use std::io::{self, Cursor};
use std::{
    collections::HashMap,
    sync::{Arc, RwLock},
};
use tracing::{instrument, warn};

use super::{BlobService, BlobWriter};
use crate::{B3Digest, Error};

#[derive(Clone, Default)]
pub struct MemoryBlobService {
    db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>,
}

impl BlobService for MemoryBlobService {
    #[instrument(skip(self, digest), fields(blob.digest=%digest))]
    fn has(&self, digest: &B3Digest) -> Result<bool, Error> {
        let db = self.db.read().unwrap();
        Ok(db.contains_key(digest))
    }

    fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn io::Read + Send>>, Error> {
        let db = self.db.read().unwrap();

        match db.get(digest).map(|x| Cursor::new(x.clone())) {
            Some(result) => Ok(Some(Box::new(result))),
            None => Ok(None),
        }
    }

    #[instrument(skip(self))]
    fn open_write(&self) -> Result<Box<dyn BlobWriter>, Error> {
        Ok(Box::new(MemoryBlobWriter::new(self.db.clone())))
    }
}

pub struct MemoryBlobWriter {
    db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>,

    /// Contains the Vec and hasher, or None if already closed
    writers: Option<(Vec<u8>, blake3::Hasher)>,

    /// The digest that has been returned, if we successfully closed.
    digest: Option<B3Digest>,
}

impl MemoryBlobWriter {
    fn new(db: Arc<RwLock<HashMap<B3Digest, Vec<u8>>>>) -> Self {
        Self {
            db,
            writers: Some((Vec::new(), blake3::Hasher::new())),
            digest: None,
        }
    }
}
impl std::io::Write for MemoryBlobWriter {
    fn write(&mut self, b: &[u8]) -> std::io::Result<usize> {
        match &mut self.writers {
            None => Err(io::Error::new(
                io::ErrorKind::NotConnected,
                "already closed",
            )),
            Some((ref mut buf, ref mut hasher)) => {
                let bytes_written = buf.write(b)?;
                hasher.write(&buf[..bytes_written])
            }
        }
    }

    fn flush(&mut self) -> std::io::Result<()> {
        match &mut self.writers {
            None => Err(io::Error::new(
                io::ErrorKind::NotConnected,
                "already closed",
            )),
            Some(_) => Ok(()),
        }
    }
}

impl BlobWriter for MemoryBlobWriter {
    fn close(&mut self) -> Result<B3Digest, Error> {
        if self.writers.is_none() {
            match &self.digest {
                Some(digest) => Ok(digest.clone()),
                None => Err(crate::Error::StorageError(
                    "previously closed with error".to_string(),
                )),
            }
        } else {
            let (buf, hasher) = self.writers.take().unwrap();

            // We know self.hasher is doing blake3 hashing, so this won't fail.
            let digest = B3Digest::from_vec(hasher.finalize().as_bytes().to_vec()).unwrap();

            // Only insert if the blob doesn't already exist.
            let db = self.db.read()?;
            if !db.contains_key(&digest) {
                // drop the read lock, so we can open for writing.
                drop(db);

                // open the database for writing.
                let mut db = self.db.write()?;

                // and put buf in there. This will move buf out.
                db.insert(digest.clone(), buf);
            }

            self.digest = Some(digest.clone());

            Ok(digest)
        }
    }
}