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// Copyright 2019 TiKV Project Authors. Licensed under Apache-2.0.

//! External storage support.
//! Cloud provider backends can be found under components/cloud

#[macro_use]
extern crate slog_global;
#[allow(unused_extern_crates)]
extern crate tikv_alloc;

use std::io::{self, Write};
use std::marker::Unpin;
use std::sync::Arc;
use std::time::{Duration, Instant};

use file_system::File;
use futures_io::AsyncRead;
use futures_util::AsyncReadExt;
use tikv_util::stream::{block_on_external_io, READ_BUF_SIZE};
use tikv_util::time::Limiter;
use tokio::time::timeout;

mod local;
pub use local::LocalStorage;
mod noop;
pub use noop::NoopStorage;
mod metrics;
use metrics::EXT_STORAGE_CREATE_HISTOGRAM;
#[cfg(feature = "cloud-storage-dylib")]
pub mod dylib_client;
#[cfg(feature = "cloud-storage-grpc")]
pub mod grpc_client;
#[cfg(any(feature = "cloud-storage-dylib", feature = "cloud-storage-grpc"))]
pub mod request;

pub fn record_storage_create(start: Instant, storage: &dyn ExternalStorage) {
    EXT_STORAGE_CREATE_HISTOGRAM
        .with_label_values(&[storage.name()])
        .observe(start.elapsed().as_secs_f64());
}

/// An abstraction of an external storage.
// TODO: these should all be returning a future (i.e. async fn).
pub trait ExternalStorage: 'static + Send + Sync {
    fn name(&self) -> &'static str;

    fn url(&self) -> io::Result<url::Url>;

    /// Write all contents of the read to the given path.
    fn write(
        &self,
        name: &str,
        reader: Box<dyn AsyncRead + Send + Unpin>,
        content_length: u64,
    ) -> io::Result<()>;

    /// Read all contents of the given path.
    fn read(&self, name: &str) -> Box<dyn AsyncRead + Unpin + '_>;

    /// Read from external storage and restore to the given path
    fn restore(
        &self,
        storage_name: &str,
        restore_name: std::path::PathBuf,
        expected_length: u64,
        speed_limiter: &Limiter,
    ) -> io::Result<()> {
        let mut input = self.read(storage_name);
        let output: &mut dyn Write = &mut File::create(restore_name)?;
        // the minimum speed of reading data, in bytes/second.
        // if reading speed is slower than this rate, we will stop with
        // a "TimedOut" error.
        // (at 8 KB/s for a 2 MB buffer, this means we timeout after 4m16s.)
        let min_read_speed: usize = 8192;
        block_on_external_io(read_external_storage_into_file(
            &mut input,
            output,
            speed_limiter,
            expected_length,
            min_read_speed,
        ))
    }
}

impl ExternalStorage for Arc<dyn ExternalStorage> {
    fn name(&self) -> &'static str {
        (**self).name()
    }

    fn url(&self) -> io::Result<url::Url> {
        (**self).url()
    }

    fn write(
        &self,
        name: &str,
        reader: Box<dyn AsyncRead + Send + Unpin>,
        content_length: u64,
    ) -> io::Result<()> {
        (**self).write(name, reader, content_length)
    }

    fn read(&self, name: &str) -> Box<dyn AsyncRead + Unpin + '_> {
        (**self).read(name)
    }
}

impl ExternalStorage for Box<dyn ExternalStorage> {
    fn name(&self) -> &'static str {
        self.as_ref().name()
    }

    fn url(&self) -> io::Result<url::Url> {
        self.as_ref().url()
    }

    fn write(
        &self,
        name: &str,
        reader: Box<dyn AsyncRead + Send + Unpin>,
        content_length: u64,
    ) -> io::Result<()> {
        self.as_ref().write(name, reader, content_length)
    }

    fn read(&self, name: &str) -> Box<dyn AsyncRead + Unpin + '_> {
        self.as_ref().read(name)
    }
}

pub async fn read_external_storage_into_file(
    input: &mut (dyn AsyncRead + Unpin),
    output: &mut dyn Write,
    speed_limiter: &Limiter,
    expected_length: u64,
    min_read_speed: usize,
) -> io::Result<()> {
    let dur = Duration::from_secs((READ_BUF_SIZE / min_read_speed) as u64);

    // do the I/O copy from external_storage to the local file.
    let mut buffer = vec![0u8; READ_BUF_SIZE];
    let mut file_length = 0;

    loop {
        // separate the speed limiting from actual reading so it won't
        // affect the timeout calculation.
        let bytes_read = timeout(dur, input.read(&mut buffer))
            .await
            .map_err(|_| io::ErrorKind::TimedOut)??;
        if bytes_read == 0 {
            break;
        }
        speed_limiter.consume(bytes_read).await;
        output.write_all(&buffer[..bytes_read])?;
        file_length += bytes_read as u64;
    }

    if expected_length != 0 && expected_length != file_length {
        return Err(io::Error::new(
            io::ErrorKind::InvalidData,
            format!(
                "downloaded size {}, expected {}",
                file_length, expected_length
            ),
        ));
    }

    Ok(())
}