// Copyright 2021 Huw Griffiths
// Copyright 2025 Florian Fischer
//
// 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 ui

import (
	"math"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/inpututil"
)

const LONGTAP_THRESHOLD = 60

type TouchType int

const (
	_tap TouchType = iota + 1
	_longtap
	_pan
	_pinch
)

var touchTypes = struct {
	tap     TouchType
	longtap TouchType
	pan     TouchType
	pinch   TouchType
}{
	tap:     _tap,
	longtap: _longtap,
	pan:     _pan,
	pinch:   _pinch,
}

// TouchInput is a "manager" for touch input and provides logical encapsulations of
// touch interactions like panning, pinching, and tapping.
type TouchInput struct {
	touchIDs []ebiten.TouchID
	touches  map[ebiten.TouchID]*touch

	pinch   *pinch
	pan     *pan
	longtap *longtap
	taps    []tap
}

func (t *TouchInput) consumetap(i int) {
	if len(t.taps) == 1 {
		t.taps = []tap{}
	} else {
		t.taps[i] = t.taps[len(t.taps)-1]
	}
}

var TouchManager *TouchInput

func init() {
	TouchManager = NewTouchInput()
}

func NewTouchInput() *TouchInput {
	return &TouchInput{
		touches: map[ebiten.TouchID]*touch{},
	}
}

// hypotenuse of a right triangle.
func hypotenuse(xa, ya, xb, yb int) float64 {
	x := math.Abs(float64(xa - xb))
	y := math.Abs(float64(ya - yb))
	return math.Sqrt(x*x + y*y)
}

// Update the touch input manager.
// After a call to Update, if we have two touches, then we have a pinch, if we
// have one touch, held longer than (N)ms, then we have a pan.
// If we have quickly released presses, then they are represented in taps.
func (in *TouchInput) Update() error {
	in.taps = []tap{}

	// What's gone?
	for id, t := range in.touches {
		if inpututil.IsTouchJustReleased(id) {
			if in.pinch != nil && (id == in.pinch.id1 || id == in.pinch.id2) {
				// FIXME: what about this frame's movement?
				in.pinch = nil
			}
			if in.pan != nil && id == in.pan.id {
				// FIXME: what about this frame's movement?
				in.pan = nil
			}

			if in.longtap != nil && id == in.longtap.id {
				// FIXME: what about this frame's movement?
				in.longtap = nil
			}

			// If this one has not been touched long, or moved far, then it's a tap.
			diff := hypotenuse(t.originX, t.originY, t.currX, t.currY)
			if !t.wasPinch && !t.isPan && t.duration <= LONGTAP_THRESHOLD && diff < 5 {
				in.taps = append(in.taps, tap{
					x: t.currX,
					y: t.currY,
				})
			}

			delete(in.touches, id)
		}
	}

	// What's new?
	in.touchIDs = inpututil.AppendJustPressedTouchIDs(in.touchIDs[:0])
	for _, id := range in.touchIDs {
		x, y := ebiten.TouchPosition(id)
		in.touches[ebiten.TouchID(id)] = &touch{
			originX: x, originY: y,
			currX: x, currY: y,
		}
	}

	// What's going on?
	in.touchIDs = ebiten.AppendTouchIDs(in.touchIDs[:0])
	for _, id := range in.touchIDs {
		t := in.touches[id]
		t.duration = inpututil.TouchPressDuration(id)
		t.currX, t.currY = ebiten.TouchPosition(id)
	}

	if len(in.touches) == 2 {
		// Potential pinch?
		// If the diff between their origins is different to the diff between
		// their currents and if these two are not already a pinch, then this is
		// a new pinch!
		id1, id2 := in.touchIDs[0], in.touchIDs[1]
		t1, t2 := in.touches[id1], in.touches[id2]
		originDiff := hypotenuse(t1.originX, t1.originY, t2.originX, t2.originY)
		currDiff := hypotenuse(t1.currX, t1.currY, t2.currX, t2.currY)
		if in.pinch == nil && in.pan == nil && in.longtap == nil && math.Abs(originDiff-currDiff) > 3 {
			t1.wasPinch = true
			t2.wasPinch = true
			in.pinch = &pinch{
				id1:     id1,
				id2:     id2,
				originH: originDiff,
				prevH:   originDiff,
			}
		}
	} else if len(in.touches) == 1 {
		// Potential pan or long tap.
		id := in.touchIDs[0]
		t := in.touches[id]
		// The input type is not decided yet
		if !t.wasPinch && !t.isPan && !t.isLongtap {
			diff := math.Abs(hypotenuse(t.originX, t.originY, t.currX, t.currY))
			if diff > 0.5 {
				t.isPan = true
				in.pan = &pan{
					id:      id,
					originX: t.originX,
					originY: t.originY,
					prevX:   t.originX,
					prevY:   t.originY,
				}
			} else if t.duration > LONGTAP_THRESHOLD {
				id := in.touchIDs[0]
				t := in.touches[id]
				t.isLongtap = true
				in.longtap = &longtap{
					id:       id,
					tap:      tap{t.originX, t.originY},
					duration: t.duration,
				}
			}
		}
	}

	return nil
}

type touch struct {
	originX, originY           int
	currX, currY               int
	duration                   int
	wasPinch, isPan, isLongtap bool
}

type pinch struct {
	id1, id2 ebiten.TouchID
	originH  float64
	prevH    float64
}

func (p *pinch) currentH() float64 {
	x1, y1 := ebiten.TouchPosition(p.id1)
	x2, y2 := ebiten.TouchPosition(p.id2)
	return hypotenuse(x1, y1, x2, y2)
}

func (p *pinch) Total() float64 {
	return -(p.currentH() - p.originH)
}

// Incremental zoom that has occurred in this frame.
func (p *pinch) Incremental() float64 {
	curr := p.currentH()
	delta := curr - p.prevH
	p.prevH = curr
	return -delta
}

type pan struct {
	id ebiten.TouchID

	prevX, prevY     int
	originX, originY int
}

// Total panning that has occurred since this pan started.
func (p *pan) Total() (float64, float64) {
	currX, currY := ebiten.TouchPosition(p.id)
	return float64(currX - p.originX), float64(currY - p.originY)
}

// Incremental panning that has occurred in this frame.
func (p *pan) Incremental() (float64, float64) {
	currX, currY := ebiten.TouchPosition(p.id)
	deltaX, deltaY := currX-p.prevX, currY-p.prevY

	p.prevX, p.prevY = currX, currY

	return float64(deltaX), float64(deltaY)
}

type tap struct {
	x, y int
}

type longtap struct {
	tap
	id       ebiten.TouchID
	duration int
}