<?php

declare(strict_types=1);

define('REPO_RAW_BASE_URL', getenv('REPO_RAW_BASE_URL') ?: 'https://git.fnet.cz/lachtan/get/raw/branch/master/');
const MANIFEST_PATH = 'manifest.yaml';
const TEMPLATES_DIRECTORY = __DIR__ . '/../templates';
const FETCH_TIMEOUT_SECONDS = 5;

function sendPlainTextError(int $statusCode, string $message): never
{
    http_response_code($statusCode);
    header('Content-Type: text/plain; charset=utf-8');
    echo $message . "\n";
    exit;
}

function fetchRaw(string $relativePath): string|false
{
    $url = REPO_RAW_BASE_URL . ltrim($relativePath, '/');

    $curl = curl_init($url);
    curl_setopt_array($curl, [
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_FAILONERROR => true,
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_MAXREDIRS => 3,
        CURLOPT_TIMEOUT => FETCH_TIMEOUT_SECONDS,
    ]);

    $content = curl_exec($curl);

    return is_string($content) ? $content : false;
}

function escapeForDoubleQuotedShellString(string $value): string
{
    return str_replace(['\\', '"', '$', '`'], ['\\\\', '\\"', '\\$', '\\`'], $value);
}

function resolveHomePath(string $path): string
{
    if ($path === '~' || str_starts_with($path, '~/')) {
        return '$HOME' . escapeForDoubleQuotedShellString(substr($path, 1));
    }

    return escapeForDoubleQuotedShellString($path);
}

function renderScriptTemplate(string $templateName, array $placeholders): string|false
{
    $path = TEMPLATES_DIRECTORY . '/' . $templateName . '.sh.tpl';

    if (!is_file($path)) {
        return false;
    }

    $script = file_get_contents($path);

    foreach ($placeholders as $key => $value) {
        $script = str_replace('{{' . $key . '}}', $value, $script);
    }

    return $script;
}

$requestPath = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH) ?? '/';
$name = trim(rawurldecode($requestPath), '/');

if ($name === '') {
    sendPlainTextError(400, 'Missing name of the installable item');
}

$manifestYaml = fetchRaw(MANIFEST_PATH);

if ($manifestYaml === false) {
    sendPlainTextError(502, 'Failed to fetch the manifest from git.fnet.cz');
}

$manifest = yaml_parse($manifestYaml);

if ($manifest === false) {
    sendPlainTextError(502, 'Failed to parse the manifest from git.fnet.cz');
}

$entry = $manifest[$name] ?? null;

if ($entry === null) {
    sendPlainTextError(404, "Unknown item '$name'");
}

if (!is_string($entry['source'] ?? null) || !is_string($entry['target'] ?? null) || !is_string($entry['template'] ?? null)) {
    sendPlainTextError(500, "Malformed manifest entry for item '$name'");
}

$variables = [
    'SOURCE_URL' => REPO_RAW_BASE_URL . escapeForDoubleQuotedShellString(ltrim($entry['source'], '/')),
    'TARGET_PATH' => resolveHomePath($entry['target']),
    'POST_INSTALL' => $entry['post_install'] ?? '',
];

$script = renderScriptTemplate($entry['template'], $variables);

if ($script === false) {
    sendPlainTextError(500, 'Template for this item is missing');
}

header('Content-Type: text/x-shellscript; charset=utf-8');
echo $script;