg,
		yMin:         int16(yMin),
		yMax:         int16(yMax),
		transparent:  transparent,
		workers:      workers}
	tu.cond = sync.NewCond(&tu.mu)
	return &tu
}

func (tu *tileUpdater) checkIP(r *http.Request) bool {
	if len(tu.ips) == 0 {
		return true
	}

	idx := strings.LastIndex(r.RemoteAddr, ":")
	if idx < 0 {
		log.Printf("WARN: cannot extract host from '%s'.\n", r.RemoteAddr)
		return false
	}

	host := strings.Trim(r.RemoteAddr[:idx], "[]")
	ip := net.ParseIP(host)
	if ip == nil {
		log.Printf("WARN: cannot get IP for host '%s'.\n", host)
		return false
	}

	for i := range tu.ips {
		if bytes.Compare(tu.ips[i], ip) == 0 {
			return true
		}
	}

	return false
}

func (tu *tileUpdater) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
	if !tu.checkIP(r) {
		log.Printf("WARN: Unauthorized update request from '%s'\n", r.RemoteAddr)
		http.Error(rw, http.StatusText(http.StatusUnauthorized), http.StatusUnauthorized)
		return
	}

	var err error
	var newChanges []xz
	decoder := json.NewDecoder(r.Body)
	if err = decoder.Decode(&newChanges); err != nil {
		log.Printf("WARN: JSON document broken: %s\n", err)
		http.Error(rw, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
		return
	}

	if len(newChanges) > 0 {
		tu.cond.L.Lock()
		for _, c := range newChanges {
			tu.changes[c.quantize()] = struct{}{}
		}
		tu.cond.L.Unlock()
		tu.cond.Signal()
	}

	rw.WriteHeader(http.StatusOK)
}

func extractChanges(changes map[xz]struct{}) []xzc {
	chs := make([]xzc, len(changes))
	var i int
	for ch := range changes {
		chs[i] = xzc{ch, false}
		i++
	}
	return chs
}

func activeChanges(changes []xzc) []xz {
	chs := make([]xz, 0, len(changes))
	for i := range changes {
		if !changes[i].canceled {
			chs = append(chs, changes[i].xz)
		}
	}
	return chs
}

func (tu *tileUpdater) doUpdates() {

	bth := common.NewBaseTileHash(maxHashedTiles)

	baseDir := filepath.Join(tu.mapDir, "8")

	for {
		tu.cond.L.Lock()
		for len(tu.changes) == 0 {
			tu.cond.Wait()
		}
		changes := extractChanges(tu.changes)
		tu.changes = map[xz]struct{}{}
		tu.cond.L.Unlock()

		jobs := make(chan *xzc)
		var done sync.WaitGroup

		var proto string
		if strings.ContainsRune(tu.redisAddress, '/') {
			proto = "unix"
		} else {
			proto = "tcp"
		}

		for i, n := 0, common.Min(tu.workers, len(changes)); i < n; i++ {
			var client *common.RedisClient
			var err error
			if client, err = common.NewRedisClient(proto, tu.redisAddress); err != nil {
				log.Printf("WARN: Cannot connect to redis server: %s\n", err)
				continue
			}
			btc := common.NewBaseTileCreator(
				client, tu.colors, tu.bg,
				tu.yMin, tu.yMax,
				tu.transparent, baseDir)
			done.Add(1)
			go tu.updateBaseTiles(jobs, btc, &done, bth.Update)
		}

		for i := range changes {
			jobs <- &changes[i]
		}
		close(jobs)
		done.Wait()

		actChs := activeChanges(changes)

		if len(actChs) == 0 {
			continue
		}

		parentJobs := make(map[xz]uint16)
		for i := range actChs {
			pxz := actChs[i].parent()
			parentJobs[pxz.xz] |= pxz.Mask
		}

