/**
 * @fileoverview Mock Express Request object with a body that can be read.
 */
const _ = require('lodash');
const {Readable} = require('stream');

/**
 * Mock req for getting the request body from.
 * This is required because an Express request is a Readable stream, that we
 * use in order to get the raw body for hmac calculations.
 */
class MockRequest extends Readable {
    /**
     * Constructor for MockRequest
     *
     * @param {Object?} opt             - Options object
     * @param {string?} opt.mockBody    - Mock body for the request
     */
    constructor(opt) {
        super(opt);

        this._mockReqLengthRead = 0;
        this._mockReqTotalLength = 0;
        const body = _.get(opt, 'mockBody');

        if (!_.isUndefined(body)) {
            this._mockReqBody = body;
            this._mockReqTotalLength = this._mockReqBody.length;
        }

        //
        // Set appropriate headers
        //
        this.headers = {};
        if (this._mockReqTotalLength > 0) {
            this.headers = {
                'content-length': this._mockReqTotalLength,
                'content-type': 'application/json; charset=utf-8'
            };
        }
    }

    /**
     * Called whenver the readable string needs more bytes.
     * We use it to return the next section of our mockBody.
     *
     * @param {number} size     - the number of bytes to read.
     */
    _read(size) {
        if (this._mockReqLengthRead >= this._mockReqTotalLength) {
            this.push(null);
        } else {
            const remaining = this._mockReqTotalLength - this._mockReqLengthRead;
            const toRead = Math.min(remaining, size);
            const str = this._mockReqBody.substr(this._mockReqLengthRead, toRead);
            const buf = Buffer.from(str, 'utf-8');
            this.push(buf);
            this._mockReqLengthRead += toRead;
        }
    }
}

/**
 * Export the MockRequest
 */
module.exports = {
    MockRequest
};