<?php

namespace App\Content;

use App\Domain\InvalidPage;
use App\Domain\StaleWrite;
use Doctrine\DBAL\Connection;

/**
 * Header, footer and reusable sections – block documents that are not pages.
 *
 * They use the same block contracts, the same validator and the same editor as a page, so a
 * section behaves everywhere the same way. What differs is the heading rule: a page needs exactly
 * one main heading, while a header, a footer or a section that appears on many pages must not
 * bring one of its own.
 *
 * A page links a section instead of copying it. Copying already exists as the section presets;
 * linking means one change reaches every page that uses it, which is the whole point.
 */
final class PartialRepository
{
    public const KINDS = ['header' => 'Kopfbereich', 'footer' => 'Fußbereich', 'section' => 'Wiederverwendbare Sektion'];
    /** A linked section may itself link one, but not deeper – and never in a circle. */
    public const MAX_NESTING = 3;

    public function __construct(private Connection $db, private DocumentValidator $validator, private RichText $richText = new RichText())
    {
    }

    /** @return list<array{id: string, kind: string, slug: string, name: string, document: array, version: int}> */
    public function all(string $locale = 'de'): array
    {
        return array_map($this->present(...), $this->db->fetchAllAssociative(
            'SELECT * FROM partial WHERE website_id = ? AND locale = ? ORDER BY kind, name',
            ['default', $locale],
        ));
    }

    public function find(string $id): ?array
    {
        $row = $this->db->fetchAssociative('SELECT * FROM partial WHERE id = ? AND website_id = ?', [$id, 'default']);

        return false === $row ? null : $this->present($row);
    }

    public function findByKind(string $kind, string $slug = 'default', string $locale = 'de'): ?array
    {
        $row = $this->db->fetchAssociative(
            'SELECT * FROM partial WHERE website_id = ? AND locale = ? AND kind = ? AND slug = ?',
            ['default', $locale, $kind, $slug],
        );

        return false === $row ? null : $this->present($row);
    }

    private function present(array $row): array
    {
        return [
            'id' => $row['id'], 'kind' => $row['kind'], 'slug' => $row['slug'], 'name' => $row['name'],
            'document' => json_decode($row['document'], true, 512, JSON_THROW_ON_ERROR),
            'version' => (int) $row['version'],
        ];
    }

    /**
     * The header or footer areas a page can choose from, by address.
     *
     * @return array<string, string> address => name
     */
    public function choices(string $kind, string $locale = 'de'): array
    {
        $choices = [];
        foreach ($this->db->fetchAllAssociative(
            'SELECT slug, name FROM partial WHERE website_id = ? AND locale = ? AND kind = ? ORDER BY slug = ? DESC, name',
            ['default', $locale, $kind, 'default'],
        ) as $row) {
            $choices[$row['slug']] = $row['name'];
        }

        return $choices;
    }

    public function create(string $kind, string $slug, string $name, array $document, string $locale = 'de'): string
    {
        if (!isset(self::KINDS[$kind])) {
            throw new InvalidPage('Unbekannte Art von Bereich.');
        }
        $slug = strtolower(trim($slug));
        if (1 !== preg_match('/^[a-z0-9]+(?:-[a-z0-9]+)*$/D', $slug) || strlen($slug) > 80) {
            throw new InvalidPage('Die Adresse darf nur Kleinbuchstaben, Ziffern und einzelne Bindestriche enthalten.');
        }
        $name = trim($name);
        if ('' === $name || mb_strlen($name) > 120) {
            throw new InvalidPage('Bitte gib einen Namen mit höchstens 120 Zeichen an.');
        }
        // Several headers and footers are allowed since pages may choose one: the first one
        // keeps the address "default" and is what a page without an own choice gets.
        if ('section' !== $kind && null === $this->findByKind($kind, 'default', $locale)) {
            $slug = 'default';
        }
        $document = $this->richText->normaliseDocument($document);
        $this->validator->validate($document, false, true);
        if (null !== $this->findByKind($kind, $slug, $locale)) {
            throw new InvalidPage(sprintf('„%s“ ist als Adresse bereits vergeben.', $slug));
        }
        $id = bin2hex(random_bytes(16));
        $this->db->insert('partial', [
            'id' => $id, 'website_id' => 'default', 'locale' => $locale,
            'kind' => $kind, 'slug' => $slug, 'name' => $name,
            'document' => json_encode($document, JSON_THROW_ON_ERROR | JSON_UNESCAPED_UNICODE),
            'version' => 1,
        ]);

