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use std::{borrow::Cow, convert::TryFrom, fmt::Display};

use crate::SimpleDnsError;

use super::{DnsPacketContent, MAX_CHARACTER_STRING_LENGTH};

/// CharacterString is expressed in one or two ways:
/// - as a contiguous set of characters without interior spaces,
/// - or as a string beginning with a " and ending with a ".  
///
/// Inside a " delimited string any character can occur, except for a " itself,  
/// which must be quoted using \ (back slash).
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct CharacterString<'a> {
    pub(crate) data: Cow<'a, [u8]>,
}

impl<'a> CharacterString<'a> {
    /// Creates a new validated CharacterString
    pub fn new(data: &'a [u8]) -> crate::Result<Self> {
        Self::internal_new(Cow::Borrowed(data))
    }

    fn internal_new(data: Cow<'a, [u8]>) -> crate::Result<Self> {
        if data.len() > MAX_CHARACTER_STRING_LENGTH || !Self::is_valid(&data) {
            return Err(SimpleDnsError::InvalidCharacterString);
        }

        Ok(Self { data })
    }

    fn is_valid(data: &'_ [u8]) -> bool {
        if data[0] == b'"' {
            if data[data.len() - 1] != b'"' {
                return false;
            }

            for (p, c) in data[1..data.len() - 1].iter().enumerate() {
                if *c == b'"' && data[p] != b'\\' {
                    return false;
                }
            }

            return true;
        }

        return data.iter().all(|c| *c != b' ');
    }

    /// Transforms the inner data into it's owned type
    pub fn into_owned<'b>(self) -> CharacterString<'b> {
        CharacterString {
            data: self.data.into_owned().into(),
        }
    }
}

impl<'a> DnsPacketContent<'a> for CharacterString<'a> {
    fn parse(data: &'a [u8], position: usize) -> crate::Result<Self>
    where
        Self: Sized,
    {
        let length = data[position] as usize;

        if length == 0 || Self::is_valid(&data[position + 1..position + 1 + length]) {
            Ok(Self {
                data: Cow::Borrowed(&data[position + 1..position + 1 + length]),
            })
        } else {
            Err(SimpleDnsError::InvalidCharacterString)
        }
    }

    fn append_to_vec(&self, out: &mut Vec<u8>) -> crate::Result<()> {
        out.push(self.data.len() as u8);
        out.extend(self.data.iter());

        Ok(())
    }

    fn len(&self) -> usize {
        self.data.len() + 1
    }
}

impl<'a> TryFrom<&'a str> for CharacterString<'a> {
    type Error = crate::SimpleDnsError;

    fn try_from(value: &'a str) -> Result<Self, Self::Error> {
        CharacterString::internal_new(Cow::Borrowed(value.as_bytes()))
    }
}

impl<'a> TryFrom<String> for CharacterString<'a> {
    type Error = crate::SimpleDnsError;

    fn try_from(value: String) -> Result<Self, Self::Error> {
        CharacterString::internal_new(Cow::Owned(value.as_bytes().into()))
    }
}

impl<'a> Display for CharacterString<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let s = std::str::from_utf8(&self.data).unwrap();
        f.write_str(s)
    }
}

#[cfg(test)]
mod tests {
    use std::{
        collections::hash_map::DefaultHasher,
        hash::{Hash, Hasher},
    };

    use super::*;

    #[test]
    fn construct_valid_character_string() {
        assert!(CharacterString::new(b"Iamvalid").is_ok());
        assert!(CharacterString::new(br#""I am valid""#).is_ok());
        assert!(CharacterString::new(br#""I am \" also valid""#).is_ok());
        assert!(CharacterString::new(b"I am invalid").is_err());

        let long_string = [0u8; 300];
        assert!(CharacterString::new(&long_string).is_err());
    }

    #[test]
    fn parse() {
        let c_string = CharacterString::parse(b"\x0esome_long_text", 0);
        assert!(c_string.is_ok());
        let c_string = c_string.unwrap();
        assert_eq!(15, c_string.len());
        assert_eq!("some_long_text", c_string.to_string());
    }

    #[test]
    fn append_to_vec() {
        let mut out = Vec::new();
        let c_string = CharacterString::new("some_long_text".as_bytes()).unwrap();
        c_string.append_to_vec(&mut out).unwrap();

        assert_eq!(b"\x0esome_long_text", &out[..]);
    }

    #[test]
    fn eq() {
        let a = CharacterString::new(b"text").unwrap();
        let b = CharacterString::new(b"text").unwrap();

        assert_eq!(a, b);
        assert_eq!(get_hash(a), get_hash(b));
    }

    fn get_hash(string: CharacterString) -> u64 {
        let mut hasher = DefaultHasher::default();
        string.hash(&mut hasher);
        hasher.finish()
    }
}