1 files changed, 73 insertions, 0 deletions
diff --git a/src/expression.rs b/src/expression.rs
new file mode 100644
index 0000000..5f2660b
--- /dev/null
+++ b/src/expression.rs
@@ -0,0 +1,73 @@
+use crate::context::Context;
+use crate::function::FunctionArgument;
+use crate::string::{ContainsAndSkipBrackets, SplitMatchingBracket};
+
+pub struct Expression {
+    repr: String,
+}
+
+impl Expression {
+    pub fn from_string(str: &str) -> Self {
+        Self {
+            repr: str.replace(' ', ""),
+        }
+    }
+
+    pub fn evaluate(&self, context: &Context) -> Result<f64, String> {
+        let (repr, oprepr) = {
+            if self.repr.starts_with('(') {
+                let (oprepr, r) = self.repr.split_on_matching_bracket();
+                if r.is_empty() {
+                    let repr = oprepr[1..oprepr.len() - 1].to_string();
+                    (repr.clone(), repr)
+                } else {
+                    (self.repr.to_string(), r.to_string())
+                }
+            } else {
+                (self.repr.to_string(), self.repr.to_string())
+            }
+        };
+
+        let curop: Option<_> = {
+            let mut o = None;
+            for op in context.operations() {
+                if oprepr.contains_and_skip_brackets(op.sign().to_string().as_str()) {
+                    o = Some(op);
+                    break;
+                }
+            }
+            o
+        };
+
+        if let Some(op) = curop {
+            let (first, rest) = repr.split_once_and_skipt_brackets(op.sign()).unwrap();
+            let first_expr = Expression::from_string(first);
+            let rest_expr = Expression::from_string(rest);
+            Ok(op.evaluate(first_expr.evaluate(context)?, rest_expr.evaluate(context)?))
+        } else {
+            if let Ok(r) = repr.parse::<f64>() {
+                Ok(r)
+            } else {
+                if let Some((func, args)) = repr.split_once('(') {
+                    let mut argv = Vec::new();
+
+                    for arg in args[..args.len() - 1].split(',') {
+                        argv.push(Expression::from_string(arg).evaluate(context)?);
+                    }
+
+                    if let Some(func) = context.function(func) {
+                        Ok(func.eval(FunctionArgument::new(argv)))
+                    } else {
+                        Err(format!("function '{func}' not found"))
+                    }
+                } else {
+                    if let Some(res) = context.variable(&repr) {
+                        Ok(*res)
+                    } else {
+                        Err(format!("variable '{repr}' not found"))
+                    }
+                }
+            }
+        }
+    }
+}