<?php

declare(strict_types=1);

namespace LIT\MCP\Integrations\Divi\Compose;

use LIT\MCP\Integrations\Divi\BlockTree\AttrMap;
use LIT\MCP\Integrations\Divi\BlockTree\Block;
use LIT\MCP\Integrations\Divi\Schema\ModuleCatalog;

/**
 * Which node may sit where (spec §5.4 "Struktur"): page → sections; regular section → rows;
 * fullwidth section → fullwidth modules (catalog category "fullwidth-module"); column/group →
 * modules; column → a nested row too (Divi 5 row is "nestable": true; neither the server
 * – BlockParserStore::is_nested_module() only adds et_pb_row_nested – nor the builder's drop
 * rules limit the depth); parent module → its child modules (catalog). Columns only come with
 * their row; specialty sections, specialty columns (module.advanced.specialtyColumns or
 * row-inner children, ColumnModule.php:306-324) and read-only nodes (opaque, non-Divi) are not
 * rebuilt. Pure PHP.
 */
final class StructureRules
{
    private const COLUMNS = ['divi/column', 'divi/column-inner'];
    private const ROWS = ['divi/row', 'divi/row-inner'];
    private const FULLWIDTH = 'fullwidth-module';

    public function __construct(private ModuleCatalog $catalog)
    {
    }

    /** Null when $child may be placed into $parent (null = top level of the page), else the German reason. */
    public function violation(?Block $parent, string $child): ?string
    {
        if (! $this->catalog->has($child)) {
            return sprintf('unbekanntes Modul "%s" (siehe lit-divi-catalog)', $child);
        }

        if ($parent === null) {
            return $child === 'divi/section' ? null : 'auf oberster Ebene sind nur Abschnitte (section) erlaubt';
        }

        if (! $parent->isDivi() || $parent->isOpaque()) {
            return 'der Zielknoten ist nur lesbar (globales Modul oder fremder Block)';
        }

        $parentName = $parent->name();
        if ($parentName === 'divi/section') {
            return $this->inSection($parent, $child);
        }

        if (in_array($parentName, self::ROWS, true)) {
            return 'Spalten entstehen mit der Zeile ("columns"); eine neue Zeile mit der gewünschten Aufteilung '
                . 'einfügen';
        }

        if (in_array($parentName, self::COLUMNS, true) && self::isSpecialtyColumn($parent)) {
            return 'Spezialspalten (specialty) nur im Divi-Builder umbauen; Module in ihre inneren Spalten einfügen';
        }

        if (in_array($parentName, self::COLUMNS, true) || $parentName === 'divi/group') {
            // A nested row: only straight into a (Divi 5) column – like the builder's drop target.
            $nestedRow = $child === 'divi/row' && $parentName === 'divi/column';

            return $this->isPlainModule($child) || $child === 'divi/group' || $nestedRow
                ? null
                : sprintf('%s passt nicht in eine Spalte', $child);
        }

        $children = $this->catalog->childrenOf($parentName);
        if ($children === []) {
            return sprintf('%s kann keine Kind-Module enthalten', $parentName);
        }

        return in_array($child, $children, true)
            ? null
            : sprintf('%s erlaubt nur %s als Kind', $parentName, implode(', ', $children));
    }

    /** A module that goes into a column: catalog category "module" (not "fullwidth-module"). */
    public function isPlainModule(string $name): bool
    {
        return $this->catalog->category($name) === 'module';
    }

    /** A column of a specialty section: it holds inner rows, not modules. */
    private static function isSpecialtyColumn(Block $column): bool
    {
        $specialty = AttrMap::desktop($column->attrs(), 'module.advanced.specialtyColumns');
        if ($specialty !== null && $specialty !== '') {
            return true;
        }

        foreach ($column->children() as $child) {
            if ($child->name() === 'divi/row-inner') {
                return true;
            }
        }

        return false;
    }

    private function inSection(Block $section, string $child): ?string
    {
        $type = AttrMap::desktop($section->attrs(), 'module.advanced.type');
        if ($type === 'specialty') {
            return 'Spezialabschnitte (specialty) nur im Divi-Builder umbauen; Module in ihre Spalten einfügen';
        }

        if ($type === 'fullwidth') {
            return $this->catalog->category($child) === self::FULLWIDTH
                ? null
                : 'in einen Vollbreite-Abschnitt passen nur fullwidth-Module';
        }

        return $child === 'divi/row' ? null : 'ein Abschnitt enthält Zeilen (row)';
    }
}