BibTeXKey.php

<?php

namespace App\Rules;

use App\EntryType;
use Illuminate\Contracts\Validation\Rule;

/**
 * Class BibTeXKey
 * @package App\Rules
 *
 * Rule to verify whether a given BibTeX citation key is valid.
 * Currently a key is only invalid if:
 * - The given entry type has no bibtex key and the citationkey is non-empty
 * - The given entry type has a bibtex key, and the citationkey is empty, and neither author or editor are supplied to
 *   automatically generate a key
 */
class BibTeXKey implements Rule
{
    private $authors;
    private $editors;
    private $type;
    private $message = "";

    /**
     * Create a new rule instance.
     * @param int $type
     * @param array|null $authors
     * @param array|null $editors
     */
    public function __construct(int $type, ?array $authors, ?array $editors)
    {
        $this->type = EntryType::find($type);
        $this->authors = $authors;
        $this->editors = $editors;
    }

    /**
     * Determine if the validation rule passes.
     *
     * @param  string $attribute
     * @param  mixed $value
     * @return bool
     */
    public function passes($attribute, $value)
    {
        return false;
    }

    /**
     * Get the validation error message.
     *
     * @return string
     */
    public function message()
    {
        return $this->message;
    }
}

validation.php

        $this->validate($request, [
            'title' => 'required|string|max:191',
            'subtitle' => 'nullable|string|max:191',
            'type' => 'required|integer|exists:entry_types,id',
            'category' => 'required|integer|exists:categories,id',
            'categorysubid' => 'nullable|string',
            'categoryid' => ['required', 'integer',
                new UniqueCategoryId($request->get('category'), $request->get('categorysubid'), $entry->id)],
            'pubyear' => 'required_with:pubmonth|nullable|integer',
            'pubmonth' => 'required_with:pubday|nullable|integer|between:1,12',
            'pubday' => ['nullable', 'integer', 'between:1,31',
                new ValidDay($request->get('pubyear'), $request->get('pubmonth'))],
            'isbn' => 'nullable|string',
            'citationkey' => ['nullable', new BibTeXKey($request->get('type'), $request->get('authors'), $request->get('editors')),
                'string', 'unique:entries,citation_key,' . $entry->id],
            'abstract' => 'nullable|string',
            'publisher' => 'nullable|integer|exists:publishers,id',
            'creators' => 'nullable|array',
            'creators.*' => 'integer|exists:creators,id',
            'editors' => 'nullable|array',
            'editors.*' => 'integer|exists:creators,id',
            'collections' => 'nullable|array',
            'collections.*' => 'integer|exists:collections,id',
            'keywords' => 'nullable|array',
            'keywords.*' => 'integer|exists:keywords,id',
            'edition' => 'nullable|string',
            'volume' => 'nullable|string',
            'page_start' => 'nullable|integer',
            'page_end' => 'nullable|integer',
            'issue' => 'nullable|integer'
        ]);