state!

mono-fmt-macro/src/lib.rs

@@ -11,6 +11,8 @@ use syn::{
     Expr, LitStr, Token,
 };
 
+mod parser;
+
 // TODO: Rewrite using state machine please
 
 struct Input {

mono-fmt-macro/src/parser.rs

@@ -0,0 +1,79 @@
+use std::{iter::Peekable, str::Chars};
+
+#[derive(Debug, PartialEq, Default)]
+pub struct Align {
+    amount: usize,
+    char: Option<char>,
+}
+
+#[derive(Debug, PartialEq, Default)]
+pub enum Argument {
+    #[default]
+    Positional,
+    PositionalExplicit(usize),
+    Keyword(String),
+}
+
+#[derive(Debug, PartialEq, Default)]
+pub enum FmtType {
+    #[default]
+    Default,
+    Debug,
+    LowerHex,
+    UpperHex,
+    Other(String),
+}
+
+#[derive(Debug, PartialEq, Default)]
+pub struct FmtSpec {
+    arg: Argument,
+    align: Option<Align>,
+    sign: Option<char>,
+    alternate: bool,
+    zero: bool,
+    width: Option<usize>,
+    precision: Option<usize>,
+    kind: FmtType,
+}
+
+struct FmtSpecParser<'a> {
+    chars: &'a mut Peekable<Chars<'a>>,
+    state: State,
+    argument: FmtSpec,
+}
+
+#[derive(PartialEq)]
+enum State {
+    Initial,
+    Argument,
+    // : here
+    Fill,
+    Align,
+    Sign,
+    Zero,
+    Width,
+    Precision,
+    Type,
+    Done,
+}
+
+impl<'a> FmtSpecParser<'a> {
+    pub fn new(chars: &'a mut Peekable<Chars<'a>>) -> Self {
+        Self {
+            chars,
+            state: State::Initial,
+            argument: FmtSpec::default(),
+        }
+    }
+
+    fn parse(mut self) -> Result<FmtSpec, ()> {
+        while self.state != State::Done {
+            self.step()?;
+        }
+        Ok(self.argument)
+    }
+
+    fn step(&mut self) -> Result<(), ()> {
+        todo!()
+    }
+}