use crate::header::{Directory, Entry, FileMetadata};
use crate::private::Sealed;
use crate::{cfg_fs, cfg_integrity, split_path};
use async_trait::async_trait;
use pin_project::pin_project;
use std::io::{Cursor, SeekFrom};
use std::pin::Pin;
use std::task::{Context, Poll};
use tokio::io::{self, AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt, Take};

cfg_fs! {
  use std::path::{Path, PathBuf};
  use tokio::fs::File as TokioFile;
}

cfg_integrity! {
  use sha2::digest::Digest;
  use sha2::Sha256;
}

/// Generic asar archive reader.
///
/// It supports any reader that implements [`AsyncRead`], [`AsyncSeek`] and
/// [`Unpin`], and adds more methods if the reader implements [`Send`] or
/// ([`Local`](LocalDuplicable))[`Duplicable`].
#[derive(Debug)]
pub struct Archive<R: AsyncRead + AsyncSeek + Unpin> {
  pub(crate) offset: u64,
  pub(crate) header: Directory,
  pub(crate) reader: R,
}

/// Checks if a file is in asar format by reading and checking first 16 bytes.
///
/// Returns `Some(header_len)` if it is an asar archive, or `None` if it isn't.
pub async fn check_asar_format(reader: &mut (impl AsyncRead + Unpin)) -> io::Result<Option<u32>> {
  let [mut four, mut i1, mut i2, mut header_len] = [0; 4];
  for x in [&mut four, &mut i1, &mut i2, &mut header_len] {
    *x = reader.read_u32_le().await?;
  }

  let padding = match header_len % 4 {
    0 => 0,
    r => 4 - r,
  };

  let i1_e = header_len + padding + 8;
  let i2_e = header_len + padding + 4;

  if four == 4 && i1 == i1_e && i2 == i2_e {
    Ok(Some(header_len))
  } else {
    Ok(None)
  }
}

impl<R: AsyncRead + AsyncSeek + Unpin> Archive<R> {
  /// Parses an asar archive into `Archive`.
  pub async fn new(mut reader: R) -> io::Result<Self> {
    let header_len = check_asar_format(&mut reader)
      .await?
      .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "file format check failed"))?;

    let mut header_bytes = vec![0; header_len as _];
    reader.read_exact(&mut header_bytes).await?;

    let header = serde_json::from_slice(&header_bytes).map_err(io::Error::from)?;
    let offset = match header_len % 4 {
      0 => header_len + 16,
      r => header_len + 16 + 4 - r,
    } as u64;

    Ok(Self {
      offset,
      header,
      reader,
    })
  }

  /// Returns a reference to its inner reader.
  pub fn reader(&self) -> &R {
    &self.reader
  }

  /// Returns mutable reference to its inner reader.
  ///
  /// It is mostly OK to seek the reader's cursor, since every time accessing
  /// its file will reset the cursor to the file's position. However, write
  /// access will compromise [`Archive`]'s functionality. Use with great care!
  pub fn reader_mut(&mut self) -> &mut R {
    &mut self.reader
  }

  /// Drops the inner state and returns the reader.
  pub fn into_reader(self) -> R {
    self.reader
  }
}

cfg_fs! {
  impl Archive<DuplicableFile> {
    /// Opens a file and parses it into [`Archive`].
    pub async fn new_from_file(path: impl Into<PathBuf>) -> io::Result<Self> {
      Self::new(DuplicableFile::open(path).await?).await
    }
  }
}

impl<R: AsyncRead + AsyncSeek + Unpin> Archive<R> {
  /// Returns a file from the archive by taking mutable reference.
  pub async fn get(&mut self, path: &str) -> io::Result<File<&mut R>> {
    let entry = self.header.search_segments(&split_path(path));
    match entry {
      Some(Entry::File(metadata)) => {
        (self.reader)
          .seek(SeekFrom::Start(self.offset + metadata.offset()?))
          .await?;
        Ok(File {
          offset: self.offset,
          metadata: metadata.clone(),
          content: (&mut self.reader).take(metadata.size),
        })
      }
      Some(Entry::Directory(_)) => Err(io::Error::from_raw_os_error(libc::EISDIR)),
      None => Err(io::ErrorKind::NotFound.into()),
    }
  }

