refactor(router): move fp_utils module to common_utils crate (#391)

Co-authored-by: Arun Raj M <jarnura47@gmail.com>
Co-authored-by: Nishant Joshi <nishant.joshi@juspay.in>

crates/common_utils/src/fp_utils.rs

@@ -0,0 +1,39 @@
+//! Functional programming utilities
+
+/// The Applicative trait provides a pure behavior,
+/// which can be used to create values of type f a from values of type a.
+pub trait Applicative<R> {
+    /// The Associative type acts as a (f a) wrapper for Self.
+    type WrappedSelf<T>;
+
+    /// Applicative::pure(_) is abstraction with lifts any arbitrary type to underlying higher
+    /// order type
+    fn pure(v: R) -> Self::WrappedSelf<R>;
+}
+
+impl<R> Applicative<R> for Option<R> {
+    type WrappedSelf<T> = Option<T>;
+    fn pure(v: R) -> Self::WrappedSelf<R> {
+        Some(v)
+    }
+}
+
+impl<R, E> Applicative<R> for Result<R, E> {
+    type WrappedSelf<T> = Result<T, E>;
+    fn pure(v: R) -> Self::WrappedSelf<R> {
+        Ok(v)
+    }
+}
+
+/// This function wraps the evaluated result of `f` into current context,
+/// based on the condition provided into the `predicate`
+pub fn when<W: Applicative<(), WrappedSelf<()> = W>, F>(predicate: bool, f: F) -> W
+where
+    F: FnOnce() -> W,
+{
+    if predicate {
+        f()
+    } else {
+        W::pure(())
+    }
+}

crates/common_utils/src/lib.rs

@@ -7,6 +7,7 @@ pub mod crypto;
 pub mod custom_serde;
 pub mod errors;
 pub mod ext_traits;
+pub mod fp_utils;
 pub mod pii;
 pub mod validation;