From 002215303a0fda40e81c459bf5ce8323304f9ca9 Mon Sep 17 00:00:00 2001
From: robonen <robonenandrew@gmail.com>
Date: Thu, 11 Apr 2024 00:11:29 +0700
Subject: [PATCH] feat(packages/stdlib): levenshtein distance util

---
 packages/stdlib/src/text/index.ts             |  1 +
 .../text/levenshtein-distance/index.test.ts   | 32 ++++++++++++++
 .../src/text/levenshtein-distance/index.ts    | 44 +++++++++++++++++++
 3 files changed, 77 insertions(+)
 create mode 100644 packages/stdlib/src/text/index.ts
 create mode 100644 packages/stdlib/src/text/levenshtein-distance/index.test.ts
 create mode 100644 packages/stdlib/src/text/levenshtein-distance/index.ts

diff --git a/packages/stdlib/src/text/index.ts b/packages/stdlib/src/text/index.ts
new file mode 100644
index 0000000..106ddd8
--- /dev/null
+++ b/packages/stdlib/src/text/index.ts
@@ -0,0 +1 @@
+export * from './levenshtein-distance';
\ No newline at end of file
diff --git a/packages/stdlib/src/text/levenshtein-distance/index.test.ts b/packages/stdlib/src/text/levenshtein-distance/index.test.ts
new file mode 100644
index 0000000..4989e5b
--- /dev/null
+++ b/packages/stdlib/src/text/levenshtein-distance/index.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+import levenshteinDistance from '.';
+  
+describe('levenshteinDistance', () => {
+    it('should calculate edit distance between two strings', () => {  
+      // just one substitution I at the beginning
+      expect(levenshteinDistance('islander', 'slander')).toBe(1);
+  
+      // substitution M->K, T->M and add an A to the end
+      expect(levenshteinDistance('mart', 'karma')).toBe(3);
+  
+      // substitution K->S, E->I and insert G at the end
+      expect(levenshteinDistance('kitten', 'sitting')).toBe(3);
+  
+      // should add 4 letters FOOT at the beginning
+      expect(levenshteinDistance('ball', 'football')).toBe(4);
+  
+      // should delete 4 letters FOOT at the beginning
+      expect(levenshteinDistance('football', 'foot')).toBe(4);
+  
+      // needs to substitute the first 5 chars INTEN->EXECU
+      expect(levenshteinDistance('intention', 'execution')).toBe(5);
+    });
+
+    it('should handle edge cases', () => {
+        expect(levenshteinDistance('', '')).toBe(0);
+        expect(levenshteinDistance('a', '')).toBe(1);
+        expect(levenshteinDistance('', 'a')).toBe(1);
+        expect(levenshteinDistance('abc', '')).toBe(3);
+        expect(levenshteinDistance('', 'abc')).toBe(3);
+    });
+  });
\ No newline at end of file
diff --git a/packages/stdlib/src/text/levenshtein-distance/index.ts b/packages/stdlib/src/text/levenshtein-distance/index.ts
new file mode 100644
index 0000000..48728e2
--- /dev/null
+++ b/packages/stdlib/src/text/levenshtein-distance/index.ts
@@ -0,0 +1,44 @@
+/**
+ * Calculate the Levenshtein distance between two strings
+ * 
+ * @param {string} a First string
+ * @param {string} b Second string
+ * @returns {number} The Levenshtein distance between the two strings
+ */
+export default function levenshteinDistance(a: string, b: string): number {
+    // If the strings are equal, the distance is 0
+    if (a === b) return 0;
+
+    // If either string is empty, the distance is the length of the other string
+    if (a.length === 0) return b.length;
+    if (b.length === 0) return a.length;
+
+    // Create empty edit distance matrix for all possible modifications of
+    // substrings of a to substrings of b
+    const distanceMatrix = Array(b.length + 1).fill(null).map(() => Array(a.length + 1).fill(null));
+
+    // Fill the first row of the matrix
+    // If this is the first row, we're transforming from an empty string to a
+    // In this case, the number of operations equals the length of a substring
+    for (let i = 0; i <= a.length; i++)
+        distanceMatrix[0]![i]! = i;
+
+    // Fill the first column of the matrix
+    // If this is the first column, we're transforming empty string to b
+    // In this case, the number of operations equals the length of b substring
+    for (let j = 0; j <= b.length; j++)
+        distanceMatrix[j]![0]! = j;
+
+    for (let j = 1; j <= b.length; j++) {
+        for (let i = 1; i <= a.length; i++) {
+            const indicator = a[i - 1] === b[j - 1] ? 0 : 1;
+            distanceMatrix[j]![i]! = Math.min(
+                distanceMatrix[j]![i - 1]! + 1, // deletion
+                distanceMatrix[j - 1]![i]! + 1, // insertion
+                distanceMatrix[j - 1]![i - 1]! + indicator // substitution
+            );
+        }
+    }
+
+    return distanceMatrix[b.length]![a.length]!;
+}