use super::{SeqRead, SeqWrite};
use crate::os::{map_ring, unmap_ring};
use crate::{Result, Size};

use std::cmp;
use std::io::{self, BufRead, Read, Write};
use std::ops::Deref;

/// Fixed-size reliable read/write buffer with sequential address mapping.
///
/// This uses a circular address mapping scheme. That is, for any buffer of
/// size `N`, the pointer address range of `0..N` maps to the same physical
/// memory as the range `N..2*N`. This guarantees that the entire read or
/// write range may be addressed as a single sequence of bytes.
///
/// Unlike the [`InfiniteRing`], this type otherise acts as a "normal" buffer.
/// Writes fill up the buffer, and when full, no furthur writes may be
/// performed until a read occurs. The writable length sequence is the capacity
/// of the buffer, less any pending readable bytes.
///
/// # Examples
///
/// ```
/// use vmap::io::{Ring, SeqWrite};
/// use std::io::{BufRead, Read, Write};
///
/// # fn main() -> std::io::Result<()> {
/// let mut buf = Ring::new(4000).unwrap();
/// let mut i = 1;
///
/// // Fill up the buffer with lines.
/// while buf.write_len() > 20 {
///     write!(&mut buf, "this is test line {}\n", i)?;
///     i += 1;
/// }
///
/// // No more space is available.
/// assert!(write!(&mut buf, "this is test line {}\n", i).is_err());
///
/// let mut line = String::new();
///
/// // Read the first line written.
/// let len = buf.read_line(&mut line)?;
/// assert_eq!(line, "this is test line 1\n");
///
/// line.clear();
///
/// // Read the second line written.
/// let len = buf.read_line(&mut line)?;
/// assert_eq!(line, "this is test line 2\n");
///
/// // Now there is enough space to write more.
/// write!(&mut buf, "this is test line {}\n", i)?;
/// # Ok(())
/// # }
/// ```
#[derive(Debug)]
pub struct Ring {
    ptr: *mut u8,
    len: usize,
    rpos: u64,
    wpos: u64,
}

impl Ring {
    /// Constructs a new buffer instance.
    ///
    /// The hint is a minimum size for the buffer. This size will be rounded up
    /// to the nearest page size for the actual capacity. The allocation will
    /// occupy double the space in the virtual memory table, but the physical
    /// memory usage will remain at the desired capacity.
    pub fn new(hint: usize) -> Result<Self> {
        let len = Size::alloc().round(hint);
        let ptr = map_ring(len)?;
        Ok(Self {
            ptr,
            len,
            rpos: 0,
            wpos: 0,
        })
    }

    /// Clears the buffer, resetting the filled region to empty.
    ///
    /// The number of initialized bytes is not changed, and the contents of the buffer are not modified.
    pub fn clear(&mut self) {
        self.rpos = 0;
        self.wpos = 0;
    }
}

impl Drop for Ring {
    fn drop(&mut self) {
        unsafe { unmap_ring(self.ptr, self.write_capacity()) }.unwrap_or_default();
    }
}

impl SeqRead for Ring {
    fn as_read_ptr(&self) -> *const u8 {
        self.ptr
    }

    fn read_offset(&self) -> usize {
        self.rpos as usize % self.len
    }

    fn read_len(&self) -> usize {
        (self.wpos - self.rpos) as usize
    }
}

impl SeqWrite for Ring {
    fn as_write_ptr(&mut self) -> *mut u8 {
        self.ptr
    }

    fn write_offset(&self) -> usize {
        self.wpos as usize % self.len
    }

    fn write_len(&self) -> usize {
        self.write_capacity() - self.read_len()
    }

    fn write_capacity(&self) -> usize {
        self.len
    }

    fn feed(&mut self, len: usize) {
        self.wpos += cmp::min(len, self.write_len()) as u64;
    }
}

impl BufRead for Ring {
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        Ok(self.as_read_slice(std::usize::MAX))
    }

    fn consume(&mut self, len: usize) {
        self.rpos += cmp::min(len, self.read_len()) as u64;
    }
}

impl Read for Ring {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.read_from(buf)
    }
}

impl Write for Ring {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.write_into(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

impl Deref for Ring {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &Self::Target {
        self.as_read_slice(usize::MAX)
    }
}

impl AsRef<[u8]> for Ring
where
    <Ring as Deref>::Target: AsRef<[u8]>,
{
    fn as_ref(&self) -> &[u8] {
        self.deref()
    }
}

