From 50fa80df278ecde149af14b904cbf1604d2fc3c0 Mon Sep 17 00:00:00 2001
From: electria <elec3137+git@proton.me>
Date: Thu, 18 Jun 2026 18:53:18 -0700
Subject: [PATCH] feat: add parsing function and test

---
 src/main.rs  |   2 +
 src/parse.rs | 163 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 165 insertions(+)
 create mode 100644 src/parse.rs

diff --git a/src/main.rs b/src/main.rs
index e7a11a9..87c15c4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,5 @@
+mod parse;
+
 fn main() {
     println!("Hello, world!");
 }
diff --git a/src/parse.rs b/src/parse.rs
new file mode 100644
index 0000000..26c4aa5
--- /dev/null
+++ b/src/parse.rs
@@ -0,0 +1,163 @@
+#![allow(dead_code)]
+use std::str::FromStr;
+
+use rug::{Float, float::ParseFloatError, ops::CompleteRound};
+
+#[derive(Clone, Debug, thiserror::Error)]
+enum Error {
+    #[error("invalid function: {0}")]
+    InvalidFunction(String),
+    #[error("invalid operator: {0}")]
+    InvalidOperator(char),
+    #[error("failed to parse number '{0}': {1}")]
+    NumberParsing(String, ParseFloatError),
+}
+
+#[derive(Clone, Debug, PartialEq)]
+enum Node {
+    Function(Function),
+    ParenthesisStart,
+    ParenthesisEnd,
+    Number(Float),
+    Operator(Operator),
+}
+
+#[derive(Clone, Debug, PartialEq)]
+enum Operator {
+    Plus,
+    Minus,
+}
+impl TryFrom<char> for Operator {
+    type Error = ();
+    fn try_from(value: char) -> Result<Self, Self::Error> {
+        match value {
+            '+' => Ok(Self::Plus),
+            '-' => Ok(Self::Minus),
+            _ => Err(()),
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+enum Function {
+    Sine,
+    Cosine,
+}
+impl FromStr for Function {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "sin" => Ok(Self::Sine),
+            "cos" => Ok(Self::Cosine),
+            _ => Err(()),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default)]
+enum ParsingState {
+    #[default]
+    Start,
+    ReadingFunctionName(usize),
+    ReadingNumber(usize),
+}
+
+fn nodes_from_str(s: &str) -> Result<Vec<Node>, Error> {
+    let mut nodes = Vec::new();
+    let mut state = ParsingState::default();
+
+    let is_ignored_char = |c: &char| match c {
+        ' ' | '&' => false,
+        _ => true,
+    };
+
+    let filtered_string: String = s.chars().filter(is_ignored_char).collect();
+
+    for (i, c) in filtered_string.chars().enumerate() {
+        let mut start = false;
+        match state {
+            ParsingState::Start => start = true,
+            ParsingState::ReadingFunctionName(start_index) => {
+                if !c.is_alphabetic() {
+                    nodes.push(Node::Function(
+                        filtered_string[start_index..i].parse().map_err(|()| {
+                            Error::InvalidFunction(filtered_string[start_index..i].to_owned())
+                        })?,
+                    ));
+
+                    state = ParsingState::Start;
+                    start = true;
+                }
+            }
+            ParsingState::ReadingNumber(start_index) => {
+                if !c.is_numeric() {
+                    nodes.push(Node::Number(
+                        Float::parse_radix(&filtered_string[start_index..i], 10)
+                            .map_err(|e| {
+                                Error::NumberParsing(filtered_string[start_index..i].to_owned(), e)
+                            })?
+                            .complete(512),
+                    ));
+
+                    state = ParsingState::Start;
+                    start = true;
+                }
+            }
+        }
+
+        if start {
+            if c.is_alphabetic() {
+                state = ParsingState::ReadingFunctionName(i);
+            } else if c.is_numeric() {
+                state = ParsingState::ReadingNumber(i);
+            } else if c == '(' {
+                nodes.push(Node::ParenthesisStart);
+            } else if c == ')' {
+                nodes.push(Node::ParenthesisEnd);
+            } else {
+                nodes.push(Node::Operator(
+                    c.try_into().map_err(|()| Error::InvalidOperator(c))?,
+                ));
+            }
+        }
+    }
+
+    let i = filtered_string.len();
+    match state {
+        ParsingState::Start => {}
+        ParsingState::ReadingFunctionName(start_index) => {
+            nodes.push(Node::Function(
+                filtered_string[start_index..i].parse().map_err(|()| {
+                    Error::InvalidFunction(filtered_string[start_index..i].to_owned())
+                })?,
+            ));
+        }
+        ParsingState::ReadingNumber(start_index) => {
+            nodes.push(Node::Number(
+                Float::parse_radix(&filtered_string[start_index..i], 10)
+                    .map_err(|e| {
+                        Error::NumberParsing(filtered_string[start_index..i].to_owned(), e)
+                    })?
+                    .complete(512),
+            ));
+        }
+    }
+
+    Ok(nodes)
+}
+
+#[test]
+fn test_nodes_from_str() {
+    assert_eq!(
+        nodes_from_str("sin(2) + 1").unwrap().as_slice(),
+        vec![
+            Node::Function(Function::Sine),
+            Node::ParenthesisStart,
+            Node::Number(Float::with_val(512, 2)),
+            Node::ParenthesisEnd,
+            Node::Operator(Operator::Plus),
+            Node::Number(Float::with_val(512, 1))
+        ]
+        .as_slice(),
+    )
+}