use std::borrow::Borrow;

use quick_xml::{
    events::{BytesStart, Event},
    NsReader, Writer,
};
use tokio::io::{AsyncBufRead, AsyncWrite};
use base64::{Engine as _, engine::general_purpose};

use super::skip_text;
use anyhow::{anyhow, Result};

pub enum Mechanism {
    Plain,
}

impl Mechanism {
    pub fn to_str(&self) -> &'static str {
        match self {
            Mechanism::Plain => "PLAIN",
        }
    }

    pub fn from_str(input: &[u8]) -> Result<Mechanism> {
        match input {
            b"PLAIN" => Ok(Mechanism::Plain),
            _ => Err(anyhow!("unknown auth mechanism: {input:?}")),
        }
    }
}

#[derive(PartialEq, Debug)]
pub struct AuthBody {
    pub login: String,
    pub password: String,
}

impl AuthBody {
    pub fn from_str(input: &[u8]) -> Result<AuthBody> {
        match general_purpose::STANDARD.decode(input){
            Ok(decoded_body) => {
                match String::from_utf8(decoded_body) {
                    Ok(parsed_to_string) => {
                        let separated_words: Vec<&str> = parsed_to_string.split("\x00").collect::<Vec<_>>().clone();
                        if separated_words.len() == 3 {
                            // first segment ignored (might be needed in the future)
                            Ok(AuthBody { login: separated_words[1].to_string(), password: separated_words[2].to_string() })
                        } else { return Err(anyhow!("Incorrect auth format")) }
                    },
                    Err(e) => return Err(anyhow!(e))
                }
            },
            Err(e) => return Err(anyhow!(e))
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn test_returning_auth_body() {
        let orig = b"\x00login\x00pass";
        let encoded = general_purpose::STANDARD.encode(orig);
        let expected = AuthBody {login: "login".to_string(), password: "pass".to_string()};
        let result = AuthBody::from_str(encoded.as_bytes()).unwrap();

        assert_eq!(expected, result);
    }

    #[test]
    fn test_ignoring_first_segment() {
        let orig = b"ignored\x00login\x00pass";
        let encoded = general_purpose::STANDARD.encode(orig);
        let expected = AuthBody {login: "login".to_string(), password: "pass".to_string()};
        let result = AuthBody::from_str(encoded.as_bytes()).unwrap();

        assert_eq!(expected, result);
    }

    #[test]
    fn test_returning_auth_body_with_empty_strings() {
        let orig = b"\x00\x00";
        let encoded = general_purpose::STANDARD.encode(orig);
        let expected = AuthBody {login: "".to_string(), password: "".to_string()};
        let result = AuthBody::from_str(encoded.as_bytes()).unwrap();

        assert_eq!(expected, result);
    }


    #[test]
    fn test_fail_if_size_less_then_3() {
        let orig = b"login\x00pass";
        let encoded = general_purpose::STANDARD.encode(orig);
        let expected = AuthBody {login: "login".to_string(), password: "pass".to_string()};
        let result = AuthBody::from_str(encoded.as_bytes());

        assert!(result.is_err());
    }

    #[test]
    fn test_fail_if_size_greater_then_3() {
        let orig = b"first\x00login\x00pass\x00other";
        let encoded = general_purpose::STANDARD.encode(orig);
        let expected = AuthBody {login: "login".to_string(), password: "pass".to_string()};
        let result = AuthBody::from_str(encoded.as_bytes());

        assert!(result.is_err());
    }

}

pub struct Auth {
    pub mechanism: Mechanism,
    pub body: Vec<u8>,
}

impl Auth {
    pub async fn parse(
        reader: &mut NsReader<impl AsyncBufRead + Unpin>,
        buf: &mut Vec<u8>,
    ) -> Result<Auth> {
        let event = skip_text!(reader, buf);
        let mechanism = if let Event::Start(bytes) = event {
            let mut mechanism = None;
            for attr in bytes.attributes() {
                let attr = attr?;
                if attr.key.0 == b"mechanism" {
                    mechanism = Some(attr.value)
                }
            }
            if let Some(mechanism) = mechanism {
                Mechanism::from_str(mechanism.borrow())?
            } else {
                return Err(anyhow!("expected mechanism attribute in <auth>"));
            }
        } else {
            return Err(anyhow!("expected start of <auth>"));
        };
        let body = if let Event::Text(text) = reader.read_event_into_async(buf).await? {
            text.into_inner().into_owned()
        } else {
            return Err(anyhow!("expected text body in <auth>"));
        };
        if let Event::End(_) = reader.read_event_into_async(buf).await? {
            //TODO
        } else {
            return Err(anyhow!("expected end of <auth>"));
        };

        Ok(Auth { mechanism, body })
    }
}

pub struct Success;

impl Success {
    pub async fn write_xml(&self, writer: &mut Writer<impl AsyncWrite + Unpin>) -> Result<()> {
        let event = BytesStart::new(r#"success xmlns="urn:ietf:params:xml:ns:xmpp-sasl""#);
        writer.write_event_async(Event::Empty(event)).await?;
        Ok(())
    }
}