use std::{
    cmp,
    io::{self, Read, Write},
    ptr,
};

use poule::Reset;

#[derive(Debug, PartialEq, Eq, Clone, Default)]
pub struct BufferMetadata {
    position: usize,
    end: usize,
}

#[derive(Debug, PartialEq, Clone)]
pub struct Buffer {
    inner: trailer::Trailer<BufferMetadata>,
}

impl Buffer {
    pub fn with_capacity(capacity: usize) -> Buffer {
        let mut inner: trailer::Trailer<BufferMetadata> = trailer::Trailer::new(capacity);
        inner.position = 0;
        inner.end = 0;

        Buffer { inner }
    }

    /*pub fn from_slice(sl: &[u8]) -> Buffer {
      Buffer {
        memory:   Vec::from(sl),
        capacity: sl.len(),
        position: 0,
        end:      sl.len()
      }
      unimplemented!()
    }
      */

    pub fn grow(&mut self, new_size: usize) -> bool {
        if self.inner.capacity() >= new_size {
            return false;
        }

        /*
        self.memory.resize(new_size, 0);
        self.capacity = new_size;
        true
          */
        unimplemented!()
    }

    pub fn available_data(&self) -> usize {
        self.inner.end - self.inner.position
    }

    pub fn available_space(&self) -> usize {
        self.inner.capacity() - self.inner.end
    }

    pub fn capacity(&self) -> usize {
        self.inner.capacity()
    }

    pub fn empty(&self) -> bool {
        self.inner.position == self.inner.end
    }

    pub fn consume(&mut self, count: usize) -> usize {
        let cnt = cmp::min(count, self.available_data());
        self.inner.position += cnt;
        if self.inner.position > self.inner.capacity() / 2 {
            //trace!("consume shift: pos {}, end {}", self.position, self.end);
            self.shift();
        }
        cnt
    }

    pub fn fill(&mut self, count: usize) -> usize {
        let cnt = cmp::min(count, self.available_space());
        self.inner.end += cnt;
        if self.available_space() < self.available_data() + cnt {
            //trace!("fill shift: pos {}, end {}", self.position, self.end);
            self.shift();
        }

        cnt
    }

    pub fn reset(&mut self) {
        self.inner.position = 0;
        self.inner.end = 0;
    }

    pub fn data(&self) -> &[u8] {
        &self.inner.bytes()[self.inner.position..self.inner.end]
    }

    pub fn space(&mut self) -> &mut [u8] {
        let range = self.inner.end..self.inner.capacity();
        &mut self.inner.bytes_mut()[range]
    }

    pub fn shift(&mut self) {
        if self.inner.position > 0 {
            unsafe {
                let length = self.inner.end - self.inner.position;
                ptr::copy(
                    self.inner.bytes()[self.inner.position..self.inner.end].as_ptr(),
                    self.inner.bytes_mut()[..length].as_mut_ptr(),
                    length,
                );
                self.inner.position = 0;
                self.inner.end = length;
            }
        }
    }

    pub fn delete_slice(&mut self, start: usize, length: usize) -> Option<usize> {
        if start + length >= self.available_data() {
            return None;
        }

        unsafe {
            let begin = self.inner.position + start;
            let next_end = self.inner.end - length;
            ptr::copy(
                self.inner.bytes()[begin + length..self.inner.end].as_ptr(),
                self.inner.bytes_mut()[begin..next_end].as_mut_ptr(),
                self.inner.end - (begin + length),
            );
            self.inner.end = next_end;
        }
        Some(self.available_data())
    }

    pub fn replace_slice(&mut self, data: &[u8], start: usize, length: usize) -> Option<usize> {
        let data_len = data.len();
        if start + length > self.available_data()
            || self.inner.position + start + data_len > self.capacity()
        {
            return None;
        }

        unsafe {
            let begin = self.inner.position + start;
            let slice_end = begin + data_len;
            // we reduced the data size
            if data_len < length {
                ptr::copy(
                    data.as_ptr(),
                    self.inner.bytes_mut()[begin..slice_end].as_mut_ptr(),
                    data_len,
                );

                ptr::copy(
                    self.inner.bytes()[start + length..self.inner.end].as_ptr(),
                    self.inner.bytes_mut()[slice_end..].as_mut_ptr(),
                    self.inner.end - (start + length),
                );
                self.inner.end -= length - data_len;

