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    use crate::core::PackageId;
    use crate::sources::registry::{LoadResponse, MaybeLock, RegistryConfig, RegistryData};
    use crate::util::errors::CargoResult;
    use crate::util::{Config, Filesystem};
    use cargo_util::{paths, Sha256};
    use std::fs::File;
    use std::io::SeekFrom;
    use std::io::{self, prelude::*};
    use std::path::Path;
    use std::task::Poll;

    /// A local registry is a registry that lives on the filesystem as a set of
    /// `.crate` files with an `index` directory in the same format as a remote
    /// registry.
    pub struct LocalRegistry<'cfg> {
        index_path: Filesystem,
        root: Filesystem,
        src_path: Filesystem,
        config: &'cfg Config,
        updated: bool,
        quiet: bool,
    }

    impl<'cfg> LocalRegistry<'cfg> {
        pub fn new(root: &Path, config: &'cfg Config, name: &str) -> LocalRegistry<'cfg> {
            LocalRegistry {
                src_path: config.registry_source_path().join(name),
                index_path: Filesystem::new(root.join("index")),
                root: Filesystem::new(root.to_path_buf()),
                config,
                updated: false,
                quiet: false,
            }
        }
    }

    impl<'cfg> RegistryData for LocalRegistry<'cfg> {
        fn prepare(&self) -> CargoResult<()> {
            Ok(())
        }

        fn index_path(&self) -> &Filesystem {
            &self.index_path
        }

        fn assert_index_locked<'a>(&self, path: &'a Filesystem) -> &'a Path {
            // Note that the `*_unlocked` variant is used here since we're not
            // modifying the index and it's required to be externally synchronized.
            path.as_path_unlocked()
        }

        fn load(
            &mut self,
            root: &Path,
            path: &Path,
            _index_version: Option<&str>,
        ) -> Poll<CargoResult<LoadResponse>> {
            if self.updated {
                let raw_data = match paths::read_bytes(&root.join(path)) {
                    Err(e)
                        if e.downcast_ref::<io::Error>()
                            .map_or(false, |ioe| ioe.kind() == io::ErrorKind::NotFound) =>
                    {
                        return Poll::Ready(Ok(LoadResponse::NotFound));
                    }
                    r => r,
                }?;
                Poll::Ready(Ok(LoadResponse::Data {
                    raw_data,
                    index_version: None,
                }))
            } else {
                Poll::Pending
            }
        }

        fn config(&mut self) -> Poll<CargoResult<Option<RegistryConfig>>> {
            // Local registries don't have configuration for remote APIs or anything
            // like that
            Poll::Ready(Ok(None))
        }

        fn block_until_ready(&mut self) -> CargoResult<()> {
            if self.updated {
                return Ok(());
            }
            // Nothing to update, we just use what's on disk. Verify it actually
            // exists though. We don't use any locks as we're just checking whether
            // these directories exist.
            let root = self.root.clone().into_path_unlocked();
            if !root.is_dir() {
                anyhow::bail!("local registry path is not a directory: {}", root.display());
            }
            let index_path = self.index_path.clone().into_path_unlocked();
            if !index_path.is_dir() {
                anyhow::bail!(
                    "local registry index path is not a directory: {}",
                    index_path.display()
                );
            }
            self.updated = true;
            Ok(())
        }

        fn invalidate_cache(&mut self) {
            // Local registry has no cache - just reads from disk.
        }

        fn set_quiet(&mut self, _quiet: bool) {
            self.quiet = true;
        }

        fn is_updated(&self) -> bool {
            self.updated
        }

        fn download(&mut self, pkg: PackageId, checksum: &str) -> CargoResult<MaybeLock> {
            let crate_file = format!("{}-{}.crate", pkg.name(), pkg.version());

            // Note that the usage of `into_path_unlocked` here is because the local
            // crate files here never change in that we're not the one writing them,
            // so it's not our responsibility to synchronize access to them.
            let path = self.root.join(&crate_file).into_path_unlocked();
            let mut crate_file = paths::open(&path)?;

            // If we've already got an unpacked version of this crate, then skip the
            // checksum below as it is in theory already verified.
            let dst = format!("{}-{}", pkg.name(), pkg.version());
            if self.src_path.join(dst).into_path_unlocked().exists() {
                return Ok(MaybeLock::Ready(crate_file));
            }

            if !self.quiet {
                self.config.shell().status("Unpacking", pkg)?;
            }

            // We don't actually need to download anything per-se, we just need to
            // verify the checksum matches the .crate file itself.
            let actual = Sha256::new().update_file(&crate_file)?.finish_hex();
            if actual != checksum {
                anyhow::bail!("failed to verify the checksum of `{}`", pkg)
            }

            crate_file.seek(SeekFrom::Start(0))?;

            Ok(MaybeLock::Ready(crate_file))
        }

        fn finish_download(
            &mut self,
            _pkg: PackageId,
            _checksum: &str,
            _data: &[u8],
        ) -> CargoResult<File> {
            panic!("this source doesn't download")
        }
    }