use std::{
    fmt::Write,
    ops,
};
#[cfg(feature = "gemini_srv")]
use std::convert::TryInto;
#[cfg(feature = "scgi_srv")]
use std::{
    collections::HashMap,
    convert::TryFrom,
    path::Path,
};
use anyhow::*;
use percent_encoding::percent_decode_str;
use uriparse::URIReference;
#[cfg(feature="user_management")]
use serde::{Serialize, de::DeserializeOwned};
#[cfg(feature = "gemini_srv")]
use ring::digest;

#[cfg(feature="user_management")]
use crate::user_management::{UserManager, User};

#[derive(Clone)]
/// A request from a Gemini client to the app
///
/// When originally sent out by a client, a request is literally just a URL, and honestly,
/// if you want to use it as just a URL, that'll work fine!
///
/// That said, kochab and any proxies the request might hit add a little bit more
/// information that you can use, like
/// * [What TLS certificate (if any) did the client use](Self::certificate)
/// * [What part of the path is relevant (ie, everything after the route)](Self::trailing_segments)
/// * [Is the user registered with the user database?](Self::user)
///
/// The only way to get your hands on one of these bad boys is when you register an [`Fn`]
/// based handler to a [`Server`](crate::Server), and a user makes a request to the
/// endpoint.
pub struct Request {
    uri: URIReference<'static>,
    input: Option<String>,
    certificate: Option<[u8; 32]>,
    trailing_segments: Option<Vec<String>>,
    #[cfg(feature="user_management")]
    manager: &'static UserManager,
    #[cfg(feature = "scgi_srv")]
    headers: HashMap<String, String>,
    #[cfg(feature = "scgi_srv")]
    script_path: Option<String>,
}

impl Request {
    /// Construct a new request
    ///
    /// When in `gemini_srv` mode, this is done using a URL.  If you do construct a
    /// request this way, by default it will not have a certificate attached, so make
    /// sure you add in a certificate with [`Request::set_cert()`].
    ///
    /// By contrast, in `scgi_srv` mode, the certificate fingerprint is grabbed out of the
    /// request parameters, so you don't need to do anything.  The headers passed should
    /// be the header sent by the SCGI client.
    ///
    /// When in SCGI mode, the following headers are expected:
    ///
    /// * `PATH_INFO`: The part of the path following the route the app is bound to
    /// * `QUERY_STRING`: The part of the request following ?, url encoded.  Will produce
    ///   an error if it contains invalid UTF-8.  No error if missing
    /// * `TLS_CLIENT_HASH`: Optional.  The base64 or hex encoded SHA256 sum of the DER
    ///   certificate of the requester.
    /// * `SCRIPT_PATH` or `SCRIPT_NAME`:  The base path the app is mounted on
    ///
    /// # Errors
    ///
    /// Produces an error if:
    /// * The SCGI server didn't include the mandatory `PATH_INFO` header
    /// * The provided URI reference is invalid, including if the SCGI server sent an
    ///   invalid `PATH_INFO`
    /// * The `TLS_CLIENT_HASH` sent by the SCGI server isn't sha256, or is encoded with
    ///   something other than base64 or hexadecimal
    pub (crate) fn new(
        #[cfg(feature = "gemini_srv")]
        mut uri: URIReference<'static>,
        #[cfg(feature = "scgi_srv")]
        headers: HashMap<String, String>,
        #[cfg(feature="user_management")]
        manager: &'static UserManager,
    ) -> Result<Self> {
        #[cfg(feature = "scgi_srv")]
        #[allow(clippy::or_fun_call)] // Lay off it's a macro
        let (mut uri, certificate, script_path) = (
            URIReference::try_from(
                format!(
                    "{}{}",
                    headers.get("PATH_INFO")
                        .context("PATH_INFO header not received from SCGI client")?
                        .as_str(),
                    headers.get("QUERY_STRING")
                        .map(|q| format!("?{}", q))
                        .unwrap_or_else(String::new),
                ).as_str()
            )
                .context("Request URI is invalid")?
                .into_owned(),
            match headers.get("TLS_CLIENT_HASH").map(hash_decode) {
                Some(maybe_hash @ Some(_))  => maybe_hash,
                Some(None) => bail!("Received malformed TLS client hash from upstream.  Expected 256 bit hex or b64 encoded"),
                None => None,
            },
            headers.get("SCRIPT_PATH")
                .or_else(|| headers.get("SCRIPT_NAME"))
                .cloned()
        );

