<?php
/**
 * Copyright 2017 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
 *
 *      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.
 */

namespace Google\Cloud\Core;

/**
 * Represents a Timestamp value.
 *
 * Nanosecond precision is preserved by passing nanoseconds as a separate
 * argument to the constructor. If nanoseconds are given, any subsecond
 * precision in the timestamp will be overridden when encoding the timestamp
 * as a string.
 *
 * Example:
 * ```
 * use Google\Cloud\Core\Timestamp;
 *
 * $timestamp = new Timestamp(new \DateTime('2003-02-05 11:15:02.421827Z'));
 * ```
 *
 * ```
 * // Timestamps can be cast to strings.
 * echo (string) $timestamp;
 * ```
 */
class Timestamp
{
    use TimeTrait;

    const FORMAT = 'Y-m-d\TH:i:s.u\Z';
    const FORMAT_NO_MS = 'Y-m-d\TH:i:s\Z';
    const FORMAT_INTERPOLATE = 'Y-m-d\TH:i:s.%\s\Z';

    /**
     * @var \DateTimeInterface
     */
    private $value;

    /**
     * @var int
     */
    private $nanoSeconds;

    /**
     * @param \DateTimeInterface $value The timestamp value. Use of
     *        `DateTimeImmutable` is highly recommended over `DateTime` in order
     *        to avoid side effects.
     * @param int $nanoSeconds [optional] The number of nanoseconds in the
     *        timestamp. If omitted, subsecond precision will be obtained from
     *        the instance of `\DateTimeInterface` provided in the first
     *        argument. If provided, any precision in `$value` below seconds
     *        will be disregarded.
     */
    public function __construct(\DateTimeInterface $value, $nanoSeconds = null)
    {
        $this->value = $value;

        $this->nanoSeconds = $nanoSeconds !== null
            ? (int) $nanoSeconds
            : null;
    }

    /**
     * Get the underlying `\DateTimeInterface` implementation.
     *
     * Please note that if you provided nanoseconds when creating the timestamp,
     * they will not be included in this value.
     *
     * Example:
     * ```
     * $dateTime = $timestamp->get();
     * ```
     *
     * @return \DateTimeInterface
     */
    public function get()
    {
        return $this->value;
    }

    /**
     * Return the number of nanoseconds.
     *
     * Example:
     * ```
     * $nanos = $timestamp->nanoSeconds();
     * ```
     *
     * @return int
     */
    public function nanoSeconds()
    {
        return $this->nanoSeconds === null
            ? (int) $this->value->format('u') * 1000
            : $this->nanoSeconds;
    }

    /**
     * Format the value as a string.
     *
     * Example:
     * ```
     * $value = $timestamp->formatAsString();
     * ```
     *
     * @return string
     */
    public function formatAsString()
    {
        return $this->formatTimeAsString(
            $this->value,
            $this->nanoSeconds
        );
    }

    /**
     * Format the value as a string.
     *
     * @return string
     * @access private
     */
    public function __toString()
    {
        return $this->formatAsString();
    }

    /**
     * Format a timestamp for the API with nanosecond precision.
     *
     * @return array
     */
    public function formatForApi()
    {
        return $this->formatTimeAsArray($this->value, $this->nanoSeconds());
    }
}