use crate::error::unexpected::{self, Intoable, Mappable};
use crate::{origin, util};

use std::path::{Path, PathBuf};
use std::{collections, fs, io, sync};

use futures::stream;

#[derive(Clone)]
struct RepoSnapshot {
    repo: sync::Arc<gix::ThreadSafeRepository>,
    tree_object_id: gix::ObjectId,
}

#[derive(thiserror::Error, Debug)]
enum CreateRepoSnapshotError {
    #[error("invalid branch name")]
    InvalidBranchName,

    #[error(transparent)]
    Unexpected(#[from] unexpected::Error),
}

/// Implements the Store trait for Descr::Git, storing the git repos on disk. If any non-git Descrs
/// are used then this implementation will panic.
pub struct FSStore {
    dir_path: PathBuf,

    // to prevent against syncing the same origin more than once at a time, but still allowing
    // more than one origin to be syncing at a time
    sync_guard: sync::Mutex<collections::HashMap<origin::Descr, ()>>,

    repo_snapshots: sync::RwLock<collections::HashMap<origin::Descr, sync::Arc<RepoSnapshot>>>,
}

impl FSStore {
    pub fn new(config: &origin::Config) -> io::Result<Self> {
        let dir_path = config.store_dir_path.join("git");
        fs::create_dir_all(&dir_path)?;
        Ok(Self {
            dir_path,
            sync_guard: sync::Mutex::new(collections::HashMap::new()),
            repo_snapshots: sync::RwLock::new(collections::HashMap::new()),
        })
    }

    fn repo_path(&self, descr: &origin::Descr) -> PathBuf {
        self.dir_path.join(descr.id())
    }

    fn descr_file_path(&self, descr_id: &str) -> PathBuf {
        self.dir_path.join(descr_id).join("descr.json")
    }

    fn branch_ref(&self, branch_name: &str) -> String {
        format!("origin/{branch_name}")
    }

    fn deconstruct_descr(descr: &origin::Descr) -> (&str, &str) {
        let origin::Descr::Git {
            ref url,
            ref branch_name,
        } = descr;
        (url, branch_name)
    }

    fn create_repo_snapshot(
        &self,
        repo: gix::Repository,
        descr: &origin::Descr,
    ) -> Result<RepoSnapshot, CreateRepoSnapshotError> {
        let (_, branch_name) = Self::deconstruct_descr(descr);
        let branch_ref = self.branch_ref(branch_name);

        let commit_object_id = repo
            .try_find_reference(&branch_ref)
            .map_unexpected_while(|| format!("finding branch ref {branch_ref}"))?
            .ok_or(CreateRepoSnapshotError::InvalidBranchName)?
            .peel_to_id_in_place()
            .or_unexpected_while("peeling id in place")?
            .detach();

        let tree_object_id = repo
            .find_object(commit_object_id)
            .map_unexpected_while(|| format!("finding commit object {commit_object_id}"))?
            .try_to_commit_ref()
            .map_unexpected_while(|| format!("parsing {commit_object_id} as commit"))?
            .tree();

        Ok(RepoSnapshot {
            repo: sync::Arc::new(repo.into()),
            tree_object_id,
        })
    }

    fn get_repo_snapshot(
        &self,
        descr: &origin::Descr,
    ) -> Result<Option<sync::Arc<RepoSnapshot>>, unexpected::Error> {
        {
            let repo_snapshots = self.repo_snapshots.read().unwrap();
            if let Some(repo_snapshot) = repo_snapshots.get(descr) {
                return Ok(Some(repo_snapshot.clone()));
            }
        }

        let repo_path = self.repo_path(descr);

        match fs::read_dir(&repo_path) {
            Ok(_) => (),
            Err(e) => match e.kind() {
                io::ErrorKind::NotFound => return Ok(None),
                _ => {
                    return Err(e.into_unexpected_while(format!(
                        "checking if {} exists",
                        repo_path.display()
                    )))
                }
            },
        }

        let repo = gix::open(&repo_path)
            .map_unexpected_while(|| format!("opening {} as git repo", repo_path.display()))?;

        let repo_snapshot = self
            .create_repo_snapshot(repo, descr)
            .map_err(|e| match e {
                // it's not expected that the branch name is invalid at this point, it must have
                // existed for sync to have been successful.
                CreateRepoSnapshotError::InvalidBranchName => e.into_unexpected().into(),
                CreateRepoSnapshotError::Unexpected(e) => e,
            })?;

        let repo_snapshot = sync::Arc::new(repo_snapshot);

        let mut repo_snapshots = self.repo_snapshots.write().unwrap();

        (*repo_snapshots).insert(descr.clone(), repo_snapshot.clone());

