<?php

declare(strict_types=1);

namespace LIT\MCP\Integrations\Divi\Compose;

use InvalidArgumentException;
use LIT\MCP\Integrations\Divi\BlockTree\AttrMap;
use LIT\MCP\Integrations\Divi\BlockTree\Block;
use LIT\MCP\Integrations\Divi\Design\DesignSystem;
use LIT\MCP\Integrations\Divi\Schema\ModuleCatalog;
use LIT\MCP\Integrations\Divi\Schema\ShortformMap;

/**
 * Builds new Divi blocks from node descriptions (spec §5.4): short form, full form ("attrs")
 * or both; sections with rows ("columns": "1_3,2_3") and modules; parent modules with
 * "items"; presets by name; automatic admin labels "<Abschnitt> – <Modul>" (spec §5.5).
 * Every error is collected with its input path; blocks are only usable when there are none.
 * Pure PHP.
 *
 * Divi saves bypass kses (D7): every client string reaches the attributes only through
 * ShortformWriter / AttrWriter::cleanValue() (the single choke point) – short-form fields,
 * full-form attrs, admin labels, background_color (ShortformWriter::color(), ruling S13) and
 * preset ids. A value that fails there is an error, never stored raw (S13). What Composer
 * writes itself is not client text: the builder version (checked in the constructor), block
 * names (catalog + StructureRules + Block::create), "fullwidth" and column flexTypes built
 * from digits. Design-system names that match several entries are errors listing the ids
 * (ruling S13a: colors/variables in Placeholders, presets in DesignSystem::modulePresetId()).
 */
final class Composer
{
    private const COMMON = ['type', 'label', 'preset', 'attrs'];
    private const SECTION = ['section_type', 'background_color', 'rows', 'modules'];
    private const ROW = ['columns', 'modules'];

    /** Keys of one lit-divi-update change ("id" names the node, read by the ability). */
    private const UPDATE = ['id', 'set', 'attrs', 'preset', 'label'];

    /** Column fractions Divi's flex layout knows besides multiples of 1/24. */
    private const SPECIAL_WIDTHS = ['1_5', '2_5', '3_5', '4_5', '1_7', '1_9', '1_10', '1_11'];

    /** ET_BUILDER_PRODUCT_VERSION, e.g. "5.2.1" – written into every new block. */
    private const VERSION = '/^[0-9][0-9A-Za-z.+-]*$/D';

    private const LABEL_PATH = 'module.meta.adminLabel';

    /** @var array<string, string> */
    private array $errors = [];

    /** @var list<string> */
    private array $invalidPaths = [];

    /** @throws InvalidArgumentException When $builderVersion is no version number. */
    public function __construct(
        private ModuleCatalog $catalog,
        private StructureRules $rules,
        private ShortformWriter $shortform,
        private AttrWriter $attrWriter,
        private DesignSystem $design,
        private string $builderVersion
    ) {
        if (preg_match(self::VERSION, $builderVersion) !== 1) {
            throw new InvalidArgumentException(sprintf('"%s" is not a Divi builder version.', $builderVersion));
        }
    }

    /**
     * @param array<array-key, mixed> $specs   Node descriptions.
     * @param Block|null              $parent  Block the nodes go into (null = top level of the page).
     * @param string                  $field   Input path of $specs for error keys, e.g. "nodes".
     * @param string                  $context Admin label of the surrounding section ("" if none).
     * @return array{blocks: list<Block>, errors: array<string, string>, invalid_paths: list<string>}
     */
    public function compose(array $specs, ?Block $parent, string $field, string $context = ''): array
    {
        $this->errors = [];
        $this->invalidPaths = [];
        $blocks = [];
        foreach (array_values($specs) as $position => $spec) {
            $block = $this->node($spec, $parent, sprintf('%s[%d]', $field, $position), $context);
            if ($block !== null) {
                $blocks[] = $block;
            }
        }

        return ['blocks' => $blocks, 'errors' => $this->errors, 'invalid_paths' => $this->invalidPaths];
    }

