// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

/*! I/O helpers. */

use {
    crate::{
        error::{DebianError, Result},
        repository::release::ChecksumType,
    },
    async_compression::futures::bufread::{
        BzDecoder, BzEncoder, GzipDecoder, GzipEncoder, LzmaDecoder, LzmaEncoder, XzDecoder,
        XzEncoder,
    },
    async_trait::async_trait,
    futures::{AsyncBufRead, AsyncRead, AsyncWrite},
    pgp::crypto::Hasher,
    pgp_cleartext::CleartextHasher,
    pin_project::pin_project,
    std::{
        collections::HashMap,
        fmt::Formatter,
        pin::Pin,
        task::{Context, Poll},
    },
};

/// Represents a content digest.
#[derive(Clone, Eq, PartialEq, PartialOrd)]
pub enum ContentDigest {
    /// An MD5 digest.
    Md5(Vec<u8>),
    /// A SHA-1 digest.
    Sha1(Vec<u8>),
    /// A SHA-256 digest.
    Sha256(Vec<u8>),
}

impl std::fmt::Debug for ContentDigest {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Md5(data) => write!(f, "Md5({})", hex::encode(data)),
            Self::Sha1(data) => write!(f, "Sha1({})", hex::encode(data)),
            Self::Sha256(data) => write!(f, "Sha256({})", hex::encode(data)),
        }
    }
}

impl ContentDigest {
    /// Create a new MD5 instance by parsing a hex digest.
    pub fn md5_hex(digest: &str) -> Result<Self> {
        Self::from_hex_digest(ChecksumType::Md5, digest)
    }

    /// Create a new SHA-1 instance by parsing a hex digest.
    pub fn sha1_hex(digest: &str) -> Result<Self> {
        Self::from_hex_digest(ChecksumType::Sha1, digest)
    }

    /// Create a new SHA-256 instance by parsing a hex digest.
    pub fn sha256_hex(digest: &str) -> Result<Self> {
        Self::from_hex_digest(ChecksumType::Sha256, digest)
    }

    /// Obtain an instance by parsing a hex string as a [ChecksumType].
    pub fn from_hex_digest(checksum: ChecksumType, digest: &str) -> Result<Self> {
        let digest = hex::decode(digest)
            .map_err(|e| DebianError::ContentDigestBadHex(digest.to_string(), e))?;

        Ok(match checksum {
            ChecksumType::Md5 => Self::Md5(digest),
            ChecksumType::Sha1 => Self::Sha1(digest),
            ChecksumType::Sha256 => Self::Sha256(digest),
        })
    }

    /// Create a new hasher matching for the type of this digest.
    pub fn new_hasher(&self) -> Box<dyn Hasher + Send> {
        Box::new(match self {
            Self::Md5(_) => CleartextHasher::md5(),
            Self::Sha1(_) => CleartextHasher::sha1(),
            Self::Sha256(_) => CleartextHasher::sha256(),
        })
    }

    /// Obtain the digest bytes for this content digest.
    pub fn digest_bytes(&self) -> &[u8] {
        match self {
            Self::Md5(x) => x,
            Self::Sha1(x) => x,
            Self::Sha256(x) => x,
        }
    }

    /// Obtain the hex encoded content digest.
    pub fn digest_hex(&self) -> String {
        hex::encode(self.digest_bytes())
    }

    /// Obtain the [ChecksumType] for this digest.
    pub fn checksum_type(&self) -> ChecksumType {
        match self {
            Self::Md5(_) => ChecksumType::Md5,
            Self::Sha1(_) => ChecksumType::Sha1,
            Self::Sha256(_) => ChecksumType::Sha256,
        }
    }

    /// Obtain the name of the field in `[In]Release` files that holds this digest type.
    ///
    /// This also corresponds to the directory name for `by-hash` paths.
    pub fn release_field_name(&self) -> &'static str {
        self.checksum_type().field_name()
    }
}

/// Compression format used by Debian primitives.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub enum Compression {
    /// No compression (no extension).
    None,

