rxdb/src/plugins/utils/utils-revision.ts

A local-first realtime NoSQL Database for JavaScript applications - https://rxdb.info/

import type {
    RxDocumentData
} from '../../types/index.d.ts';
import { newRxError } from '../../rx-error.ts';

/**
 * Parses the full revision.
 * Do NOT use this if you only need the revision height,
 * then use getHeightOfRevision() instead which is faster.
 */
export function parseRevision(revision: string): { height: number; hash: string; } {
    const dashIndex = revision.indexOf('-');
    if (dashIndex === -1) {
        throw new Error('malformatted revision: ' + revision);
    }
    let height: number;
    if (dashIndex === 1) {
        height = revision.charCodeAt(0) - 48;
    } else {
        height = 0;
        for (let i = 0; i < dashIndex; i++) {
            height = height * 10 + (revision.charCodeAt(i) - 48);
        }
    }
    return {
        height,
        hash: revision.substring(dashIndex + 1)
    };
}

/**
 * @hotPath Performance is very important here
 * because we need to parse the revision height very often.
 * Uses indexOf + charCodeAt for maximum performance.
 * Single-digit heights (most common) use a fast path
 * that avoids parseInt entirely.
 */
export function getHeightOfRevision(revision: string): number {
    const dashIndex = revision.indexOf('-');
    if (dashIndex === -1) {
        throw newRxError('SNH', { args: { revision } });
    }
    // Fast path for single-digit revision heights (most common case)
    if (dashIndex === 1) {
        return revision.charCodeAt(0) - 48;
    }
    // Manual number parsing for multi-digit heights (avoids parseInt + substring)
    let num = 0;
    for (let i = 0; i < dashIndex; i++) {
        num = num * 10 + (revision.charCodeAt(i) - 48);
    }
    return num;
}


/**
 * Creates the next write revision for a given document.
 */
export function createRevision<RxDocType>(
    databaseInstanceToken: string,
    previousDocData?: RxDocumentData<RxDocType>
): string {
    const newRevisionHeight = !previousDocData ? 1 : getHeightOfRevision(previousDocData._rev) + 1
    return newRevisionHeight + '-' + databaseInstanceToken;
}