// Copyright 2015 Hajime Hoshi
//
// 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.

// +build darwin freebsd linux windows
// +build !js
// +build !android
// +build !ios

package ui

import (
	"image"
	"math"
	"runtime"
	"sync"
	"time"

	"github.com/go-gl/glfw/v3.2/glfw"
	"github.com/hajimehoshi/ebiten/internal/opengl"
)

type userInterface struct {
	title                string
	window               *glfw.Window
	width                int
	windowWidth          int
	height               int
	scale                float64
	cachedDeviceScale    float64
	cachedGLFWScale      float64
	fullscreenScale      float64
	funcs                chan func()
	running              bool
	sizeChanged          bool
	origPosX             int
	origPosY             int
	initFullscreen       bool
	initCursorVisible    bool
	initIconImages       []image.Image
	runnableInBackground bool
	m                    sync.Mutex
}

var (
	currentUI = &userInterface{
		sizeChanged:       true,
		origPosX:          -1,
		origPosY:          -1,
		initCursorVisible: true,
	}
	currentUIInitialized = make(chan struct{})
)

func init() {
	runtime.LockOSThread()
}

func initialize() error {
	if err := glfw.Init(); err != nil {
		return err
	}
	glfw.WindowHint(glfw.Visible, glfw.False)
	glfw.WindowHint(glfw.Resizable, glfw.False)
	glfw.WindowHint(glfw.ContextVersionMajor, 2)
	glfw.WindowHint(glfw.ContextVersionMinor, 1)

	// As start, create an window with temporary size to create OpenGL context thread.
	window, err := glfw.CreateWindow(16, 16, "", nil, nil)
	if err != nil {
		return err
	}
	hideConsoleWindowOnWindows()
	currentUI.window = window
	currentUI.funcs = make(chan func())

	currentUI.window.MakeContextCurrent()

	mode := glfw.CursorNormal
	if !currentUI.isInitCursorVisible() {
		mode = glfw.CursorHidden
	}
	if i := currentUI.getInitIconImages(); i != nil {
		currentUI.window.SetIcon(i)
	}
	currentUI.window.SetInputMode(glfw.CursorMode, mode)
	currentUI.window.SetInputMode(glfw.StickyMouseButtonsMode, glfw.True)
	currentUI.window.SetInputMode(glfw.StickyKeysMode, glfw.True)
	return nil
}

func RunMainThreadLoop(ch <-chan error) error {
	// This must be called on the main thread.

	if err := initialize(); err != nil {
		return err
	}
	close(currentUIInitialized)

	// TODO: Check this is done on the main thread.
	currentUI.setRunning(true)
	defer func() {
		currentUI.setRunning(false)
	}()
	for {
		select {
		case f := <-currentUI.funcs:
			f()
		case err := <-ch:
			// ch returns a value not only when an error occur but also it is closed.
			return err
		}
	}
}

func (u *userInterface) isRunning() bool {
	u.m.Lock()
	v := u.running
	u.m.Unlock()
	return v
}

func (u *userInterface) setRunning(running bool) {
	u.m.Lock()
	u.running = running
	u.m.Unlock()
}

func (u *userInterface) isInitFullscreen() bool {
	u.m.Lock()
	v := u.initFullscreen
	u.m.Unlock()
	return v
}

func (u *userInterface) setInitFullscreen(initFullscreen bool) {
	u.m.Lock()
	u.initFullscreen = initFullscreen
	u.m.Unlock()
}

func (u *userInterface) isInitCursorVisible() bool {
	u.m.Lock()
	v := u.initCursorVisible
	u.m.Unlock()
	return v
}

func (u *userInterface) setInitCursorVisible(visible bool) {
	u.m.Lock()
	u.initCursorVisible = visible
	u.m.Unlock()
}

func (u *userInterface) isRunnableInBackground() bool {
	u.m.Lock()
	v := u.runnableInBackground
	u.m.Unlock()
	return v
}

