// Copyright 2017 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package text offers functions to draw texts on an Ebiten's image.
//
// For the example using a TTF font, see font package in the examples.
package text

import (
	"image"
	"image/color"
	"math"

	"golang.org/x/image/font"
	"golang.org/x/image/math/fixed"

	"github.com/hajimehoshi/ebiten"
	"github.com/hajimehoshi/ebiten/internal/sync"
)

var (
	monotonicClock int64
)

func now() int64 {
	monotonicClock++
	return monotonicClock
}

func fixed26_6ToFloat64(x fixed.Int26_6) float64 {
	return float64(x) / (1 << 6)
}

const (
	cacheLimit = 512 // This is an arbitrary number.
)

type colorMCacheKey uint32

type colorMCacheEntry struct {
	m     ebiten.ColorM
	atime int64
}

var (
	colorMCache = map[colorMCacheKey]*colorMCacheEntry{}
)

func drawGlyph(dst *ebiten.Image, face font.Face, r rune, x, y fixed.Int26_6, clr color.Color) {
	// RGBA() is in [0 - 0xffff]. Adjust them in [0 - 0xff].
	cr, cg, cb, ca := clr.RGBA()
	cr >>= 8
	cg >>= 8
	cb >>= 8
	ca >>= 8
	if ca == 0 {
		return
	}

	img := getGlyphImage(face, r)
	if img == nil {
		return
	}

	b := getGlyphBounds(face, r)
	op := &ebiten.DrawImageOptions{}
	op.GeoM.Translate(fixed26_6ToFloat64(x+b.Min.X), fixed26_6ToFloat64(y+b.Min.Y))

	key := colorMCacheKey(uint32(cr) | (uint32(cg) << 8) | (uint32(cb) << 16) | (uint32(ca) << 24))
	e, ok := colorMCache[key]
	if ok {
		e.atime = now()
	} else {
		if len(colorMCache) > cacheLimit {
			oldest := int64(math.MaxInt64)
			oldestKey := colorMCacheKey(0)
			for key, c := range colorMCache {
				if c.atime < oldest {
					oldestKey = key
					oldest = c.atime
				}
			}
			delete(colorMCache, oldestKey)
		}

		cm := ebiten.ColorM{}
		rf := float64(cr) / float64(ca)
		gf := float64(cg) / float64(ca)
		bf := float64(cb) / float64(ca)
		af := float64(ca) / 0xff
		cm.Scale(rf, gf, bf, af)
		e = &colorMCacheEntry{
			m:     cm,
			atime: now(),
		}
		colorMCache[key] = e
	}
	op.ColorM = e.m

	_ = dst.DrawImage(img, op)
}

var (
	// Use pointers to avoid copying on browsers.
	glyphBoundsCache = map[font.Face]map[rune]*fixed.Rectangle26_6{}
)

func getGlyphBounds(face font.Face, r rune) *fixed.Rectangle26_6 {
	if _, ok := glyphBoundsCache[face]; !ok {
		glyphBoundsCache[face] = map[rune]*fixed.Rectangle26_6{}
	}
	if b, ok := glyphBoundsCache[face][r]; ok {
		return b
	}
	b, _, _ := face.GlyphBounds(r)
	glyphBoundsCache[face][r] = &b
	return &b
}

type glyphImageCacheEntry struct {
	image *ebiten.Image
	atime int64
}

var (
	glyphImageCache = map[font.Face]map[rune]*glyphImageCacheEntry{}
	emptyGlyphs     = map[font.Face]map[rune]struct{}{}
)

func getGlyphImage(face font.Face, r rune) *ebiten.Image {
	if _, ok := emptyGlyphs[face]; !ok {
		emptyGlyphs[face] = map[rune]struct{}{}
	}
	if _, ok := glyphImageCache[face]; !ok {
		glyphImageCache[face] = map[rune]*glyphImageCacheEntry{}
	}

	if _, ok := emptyGlyphs[face][r]; ok {
		return nil
	}
	if e, ok := glyphImageCache[face][r]; ok {
		e.atime = now()
		return e.image
	}

	b := getGlyphBounds(face, r)
	w, h := (b.Max.X - b.Min.X).Ceil(), (b.Max.Y - b.Min.Y).Ceil()
	if w == 0 || h == 0 {
		emptyGlyphs[face][r] = struct{}{}
		return nil
	}

	if len(glyphImageCache[face]) > cacheLimit {
		oldest := int64(math.MaxInt64)
		oldestKey := rune(-1)
		for r, e := range glyphImageCache[face] {
			if e.atime < oldest {
				oldestKey = r
				oldest = e.atime
			}
		}
		glyphImageCache[face][oldestKey].image.Dispose()
		delete(glyphImageCache[face], oldestKey)
	}

	rgba := image.NewRGBA(image.Rect(0, 0, w, h))
	d := font.Drawer{
		Dst:  rgba,
		Src:  image.White,
		Face: face,
	}
	d.Dot = fixed.Point26_6{-b.Min.X, -b.Min.Y}
	d.DrawString(string(r))

	img, _ := ebiten.NewImageFromImage(rgba, ebiten.FilterDefault)
	glyphImageCache[face][r] = &glyphImageCacheEntry{
		image: img,
		atime: now(),
	}
	return img
}

var textM sync.Mutex

// Draw draws a given text on a given destination image dst.
//
// face is the font for text rendering.
// (x, y) represents a 'dot' (period) position.
// Be careful that this doesn't represent left-upper corner position.
// clr is the color for text rendering.
//
// Glyphs used for rendering are cached in least-recently-used way.
// It is OK to call this function with a same text and a same face at every frame in terms of performance.
//
// Be careful that the passed font face is held by this package and is never released.
// This is a known issue (#498).
//
// This function is concurrent-safe.
func Draw(dst *ebiten.Image, text string, face font.Face, x, y int, clr color.Color) {
	textM.Lock()

	fx := fixed.I(x)
	prevR := rune(-1)

	runes := []rune(text)
	for _, r := range runes {
		if prevR >= 0 {
			fx += face.Kern(prevR, r)
		}
		drawGlyph(dst, face, r, fx, fixed.I(y), clr)
		fx += glyphAdvance(face, r)

		prevR = r
	}

	textM.Unlock()
}