From b111ee38909e17e916ee6cf801cc22ea147c2f85 Mon Sep 17 00:00:00 2001
From: Simon Gardling <titaniumtown@gmail.com>
Date: Wed, 16 Feb 2022 13:34:18 -0500
Subject: [PATCH] SOO much better error handling!

---
 src/lib.rs   | 18 ++++++++++++++++--
 www/index.js |  7 +++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index a7bde29..1a27ef2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -57,12 +57,26 @@ impl ChartManager {
     // Used in order to hook into `panic!()` to log in the browser's console
     pub fn init_panic_hook() { panic::set_hook(Box::new(console_error_panic_hook::hook)); }
 
+    pub fn test_func(function_string: String) -> String {
+        let expr: Expr = function_string.parse().unwrap();
+        let func_result = expr.bind("x");
+        match func_result {
+            Ok(_) => "".to_string(),
+            Err(error) => format!("{}", error),
+        }
+    }
+
+    fn get_func(&self) -> impl Fn(f64) -> f64 {
+        let expr: Expr = self.func_str.parse().unwrap();
+        let func = expr.bind("x").unwrap();
+        return func;
+    }
+
     #[inline]
     fn draw(
         &mut self, element: HtmlCanvasElement,
     ) -> DrawResult<(impl Fn((i32, i32)) -> Option<(f32, f32)>, f32)> {
-        let expr: Expr = self.func_str.parse().unwrap();
-        let func = expr.bind("x").unwrap();
+        let func = self.get_func();
 
         let backend = CanvasBackend::with_canvas_object(element).unwrap();
         let root = backend.into_drawing_area();
diff --git a/www/index.js b/www/index.js
index a8e6ef7..0970ae9 100644
--- a/www/index.js
+++ b/www/index.js
@@ -78,6 +78,13 @@ function updatePlot() {
         chart_manager = ChartManager.new(math_function.value, Number(minX.value), Number(maxX.value), Number(minY.value), Number(maxY.value), Number(num_interval.value), Number(resolution.value));
     }
 
+    const test_result = ChartManager.test_func(math_function.value);
+    if (test_result != "") {
+        status.style.color = "red";
+        status.innerText = test_result;
+        return;
+    }
+
     try {
         const start = performance.now();
         chart = chart_manager.update(canvas, math_function.value, Number(minX.value), Number(maxX.value), Number(minY.value), Number(maxY.value), Number(num_interval.value), Number(resolution.value));