  /// Returns the entry ("metadata") of specified path.
  pub fn get_entry(&self, path: &str) -> Option<&Entry> {
    self.header.search_segments(&split_path(path))
  }
}

macro_rules! impl_get_owned {
  (
    $(#[$attr:ident $($args:tt)*])*
    $get_owned:ident,
    $duplicate:ident $(,)?
  ) => {
    impl<R: AsyncRead + AsyncSeek + $duplicate + Unpin> Archive<R> {
      $(#[$attr $($args)*])*
      pub async fn $get_owned(&self, path: &str) -> io::Result<File<R>> {
        let entry = self.header.search_segments(&split_path(path));
        match entry {
          Some(Entry::File(metadata)) => {
            let mut file = self.reader.duplicate().await?;
            let seek_from = SeekFrom::Start(self.offset + metadata.offset()?);
            file.seek(seek_from).await?;
            Ok(File {
              offset: self.offset,
              metadata: metadata.clone(),
              content: file.take(metadata.size),
            })
          }
          Some(_) => Err(io::Error::from_raw_os_error(libc::EISDIR)),
          None => Err(io::Error::from_raw_os_error(libc::ENOENT)),
        }
      }
    }
  }
}

impl_get_owned! {
  /// Returns a file from the archive by duplicating the inner reader.
  ///
  /// Contrary to [`Archive::read`], it allows multiple read access over a single
  /// archive by creating a new file handle for every file. Useful when building a
  /// virtual file system like how Electron does.
  get_owned,
  Duplicable,
}

impl_get_owned! {
  /// Returns a file from the archive by duplicating the inner reader, without `Sync`.
  ///
  /// See [`Archive::read_owned`] for more information.
  get_owned_local,
  LocalDuplicable,
}

cfg_fs! {
  impl<R: AsyncRead + AsyncSeek + Send + Unpin> Archive<R> {
    /// Extracts the archive to a folder.
    pub async fn extract(&mut self, path: impl AsRef<Path>) -> io::Result<()> {
      let path = path.as_ref();
      for (name, entry) in self.header.files.iter() {
        crate::extract::extract_entry(&mut self.reader, self.offset, name, entry, path).await?;
      }
      Ok(())
    }
  }

  impl<R: AsyncRead + AsyncSeek + Unpin> Archive<R> {
    /// Extracts the archive to a folder.
    ///
    /// This method is intended for `R: !Send`. Otherwise, use
    /// [`Archive::extract`] instead.
    pub async fn extract_local(&mut self, path: impl AsRef<Path>) -> io::Result<()> {
      let path = path.as_ref();
      for (name, entry) in self.header.files.iter() {
        crate::extract::extract_entry_local(&mut self.reader, self.offset, name, entry, path).await?;
      }
      Ok(())
    }
  }
}

/// File from an asar archive.
#[pin_project]
pub struct File<R: AsyncRead + AsyncSeek + Unpin> {
  pub(crate) offset: u64,
  pub(crate) metadata: FileMetadata,
  #[pin]
  pub(crate) content: Take<R>,
}

impl<R: AsyncRead + AsyncSeek + Unpin> File<R> {
  /// Gets the metadata of the file.
  pub fn metadata(&self) -> &FileMetadata {
    &self.metadata
  }

  cfg_integrity! {
    pub async fn check_integrity(&mut self) -> io::Result<bool> {
      if let Some(integrity) = &self.metadata.integrity {
        let block_size = integrity.block_size;
        let mut block = Vec::with_capacity(block_size as _);
        let mut global_state = Sha256::new();
        let mut size = 0;

        for block_hash in integrity.blocks.iter() {
          let read_size = (&mut self.content)
            .take(block_size as _)
            .read_to_end(&mut block)
            .await?;
          if read_size == 0 || *Sha256::digest(&block) != **block_hash {
            self.rewind().await?;
            return Ok(false);
          }
          size += read_size;
          global_state.update(&block);
          block.clear();
        }
        if self.metadata.size != size as u64 || *global_state.finalize() != *integrity.hash {
          self.rewind().await?;
          return Ok(false);
        }

        self.rewind().await?;
      }
      Ok(true)
    }
  }
}

impl<R: AsyncRead + AsyncSeek + Unpin> AsyncRead for File<R> {
  fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut io::ReadBuf<'_>,
  ) -> Poll<io::Result<()>> {
    self.project().content.poll_read(cx, buf)
  }
}

