// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import { CHAR_DOT } from "../_common/constants.js";
import { assertPath } from "../_common/assert_path.js";
import { isPosixPathSeparator } from "./_util.js";
/**
 * Return the extension of the `path` with leading period.
 *
 * @example Usage
 * ```ts
 * import { extname } from "@std/path/posix/extname";
 * import { assertEquals } from "@std/assert";
 *
 * assertEquals(extname("/home/user/Documents/file.ts"), ".ts");
 * assertEquals(extname("/home/user/Documents/"), "");
 * assertEquals(extname("/home/user/Documents/image.png"), ".png");
 * ```
 *
 * @example Working with URLs
 *
 * Note: This function doesn't automatically strip hash and query parts from
 * URLs. If your URL contains a hash or query, remove them before passing the
 * URL to the function. This can be done by passing the URL to `new URL(url)`,
 * and setting the `hash` and `search` properties to empty strings.
 *
 * ```ts
 * import { extname } from "@std/path/posix/extname";
 * import { assertEquals } from "@std/assert";
 *
 * assertEquals(extname("https://deno.land/std/path/mod.ts"), ".ts");
 * assertEquals(extname("https://deno.land/std/path/mod.ts?a=b"), ".ts?a=b");
 * assertEquals(extname("https://deno.land/std/path/mod.ts#header"), ".ts#header");
 * ```
 *
 * Note: If you are working with file URLs,
 * use the new version of `extname` from `@std/path/posix/unstable-extname`.
 *
 * @param path The path to get the extension from.
 * @returns The extension (ex. for `file.ts` returns `.ts`).
 */
export function extname(path) {
    assertPath(path);
    let startDot = -1;
    let startPart = 0;
    let end = -1;
    let matchedSlash = true;
    // Track the state of characters (if any) we see before our first dot and
    // after any path separator we find
    let preDotState = 0;
    for (let i = path.length - 1; i >= 0; --i) {
        const code = path.charCodeAt(i);
        if (isPosixPathSeparator(code)) {
            // If we reached a path separator that was not part of a set of path
            // separators at the end of the string, stop now
            if (!matchedSlash) {
                startPart = i + 1;
                break;
            }
            continue;
        }
        if (end === -1) {
            // We saw the first non-path separator, mark this as the end of our
            // extension
            matchedSlash = false;
            end = i + 1;
        }
        if (code === CHAR_DOT) {
            // If this is our first dot, mark it as the start of our extension
            if (startDot === -1)
                startDot = i;
            else if (preDotState !== 1)
                preDotState = 1;
        }
        else if (startDot !== -1) {
            // We saw a non-dot and non-path separator before our dot, so we should
            // have a good chance at having a non-empty extension
            preDotState = -1;
        }
    }
    if (startDot === -1 ||
        end === -1 ||
        // We saw a non-dot character immediately before the dot
        preDotState === 0 ||
        // The (right-most) trimmed path component is exactly '..'
        (preDotState === 1 && startDot === end - 1 && startDot === startPart + 1)) {
        return "";
    }
    return path.slice(startDot, end);
}
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