func (u *userInterface) setRunnableInBackground(runnableInBackground bool) {
	u.m.Lock()
	u.runnableInBackground = runnableInBackground
	u.m.Unlock()
}

func (u *userInterface) getInitIconImages() []image.Image {
	u.m.Lock()
	i := u.initIconImages
	u.m.Unlock()
	return i
}

func (u *userInterface) setInitIconImages(iconImages []image.Image) {
	u.m.Lock()
	u.initIconImages = iconImages
	u.m.Unlock()
}

func (u *userInterface) runOnMainThread(f func() error) error {
	if u.funcs == nil {
		// already closed
		return nil
	}
	ch := make(chan struct{})
	var err error
	u.funcs <- func() {
		err = f()
		close(ch)
	}
	<-ch
	return err
}

func SetScreenSize(width, height int) bool {
	u := currentUI
	if !u.isRunning() {
		panic("ui: Run is not called yet")
	}
	r := false
	_ = u.runOnMainThread(func() error {
		r = u.setScreenSize(width, height, u.scale, u.fullscreen())
		return nil
	})
	return r
}

func SetScreenScale(scale float64) bool {
	u := currentUI
	if !u.isRunning() {
		panic("ui: Run is not called yet")
	}
	r := false
	_ = u.runOnMainThread(func() error {
		r = u.setScreenSize(u.width, u.height, scale, u.fullscreen())
		return nil
	})
	return r
}

func ScreenScale() float64 {
	u := currentUI
	if !u.isRunning() {
		return 0
	}
	s := 0.0
	_ = u.runOnMainThread(func() error {
		s = u.scale
		return nil
	})
	return s
}

func (u *userInterface) fullscreen() bool {
	if !u.isRunning() {
		panic("not reached")
	}
	return u.window.GetMonitor() != nil
}

func IsFullscreen() bool {
	u := currentUI
	if !u.isRunning() {
		return u.isInitFullscreen()
	}
	return u.fullscreen()
}

func SetFullscreen(fullscreen bool) {
	u := currentUI
	if !u.isRunning() {
		u.setInitFullscreen(fullscreen)
		return
	}
	_ = u.runOnMainThread(func() error {
		u := currentUI
		u.setScreenSize(u.width, u.height, u.scale, fullscreen)
		return nil
	})
}

func SetRunnableInBackground(runnableInBackground bool) {
	currentUI.setRunnableInBackground(runnableInBackground)
}

func IsRunnableInBackground() bool {
	return currentUI.isRunnableInBackground()
}

func SetWindowIcon(iconImages []image.Image) {
	if !currentUI.isRunning() {
		currentUI.setInitIconImages(iconImages)
		return
	}
	_ = currentUI.runOnMainThread(func() error {
		currentUI.window.SetIcon(iconImages)
		return nil
	})
}

func ScreenOffset() (float64, float64) {
	u := currentUI
	if !u.isRunning() {
		return 0, 0
	}
	if !IsFullscreen() {
		if u.width == u.windowWidth {
			return 0, 0
		}
		return (float64(u.windowWidth)*u.actualScreenScale() - float64(u.width)*u.actualScreenScale()) / 2, 0
	}
	ox := 0.0
	oy := 0.0
	m := glfw.GetPrimaryMonitor()
	v := m.GetVideoMode()
	_ = u.runOnMainThread(func() error {
		ox = (float64(v.Width)*u.deviceScale()/u.glfwScale() - float64(u.width)*u.actualScreenScale()) / 2
		oy = (float64(v.Height)*u.deviceScale()/u.glfwScale() - float64(u.height)*u.actualScreenScale()) / 2
		return nil
	})
	return ox, oy
}

func adjustCursorPosition(x, y int) (int, int) {
	u := currentUI
	if !u.isRunning() {
		return x, y
	}
	ox, oy := ScreenOffset()
	s := 0.0
	_ = currentUI.runOnMainThread(func() error {
		s = currentUI.actualScreenScale()
		return nil
	})
	return x - int(ox/s), y - int(oy/s)
}

