use crate::Error;
use commonware_utils::{from_hex, hex};
#[cfg(unix)]
use std::path::Path;
use std::{path::PathBuf, sync::Arc};
use tokio::{fs, sync::Mutex};

#[cfg(not(unix))]
mod fallback;
#[cfg(unix)]
mod unix;

/// Syncs a directory to ensure directory entry changes are durable.
/// On Unix, directory metadata (file creation/deletion) must be explicitly
/// fsynced.
#[cfg(unix)]
async fn sync_dir(path: &Path) -> Result<(), Error> {
    let dir = fs::File::open(path).await.map_err(|e| {
        Error::BlobOpenFailed(
            path.to_string_lossy().to_string(),
            "directory".to_string(),
            e,
        )
    })?;
    dir.sync_all().await.map_err(|e| {
        Error::BlobSyncFailed(
            path.to_string_lossy().to_string(),
            "directory".to_string(),
            e,
        )
    })
}

#[derive(Clone)]
pub struct Config {
    pub storage_directory: PathBuf,
    pub maximum_buffer_size: usize,
}

impl Config {
    pub fn new(storage_directory: PathBuf, maximum_buffer_size: usize) -> Self {
        Self {
            storage_directory,
            maximum_buffer_size,
        }
    }
}

#[derive(Clone)]
pub struct Storage {
    lock: Arc<Mutex<()>>,
    cfg: Config,
}

impl Storage {
    pub fn new(cfg: Config) -> Self {
        Self {
            lock: Arc::new(Mutex::new(())),
            cfg,
        }
    }
}

impl crate::Storage for Storage {
    #[cfg(unix)]
    type Blob = unix::Blob;
    #[cfg(not(unix))]
    type Blob = fallback::Blob;

    async fn open(&self, partition: &str, name: &[u8]) -> Result<(Self::Blob, u64), Error> {
        // Acquire the filesystem lock
        let _guard = self.lock.lock().await;

        // Construct the full path
        let path = self.cfg.storage_directory.join(partition).join(hex(name));
        let parent = match path.parent() {
            Some(parent) => parent,
            None => return Err(Error::PartitionCreationFailed(partition.into())),
        };

        // Check if partition exists before creating
        #[cfg(unix)]
        let parent_existed = parent.exists();

        // Create the partition directory, if it does not exist
        fs::create_dir_all(parent)
            .await
            .map_err(|_| Error::PartitionCreationFailed(partition.into()))?;

        // Open the file, creating it if it doesn't exist
        let mut file = fs::OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            .truncate(false)
            .open(&path)
            .await
            .map_err(|e| Error::BlobOpenFailed(partition.into(), hex(name), e))?;

        // Assume empty files are newly created. Existing empty files will be synced too; that's OK.
        let len = file.metadata().await.map_err(|_| Error::ReadFailed)?.len();
        let newly_created = len == 0;

        // Only sync if we created a new file
        if newly_created {
            // Sync the file to ensure it is durable
            file.sync_all()
                .await
                .map_err(|e| Error::BlobSyncFailed(partition.into(), hex(name), e))?;

            // Windows doesn't have a notion of syncing a directory entry to ensure that it's
            // durably persisted. See https://github.com/commonwarexyz/monorepo/issues/2026.
            #[cfg(unix)]
            {
                // Sync the parent directory to ensure the directory entry is durable.
                sync_dir(parent).await?;

                // Sync storage directory if parent directory did not exist
                if !parent_existed {
                    sync_dir(&self.cfg.storage_directory).await?;
                }
            }
        }

        // Set the maximum buffer size
        file.set_max_buf_size(self.cfg.maximum_buffer_size);

        #[cfg(unix)]
        {
            // Convert to a blocking std::fs::File
            let file = file.into_std().await;

            // Construct the blob
            Ok((Self::Blob::new(partition.into(), name, file), len))
        }
        #[cfg(not(unix))]
        {
            // Construct the blob
            Ok((Self::Blob::new(partition.into(), name, file), len))
        }
    }

    async fn remove(&self, partition: &str, name: Option<&[u8]>) -> Result<(), Error> {
        // Acquire the filesystem lock
        let _guard = self.lock.lock().await;

        // Remove all related files
        let path = self.cfg.storage_directory.join(partition);
        if let Some(name) = name {
            let blob_path = path.join(hex(name));
            fs::remove_file(blob_path)
                .await
                .map_err(|_| Error::BlobMissing(partition.into(), hex(name)))?;

            // Sync the partition directory to ensure the removal is durable.
            // Windows doesn't have a notion of syncing a directory entry to ensure that it's
            // durably persisted. See https://github.com/commonwarexyz/monorepo/issues/2026.
            #[cfg(unix)]
            sync_dir(&path).await?;
        } else {
            fs::remove_dir_all(&path)
                .await
                .map_err(|_| Error::PartitionMissing(partition.into()))?;

            // Sync the storage directory to ensure the removal is durable.
            // Windows doesn't have a notion of syncing a directory entry to ensure that it's
            // durably persisted. See https://github.com/commonwarexyz/monorepo/issues/2026.
            #[cfg(unix)]
            sync_dir(&self.cfg.storage_directory).await?;
        }
        Ok(())
    }

    async fn scan(&self, partition: &str) -> Result<Vec<Vec<u8>>, Error> {
        // Acquire the filesystem lock
        let _guard = self.lock.lock().await;

        // Scan the partition directory
        let path = self.cfg.storage_directory.join(partition);
        let mut entries = fs::read_dir(path)
            .await
            .map_err(|_| Error::PartitionMissing(partition.into()))?;
        let mut blobs = Vec::new();
        while let Some(entry) = entries.next_entry().await.map_err(|_| Error::ReadFailed)? {
            let file_type = entry.file_type().await.map_err(|_| Error::ReadFailed)?;
            if !file_type.is_file() {
                return Err(Error::PartitionCorrupt(partition.into()));
            }
            if let Some(name) = entry.file_name().to_str() {
                let name = from_hex(name).ok_or(Error::PartitionCorrupt(partition.into()))?;
                blobs.push(name);
            }
        }
        Ok(blobs)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::storage::tests::run_storage_tests;
    use rand::{Rng as _, SeedableRng};
    use std::env;

    #[tokio::test]
    async fn test_storage() {
        let mut rng = rand::rngs::StdRng::from_entropy();
        let storage_directory = env::temp_dir().join(format!("storage_tokio_{}", rng.gen::<u64>()));
        let config = Config::new(storage_directory, 2 * 1024 * 1024);
        let storage = Storage::new(config);
        run_storage_tests(storage).await;
    }
}