use std::{
    collections::HashSet,
    convert::TryFrom,
    fmt::Write,
};

use super::{
    context::Context,
    error::Error,
    percent_encoded_character_decoder::PercentEncodedCharacterDecoder,
};

pub fn decode_element<T>(
    element: T,
    allowed_characters: &'static HashSet<char>,
    context: Context,
) -> Result<Vec<u8>, Error>
where
    T: AsRef<str>,
{
    let mut decoding_pec = false;
    let mut pec_decoder = PercentEncodedCharacterDecoder::new();
    element
        .as_ref()
        .chars()
        .filter_map(|c| {
            if decoding_pec {
                pec_decoder.next(c).map_err(Into::into).transpose().map(|c| {
                    decoding_pec = false;
                    c
                })
            } else if c == '%' {
                decoding_pec = true;
                None
            } else if allowed_characters.contains(&c) {
                Some(Ok(c as u8))
            } else {
                Some(Err(Error::IllegalCharacter(context)))
            }
        })
        .collect()
}

pub fn encode_element(
    element: &[u8],
    allowed_characters: &HashSet<char>,
) -> String {
    let mut encoding = String::with_capacity(element.len());
    for ci in element {
        match char::try_from(*ci) {
            Ok(c) if allowed_characters.contains(&c) => encoding.push(c),
            _ => write!(encoding, "%{:02X}", ci).unwrap(),
        }
    }
    encoding
}