From 86968f4fdb496c69e5f6aaf588859cb32a97345c Mon Sep 17 00:00:00 2001
From: Tess Gauthier <tessgauthier@microsoft.com>
Date: Thu, 7 Mar 2024 10:54:52 -0500
Subject: [PATCH] implement sub function

---
 dsc_lib/src/functions/mod.rs |  2 +
 dsc_lib/src/functions/sub.rs | 76 ++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 dsc_lib/src/functions/sub.rs

diff --git a/dsc_lib/src/functions/mod.rs b/dsc_lib/src/functions/mod.rs
index 023f9558f..90389c4bb 100644
--- a/dsc_lib/src/functions/mod.rs
+++ b/dsc_lib/src/functions/mod.rs
@@ -15,6 +15,7 @@ pub mod envvar;
 pub mod mul;
 pub mod parameters;
 pub mod resource_id;
+pub mod sub;
 
 /// The kind of argument that a function accepts.
 #[derive(Debug, PartialEq)]
@@ -64,6 +65,7 @@ impl FunctionDispatcher {
         functions.insert("mul".to_string(), Box::new(mul::Mul{}));
         functions.insert("parameters".to_string(), Box::new(parameters::Parameters{}));
         functions.insert("resourceId".to_string(), Box::new(resource_id::ResourceId{}));
+        functions.insert("sub".to_string(), Box::new(sub::Sub{}));
         Self {
             functions,
         }
diff --git a/dsc_lib/src/functions/sub.rs b/dsc_lib/src/functions/sub.rs
new file mode 100644
index 000000000..8f584ea10
--- /dev/null
+++ b/dsc_lib/src/functions/sub.rs
@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+use crate::DscError;
+use crate::configure::context::Context;
+use crate::functions::{AcceptedArgKind, Function};
+use serde_json::Value;
+use tracing::debug;
+
+#[derive(Debug, Default)]
+pub struct Sub {}
+
+impl Function for Sub {
+    fn min_args(&self) -> usize {
+        2
+    }
+
+    fn max_args(&self) -> usize {
+        2
+    }
+
+    fn accepted_arg_types(&self) -> Vec<AcceptedArgKind> {
+        vec![AcceptedArgKind::Number]
+    }
+
+    fn invoke(&self, args: &[Value], _context: &Context) -> Result<Value, DscError> {
+        debug!("sub function");
+        if let (Some(arg1), Some(arg2)) = (args[0].as_i64(), args[1].as_i64()) {
+            Ok(Value::Number((arg1 - arg2).into()))
+        } else {
+            Err(DscError::Parser("Invalid argument(s)".to_string()))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::configure::context::Context;
+    use crate::parser::Statement;
+
+    #[test]
+    fn numbers() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser.parse_and_execute("[sub(7, 3)]", &Context::new()).unwrap();
+        assert_eq!(result, 4);
+    }
+
+    #[test]
+    fn nested() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser.parse_and_execute("[sub(9, sub(5, 3))]", &Context::new()).unwrap();
+        assert_eq!(result, 7);
+    }
+
+    #[test]
+    fn invalid_one_parameter() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser.parse_and_execute("[sub(5)]", &Context::new());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn overflow_result() {
+        let mut parser = Statement::new().unwrap();
+        // max value for i64 is 2^63 -1 (or 9,223,372,036,854,775,807)
+        let result = parser.parse_and_execute("[sub(9223372036854775807, -2)]", &Context::new());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn overflow_input() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser.parse_and_execute("[sub(9223372036854775808, 2)]", &Context::new());
+        assert!(result.is_err());
+    }
+}