package ui

import (
	"math"

	"opslag.de/schobers/galleg/allegro5"
	"opslag.de/schobers/geom"
)

var _ Control = &ContentScrollbar{}

type ContentScrollbarValueChangedFn func(float64)

type ContentScrollbar struct {
	ControlBase
	Length         float64
	Value          float64
	Orientation    Orientation
	OnChanged      ContentScrollbarValueChangedFn
	handle         *contentScrollbarHandle
	barLength      float64
	scrollDistance float64
}

type contentScrollbarHandle struct {
	ControlBase
}

func (h *contentScrollbarHandle) Render(ctx Context) {
	var c = ctx.Palette().Primary()
	if h.IsOver {
		if h.IsPressed {
		} else {
		}
	}
	var min = h.Bounds.Min.To32()
	var max = h.Bounds.Max.To32()
	allegro5.DrawFilledRectangle(min.X, min.Y, max.X, max.Y, c)
}

func (s *ContentScrollbar) Created(ctx Context, p Container) error {
	s.ControlBase.Created(ctx, p)
	s.handle = &contentScrollbarHandle{}
	s.handle.Created(ctx, nil)
	return nil
}

func (s *ContentScrollbar) Destroyed(ctx Context) {
	s.handle.Destroyed(ctx)
}

func (s *ContentScrollbar) length() (float64, float64) {
	var min, max float64
	switch s.Orientation {
	case OrientationHorizontal:
		min = s.Bounds.Min.X
		max = s.Bounds.Max.X
	default:
		min = s.Bounds.Min.Y
		max = s.Bounds.Max.Y
	}
	return max - min, min
}

func (s *ContentScrollbar) updateBarLength() {
	var length, _ = s.length()
	var bar = length
	if s.Length > length {
		bar = length * length / s.Length
	}
	if bar < 20 {
		if length < 40 {
			bar = .5 * length
		} else {
			bar = 20
		}
	}
	s.barLength = bar
	var d = s.Length - length
	if d < 0 {
		d = 0
	}
	s.scrollDistance = d
}

func (s *ContentScrollbar) barViewCenter() float64 {
	switch s.Orientation {
	case OrientationHorizontal:
		return (s.Bounds.Min.Y + s.Bounds.Max.Y) * .5
	default:
		return (s.Bounds.Min.X + s.Bounds.Max.X) * .5
	}
}

func (s *ContentScrollbar) toValue(x, y float64) float64 {
	var pos = y
	if OrientationHorizontal == s.Orientation {
		pos = x
	}
	var length, min = s.length()
	if length == 0 {
		return 0
	}
	var offset = (pos - .5*s.barLength - min) / (length - s.barLength)
	if offset < 0 {
		return 0
	} else if offset > 1 {
		return s.scrollDistance
	}
	return s.scrollDistance * offset
}

func (s *ContentScrollbar) change(v float64) {
	if v != s.Value {
		s.Value = v
		var onChanged = s.OnChanged
		if nil != onChanged {
			onChanged(v)
		}
	}
}

func (s *ContentScrollbar) snapTo(x, y int) {
	var val = s.toValue(float64(x), float64(y))
	s.change(val)
}

func (s *ContentScrollbar) increment(d int) {
	if s.Orientation == OrientationVertical {
		d *= -1
	}
	var val = s.Value + float64(d)*ScrollbarWidth
	if val < 0 {
		val = 0
	} else if val > s.scrollDistance {
		val = s.scrollDistance
	}
	s.change(val)
}

func (s *ContentScrollbar) Handle(ctx Context, ev allegro5.Event) {
	s.ControlBase.Handle(ctx, ev)
	s.handle.Handle(ctx, ev)
	switch e := ev.(type) {
	case *allegro5.MouseMoveEvent:
		if s.handle.IsPressed {
			s.snapTo(e.X, e.Y)
		}
		if 0 != e.DeltaZ && s.IsOver {
			var d = e.DeltaZ
			if allegro5.IsAnyKeyDown(allegro5.KeyLShift, allegro5.KeyRShift) {
				d *= 10
			}
			s.increment(d)
		}
	case *allegro5.MouseButtonDownEvent:
		if !s.handle.IsPressed && s.IsOver {
			s.snapTo(e.X, e.Y)
		}
	}
}

func (s *ContentScrollbar) DesiredSize(Context) geom.PointF {
	switch s.Orientation {
	case OrientationHorizontal:
		return geom.PtF(math.NaN(), ScrollbarWidth)
	}
	return geom.PtF(ScrollbarWidth, math.NaN())
}

func (s *ContentScrollbar) SetRect(rect geom.RectangleF) {
	switch s.Orientation {
	case OrientationHorizontal:
		if rect.Dy() > ScrollbarWidth {
			rect.Min.Y = rect.Max.Y - ScrollbarWidth
		}
	default:
		if rect.Dx() > ScrollbarWidth {
			rect.Min.X = rect.Max.X - ScrollbarWidth
		}
	}
	s.ControlBase.SetRect(rect)
	s.updateBarLength()

	var offset float64
	if 0 < s.scrollDistance {
		offset = s.Value / s.scrollDistance
	}
	var length, min = s.length()
	var begin = min + (length-s.barLength)*offset
	var end = begin + s.barLength
	switch s.Orientation {
	case OrientationHorizontal:
		s.handle.SetRect(geom.RectF(begin, rect.Min.Y, end, rect.Max.Y))
	default:
		s.handle.SetRect(geom.RectF(rect.Min.X, begin, rect.Max.X, end))
	}
}

func (s *ContentScrollbar) Render(ctx Context) {
	s.handle.Render(ctx)
	s.ControlBase.Render(ctx)
}