jsonc-parser 0.25.2

use std::borrow::Cow;

pub struct ParseStringError {
  pub byte_index: usize,
  pub kind: ParseStringErrorKind,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum ParseStringErrorKind {
  InvalidEscapeInSingleQuoteString,
  InvalidEscapeInDoubleQuoteString,
  ExpectedFourHexDigits,
  InvalidUnicodeEscapeSequence(String),
  InvalidEscape,
  UnterminatedStringLiteral,
}

impl std::error::Error for ParseStringErrorKind {}

impl std::fmt::Display for ParseStringErrorKind {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    match self {
      ParseStringErrorKind::InvalidEscapeInSingleQuoteString => {
        write!(f, "Invalid escape in single quote string")
      }
      ParseStringErrorKind::InvalidEscapeInDoubleQuoteString => {
        write!(f, "Invalid escape in double quote string")
      }
      ParseStringErrorKind::ExpectedFourHexDigits => {
        write!(f, "Expected four hex digits")
      }
      ParseStringErrorKind::InvalidUnicodeEscapeSequence(value) => {
        write!(
          f,
          "Invalid unicode escape sequence. '{}' is not a valid UTF8 character",
          value
        )
      }
      ParseStringErrorKind::InvalidEscape => {
        write!(f, "Invalid escape")
      }
      ParseStringErrorKind::UnterminatedStringLiteral => {
        write!(f, "Unterminated string literal")
      }
    }
  }
}

pub trait CharProvider<'a> {
  fn current_char(&mut self) -> Option<char>;
  fn byte_index(&self) -> usize;
  fn move_next_char(&mut self) -> Option<char>;
  fn text(&self) -> &'a str;
}

#[cfg(feature = "cst")]
pub fn parse_string(text: &str) -> Result<Cow<str>, ParseStringError> {
  struct StringCharProvider<'a> {
    text: &'a str,
    byte_index: usize,
    current_char: Option<char>,
    chars: std::str::Chars<'a>,
  }

  impl<'a> CharProvider<'a> for StringCharProvider<'a> {
    fn current_char(&mut self) -> Option<char> {
      self.current_char
    }

    fn byte_index(&self) -> usize {
      self.byte_index
    }

    fn move_next_char(&mut self) -> Option<char> {
      if let Some(current_char) = self.current_char {
        self.byte_index += current_char.len_utf8();
      }
      self.current_char = self.chars.next();
      self.current_char
    }

    fn text(&self) -> &'a str {
      self.text
    }
  }

  let mut chars = text.chars();
  let mut provider = StringCharProvider {
    text,
    byte_index: 0,
    current_char: chars.next(),
    chars,
  };

  parse_string_with_char_provider(&mut provider)
}

pub fn parse_string_with_char_provider<'a, T: CharProvider<'a>>(
  chars: &mut T,
) -> Result<Cow<'a, str>, ParseStringError> {
  debug_assert!(
    chars.current_char() == Some('\'') || chars.current_char() == Some('"'),
    "Expected \", was {:?}",
    chars.current_char()
  );
  let is_double_quote = chars.current_char() == Some('"');
  let mut last_start_byte_index = chars.byte_index() + 1;
  let mut text: Option<String> = None;
  let mut last_was_backslash = false;
  let mut found_end_string = false;
  let token_start = chars.byte_index();

  while let Some(current_char) = chars.move_next_char() {
    if last_was_backslash {
      let escape_start = chars.byte_index() - 1; // -1 for backslash
      match current_char {
        '"' | '\'' | '\\' | '/' | 'b' | 'f' | 'u' | 'r' | 'n' | 't' => {
          if current_char == '"' {
            if !is_double_quote {
              return Err(ParseStringError {
                byte_index: escape_start,
                kind: ParseStringErrorKind::InvalidEscapeInSingleQuoteString,
              });
            }
          } else if current_char == '\'' && is_double_quote {
            return Err(ParseStringError {
              byte_index: escape_start,
              kind: ParseStringErrorKind::InvalidEscapeInDoubleQuoteString,
            });
          }

          let previous_text = &chars.text()[last_start_byte_index..escape_start];
          if text.is_none() {
            text = Some(String::new());
          }
          let text = text.as_mut().unwrap();
          text.push_str(previous_text);
          if current_char == 'u' {
            let mut hex_text = String::new();
            // expect four hex values
            for _ in 0..4 {
              let current_char = chars.move_next_char();
              if !is_hex(current_char) {
                return Err(ParseStringError {
                  byte_index: escape_start,
                  kind: ParseStringErrorKind::ExpectedFourHexDigits,
                });
              }
              if let Some(current_char) = current_char {
                hex_text.push(current_char);
              }
            }

            let hex_u32 = u32::from_str_radix(&hex_text, 16);
            let hex_char = match hex_u32.ok().and_then(std::char::from_u32) {
              Some(hex_char) => hex_char,
              None => {
                return Err(ParseStringError {
                  byte_index: escape_start,
                  kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text),
                });
              }
            };
            text.push(hex_char);
            last_start_byte_index = chars.byte_index() + chars.current_char().map(|c| c.len_utf8()).unwrap_or(0);
          } else {
            text.push(match current_char {
              'b' => '\u{08}',
              'f' => '\u{0C}',
              't' => '\t',
              'r' => '\r',
              'n' => '\n',
              _ => current_char,
            });
            last_start_byte_index = chars.byte_index() + current_char.len_utf8();
          }
        }
        _ => {
          return Err(ParseStringError {
            byte_index: escape_start,
            kind: ParseStringErrorKind::InvalidEscape,
          });
        }
      }
      last_was_backslash = false;
    } else if is_double_quote && current_char == '"' || !is_double_quote && current_char == '\'' {
      found_end_string = true;
      break;
    } else {
      last_was_backslash = current_char == '\\';
    }
  }

  if found_end_string {
    chars.move_next_char();
    let final_segment = &chars.text()[last_start_byte_index..chars.byte_index() - 1];
    Ok(match text {
      Some(mut text) => {
        text.push_str(final_segment);
        Cow::Owned(text)
      }
      None => Cow::Borrowed(final_segment),
    })
  } else {
    Err(ParseStringError {
      byte_index: token_start,
      kind: ParseStringErrorKind::UnterminatedStringLiteral,
    })
  }
}

fn is_hex(c: Option<char>) -> bool {
  let Some(c) = c else {
    return false;
  };
  is_digit(c) || ('a'..='f').contains(&c) || ('A'..='F').contains(&c)
}

fn is_digit(c: char) -> bool {
  c.is_ascii_digit()
}