//! Everything related to Gemini client except cert verification

pub mod builder;
pub mod response;

#[cfg(test)]
pub mod tests;

pub use response::Response;

#[cfg(feature = "hickory")]
use crate::dns::DnsClient;
#[cfg(feature = "hickory")]
use hickory_client::rr::IntoName;
#[cfg(feature = "hickory")]
use std::net::SocketAddr;

use crate::{
    certs::{SelfsignedCertVerifier, ServerName},
    error::*,
    into_url::IntoUrl,
    status::*,
};
use builder::ClientBuilder;

use std::sync::Arc;

use tokio::{
    io::{AsyncBufReadExt, AsyncReadExt, AsyncWriteExt, BufReader},
    net::TcpStream,
};
use tokio_rustls::{client::TlsStream, rustls, TlsConnector};

pub type ThisResponse = Response<BufReader<TlsStream<TcpStream>>>;

pub struct Client {
    pub(crate) connector: TlsConnector,
    pub(crate) ss_verifier: Option<Arc<dyn SelfsignedCertVerifier>>,
    #[cfg(feature = "hickory")]
    pub(crate) dns: Option<DnsClient>,
}

impl Client {
    /// Construct a Client with a customized configuration,
    /// see [`ClientBuilder`] methods.
    pub fn builder() -> ClientBuilder {
        ClientBuilder::new()
    }
}

impl Client {
    /// Perform a Gemini request with the specified URL.
    /// Host and port (1965 by default) are parsed from `url`
    /// after scheme and userinfo checks.
    /// On success, [`Response`] is returned.
    ///
    /// Automatically follows redirections up to 5 times.
    /// To avoid this behavior, use [`Client::request_with_no_redirect`],
    /// this function is also called here under the hood.
    ///
    /// Returns an error if a scheme is not `gemini://` or
    /// a userinfo portion (`user:password@`) is present in the URL.
    /// To avoid this checks, most probably for proxying requests,
    /// use [`Client::request_with_host`].
    ///
    /// # Errors
    /// - See [`Client::request_with_no_redirect`].
    pub async fn request(&self, url: impl IntoUrl) -> Result<ThisResponse, LibError> {
        // first request
        let mut resp = self.request_with_no_redirect(url).await?;

        let mut i: u8 = 0;
        const MAX: u8 = 5;

        // repeat requests until we get a non-30 status
        // or hit the redirection depth limit
        loop {
            if resp.status().reply_type() == ReplyType::Redirect && i < MAX {
                resp = self.request_with_no_redirect(resp.message()).await?;
                i += 1;
                continue;
            }
            return Ok(resp);
        }
    }

    /// Perform a Gemini request with the specified URL
    /// **without** following redirections.
    /// Host and port (1965 by default) are parsed from `url`
    /// after scheme and userinfo checks.
    /// On success, [`Response`] is returned.
    ///
    /// # Errors
    /// - [`InvalidUrl::ParseError`] means that the given URL cannot be parsed.
    /// - [`InvalidUrl::SchemeNotGemini`] is returned when a scheme is not `gemini://`,
    ///   for proxying requests use [`Client::request_with_host`].
    /// - [`InvalidUrl::UserinfoPresent`] is returned when the given URL contains
    ///   a userinfo portion (`user:password@`) -- it is forbidden by the Gemini specification.
    /// - See [`Client::request_with_host`] for the rest.
    pub async fn request_with_no_redirect(
        &self,
        url: impl IntoUrl,
    ) -> Result<ThisResponse, LibError> {
        let url = url.into_url()?;

        let host = url.host_str().ok_or(InvalidUrl::ConvertError)?;
        let port = url.port().unwrap_or(1965);

