added base graph logic for cycle detection

README.md

@@ -1,3 +1,9 @@
 # spotify-manager
 
 Personal Spotify playlist manager. Features inbound!
+
+## notes
+
+- graphing
+  - stores links as from-to pairs
+  - fetches all playlists and links of the user into memory and then works with data. assumption is graphs won't be too big

controllers/operations.js

@@ -2,6 +2,7 @@ const typedefs = require("../typedefs");
 const logger = require("../utils/logger")(module);
 
 const { axiosInstance } = require("../utils/axios");
+const myGraph = require("../utils/graph");
 const { parseSpotifyUri, parseSpotifyLink } = require("../utils/spotifyUriTransformer");
 
 
@@ -93,7 +94,6 @@ const updateUser = async (req, res) => {
 			toRemove = [];
 		}
 		let toRemoveIDs = toRemove.map(pl => pl.playlistID);
-		logger.debug("removeIDs", { toRemoveIDs });
 		let removedLinks = 0;
 
 		if (toRemove.length) {
@@ -138,7 +138,7 @@ const updateUser = async (req, res) => {
 }
 
 /**
- * Fetch user's stored playlists
+ * Fetch user's stored playlists and links
  * @param {typedefs.Req} req
  * @param {typedefs.Res} res
  */
@@ -146,7 +146,7 @@ const fetchUser = async (req, res) => {
 	try {
 		const userURI = parseSpotifyUri(req.session.user.uri);
 
-		let currentPlaylists = await Playlists.findAll({
+		const currentPlaylists = await Playlists.findAll({
 			attributes: ["playlistID", "playlistName"],
 			raw: true,
 			where: {
@@ -154,7 +154,18 @@ const fetchUser = async (req, res) => {
 			},
 		});
 
-		return res.status(200).send(currentPlaylists);
+		const currentLinks = await Links.findAll({
+			attributes: ["from", "to"],
+			raw: true,
+			where: {
+				userID: userURI.id
+			},
+		});
+
+		return res.status(200).send({
+			playlists: currentPlaylists,
+			links: currentLinks
+		});
 	} catch (error) {
 		logger.error('fetchUser', { error });
 		return res.sendStatus(500);
@@ -175,19 +186,17 @@ const createLink = async (req, res) => {
 			fromPl = parseSpotifyLink(req.body["from"]);
 			toPl = parseSpotifyLink(req.body["to"]);
 			if (fromPl.type !== "playlist" || toPl.type !== "playlist") {
-				return res.sendStatus(400);
+				return res.status(400).send({ message: "Invalid Spotify playlist link" });
 			}
 		} catch (error) {
 			logger.error("parseSpotifyLink", { error });
-			return res.sendStatus(400);
+			return res.status(400).send({ message: "Invalid Spotify playlist link" });
 		}
 
 		let playlists = await Playlists.findAll({
 			attributes: ["playlistID"],
 			raw: true,
-			where: {
-				userID: userURI.id
-			}
+			where: { userID: userURI.id }
 		});
 		playlists = playlists.map(pl => pl.playlistID);
 
@@ -212,6 +221,19 @@ const createLink = async (req, res) => {
 			return res.sendStatus(409);
 		}
 
+		const allLinks = await Links.findAll({
+			attributes: ["from", "to"],
+			raw: true,
+			where: { userID: userURI.id }
+		});
+
+		const newGraph = new myGraph(playlists, [...allLinks, { from: fromPl.id, to: toPl.id }]);
+
+		if (newGraph.detectCycle()) {
+			logger.error("potential cycle detected");
+			return res.status(400).send({ message: "Proposed link cannot cause a cycle in the graph" });
+		}
+
 		const newLink = await Links.create({
 			userID: userURI.id,
 			from: fromPl.id,
@@ -244,11 +266,11 @@ const removeLink = async (req, res) => {
 			fromPl = parseSpotifyLink(req.body["from"]);
 			toPl = parseSpotifyLink(req.body["to"]);
 			if (fromPl.type !== "playlist" || toPl.type !== "playlist") {
-				return res.sendStatus(400);
+				return res.status(400).send({ message: "Invalid Spotify playlist link" });
 			}
 		} catch (error) {
 			logger.error("parseSpotifyLink", { error });
-			return res.sendStatus(400);
+			return res.status(400).send({ message: "Invalid Spotify playlist link" });
 		}
 
 		// check if exists

controllers/playlists.js

@@ -98,11 +98,11 @@ const getPlaylistDetails = async (req, res) => {
 		try {
 			uri = parseSpotifyLink(req.query.playlist_link)
 			if (uri.type !== "playlist") {
-				return res.status(400).send("Not a playlist link");
+				return res.status(400).send({ message: "Invalid Spotify playlist link" });
 			}
 		} catch (error) {
 			logger.error("parseSpotifyLink", { error });
-			return res.sendStatus(400);
+			return res.status(400).send({ message: "Invalid Spotify playlist link" });
 		}
 
 		const response = await axiosInstance.get(

routes/operations.js

@@ -23,7 +23,7 @@ router.post(
 	createLinkValidator,
 	validate,
 	createLink
-)
+);
 
 router.delete(
 	"/link",
@@ -31,5 +31,6 @@ router.delete(
 	removeLinkValidator,
 	validate,
 	removeLink
-)
+);
+
 module.exports = router;

utils/graph.js

@@ -0,0 +1,79 @@
+const logger = require("./logger")(module);
+
+const typedefs = require("../typedefs");
+
+/**
+ * Directed graph, may or may not be connected.
+ * 
+ * NOTE: Assumes that nodes and edges are valid.
+ */
+class myGraph {
+	/**
+	 * @param {string[]} nodes Graph nodes IDs
+	 * @param {{ from: string, to: string }[]} edges Graph edges b/w nodes
+	*/
+	constructor(nodes, edges) {
+		this.nodes = [...nodes];
+		this.edges = structuredClone(edges);
+	}
+
+	/**
+	 * @param {type} node
+	 * @returns {string[]}
+	 */
+	getNeighbors(node) {
+		return this.edges.filter(edge => edge.from == node).map(edge => edge.to);
+	}
+
+	/**
+	 * Kahn's topological sort
+	 * @returns {string[]}
+	 */
+	topoSort() {
+		let inDegree = {};
+		let zeroInDegreeQueue = [];
+		let topologicalOrder = [];
+
+		// Initialize inDegree of all nodes to 0
+		for (let node of this.nodes) {
+			inDegree[node] = 0;
+		}
+
+		// Calculate inDegree of each node
+		for (let edge of this.edges) {
+			inDegree[edge.to]++;
+		}
+
+		// Collect nodes with 0 inDegree
+		for (let node of this.nodes) {
+			if (inDegree[node] === 0) {
+				zeroInDegreeQueue.push(node);
+			}
+		}
+
+		// process nodes with 0 inDegree
+		while (zeroInDegreeQueue.length > 0) {
+			let node = zeroInDegreeQueue.shift();
+			topologicalOrder.push(node);
+
+			for (let neighbor of this.getNeighbors(node)) {
+				inDegree[neighbor]--;
+				if (inDegree[neighbor] === 0) {
+					zeroInDegreeQueue.push(neighbor);
+				}
+			}
+		}
+		return topologicalOrder;
+	}
+
+	/**
+	 * Check if the graph contains a cycle
+	 * @returns {boolean}
+	 */
+	detectCycle() {
+		// If topological order includes all nodes, no cycle exists
+		return this.topoSort().length < this.nodes.length;
+	}
+}
+
+module.exports = myGraph;