    /**
     * Applies short-form fields ("set"), full-form attrs, preset and label to an existing block
     * (lit-divi-update); errors like compose(). The block itself is not changed – the caller
     * sets the returned attrs. "preset": null and "label": null remove them.
     *
     * @param array<array-key, mixed> $change id, set, attrs, preset, label
     * @return array{attrs: array<string, mixed>, errors: array<string, string>, invalid_paths: list<string>}
     */
    public function update(Block $block, array $change, string $field): array
    {
        $this->errors = [];
        $this->invalidPaths = [];
        $attrs = $block->attrs();
        if (! $block->isDivi() || $block->isOpaque()) {
            $this->errors[$field . '.id'] = 'nur lesbar (globales Modul oder fremder Block)';

            return ['attrs' => $attrs, 'errors' => $this->errors, 'invalid_paths' => []];
        }

        $this->unknownKeys($change, self::UPDATE, $field);
        if (array_key_exists('set', $change)) {
            if (! is_array($change['set']) || $change['set'] === [] || array_is_list($change['set'])) {
                $this->errors[$field . '.set'] = 'Objekt mit Kurzform-Feldern erwartet';
            } else {
                $result = $this->shortform->apply($block->shortName(), $attrs, $change['set'], $field . '.set');
                $attrs = $result['attrs'];
                $this->errors += $result['errors'];
            }
        }

        $attrs = $this->presetAndAttrs($block->name(), $attrs, $change, $field);
        if (array_key_exists('label', $change)) {
            $attrs = $change['label'] === null || $change['label'] === ''
                ? AttrMap::remove($attrs, self::LABEL_PATH)
                : $this->label($block->name(), $attrs, $change['label'], $field . '.label');
        }

        return ['attrs' => $attrs, 'errors' => $this->errors, 'invalid_paths' => $this->invalidPaths];
    }

    /** Admin label for a new module: "<Abschnitt> – <Modultitel>" or the title alone. */
    public function autoLabel(string $name, string $context): string
    {
        $title = $this->catalog->title($name);

        return $context === '' ? $title : $context . ' – ' . $title;
    }

    private function node(mixed $spec, ?Block $parent, string $path, string $context): ?Block
    {
        if (! is_array($spec) || array_is_list($spec)) {
            $this->errors[$path] = 'Objekt mit "type" erwartet';

            return null;
        }

        $type = $this->typeOf($spec, $parent);
        if ($type === null) {
            $this->errors[$path . '.type'] = 'type fehlt';

            return null;
        }

        $violation = $this->rules->violation($parent, $type);
        if ($violation !== null) {
            $this->errors[$path . '.type'] = $violation;

            return null;
        }

        return match ($type) {
            'divi/section' => $this->section($spec, $path),
            'divi/row' => $this->row($spec, $path, $context),
            default => $this->module($type, $spec, $path, $context),
        };
    }

    /** @param array<array-key, mixed> $spec */
    private function typeOf(array $spec, ?Block $parent): ?string
    {
        if (is_string($spec['type'] ?? null) && trim($spec['type']) !== '') {
            return ModuleCatalog::normalize($spec['type']);
        }

        if (array_key_exists('type', $spec)) {
            return null;
        }

        $children = $parent === null ? [] : $this->catalog->childrenOf($parent->name());

        return count($children) === 1 ? $children[0] : null;
    }

    /** @param array<array-key, mixed> $spec */
    private function section(array $spec, string $path): Block
    {
        $this->unknownKeys($spec, array_merge(self::COMMON, self::SECTION), $path);
        $type = $spec['section_type'] ?? 'regular';
        $attrs = ['builderVersion' => $this->builderVersion];
        if ($type === 'fullwidth') {
            $attrs = AttrMap::set($attrs, 'module.advanced.type', ['desktop' => ['value' => 'fullwidth']]);
        } elseif ($type !== 'regular') {
            $this->errors[$path . '.section_type'] = 'regular oder fullwidth erwartet (specialty nur im Divi-Builder)';
        }

        if (array_key_exists('background_color', $spec)) {
            $attrs = $this->backgroundColor($attrs, $spec['background_color'], $path . '.background_color');
        }