        // Send out a warning if the server did not specify a SCRIPT_PATH.
        // This should only be done once to avoid spaming log files
        #[cfg(feature = "scgi_srv")]
        if script_path.is_none() {
            static WARN: std::sync::Once = std::sync::Once::new();
            WARN.call_once(||
                warn!(concat!(
                    "The SCGI server did not send a SCRIPT_PATH, indicating that it",
                    " doesn't comply with Gemini's SCGI spec.  This will cause a problem",
                    " if the app needs to rewrite a URL.  Please consult the proxy server",
                    " to identify why this is."
                ))
            )
        }

        uri.normalize();

        let input = match uri.query().filter(|q| !q.is_empty()) {
            None => None,
            Some(query) => {
                let input = percent_decode_str(query.as_str())
                    .decode_utf8()
                    .context("Request URI query contains invalid UTF-8")?
                    .into_owned();
                Some(input)
            }
        };

        Ok(Self {
            uri,
            input,
            #[cfg(feature = "scgi_srv")]
            certificate,
            #[cfg(feature = "gemini_srv")]
            certificate: None,
            trailing_segments: None,
            #[cfg(feature = "scgi_srv")]
            headers,
            #[cfg(feature = "scgi_srv")]
            script_path,
            #[cfg(feature="user_management")]
            manager,
        })
    }

    /// The URI reference requested by the user
    ///
    /// Although they are not exactly the same thing, it is generally preferred to use the
    /// [`Request::trailing_segments()`] method if possible.
    ///
    /// Returns the URIReference requested by the user.  **If running in SCGI mode, this
    /// will contain only the parts of the URIReference that were relevant to the app.**
    /// This means you will get `/path`, not `/app/path`.
    ///
    /// When running in `scgi_srv` mode, this is guaranteed to be a relative reference.
    /// When running in `gemini_srv` mode, clients are obliged by the spec to send a full
    /// URI, but if a client fails to respect this, kochab will still accept and pass on
    /// the relative reference.
    pub const fn uri(&self) -> &URIReference {
        &self.uri
    }

    #[allow(clippy::missing_const_for_fn)]
    /// All of the path segments following the route to which this request was bound.
    ///
    /// For example, if this handler was bound to the `/api` route, and a request was
    /// received to `/api/v1/endpoint`, then this value would be `["v1", "endpoint"]`.
    /// This should not be confused with [`path_segments()`](Self::path_segments()), which
    /// contains *all* of the segments, not just those trailing the route.
    pub fn trailing_segments(&self) -> &Vec<String> {
        self.trailing_segments.as_ref().unwrap()
    }

    /// All of the segments in this path, percent decoded
    ///
    /// For example, for a request to `/api/v1/endpoint`, this would return `["api", "v1",
    /// "endpoint"]`, no matter what route the handler that received this request was
    /// bound to.  This is not to be confused with
    /// [`trailing_segments()`](Self::trailing_segments), which contains only the segments
    /// following the bound route.
    ///
    /// Additionally, unlike `trailing_segments()`, this method percent decodes the path.
    pub fn path_segments(&self) -> Vec<String> {
        self.uri()
            .path()
            .segments()
            .iter()
            .map(|segment| percent_decode_str(segment.as_str()).decode_utf8_lossy().into_owned())
            .collect::<Vec<String>>()
    }