            // we put more data in the buffer
            } else {
                ptr::copy(
                    self.inner.bytes()[start + length..self.inner.end].as_ptr(),
                    self.inner.bytes_mut()[start + data_len..].as_mut_ptr(),
                    self.inner.end - (start + length),
                );
                ptr::copy(
                    data.as_ptr(),
                    self.inner.bytes_mut()[begin..slice_end].as_mut_ptr(),
                    data_len,
                );
                self.inner.end += data_len - length;
            }
        }
        Some(self.available_data())
    }

    pub fn insert_slice(&mut self, data: &[u8], start: usize) -> Option<usize> {
        let data_len = data.len();
        if start > self.available_data()
            || self.inner.position + self.inner.end + data_len > self.capacity()
        {
            return None;
        }

        unsafe {
            let begin = self.inner.position + start;
            let slice_end = begin + data_len;
            ptr::copy(
                self.inner.bytes()[start..self.inner.end].as_ptr(),
                self.inner.bytes_mut()[start + data_len..].as_mut_ptr(),
                self.inner.end - start,
            );
            ptr::copy(
                data.as_ptr(),
                self.inner.bytes_mut()[begin..slice_end].as_mut_ptr(),
                data_len,
            );
            self.inner.end += data_len;
        }
        Some(self.available_data())
    }
}

impl Write for Buffer {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        match self.space().write(buf) {
            Ok(size) => {
                self.fill(size);
                Ok(size)
            }
            err => err,
        }
    }

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

impl Read for Buffer {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let len = cmp::min(self.available_data(), buf.len());
        unsafe {
            ptr::copy(
                self.inner.bytes()[self.inner.position..self.inner.position + len].as_ptr(),
                buf.as_mut_ptr(),
                len,
            );
            self.inner.position += len;
        }
        Ok(len)
    }
}

impl Reset for Buffer {
    fn reset(&mut self) {
        self.reset();
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Write;

    #[test]
    fn fill_and_consume() {
        let mut b = Buffer::with_capacity(10);
        assert_eq!(b.available_data(), 0);
        assert_eq!(b.available_space(), 10);
        let res = b.write(&b"abcd"[..]);
        assert_eq!(res.ok(), Some(4));
        assert_eq!(b.available_data(), 4);
        assert_eq!(b.available_space(), 6);

        assert_eq!(b.data(), &b"abcd"[..]);

        b.consume(2);
        assert_eq!(b.available_data(), 2);
        assert_eq!(b.available_space(), 6);
        assert_eq!(b.data(), &b"cd"[..]);

        b.shift();
        assert_eq!(b.available_data(), 2);
        assert_eq!(b.available_space(), 8);
        assert_eq!(b.data(), &b"cd"[..]);

        assert_eq!(b.write(&b"efghijklmnop"[..]).ok(), Some(8));
        assert_eq!(b.available_data(), 10);
        assert_eq!(b.available_space(), 0);
        assert_eq!(b.data(), &b"cdefghijkl"[..]);
        b.shift();
        assert_eq!(b.available_data(), 10);
        assert_eq!(b.available_space(), 0);
        assert_eq!(b.data(), &b"cdefghijkl"[..]);
    }

    #[test]
    fn delete() {
        let mut b = Buffer::with_capacity(10);
        let _ = b.write(&b"abcdefgh"[..]).expect("should write");
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);

        assert_eq!(b.delete_slice(2, 3), Some(5));
        assert_eq!(b.available_data(), 5);
        assert_eq!(b.available_space(), 5);
        assert_eq!(b.data(), &b"abfgh"[..]);

        assert_eq!(b.delete_slice(5, 2), None);
        assert_eq!(b.delete_slice(4, 2), None);
    }

    #[test]
    fn replace() {
        let mut b = Buffer::with_capacity(10);
        let _ = b.write(&b"abcdefgh"[..]).expect("should write");
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);

        assert_eq!(b.replace_slice(&b"ABC"[..], 2, 3), Some(8));
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);
        assert_eq!(b.data(), &b"abABCfgh"[..]);

        assert_eq!(b.replace_slice(&b"XYZ"[..], 8, 3), None);
        assert_eq!(b.replace_slice(&b"XYZ"[..], 6, 3), None);

        assert_eq!(b.replace_slice(&b"XYZ"[..], 2, 4), Some(7));
        assert_eq!(b.available_data(), 7);
        assert_eq!(b.available_space(), 3);
        assert_eq!(b.data(), &b"abXYZgh"[..]);

        assert_eq!(b.replace_slice(&b"123"[..], 2, 2), Some(8));
        assert_eq!(b.available_data(), 8);
        assert_eq!(b.available_space(), 2);
        assert_eq!(b.data(), &b"ab123Zgh"[..]);
    }
}