use std::{io, ptr};

use bytes::{BufMut, BytesMut};
use http::Version;

use crate::extensions::Extensions;

const DEC_DIGITS_LUT: &[u8] = b"0001020304050607080910111213141516171819\
      2021222324252627282930313233343536373839\
      4041424344454647484950515253545556575859\
      6061626364656667686970717273747576777879\
      8081828384858687888990919293949596979899";

pub(crate) const STATUS_LINE_BUF_SIZE: usize = 13;

pub(crate) fn write_status_line(version: Version, mut n: u16, bytes: &mut BytesMut) {
    let mut buf: [u8; STATUS_LINE_BUF_SIZE] = *b"HTTP/1.1     ";
    match version {
        Version::HTTP_2 => buf[5] = b'2',
        Version::HTTP_10 => buf[7] = b'0',
        Version::HTTP_09 => {
            buf[5] = b'0';
            buf[7] = b'9';
        }
        _ => (),
    }

    let mut curr: isize = 12;
    let buf_ptr = buf.as_mut_ptr();
    let lut_ptr = DEC_DIGITS_LUT.as_ptr();
    let four = n > 999;

    // decode 2 more chars, if > 2 chars
    let d1 = (n % 100) << 1;
    n /= 100;
    curr -= 2;
    unsafe {
        ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(curr), 2);
    }

    // decode last 1 or 2 chars
    if n < 10 {
        curr -= 1;
        unsafe {
            *buf_ptr.offset(curr) = (n as u8) + b'0';
        }
    } else {
        let d1 = n << 1;
        curr -= 2;
        unsafe {
            ptr::copy_nonoverlapping(
                lut_ptr.offset(d1 as isize),
                buf_ptr.offset(curr),
                2,
            );
        }
    }

    bytes.put_slice(&buf);
    if four {
        bytes.put_u8(b' ');
    }
}

const DIGITS_START: u8 = b'0';

/// NOTE: bytes object has to contain enough space
pub fn write_content_length(n: usize, bytes: &mut BytesMut) {
    bytes.put_slice(b"\r\ncontent-length: ");

    if n < 10 {
        bytes.put_u8(DIGITS_START + (n as u8));
    } else if n < 100 {
        let n = n as u8;

        let d10 = n / 10;
        let d1 = n % 10;

        bytes.put_u8(DIGITS_START + d10);
        bytes.put_u8(DIGITS_START + d1);
    } else if n < 1000 {
        let n = n as u16;

        let d100 = (n / 100) as u8;
        let d10 = ((n / 10) % 10) as u8;
        let d1 = (n % 10) as u8;

        bytes.put_u8(DIGITS_START + d100);
        bytes.put_u8(DIGITS_START + d10);
        bytes.put_u8(DIGITS_START + d1);
    } else if n < 10000 {
        let n = n as u16;

        let d1000 = (n / 1000) as u8;
        let d100 = ((n / 100) % 10) as u8;
        let d10 = ((n / 10) % 10) as u8;
        let d1 = (n % 10) as u8;

        bytes.put_u8(DIGITS_START + d1000);
        bytes.put_u8(DIGITS_START + d100);
        bytes.put_u8(DIGITS_START + d10);
        bytes.put_u8(DIGITS_START + d1);
    } else {
        write_usize(n, bytes);
    }

    bytes.put_slice(b"\r\n");
}

pub(crate) fn write_usize(n: usize, bytes: &mut BytesMut) {
    let mut n = n;
    
    // 20 chars is max length of a usize (2^64)
    // digits will be added to the buffer from lsd to msd
    let mut buf = BytesMut::with_capacity(20);

    while n > 9 {
        // "pop" the least-significant digit
        let lsd = (n % 10) as u8;

        // remove the lsd from n
        n = n / 10;

        buf.put_u8(DIGITS_START + lsd);
    }

    // put msd to result buffer
    bytes.put_u8(DIGITS_START + (n as u8));
    
    // put, in reverse (msd to lsd), remaining digits to buffer
    for i in (0..buf.len()).rev() {
        bytes.put_u8(buf[i]);
    }
}

pub(crate) struct Writer<'a>(pub &'a mut BytesMut);

impl<'a> io::Write for Writer<'a> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.0.extend_from_slice(buf);
        Ok(buf.len())
    }
    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

pub(crate) trait DataFactory {
    fn set(&self, ext: &mut Extensions);
}

pub(crate) struct Data<T>(pub(crate) T);

impl<T: Clone + 'static> DataFactory for Data<T> {
    fn set(&self, ext: &mut Extensions) {
        ext.insert(self.0.clone())
    }
}

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

    #[test]
    fn test_write_content_length() {
        let mut bytes = BytesMut::new();
        bytes.reserve(50);
        write_content_length(0, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 0\r\n"[..]);
        bytes.reserve(50);
        write_content_length(9, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 9\r\n"[..]);
        bytes.reserve(50);
        write_content_length(10, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 10\r\n"[..]);
        bytes.reserve(50);
        write_content_length(99, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 99\r\n"[..]);
        bytes.reserve(50);
        write_content_length(100, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 100\r\n"[..]);
        bytes.reserve(50);
        write_content_length(101, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 101\r\n"[..]);
        bytes.reserve(50);
        write_content_length(998, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 998\r\n"[..]);
        bytes.reserve(50);
        write_content_length(1000, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 1000\r\n"[..]);
        bytes.reserve(50);
        write_content_length(1001, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 1001\r\n"[..]);
        bytes.reserve(50);
        write_content_length(5909, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 5909\r\n"[..]);
        bytes.reserve(50);
        write_content_length(10001, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 10001\r\n"[..]);
        bytes.reserve(50);
        write_content_length(59094, &mut bytes);
        assert_eq!(bytes.split().freeze(), b"\r\ncontent-length: 59094\r\n"[..]);

        bytes.reserve(50);
        write_content_length(590947, &mut bytes);
        assert_eq!(
            bytes.split().freeze(),
            b"\r\ncontent-length: 590947\r\n"[..]
        );
        bytes.reserve(50);
        write_content_length(5909471, &mut bytes);
        assert_eq!(
            bytes.split().freeze(),
            b"\r\ncontent-length: 5909471\r\n"[..]
        );
        bytes.reserve(50);
        write_content_length(59094718, &mut bytes);
        assert_eq!(
            bytes.split().freeze(),
            b"\r\ncontent-length: 59094718\r\n"[..]
        );
    }
}