/*
 Cargo KConfig - KConfig parser
 Copyright (C) 2022  Sjoerd van Leent

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*/

//! Additional String helper functions

/// Escapes a given value into an escaped string
pub fn escape(value: &str) -> String {
    format!(
        "\"{}\"",
        value
            .chars()
            .flat_map(|c| match c {
                '"' => vec!['\\', '"'],
                '\n' => vec!['\\', 'n'],
                '\r' => vec!['\\', 'r'],
                '\t' => vec!['\\', 't'],
                '\\' => vec!['\\', '\\'],
                _ => vec![c],
            })
            .collect::<String>()
    )
}

/// Parses a string value and removes escapes
pub fn parse(value: &str) -> Result<String, String> {
    let mut chars = value.chars();
    // Trim the left and right double quotes
    if value.len() < 2 || chars.next() != Some('\"') || chars.last() != Some('\"') {
        return Err(format!(
            "Could not find starting or ending double quote in: {}",
            value
        ));
    }
    let basic = value[1..value.len() - 1].chars();

    // Build the string into result
    let mut result: String = "".to_string();

    // If the state is Normal, then it is a normal character, which is appended
    // into result, if the state is Escape, then an escape character (\) has been
    // found prior to the current character, and the character needs unescaping.
    enum State {
        Normal,
        Escaped,
    }
    let mut state = State::Normal;
    for c in basic {
        match state {
            State::Normal => match c {
                '\\' => state = State::Escaped,
                _ => result += &format!("{}", c),
            },
            State::Escaped => {
                match c {
                    '"' => result += "\"",
                    'n' => result += "\n",
                    'r' => result += "\r",
                    't' => result += "\t",
                    '\\' => result += "\\",
                    _ => return Err(format!("Expected escape symbol, found: {}", c)),
                };
                state = State::Normal;
            }
        }
    }
    // If the state remained into escaped, it means that the last character has not
    // been properly closed.
    if let State::Escaped = state {
        return Err("Expected input to be closed, found escape token: \\".to_string());
    }
    Ok(result)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_escape_and_parse_string() {
        let escaped = escape("foo\"\n\r\t\\bar");
        let parsed = parse(&escaped).unwrap();

        assert_eq!("foo\"\n\r\t\\bar", parsed);
        assert_eq!("\"foo\\\"\\n\\r\\t\\\\bar\"", escaped);
    }

    #[test]
    fn test_wrong_escape() {
        assert_eq!(true, parse("\"\\w\"").is_err());
    }

    #[test]
    fn test_attempt_parse_without_opening_quote() {
        assert_eq!(true, parse("a\"").is_err());
    }

    #[test]
    fn test_attempt_parse_without_closing_quote() {
        assert_eq!(true, parse("\"a").is_err());
    }

    #[test]
    fn test_did_not_end_escape() {
        assert_eq!(true, parse("\"\\\"").is_err());
    }
}