use std::{
    io::{self, BufRead, Read, Write},
    pin::Pin,
    sync::Arc,
};

use data_encoding::BASE64;
use futures::{Stream, TryStreamExt};
use nix_compat::{
    narinfo::{self, NarInfo},
    nixbase32,
};
use reqwest::StatusCode;
use sha2::{digest::FixedOutput, Digest, Sha256};
use tonic::async_trait;
use tracing::{debug, instrument, warn};
use tvix_castore::{
    blobservice::BlobService, directoryservice::DirectoryService, proto as castorepb, Error,
};

use crate::proto::PathInfo;

use super::PathInfoService;

/// NixHTTPPathInfoService acts as a bridge in between the Nix HTTP Binary cache
/// protocol provided by Nix binary caches such as cache.nixos.org, and the Tvix
/// Store Model.
/// It implements the [PathInfoService] trait in an interesting way:
/// Every [PathInfoService::get] fetches the .narinfo and referred NAR file,
/// inserting components into a [BlobService] and [DirectoryService], then
/// returning a [PathInfo] struct with the root.
///
/// Due to this being quite a costly operation, clients are expected to layer
/// this service with store composition, so they're only ingested once.
///
/// The client is expected to be (indirectly) using the same [BlobService] and
/// [DirectoryService], so able to fetch referred Directories and Blobs.
/// [PathInfoService::put] and [PathInfoService::nar] are not implemented and
/// return an error if called.
/// TODO: what about reading from nix-cache-info?
pub struct NixHTTPPathInfoService {
    base_url: url::Url,
    http_client: reqwest::Client,

    blob_service: Arc<dyn BlobService>,
    directory_service: Arc<dyn DirectoryService>,

    /// An optional list of [narinfo::PubKey].
    /// If set, the .narinfo files received need to have correct signature by at least one of these.
    public_keys: Option<Vec<narinfo::PubKey>>,
}

impl NixHTTPPathInfoService {
    pub fn new(
        base_url: url::Url,
        blob_service: Arc<dyn BlobService>,
        directory_service: Arc<dyn DirectoryService>,
    ) -> Self {
        Self {
            base_url,
            http_client: reqwest::Client::new(),
            blob_service,
            directory_service,

            public_keys: None,
        }
    }

    /// Configures [Self] to validate NARInfo fingerprints with the public keys passed.
    pub fn set_public_keys(&mut self, public_keys: Vec<narinfo::PubKey>) {
        self.public_keys = Some(public_keys);
    }
}

#[async_trait]
impl PathInfoService for NixHTTPPathInfoService {
    #[instrument(skip_all, err, fields(path.digest=BASE64.encode(&digest)))]
    async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
        let narinfo_url = self
            .base_url
            .join(&format!("{}.narinfo", nixbase32::encode(&digest)))
            .map_err(|e| {
                warn!(e = %e, "unable to join URL");
                io::Error::new(io::ErrorKind::InvalidInput, "unable to join url")
            })?;

        debug!(narinfo_url= %narinfo_url, "constructed NARInfo url");

        let resp = self
            .http_client
            .get(narinfo_url)
            .send()
            .await
            .map_err(|e| {
                warn!(e=%e,"unable to send NARInfo request");
                io::Error::new(
                    io::ErrorKind::InvalidInput,
                    "unable to send NARInfo request",
                )
            })?;

        // In the case of a 404, return a NotFound.
        // We also return a NotFound in case of a 403 - this is to match the behaviour as Nix,
        // when querying nix-cache.s3.amazonaws.com directly, rather than cache.nixos.org.
        if resp.status() == StatusCode::NOT_FOUND || resp.status() == StatusCode::FORBIDDEN {
            return Ok(None);
        }

        let narinfo_str = resp.text().await.map_err(|e| {
            warn!(e=%e,"unable to decode response as string");
            io::Error::new(
                io::ErrorKind::InvalidData,
                "unable to decode response as string",
            )
        })?;

        // parse the received narinfo
        let narinfo = NarInfo::parse(&narinfo_str).map_err(|e| {
            warn!(e=%e,"unable to parse response as NarInfo");
            io::Error::new(
                io::ErrorKind::InvalidData,
                "unable to parse response as NarInfo",
            )
        })?;

        // if [self.public_keys] is set, ensure there's at least one valid signature.
        if let Some(public_keys) = &self.public_keys {
            let fingerprint = narinfo.fingerprint();

            if !public_keys.iter().any(|pubkey| {
                narinfo
                    .signatures
                    .iter()
                    .any(|sig| pubkey.verify(&fingerprint, sig))
            }) {
                warn!("no valid signature found");
                Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    "no valid signature found",
                ))?;
            }
        }

        // Convert to a (sparse) PathInfo. We still need to populate the node field,
        // and for this we need to download the NAR file.
        // FUTUREWORK: Keep some database around mapping from narsha256 to
        // (unnamed) rootnode, so we can use that (and the name from the
        // StorePath) and avoid downloading the same NAR a second time.
        let pathinfo: PathInfo = (&narinfo).into();

