72 lines
2.1 KiB
TypeScript
72 lines
2.1 KiB
TypeScript
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
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// This module is browser compatible.
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import { CHAR_DOT } from "../_common/constants.ts";
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import { assertPath } from "../_common/assert_path.ts";
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import { isPosixPathSeparator } from "./_util.ts";
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/**
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* Return the extension of the `path` with leading period.
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*
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* @example
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* ```ts
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* import { extname } from "@std/path/extname";
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*
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* console.log(extname("/home/user/Documents/")); // ""
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* console.log(extname("/home/user/Documents/image.png")); // ".png"
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* ```
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*
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* @param path with extension
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* @returns extension (ex. for `file.ts` returns `.ts`)
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*/
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export function extname(path: string): string {
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assertPath(path);
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let startDot = -1;
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let startPart = 0;
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let end = -1;
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let matchedSlash = true;
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// Track the state of characters (if any) we see before our first dot and
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// after any path separator we find
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let preDotState = 0;
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for (let i = path.length - 1; i >= 0; --i) {
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const code = path.charCodeAt(i);
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if (isPosixPathSeparator(code)) {
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// If we reached a path separator that was not part of a set of path
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// separators at the end of the string, stop now
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if (!matchedSlash) {
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startPart = i + 1;
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break;
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}
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continue;
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}
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if (end === -1) {
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// We saw the first non-path separator, mark this as the end of our
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// extension
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matchedSlash = false;
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end = i + 1;
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}
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if (code === CHAR_DOT) {
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// If this is our first dot, mark it as the start of our extension
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if (startDot === -1) startDot = i;
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else if (preDotState !== 1) preDotState = 1;
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} else if (startDot !== -1) {
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// We saw a non-dot and non-path separator before our dot, so we should
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// have a good chance at having a non-empty extension
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preDotState = -1;
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}
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}
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if (
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startDot === -1 ||
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end === -1 ||
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// We saw a non-dot character immediately before the dot
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preDotState === 0 ||
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// The (right-most) trimmed path component is exactly '..'
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(preDotState === 1 && startDot === end - 1 && startDot === startPart + 1)
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) {
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return "";
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}
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return path.slice(startDot, end);
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}
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