/// Fixed-size lossy read/write buffer with sequential address mapping.
///
/// This uses a circular address mapping scheme. That is, for any buffer of
/// size `N`, the pointer address range of `0..N` maps to the same physical
/// memory as the range `N..2*N`. This guarantees that the entire read or
/// write range may be addressed as a single sequence of bytes.
///
/// Unlike the [`Ring`], writes to this type may evict bytes from the read side
/// of the queue. The writeable size is always equal to the overall capacity of
/// the buffer.
///
/// # Examples
///
/// ```
/// use vmap::io::{InfiniteRing, SeqRead, SeqWrite};
/// use std::io::{BufRead, Read, Write};
///
/// # fn main() -> std::io::Result<()> {
/// let mut buf = InfiniteRing::new(4000).unwrap();
/// let mut i = 1;
/// let mut total = 0;
/// while total < buf.write_capacity() {
///     let tmp = format!("this is test line {}\n", i);
///     write!(buf, "{}", tmp);
///     total += tmp.len();
///     i += 1;
/// }
///
/// // skip over the overwritten tail
/// buf.consume(20 - buf.read_offset());
///
/// // read the next line
/// let mut line = String::new();
/// let len = buf.read_line(&mut line)?;
///
/// assert_eq!(len, 20);
/// assert_eq!(&line[line.len()-20..], "this is test line 2\n");
/// # Ok(())
/// # }
/// ```
#[derive(Debug)]
pub struct InfiniteRing {
    ptr: *mut u8,
    len: usize,
    rlen: u64,
    wpos: u64,
}

impl InfiniteRing {
    /// Constructs a new ring buffer instance.
    ///
    /// The hint is a minimum size for the buffer. This size will be rounded up
    /// to the nearest page size for the actual capacity. The allocation will
    /// occupy double the space in the virtual memory table, but the physical
    /// memory usage will remain at the desired capacity.
    pub fn new(hint: usize) -> Result<Self> {
        let len = Size::alloc().round(hint);
        let ptr = map_ring(len)?;
        Ok(Self {
            ptr,
            len,
            rlen: 0,
            wpos: 0,
        })
    }
}

impl Drop for InfiniteRing {
    fn drop(&mut self) {
        unsafe { unmap_ring(self.ptr, self.write_capacity()) }.unwrap_or_default()
    }
}

impl SeqRead for InfiniteRing {
    fn as_read_ptr(&self) -> *const u8 {
        self.ptr
    }
    fn read_offset(&self) -> usize {
        (self.wpos - self.rlen) as usize % self.len
    }
    fn read_len(&self) -> usize {
        self.rlen as usize
    }
}

impl SeqWrite for InfiniteRing {
    fn as_write_ptr(&mut self) -> *mut u8 {
        self.ptr
    }
    fn write_offset(&self) -> usize {
        self.wpos as usize % self.len
    }
    fn write_len(&self) -> usize {
        self.write_capacity()
    }
    fn write_capacity(&self) -> usize {
        self.len
    }
    fn feed(&mut self, len: usize) {
        self.wpos += cmp::min(len, self.write_len()) as u64;
        self.rlen = cmp::min(self.rlen + len as u64, self.len as u64);
    }
}

impl BufRead for InfiniteRing {
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        Ok(self.as_read_slice(std::usize::MAX))
    }

    fn consume(&mut self, len: usize) {
        self.rlen -= cmp::min(len, self.read_len()) as u64;
    }
}

impl Read for InfiniteRing {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.read_from(buf)
    }
}

impl Write for InfiniteRing {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.write_into(buf)
    }

    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        let len = {
            let dst = self.as_write_slice(buf.len());
            let len = dst.len();
            let tail = buf.len() - len;
            dst.copy_from_slice(&buf[tail..]);
            len
        };
        self.feed(len);
        Ok(())
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

impl Deref for InfiniteRing {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &Self::Target {
        self.as_read_slice(usize::MAX)
    }
}

impl AsRef<[u8]> for InfiniteRing
where
    <InfiniteRing as Deref>::Target: AsRef<[u8]>,
{
    fn as_ref(&self) -> &[u8] {
        self.deref()
    }
}