    /// XZ compression (.xz extension).
    Xz,

    /// Gzip compression (.gz extension).
    Gzip,

    /// Bzip2 compression (.bz2 extension).
    Bzip2,

    /// LZMA compression (.lzma extension).
    Lzma,
}

impl Compression {
    /// Filename extension for files compressed in this format.
    pub fn extension(&self) -> &'static str {
        match self {
            Self::None => "",
            Self::Xz => ".xz",
            Self::Gzip => ".gz",
            Self::Bzip2 => ".bz2",
            Self::Lzma => ".lzma",
        }
    }

    /// The default retrieval preference order for client.
    pub fn default_preferred_order() -> impl Iterator<Item = Compression> {
        [Self::Xz, Self::Lzma, Self::Gzip, Self::Bzip2, Self::None].into_iter()
    }
}

/// Wrap a reader with transparent decompression.
pub async fn read_decompressed(
    stream: Pin<Box<dyn AsyncBufRead + Send>>,
    compression: Compression,
) -> Result<Pin<Box<dyn AsyncRead + Send>>> {
    Ok(match compression {
        Compression::None => Box::pin(stream),
        Compression::Gzip => Box::pin(GzipDecoder::new(stream)),
        Compression::Xz => Box::pin(XzDecoder::new(stream)),
        Compression::Bzip2 => Box::pin(BzDecoder::new(stream)),
        Compression::Lzma => Box::pin(LzmaDecoder::new(stream)),
    })
}

/// Wrap a reader with transparent compression.
pub fn read_compressed<'a>(
    stream: impl AsyncBufRead + Send + 'a,
    compression: Compression,
) -> Pin<Box<dyn AsyncRead + Send + 'a>> {
    match compression {
        Compression::None => Box::pin(stream),
        Compression::Gzip => Box::pin(GzipEncoder::new(stream)),
        Compression::Xz => Box::pin(XzEncoder::new(stream)),
        Compression::Bzip2 => Box::pin(BzEncoder::new(stream)),
        Compression::Lzma => Box::pin(LzmaEncoder::new(stream)),
    }
}

/// Drain content from a reader to a black hole.
pub async fn drain_reader(reader: impl AsyncRead) -> std::io::Result<u64> {
    let mut sink = futures::io::sink();
    futures::io::copy(reader, &mut sink).await
}

/// An adapter for [AsyncRead] streams that validates source size and digest.
///
/// Validation only occurs once the expected source size bytes have been read.
///
/// If the reader consumes less than the expected number of bytes, no validation
/// occurs and incorrect data could have been read. Therefore it is **strongly recommended**
/// for readers to drain this reader. e.g. by using [drain_reader()].
#[pin_project]
pub struct ContentValidatingReader<R> {
    hasher: Option<Box<dyn pgp::crypto::Hasher + Send>>,
    expected_size: u64,
    expected_digest: ContentDigest,
    #[pin]
    source: R,
    bytes_read: u64,
}

impl<R> ContentValidatingReader<R> {
    /// Create a new instance bound to a source and having expected size and content digest.
    pub fn new(source: R, expected_size: u64, expected_digest: ContentDigest) -> Self {
        Self {
            hasher: Some(expected_digest.new_hasher()),
            expected_size,
            expected_digest,
            source,
            bytes_read: 0,
        }
    }
}

impl<R> AsyncRead for ContentValidatingReader<R>
where
    R: AsyncRead + Unpin,
{
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<std::io::Result<usize>> {
        let mut this = self.project();

        match this.source.as_mut().poll_read(cx, buf) {
            Poll::Ready(Ok(size)) => {
                if size > 0 {
                    if let Some(hasher) = this.hasher.as_mut() {
                        hasher.update(&buf[0..size]);
                    } else {
                        panic!("hasher destroyed prematurely");
                    }

                    *this.bytes_read += size as u64;
                }

                match this.bytes_read.cmp(&this.expected_size) {
                    std::cmp::Ordering::Equal => {
                        if let Some(hasher) = this.hasher.take() {
                            let got_digest = hasher.finish();

                            if got_digest != this.expected_digest.digest_bytes() {
                                return Poll::Ready(Err(std::io::Error::new(
                                    std::io::ErrorKind::Other,
                                    format!(
                                        "digest mismatch of retrieved content: expected {}, got {}",
                                        this.expected_digest.digest_hex(),
                                        hex::encode(got_digest)
                                    ),
                                )));
                            }
                        }
                    }
                    std::cmp::Ordering::Greater => {
                        return Poll::Ready(Err(std::io::Error::new(
                            std::io::ErrorKind::Other,
                            format!(
                                "extra bytes read: expected {}; got {}",
                                this.expected_size, this.bytes_read
                            ),
                        )));
                    }
                    std::cmp::Ordering::Less => {}
                }

