/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.android.vending.expansion.downloader.impl;

import android.text.format.Time;

import java.util.Calendar;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Helper for parsing an HTTP date.
 */
public final class HttpDateTime {

	/*
     * Regular expression for parsing HTTP-date. Wdy, DD Mon YYYY HH:MM:SS GMT
     * RFC 822, updated by RFC 1123 Weekday, DD-Mon-YY HH:MM:SS GMT RFC 850,
     * obsoleted by RFC 1036 Wdy Mon DD HH:MM:SS YYYY ANSI C's asctime() format
     * with following variations Wdy, DD-Mon-YYYY HH:MM:SS GMT Wdy, (SP)D Mon
     * YYYY HH:MM:SS GMT Wdy,DD Mon YYYY HH:MM:SS GMT Wdy, DD-Mon-YY HH:MM:SS
     * GMT Wdy, DD Mon YYYY HH:MM:SS -HHMM Wdy, DD Mon YYYY HH:MM:SS Wdy Mon
     * (SP)D HH:MM:SS YYYY Wdy Mon DD HH:MM:SS YYYY GMT HH can be H if the first
     * digit is zero. Mon can be the full name of the month.
     */
	private static final String HTTP_DATE_RFC_REGEXP =
			"([0-9]{1,2})[- ]([A-Za-z]{3,9})[- ]([0-9]{2,4})[ ]"
			+ "([0-9]{1,2}:[0-9][0-9]:[0-9][0-9])";

	private static final String HTTP_DATE_ANSIC_REGEXP =
			"[ ]([A-Za-z]{3,9})[ ]+([0-9]{1,2})[ ]"
			+ "([0-9]{1,2}:[0-9][0-9]:[0-9][0-9])[ ]([0-9]{2,4})";

	/**
     * The compiled version of the HTTP-date regular expressions.
     */
	private static final Pattern HTTP_DATE_RFC_PATTERN =
			Pattern.compile(HTTP_DATE_RFC_REGEXP);
	private static final Pattern HTTP_DATE_ANSIC_PATTERN =
			Pattern.compile(HTTP_DATE_ANSIC_REGEXP);

	private static class TimeOfDay {
		TimeOfDay(int h, int m, int s) {
			this.hour = h;
			this.minute = m;
			this.second = s;
		}

		int hour;
		int minute;
		int second;
	}

	public static long parse(String timeString)
			throws IllegalArgumentException {

		int date = 1;
		int month = Calendar.JANUARY;
		int year = 1970;
		TimeOfDay timeOfDay;

		Matcher rfcMatcher = HTTP_DATE_RFC_PATTERN.matcher(timeString);
		if (rfcMatcher.find()) {
			date = getDate(rfcMatcher.group(1));
			month = getMonth(rfcMatcher.group(2));
			year = getYear(rfcMatcher.group(3));
			timeOfDay = getTime(rfcMatcher.group(4));
		} else {
			Matcher ansicMatcher = HTTP_DATE_ANSIC_PATTERN.matcher(timeString);
			if (ansicMatcher.find()) {
				month = getMonth(ansicMatcher.group(1));
				date = getDate(ansicMatcher.group(2));
				timeOfDay = getTime(ansicMatcher.group(3));
				year = getYear(ansicMatcher.group(4));
			} else {
				throw new IllegalArgumentException();
			}
		}

		// FIXME: Y2038 BUG!
		if (year >= 2038) {
			year = 2038;
			month = Calendar.JANUARY;
			date = 1;
		}

		Time time = new Time(Time.TIMEZONE_UTC);
		time.set(timeOfDay.second, timeOfDay.minute, timeOfDay.hour, date,
				month, year);
		return time.toMillis(false /* use isDst */);
	}

	private static int getDate(String dateString) {
		if (dateString.length() == 2) {
			return (dateString.charAt(0) - '0') * 10 + (dateString.charAt(1) - '0');
		} else {
			return (dateString.charAt(0) - '0');
		}
	}

	/*
     * jan = 9 + 0 + 13 = 22 feb = 5 + 4 + 1 = 10 mar = 12 + 0 + 17 = 29 apr = 0
     * + 15 + 17 = 32 may = 12 + 0 + 24 = 36 jun = 9 + 20 + 13 = 42 jul = 9 + 20
     * + 11 = 40 aug = 0 + 20 + 6 = 26 sep = 18 + 4 + 15 = 37 oct = 14 + 2 + 19
     * = 35 nov = 13 + 14 + 21 = 48 dec = 3 + 4 + 2 = 9
     */
	private static int getMonth(String monthString) {
		int hash = Character.toLowerCase(monthString.charAt(0)) +
				   Character.toLowerCase(monthString.charAt(1)) +
				   Character.toLowerCase(monthString.charAt(2)) - 3 * 'a';
		switch (hash) {
			case 22:
				return Calendar.JANUARY;
			case 10:
				return Calendar.FEBRUARY;
			case 29:
				return Calendar.MARCH;
			case 32:
				return Calendar.APRIL;
			case 36:
				return Calendar.MAY;
			case 42:
				return Calendar.JUNE;
			case 40:
				return Calendar.JULY;
			case 26:
				return Calendar.AUGUST;
			case 37:
				return Calendar.SEPTEMBER;
			case 35:
				return Calendar.OCTOBER;
			case 48:
				return Calendar.NOVEMBER;
			case 9:
				return Calendar.DECEMBER;
			default:
				throw new IllegalArgumentException();
		}
	}

	private static int getYear(String yearString) {
		if (yearString.length() == 2) {
			int year = (yearString.charAt(0) - '0') * 10 + (yearString.charAt(1) - '0');
			if (year >= 70) {
				return year + 1900;
			} else {
				return year + 2000;
			}
		} else if (yearString.length() == 3) {
			// According to RFC 2822, three digit years should be added to 1900.
			int year = (yearString.charAt(0) - '0') * 100 + (yearString.charAt(1) - '0') * 10 + (yearString.charAt(2) - '0');
			return year + 1900;
		} else if (yearString.length() == 4) {
			return (yearString.charAt(0) - '0') * 1000 + (yearString.charAt(1) - '0') * 100 + (yearString.charAt(2) - '0') * 10 + (yearString.charAt(3) - '0');
		} else {
			return 1970;
		}
	}

	private static TimeOfDay getTime(String timeString) {
		// HH might be H
		int i = 0;
		int hour = timeString.charAt(i++) - '0';
		if (timeString.charAt(i) != ':')
			hour = hour * 10 + (timeString.charAt(i++) - '0');
		// Skip ':'
		i++;

		int minute = (timeString.charAt(i++) - '0') * 10 + (timeString.charAt(i++) - '0');
		// Skip ':'
		i++;

		int second = (timeString.charAt(i++) - '0') * 10 + (timeString.charAt(i++) - '0');

		return new TimeOfDay(hour, minute, second);
	}
}