        // create a request for the NAR file itself.
        let nar_url = self.base_url.join(narinfo.url).map_err(|e| {
            warn!(e = %e, "unable to join URL");
            io::Error::new(io::ErrorKind::InvalidInput, "unable to join url")
        })?;
        debug!(nar_url= %nar_url, "constructed NAR url");

        let resp = self
            .http_client
            .get(nar_url.clone())
            .send()
            .await
            .map_err(|e| {
                warn!(e=%e,"unable to send NAR request");
                io::Error::new(io::ErrorKind::InvalidInput, "unable to send NAR request")
            })?;

        // if the request is not successful, return an error.
        if !resp.status().is_success() {
            return Err(Error::StorageError(format!(
                "unable to retrieve NAR at {}, status {}",
                nar_url,
                resp.status()
            )));
        }

        // get an AsyncRead of the response body.
        let async_r = tokio_util::io::StreamReader::new(resp.bytes_stream().map_err(|e| {
            let e = e.without_url();
            warn!(e=%e, "failed to get response body");
            io::Error::new(io::ErrorKind::BrokenPipe, e.to_string())
        }));
        let sync_r = tokio_util::io::SyncIoBridge::new(async_r);

        // handle decompression, by wrapping the reader.
        let sync_r: Box<dyn BufRead + Send> = match narinfo.compression {
            Some("none") => Box::new(sync_r),
            Some("xz") => Box::new(io::BufReader::new(xz2::read::XzDecoder::new(sync_r))),
            Some(comp) => {
                return Err(Error::InvalidRequest(
                    format!("unsupported compression: {}", comp).to_string(),
                ))
            }
            None => {
                return Err(Error::InvalidRequest(
                    "unsupported compression: bzip2".to_string(),
                ))
            }
        };

        let res = tokio::task::spawn_blocking({
            let blob_service = self.blob_service.clone();
            let directory_service = self.directory_service.clone();
            move || -> io::Result<_> {
                // Wrap the reader once more, so we can calculate NarSize and NarHash
                let mut sync_r = io::BufReader::new(NarReader::from(sync_r));
                let root_node = crate::nar::read_nar(&mut sync_r, blob_service, directory_service)?;

                let (_, nar_hash, nar_size) = sync_r.into_inner().into_inner();

                Ok((root_node, nar_hash, nar_size))
            }
        })
        .await
        .unwrap();

        match res {
            Ok((root_node, nar_hash, nar_size)) => {
                // ensure the ingested narhash and narsize do actually match.
                if narinfo.nar_size != nar_size {
                    warn!(
                        narinfo.nar_size = narinfo.nar_size,
                        http.nar_size = nar_size,
                        "NARSize mismatch"
                    );
                    Err(io::Error::new(
                        io::ErrorKind::InvalidData,
                        "NarSize mismatch".to_string(),
                    ))?;
                } else if narinfo.nar_hash != nar_hash {
                    warn!(
                        narinfo.nar_hash = BASE64.encode(&narinfo.nar_hash),
                        http.nar_hash = BASE64.encode(&nar_hash),
                        "NarHash mismatch"
                    );
                    Err(io::Error::new(
                        io::ErrorKind::InvalidData,
                        "NarHash mismatch".to_string(),
                    ))?;
                }

                Ok(Some(PathInfo {
                    node: Some(castorepb::Node {
                        // set the name of the root node to the digest-name of the store path.
                        node: Some(
                            root_node.rename(narinfo.store_path.to_string().to_owned().into()),
                        ),
                    }),
                    references: pathinfo.references,
                    narinfo: pathinfo.narinfo,
                }))
            }
            Err(e) => Err(e.into()),
        }
    }

    #[instrument(skip_all, fields(path_info=?_path_info))]
    async fn put(&self, _path_info: PathInfo) -> Result<PathInfo, Error> {
        Err(Error::InvalidRequest(
            "put not supported for this backend".to_string(),
        ))
    }

    #[instrument(skip_all, fields(root_node=?root_node))]
    async fn calculate_nar(
        &self,
        root_node: &castorepb::node::Node,
    ) -> Result<(u64, [u8; 32]), Error> {
        Err(Error::InvalidRequest(
            "calculate_nar not supported for this backend".to_string(),
        ))
    }

    fn list(&self) -> Pin<Box<dyn Stream<Item = Result<PathInfo, Error>> + Send>> {
        Box::pin(futures::stream::once(async {
            Err(Error::InvalidRequest(
                "list not supported for this backend".to_string(),
            ))
        }))
    }
}

/// Small helper reader implementing [std::io::Read].
/// It can be used to wrap another reader, counts the number of bytes read
/// and the sha256 digest of the contents.
struct NarReader<R: Read> {
    r: R,

    sha256: sha2::Sha256,
    bytes_read: u64,
}

impl<R: Read> NarReader<R> {
    pub fn from(inner: R) -> Self {
        Self {
            r: inner,
            sha256: Sha256::new(),
            bytes_read: 0,
        }
    }

    /// Returns the (remaining) inner reader, the sha256 digest and the number of bytes read.
    pub fn into_inner(self) -> (R, [u8; 32], u64) {
        (self.r, self.sha256.finalize_fixed().into(), self.bytes_read)
    }
}

impl<R: Read> Read for NarReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.r.read(buf).map(|n| {
            self.bytes_read += n as u64;
            self.sha256.write_all(&buf[..n]).unwrap();
            n
        })
    }
}
