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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::collections::Bound;
use std::ops::Range;
use std::ops::RangeBounds;

use bytes::Buf;
use bytes::BufMut;

use crate::raw::*;
use crate::*;

/// BlockingReader is designed to read data from given path in an blocking
/// manner.
pub struct BlockingReader {
    pub(crate) inner: oio::BlockingReader,
}

impl BlockingReader {
    /// Create a new blocking reader.
    ///
    /// Create will use internal information to decide the most suitable
    /// implementation for users.
    ///
    /// We don't want to expose those details to users so keep this function
    /// in crate only.
    pub(crate) fn create(acc: Accessor, path: &str, op: OpRead) -> crate::Result<Self> {
        let (_, r) = acc.blocking_read(path, op)?;

        Ok(BlockingReader { inner: r })
    }

    /// Read give range from reader into [`Buffer`].
    ///
    /// This operation is zero-copy, which means it keeps the [`Bytes`] returned by underlying
    /// storage services without any extra copy or intensive memory allocations.
    ///
    /// # Notes
    ///
    /// - Buffer length smaller than range means we have reached the end of file.
    pub fn read(&self, range: impl RangeBounds<u64>) -> Result<Buffer> {
        let start = match range.start_bound().cloned() {
            Bound::Included(start) => start,
            Bound::Excluded(start) => start + 1,
            Bound::Unbounded => 0,
        };

        let end = match range.end_bound().cloned() {
            Bound::Included(end) => Some(end + 1),
            Bound::Excluded(end) => Some(end),
            Bound::Unbounded => None,
        };

        // If range is empty, return Ok(0) directly.
        if let Some(end) = end {
            if end <= start {
                return Ok(Buffer::new());
            }
        }

        let mut bufs = Vec::new();
        let mut offset = start;

        loop {
            // TODO: use service preferred io size instead.
            let limit = end.map(|end| end - offset).unwrap_or(4 * 1024 * 1024) as usize;
            let bs = self.inner.read_at(offset, limit)?;
            let n = bs.remaining();
            bufs.push(bs);
            if n < limit {
                return Ok(bufs.into_iter().flatten().collect());
            }

            offset += n as u64;
            if Some(offset) == end {
                return Ok(bufs.into_iter().flatten().collect());
            }
        }
    }

    ///
    /// This operation will copy and write bytes into given [`BufMut`]. Allocation happens while
    /// [`BufMut`] doesn't have enough space.
    ///
    /// # Notes
    ///
    /// - Returning length smaller than range means we have reached the end of file.
    pub fn read_into(&self, buf: &mut impl BufMut, range: impl RangeBounds<u64>) -> Result<usize> {
        let start = match range.start_bound().cloned() {
            Bound::Included(start) => start,
            Bound::Excluded(start) => start + 1,
            Bound::Unbounded => 0,
        };

        let end = match range.end_bound().cloned() {
            Bound::Included(end) => Some(end + 1),
            Bound::Excluded(end) => Some(end),
            Bound::Unbounded => None,
        };

        // If range is empty, return Ok(0) directly.
        if let Some(end) = end {
            if end <= start {
                return Ok(0);
            }
        }

        let mut offset = start;
        let mut read = 0;

        loop {
            // TODO: use service preferred io size instead.
            let limit = end.map(|end| end - offset).unwrap_or(4 * 1024 * 1024) as usize;
            let bs = self.inner.read_at(offset, limit)?;
            let n = bs.remaining();
            buf.put(bs);
            read += n as u64;
            if n < limit {
                return Ok(read as _);
            }

            offset += n as u64;
            if Some(offset) == end {
                return Ok(read as _);
            }
        }
    }

    /// Convert reader into [`StdReader`] which implements [`futures::AsyncRead`],
    /// [`futures::AsyncSeek`] and [`futures::AsyncBufRead`].
    #[inline]
    pub fn into_std_read(self, range: Range<u64>) -> StdReader {
        // TODO: the capacity should be decided by services.
        StdReader::new(self.inner, range)
    }

    /// Convert reader into [`StdBytesIterator`] which implements [`Iterator`].
    #[inline]
    pub fn into_bytes_iterator(self, range: Range<u64>) -> StdBytesIterator {
        StdBytesIterator::new(self.inner, range)
    }
}