class.php

<?php
namespace F3\Changelog;

use Composer\Semver\Semver;
use F3\Changelog\Exception\NoTagsFound;
use F3\Changelog\Exception\TagNotFound;
use F3\ReleaseNotesGenerator\GitGateway;

class ReleaseNotes
{
    /**
     * @var GitGateway
     */
    private $git;

    public function write(Printer $printer, string $tag = null)
    {
        $tags = $this->git->getTags();
        if (empty($tags)) {
            throw new NoTagsFound();
        }
        $tags = Semver::rsort($tags);
        $tag = $tag ?: reset($tags);
        $index = array_search($tag, $tags);
        if (false === $index) {
            throw new TagNotFound($tag);
        }
        if (++$index < count($tags)) {
            $url = $this->git->getDiffUrl($tags[$index], $tag);
            $revisions = $this->git->getRevisions($tags[$index], $tag);
        } else {
            $url = null;
            $revisions = $this->git->getRevisions(null, $tag);
        }
        $printer->header($tag, $this->git->getCommit($tag)->getDate(), $url);
        foreach ($revisions as $revision) {
            $commit = $this->git->getCommit($revision);
            $printer->change($commit->getSubject(), $commit->getAuthor());
        }
    }
}

interface GitGateway
{
    /**
     * Get commit details by revision (hash or tag)
     *
     * @param string $revision
     * @return Commit
     */
    public function getCommit(string $revision): Commit;

    /**
     * Get list of tags
     *
     * @return string[]
     */
    public function getTags(): array;

    /**
     * Get the url show the diff between revisions

     * @param string $from
     * @param string $to
     * @return string
     */
    public function getDiffUrl(string $from, string $to): string;

    /**
     * Get all revisions between $from and $to
     * Equivalent: "git log <to>" or "git log <from>..<to>"
     *
     * @param string $from
     * @param string $to
     * @return array|\string[] Hashes
     */
    public function getRevisions(string $from = null, string $to = null): array;
}

interface Printer
{
    public function header(string $tag, \DateTimeInterface $date, string $url = null);
    public function change(string $subject, string $author = null);
}