"use strict";
const utils = require("./utils.js");

function DataReader() {
	this.data = null; // type : see implementation
	this.length = 0;
	this.index = 0;
	this.zero = 0;
}
DataReader.prototype = {
	/**
	 * Check that the offset will not go too far.
	 * @param {string} offset the additional offset to check.
	 * @throws {Error} an Error if the offset is out of bounds.
	 */
	checkOffset(offset) {
		this.checkIndex(this.index + offset);
	},
	/**
	 * Check that the specifed index will not be too far.
	 * @param {string} newIndex the index to check.
	 * @throws {Error} an Error if the index is out of bounds.
	 */
	checkIndex(newIndex) {
		if (this.length < this.zero + newIndex || newIndex < 0) {
			throw new Error(
				"End of data reached (data length = " +
					this.length +
					", asked index = " +
					newIndex +
					"). Corrupted zip ?"
			);
		}
	},
	/**
	 * Change the index.
	 * @param {number} newIndex The new index.
	 * @throws {Error} if the new index is out of the data.
	 */
	setIndex(newIndex) {
		this.checkIndex(newIndex);
		this.index = newIndex;
	},
	/**
	 * Skip the next n bytes.
	 * @param {number} n the number of bytes to skip.
	 * @throws {Error} if the new index is out of the data.
	 */
	skip(n) {
		this.setIndex(this.index + n);
	},
	/**
	 * Get the byte at the specified index.
	 * @param {number} i the index to use.
	 * @return {number} a byte.
	 */
	byteAt() {
		// see implementations
	},
	/**
	 * Get the next number with a given byte size.
	 * @param {number} size the number of bytes to read.
	 * @return {number} the corresponding number.
	 */
	readInt(size) {
		let result = 0,
			i;
		this.checkOffset(size);
		for (i = this.index + size - 1; i >= this.index; i--) {
			result = (result << 8) + this.byteAt(i);
		}
		this.index += size;
		return result;
	},
	/**
	 * Get the next string with a given byte size.
	 * @param {number} size the number of bytes to read.
	 * @return {string} the corresponding string.
	 */
	readString(size) {
		return utils.transformTo("string", this.readData(size));
	},
	/**
	 * Get raw data without conversion, <size> bytes.
	 * @param {number} size the number of bytes to read.
	 * @return {Object} the raw data, implementation specific.
	 */
	readData() {
		// see implementations
	},
	/**
	 * Find the last occurence of a zip signature (4 bytes).
	 * @param {string} sig the signature to find.
	 * @return {number} the index of the last occurence, -1 if not found.
	 */
	lastIndexOfSignature() {
		// see implementations
	},
	/**
	 * Get the next date.
	 * @return {Date} the date.
	 */
	readDate() {
		const dostime = this.readInt(4);
		return new Date(
			((dostime >> 25) & 0x7f) + 1980, // year
			((dostime >> 21) & 0x0f) - 1, // month
			(dostime >> 16) & 0x1f, // day
			(dostime >> 11) & 0x1f, // hour
			(dostime >> 5) & 0x3f, // minute
			(dostime & 0x1f) << 1
		); // second
	},
};
module.exports = DataReader;