1 files changed, 71 insertions, 0 deletions

diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..e05d4e3
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,71 @@
+/* Copyright (C) 2019  Akshay Oppiliappan <[email protected]>
+ * Refer to LICENCE for more information.
+ * */
+
+use std::iter::ExactSizeIterator;
+
+use crate::lex;
+
+#[derive(Debug)]
+pub enum CalcError {
+    Math(Math),
+    Syntax(String),
+    Parser(String),
+    Help,
+}
+
+#[derive(Debug)]
+pub enum Math {
+    DivideByZero,
+    OutOfBounds,
+    UnknownBase,
+}
+
+pub fn handler(e: CalcError) -> String {
+    match e {
+        CalcError::Math(math_err) => match math_err {
+            Math::DivideByZero => "Math Error: Divide by zero error!".to_string(),
+            Math::OutOfBounds => "Domain Error: Out of bounds!".to_string(),
+            Math::UnknownBase => "Base too large! Accepted ranges: 0 - 36".to_string(),
+        },
+        CalcError::Syntax(details) => format!("Syntax Error: {}", details),
+        CalcError::Parser(details) => format!("Parser Error: {}", details),
+        CalcError::Help => {
+            // calculate max width but ideally this should be calculated once
+            let mut max_width = 79; // capped at 79
+            if let Some((w, _)) = term_size::dimensions() {
+                if w < max_width {
+                    max_width = w;
+                }
+            }
+            let operators: Vec<_> = lex::OPERATORS.keys().map(|c| c.to_string()).collect();
+            format!(
+                "Constants\n{}\nFunctions\n{}\nOperators\n{}\n",
+                blocks(max_width, lex::CONSTANTS.keys().cloned()),
+                blocks(max_width, lex::FUNCTIONS.keys().cloned()),
+                operators.join(" ")
+            )
+        }
+    }
+}
+
+/// Convert iterator into strings of chunks of 8 right padded with space.
+fn blocks(
+    max_width: usize,
+    mut iter: impl Iterator<Item = &'static str> + ExactSizeIterator,
+) -> String {
+    // multiply by eight since we are formatting it into chunks of 8
+    let items_per_line = max_width / 8;
+    let full_bytes = (iter.len() - iter.len() % items_per_line) * 8;
+    let part_bytes = iter.len() % items_per_line * 8; // leftovers
+    let n_newlines = iter.len() / items_per_line + if part_bytes > 0 { 1 } else { 0 };
+    let mut s = String::with_capacity(full_bytes + part_bytes + n_newlines);
+    for _ in 0..n_newlines {
+        for item in iter.by_ref().take(items_per_line) {
+            s.extend(format!("{:>8}", item).chars());
+        }
+        s.push('\n');
+    }
+    debug_assert_eq!(s.capacity(), s.len()); // check capacity calculation
+    s
+}