        $attrs = $this->common('divi/section', $attrs, $spec, $path, null);
        $label = AttrMap::desktop($attrs, self::LABEL_PATH);
        $context = is_string($label) ? $label : '';
        $section = Block::create('divi/section', $attrs);

        $hasRows = array_key_exists('rows', $spec);
        $hasModules = array_key_exists('modules', $spec);
        if ($type === 'fullwidth') {
            if ($hasRows) {
                $this->errors[$path . '.rows'] = 'ein Vollbreite-Abschnitt (section_type fullwidth) hat keine Zeilen; '
                    . 'fullwidth-Module unter "modules" angeben';
            }
            $this->children($section, $spec['modules'] ?? [], $path . '.modules', $context);
        } elseif ($hasRows && $hasModules) {
            $this->errors[$path] = 'entweder rows oder modules angeben';
        } elseif ($hasModules) {
            $this->children($section, [['type' => 'row', 'modules' => $spec['modules']]], $path . '.modules', $context);
        } else {
            $this->children($section, $spec['rows'] ?? [], $path . '.rows', $context);
        }

        return $section;
    }

    /** @param array<array-key, mixed> $spec */
    private function row(array $spec, string $path, string $context): Block
    {
        $this->unknownKeys($spec, array_merge(self::COMMON, self::ROW), $path);
        $widths = $this->widths($spec['columns'] ?? '4_4', $path . '.columns');
        $label = $context === '' ? null : $context . ' – Zeile';
        $attrs = $this->common('divi/row', ['builderVersion' => $this->builderVersion], $spec, $path, $label);
        $row = Block::create('divi/row', $attrs);

        $modules = $spec['modules'] ?? [];
        if (! is_array($modules) || ! array_is_list($modules)) {
            $this->errors[$path . '.modules'] = 'Liste erwartet (je Spalte eine Liste von Modulen)';
            $modules = [];
        }

        // One column: a flat list of modules is accepted.
        $first = $modules[0] ?? null;
        if (count($widths) === 1 && is_array($first) && ! array_is_list($first)) {
            $modules = [$modules];
        }

        if (count($modules) > count($widths)) {
            $this->errors[$path . '.modules'] = sprintf(
                '%d Spalten, aber %d Modul-Listen',
                count($widths),
                count($modules)
            );
        }

        foreach ($widths as $position => $width) {
            $column = Block::create('divi/column', AttrMap::set(
                ['builderVersion' => $this->builderVersion],
                'module.decoration.sizing',
                ['desktop' => ['value' => ['flexType' => $width]]]
            ));
            $row->insertChild($position, $column);
            $this->children($column, $modules[$position] ?? [], sprintf('%s.modules[%d]', $path, $position), $context);
        }

        return $row;
    }

    /** @param array<array-key, mixed> $spec */
    private function module(string $name, array $spec, string $path, string $context): Block
    {
        $short = ModuleCatalog::shortName($name);
        $fields = array_keys(ShortformMap::fields($short));
        $hasItems = $this->catalog->childrenOf($name) !== [];
        $allowed = array_merge(
            self::COMMON,
            $fields,
            $hasItems ? ['items'] : [],
            $name === 'divi/group' ? ['modules'] : []
        );
        $this->unknownKeys($spec, $allowed, $path);

        // "type" and "label" of a node are its module type and admin label; the short-form fields
        // of the same name (contact-field type, social network label) go through lit-divi-update "set".
        $values = array_intersect_key($spec, array_flip(array_diff($fields, self::COMMON)));
        if ($name === 'divi/heading' && ! array_key_exists('level', $values)) {
            $values['level'] = 'h2';
        }

        $attrs = ['builderVersion' => $this->builderVersion];
        if ($values !== []) {
            $result = $this->shortform->apply($short, $attrs, $values, $path);
            $attrs = $result['attrs'];
            $this->errors += $result['errors'];
        }

