/*
 * Copyright (C) 2007 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.android.internal.http;

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);        
    }
}