From eb8c1a0a372725290aaed170686925798a710fdb Mon Sep 17 00:00:00 2001
From: Kasper <kasperkh.kh@gmail.com>
Date: Mon, 13 Jan 2020 23:38:31 +0100
Subject: [PATCH] Moved addition/subtraction to units.rs

---
 src/evaluator.rs | 30 ++++++------------------------
 src/units.rs     | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 24 deletions(-)

diff --git a/src/evaluator.rs b/src/evaluator.rs
index 05bca72..6f4eb76 100644
--- a/src/evaluator.rs
+++ b/src/evaluator.rs
@@ -1,6 +1,6 @@
 use decimal::d128;
 use crate::Token;
-use crate::units::{Unit, UnitType, Number, convert};
+use crate::units::{Unit, UnitType, Number, convert, add, subtract};
 use crate::parser::AstNode;
 use crate::Operator::{Caret, Divide, Minus, Modulo, Multiply, Plus};
 use crate::Constant::{Pi, E};
@@ -215,12 +215,8 @@ fn evaluate_node(ast_node: &AstNode) -> Result<Number, String> {
         To => {
           if let Token::Unit(right_unit) = right_child.token {
             let left = evaluate_node(left_child)?;
-            if left.unit.category() == right_unit.category() {
-              let result = convert(left, right_unit)?;
-              return Ok(result)
-            } else {
-              return Err(format!("Cannot convert from {:?} to {:?}", left.unit, right_unit))
-            }
+            let result = convert(left, right_unit)?;
+            return Ok(result)
           } else {
             return Err("Right side of To operator needs to be a unit".to_string())
           }
@@ -231,7 +227,7 @@ fn evaluate_node(ast_node: &AstNode) -> Result<Number, String> {
           if left.unit == Unit::NoUnit {
             return Ok(Number::new(left.value * right.value, right.unit))
           } else {
-            return Err("child[0] of the Of operator must be NoUnit".to_string())
+            return Err("Left side of the Of operator must be NoUnit".to_string())
           }
         },
       }
@@ -243,24 +239,10 @@ fn evaluate_node(ast_node: &AstNode) -> Result<Number, String> {
       let right = evaluate_node(right_child)?;
       match operator {
         Plus => {
-          if left.unit == right.unit {
-            Ok(Number::new(left.value + right.value, left.unit))
-          } else if left.unit.category() == right.unit.category() {
-            let result = left.value * left.unit.weight() + right.value * right.unit.weight();
-            Ok(Number::new(result, Unit::Millimeter))
-          } else {
-            return Err(format!("Cannot add {:?} and {:?}", left.unit, right.unit))
-          }
+          Ok(add(left, right)?)
         },
         Minus => {
-          if left.unit == right.unit {
-            Ok(Number::new(left.value - right.value, left.unit))
-          } else if left.unit.category() == right.unit.category() {
-            let result = left.value * left.unit.weight() - right.value * right.unit.weight();
-            Ok(Number::new(result, Unit::Millimeter))
-          } else {
-            return Err(format!("Cannot subtract {:?} by {:?}", left.unit, right.unit))
-          }
+          Ok(subtract(left, right)?)
         },
         Multiply => {
           if left.unit == Unit::NoUnit && right.unit == Unit::NoUnit {
diff --git a/src/units.rs b/src/units.rs
index ec287d0..dc6415e 100644
--- a/src/units.rs
+++ b/src/units.rs
@@ -228,6 +228,9 @@ fn get_convertion_factor(unit: Unit, to_unit: Unit) -> d128 {
 }
 
 pub fn convert(number: Number, to_unit: Unit) -> Result<Number, String> {
+  if number.unit.category() != to_unit.category() {
+    return Err(format!("Cannot convert from {:?} to {:?}", number.unit, to_unit));
+  }
   let value = number.value;
   let ok = |new_value| {
     Ok(Number::new(new_value, to_unit))
@@ -251,6 +254,38 @@ pub fn convert(number: Number, to_unit: Unit) -> Result<Number, String> {
   }
 }
 
+pub fn add(left: Number, right: Number) -> Result<Number, String> {
+  if left.unit == right.unit {
+    Ok(Number::new(left.value + right.value, left.unit))
+  } else if left.unit.category() == right.unit.category() && left.unit.category() != Temperature {
+    if left.unit.weight() > right.unit.weight() {
+      let left_converted = convert(left, right.unit)?;
+      Ok(Number::new(left_converted.value + right.value, right.unit))
+    } else {
+      let right_converted = convert(right, left.unit)?;
+      Ok(Number::new(right_converted.value + left.value, left.unit))
+    }
+  } else {
+    return Err(format!("Cannot add {:?} and {:?}", left.unit, right.unit))
+  }
+}
+
+pub fn subtract(left: Number, right: Number) -> Result<Number, String> {
+  if left.unit == right.unit {
+    Ok(Number::new(left.value - right.value, left.unit))
+  } else if left.unit.category() == right.unit.category() && left.unit.category() != Temperature {
+    if left.unit.weight() > right.unit.weight() {
+      let left_converted = convert(left, right.unit)?;
+      Ok(Number::new(left_converted.value - right.value, right.unit))
+    } else {
+      let right_converted = convert(right, left.unit)?;
+      Ok(Number::new(right_converted.value - left.value, left.unit))
+    }
+  } else {
+    return Err(format!("Cannot subtract {:?} by {:?}", left.unit, right.unit))
+  }
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;