<?php

declare(strict_types=1);

namespace App\Services\Git;

use App\Services\Git\Contracts\RepositoryProvider;
use Carbon\CarbonImmutable;
use Illuminate\Http\Client\ConnectionException;
use Illuminate\Http\Client\PendingRequest;
use Illuminate\Http\Client\Response;
use Illuminate\Support\Facades\Http;

/**
 * Reads repositories from a self-hosted Gitea instance.
 *
 * Gitea's REST API is modelled on GitHub's but is not identical, and the
 * differences that matter are handled here rather than leaking outwards:
 *
 * - Counters are named `stars_count` / `forks_count`, not `stargazers_count`.
 * - Topics live on their own endpoint instead of the repository payload.
 * - Issues accept `type=issues`, which filters out pull requests server-side.
 * - There is no contributors endpoint, so the count is derived from the
 *   distinct authors of recent commits (see contributorCount()).
 * - Authentication uses the `token` scheme rather than `Bearer`.
 */
class GiteaProvider implements RepositoryProvider
{
    /**
     * How many recent commits to inspect when approximating the contributor
     * count. One request, and enough history to be representative without
     * walking the whole log.
     */
    protected const COMMIT_SAMPLE = 100;

    public function __construct(
        protected string $baseUrl,
        protected ?string $token = null,
        protected ?string $defaultOwner = null,
    ) {}

    /**
     * @param  array<string, mixed>  $config
     */
    public static function fromConfig(array $config): self
    {
        $url = rtrim((string) ($config['url'] ?? ''), '/');

        return new self(
            // Gitea always serves its API under /api/v1 of the instance root.
            baseUrl: $url === '' ? '' : $url.'/api/v1',
            token: $config['token'] ?? null,
            defaultOwner: $config['default_owner'] ?? null,
        );
    }

    /**
     * Unlike a hosted service, a self-hosted instance has no default address:
     * without GITEA_URL there is nothing to talk to.
     */
    public function isConfigured(): bool
    {
        return filled($this->baseUrl);
    }

    public function fetch(string $fullName): RepositorySnapshot
    {
        if (! $this->isConfigured()) {
            throw new GitException(
                'The Gitea instance is not configured: set GITEA_URL to your instance root, e.g. https://git.example.org.'
            );
        }

        $fullName = $this->qualify($fullName);

        $response = $this->get("/repos/{$fullName}");

        if ($response->status() === 404) {
            throw GitException::notFound($fullName);
        }

        // A private repository on a self-hosted instance answers 403 without a
        // token, which is a configuration problem rather than a missing repo.
        if ($response->status() === 403) {
            throw new GitException(
                "Gitea denied access to [{$fullName}]. If it is private, set GITEA_TOKEN to a token that can read it.",
                status: 403,
            );
        }

        $this->assertSuccessful($response, $fullName);

        $data = (array) $response->json();

        return new RepositorySnapshot(
            fullName: (string) ($data['full_name'] ?? $fullName),
            htmlUrl: $data['html_url'] ?? null,
            description: filled($data['description'] ?? null) ? $data['description'] : null,
            homepage: filled($data['website'] ?? null) ? $data['website'] : null,
            defaultBranch: $data['default_branch'] ?? null,
            primaryLanguage: filled($data['language'] ?? null) ? $data['language'] : null,
            // Gitea does not report a licence in the repository payload.
            license: null,
            topics: $this->topics($fullName, $data),
            languages: $this->languages($fullName),
            stars: (int) ($data['stars_count'] ?? 0),
            forks: (int) ($data['forks_count'] ?? 0),
            watchers: (int) ($data['watchers_count'] ?? 0),
            openIssuesCount: (int) ($data['open_issues_count'] ?? 0),
            contributorsCount: $this->contributorCount($fullName),
            commitsLastYear: 0,
            isArchived: (bool) ($data['archived'] ?? false),
            isFork: (bool) ($data['fork'] ?? false),
            // Gitea has no `pushed_at`; `updated_at` moves on push.
            pushedAt: $this->date($data['updated_at'] ?? null),
            createdAt: $this->date($data['created_at'] ?? null),
            issues: $this->issues($fullName),
        );
    }

    /**
     * Open issues worth showing a newcomer.
     *
     * @return array<int, IssueSnapshot>
     */
    protected function issues(string $fullName): array
    {
        $response = $this->get("/repos/{$fullName}/issues", [
            'state' => 'open',
            // Gitea can exclude pull requests server-side, unlike GitHub.
            'type' => 'issues',
            'limit' => 100,
        ]);

        if ($response->failed()) {
            return [];
        }

        $issues = [];

        foreach ((array) $response->json() as $issue) {
            $labels = array_values(array_map(
                fn (array $label) => (string) ($label['name'] ?? ''),
                (array) ($issue['labels'] ?? []),
            ));