		for level := 7; level >= 0; level-- {
			pJobs := make(chan xzm)
			for i, n := 0, common.Min(len(parentJobs), tu.workers); i < n; i++ {
				done.Add(1)
				go tu.updatePyramidTiles(level, pJobs, &done)
			}
			ppJobs := make(map[xz]uint16)
			for c, mask := range parentJobs {
				pJobs <- xzm{c, mask}
				pxz := c.parent()
				ppJobs[pxz.xz] |= pxz.Mask
			}
			close(pJobs)
			done.Wait()
			parentJobs = ppJobs
		}

		if tu.btu != nil {
			tu.btu.BaseTilesUpdated(actChs)
		}
	}
}

func (tu *tileUpdater) updatePyramidTiles(
	level int, jobs chan xzm, done *sync.WaitGroup) {

	defer done.Done()
	scratch := image.NewRGBA(image.Rect(0, 0, 256, 256))
	resized := image.NewRGBA(image.Rect(0, 0, 128, 128))

	for job := range jobs {
		if err := tu.updatePyramidTile(scratch, resized, level, job); err != nil {
			log.Printf("Updating pyramid tile failed: %s\n", err)
		}
	}
}

/*
  (0,0)    (128, 0)
  (0, 128) (128, 128)
*/

var dps = [4]image.Point{
	image.Pt(0, 128),
	image.Pt(128, 128),
	image.Pt(0, 0),
	image.Pt(128, 0),
}

var ofs = [4][2]int{
	{0, 0},
	{1, 0},
	{0, 1},
	{1, 1}}

var windowSize = image.Pt(128, 128)

func (tu *tileUpdater) updatePyramidTile(scratch, resized *image.RGBA, level int, j xzm) error {

	var orig image.Image

	origPath := filepath.Join(
		tu.mapDir,
		strconv.Itoa(level),
		strconv.Itoa(int(j.X)),
		strconv.Itoa(int(j.Z))+".png")

	sr := resized.Bounds()
	levelDir := strconv.Itoa(level + 1)
	for i := uint16(0); i < 4; i++ {
		if j.Mask&(1<<i) != 0 {
			//log.Printf("level %d: modified %d\n", level, i)
			o := ofs[i]
			bx, bz := int(2*j.X), int(2*j.Z)
			path := filepath.Join(
				tu.mapDir,
				levelDir,
				strconv.Itoa(bx+o[0]),
				strconv.Itoa(bz+o[1])+".png")
			img := common.LoadPNG(path, tu.bg)
			if err := rez.Convert(resized, img, common.ResizeFilter); err != nil {
				return err
			}
			r := sr.Sub(sr.Min).Add(dps[i])
			draw.Draw(scratch, r, resized, sr.Min, draw.Src)
		} else {
			// Load lazy
			if orig == nil {
				orig = common.LoadPNG(origPath, tu.bg)
			}
			//log.Printf("level %d: copied %d\n", level, i)
			min := orig.Bounds().Min.Add(dps[i])
			r := image.Rectangle{min, min.Add(windowSize)}
			draw.Draw(scratch, r, orig, min, draw.Src)
		}
	}

	return common.SaveAsPNGAtomic(origPath, scratch)
}

func (tu *tileUpdater) updateBaseTiles(
	jobs chan *xzc,
	btc *common.BaseTileCreator,
	done *sync.WaitGroup,
	update common.BaseTileUpdateFunc) {

	type jobWriter struct {
		job *xzc
		wFn func() (bool, error)
	}

	jWs := make(chan jobWriter)

	go func() {
		for jw := range jWs {
			updated, err := jw.wFn()
			if err != nil {
				log.Printf("WARN: writing tile failed: %v.\n", err)
			}
			if !updated {
				jw.job.canceled = true
			}
		}
	}()

	defer func() {
		close(jWs)
		btc.Close()
		done.Done()
	}()

	for job := range jobs {
		xz := job.dequantize()
		if err := btc.RenderArea(xz.X-1, xz.Z-1); err != nil {
			log.Printf("WARN: rendering tile failed: %v.\n", err)
			job.canceled = true
			continue
		}
		jWs <- jobWriter{job, btc.WriteFunc(int(job.X), int(job.Z), update)}
	}
}