From 3ea64ecd003c4499b8f6c3d8187dd0a9d46653b6 Mon Sep 17 00:00:00 2001
From: Tomaz Haidar <tomaz_haidar@hotmail.com>
Date: Mon, 15 Apr 2024 17:55:04 -0300
Subject: [PATCH] add functional if statement

---
 src/result-async.ts  | 17 +++++++++++++++++
 src/result.ts        | 15 +++++++++++++++
 tests/result-test.ts | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+)

diff --git a/src/result-async.ts b/src/result-async.ts
index 62cbc40..fce3b55 100644
--- a/src/result-async.ts
+++ b/src/result-async.ts
@@ -252,6 +252,23 @@ export class ResultAsync<T, E> implements PromiseLike<Result<T, E>> {
     )
   }
 
+  if(fCondition: (t: T) => boolean) {
+    return {
+      true: <X1, Y1>(fTrue: (t: T) => ResultAsync<X1, Y1>) => ({
+        false: <X2, Y2>(fFalse: (t: T) => ResultAsync<X2, Y2>): ResultAsync<X1 | X2, Y1 | Y2 | E> =>
+          new ResultAsync(this.innerPromise.then(async res => {
+            const condition = fCondition(res.value)
+            if (res.isOk()) {
+              return condition ? fTrue(res.value) : fFalse(res.value)
+            }
+
+            return errAsync(res.error)
+          })),
+
+      }),
+    }
+  }
+
   orElse<R extends Result<unknown, unknown>>(
     f: (e: E) => R,
   ): ResultAsync<InferOkTypes<R> | T, InferErrTypes<R>>
diff --git a/src/result.ts b/src/result.ts
index f13b91d..3724e5b 100644
--- a/src/result.ts
+++ b/src/result.ts
@@ -216,6 +216,21 @@ export class Result<T, E> implements Resultable<T, E> {
     return err(this.error)
   }
 
+  if(fCondition: (t: T) => boolean) {
+    return {
+      true: <X1, Y1>(fTrue: (t: T) => Result<X1, Y1>) => ({
+        false: <X2, Y2>(fFalse: (t: T) => Result<X2, Y2>): Result<X1 | X2, Y1 | Y2 | E> => {
+          const condition = fCondition(this.value)
+          if (this.state.ok) {
+            return condition ? fTrue(this.value) : fFalse(this.value)
+          }
+
+          return err(this.error)
+        },
+      }),
+    }
+  }
+
   /**
    * Takes an `Err` value and maps it to a `Result<T, SomeNewType>`.
    *
diff --git a/tests/result-test.ts b/tests/result-test.ts
index 546c705..8c29c7e 100644
--- a/tests/result-test.ts
+++ b/tests/result-test.ts
@@ -108,6 +108,24 @@ await describe('Result.Ok', async () => {
     })
   })
 
+  await describe('if', async () => {
+    await it('returns the "true" part of the statement', async () => {
+      const okVal = ok(12)
+      const result = okVal.if(val => val > 10)
+        .true(v => ok(`The number ${v} is gerater than 10`))
+        .false(v => ok(`The number ${v} is smaller or equal to 10`))
+      deepEqual(result, ok('The number 12 is gerater than 10'))
+    })
+
+    await it('returns the "false" part of the statement', async () => {
+      const okVal = ok(9)
+      const result = okVal.if(val => val > 10)
+        .true(v => ok(`The number ${v} is gerater than 10`))
+        .false(v => ok(`The number ${v} is smaller or equal to 10`))
+      deepEqual(result, ok('The number 9 is smaller or equal to 10'))
+    })
+  })
+
   await describe('orElse', async () => {
     await it('Skips orElse on an Ok value', async () => {
       const okVal = ok(12)
@@ -566,6 +584,27 @@ await describe('ResultAsync', async () => {
     })
   })
 
+  await describe('if', async () => {
+    await it('returns the "true" part of the statement', async () => {
+      const okVal = okAsync(12)
+      const result = okVal.if(val => val > 10)
+        .true(v => okAsync(`The number ${v} is gerater than 10`))
+        .false(v => okAsync(`The number ${v} is smaller or equal to 10`))
+
+      isTrue(result instanceof ResultAsync)
+      deepEqual(result, okAsync('The number 12 is gerater than 10'))
+    })
+
+    await it('returns the "false" part of the statement', async () => {
+      const okVal = okAsync(9)
+      const result = okVal.if(val => val > 10)
+        .true(v => okAsync(`The number ${v} is gerater than 10`))
+        .false(v => okAsync(`The number ${v} is smaller or equal to 10`))
+      isTrue(result instanceof ResultAsync)
+      deepEqual(result, okAsync('The number 9 is smaller or equal to 10'))
+    })
+  })
+
   await describe('orElse', async () => {
     await it('Skips orElse on an Ok value', async () => {
       const okVal = okAsync(12)