From 09eb85fda469c1467662d7c9ae381a0b943c1a07 Mon Sep 17 00:00:00 2001
From: David Senk <david@senk.me>
Date: Thu, 7 Sep 2023 14:56:38 -0400
Subject: [PATCH] basic functionality

---
 src/main.rs | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 69 insertions(+), 3 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 6e43406..c0cdd89 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,15 @@
 use std::io;
 use std::io::Write;
+use std::str::FromStr;
 
 fn main() {
-    println!("Hello, world!");
+    println!("RPN Calculator");
+
+    let mut stack: Vec<f64> = Vec::new();
 
     loop {
         let mut input = String::new();
+
         print!("> ");
 
         io::stdout()
@@ -16,8 +20,70 @@ fn main() {
             .read_line(&mut input)
             .expect("failed to read line");
 
-        let output = input.trim();
+        let func = match input.trim() {
+            "q" => Function::Quit,
+            "+" => Function::Add,
+            "-" => Function::Subtract,
+            "*" | "x" => Function::Multiply,
+            "/" => Function::Divide,
+            "%" => Function::Modulo,
+            _ => Function::Push(f64::from_str(input.trim()).expect("valid number")),
+        };
 
-        println!("input received: '{output}'");
+        match func {
+            Function::Push(x) => stack.push(x),
+            Function::Quit => break,
+            others => operate(&mut stack, others),
+        }
+
+        println!("Current Stack: ");
+
+        for i in &stack {
+            println!("{i}");
+        }
+    }
+}
+
+enum Function {
+    Add,
+    Subtract,
+    Multiply,
+    Divide,
+    Modulo,
+    Push(f64),
+    Quit,
+}
+
+fn stack_too_small_err(func: &str) {
+    println!("Stack must contain at least 2 numbers to {func}!");
+}
+
+fn operate(stack: &mut Vec<f64>, func: Function) {
+    if stack.len() < 2 {
+        match func {
+            Function::Add => stack_too_small_err("add"),
+            Function::Subtract => stack_too_small_err("subtract"),
+            Function::Multiply => stack_too_small_err("multiply"),
+            Function::Divide => stack_too_small_err("divide"),
+            Function::Modulo => stack_too_small_err("modulo"),
+            _ => {}
+        }
+        return;
+    }
+
+    let x = stack.pop().unwrap_or(0f64);
+    let y = stack.pop().unwrap_or(0f64);
+
+    match func {
+        Function::Add => stack.push(x + y),
+        Function::Subtract => stack.push(x - y),
+        Function::Divide => stack.push(y / x),
+        //x is at top of stack, but divide is order
+        //dependent. We're dividing the number input prior
+        //to x (y), by x. i.e. x: 3, y: 6, push = 0.5
+        Function::Multiply => stack.push(x * y),
+        Function::Modulo => stack.push(y % x),
+        //same reason as division above
+        _ => {} //do nothing, as we don't know what to do with it
     }
 }