        Ok(Some(repo_snapshot))
    }

    fn sync_inner(&self, descr: &origin::Descr) -> Result<gix::Repository, origin::SyncError> {
        use gix::clone::Error as gixCloneErr;
        use gix::progress::Discard;

        let should_interrupt = &core::sync::atomic::AtomicBool::new(false);
        let repo_path = &self.repo_path(descr);

        // if the path doesn't exist then use the gix clone feature to clone it into the
        // directory.
        if fs::read_dir(repo_path).is_err() {
            fs::create_dir_all(repo_path)
                .map_unexpected_while(|| format!("creating {}", repo_path.display()))?;

            let (url, branch_name) = Self::deconstruct_descr(descr);

            let (repo, _) = gix::prepare_clone_bare(url.clone(), repo_path)
                .map_err(|e| match e {
                    gixCloneErr::Init(gix::init::Error::InvalidBranchName { .. }) => {
                        origin::SyncError::InvalidBranchName
                    }
                    gixCloneErr::UrlParse(_) | gixCloneErr::CanonicalizeUrl { .. } => {
                        origin::SyncError::InvalidURL
                    }
                    _ => e
                        .into_unexpected_while(format!(
                            "cloning {} into {}",
                            url,
                            repo_path.display()
                        ))
                        .into(),
                })?
                .fetch_only(Discard, should_interrupt)
                .map_err(|_| origin::SyncError::InvalidURL)?;

            // Check to make sure the branch name exists
            // TODO if this fails we should delete repo_path
            let branch_ref = self.branch_ref(branch_name);
            repo.try_find_reference(&branch_ref)
                .map_unexpected_while(|| format!("finding branch ref {branch_ref}"))?
                .ok_or(origin::SyncError::InvalidBranchName)?;

            // Add the descr to the repo directory, so we can know the actual descr later
            // TODO if this fails we should delete repo_path
            let file_path = self.descr_file_path(descr.id().as_ref());
            let descr_file = fs::File::create(&file_path)
                .map_unexpected_while(|| format!("creating {}", file_path.display()))?;

            serde_json::to_writer(descr_file, &descr)
                .map_unexpected_while(|| format!("writing descr to {}", file_path.display()))?;

            return Ok(repo);
        }

        let direction = gix::remote::Direction::Fetch;

        let repo = gix::open(repo_path)
            .map_unexpected_while(|| format!("opening repo at {}", repo_path.display()))?;

        let remote = repo
            .find_default_remote(direction)
            .ok_or_else(|| unexpected::Error::from("no default configured"))?
            .or_unexpected_while("finding default remote for fetching")?;

        remote
            .connect(direction)
            .or_unexpected_while("connecting to remote")?
            .prepare_fetch(Discard, Default::default())
            .or_unexpected_while("preparing fetch")?
            .receive(Discard, should_interrupt)
            .or_unexpected_while("fetching from remote")?;

        Ok(repo)
    }
}

impl super::Store for FSStore {
    fn sync(&self, descr: &origin::Descr) -> Result<(), origin::SyncError> {
        // attempt to lock this descr for syncing, doing so within a new scope so the mutex
        // isn't actually being held for the whole method duration.
        let is_already_syncing = {
            self.sync_guard
                .lock()
                .unwrap()
                .insert(descr.clone(), ())
                .is_some()
        };

        if is_already_syncing {
            return Err(origin::SyncError::AlreadyInProgress);
        }

        let res = self.sync_inner(descr);

        self.sync_guard.lock().unwrap().remove(descr);

        let repo = match res {
            Ok(repo) => repo,
            Err(e) => return Err(e),
        };

        // repo is synced at this point (though the sync lock is still held), just gotta create
        // the RepoSnapshot and store it.
        //
        // TODO this is a bit of a memory leak, but by the time we get
        // to that point this should all be backed by something which isn't local storage
        // anyway.

        // calling this while the sync lock is held isn't ideal, but it's convenient and
        // shouldn't be too terrible generally
        let repo_snapshot = self
            .create_repo_snapshot(repo, descr)
            .map_err(|e| match e {
                CreateRepoSnapshotError::InvalidBranchName => origin::SyncError::InvalidBranchName,
                CreateRepoSnapshotError::Unexpected(e) => origin::SyncError::Unexpected(e),
            })?;

        let mut repo_snapshots = self.repo_snapshots.write().unwrap();
        (*repo_snapshots).insert(descr.clone(), sync::Arc::new(repo_snapshot));

