import { CHAR_DOT, CHAR_FORWARD_SLASH } from './constants';

export function parse(path: string) {
    const ret = { root: '', dir: '', base: '', ext: '', name: '' };
    if (path.length === 0) {
        return ret;
    }
    const isAbsolute = path.charCodeAt(0) === CHAR_FORWARD_SLASH;
    let start: number;
    if (isAbsolute) {
        ret.root = '/';
        start = 1;
    } else {
        start = 0;
    }
    let startDot = -1;
    let startPart = 0;
    let end = -1;
    let matchedSlash = true;
    let i = path.length - 1;
    // Track the state of characters (if any) we see before our first dot and
    // after any path separator we find
    let preDotState = 0;
    // Get non-dir info
    for (; i >= start; --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) {
                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 (end !== -1) {
        start = startPart === 0 && isAbsolute ? 1 : startPart;
        if (
            startDot === -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)
        ) {
            ret.base = ret.name = path.slice(start, end);
        } else {
            ret.name = path.slice(start, startDot);
            ret.base = path.slice(start, end);
            ret.ext = path.slice(startDot, end);
        }
    }
    if (startPart > 0) {
        ret.dir = path.slice(0, startPart - 1);
    } else if (isAbsolute) {
        ret.dir = '/';
    }
    return ret;
}