package gel

import (
	"image"
	"image/color"

	l "github.com/p9c/p9/pkg/gel/gio/layout"
	"github.com/p9c/p9/pkg/gel/gio/op"
	"github.com/p9c/p9/pkg/gel/gio/op/clip"
	"github.com/p9c/p9/pkg/gel/gio/op/paint"
	"github.com/p9c/p9/pkg/gel/gio/unit"

	"github.com/p9c/p9/pkg/gel/f32color"
)

type Slider struct {
	*Window
	min, max float32
	color    color.NRGBA
	float    *Float
}

// Slider is for selecting a value in a range.
func (w *Window) Slider() *Slider {
	return &Slider{
		Window: w,
		color:  w.Colors.GetNRGBAFromName("Primary"),
	}
}

// Min sets the value at the left hand side
func (s *Slider) Min(min float32) *Slider {
	s.min = min
	return s
}

// Max sets the value at the right hand side
func (s *Slider) Max(max float32) *Slider {
	s.max = max
	return s
}

// Color sets the color to draw the slider in
func (s *Slider) Color(color string) *Slider {
	s.color = s.Theme.Colors.GetNRGBAFromName(color)
	return s
}

// Float sets the initial value
func (s *Slider) Float(f *Float) *Slider {
	s.float = f
	return s
}

// Fn renders the slider
func (s *Slider) Fn(gtx l.Context) l.Dimensions {
	thumbRadiusInt := gtx.Dp(unit.Dp(6))
	trackWidth := gtx.Dp(unit.Dp(2))
	thumbRadius := thumbRadiusInt
	halfWidthInt := 2 * thumbRadiusInt
	halfWidth := halfWidthInt

	size := gtx.Constraints.Min
	// Keep a minimum length so that the track is always visible.
	minLength := halfWidthInt + 3*thumbRadiusInt + halfWidthInt
	if size.X < minLength {
		size.X = minLength
	}
	size.Y = 2 * halfWidthInt

	st := op.Offset(image.Pt(halfWidth, 0)).Push(gtx.Ops)
	gtx.Constraints.Min = image.Pt(size.X-2*halfWidthInt, size.Y)
	s.float.Fn(gtx, halfWidthInt, s.min, s.max)
	thumbPos := halfWidth + int(s.float.Pos())
	st.Pop()

	col := s.color
	if !gtx.Source.Enabled() {
		col = f32color.MulAlpha(col, 150)
	}

	// Draw track before thumb.
	trackMinY := halfWidth - trackWidth/2
	trackMaxY := halfWidth + trackWidth/2
	trackBeforeThumb := image.Rectangle{
		Min: image.Pt(halfWidth, trackMinY),
		Max: image.Pt(thumbPos, trackMaxY),
	}
	st1 := clip.Rect(trackBeforeThumb).Push(gtx.Ops)
	paint.ColorOp{Color: col}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	st1.Pop()

	// Draw track after thumb.
	trackAfterThumb := image.Rectangle{
		Min: image.Pt(thumbPos, trackMinY),
		Max: image.Pt(size.X-halfWidth, trackMaxY),
	}
	st2 := clip.Rect(trackAfterThumb).Push(gtx.Ops)
	paint.ColorOp{Color: f32color.MulAlpha(col, 96)}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	st2.Pop()

	// Draw thumb.
	thumbRect := image.Rectangle{
		Min: image.Pt(thumbPos-thumbRadius, halfWidth-thumbRadius),
		Max: image.Pt(thumbPos+thumbRadius, halfWidth+thumbRadius),
	}
	st3 := clip.UniformRRect(thumbRect, thumbRadius).Push(gtx.Ops)
	paint.ColorOp{Color: col}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	st3.Pop()

	return l.Dimensions{Size: size}
}