/*
 * Copyright (C) 2015 Google Inc.
 *
 * 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.gson.internal.bind.util;

import java.text.ParseException;
import java.text.ParsePosition;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Locale;
import java.util.TimeZone;

/**
 * Utilities methods for manipulating dates in iso8601 format. This is much faster and GC friendly
 * than using SimpleDateFormat so highly suitable if you (un)serialize lots of date objects.
 *
 * <p>Supported parse format:
 * [yyyy-MM-dd|yyyyMMdd][T(hh:mm[:ss[.sss]]|hhmm[ss[.sss]])]?[Z|[+-]hh[:]mm]]
 *
 * @see <a href="http://www.w3.org/TR/NOTE-datetime">this specification</a>
 */
// Date parsing code from Jackson databind ISO8601Utils.java
// https://github.com/FasterXML/jackson-databind/blob/2.8/src/main/java/com/fasterxml/jackson/databind/util/ISO8601Utils.java
public class ISO8601Utils {
  private ISO8601Utils() {}

  /**
   * ID to represent the 'UTC' string, default timezone since Jackson 2.7
   *
   * @since 2.7
   */
  private static final String UTC_ID = "UTC";

  /**
   * The UTC timezone, prefetched to avoid more lookups.
   *
   * @since 2.7
   */
  private static final TimeZone TIMEZONE_UTC = TimeZone.getTimeZone(UTC_ID);

  /*
  /**********************************************************
  /* Formatting
  /**********************************************************
   */

  /**
   * Format a date into 'yyyy-MM-ddThh:mm:ssZ' (default timezone, no milliseconds precision)
   *
   * @param date the date to format
   * @return the date formatted as 'yyyy-MM-ddThh:mm:ssZ'
   */
  public static String format(Date date) {
    return format(date, false, TIMEZONE_UTC);
  }

  /**
   * Format a date into 'yyyy-MM-ddThh:mm:ss[.sss]Z' (GMT timezone)
   *
   * @param date the date to format
   * @param millis true to include millis precision otherwise false
   * @return the date formatted as 'yyyy-MM-ddThh:mm:ss[.sss]Z'
   */
  public static String format(Date date, boolean millis) {
    return format(date, millis, TIMEZONE_UTC);
  }

  /**
   * Format date into yyyy-MM-ddThh:mm:ss[.sss][Z|[+-]hh:mm]
   *
   * @param date the date to format
   * @param millis true to include millis precision otherwise false
   * @param tz timezone to use for the formatting (UTC will produce 'Z')
   * @return the date formatted as yyyy-MM-ddThh:mm:ss[.sss][Z|[+-]hh:mm]
   */
  public static String format(Date date, boolean millis, TimeZone tz) {
    Calendar calendar = new GregorianCalendar(tz, Locale.US);
    calendar.setTime(date);

    // estimate capacity of buffer as close as we can (yeah, that's pedantic ;)
    int capacity = "yyyy-MM-ddThh:mm:ss".length();
    capacity += millis ? ".sss".length() : 0;
    capacity += tz.getRawOffset() == 0 ? "Z".length() : "+hh:mm".length();
    StringBuilder formatted = new StringBuilder(capacity);

    padInt(formatted, calendar.get(Calendar.YEAR), "yyyy".length());
    formatted.append('-');
    padInt(formatted, calendar.get(Calendar.MONTH) + 1, "MM".length());
    formatted.append('-');
    padInt(formatted, calendar.get(Calendar.DAY_OF_MONTH), "dd".length());
    formatted.append('T');
    padInt(formatted, calendar.get(Calendar.HOUR_OF_DAY), "hh".length());
    formatted.append(':');
    padInt(formatted, calendar.get(Calendar.MINUTE), "mm".length());
    formatted.append(':');
    padInt(formatted, calendar.get(Calendar.SECOND), "ss".length());
    if (millis) {
      formatted.append('.');
      padInt(formatted, calendar.get(Calendar.MILLISECOND), "sss".length());
    }

    int offset = tz.getOffset(calendar.getTimeInMillis());
    if (offset != 0) {
      int hours = Math.abs((offset / (60 * 1000)) / 60);
      int minutes = Math.abs((offset / (60 * 1000)) % 60);
      formatted.append(offset < 0 ? '-' : '+');
      padInt(formatted, hours, "hh".length());
      formatted.append(':');
      padInt(formatted, minutes, "mm".length());
    } else {
      formatted.append('Z');
    }

    return formatted.toString();
  }

  /*
  /**********************************************************
  /* Parsing
  /**********************************************************
   */