        $block = Block::create($name, $this->common($name, $attrs, $spec, $path, $this->autoLabel($name, $context)));
        if ($hasItems) {
            $this->children($block, $spec['items'] ?? [], $path . '.items', $context);
        } elseif ($name === 'divi/group') {
            $this->children($block, $spec['modules'] ?? [], $path . '.modules', $context);
        }

        return $block;
    }

    /**
     * Preset, full-form attrs and admin label of a new block. The label is $spec's "label"
     * when given ("" = none), else $autoLabel.
     *
     * @param array<string, mixed>    $attrs
     * @param array<array-key, mixed> $spec
     * @return array<string, mixed>
     */
    private function common(string $name, array $attrs, array $spec, string $path, ?string $autoLabel): array
    {
        $attrs = $this->presetAndAttrs($name, $attrs, $spec, $path);
        $label = array_key_exists('label', $spec) && $spec['label'] !== null ? $spec['label'] : $autoLabel;
        if ($label === null || $label === '') {
            return $attrs;
        }

        return $this->label($name, $attrs, $label, $path . '.label');
    }

    /**
     * @param array<string, mixed>    $attrs
     * @param array<array-key, mixed> $spec
     * @return array<string, mixed>
     */
    private function presetAndAttrs(string $name, array $attrs, array $spec, string $path): array
    {
        if (array_key_exists('preset', $spec)) {
            $attrs = $this->preset($name, $attrs, $spec['preset'], $path . '.preset');
        }

        if (! array_key_exists('attrs', $spec)) {
            return $attrs;
        }

        if (! is_array($spec['attrs']) || array_is_list($spec['attrs'])) {
            $this->errors[$path . '.attrs'] = 'Objekt "Attributpfad": {Breakpoint: Wert} erwartet';

            return $attrs;
        }

        $result = $this->attrWriter->apply($name, $attrs, $spec['attrs'], $path . '.attrs');
        $this->errors += $result['errors'];
        array_push($this->invalidPaths, ...$result['invalid_paths']);

        return $result['attrs'];
    }

    /**
     * The admin label, cleaned as text at the choke point (ruling S13): a label that fails there,
     * or that still carries a reference, is an error and nothing is written.
     *
     * @param array<string, mixed> $attrs
     * @return array<string, mixed>
     */
    private function label(string $name, array $attrs, mixed $label, string $path): array
    {
        if (! is_string($label)) {
            $this->errors[$path] = 'Text erwartet';

            return $attrs;
        }

        try {
            $clean = $this->attrWriter->cleanValue($name, self::LABEL_PATH, $label, null, 'text');
        } catch (InvalidArgumentException $e) {
            $this->errors[$path] = $e->getMessage();

            return $attrs;
        }

        if (! is_string($clean) || VariableRef::contains($clean)) {
            $this->errors[$path] = 'Beschriftung: nur Text, keine Divi-Verweise oder Platzhalter';

            return $attrs;
        }

        return $clean === '' ? $attrs : AttrMap::set($attrs, self::LABEL_PATH, ['desktop' => ['value' => $clean]]);
    }

    /**
     * @param array<string, mixed> $attrs
     * @return array<string, mixed>
     */
    private function preset(string $name, array $attrs, mixed $preset, string $path): array
    {
        if ($preset === null || $preset === '') {
            unset($attrs['modulePreset']);

            return $attrs;
        }

        try {
            $id = is_string($preset) ? $this->design->modulePresetId($name, $preset) : null;
        } catch (InvalidArgumentException $e) {
            // Ruling S13a: a name several presets share (DesignSystem lists their ids).
            $this->errors[$path] = $e->getMessage();

            return $attrs;
        }

        if ($id === null) {
            $names = $this->design->modulePresetNames($name);
            $this->errors[$path] = sprintf(
                'unbekanntes Preset; vorhanden für %s: %s',
                $name,
                $names === [] ? '(keine)' : implode(', ', $names)
            );

            return $attrs;
        }

        // Design-system data, but still through the choke point: an id text() would change is refused.
        try {
            $clean = $this->attrWriter->cleanValue($name, 'modulePreset', $id, null, 'text');
        } catch (InvalidArgumentException $e) {
            $clean = null;
        }

        if ($clean !== $id) {
            $this->errors[$path] = sprintf('Preset-ID "%s" ist ungültig', $id);