func IsCursorVisible() bool {
	u := currentUI
	if !u.isRunning() {
		return u.isInitCursorVisible()
	}
	v := false
	_ = currentUI.runOnMainThread(func() error {
		v = currentUI.window.GetInputMode(glfw.CursorMode) == glfw.CursorNormal
		return nil
	})
	return v
}

func SetCursorVisibility(visible bool) {
	u := currentUI
	if !u.isRunning() {
		u.setInitCursorVisible(visible)
		return
	}
	_ = currentUI.runOnMainThread(func() error {
		c := glfw.CursorNormal
		if !visible {
			c = glfw.CursorHidden
		}
		currentUI.window.SetInputMode(glfw.CursorMode, c)
		return nil
	})
}

func Run(width, height int, scale float64, title string, g GraphicsContext) error {
	<-currentUIInitialized

	u := currentUI
	// GLContext must be created before setting the screen size, which requires
	// swapping buffers.
	opengl.Init(currentUI.runOnMainThread)
	_ = u.runOnMainThread(func() error {
		m := glfw.GetPrimaryMonitor()
		v := m.GetVideoMode()

		// The game is in window mode (not fullscreen mode) at the first state.
		// Don't refer u.initFullscreen here to avoid some GLFW problems.
		u.setScreenSize(width, height, scale, false)
		u.title = title
		u.window.SetTitle(title)
		u.window.Show()

		w, h := u.glfwSize()
		x := (v.Width - w) / 2
		y := (v.Height - h) / 3
		x, y = adjustWindowPosition(x, y)
		u.window.SetPos(x, y)
		return nil
	})
	return u.loop(g)
}

func (u *userInterface) glfwScale() float64 {
	if u.cachedGLFWScale == 0 {
		u.cachedGLFWScale = glfwScale()
	}
	return u.cachedGLFWScale
}

func (u *userInterface) deviceScale() float64 {
	if u.cachedDeviceScale == 0 {
		u.cachedDeviceScale = deviceScale()
	}
	return u.cachedDeviceScale
}

func (u *userInterface) glfwSize() (int, int) {
	w := int(float64(u.windowWidth) * u.getScale() * u.glfwScale())
	h := int(float64(u.height) * u.getScale() * u.glfwScale())
	return w, h
}

func (u *userInterface) getScale() float64 {
	if !u.fullscreen() {
		return u.scale
	}
	if u.fullscreenScale == 0 {
		m := glfw.GetPrimaryMonitor()
		v := m.GetVideoMode()
		sw := float64(v.Width) / u.glfwScale() / float64(u.width)
		sh := float64(v.Height) / u.glfwScale() / float64(u.height)
		s := sw
		if s > sh {
			s = sh
		}
		u.fullscreenScale = s
	}
	return u.fullscreenScale
}

func (u *userInterface) actualScreenScale() float64 {
	return u.getScale() * u.deviceScale()
}

func (u *userInterface) pollEvents() {
	glfw.PollEvents()
	currentInput.update(u.window, u.getScale()*u.glfwScale())
}

func (u *userInterface) update(g GraphicsContext) error {
	shouldClose := false
	_ = u.runOnMainThread(func() error {
		shouldClose = u.window.ShouldClose()
		return nil
	})
	if shouldClose {
		return &RegularTermination{}
	}

	_ = u.runOnMainThread(func() error {
		if u.isInitFullscreen() {
			u := currentUI
			u.setScreenSize(u.width, u.height, u.scale, true)
			u.setInitFullscreen(false)
		}
		return nil
	})

	actualScale := 0.0
	sizeChanged := false
	_ = u.runOnMainThread(func() error {
		if !u.sizeChanged {
			return nil
		}
		u.sizeChanged = false
		actualScale = u.actualScreenScale()
		sizeChanged = true
		return nil
	})
	if sizeChanged {
		g.SetSize(u.width, u.height, actualScale)
	}