        Ok(())
    }

    fn all_descrs(&self) -> Result<Vec<origin::Descr>, origin::AllDescrsError> {
        fs::read_dir(&self.dir_path).or_unexpected()?.map(
                |dir_entry_res: io::Result<fs::DirEntry>| -> Result<origin::Descr, origin::AllDescrsError> {
                    let descr_id: String = dir_entry_res
                        .or_unexpected()?
                        .file_name()
                        .to_str()
                        .ok_or_else(|| {
                            unexpected::Error::from("couldn't convert os string to &str")
                        })?
                        .into();

                    let descr_file_path = self.descr_file_path(descr_id.as_ref());

                    // TODO it's possible that opening the file will fail if syncing is
                    // still ongoing, as writing the descr file is the last step after
                    // initial sync has succeeded.
                    let descr_file = fs::File::open(descr_file_path.as_path())
                        .map_unexpected_while(|| {
                            format!("opening descr file {}", descr_file_path.display())
                        })?;

                    let descr = serde_json::from_reader(descr_file).map_unexpected_while(|| {
                        format!("reading descr file {}", descr_file_path.display())
                    })?;

                    Ok(descr)
                },
            ).try_collect()
    }

    fn get_file<'store>(
        &'store self,
        descr: &origin::Descr,
        path: &str,
    ) -> Result<util::BoxByteStream, origin::GetFileError> {
        let repo_snapshot = match self.get_repo_snapshot(descr) {
            Ok(Some(repo_snapshot)) => repo_snapshot,
            Ok(None) => return Err(origin::GetFileError::DescrNotSynced),
            Err(e) => return Err(e.into()),
        };

        let mut clean_path = Path::new(path);
        clean_path = clean_path.strip_prefix("/").unwrap_or(clean_path);

        let repo = repo_snapshot.repo.to_thread_local();

        let file_object = repo
            .find_object(repo_snapshot.tree_object_id)
            .map_unexpected_while(|| {
                format!("finding tree object {}", repo_snapshot.tree_object_id)
            })?
            .peel_to_tree()
            .map_unexpected_while(|| {
                format!("peeling tree object {}", repo_snapshot.tree_object_id)
            })?
            .lookup_entry_by_path(clean_path)
            .map_unexpected_while(|| {
                format!(
                    "looking up {} in tree object {}",
                    clean_path.display(),
                    repo_snapshot.tree_object_id
                )
            })?
            .ok_or(origin::GetFileError::FileNotFound)?
            .object()
            .or_unexpected()?;

        // TODO this is very not ideal, the whole file is first read totally into memory, and then
        // that is cloned.
        let data = bytes::Bytes::copy_from_slice(file_object.data.as_slice());
        Ok(Box::pin(stream::once(async move { Ok(data) })))
    }
}

#[cfg(test)]
mod tests {
    use crate::origin::{self, Config, Store};
    use futures::StreamExt;
    use tempdir::TempDir;

    #[tokio::test]
    async fn basic() {
        let tmp_dir = TempDir::new("origin_store_git").unwrap();
        let config = Config {
            store_dir_path: tmp_dir.path().to_path_buf(),
        };

        let curr_dir = format!("file://{}", std::env::current_dir().unwrap().display());

        let descr = origin::Descr::Git {
            url: curr_dir.clone(),
            branch_name: String::from("main"),
        };

        let other_descr = origin::Descr::Git {
            url: curr_dir.clone(),
            branch_name: String::from("some_other_branch"),
        };

        let store = super::FSStore::new(&config).expect("store created");

        store.sync(&descr).expect("sync should succeed");
        store.sync(&descr).expect("second sync should succeed");

        // RepoSnapshot doesn't exist
        match store.get_file(&other_descr, "DNE") {
            Err(origin::GetFileError::DescrNotSynced) => (),
            _ => assert!(false, "descr should have not been found"),
        };

        let assert_file_dne = |path: &str| match store.get_file(&descr, path) {
            Err(origin::GetFileError::FileNotFound) => (),
            _ => assert!(false, "file should have not been found"),
        };

        let assert_file_not_empty = |path: &str| {
            use bytes::BufMut;

            let mut f = store.get_file(&descr, path).expect("file not retrieved");
            let mut body = bytes::BytesMut::new();

            async move {
                while let Some(chunk) = f.next().await {
                    body.put(chunk.unwrap())
                }
                assert!(body.len() > 0);
            }
        };

        assert_file_not_empty("src/lib.rs").await;
        assert_file_not_empty("/src/lib.rs").await;
        assert_file_dne("DNE");
        assert_file_dne("src/../src/lib.rs");

        let descrs = store.all_descrs().expect("all_descrs called");

        assert_eq!(1, descrs.len());
        assert_eq!(descr, descrs[0]);
    }
}