// Copyright 2018-2026 the Deno authors. MIT license.
// This module is browser compatible.

export function common(paths: string[], sep: string): string {
  const [first = "", ...remaining] = paths;
  const parts = first.split(sep);

  let endOfPrefix = parts.length;
  let append = "";
  for (const path of remaining) {
    const compare = path.split(sep);
    if (compare.length <= endOfPrefix) {
      endOfPrefix = compare.length;
      append = "";
    }

    for (let i = 0; i < endOfPrefix; i++) {
      if (compare[i] !== parts[i]) {
        endOfPrefix = i;
        append = i === 0 ? "" : sep;
        break;
      }
    }
  }
  return parts.slice(0, endOfPrefix).join(sep) + append;
}