// Copyright 2016 Google Inc. All Rights Reserved.

//

// 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

//

//   https://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.

#include "time_zone_fixed.h"

#include <algorithm>

#include <cassert>

#include <chrono>

#include <cstring>

#include <string>

namespace cctz {

namespace {

// The prefix used for the internal names of fixed-offset zones.

const char kFixedZonePrefix[] = "Fixed/UTC";

const char kDigits[] = "0123456789";

char* Format02d(char* p, int v) {

  *p++ = kDigits[(v / 10) % 10];

  *p++ = kDigits[v % 10];

  return p;

}

int Parse02d(const char* p) {

  if (const char* ap = std::strchr(kDigits, *p)) {

    int v = static_cast<int>(ap - kDigits);

    if (const char* bp = std::strchr(kDigits, *++p)) {

      return (v * 10) + static_cast<int>(bp - kDigits);

    }

  }

  return -1;

}

}  // namespace

bool FixedOffsetFromName(const std::string& name, seconds* offset) {

  if (name == "UTC" || name == "UTC0") {

    *offset = seconds::zero();

    return true;

  }

  const std::size_t prefix_len = sizeof(kFixedZonePrefix) - 1;

  const char* const ep = kFixedZonePrefix + prefix_len;

  if (name.size() != prefix_len + 9)  // <prefix>+99:99:99

    return false;

  if (!std::equal(kFixedZonePrefix, ep, name.begin()))

    return false;

  const char* np = name.data() + prefix_len;

  if (np[0] != '+' && np[0] != '-')

    return false;

  if (np[3] != ':' || np[6] != ':')  // see note below about large offsets

    return false;

  int hours = Parse02d(np + 1);

  if (hours == -1) return false;

  int mins = Parse02d(np + 4);

  if (mins == -1) return false;

  int secs = Parse02d(np + 7);

  if (secs == -1) return false;

  secs += ((hours * 60) + mins) * 60;

  if (secs > 24 * 60 * 60) return false;  // outside supported offset range

  *offset = seconds(secs * (np[0] == '-' ? -1 : 1));  // "-" means west

  return true;

}

std::string FixedOffsetToName(const seconds& offset) {

  if (offset == seconds::zero()) return "UTC";

  if (offset < std::chrono::hours(-24) || offset > std::chrono::hours(24)) {

    // We don't support fixed-offset zones more than 24 hours

    // away from UTC to avoid complications in rendering such

    // offsets and to (somewhat) limit the total number of zones.

    return "UTC";

  }

  int offset_seconds = static_cast<int>(offset.count());

  const char sign = (offset_seconds < 0 ? '-' : '+');

  int offset_minutes = offset_seconds / 60;

  offset_seconds %= 60;

  if (sign == '-') {

    if (offset_seconds > 0) {

      offset_seconds -= 60;

      offset_minutes += 1;

    }

    offset_seconds = -offset_seconds;

    offset_minutes = -offset_minutes;

  }

  int offset_hours = offset_minutes / 60;

  offset_minutes %= 60;

  const std::size_t prefix_len = sizeof(kFixedZonePrefix) - 1;

  char buf[prefix_len + sizeof("-24:00:00")];

  char* ep = std::copy_n(kFixedZonePrefix, prefix_len, buf);

  *ep++ = sign;

  ep = Format02d(ep, offset_hours);

  *ep++ = ':';

  ep = Format02d(ep, offset_minutes);

  *ep++ = ':';

  ep = Format02d(ep, offset_seconds);

  *ep++ = '\0';

  assert(ep == buf + sizeof(buf));

  return buf;

}

std::string FixedOffsetToAbbr(const seconds& offset) {

  std::string abbr = FixedOffsetToName(offset);

  const std::size_t prefix_len = sizeof(kFixedZonePrefix) - 1;

  if (abbr.size() == prefix_len + 9) {         // <prefix>+99:99:99

    abbr.erase(0, prefix_len);                 // +99:99:99

    abbr.erase(6, 1);                          // +99:9999

    abbr.erase(3, 1);                          // +999999

    if (abbr[5] == '0' && abbr[6] == '0') {    // +999900

      abbr.erase(5, 2);                        // +9999

      if (abbr[3] == '0' && abbr[4] == '0') {  // +9900

        abbr.erase(3, 2);                      // +99

      }

    }

  }

  return abbr;

}

}  // namespace cctz