/*!
 * Copyright (c) Microsoft Corporation and contributors. All rights reserved.
 * Licensed under the MIT License.
 */

import fs from "fs";

import { assert } from "@fluidframework/core-utils/internal";
import type {
	IDocumentDeltaStorageService,
	IStream,
	ISequencedDocumentMessage,
} from "@fluidframework/driver-definitions/internal";
import { emptyMessageStream } from "@fluidframework/driver-utils/internal";

/**
 * Provides access to the underlying delta storage on the local file storage for file driver.
 * @internal
 */
export class FileDeltaStorageService implements IDocumentDeltaStorageService {
	private readonly messages: ISequencedDocumentMessage[];
	private lastOps: ISequencedDocumentMessage[] = [];

	constructor(private readonly path: string) {
		this.messages = [];
		let counter = 0;
		while (true) {
			const filename = `${this.path}//messages${counter === 0 ? "" : counter}.json`;
			if (!fs.existsSync(filename)) {
				if (counter === 0) {
					throw new Error(`file ${filename} not found`);
				}
				break;
			}
			const data = fs.readFileSync(filename);
			this.messages = this.messages.concat(JSON.parse(data.toString("utf-8")));
			counter++;
		}
	}

	public fetchMessages(
		from: number,
		to: number | undefined,
		abortSignal?: AbortSignal,
		cachedOnly?: boolean,
	): IStream<ISequencedDocumentMessage[]> {
		return emptyMessageStream;
	}

	public get ops(): readonly Readonly<ISequencedDocumentMessage>[] {
		return this.messages;
	}

	/**
	 * Retrieve ops within the exclusive sequence number range.
	 *
	 * @param from - First op to be fetched.
	 * @param to - Last op to be fetched. This is exclusive.
	 */
	public getFromWebSocket(from: number, to: number): ISequencedDocumentMessage[] {
		const readFrom = Math.max(from, 0); // Inclusive
		const readTo = Math.min(to, this.messages.length); // Exclusive

		if (readFrom >= this.messages.length || readTo <= 0 || readFrom >= readTo) {
			return [];
		}

		// Optimizations for multiple readers (replay tool)
		if (this.lastOps.length > 0 && this.lastOps[0].sequenceNumber === readFrom + 1) {
			return this.lastOps;
		}
		this.lastOps = this.messages.slice(readFrom, readTo);
		assert(
			this.lastOps[0].sequenceNumber === readFrom + 1,
			0x091 /* "Retrieved ops' first sequence number has unexpected value!" */,
		);
		return this.lastOps;
	}
}