    /// View any input sent by the user in the query string
    ///
    /// Any zero-length input is treated as no input at all, and will be reported as
    /// [`None`].  This is done in order to provide compatibility with the SCGI header
    /// common practice of reporting no query string as a blank input.
    pub fn input(&self) -> Option<&str> {
        self.input.as_deref()
    }

    #[cfg(feature="scgi_srv")]
    /// View any headers sent by the SCGI client
    ///
    /// When an SCGI client delivers a request (e.g. when your gemini server sends a
    /// request to this app), it includes many headers which aren't always included in
    /// the request otherwise.  Bear in mind that **not all SCGI clients send the same
    /// headers**, and these are *never* available when operating in `gemini_srv` mode.
    ///
    /// By using this method, you are almost certainly reducing the number of proxy
    /// servers your app supports, and you are  strongly encouraged to find a different
    /// method.
    ///
    /// Some examples of headers mollybrown sets are:
    ///  - `REMOTE_ADDR` (The user's IP address and port)
    ///  - `TLS_CLIENT_SUBJECT_CN` (The CommonName on the user's certificate, when present)
    ///  - `SERVER_NAME` (The host name of the server the request was received on)
    ///  - `SERVER_SOFTWARE` (= "MOLLY_BROWN")
    ///  - `SCRIPT_PATH` (The prefix the script is being served on)
    pub const fn headers(&self) -> &HashMap<String, String> {
        &self.headers
    }

    #[cfg(feature = "gemini_srv")]
    pub (crate) fn set_cert(&mut self, cert: Option<rustls::Certificate>) {
        self.certificate = cert.map(|cert| {
            digest::digest(&digest::SHA256, cert.0.as_ref())
                .as_ref()
                .try_into()
                .expect("SHA256 didn't return 256 bits")
        });
    }

    /// Sets the segments returned by [`Request::trailing_segments()`]
    pub (crate) fn set_trailing(&mut self, segments: Vec<String>) {
        self.trailing_segments = Some(segments);
    }

    #[allow(clippy::missing_const_for_fn)]
    /// Get the fingerprint of the certificate the user is connecting with
    ///
    /// Please not that this is **not** the full certificate, just it's fingerprint
    /// represented as bytes.  The full certificate is not currently exposed, since some
    /// SCGI servers may not receive it.
    ///
    /// If you are planning on displaying the certificate to the user, you may want to
    /// consider using [`fingerprint()`], which stringifies the output of this method.
    ///
    /// [`fingerprint()`]: Request::fingerprint
    pub fn certificate(&self) -> Option<&[u8; 32]> {
        self.certificate.as_ref()
    }

    /// Get the user's certificate as a [`String`] contain the hex fingerprint
    ///
    /// This is a convenience method for stringiying the certificate fingerprint from the
    /// [`certificate()`] method.  If you're using this fingerprint as a key for some user
    /// data, you may want to perfer the former method.  This method should be used when
    /// the fingerprint is being displayed to the user.
    ///
    /// The returned fingerprint will always be a 64 character string containing lowercase
    /// hex digits, such as
    /// `5e7097dc25dc62867ee4e0d3214a74b83156e613fdf92ca05e08c79efb14b90e`
    ///
    /// [`certificate()`]: Request::certificate
    pub fn fingerprint(&self) -> Option<String> {
        self.certificate.as_ref().map(|c| {
            let mut message = String::with_capacity(64);

            for byte in c {
                write!(&mut message, "{:x}", byte).unwrap();
            }

            message
        })
    }

    #[cfg(feature="user_management")]
    /// Attempt to determine the user who sent this request
    ///
    /// May return a variant depending on if the client used a client certificate, and if
    /// they've registered as a user yet.
    pub fn user<UserData>(&self) -> Result<User<UserData>>
    where
        UserData: Serialize + DeserializeOwned
    {
        Ok(self.manager.get_user_by_cert(self.certificate())?)
    }

