/**
 * Groups a flat list of file paths into a directory tree, the way GitLab's
 * MR "Changes" file list (and most file explorers) present them, instead of
 * one flat line per full path.
 */

export interface TreeRow {
	depth: number;
	label: string;
	isDir: boolean;
	/** Index into the original `paths` array. Present only for file rows. */
	fileIndex?: number;
}

interface Node {
	children: Map<string, Node>;
	fileIndex?: number;
}

export function buildTreeRows(paths: readonly string[]): TreeRow[] {
	const root: Node = { children: new Map() };

	paths.forEach((path, index) => {
		const parts = path.split("/").filter(Boolean);
		let node = root;
		parts.forEach((part, i) => {
			let child = node.children.get(part);
			if (!child) {
				child = { children: new Map() };
				node.children.set(part, child);
			}
			node = child;
			if (i === parts.length - 1) node.fileIndex = index;
		});
	});

	const rows: TreeRow[] = [];
	function walk(node: Node, depth: number): void {
		for (const [name, child] of node.children) {
			const isDir = child.children.size > 0;
			if (isDir) {
				rows.push({ depth, label: `${name}/`, isDir: true });
				walk(child, depth + 1);
			} else {
				rows.push({ depth, label: name, isDir: false, fileIndex: child.fileIndex });
			}
		}
	}
	walk(root, 0);
	return rows;
}