                Poll::Ready(Ok(size))
            }
            res => res,
        }
    }
}

/// Holds multiple flavors of content digests.
#[derive(Clone, Debug)]
pub struct MultiContentDigest {
    pub md5: ContentDigest,
    pub sha1: ContentDigest,
    pub sha256: ContentDigest,
}

impl MultiContentDigest {
    /// Whether this digest matches another one.
    pub fn matches_digest(&self, other: &ContentDigest) -> bool {
        match other {
            ContentDigest::Md5(_) => &self.md5 == other,
            ContentDigest::Sha1(_) => &self.sha1 == other,
            ContentDigest::Sha256(_) => &self.sha256 == other,
        }
    }

    /// Obtain the [ContentDigest] for a given [ChecksumType].
    pub fn digest_from_checksum(&self, checksum: ChecksumType) -> &ContentDigest {
        match checksum {
            ChecksumType::Md5 => &self.md5,
            ChecksumType::Sha1 => &self.sha1,
            ChecksumType::Sha256 => &self.sha256,
        }
    }

    /// Obtain an iterator of [ContentDigest] in this instance.
    pub fn iter_digests(&self) -> impl Iterator<Item = &ContentDigest> + '_ {
        [&self.md5, &self.sha1, &self.sha256].into_iter()
    }
}

/// A content digester that simultaneously computes multiple digest types.
pub struct MultiDigester {
    md5: Box<dyn Hasher + Send>,
    sha1: Box<dyn Hasher + Send>,
    sha256: Box<dyn Hasher + Send>,
}

impl Default for MultiDigester {
    fn default() -> Self {
        Self {
            md5: Box::new(CleartextHasher::md5()),
            sha1: Box::new(CleartextHasher::sha1()),
            sha256: Box::new(CleartextHasher::sha256()),
        }
    }
}

impl MultiDigester {
    /// Write content into the digesters.
    pub fn update(&mut self, data: &[u8]) {
        self.md5.update(data);
        self.sha1.update(data);
        self.sha256.update(data);
    }

    /// Finish digesting content.
    ///
    /// Consumes the instance and returns a [MultiContentDigest] holding all the digests.
    pub fn finish(self) -> MultiContentDigest {
        MultiContentDigest {
            md5: ContentDigest::Md5(self.md5.finish()),
            sha1: ContentDigest::Sha1(self.sha1.finish()),
            sha256: ContentDigest::Sha256(self.sha256.finish()),
        }
    }
}

/// An [AsyncRead] stream adapter that computes multiple [ContentDigest] as data is read.
#[pin_project]
pub struct DigestingReader<R> {
    digester: MultiDigester,
    #[pin]
    source: R,
}

impl<R> DigestingReader<R> {
    /// Construct a new instance from a source reader.
    pub fn new(source: R) -> Self {
        Self {
            digester: MultiDigester::default(),
            source,
        }
    }

    /// Finish the stream.
    ///
    /// Returns the source reader and a resolved [MultiContentDigest].
    pub fn finish(self) -> (R, MultiContentDigest) {
        (self.source, self.digester.finish())
    }
}

impl<R> AsyncRead for DigestingReader<R>
where
    R: AsyncRead + Unpin,
{
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<std::io::Result<usize>> {
        let mut this = self.project();

        match this.source.as_mut().poll_read(cx, buf) {
            Poll::Ready(Ok(size)) => {
                if size > 0 {
                    this.digester.update(&buf[0..size]);
                }

                Poll::Ready(Ok(size))
            }
            res => res,
        }
    }
}

/// An [AsyncWrite] stream adapter that computes multiple [ContentDigest] as data is written.
#[pin_project]
pub struct DigestingWriter<W> {
    digester: MultiDigester,
    #[pin]
    dest: W,
}

impl<W> DigestingWriter<W> {
    /// Construct a new instance from a destination writer.
    pub fn new(dest: W) -> Self {
        Self {
            digester: MultiDigester::default(),
            dest,
        }
    }

