export interface DiffPosition {
	path: string;
	line: number;
	side: "LEFT" | "RIGHT";
}

export interface ParsedDiff {
	positions: Map<string, DiffPosition>;
}

function key(path: string, line: number, side: "LEFT" | "RIGHT"): string {
	return `${side}:${path}:${line}`;
}

function cleanPath(raw: string): string {
	const withoutTimestamp = raw.split("\t", 1)[0];
	if (withoutTimestamp === "/dev/null") return withoutTimestamp;
	return withoutTimestamp.replace(/^[ab]\//, "");
}

export function parseDiff(diff: string): ParsedDiff {
	const positions = new Map<string, DiffPosition>();
	let oldPath = "";
	let newPath = "";
	let oldLine = 0;
	let newLine = 0;
	let inHunk = false;

	for (const line of diff.split("\n")) {
		if (line.startsWith("diff --git ")) {
			inHunk = false;
			const match = /^diff --git a\/(.+) b\/(.+)$/.exec(line);
			if (match) {
				oldPath = match[1];
				newPath = match[2];
			}
			continue;
		}
		if (line.startsWith("--- ")) {
			oldPath = cleanPath(line.slice(4));
			continue;
		}
		if (line.startsWith("+++ ")) {
			newPath = cleanPath(line.slice(4));
			continue;
		}
		const hunk = /^@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@/.exec(line);
		if (hunk) {
			oldLine = Number(hunk[1]);
			newLine = Number(hunk[2]);
			inHunk = true;
			continue;
		}
		if (!inHunk || line.startsWith("\\ No newline")) continue;
		if (line.startsWith("-") && oldPath !== "/dev/null") {
			positions.set(key(oldPath, oldLine, "LEFT"), {
				path: oldPath,
				line: oldLine,
				side: "LEFT",
			});
			oldLine++;
			continue;
		}
		if (line.startsWith("+") && newPath !== "/dev/null") {
			positions.set(key(newPath, newLine, "RIGHT"), {
				path: newPath,
				line: newLine,
				side: "RIGHT",
			});
			newLine++;
			continue;
		}
		oldLine++;
		newLine++;
	}

	return { positions };
}

export function isChangedPosition(
	parsed: ParsedDiff,
	path: string,
	line: number,
	side: "LEFT" | "RIGHT",
): boolean {
	return parsed.positions.has(key(path, line, side));
}