        self.request_with_host(url.as_str(), host, port).await
    }

    /// Perform a Gemini request with the specified host, port and URL.
    /// Non-`gemini://` URLs is OK if the remote server supports proxying.
    ///
    /// # Errors
    /// - [`InvalidUrl::ConvertError`] means that a hostname cannot be
    ///   converted into [`pki_types::ServerName`].
    /// - [`LibError::HostLookupError`] means that a DNS server returned no records,
    ///   i.&nbsp;e. that domain does not exist.
    /// - [`LibError::DnsClientError`] (crate feature `hickory`)
    ///   wraps a Hickory DNS client error related to a connection failure
    ///   or an invalid DNS server response.
    /// - [`std::io::Error`] is returned in many cases:
    ///   could not open a TCP connection, perform a TLS handshake,
    ///   write to or read from the TCP stream.
    ///   Check the ErrorKind and/or the inner error
    ///   if you need to determine what exactly happened.
    /// - [`LibError::StatusOutOfRange`] means that a Gemini server returned
    ///   an invalid status code (less than 10 or greater than 69).
    /// - [`LibError::DataNotUtf8`] is returned when metadata (the text after a status code)
    ///   is not in UTF-8 and cannot be converted to a string without errors.
    pub async fn request_with_host(
        &self,
        url_str: &str,
        host: &str,
        port: u16,
    ) -> Result<ThisResponse, LibError> {
        let domain = ServerName::try_from(host)
            .map_err(|_| InvalidUrl::ConvertError)?
            .to_owned();

        // TCP connection
        let stream = self.try_connect(host, port).await?;
        // TLS connection via tokio-rustls
        let stream = self.connector.connect(domain, stream).await?;

        // certificate verification
        if let Some(ssv) = &self.ss_verifier {
            let cert = stream
                .get_ref()
                .1 // rustls::ClientConnection
                .peer_certificates()
                .unwrap() // i think handshake already completed if we awaited on connector.connect?
                .first()
                .ok_or(rustls::Error::NoCertificatesPresented)?;

            if !ssv.verify(cert, host, port).await? {
                return Err(rustls::CertificateError::ApplicationVerificationFailure.into());
            }
        }

        self.perform_io(url_str, stream).await
    }

    pub(crate) async fn perform_io<IO: AsyncReadExt + AsyncWriteExt + Unpin>(
        &self,
        url_str: &str,
        mut stream: IO,
    ) -> Result<Response<BufReader<IO>>, LibError> {
        // Write URL, then CRLF
        stream.write_all(url_str.as_bytes()).await?;
        stream.write_all(b"\r\n").await?;
        stream.flush().await?;

        let status = {
            let mut buf: [u8; 3] = [0, 0, 0]; // 2 digits, space
            stream.read_exact(&mut buf).await?;
            Status::parse_status(&buf)?
        };

        let mut stream = BufReader::new(stream);

        let message = {
            let mut result: Vec<u8> = Vec::new();
            let mut buf = [0u8]; // buffer for LF (\n)

            // reading message after status code
            // until CRLF (\r\n)
            loop {
                // until CR
                stream.read_until(b'\r', &mut result).await?;
                // now read next char...
                stream.read_exact(&mut buf).await?;
                if buf[0] == b'\n' {
                    // ...and check if it's LF
                    break;
                } else {
                    // ...otherwise, CR is a part of message, not a CRLF terminator,
                    // so append that one byte that's supposed to be LF (but not LF)
                    // to the message buffer
                    result.push(buf[0]);
                }
            }

            // trim last CR
            if result.last().is_some_and(|c| c == &b'\r') {
                result.pop();
            }

            // Vec<u8> -> ASCII or UTF-8 String
            String::from_utf8(result)?
        };

        Ok(Response::new(status, message, stream))
    }

    async fn try_connect(&self, host: &str, port: u16) -> Result<TcpStream, LibError> {
        let mut last_err: Option<std::io::Error> = None;

        #[cfg(feature = "hickory")]
        if let Some(dns) = &self.dns {
            let mut dns = dns.clone();
            let name = host.into_name()?;

            for ip_addr in dns.query_ipv4(name.clone()).await? {
                match TcpStream::connect(SocketAddr::new(ip_addr, port)).await {
                    Ok(stream) => {
                        return Ok(stream);
                    }
                    Err(err) => {
                        last_err = Some(err);
                    }
                }
            }

            for ip_addr in dns.query_ipv6(name).await? {
                match TcpStream::connect(SocketAddr::new(ip_addr, port)).await {
                    Ok(stream) => {
                        return Ok(stream);
                    }
                    Err(err) => {
                        last_err = Some(err);
                    }
                }
            }

            if let Some(err) = last_err {
                return Err(err.into());
            }

            return Err(LibError::HostLookupError);
        }

        for addr in tokio::net::lookup_host((host, port)).await? {
            match TcpStream::connect(addr).await {
                Ok(stream) => {
                    return Ok(stream);
                }
                Err(err) => {
                    last_err = Some(err);
                }
            }
        }

        if let Some(err) = last_err {
            return Err(err.into());
        }

        Err(LibError::HostLookupError)
    }
}