	_ = u.runOnMainThread(func() error {
		u.pollEvents()
		for !u.isRunnableInBackground() && u.window.GetAttrib(glfw.Focused) == 0 {
			// Wait for an arbitrary period to avoid busy loop.
			time.Sleep(time.Second / 60)
			u.pollEvents()
			if u.window.ShouldClose() {
				return nil
			}
		}
		return nil
	})
	if err := g.Update(); err != nil {
		return err
	}
	currentInput.runeBuffer = currentInput.runeBuffer[:0]
	return nil
}

func (u *userInterface) loop(g GraphicsContext) error {
	defer func() {
		_ = u.runOnMainThread(func() error {
			glfw.Terminate()
			return nil
		})
	}()
	for {
		if err := u.update(g); err != nil {
			return err
		}
		// The bound framebuffer must be the default one (0) before swapping buffers.
		opengl.GetContext().BindScreenFramebuffer()
		_ = u.runOnMainThread(func() error {
			u.swapBuffers()
			return nil
		})
	}
}

func (u *userInterface) swapBuffers() {
	u.window.SwapBuffers()
}

func (u *userInterface) setScreenSize(width, height int, scale float64, fullscreen bool) bool {
	if u.width == width && u.height == height && u.scale == scale && u.fullscreen() == fullscreen {
		return false
	}

	// On Windows, giving a too small width doesn't call a callback (#165).
	// To prevent hanging up, return asap if the width is too small.
	// 252 is an arbitrary number and I guess this is small enough.
	const minWindowWidth = 252

	u.width = width
	u.windowWidth = width
	s := scale * u.deviceScale()
	if int(float64(width)*s) < minWindowWidth {
		u.windowWidth = int(math.Ceil(minWindowWidth / s))
	}
	u.height = height
	u.scale = scale
	u.fullscreenScale = 0

	// To make sure the current existing framebuffers are rendered,
	// swap buffers here before SetSize is called.
	u.swapBuffers()

	if fullscreen {
		if u.origPosX < 0 && u.origPosY < 0 {
			u.origPosX, u.origPosY = u.window.GetPos()
		}
		m := glfw.GetPrimaryMonitor()
		v := m.GetVideoMode()
		u.window.SetMonitor(m, 0, 0, v.Width, v.Height, v.RefreshRate)
	} else {
		if u.origPosX >= 0 && u.origPosY >= 0 {
			x := u.origPosX
			y := u.origPosY
			u.window.SetMonitor(nil, x, y, 16, 16, 0)
			u.origPosX = -1
			u.origPosY = -1
		}

		oldW, oldH := u.window.GetSize()
		newW, newH := u.glfwSize()
		if oldW != newW || oldH != newH {
			ch := make(chan struct{})
			u.window.SetFramebufferSizeCallback(func(_ *glfw.Window, _, _ int) {
				u.window.SetFramebufferSizeCallback(nil)
				close(ch)
			})
			u.window.SetSize(u.glfwSize())
		event:
			for {
				glfw.PollEvents()
				select {
				case <-ch:
					break event
				default:
				}
			}
		}
		// Window title might be lost on macOS after coming back from fullscreen.
		u.window.SetTitle(u.title)
	}
	// SwapInterval is affected by the current monitor of the window.
	// This needs to be called at least after SetMonitor.
	// Without SwapInterval after SetMonitor, vsynch doesn't work (#375).
	//
	// TODO: (#405) If triple buffering is needed, SwapInterval(0) should be called,
	// but is this correct? If glfw.SwapInterval(0) and the driver doesn't support triple
	// buffering, what will happen?
	glfw.SwapInterval(1)

	// TODO: Rename this variable?
	u.sizeChanged = true
	return true
}