feat: Add shortest paths placeholder function (#39)

Co-authored-by: Copilot <[email protected]>

Author: Sirivasv

src/bmssp.mjs

@@ -4,21 +4,42 @@ class BMSSP {
     this.graph = [];
     // Set to store unique node IDs
     this.nodeIDs = new Set();
-    // Array to store shortest paths
-    this.shortestPaths = [];
+    // Map to store shortest paths
+    this.shortestPaths = new Map();
 
     for (let edge of inputGraph) {
       // Create a deep copy of each edge array
       this.graph.push([...edge]);
+
       // Add node IDs to the set
       this.nodeIDs.add(edge[0]);
       this.nodeIDs.add(edge[1]);
     }
 
-    // Initialize shortest paths with Infinity on each nodeID (after all nodes are collected)
+    // Initialize shortest paths map
+    this.initializeShortestPaths();
+  }
+
+  // Method to initialize the shortest paths map
+  initializeShortestPaths() {
     for (let nodeId of this.nodeIDs) {
-      this.shortestPaths.push([nodeId, Infinity]);
+      this.shortestPaths.set(nodeId, Infinity);
+    }
+  }
+
+  // Method to calculate shortest paths (placeholder implementation)
+  calculateShortestPaths(startNode) {
+    // To clean the state before calculation
+    this.initializeShortestPaths();
+
+    // validate startNode
+    if (!this.nodeIDs.has(startNode)) {
+      throw new Error("Start node not found in the graph");
     }
+
+    // Placeholder logic for shortest path calculation
+    // This should be replaced with an actual implementation of BMSSP algorithm
+    this.shortestPaths.set(startNode, 0);
   }
 }
 

test/main.test.mjs

@@ -2,6 +2,7 @@ import { describe, test, expect } from "@jest/globals";
 import { BMSSP } from "../index.mjs";
 import fs from "fs";
 
+// Load the roadNet-CA.txt graph and parse it into an array of edges
 let roadNetCA = (() => {
   let graph = [];
   const filePath = new URL("./roadNet-CA.txt", import.meta.url).pathname;
@@ -19,16 +20,17 @@ let roadNetCA = (() => {
   return graph;
 })();
 
+// Have an initialized BMSSP instance for tests
+const myBMSSP = new BMSSP(roadNetCA);
+
 describe("BMSSP constructor", () => {
   test("initializes the graph correctly", () => {
-    const myBMSSP = new BMSSP(roadNetCA);
     expect(myBMSSP.graph).toEqual(roadNetCA);
   });
 });
 
 describe("BMSSP nodeIDs", () => {
   test("stores unique node IDs correctly", () => {
-    const myBMSSP = new BMSSP(roadNetCA);
     const uniqueNodeIDs = new Set();
     roadNetCA.forEach((edge) => {
       uniqueNodeIDs.add(edge[0]);
@@ -40,11 +42,24 @@ describe("BMSSP nodeIDs", () => {
 
 describe("BMSSP shortestPaths", () => {
   test("initializes shortest paths with Infinity", () => {
-    const myBMSSP = new BMSSP(roadNetCA);
-    const expectedShortestPaths = [];
+    const expectedShortestPaths = new Map();
     myBMSSP.nodeIDs.forEach((nodeId) => {
-      expectedShortestPaths.push([nodeId, Infinity]);
+      expectedShortestPaths.set(nodeId, Infinity);
     });
     expect(myBMSSP.shortestPaths).toEqual(expectedShortestPaths);
   });
 });
+
+describe("BMSSP initialize calculateShortestPaths", () => {
+  test("sets the distance to the start node to 0", () => {
+    const startNode = [...myBMSSP.nodeIDs][0];
+    myBMSSP.calculateShortestPaths(startNode);
+    expect(myBMSSP.shortestPaths.get(startNode)).toBe(0);
+  });
+  test("throws an error if the start node is not in the graph", () => {
+    const invalidStartNode = -1; // Assuming -1 is not a valid node ID in the graph
+    expect(() => {
+      myBMSSP.calculateShortestPaths(invalidStartNode);
+    }).toThrow("Start node not found in the graph");
+  });
+});