From 222fd60a95d08e9792e5cf04bef843032613f90a Mon Sep 17 00:00:00 2001
From: Dario Pizzamiglio <1150680+mediuminvader@users.noreply.github.com>
Date: Tue, 27 Feb 2024 18:02:53 +0100
Subject: [PATCH] Add Decode

---
 dozer-sql/expression/src/scalar/common.rs | 22 +++++++++++
 dozer-sql/expression/src/scalar/field.rs  | 45 ++++++++++++++++++++++-
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/dozer-sql/expression/src/scalar/common.rs b/dozer-sql/expression/src/scalar/common.rs
index c2549dbe9f..424cbbc87f 100644
--- a/dozer-sql/expression/src/scalar/common.rs
+++ b/dozer-sql/expression/src/scalar/common.rs
@@ -11,6 +11,7 @@ use dozer_types::types::Record;
 use dozer_types::types::{Field, FieldType, Schema};
 use std::fmt::{Display, Formatter};
 
+use super::field::{evaluate_decode, validate_decode};
 use super::string::{
     evaluate_chr, evaluate_replace, evaluate_substr, validate_replace, validate_substr,
 };
@@ -27,6 +28,7 @@ pub enum ScalarFunctionType {
     Substr,
     Nvl,
     Replace,
+    Decode,
 }
 
 impl Display for ScalarFunctionType {
@@ -42,6 +44,7 @@ impl Display for ScalarFunctionType {
             ScalarFunctionType::Substr => f.write_str("SUBSTR"),
             ScalarFunctionType::Nvl => f.write_str("NVL"),
             ScalarFunctionType::Replace => f.write_str("REPLACE"),
+            ScalarFunctionType::Decode => f.write_str("DECODE"),
         }
     }
 }
@@ -92,6 +95,7 @@ pub(crate) fn get_scalar_function_type(
             Ok(validate_two_arguments(args, schema, ScalarFunctionType::Nvl)?.0)
         }
         ScalarFunctionType::Replace => validate_replace(args, schema),
+        ScalarFunctionType::Decode => validate_decode(args, schema),
     }
 }
 
@@ -171,6 +175,24 @@ impl ScalarFunctionType {
                     record,
                 )
             }
+            ScalarFunctionType::Decode => {
+                validate_decode(args, schema)?;
+
+                let (arg0, results) = args.split_at_mut(1);
+                let (results, default) = if results.len() % 2 == 0 {
+                    results.split_at_mut(results.len() - 1)
+                } else {
+                    results.split_at_mut(results.len())
+                };
+
+                let default = if default.len() == 0 {
+                    None
+                } else {
+                    Some(default[0].clone())
+                };
+
+                evaluate_decode(schema, &mut arg0[0], results, default, record)
+            }
         }
     }
 }
diff --git a/dozer-sql/expression/src/scalar/field.rs b/dozer-sql/expression/src/scalar/field.rs
index e85c199258..330e6e3a0e 100644
--- a/dozer-sql/expression/src/scalar/field.rs
+++ b/dozer-sql/expression/src/scalar/field.rs
@@ -1,5 +1,5 @@
 use crate::error::Error;
-use crate::execution::Expression;
+use crate::execution::{Expression, ExpressionType};
 use dozer_types::types::Record;
 use dozer_types::types::{Field, Schema};
 
@@ -17,3 +17,46 @@ pub(crate) fn evaluate_nvl(
         Ok(arg_field)
     }
 }
+
+pub fn validate_decode(args: &[Expression], schema: &Schema) -> Result<ExpressionType, Error> {
+    if args.len() < 3 {
+        return Err(Error::InvalidNumberOfArguments {
+            function_name: "decode".to_string(),
+            expected: 3..usize::MAX,
+            actual: args.len(),
+        });
+    }
+
+    let ret_type = args[2].get_type(schema)?.return_type;
+
+    Ok(ExpressionType::new(
+        ret_type,
+        false,
+        dozer_types::types::SourceDefinition::Dynamic,
+        false,
+    ))
+}
+
+pub(crate) fn evaluate_decode(
+    schema: &Schema,
+    arg: &mut Expression,
+    results: &mut [Expression],
+    default: Option<Expression>,
+    record: &Record,
+) -> Result<Field, Error> {
+    let arg_field = arg.evaluate(record, schema)?;
+    let mut i = 0;
+    while i < results.len() {
+        let result = &mut results[i];
+        let result_field = result.evaluate(record, schema)?;
+        if arg_field == result_field {
+            return Ok(results[i + 1].evaluate(record, schema)?);
+        }
+        i += 2;
+    }
+    if let Some(mut default) = default {
+        default.evaluate(record, schema)
+    } else {
+        Ok(Field::Null)
+    }
+}