        return $id;
    }

    public function save(string $id, array $document, int $expectedVersion): void
    {
        $document = $this->richText->normaliseDocument($document);
        $this->validator->validate($document, false, true);
        $this->db->transactional(function () use ($id, $document, $expectedVersion): void {
            // A section must not end up containing itself, directly or through another section.
            $this->guardAgainstCycles($id, $document);
            $changed = $this->db->executeStatement(
                'UPDATE partial SET document = ?, version = version + 1 WHERE id = ? AND version = ?',
                [json_encode($document, JSON_THROW_ON_ERROR | JSON_UNESCAPED_UNICODE), $id, $expectedVersion],
            );
            if (1 !== $changed) {
                throw new StaleWrite('Der Bereich wurde inzwischen geändert. Lade die Seite neu, bevor du speicherst.');
            }
        });
    }

    public function delete(string $id): void
    {
        $partial = $this->find($id);
        if (null === $partial) {
            throw new InvalidPage('Diesen Bereich gibt es nicht mehr.');
        }
        if ('section' !== $partial['kind']) {
            throw new InvalidPage('Kopf- und Fußbereich können nicht gelöscht werden. Leere sie stattdessen.');
        }
        // A page that links a removed section shows a placeholder instead of losing its layout,
        // so removal is allowed – but the editor should know where it is still in use.
        $this->db->executeStatement('DELETE FROM partial WHERE id = ?', [$id]);
    }

    /**
     * Resolves a linked section for rendering.
     *
     * @return array{name: string, document: array}|null
     */
    public function resolveSection(string $slug, string $locale = 'de'): ?array
    {
        $partial = $this->findByKind('section', $slug, $locale);

        return null === $partial ? null : ['name' => $partial['name'], 'document' => $partial['document']];
    }

    /** @throws InvalidPage when the document would make a section contain itself */
    private function guardAgainstCycles(string $id, array $document, int $depth = 0): void
    {
        $partial = $this->find($id);
        if (null === $partial || 'section' !== $partial['kind']) {
            return;
        }
        foreach ($this->referencedSlugs($document) as $slug) {
            if ($slug === $partial['slug']) {
                throw new InvalidPage('Eine Sektion kann sich nicht selbst enthalten.');
            }
            if ($depth + 1 >= self::MAX_NESTING) {
                throw new InvalidPage(sprintf('Sektionen dürfen höchstens %d Ebenen tief verschachtelt werden.', self::MAX_NESTING));
            }
            $nested = $this->findByKind('section', $slug, $partial['locale'] ?? 'de');
            if (null !== $nested) {
                $this->guardAgainstCycles($id, $nested['document'], $depth + 1);
            }
        }
    }

