feat(list): Refactor Min/Max methods with better selector and comparer overload support (#187)

Since nobody had time to migrate to 3.0.0 I'm releasing a minor version with these changes. 🤞🏻

Author: mobilebilly

__tests__/list.test.ts

@@ -561,22 +561,39 @@ test('LastOrDefault', t => {
   t.is(new List<string>().LastOrDefault('default'), 'default')
 })
 
+
 test('Max', t => {
   const people = new List<IPerson>([
+    { Age: 50, Name: 'Bob' },
     { Age: 15, Name: 'Cathy' },
-    { Age: 25, Name: 'Alice' },
-    { Age: 50, Name: 'Bob' }
+    { Age: 25, Name: 'Alice' }
+    
   ])
   t.is(
     people.Max(x => x.Age ?? 0),
-    people.Last()
+    50
   )
   t.is(
-    new List<number>([1, 2, 3, 4, 5]).Max(),
-    5
+    new List<number>([5, 4, 3, 2, 1]).Min(),
+    1
   )
 })
 
+test('Max_invalid_function_provided', t => {
+  const people = new List<IPerson>([
+    { Age: 15, Name: 'Cathy' },
+    { Age: 25, Name: 'Alice' },
+    { Age: 50, Name: 'Bob' }
+  ])
+
+  // Provide an invalid selector (wrong type) to trigger the error
+  let invalidFn = () => 0;
+  
+  t.throws(() => people.Max(invalidFn), {
+    message: /InvalidOperationException: Invalid comparer or selector function provided./
+  })
+})
+
 test('Max_undefinedComparer', t => {
   const people = new List<IPerson>([
     { Age: 15, Name: 'Cathy' },
@@ -598,10 +615,25 @@ test('Max_emptyElements', t => {
   )
 })
 
+test('Max_comparer', t => {
+  const people = new List<IPerson>([
+    { Age: 15, Name: 'Cathy' },
+    { Age: 25, Name: 'Alice' },
+    { Age: 50, Name: 'Bob' }
+  ])
+
+  let comparer = ((a: IPerson, b: IPerson) => (a.Age ?? 0) - (b.Age ?? 0));
+  
+  t.is(
+    people.Max(comparer),
+    people.Last()
+  );
+})
+
 test('Max_number', t => {
   const nums = new List<number>([
-    10,
     5,
+    10,
     -5
   ])
   t.is(
@@ -635,22 +667,38 @@ test('Max_boolean', t => {
   )
 })
 
+
 test('Min', t => {
   const people = new List<IPerson>([
+    { Age: 50, Name: 'Bob' },
     { Age: 15, Name: 'Cathy' },
-    { Age: 25, Name: 'Alice' },
-    { Age: 50, Name: 'Bob' }
+    { Age: 25, Name: 'Alice' }
+    
   ])
   t.is(
     people.Min(x => x.Age ?? 0),
-    people.First()
+    15
   )
   t.is(
-    new List<number>([1, 2, 3, 4, 5]).Min(),
+    new List<number>([5, 4, 3, 2, 1]).Min(),
     1
   )
 })
 
+test('Min_invalid_function_provided', t => {
+  const people = new List<IPerson>([
+    { Age: 15, Name: 'Cathy' },
+    { Age: 25, Name: 'Alice' },
+    { Age: 50, Name: 'Bob' }
+  ])
+
+  // Provide an invalid selector (wrong type) to trigger the error
+  let invalidFn = () => 0;
+  
+  t.throws(() => people.Min(invalidFn), {
+    message: /InvalidOperationException: Invalid comparer or selector function provided./
+  })
+})
 
 test('Min_undefinedComparer', t => {
   const people = new List<IPerson>([
@@ -664,6 +712,21 @@ test('Min_undefinedComparer', t => {
   })
 })
 
+test('Min_comparer', t => {
+  const people = new List<IPerson>([
+    { Age: 15, Name: 'Cathy' },
+    { Age: 25, Name: 'Alice' },
+    { Age: 50, Name: 'Bob' }
+  ])
+
+  let comparer = ((a: IPerson, b: IPerson) => (a.Age ?? 0) - (b.Age ?? 0));
+  
+  t.is(
+    people.Min(comparer),
+    people.First()
+  );
+})
+
 test('Min_emptyElements', t => {
   const people = new List<IPerson>([])
 
@@ -710,7 +773,6 @@ test('Min_boolean', t => {
   )
 })
 
-
 test('OfType', t => {
   const pets = new List<Pet>([
     new Dog({ Age: 8, Name: 'Barley', Vaccinated: true }),
@@ -1177,12 +1239,12 @@ test('ToDictionary', t => {
   // t.is(dictionary2['Alice'], 25)
   // Dictionary should behave just like in C#
   t.is(
-    dictionary.Max(x => x?.Value?.Age ?? 0)?.Value,
-    people.Last()
+    dictionary.Max(x => x?.Value?.Age ?? 0),
+    50
   )
   t.is(
-    dictionary.Min(x => x?.Value?.Age ?? 0)?.Value,
-    people.First()
+    dictionary.Min(x => x?.Value?.Age ?? 0),
+    15
   )
   const expectedKeys = new List(['Cathy', 'Alice', 'Bob'])
   t.deepEqual(

