+import {
+ defaultQueueSize,
+ type FixedQueueNode,
+ type IFixedQueue,
+} from './utility-types.js'
+
+/**
+ * Base fixed queue class
+ * @typeParam T - Type of fixed queue data.
+ * @internal
+ */
+export abstract class AbstractFixedQueue<T> implements IFixedQueue<T> {
+ protected start!: number
+ /** @inheritdoc */
+ public readonly capacity: number
+ /** @inheritdoc */
+ public size!: number
+ /** @inheritdoc */
+ public nodeArray: FixedQueueNode<T>[]
+
+ /**
+ * Constructs a fixed queue.
+ * @param size - Fixed queue size. @defaultValue defaultQueueSize
+ * @returns IFixedQueue.
+ */
+ constructor (size: number = defaultQueueSize) {
+ this.checkSize(size)
+ this.capacity = size
+ this.nodeArray = new Array<FixedQueueNode<T>>(this.capacity)
+ this.clear()
+ }
+
+ /** @inheritdoc */
+ public empty (): boolean {
+ return this.size === 0
+ }
+
+ /** @inheritdoc */
+ public full (): boolean {
+ return this.size === this.capacity
+ }
+
+ /** @inheritdoc */
+ public abstract enqueue (data: T, priority?: number): number
+
+ /** @inheritdoc */
+ public get (index: number): T | undefined {
+ if (this.empty() || index >= this.size) {
+ return undefined
+ }
+ index += this.start
+ if (index >= this.capacity) {
+ index -= this.capacity
+ }
+ return this.nodeArray[index].data
+ }
+
+ /** @inheritdoc */
+ public dequeue (): T | undefined {
+ if (this.empty()) {
+ return undefined
+ }
+ const index = this.start
+ --this.size
+ ++this.start
+ if (this.start === this.capacity) {
+ this.start = 0
+ }
+ return this.nodeArray[index].data
+ }
+
+ /** @inheritdoc */
+ public clear (): void {
+ this.start = 0
+ this.size = 0
+ }
+
+ /** @inheritdoc */
+ public [Symbol.iterator] (): Iterator<T> {
+ let index = this.start
+ let i = 0
+ return {
+ next: () => {
+ if (i >= this.size) {
+ return {
+ value: undefined,
+ done: true,
+ }
+ }
+ const value = this.nodeArray[index].data
+ ++index
+ ++i
+ if (index === this.capacity) {
+ index = 0
+ }
+ return {
+ value,
+ done: false,
+ }
+ },
+ }
+ }
+
+ /**
+ * Checks the fixed queue size.
+ * @param size - Queue size.
+ */
+ private checkSize (size: number): void {
+ if (!Number.isSafeInteger(size)) {
+ throw new TypeError(
+ `Invalid fixed queue size: '${size.toString()}' is not an integer`
+ )
+ }
+ if (size < 0) {
+ throw new RangeError(`Invalid fixed queue size: ${size.toString()} < 0`)
+ }
+ }
+}