            return $attrs;
        }

        $attrs['modulePreset'] = [$id];

        return $attrs;
    }

    /**
     * Ruling S13: the short-form color check (ShortformWriter::color()), never text().
     *
     * @param array<string, mixed> $attrs
     * @return array<string, mixed>
     */
    private function backgroundColor(array $attrs, mixed $color, string $path): array
    {
        try {
            $clean = $this->shortform->color('divi/section', 'module.decoration.background', $color, 'color');
        } catch (InvalidArgumentException $e) {
            $this->errors[$path] = $e->getMessage();

            return $attrs;
        }

        return AttrMap::set($attrs, 'module.decoration.background', ['desktop' => ['value' => ['color' => $clean]]]);
    }

    private function children(Block $parent, mixed $specs, string $path, string $context): void
    {
        if (! is_array($specs) || ($specs !== [] && ! array_is_list($specs))) {
            $this->errors[$path] = 'Liste erwartet';

            return;
        }

        foreach ($specs as $position => $spec) {
            $child = $this->node($spec, $parent, sprintf('%s[%d]', $path, $position), $context);
            if ($child !== null) {
                $parent->insertChild(PHP_INT_MAX, $child);
            }
        }
    }

    /**
     * "1_3,2_3" → flexTypes ["8_24", "16_24"]; the fractions must add up to exactly one row
     * (exact integer arithmetic over the common denominator, ruling S34 – no float tolerance).
     *
     * @return list<string>
     */
    private function widths(mixed $columns, string $path): array
    {
        $parts = is_string($columns) ? array_map('trim', explode(',', $columns)) : [];
        $widths = [];
        $fractions = [];
        foreach ($parts as $part) {
            $valid = preg_match('/^(\d{1,2})_(\d{1,2})$/D', $part, $match) === 1
                && (int) $match[1] >= 1
                && (int) $match[1] <= (int) $match[2];
            if (! $valid) {
                $this->errors[$path] = 'Spaltenaufteilung wie "1_2,1_2" oder "1_3,2_3" erwartet';

                return ['24_24'];
            }

            [$numerator, $denominator] = [(int) $match[1], (int) $match[2]];
            if (24 % $denominator === 0) {
                $widths[] = ($numerator * 24 / $denominator) . '_24';
            } elseif (in_array($part, self::SPECIAL_WIDTHS, true)) {
                $widths[] = $part;
            } else {
                $this->errors[$path] = sprintf('Spaltenbreite %s gibt es in Divi nicht', $part);

                return ['24_24'];
            }
            $fractions[] = [$numerator, $denominator];
        }

        if ($widths === [] || ! self::sumsToOne($fractions)) {
            $this->errors[$path] = 'die Spaltenbreiten müssen zusammen eine volle Zeile ergeben (z. B. "1_3,2_3")';

            return ['24_24'];
        }

        return $widths;
    }

    /**
     * Whether the fractions add up to exactly 1: numerators scaled to the least common
     * denominator (denominators are divisors of 24 or 5, 7, 9, 10, 11 – at most 27720).
     *
     * @param list<array{int, int}> $fractions [numerator, denominator]
     */
    private static function sumsToOne(array $fractions): bool
    {
        $common = 1;
        foreach ($fractions as [, $denominator]) {
            $common = intdiv($common * $denominator, self::gcd($common, $denominator));
        }

        $sum = 0;
        foreach ($fractions as [$numerator, $denominator]) {
            $sum += $numerator * intdiv($common, $denominator);
        }

        return $sum === $common;
    }

    private static function gcd(int $a, int $b): int
    {
        return $b === 0 ? $a : self::gcd($b, $a % $b);
    }

    /**
     * @param array<array-key, mixed> $spec
     * @param list<string>            $allowed
     */
    private function unknownKeys(array $spec, array $allowed, string $path): void
    {
        foreach (array_diff(array_map('strval', array_keys($spec)), $allowed) as $key) {
            $this->errors[$path . '.' . $key] = 'unbekanntes Feld; erlaubt: ' . implode(', ', $allowed);
        }
    }
}