src/list.ts

@@ -330,46 +330,144 @@ class List<T> {
   }
 
   /**
-   * Returns the maximum value in a generic sequence.
+   * Gets the maximum value in a generic sequence.
+   * @returns The maximum value in the sequence, or undefined if the sequence is empty.
+   */
+  public Max(): T | undefined;
+
+  /**
+ * Gets the maximum value in a generic sequence.
+ * @returns The maximum value in the sequence, or undefined if the sequence is empty.
+ * @param selector - A function to select a value from each element for comparison.
+  */
+  public Max<R>(selector: (e: T) => R): R | undefined;
+
+  /**
+   * Gets the maximum value in a generic sequence.
+   * @returns The maximum value in the sequence, or undefined if the sequence is empty.
+   * @param comparer - A custom comparison function
    */
-  public Max(comparer?: (element: T) => number): T | undefined {
+  public Max(comparer: (a: T, b: T) => number): T | undefined;
+
+  /**
+   * Gets the maximum value in a generic sequence.
+   * @returns The maximum value in the sequence, or undefined if the sequence is empty.
+    * @param comparerOrSelector - An optional custom comparison function or a selector function to select a value from each element for comparison.
+   */
+  public Max<R>(
+    comparerOrSelector?: ((a: T, b: T) => number) | ((e: T) => R)
+  ): T | R | undefined {
     if (this._elements.length === 0) return undefined;
 
-    let maxElem = this._elements[0];
-    let comparerToUse = comparer || List.getComparer<T>(maxElem);
+    if (!comparerOrSelector) {
+      // Max(): T | undefined;
+      return this.getMaxElement<T>(this._elements);
+
+    }
+
+    const fn = comparerOrSelector as Function;
+
+    if (!fn || fn.length > 2 || fn.length === 0) {
+      throw new Error('InvalidOperationException: Invalid comparer or selector function provided.')
+    }
+
+    if (fn.length === 1) {
+      // Max<R>(selector: (e: T) => R): R | undefined;
+      return this.getMaxElement<R>(this._elements.map(fn as (e: T) => R));
+    }
+
+    //fn.length === 2
+    // Max(comparer: (a: T, b: T) => number): T | undefined;
+    return this.getMaxElement<T>(this._elements, fn as (a: T, b: T) => number);
+  }
+
+  /**
+   * Returns the maximum value in a generic sequence.
+   * @param elements - The array of elements to find the maximum from.
+   * @param customComparer - An optional custom comparison function.
+   */
+  private getMaxElement<R>(elements: R[], customComparer?: ((a: R, b: R) => number)) {
+    const comparerToUse = customComparer || List.getComparer<R>(elements[0]);
 
     if (!comparerToUse) {
       throw new Error('InvalidOperationException: No comparer available.')
     }
 
-    this._elements.forEach(elem => {
-      if (comparerToUse(elem, maxElem) > 0) {
-        maxElem = elem;
-      }
-    })
-
-    return maxElem;
+    return elements.reduce(
+      (currentMax, elem) =>
+        comparerToUse(elem, currentMax) > 0 ? elem : currentMax,
+      elements[0]
+    );
   }
 
   /**
-   * Returns the minimum value in a generic sequence.
+   * Gets the minimum value in a generic sequence.
+   * @returns The minimum value in the sequence, or undefined if the sequence is empty.
+   */
+  public Min(): T | undefined;
+
+  /**
+ * Gets the minimum value in a generic sequence.
+ * @returns The minimum value in the sequence, or undefined if the sequence is empty.
+ * @param selector - A function to select a value from each element for comparison.
+  */
+  public Min<R>(selector: (e: T) => R): R | undefined;
+
+  /**
+   * Gets the minimum value in a generic sequence.
+   * @returns The minimum value in the sequence, or undefined if the sequence is empty.
+   * @param comparer - A custom comparison function
+   */
+  public Min(comparer: (a: T, b: T) => number): T | undefined;
+
+  /**
+   * Gets the minimum value in a generic sequence.
+   * @returns The minimum value in the sequence, or undefined if the sequence is empty.
+    * @param comparerOrSelector - An optional custom comparison function or a selector function to select a value from each element for comparison.
    */
-  public Min(comparer?: (element: T) => number): T | undefined {
+  public Min<R>(
+    comparerOrSelector?: ((a: T, b: T) => number) | ((e: T) => R)
+  ): T | R | undefined {
     if (this._elements.length === 0) return undefined;
 
-    let minElem = this._elements[0];
-    let comparerToUse = comparer || List.getComparer<T>(minElem);
+    if (!comparerOrSelector) {
+      // Min(): T | undefined;
+      return this.getMinElement<T>(this._elements);
+    }
+
+    const fn = comparerOrSelector as Function;
+
+    if (!fn || fn.length > 2 || fn.length === 0) {
+      throw new Error('InvalidOperationException: Invalid comparer or selector function provided.')
+    }
+
+    if (fn.length === 1) {
+      // Min<R>(selector: (e: T) => R): R | undefined;
+      return this.getMinElement<R>(this._elements.map(fn as (e: T) => R));
+    }
+
+    //fn.length === 2
+    // Min(comparer: (a: T, b: T) => number): T | undefined;
+    return this.getMinElement<T>(this._elements, fn as (a: T, b: T) => number);
+  }
+
+  /**
+   * Returns the minimum value in a generic sequence.
+   * @param elements - The array of elements to find the minimum from.
+   * @param customComparer - An optional custom comparison function.
+   */
+  private getMinElement<R>(elements: R[], customComparer?: ((a: R, b: R) => number)) {
+    const comparerToUse = customComparer || List.getComparer<R>(elements[0]);
 
     if (!comparerToUse) {
       throw new Error('InvalidOperationException: No comparer available.')
     }
 
-    this._elements.forEach(elem => {
-      if (comparerToUse(elem, minElem) < 0) {
-        minElem = elem;
-      }
-    })
-    return minElem;
+    return elements.reduce(
+      (currentMin, elem) =>
+        comparerToUse(elem, currentMin) < 0 ? elem : currentMin,
+      elements[0]
+    );
   }
 
   /**