    /** @return list<string> */
    /**
     * Dieselbe Sektion mehrfach auf einer Seite: die zweite und jede weitere Verknüpfung bekommt
     * eine Kopie mit eigenen Kennungen (`id-2`, `id-3`) und ohne Sprungziele, damit die Seite keine
     * doppelten IDs trägt - ein Anker, ein Stil und jede Skriptsuche träfen sonst nur die erste.
     *
     * Gezählt wird in Renderreihenfolge über alle Dokumente einer Seite hinweg (`$seen` teilen sich
     * Kopf, Inhalt und Fuß); verschachtelte Verknüpfungen in einer Sektion zählen mit, bis zur
     * Verschachtelungsgrenze. `$sections` bekommt die Kopien unter `slug~n`, der Verweis im
     * zurückgegebenen Dokument zeigt dorthin.
     *
     * @param array<string, array> $sections die aufgelösten Sektionen, werden um Kopien ergänzt
     * @param array<string, int>   $seen     Zähler je Slug
     * @param array<string, array> $pristine die Sektionen, wie sie gespeichert sind
     */
    public function expandRepeatedLinks(array $document, array &$sections, array &$seen, array $pristine, int $depth = 0): array
    {
        $walk = function (array $blocks) use (&$walk, &$sections, &$seen, $pristine, $depth): array {
            foreach ($blocks as $i => $block) {
                $slug = 'partialref' === ($block['type'] ?? null) && is_string($block['props']['partial'] ?? null) ? $block['props']['partial'] : null;
                if (null !== $slug && isset($pristine[$slug])) {
                    $n = $seen[$slug] = ($seen[$slug] ?? 0) + 1;
                    if (1 === $n) {
                        if ($depth < self::MAX_NESTING) {
                            $sections[$slug] = $this->expandRepeatedLinks($pristine[$slug], $sections, $seen, $pristine, $depth + 1);
                        }
                    } else {
                        $key = $slug.'~'.$n;
                        $copy = $this->renamed($pristine[$slug], '-'.$n);
                        $sections[$key] = $depth < self::MAX_NESTING ? $this->expandRepeatedLinks($copy, $sections, $seen, $pristine, $depth + 1) : $copy;
                        $blocks[$i]['props']['partial'] = $key;
                    }
                }
                if (isset($block['children']) && is_array($block['children'])) {
                    $blocks[$i]['children'] = $walk($block['children']);
                }
            }

            return $blocks;
        };
        $document['blocks'] = $walk($document['blocks'] ?? []);

        return $document;
    }

    /** Ein Dokument mit angehängter Kennung an jedem Block, ohne Sprungziele. */
    private function renamed(array $document, string $suffix): array
    {
        $walk = static function (array $blocks) use (&$walk, $suffix): array {
            foreach ($blocks as $i => $block) {
                if (isset($block['id'])) {
                    $blocks[$i]['id'] = substr((string) $block['id'], 0, 64 - strlen($suffix)).$suffix;
                }
                unset($blocks[$i]['anchor']);
                if (isset($block['children']) && is_array($block['children'])) {
                    $blocks[$i]['children'] = $walk($block['children']);
                }
            }

            return $blocks;
        };
        $document['blocks'] = $walk($document['blocks'] ?? []);

        return $document;
    }

    public function referencedSlugs(array $document): array
    {
        $slugs = [];
        $walk = function (array $blocks) use (&$walk, &$slugs): void {
            foreach ($blocks as $block) {
                if ('partialref' === ($block['type'] ?? null) && is_string($block['props']['partial'] ?? null)) {
                    $slugs[] = $block['props']['partial'];
                }
                $walk($block['children'] ?? []);
            }
        };
        $walk($document['blocks'] ?? []);

        return array_values(array_unique($slugs));
    }

    /**
     * Which pages and sections link a given section. Shown before deleting, so nobody removes
     * something that is still in use without knowing it.
     *
     * @return list<string>
     */
    public function usedBy(string $slug, string $locale = 'de'): array
    {
        $users = [];
        foreach ($this->db->fetchAllAssociative(
            'SELECT p.path, r.document FROM page p JOIN revision r ON r.id = p.draft_revision_id AND r.page_id = p.id WHERE p.website_id = ? AND p.locale = ? AND p.deleted_at IS NULL',
            ['default', $locale],
        ) as $row) {
            if (in_array($slug, $this->referencedSlugs(json_decode($row['document'], true, 512, JSON_THROW_ON_ERROR)), true)) {
                $users[] = '/'.$row['path'];
            }
        }
        foreach ($this->all($locale) as $partial) {
            if ($partial['slug'] !== $slug && in_array($slug, $this->referencedSlugs($partial['document']), true)) {
                $users[] = $partial['name'];
            }
        }

        return $users;
    }
}