Port Area plugin to Kotlin

game/plugin/areas/build.gradle

@@ -0,0 +1,6 @@
+plugin {
+    name = "Area listeners"
+    description = "Enables plugins to listen on mobs entering, moving inside of, or leaving a rectangular area."
+    authors = ["Major"]
+    dependencies = ["api"]
+}

game/plugin/areas/src/action.kt

@@ -0,0 +1,18 @@
+package org.apollo.game.plugins.area
+
+/**
+ * Defines an area action using the DSL.
+ */
+fun action(@Suppress("UNUSED_PARAMETER") name: String, builder: ActionBuilder.() -> Unit) {
+    val listener = ActionBuilder()
+    builder(listener)
+
+    actions.add(listener.build())
+}
+
+/**
+ * The [Set] of ([Area], [AreaAction]) [Pair]s.
+ */
+val actions = mutableSetOf<Pair<Area, AreaAction>>()
+
+class AreaAction(val entrance: AreaListener, val inside: AreaListener, val exit: AreaListener)

game/plugin/areas/src/area.kt

@@ -0,0 +1,94 @@
+package org.apollo.game.plugins.area
+
+import org.apollo.game.model.Position
+import org.apollo.game.model.entity.Player
+import org.apollo.game.plugins.api.component1
+import org.apollo.game.plugins.api.component2
+import org.apollo.game.plugins.api.component3
+
+/**
+ * An area in the game world.
+ */
+interface Area {
+
+    /**
+     * Returns whether or not the specified [Position] is inside this [Area].
+     */
+    operator fun contains(position: Position): Boolean
+
+}
+
+private class RectangularArea(val x: IntRange, val y: IntRange, val height: Int) : Area {
+
+    override operator fun contains(position: Position): Boolean {
+        val (x, y, z) = position
+        return x in this.x && y in this.y && z == height
+    }
+
+}
+
+/**
+ * A typealias for a function that is invoked when a player enters, moves inside of, or exits an [Area].
+ */
+internal typealias AreaListener = Player.(Position) -> Unit
+
+/**
+ * A builder for ([Area], [AreaAction]) [Pair]s.
+ */
+class ActionBuilder {
+
+    private var area: Area? = null
+
+    private var entrance: AreaListener = { }
+
+    private var inside: AreaListener = { }
+
+    private var exit: AreaListener = { }
+
+    /**
+     * Places the contents of this builder into an ([Area], [AreaAction]) [Pair].
+     */
+    fun build(): Pair<Area, AreaAction> {
+        val area = area ?: throw UnsupportedOperationException("Area must be specified.")
+        return Pair(area, AreaAction(entrance, inside, exit))
+    }
+
+    /**
+     * Sets the [Area] to listen for movement in.
+     */
+    fun area(contains: (Position) -> Boolean) {
+        this.area = object : Area {
+            override fun contains(position: Position): Boolean = contains.invoke(position)
+        }
+    }
+
+    /**
+     * Sets the [Area] to listen for movement in. Note that [IntRange]s are (inclusive, _exclusive_), i.e. the upper
+     * bound is exclusive.
+     */
+    fun area(x: IntRange, y: IntRange, height: Int = 0) {
+        this.area = RectangularArea(x, y, height)
+    }
+
+    /**
+     * Executes the specified [listener] when a player enters the related [Area].
+     */
+    fun entrance(listener: AreaListener) {
+        this.entrance = listener
+    }
+
+    /**
+     * Executes the specified [listener] when a player moves around inside the related [Area].
+     */
+    fun inside(listener: AreaListener) {
+        this.inside = listener
+    }
+
+    /**
+     * Executes the specified [listener] when a player moves exits the related [Area].
+     */
+    fun exit(listener: AreaListener) {
+        this.exit = listener
+    }
+
+}

game/plugin/areas/src/areas.plugin.kts

@@ -0,0 +1,23 @@
+
+import org.apollo.game.model.entity.Player
+import org.apollo.game.model.event.impl.MobPositionUpdateEvent
+import org.apollo.game.plugins.area.actions
+
+/**
+ * Intercepts the [MobPositionUpdateEvent] and invokes area actions if necessary.
+ */
+on_event { MobPositionUpdateEvent::class }
+    .where { mob is Player }
+    .then {
+        for ((area, action) in actions) {
+            if (mob.position in area) {
+                if (next in area) {
+                    action.inside(mob as Player, next)
+                } else {
+                    action.exit(mob as Player, next)
+                }
+            } else if (next in area) {
+                action.entrance(mob as Player, next)
+            }
+        }
+    }