js/kotlinx-coroutines-core-js/src/main/kotlin/kotlinx/coroutines/experimental/internal/LinkedList.kt

/*
 * Copyright 2016-2017 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package kotlinx.coroutines.experimental.internal

private typealias Node = LinkedListNode

/**
 * @suppress **This is unstable API and it is subject to change.**
 */
public open class LinkedListNode {
    public var next = this
        private set
    public var prev = this
        private set
    public var isRemoved: Boolean = false
        private set
    public val isFresh: Boolean = next === this

    public fun addLast(node: Node) {
        val prev = this.prev
        node.next = this
        node.prev = prev
        prev.next = node
        this.prev = node
    }

    public open fun remove(): Boolean {
        if (isRemoved) return false
        val prev = this.prev
        val next = this.next
        prev.next = next
        next.prev = prev
        isRemoved = true
        return true
    }
}

/**
 * @suppress **This is unstable API and it is subject to change.**
 */
public open class LinkedListHead : LinkedListNode() {
    public val isEmpty get() = next === this

    /**
     * Iterates over all elements in this list of a specified type.
     */
    public inline fun <reified T : Node> forEach(block: (T) -> Unit) {
        var cur: Node = next
        while (cur != this) {
            if (cur is T) block(cur)
            cur = cur.next
        }
    }

    // just a defensive programming -- makes sure that list head sentinel is never removed
    public final override fun remove() = throw UnsupportedOperationException()

    fun removeFirstOrNull(): Node? {
        val node = next
        if (node === this) return null
        node.remove()
        return node
    }
}