  /**
   * Parse a date from ISO-8601 formatted string. It expects a format
   * [yyyy-MM-dd|yyyyMMdd][T(hh:mm[:ss[.sss]]|hhmm[ss[.sss]])]?[Z|[+-]hh[:mm]]]
   *
   * @param date ISO string to parse in the appropriate format.
   * @param pos The position to start parsing from, updated to where parsing stopped.
   * @return the parsed date
   * @throws ParseException if the date is not in the appropriate format
   */
  public static Date parse(String date, ParsePosition pos) throws ParseException {
    Exception fail = null;
    try {
      int offset = pos.getIndex();

      // extract year
      int year = parseInt(date, offset, offset += 4);
      if (checkOffset(date, offset, '-')) {
        offset += 1;
      }

      // extract month
      int month = parseInt(date, offset, offset += 2);
      if (checkOffset(date, offset, '-')) {
        offset += 1;
      }

      // extract day
      int day = parseInt(date, offset, offset += 2);

      // default time value
      int hour = 0;
      int minutes = 0;
      int seconds = 0;

      // always use 0 otherwise returned date will include millis of current time
      int milliseconds = 0;

      // if the value has no time component (and no time zone), we are done
      boolean hasT = checkOffset(date, offset, 'T');

      if (!hasT && (date.length() <= offset)) {
        Calendar calendar = new GregorianCalendar(year, month - 1, day);
        calendar.setLenient(false);

        pos.setIndex(offset);
        return calendar.getTime();
      }

      if (hasT) {

        // extract hours, minutes, seconds and milliseconds
        hour = parseInt(date, offset += 1, offset += 2);
        if (checkOffset(date, offset, ':')) {
          offset += 1;
        }

        minutes = parseInt(date, offset, offset += 2);
        if (checkOffset(date, offset, ':')) {
          offset += 1;
        }
        // second and milliseconds can be optional
        if (date.length() > offset) {
          char c = date.charAt(offset);
          if (c != 'Z' && c != '+' && c != '-') {
            seconds = parseInt(date, offset, offset += 2);
            if (seconds > 59 && seconds < 63) {
              seconds = 59; // truncate up to 3 leap seconds
            }
            // milliseconds can be optional in the format
            if (checkOffset(date, offset, '.')) {
              offset += 1;
              int endOffset = indexOfNonDigit(date, offset + 1); // assume at least one digit
              int parseEndOffset = Math.min(endOffset, offset + 3); // parse up to 3 digits
              int fraction = parseInt(date, offset, parseEndOffset);
              // compensate for "missing" digits
              switch (parseEndOffset - offset) { // number of digits parsed
                case 2:
                  milliseconds = fraction * 10;
                  break;
                case 1:
                  milliseconds = fraction * 100;
                  break;
                default:
                  milliseconds = fraction;
              }
              offset = endOffset;
            }
          }
        }
      }

      // extract timezone
      if (date.length() <= offset) {
        throw new IllegalArgumentException("No time zone indicator");
      }

      TimeZone timezone = null;
      char timezoneIndicator = date.charAt(offset);

      if (timezoneIndicator == 'Z') {
        timezone = TIMEZONE_UTC;
        offset += 1;
      } else if (timezoneIndicator == '+' || timezoneIndicator == '-') {
        String timezoneOffset = date.substring(offset);

        // When timezone has no minutes, we should append it, valid timezones are, for example:
        // +00:00, +0000 and +00
        timezoneOffset = timezoneOffset.length() >= 5 ? timezoneOffset : timezoneOffset + "00";

        offset += timezoneOffset.length();
        // 18-Jun-2015, tatu: Minor simplification, skip offset of "+0000"/"+00:00"
        if (timezoneOffset.equals("+0000") || timezoneOffset.equals("+00:00")) {
          timezone = TIMEZONE_UTC;
        } else {
          // 18-Jun-2015, tatu: Looks like offsets only work from GMT, not UTC...
          //    not sure why, but that's the way it looks. Further, Javadocs for
          //    `java.util.TimeZone` specifically instruct use of GMT as base for
          //    custom timezones... odd.
          String timezoneId = "GMT" + timezoneOffset;
          // String timezoneId = "UTC" + timezoneOffset;

          timezone = TimeZone.getTimeZone(timezoneId);

