From 0e1f447fdddecba07d5ccab83d555638fbf4750f Mon Sep 17 00:00:00 2001
From: shtse8 <shtse8@gmail.com>
Date: Wed, 20 Mar 2024 03:03:24 +0800
Subject: [PATCH] Add switch utility to handle conditional logic

---
 src/index.ts         |  5 ++-
 src/switch.ts        | 73 ++++++++++++++++++++++++++++++++++++++++++++
 tests/switch.test.ts | 52 +++++++++++++++++++++++++++++++
 3 files changed, 129 insertions(+), 1 deletion(-)
 create mode 100644 src/switch.ts
 create mode 100644 tests/switch.test.ts

diff --git a/src/index.ts b/src/index.ts
index 8fd3a5b..b29ac0e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -8,6 +8,7 @@ export * from './array'
 export * from './semantic'
 export * from './chain'
 export * from './object'
+export * from './switch'
 
 import * as typed from './typed'
 import * as types from './types'
@@ -18,6 +19,7 @@ import * as array from './array'
 import * as text from './semantic'
 import * as chain from './chain'
 import * as object from './object'
+import * as switchOps from './switch'
 export default {
     ...typed,
     ...types,
@@ -27,5 +29,6 @@ export default {
     ...array,
     ...text,
     ...chain,
-    ...object
+    ...object,
+    ...switchOps
 }
\ No newline at end of file
diff --git a/src/switch.ts b/src/switch.ts
new file mode 100644
index 0000000..1f58fb9
--- /dev/null
+++ b/src/switch.ts
@@ -0,0 +1,73 @@
+class InlineSwitch<T, R = never, E = undefined> {
+    private cases = new Map<T, () => any>();
+    private defaultCase?: () => any;
+
+    constructor(private readonly value: T) { }
+
+    // Method to add a case
+    case<U>(caseValue: T, result: () => U): InlineSwitch<T, R | U> {
+        this.cases.set(caseValue, result);
+        return this as any;
+    }
+
+    // Method to set the default case
+    default<U>(result: () => U): Omit<InlineSwitch<T, R | U, never>, 'default'> {
+        if (this.defaultCase) {
+            throw new Error("Default case already set.");
+        }
+        this.defaultCase = result;
+        return this as any;
+    }
+
+    // Method to execute the switch
+    execute(): R | E {
+        const result = this.cases.get(this.value);
+        if (result) {
+            return result();
+        }
+
+        if (this.defaultCase) {
+            return this.defaultCase();
+        }
+
+        return undefined as any;
+    }
+}
+
+/**
+ * Creates a new InlineSwitch instance for given value. This utility function
+ * facilitates a fluent interface for conditional logic based on the value provided,
+ * allowing for a more readable and expressive alternative to traditional switch
+ * statements or if-else chains. The InlineSwitch class supports adding cases
+ * with `.case()` method calls and optionally setting a default case with `.default()`.
+ * The `.execute()` method evaluates the cases against the value and returns the
+ * result of the matching case or the default case, if provided.
+ *
+ * @param value The value to be matched against the defined cases in the InlineSwitch instance.
+ * @returns A new instance of InlineSwitch configured with the provided value.
+ *
+ * @example
+ * // Using inlineSwitch to determine fruit colors.
+ * const fruitColor = inlineSwitch('apple')
+ *   .case('apple', () => 'red')
+ *   .case('banana', () => 'yellow')
+ *   .case('orange', () => 'orange')
+ *   .default(() => 'unknown color')
+ *   .execute();
+ *
+ * console.log(fruitColor); // Outputs: 'red'
+ *
+ * @example
+ * // Using inlineSwitch with mixed return types and a default case.
+ * const processedValue = inlineSwitch('kiwi')
+ *   .case('apple', () => 42)
+ *   .case('banana', () => true)
+ *   .case('orange', () => 'orange')
+ *   .default(() => null)
+ *   .execute();
+ *
+ * console.log(processedValue); // Outputs: null
+ */
+export function inlineSwitch<T>(value: T) {
+    return new InlineSwitch(value);
+}
diff --git a/tests/switch.test.ts b/tests/switch.test.ts
new file mode 100644
index 0000000..6af6f76
--- /dev/null
+++ b/tests/switch.test.ts
@@ -0,0 +1,52 @@
+import { describe, test, it, expect } from 'bun:test'
+import { inlineSwitch } from '../src/index';
+
+describe('InlineSwitch', () => {
+    it('should correctly handle a matching case', () => {
+        const result = inlineSwitch('apple')
+            .case('apple', () => 'red')
+            .case('banana', () => 'yellow')
+            .execute();
+
+        expect(result).toBe('red');
+    });
+
+    it('should return the default case when no cases match', () => {
+        const result = inlineSwitch('kiwi')
+            .case('apple', () => 'red')
+            .case('banana', () => 'yellow')
+            .default(() => 'unknown color')
+            .execute();
+
+        expect(result).toBe('unknown color');
+    });
+
+    it('should handle mixed return types', () => {
+        const result = inlineSwitch('banana')
+            .case('apple', () => 42)
+            .case('banana', () => true)
+            .default(() => 'unknown')
+            .execute();
+
+        expect(result).toBe(true);
+    });
+
+    it('should throw an error if no cases match and no default case is provided', () => {
+        const result = inlineSwitch('kiwi')
+            .case('apple', () => 'red')
+            .case('banana', () => 'yellow')
+            .execute()
+
+        expect(result).toBeUndefined();
+    });
+
+    it('should prevent setting multiple default cases', () => {
+        expect(() => {
+            inlineSwitch('kiwi')
+                .default(() => 'default 1')
+                // @ts-ignore
+                .default(() => 'default 2')
+                .execute();
+        }).toThrow("Default case already set.");
+    });
+});