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

package net.shadowfacts.cacao.view

import com.mojang.blaze3d.platform.GlStateManager
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.Rect
import net.shadowfacts.cacao.geometry.Size
import net.shadowfacts.cacao.util.Color
import net.shadowfacts.cacao.util.RenderHelper
import no.birkett.kiwi.Constraint
import no.birkett.kiwi.Solver
import java.util.*

/**
 * The base Cacao View class. Provides layout anchors, properties, and helper methods.
 * Doesn't draw anything itself (unless [backgroundColor] is specified), but may be used for encapsulation/grouping.
 *
 * @author shadowfacts
 */
open class View {

	/**
	 * The constraint solver used by the [net.shadowfacts.cacao.Window] this view belongs to.
	 * Not initialized until [wasAdded] called, using it before that will throw a runtime exception.
	 */
	lateinit var solver: Solver

	/**
	 * Layout anchor for the left edge of this view in the window's coordinate system.
	 */
	val leftAnchor = LayoutVariable(this, "left")
	/**
	 * Layout anchor for the right edge of this view in the window's coordinate system.
	 */
	val rightAnchor = LayoutVariable(this, "right")
	/**
	 * Layout anchor for the top edge of this view in the window's coordinate system.
	 */
	val topAnchor = LayoutVariable(this, "top")
	/**
	 * Layout anchor for the bottom edge of this view in the window's coordinate system.
	 */
	val bottomAnchor = LayoutVariable(this, "bottom")
	/**
	 * Layout anchor for the width of this view in the window's coordinate system.
	 */
	val widthAnchor = LayoutVariable(this, "width")
	/**
	 * Layout anchor for the height of this view in the window's coordinate system.
	 */
	val heightAnchor = LayoutVariable(this, "height")
	/**
	 * Layout anchor for the center X position of this view in the window's coordinate system.
	 */
	val centerXAnchor = LayoutVariable(this, "centerX")
	/**
	 * Layout anchor for the center Y position of this view in the window's coordinate system.
	 */
	val centerYAnchor = LayoutVariable(this, "centerY")

	/**
	 * The rectangle for this view in the coordinate system of its superview view (or the window, if there is no superview).
	 * Not initialized until [didLayout] called.
	 */
	lateinit var frame: Rect
	/**
	 * The rectangle for this view in its own coordinate system.
	 * Not initialized until [didLayout] called.
	 */
	lateinit var bounds: Rect

	/**
	 * The intrinsic size of this view's content. May be null if the view doesn't have any content or there is no
	 * intrinsic size.
	 *
	 * Setting this creates/updates [no.birkett.kiwi.Strength.WEAK] constraints on this view's width/height using
	 * the size.
	 */
	var intrinsicContentSize: Size? = null
		set(value) {
			updateIntrinsicContentSizeConstraints(intrinsicContentSize, value)
			field = value
		}
	private var intrinsicContentSizeWidthConstraint: Constraint? = null
	private var intrinsicContentSizeHeightConstraint: Constraint? = null

	/**
	 * The background color of this view.
	 */
	var backgroundColor = Color.CLEAR

	/**
	 * This view's parent view. If `null`, this view is a top-level view in the [Window].
	 */
	var superview: View? = null
	// _subviews is the internal, mutable object since we only want it to by mutated by the add/removeSubview methods
	private val _subviews = LinkedList<View>()
	/**
	 * The list of all the subviews of this view.
	 * This list should never by mutated directly, only by the [addSubview]/[removeSubview] methods.
	 */
	val subviews: List<View> = _subviews

	/**
	 * Helper method for retrieve the anchor for a specific position on the given axis.
	 */
	fun getAnchor(axis: Axis, position: AxisPosition): LayoutVariable {
		return when (axis) {
			Axis.HORIZONTAL ->
				when (position) {
					AxisPosition.LEADING -> leftAnchor
					AxisPosition.CENTER -> centerXAnchor
					AxisPosition.TRAILING -> rightAnchor
				}
			Axis.VERTICAL ->
				when (position) {
					AxisPosition.LEADING -> topAnchor
					AxisPosition.CENTER -> centerYAnchor
					AxisPosition.TRAILING -> bottomAnchor
				}
		}
	}

	/**
	 * Adds the given subview as a child of this view.
	 *
	 * @param view The view to add.
	 * @return The view that was added, as a convenience.
	 */
	fun <T: View> addSubview(view: T): T {
		_subviews.add(view)
		view.superview = this
		view.solver = solver

		view.wasAdded()

		return view
	}

	/**
	 * Called when this view was added to a view hierarchy.
	 * If overridden, the super-class method must be called.
	 */
	open fun wasAdded() {
		createInternalConstraints()
		updateIntrinsicContentSizeConstraints(null, intrinsicContentSize)
	}

	/**
	 * Called during [wasAdded] to add any constraints to the [solver] that are internal to this view.
	 * If overridden, the super-class method must be called.
	 */
	open fun createInternalConstraints() {
		solver.dsl {
			rightAnchor equalTo (leftAnchor + widthAnchor)
			bottomAnchor equalTo (topAnchor + heightAnchor)
			centerXAnchor equalTo (leftAnchor + widthAnchor / 2)
			centerYAnchor equalTo (topAnchor + heightAnchor / 2)
		}
	}

	private fun updateIntrinsicContentSizeConstraints(old: Size?, new: Size?) {
		if (!this::solver.isInitialized) return

		if (old != null) {
			solver.removeConstraint(intrinsicContentSizeWidthConstraint!!)
			solver.removeConstraint(intrinsicContentSizeHeightConstraint!!)
		}
		if (new != null) {
			solver.dsl {
				this@View.intrinsicContentSizeWidthConstraint = (widthAnchor.equalTo(new.width, strength = WEAK))
				this@View.intrinsicContentSizeHeightConstraint = (heightAnchor.equalTo(new.height, strength = WEAK))
			}
		}
	}

	/**
	 * Called after this view has been laid-out.
	 * If overridden, the super-class method must be called.
	 */
	open fun didLayout() {
		subviews.forEach(View::didLayout)

		val superviewLeft = superview?.leftAnchor?.value ?: 0.0
		val superviewTop = superview?.topAnchor?.value ?: 0.0
		frame = Rect(leftAnchor.value - superviewLeft, topAnchor.value - superviewTop, widthAnchor.value, heightAnchor.value)
		bounds = Rect(0.0, 0.0, widthAnchor.value, heightAnchor.value)
	}

	/**
	 * Called to draw this view.
	 * This method should not be called directly, it is called by the parent view/window.
	 * This method may not be overridden, use [drawContent] to draw any custom content.
	 */
	fun draw() {
		GlStateManager.pushMatrix()
		GlStateManager.translated(frame.left, frame.top, 0.0)

		RenderHelper.fill(bounds, backgroundColor)

		drawContent()

		subviews.forEach(View::draw)

		GlStateManager.popMatrix()
	}

	/**
	 * Called during [draw] to draw content that's part of this view.
	 * During this method, the OpenGL coordinate system has been translated so the origin is at the top left corner
	 * of this view. Be careful not to translate additionally, and not to draw outside the [bounds] of the view.
	 */
	open fun drawContent() {}

}