          String act = timezone.getID();
          if (!act.equals(timezoneId)) {
            /* 22-Jan-2015, tatu: Looks like canonical version has colons, but we may be given
             *    one without. If so, don't sweat.
             *   Yes, very inefficient. Hopefully not hit often.
             *   If it becomes a perf problem, add 'loose' comparison instead.
             */
            String cleaned = act.replace(":", "");
            if (!cleaned.equals(timezoneId)) {
              throw new IndexOutOfBoundsException(
                  "Mismatching time zone indicator: "
                      + timezoneId
                      + " given, resolves to "
                      + timezone.getID());
            }
          }
        }
      } else {
        throw new IndexOutOfBoundsException(
            "Invalid time zone indicator '" + timezoneIndicator + "'");
      }

      Calendar calendar = new GregorianCalendar(timezone);
      calendar.setLenient(false);
      calendar.set(Calendar.YEAR, year);
      calendar.set(Calendar.MONTH, month - 1);
      calendar.set(Calendar.DAY_OF_MONTH, day);
      calendar.set(Calendar.HOUR_OF_DAY, hour);
      calendar.set(Calendar.MINUTE, minutes);
      calendar.set(Calendar.SECOND, seconds);
      calendar.set(Calendar.MILLISECOND, milliseconds);

      pos.setIndex(offset);
      return calendar.getTime();
      // If we get a ParseException it'll already have the right message/offset.
      // Other exception types can convert here.
    } catch (IndexOutOfBoundsException | IllegalArgumentException e) {
      fail = e;
    }
    String input = (date == null) ? null : ('"' + date + '"');
    String msg = fail.getMessage();
    if (msg == null || msg.isEmpty()) {
      msg = "(" + fail.getClass().getName() + ")";
    }
    ParseException ex =
        new ParseException("Failed to parse date [" + input + "]: " + msg, pos.getIndex());
    ex.initCause(fail);
    throw ex;
  }

  /**
   * Check if the expected character exist at the given offset in the value.
   *
   * @param value the string to check at the specified offset
   * @param offset the offset to look for the expected character
   * @param expected the expected character
   * @return true if the expected character exist at the given offset
   */
  private static boolean checkOffset(String value, int offset, char expected) {
    return (offset < value.length()) && (value.charAt(offset) == expected);
  }

  /**
   * Parse an integer located between 2 given offsets in a string
   *
   * @param value the string to parse
   * @param beginIndex the start index for the integer in the string
   * @param endIndex the end index for the integer in the string
   * @return the int
   * @throws NumberFormatException if the value is not a number
   */
  private static int parseInt(String value, int beginIndex, int endIndex)
      throws NumberFormatException {
    if (beginIndex < 0 || endIndex > value.length() || beginIndex > endIndex) {
      throw new NumberFormatException(value);
    }
    // use same logic as in Integer.parseInt() but less generic we're not supporting negative values
    int i = beginIndex;
    int result = 0;
    int digit;
    if (i < endIndex) {
      digit = Character.digit(value.charAt(i++), 10);
      if (digit < 0) {
        throw new NumberFormatException("Invalid number: " + value.substring(beginIndex, endIndex));
      }
      result = -digit;
    }
    while (i < endIndex) {
      digit = Character.digit(value.charAt(i++), 10);
      if (digit < 0) {
        throw new NumberFormatException("Invalid number: " + value.substring(beginIndex, endIndex));
      }
      result *= 10;
      result -= digit;
    }
    return -result;
  }

  /**
   * Zero pad a number to a specified length
   *
   * @param buffer buffer to use for padding
   * @param value the integer value to pad if necessary.
   * @param length the length of the string we should zero pad
   */
  private static void padInt(StringBuilder buffer, int value, int length) {
    String strValue = Integer.toString(value);
    for (int i = length - strValue.length(); i > 0; i--) {
      buffer.append('0');
    }
    buffer.append(strValue);
  }

  /**
   * Returns the index of the first character in the string that is not a digit, starting at offset.
   */
  private static int indexOfNonDigit(String string, int offset) {
    for (int i = offset; i < string.length(); i++) {
      char c = string.charAt(i);
      if (c < '0' || c > '9') {
        return i;
      }
    }
    return string.length();
  }
}
