<?php

declare(strict_types=1);

namespace KTXF\SystemStore;

use InvalidArgumentException;

/**
 * Optional precondition applied atomically by a system-store write or delete.
 */
final readonly class WriteCondition
{
    public const NONE = 'none';
    public const IF_ABSENT = 'if-absent';
    public const IF_MATCH = 'if-match';

    private function __construct(
        public string $mode,
        public ?string $etag = null,
    ) {
        if (!in_array($this->mode, [self::NONE, self::IF_ABSENT, self::IF_MATCH], true)) {
            throw new InvalidArgumentException('Invalid system-store write condition: ' . $this->mode);
        }

        if ($this->mode === self::IF_MATCH && ($this->etag === null || $this->etag === '')) {
            throw new InvalidArgumentException('An ETag is required for an if-match condition');
        }

        if ($this->mode !== self::IF_MATCH && $this->etag !== null) {
            throw new InvalidArgumentException('An ETag is only valid for an if-match condition');
        }
    }

    public static function none(): self
    {
        return new self(self::NONE);
    }

    public static function ifAbsent(): self
    {
        return new self(self::IF_ABSENT);
    }

    public static function ifMatch(string $etag): self
    {
        return new self(self::IF_MATCH, $etag);
    }
}