<?php

namespace MintyPHP\App\Module;

use FilesystemIterator;
use RecursiveDirectoryIterator;
use RecursiveIteratorIterator;
use RuntimeException;

/**
 * Builds a runtime PageRoot by symlinking core and enabled module pages.
 */
final class ModuleRuntimePageBuilder
{
    /**
     * @param array<string, ModuleManifest> $modules
     * @return array{core_entries: int, module_entries: int}
     */
    public function build(string $runtimeDir, string $corePagesDir, array $modules): array
    {
        $corePages = realpath($corePagesDir);
        if ($corePages === false) {
            throw new RuntimeException('Core pages/ directory not found.');
        }

        if (count($modules) === 0) {
            $this->pointRuntimeToCore($runtimeDir, $corePages);
            return ['core_entries' => 0, 'module_entries' => 0];
        }

        if (is_link($runtimeDir)) {
            unlink($runtimeDir);
        }
        if (!is_dir($runtimeDir) && !mkdir($runtimeDir, 0775, true) && !is_dir($runtimeDir)) {
            throw new RuntimeException('Cannot create runtime pages directory: ' . $runtimeDir);
        }

        $this->removeDirectoryContents($runtimeDir);

        $coreEntries = scandir($corePages);
        if ($coreEntries === false) {
            throw new RuntimeException('Cannot scan core pages directory.');
        }

        $coreCount = 0;
        foreach ($coreEntries as $entry) {
            if ($entry === '.' || $entry === '..') {
                continue;
            }
            $source = $corePages . '/' . $entry;
            $target = $runtimeDir . '/' . $entry;
            if (!@symlink($source, $target)) {
                throw new RuntimeException("Failed to create symlink: {$target} → {$source}");
            }
            $coreCount++;
        }

        $modulePageCount = 0;
        foreach ($modules as $manifest) {
            $modulePagesDir = $manifest->basePath . '/pages';
            if (!is_dir($modulePagesDir)) {
                continue;
            }
            $entries = scandir($modulePagesDir);
            if ($entries === false) {
                continue;
            }
            foreach ($entries as $entry) {
                if ($entry === '.' || $entry === '..') {
                    continue;
                }
                $source = $modulePagesDir . '/' . $entry;
                $target = $runtimeDir . '/' . $entry;
                if (file_exists($target) || is_link($target)) {
                    throw new RuntimeException(
                        "Page path collision: '{$entry}' from module '{$manifest->id}' conflicts with existing page."
                    );
                }
                if (!@symlink($source, $target)) {
                    throw new RuntimeException("Failed to create symlink: {$target} → {$source}");
                }
                $modulePageCount++;
            }
        }

        return [
            'core_entries' => $coreCount,
            'module_entries' => $modulePageCount,
        ];
    }

    public function pointRuntimeToCore(string $runtimeDir, string $corePages): void
    {
        if (is_dir($runtimeDir) && !is_link($runtimeDir)) {
            $this->removeDirectoryContents($runtimeDir);
            rmdir($runtimeDir);
        }
        if (is_link($runtimeDir)) {
            unlink($runtimeDir);
        }
        if (!@symlink($corePages, $runtimeDir)) {
            throw new RuntimeException("Failed to create symlink: {$runtimeDir} → {$corePages}");
        }
    }

    // ── Fingerprint: detect stale runtime state ─────────────────────

    /**
     * Compute the expected fingerprint for a set of modules.
     *
     * @param array<string, ModuleManifest> $modules
     */
    public static function expectedFingerprint(array $modules): string
    {
        $ids = array_map(static fn (ModuleManifest $m): string => $m->id, $modules);
        sort($ids);

        return implode(',', $ids);
    }

    /**
     * Read the persisted fingerprint from disk.
     */
    public static function readFingerprint(string $runtimeDir): string
    {
        $file = dirname($runtimeDir) . '/.module-fingerprint';

        return is_file($file) ? trim((string) file_get_contents($file)) : '';
    }

    /**
     * Write a fingerprint after a successful build so web/index.php can
     * detect stale runtime state without rebuilding on every request.
     *
     * @param array<string, ModuleManifest> $modules
     */
    public static function writeFingerprint(string $runtimeDir, array $modules): void
    {
        $file = dirname($runtimeDir) . '/.module-fingerprint';

        file_put_contents($file, self::expectedFingerprint($modules));
    }

    private function removeDirectoryContents(string $dir): void
    {
        $entries = scandir($dir);
        if ($entries === false) {
            return;
        }
        foreach ($entries as $entry) {
            if ($entry === '.' || $entry === '..') {
                continue;
            }
            $path = $dir . '/' . $entry;
            if (is_link($path)) {
                unlink($path);
                continue;
            }
            if (is_dir($path)) {
                $items = new RecursiveIteratorIterator(
                    new RecursiveDirectoryIterator($path, FilesystemIterator::SKIP_DOTS),
                    RecursiveIteratorIterator::CHILD_FIRST
                );
                foreach ($items as $item) {
                    $item->isDir() ? rmdir($item->getPathname()) : unlink($item->getPathname());
                }
                rmdir($path);
                continue;
            }
            unlink($path);
        }
    }
}