/**
 * Escape special regex characters in a string
 */
function escapeRegExp(string) {
    return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}
/**
 * Generate a unique filename by inserting a number before the extension
 * Pattern: file.png -> file-1.png -> file-2.png
 * This is used to rename displaced (hidden) uploads to avoid filename collisions.
 */
export function generateUniqueFilename(originalFilename, existingFilenames) {
    // If the filename doesn't exist, use it as-is
    if (!existingFilenames.includes(originalFilename)) {
        return originalFilename;
    }
    // Split filename into base and extension
    const lastDotIndex = originalFilename.lastIndexOf('.');
    const hasExtension = lastDotIndex > 0; // Must be after first char
    const baseName = hasExtension ? originalFilename.slice(0, lastDotIndex) : originalFilename;
    const extension = hasExtension ? originalFilename.slice(lastDotIndex) : '';
    // Find existing numeric suffixes for this filename pattern
    // Pattern: basename-N.ext
    const regex = new RegExp(`^${escapeRegExp(baseName)}-(\\d+)${escapeRegExp(extension)}$`);
    let maxSuffix = 0;
    for (const existing of existingFilenames) {
        const match = existing.match(regex);
        if (match) {
            const num = parseInt(match[1], 10);
            if (num > maxSuffix) {
                maxSuffix = num;
            }
        }
    }
    // Return the next available suffix
    return `${baseName}-${maxSuffix + 1}${extension}`;
}
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