impl<R: AsyncRead + AsyncSeek + Unpin> AsyncSeek for File<R> {
  fn start_seek(mut self: Pin<&mut Self>, position: SeekFrom) -> io::Result<()> {
    let current_relative_pos = self.metadata.size - self.content.limit();
    let offset = self.offset + self.metadata.offset()?;
    let absolute_pos = match position {
      SeekFrom::Start(pos) => SeekFrom::Start(offset + self.metadata.size.min(pos)),
      SeekFrom::Current(pos) if -pos as u64 > current_relative_pos => {
        return Err(io::Error::from_raw_os_error(libc::EINVAL))
      }
      SeekFrom::Current(pos) => {
        let relative_pos = pos.min((self.metadata.size - current_relative_pos) as i64);
        SeekFrom::Current(relative_pos)
      }
      SeekFrom::End(pos) if pos > 0 => SeekFrom::Start(offset + self.metadata.size),
      SeekFrom::End(pos) if -pos as u64 > self.metadata.size => {
        return Err(io::Error::from_raw_os_error(libc::EINVAL))
      }
      SeekFrom::End(pos) => SeekFrom::Start(offset + self.metadata.size - (-pos as u64)),
    };
    Pin::new(self.content.get_mut()).start_seek(absolute_pos)
  }

  fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
    let result = Pin::new(self.content.get_mut()).poll_complete(cx);
    match result {
      Poll::Ready(Ok(result)) => {
        let new_relative_pos = result - self.offset - self.metadata.offset()?;
        let new_limit = self.metadata.size - new_relative_pos;
        self.content.set_limit(new_limit);
        Poll::Ready(Ok(new_relative_pos))
      }
      other => other,
    }
  }
}

/// Ability to duplicate asynchronously.
///
/// [`Duplicable`] is like `Clone` with `async` and [`io::Result`]. However,
/// resulting object **must not share common state** with the original one.
///
/// This trait is currently for internal use only. You should not rely on
/// its implementations.
#[async_trait]
pub trait Duplicable: Sealed + Sized {
  async fn duplicate(&self) -> io::Result<Self>;
}

#[async_trait]
impl<T: Clone + Sync> Duplicable for Cursor<T> {
  async fn duplicate(&self) -> io::Result<Self> {
    Ok(self.clone())
  }
}

/// Ability to duplicate asynchronously without `Sync`.
///
/// See [`Duplicable`] for more information.
#[async_trait(?Send)]
pub trait LocalDuplicable: Sealed + Sized {
  async fn duplicate(&self) -> io::Result<Self>;
}

#[async_trait(?Send)]
impl<T: Clone> LocalDuplicable for Cursor<T> {
  async fn duplicate(&self) -> io::Result<Self> {
    Ok(self.clone())
  }
}

cfg_fs! {
  /// [`TokioFile`] with path that implements [`Duplicable`].
  ///
  /// A new file handle with different internal state cannot be created from an
  /// existing one. [`TokioFile::try_clone`] shares its internal cursor,
  /// and thus cannot be [`Duplicable`]. `TokioFileWithPath`, however, opens a
  /// new file handle every time [`Duplicable::duplicate`] is called.
  #[pin_project]
  pub struct DuplicableFile {
    #[pin]
    inner: TokioFile,
    path: PathBuf,
  }

  impl DuplicableFile {
    pub async fn open(path: impl Into<PathBuf>) -> io::Result<Self> {
      let path = path.into();
      let inner = TokioFile::open(&path).await?;
      Ok(Self { inner, path })
    }

    pub async fn path(&self) -> &Path {
      &self.path
    }

    pub fn into_inner(self) -> (TokioFile, PathBuf) {
      (self.inner, self.path)
    }

    pub async fn rename(&mut self, new_path: impl Into<PathBuf>) -> io::Result<()> {
      let new_path = new_path.into();
      tokio::fs::rename(&self.path, &new_path).await?;
      self.path = new_path;
      Ok(())
    }
  }

  impl AsyncRead for DuplicableFile {
    fn poll_read(
      self: Pin<&mut Self>,
      cx: &mut Context<'_>,
      buf: &mut io::ReadBuf<'_>,
    ) -> Poll<std::io::Result<()>> {
      self.project().inner.poll_read(cx, buf)
    }
  }

  impl AsyncSeek for DuplicableFile {
    fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> std::io::Result<()> {
      self.project().inner.start_seek(position)
    }

    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<std::io::Result<u64>> {
      self.project().inner.poll_complete(cx)
    }
  }

  #[async_trait]
  impl Duplicable for DuplicableFile {
    async fn duplicate(&self) -> io::Result<Self> {
      Ok(Self {
        inner: TokioFile::open(&self.path).await?,
        path: self.path.clone(),
      })
    }
  }

  #[async_trait(?Send)]
  impl LocalDuplicable for DuplicableFile {
    async fn duplicate(&self) -> io::Result<Self> {
      Ok(Self {
        inner: TokioFile::open(&self.path).await?,
        path: self.path.clone(),
      })
    }
  }
}