/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

import * as stream from 'stream';

const DefaultSize: number = 8192;
const ContentLength: string = 'Content-Length: ';
const ContentLengthSize: number = Buffer.byteLength(ContentLength, 'utf8');
const Blank: number = Buffer.from(' ', 'utf8')[0];
const BackslashR: number = Buffer.from('\r', 'utf8')[0];
const BackslashN: number = Buffer.from('\n', 'utf8')[0];

class ProtocolBuffer {

	private index: number = 0;
	private buffer: Buffer = Buffer.allocUnsafe(DefaultSize);

	public append(data: string | Buffer): void {
		let toAppend: Buffer | null = null;
		if (Buffer.isBuffer(data)) {
			toAppend = <Buffer>data;
		} else {
			toAppend = Buffer.from(<string>data, 'utf8');
		}
		if (this.buffer.length - this.index >= toAppend.length) {
			toAppend.copy(this.buffer, this.index, 0, toAppend.length);
		} else {
			let newSize = (Math.ceil((this.index + toAppend.length) / DefaultSize) + 1) * DefaultSize;
			if (this.index === 0) {
				this.buffer = Buffer.allocUnsafe(newSize);
				toAppend.copy(this.buffer, 0, 0, toAppend.length);
			} else {
				this.buffer = Buffer.concat([this.buffer.slice(0, this.index), toAppend], newSize);
			}
		}
		this.index += toAppend.length;
	}

	public tryReadContentLength(): number {
		let result = -1;
		let current = 0;
		// we are utf8 encoding...
		while (current < this.index && (this.buffer[current] === Blank || this.buffer[current] === BackslashR || this.buffer[current] === BackslashN)) {
			current++;
		}
		if (this.index < current + ContentLengthSize) {
			return result;
		}
		current += ContentLengthSize;
		let start = current;
		while (current < this.index && this.buffer[current] !== BackslashR) {
			current++;
		}
		if (current + 3 >= this.index || this.buffer[current + 1] !== BackslashN || this.buffer[current + 2] !== BackslashR || this.buffer[current + 3] !== BackslashN) {
			return result;
		}
		let data = this.buffer.toString('utf8', start, current);
		result = parseInt(data);
		this.buffer = this.buffer.slice(current + 4);
		this.index = this.index - (current + 4);
		return result;
	}

	public tryReadContent(length: number): string | null {
		if (this.index < length) {
			return null;
		}
		let result = this.buffer.toString('utf8', 0, length);
		let sourceStart = length;
		while (sourceStart < this.index && (this.buffer[sourceStart] === BackslashR || this.buffer[sourceStart] === BackslashN)) {
			sourceStart++;
		}
		this.buffer.copy(this.buffer, 0, sourceStart);
		this.index = this.index - sourceStart;
		return result;
	}
}

export interface ICallback<T> {
	(data: T): void;
}

export class Reader<T> {

	private readonly buffer: ProtocolBuffer = new ProtocolBuffer();
	private nextMessageLength: number = -1;

	public constructor(
		private readonly readable: stream.Readable,
		private readonly callback: ICallback<T>,
		private readonly onError: (error: any) => void
	) {
		this.readable.on('data', (data: Buffer) => {
			this.onLengthData(data);
		});
	}

	private onLengthData(data: Buffer): void {
		try {
			this.buffer.append(data);
			while (true) {
				if (this.nextMessageLength === -1) {
					this.nextMessageLength = this.buffer.tryReadContentLength();
					if (this.nextMessageLength === -1) {
						return;
					}
				}
				const msg = this.buffer.tryReadContent(this.nextMessageLength);
				if (msg === null) {
					return;
				}
				this.nextMessageLength = -1;
				const json = JSON.parse(msg);
				this.callback(json);
			}
		} catch (e) {
			this.onError(e);
		}
	}
}
