import { CHAR_FORWARD_SLASH } from './constants';

export function basename(path: string, ext?: string) {
    let start = 0;
    let end = -1;
    let matchedSlash = true;
    let i: number;
    if (ext !== undefined && ext.length > 0 && ext.length <= path.length) {
        if (ext === path) {
            return '';
        }
        let extIdx = ext.length - 1;
        let firstNonSlashEnd = -1;
        for (i = path.length - 1; i >= 0; --i) {
            const code = path.charCodeAt(i);
            if (code === CHAR_FORWARD_SLASH) {
                // 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) {
                    start = i + 1;
                    break;
                }
            } else {
                if (firstNonSlashEnd === -1) {
                    // We saw the first non-path separator, remember this index in case
                    // we need it if the extension ends up not matching
                    matchedSlash = false;
                    firstNonSlashEnd = i + 1;
                }
                if (extIdx >= 0) {
                    // Try to match the explicit extension
                    if (code === ext.charCodeAt(extIdx)) {
                        if (--extIdx === -1) {
                            // We matched the extension, so mark this as the end of our path
                            // component
                            end = i;
                        }
                    } else {
                        // Extension does not match, so our result is the entire path
                        // component
                        extIdx = -1;
                        end = firstNonSlashEnd;
                    }
                }
            }
        }
        if (start === end) {
            end = firstNonSlashEnd;
        } else if (end === -1) {
            end = path.length;
        }
        return path.slice(start, end);
    }
    for (i = path.length - 1; i >= 0; --i) {
        if (path.charCodeAt(i) === CHAR_FORWARD_SLASH) {
            // 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) {
                start = i + 1;
                break;
            }
        } else if (end === -1) {
            // We saw the first non-path separator, mark this as the end of our
            // path component
            matchedSlash = false;
            end = i + 1;
        }
    }
    if (end === -1) {
        return '';
    }
    return path.slice(start, end);
}