package layouts

import "image"
import "git.tebibyte.media/tomo/tomo"

var _ tomo.Layout = FlowVertical

// Flow is a grid layout where the number of rows and columns changes depending
// on the size of the container. It is designed to be used with an overflowing
// container. If the container does not overflow in the correct direction, the
// layout will behave like Contract.
type Flow bool

// FlowVertical is a vertical flow layout.
const FlowVertical Flow = true

// FlowHorizontal is a horizontal flow layout.
const FlowHorizontal Flow = false

func (flow Flow) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
	// TODO: write down somewhere that layout minimums aren't taken into
	// account when the respective direction is overflowed
	return flow.fallback().MinimumSize(hints, boxes)
}

func (flow Flow) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
	if flow.v() && !hints.OverflowY || flow.h() && !hints.OverflowX {
		flow.fallback().Arrange(hints, boxes)
	}

	// find a minor size value that will fit all boxes
	minorSize := 0
	for _, box := range boxes {
		boxSize := flow.minor(box.MinimumSize())
		if boxSize > minorSize { minorSize = boxSize }
	}
	if minorSize == 0 { return }
	minorSteps :=
		(flow.deltaMinor(hints.Bounds) + flow.minor(hints.Gap)) /
		(minorSize + flow.minor(hints.Gap))

	// arrange
	point := hints.Bounds.Min
	index := 0
	for index < len(boxes) {
		// get a slice of boxes for this major step
		stepIndexEnd := index + minorSteps
		if stepIndexEnd > len(boxes) { stepIndexEnd = len(boxes) }
		step := boxes[index:stepIndexEnd]
		index += minorSteps
		
		// find a major size that will fit all boxes on this major step
		majorSize := 0
		for _, box := range step {
			boxSize := flow.major(box.MinimumSize())
			if boxSize > majorSize { majorSize = boxSize }
		}
		if majorSize == 0 { continue }

		// arrange all boxes on this major step
		var size image.Point
		size = flow.incrMajor(size, majorSize)
		size = flow.incrMinor(size, minorSize)
		for _, box := range step {
			bounds := image.Rectangle { Min: point, Max: point.Add(size) }
			box.SetBounds(bounds)

			point = flow.incrMinor(point, minorSize + flow.minor(hints.Gap))
		}

		if flow.v() {
			point.Y += majorSize + hints.Gap.Y
			point.X = hints.Bounds.Min.X
		} else {
			point.X += majorSize + hints.Gap.X
			point.Y = hints.Bounds.Min.Y
		}
	}
}

func (flow Flow) v () bool { return flow == FlowVertical   }
func (flow Flow) h () bool { return flow == FlowHorizontal }

func (flow Flow) minor (point image.Point) int {
	if flow.v() {
		return point.X
	} else {
		return point.Y
	}
}
func (flow Flow) major (point image.Point) int {
	if flow.v() {
		return point.Y
	} else {
		return point.X
	}
}
func (flow Flow) incrMinor (point image.Point, delta int) image.Point {
	if flow.v() {
		point.X += delta
		return point
	} else {
		point.Y += delta
		return point
	}
}
func (flow Flow) incrMajor (point image.Point, delta int) image.Point {
	if flow.v() {
		point.Y += delta
		return point
	} else {
		point.X += delta
		return point
	}
}
func (flow Flow) deltaMinor (rectangle image.Rectangle) int {
	if flow.v() {
		return rectangle.Dx()
	} else {
		return rectangle.Dy()
	}
}
func (flow Flow) fallback () tomo.Layout {
	return Contract(flow)
}