            $isGoodFirst = IssueSnapshot::matchesLabelGroup($labels, 'good_first_issue');
            $isHelpWanted = IssueSnapshot::matchesLabelGroup($labels, 'help_wanted');

            // Mirroring every open issue would turn the site into a noisy
            // tracker; only the ones that are an invitation are kept.
            if (! $isGoodFirst && ! $isHelpWanted) {
                continue;
            }

            $issues[] = new IssueSnapshot(
                number: (int) $issue['number'],
                title: (string) $issue['title'],
                htmlUrl: (string) ($issue['html_url'] ?? ''),
                labels: $labels,
                isGoodFirstIssue: $isGoodFirst,
                isHelpWanted: $isHelpWanted,
                author: $issue['user']['login'] ?? null,
                // Gitea exposes `assignees` as well as the legacy `assignee`.
                assignee: $issue['assignee']['login']
                    ?? ($issue['assignees'][0]['login'] ?? null),
                comments: (int) ($issue['comments'] ?? 0),
                createdAt: $this->date($issue['created_at'] ?? null),
                updatedAt: $this->date($issue['updated_at'] ?? null),
            );
        }

        return array_slice($issues, 0, (int) config('git.max_issues_per_repository', 25));
    }

    /**
     * @param  array<string, mixed>  $repo
     * @return array<int, string>
     */
    protected function topics(string $fullName, array $repo): array
    {
        // Some Gitea versions do include topics inline; prefer that over a
        // second request.
        if (is_array($repo['topics'] ?? null) && $repo['topics'] !== []) {
            return array_values(array_map('strval', $repo['topics']));
        }

        $response = $this->get("/repos/{$fullName}/topics");

        if ($response->failed()) {
            return [];
        }

        return array_values(array_map('strval', (array) ($response->json('topics') ?? [])));
    }

    /**
     * @return array<string, int>
     */
    protected function languages(string $fullName): array
    {
        $response = $this->get("/repos/{$fullName}/languages");

        return $response->successful() ? array_map('intval', (array) $response->json()) : [];
    }

    /**
     * Gitea exposes no contributors endpoint, so this counts the distinct
     * authors of the most recent commits.
     *
     * It is an approximation by design: for a small collective's repositories
     * the recent history covers everyone who is actually involved, and it
     * costs one request instead of walking the entire log.
     */
    protected function contributorCount(string $fullName): int
    {
        $response = $this->get("/repos/{$fullName}/commits", [
            'limit' => self::COMMIT_SAMPLE,
            'stat' => 'false',
            'verification' => 'false',
            'files' => 'false',
        ]);

        if ($response->failed()) {
            return 0;
        }

        $authors = [];

        foreach ((array) $response->json() as $commit) {
            // Prefer the Gitea account; fall back to the raw commit email so
            // contributors without an account still count once each.
            $identity = $commit['author']['login']
                ?? $commit['commit']['author']['email']
                ?? null;

            if (filled($identity)) {
                $authors[mb_strtolower((string) $identity)] = true;
            }
        }

        return count($authors);
    }

    /**
     * @param  array<string, mixed>  $query
     */
    protected function get(string $path, array $query = []): Response
    {
        try {
            return $this->request()->get($this->baseUrl.$path, $query);
        } catch (ConnectionException $e) {
            throw GitException::unreachable('gitea', $e);
        }
    }

    protected function request(): PendingRequest
    {
        $request = Http::acceptJson()
            ->timeout((int) config('git.http_timeout', 15))
            ->retry(2, 300, throw: false);

        // Gitea's own scheme. It also accepts Bearer on recent versions, but
        // `token` works across every release we might meet.
        return filled($this->token)
            ? $request->withHeaders(['Authorization' => 'token '.$this->token])
            : $request;
    }

    protected function qualify(string $fullName): string
    {
        if (str_contains($fullName, '/') || blank($this->defaultOwner)) {
            return trim($fullName, '/');
        }

        return "{$this->defaultOwner}/{$fullName}";
    }

    protected function assertSuccessful(Response $response, string $fullName): void
    {
        if ($response->failed()) {
            throw new GitException(
                "Gitea answered {$response->status()} for [{$fullName}].",
                status: $response->status(),
                // A self-hosted instance being down is temporary; a 4xx is not.
                isTransient: $response->serverError(),
            );
        }
    }

    protected function date(?string $value): ?CarbonImmutable
    {
        return filled($value) ? CarbonImmutable::parse($value) : null;
    }
}