ASMR/src/main/kotlin/net/shadowfacts/cacao/view/StackView.kt

package net.shadowfacts.cacao.view

import net.shadowfacts.kiwidsl.dsl
import net.shadowfacts.cacao.LayoutVariable
import net.shadowfacts.cacao.geometry.Axis
import net.shadowfacts.cacao.geometry.AxisPosition
import net.shadowfacts.cacao.geometry.AxisPosition.*
import no.birkett.kiwi.Constraint
import java.util.*

/**
 * A view that lays out its children in a stack along either the horizontal for vertical axes.
 * This view does not have any content of its own.
 *
 * Only arranged subviews will be laid out in the stack mode, normal subviews must perform their own layout.
 *
 * @author shadowfacts
 * @param axis The primary axis that this stack lays out its children along.
 * @param distribution The mode by which this stack lays out its children along the axis perpendicular to the
 * 						primary [axis].
 */
class StackView(
		val axis: Axis,
		val distribution: Distribution = Distribution.FILL,
		val spacing: Double = 0.0
): View() {

	// the internal mutable, list of arranged subviews
	private val _arrangedSubviews = LinkedList<View>()
	/**
	 * The list of arranged subviews belonging to this stack view.
	 * This list should never be mutated directly, only be calling the [addArrangedSubview]/[removeArrangedSubview]
	 * methods.
	 */
	val arrangedSubviews: List<View> = _arrangedSubviews

	private var leadingConnection: Constraint? = null
	private var trailingConnection: Constraint? = null
	private var arrangedSubviewConnections = mutableListOf<Constraint>()

	/**
	 * Adds an arranged subview to this view.
	 * Arranged subviews are laid out according to the stack. If you wish to add a subview that is laid out separately,
	 * use the normal [addSubview] method.
	 *
	 * @param view The view to add.
	 * @param index The index in this stack to add the view at.
	 * 				By default, adds the view to the end of the stack.
	 * @return The view that was added, as a convenience.
	 */
	fun <T: View> addArrangedSubview(view: T, index: Int = arrangedSubviews.size): T {
		addSubview(view)
		_arrangedSubviews.add(index, view)

		addConstraintsForArrangedView(view, index)

		return view
	}

	private fun addConstraintsForArrangedView(view: View, index: Int) {
		if (index == 0) {
			if (leadingConnection != null) {
				solver.removeConstraint(leadingConnection)
			}
			solver.dsl {
				leadingConnection = anchor(LEADING) equalTo anchor(LEADING, view)
			}
		}
		if (index == arrangedSubviews.size - 1) {
			if (trailingConnection != null) {
				solver.removeConstraint(trailingConnection)
			}
			solver.dsl {
				trailingConnection = anchor(TRAILING, view) equalTo anchor(TRAILING)
			}
		}
		if (arrangedSubviews.size > 1) {
			solver.dsl {
				val previous = arrangedSubviews.getOrNull(index - 1)
				val next = arrangedSubviews.getOrNull(index + 1)
				if (next != null) {
					arrangedSubviewConnections.add(index, anchor(TRAILING, view) equalTo (anchor(LEADING, next) + spacing))
				}
				if (previous != null) {
					arrangedSubviewConnections.add(index - 1, anchor(TRAILING, previous) equalTo (anchor(LEADING, view) - spacing))
				}
			}
		}
		solver.dsl {
			when (distribution) {
				Distribution.LEADING ->
					perpAnchor(LEADING) equalTo perpAnchor(LEADING, view)
				Distribution.TRAILING ->
					perpAnchor(TRAILING) equalTo perpAnchor(TRAILING, view)
				Distribution.FILL -> {
					perpAnchor(LEADING) equalTo perpAnchor(LEADING, view)
					perpAnchor(TRAILING) equalTo perpAnchor(TRAILING, view)
				}
				Distribution.CENTER ->
					perpAnchor(CENTER) equalTo perpAnchor(CENTER, view)
			}
		}
	}

	private fun anchor(position: AxisPosition, view: View = this): LayoutVariable {
		return view.getAnchor(axis, position)
	}
	private fun perpAnchor(position: AxisPosition, view: View = this): LayoutVariable {
		return view.getAnchor(axis.perpendicular, position)
	}

	/**
	 * Defines the modes of how content is distributed in a stack view along the perpendicular axis (i.e. the
	 * non-primary axis).
	 *
	 * ASCII-art examples are shown below in a stack view with the primary axis [Axis.VERTICAL].
	 */
	enum class Distribution {
		/**
		 * The leading edges of arranged subviews are pinned to the leading edge of the stack view.
		 * ```
		 * ┌─────────────────────────────┐
		 * │┌─────────────┐              │
		 * ││             │              │
		 * ││             │              │
		 * ││             │              │
		 * │└─────────────┘              │
		 * │┌─────────┐                  │
		 * ││         │                  │
		 * ││         │                  │
		 * ││         │                  │
		 * │└─────────┘                  │
		 * │┌───────────────────────────┐│
		 * ││                           ││
		 * ││                           ││
		 * ││                           ││
		 * │└───────────────────────────┘│
		 * └─────────────────────────────┘
		 * ```
		 */
		LEADING,
		/**
		 * The centers of the arranged subviews are pinned to the center of the stack view.
		 * ```
		 * ┌─────────────────────────────┐
		 * │       ┌─────────────┐       │
		 * │       │             │       │
		 * │       │             │       │
		 * │       │             │       │
		 * │       └─────────────┘       │
		 * │         ┌─────────┐         │
		 * │         │         │         │
		 * │         │         │         │
		 * │         │         │         │
		 * │         └─────────┘         │
		 * │┌───────────────────────────┐│
		 * ││                           ││
		 * ││                           ││
		 * ││                           ││
		 * │└───────────────────────────┘│
		 * └─────────────────────────────┘
		 * ```
		 */
		CENTER,
		/**
		 * The trailing edges of arranged subviews are pinned to the leading edge of the stack view.
		 * ```
		 * ┌─────────────────────────────┐
		 * │              ┌─────────────┐│
		 * │              │             ││
		 * │              │             ││
		 * │              │             ││
		 * │              └─────────────┘│
		 * │                  ┌─────────┐│
		 * │                  │         ││
		 * │                  │         ││
		 * │                  │         ││
		 * │                  └─────────┘│
		 * │┌───────────────────────────┐│
		 * ││                           ││
		 * ││                           ││
		 * ││                           ││
		 * │└───────────────────────────┘│
		 * └─────────────────────────────┘
		 * ```
		 */
		TRAILING,
		/**
		 * The arranged subviews fill the perpendicular axis of the stack view.
		 * ```
		 * ┌─────────────────────────────┐
		 * │┌───────────────────────────┐│
		 * ││                           ││
		 * ││                           ││
		 * ││                           ││
		 * │└───────────────────────────┘│
		 * │┌───────────────────────────┐│
		 * ││                           ││
		 * ││                           ││
		 * ││                           ││
		 * │└───────────────────────────┘│
		 * │┌───────────────────────────┐│
		 * ││                           ││
		 * ││                           ││
		 * ││                           ││
		 * │└───────────────────────────┘│
		 * └─────────────────────────────┘
		 * ```
		 */
		FILL
	}
}