    /// Finish the stream.
    ///
    /// Returns the destination writer and a resolved [MultiContentDigest].
    pub fn finish(self) -> (W, MultiContentDigest) {
        (self.dest, self.digester.finish())
    }
}

impl<W> AsyncWrite for DigestingWriter<W>
where
    W: AsyncWrite + Unpin,
{
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<std::io::Result<usize>> {
        let mut this = self.project();

        match this.dest.as_mut().poll_write(cx, buf) {
            Poll::Ready(Ok(size)) => {
                if size > 0 {
                    this.digester.update(&buf[0..size]);
                }

                Poll::Ready(Ok(size))
            }
            res => res,
        }
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<std::io::Result<()>> {
        self.project().dest.as_mut().poll_flush(cx)
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<std::io::Result<()>> {
        self.project().dest.as_mut().poll_close(cx)
    }
}

/// Generic mechanism for obtaining content at a given path.
///
/// This trait is used to define a generic mechanism for resolving content given
/// a lookup key/path.
///
/// Implementations only need to implement `get_path()`. The other members have
/// default implementations that should do the correct thing by default.
#[async_trait]
pub trait DataResolver: Sync {
    /// Get the content of a relative path as an async reader.
    ///
    /// This obtains a reader for path data and returns the raw data without any
    /// decoding applied.
    async fn get_path(&self, path: &str) -> Result<Pin<Box<dyn AsyncRead + Send>>>;

    /// Obtain a reader that performs content integrity checking.
    ///
    /// Because content digests can only be computed once all content is read, the reader
    /// emits data as it is streaming but only compares the cryptographic digest once all
    /// data has been read. If there is a content digest mismatch, an error will be raised
    /// once the final byte is read.
    ///
    /// Validation only occurs if the stream is read to completion. Failure to read the
    /// entire stream could result in reading of unexpected content.
    async fn get_path_with_digest_verification(
        &self,
        path: &str,
        expected_size: u64,
        expected_digest: ContentDigest,
    ) -> Result<Pin<Box<dyn AsyncRead + Send>>> {
        Ok(Box::pin(ContentValidatingReader::new(
            self.get_path(path).await?,
            expected_size,
            expected_digest,
        )))
    }

    /// Get the content of a relative path with decompression transparently applied.
    async fn get_path_decoded(
        &self,
        path: &str,
        compression: Compression,
    ) -> Result<Pin<Box<dyn AsyncRead + Send>>> {
        read_decompressed(
            Box::pin(futures::io::BufReader::new(self.get_path(path).await?)),
            compression,
        )
        .await
    }

    /// Like [Self::get_path_decoded()] but also perform content integrity verification.
    ///
    /// The digest is matched against the original fetched content, before decompression.
    async fn get_path_decoded_with_digest_verification(
        &self,
        path: &str,
        compression: Compression,
        expected_size: u64,
        expected_digest: ContentDigest,
    ) -> Result<Pin<Box<dyn AsyncRead + Send>>> {
        let reader = self
            .get_path_with_digest_verification(path, expected_size, expected_digest)
            .await?;

        read_decompressed(Box::pin(futures::io::BufReader::new(reader)), compression).await
    }
}

/// A [DataResolver] that maintains a path translation table and transparently redirects lookups.
pub struct PathMappingDataResolver<R> {
    source: R,
    path_map: HashMap<String, String>,
}

impl<R: DataResolver + Send> PathMappingDataResolver<R> {
    /// Construct a new instance that forwards to a source [DataResolver].
    pub fn new(source: R) -> Self {
        Self {
            source,
            path_map: HashMap::default(),
        }
    }

    /// Register a mapping of 1 path to another.
    ///
    /// Future looks up `from_path` will resolve to `to_path`.
    pub fn add_path_map(&mut self, from_path: impl ToString, to_path: impl ToString) {
        self.path_map
            .insert(from_path.to_string(), to_path.to_string());
    }
}

#[async_trait]
impl<R: DataResolver + Send> DataResolver for PathMappingDataResolver<R> {
    async fn get_path(&self, path: &str) -> Result<Pin<Box<dyn AsyncRead + Send>>> {
        self.source
            .get_path(self.path_map.get(path).map(|s| s.as_str()).unwrap_or(path))
            .await
    }
}