    #[cfg(feature="user_management")]
    /// Expose the server's UserManager
    ///
    /// Can be used to query users, or directly access the database
    pub fn user_manager(&self) -> &'static UserManager {
        self.manager
    }

    /// Attempt to rewrite an absolute URL against the base path of the SCGI script
    ///
    /// When writing an SCGI script, you cannot assume that your script is mounted on the
    /// base path of "/".  For example, a request to the gemini server for "/app/path"
    /// might be received by your script as "/path" if your script is mounted on "/app/".
    /// In this situation, if you linked to "/", you would be sending users to "/", which
    /// is not handled by your app, instead of "/app/", where you probably intended to
    /// send the user.
    ///
    /// This method attempts to infer where the script is mounted, and rewrite an absolute
    /// url relative to that.  For example, if the application was mounted on "/app/", and
    /// you passed "/path", the result would be "/app/path".
    ///
    /// When running in `gemini_srv` mode, the application is always mounted at the base
    /// path, so this will always return the path unchanged.
    ///
    /// Not all SCGI clients will correctly report the application's path, so this may
    /// fail if unable to infer the correct path.  If this is the case, None will be
    /// returned.  Currently, the SCGI headers checked are:
    ///
    /// * `SCRIPT_PATH` (Used by [mollybrown] and [stargazer])
    /// * `SCRIPT_NAME` (Used by [GLV-1.12556])
    ///
    /// [mollybrown]: https://tildegit.org/solderpunk/molly-brown
    /// [stargazer]: https://git.sr.ht/~zethra/stargazer/
    /// [GLV-1.12556]: https://github.com/spc476/GLV-1.12556
    ///
    /// For an overview of methods for rewriting links, see [`Server::set_autorewrite()`].
    ///
    /// [`Server::set_autorewrite()`]: crate::Server::set_autorewrite()
    pub fn rewrite_path(&self, path: impl AsRef<str>) -> Option<String> {
        #[cfg(feature = "scgi_srv")] {
            self.script_path.as_ref().map(|base| {
                let base: &Path = base.as_ref();

                // Make path relative
                let mut path_as_path: &Path = path.as_ref().as_ref();
                if path_as_path.is_absolute() {
                    path_as_path = (&path.as_ref()[1..]).as_ref();
                }

                base.join(path_as_path).display().to_string()
            })
        }
        #[cfg(feature = "gemini_srv")] {
            Some(path.as_ref().to_string())
        }
    }
}

#[allow(clippy::ptr_arg)] // This is a single use function that expects a &String
#[cfg(feature = "scgi_srv")]
/// Attempt to decode a 256 bit hash
///
/// Will attempt to decode first as hexadecimal, and then as base64.  If both fail, return
/// [`None`]
fn hash_decode(hash: &String) -> Option<[u8; 32]> {
    let mut buffer = [0u8; 32];
    if hash.len() == 64 { // Looks like a hex
        // Lifted (lightly modified) from ring::test::from_hex
        for (i, digits) in hash.as_bytes().chunks(2).enumerate() {
            let hi = from_hex_digit(digits[0])?;
            let lo = from_hex_digit(digits[1])?;
            buffer[i] = (hi * 0x10) | lo;
        }
        Some(buffer)
    } else if hash.len() == 44 { // Look like base64
        base64::decode_config_slice(hash, base64::STANDARD, &mut buffer).ok()?;
        Some(buffer)
    } else {
        None
    }
}

#[cfg(feature = "scgi_srv")]
/// Attempt to decode a hex encoded nibble to u8
///
/// Returns [`None`] if not a valid hex character
fn from_hex_digit(d: u8) -> Option<u8> {
    match d {
        b'0'..=b'9' => Some(d - b'0'),
        b'a'..=b'f' => Some(d - b'a' + 10u8),
        b'A'..=b'F' => Some(d - b'A' + 10u8),
        _ => None,
    }
}

impl ops::Deref for Request {
    type Target = URIReference<'static>;

    fn deref(&self) -> &Self::Target {
        &self.uri
    }
}