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use std::{
fmt::Display,
iter::Peekable,
str::{Chars, FromStr},
};
use super::Result;
use crate::audio::{channel::DutyCycle, program::ChanSpec};
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Token {
Eof,
LineSeparator,
Pause(usize),
Jump(usize),
Tempo(u32),
ChanSpec(ChanSpec),
SetVolume(u8),
SetPitch(u8),
SetNoiseMode(bool),
SetPulseDuty(DutyCycle),
}
impl Token {
pub const fn is_eol(self) -> bool {
matches!(self, Self::Eof | Self::LineSeparator)
}
}
pub struct Lexer<'s> {
src: &'s str,
chars: Peekable<Chars<'s>>,
pos: usize,
}
impl<'s> Lexer<'s> {
pub fn new(src: &'s str) -> Self {
let chars = src.chars().peekable();
Self { src, chars, pos: 0 }
}
fn filter_char(&mut self, ch: Option<char>, advance: bool) -> Result<char> {
match ch {
Some(c) if c.is_control() && !matches!(c, '\n' | '\r' | '\t') => {
Err(invalid_char(c))
}
Some(c) => {
if advance {
self.pos += c.len_utf8();
}
Ok(c)
}
None => Ok('\0'),
}
}
fn peek(&mut self) -> Result<char> {
let c = self.chars.peek().copied();
self.filter_char(c, false)
}
fn next(&mut self) -> Result<char> {
let c = self.chars.next();
self.filter_char(c, true)
}
fn next_int<T>(&mut self) -> Result<T>
where
T: FromStr,
<T as FromStr>::Err: Display,
{
let start = self.pos;
while self.peek()?.is_ascii_digit() {
self.next()?;
}
let str = &self.src[start..self.pos];
str.parse::<T>().map_err(|e| e.to_string())
}
fn next_note(&mut self) -> Result<u8> {
if self.peek()?.is_ascii_digit() {
return self.next_int();
}
let note = match self.next()? {
'a' => 80,
'b' => 82,
'c' => 83,
'd' => 85,
'e' => 87,
'f' => 88,
'g' => 90,
c => unexpected(c)?,
};
let octave = {
let c = self.next()?;
c.to_digit(10).ok_or_else(|| format!("invalid octave: {c}"))
}?;
let off = match self.peek()? {
'#' => {
self.next()?;
1
}
'b' => {
self.next()?;
-1
}
_ => 0,
};
let pitch_u32 = (note + octave * 12).wrapping_add_signed(off);
let pitch = u8::try_from(pitch_u32).map_err(|e| format!("{e}"))?;
Ok(pitch)
}
fn next_bool(&mut self) -> Result<bool> {
match self.next_int()? {
0 => Ok(false),
_ => Ok(true),
}
}
fn next_duty_cycle(&mut self) -> Result<DutyCycle> {
match self.next_int()? {
12 => Ok(DutyCycle::Percent12),
25 => Ok(DutyCycle::Percent25),
50 => Ok(DutyCycle::Percent50),
75 => Ok(DutyCycle::Percent25Neg),
n => Err(format!("invalid duty cycle: {n}")),
}
}
fn skip_comment(&mut self) -> Result<()> {
loop {
let next = self.next()?;
if next == '\n' || next == '\0' {
break;
}
}
Ok(())
}
fn next_pause(&mut self) -> Result<Token> {
let mut count = 1;
if self.peek()?.is_ascii_digit() {
count = self.next_int()?;
}
Ok(Token::Pause(count))
}
pub fn next_token(&mut self) -> Result<Token> {
use Token as T;
loop {
let peek = self.peek()?;
if peek == ';' {
self.skip_comment()?;
} else if matches!(peek, ' ' | '\t' | '\r') {
self.next()?;
} else {
break;
}
}
let token = match self.next()? {
// chan spec
'a' => Token::ChanSpec(ChanSpec::PulseA),
'b' => Token::ChanSpec(ChanSpec::PulseB),
't' => Token::ChanSpec(ChanSpec::Triangle),
'n' => Token::ChanSpec(ChanSpec::Noise),
// volume
'v' => T::SetVolume(self.next_int()?),
// pitch
'p' => T::SetPitch(self.next_note()?),
// duty cycle
'd' => T::SetPulseDuty(self.next_duty_cycle()?),
// noise mode
'm' => T::SetNoiseMode(self.next_bool()?),
// pause
'-' => self.next_pause()?,
// jump
'j' => T::Jump(self.next_int()?),
// tempO
'o' => T::Tempo(self.next_int()?),
// eof
'\0' => T::Eof,
// new line
'\n' => T::LineSeparator,
// unexpected
c => unexpected(c)?,
};
Ok(token)
}
}
impl Iterator for Lexer<'_> {
type Item = Result<Token>;
fn next(&mut self) -> Option<Self::Item> {
Some(self.next_token())
}
}
fn invalid_char(ch: char) -> String {
match ch as u32 {
c @ 0x00..=0x7f => format!("invalid character (codepoint 0x{c:2x})"),
c => format!("invalid character (codepoint U+{c:04x})"),
}
}
fn unexpected<T>(c: char) -> Result<T> {
let msg = match c {
'\0' => "unexpected end of file".to_owned(),
'\n' => "unexpected newline character".to_owned(),
'\t' => "unexpected tab character".to_owned(),
'\r' => "unexpected return character".to_owned(),
c => format!("unexpected character {c}"),
};
Err(msg)
}
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