//! Utilities for reading and writing for the Minecraft protocol

use std::io::Write;

use byteorder::{BigEndian, WriteBytesExt};
use tokio::io::{AsyncRead, AsyncReadExt, BufReader};

// const DEFAULT_NBT_QUOTA: u32 = 2097152;
const MAX_STRING_LENGTH: u16 = 32767;
// const MAX_COMPONENT_STRING_LENGTH: u32 = 262144;

/// Read a single byte from the reader
pub async fn read_byte<T: AsyncRead + std::marker::Unpin>(
    buf: &mut BufReader<T>,
) -> Result<u8, String> {
    match AsyncReadExt::read_u8(buf).await {
        Ok(r) => Ok(r),
        Err(_) => Err("Error reading byte".to_string()),
    }
}

pub fn write_byte(buf: &mut Vec<u8>, n: u8) {
    WriteBytesExt::write_u8(buf, n).unwrap();
}

pub fn write_bytes(buf: &mut Vec<u8>, bytes: &[u8]) {
    buf.extend_from_slice(bytes);
}

// fast varints stolen from https://github.com/luojia65/mc-varint/blob/master/src/lib.rs#L67
/// Read a single varint from the reader and return the value, along with the number of bytes read
pub async fn read_varint<T: AsyncRead + std::marker::Unpin>(
    buf: &mut BufReader<T>,
) -> Result<(i32, u8), String> {
    let mut buffer = [0];
    let mut ans = 0;
    for i in 0..4 {
        buf.read_exact(&mut buffer)
            .await
            .map_err(|_| "Invalid VarInt".to_string())?;
        ans |= ((buffer[0] & 0b0111_1111) as i32) << (7 * i);
        if buffer[0] & 0b1000_0000 == 0 {
            return Ok((ans, i + 1));
        }
    }
    Ok((ans, 5))
}

pub fn write_varint(buf: &mut Vec<u8>, mut value: i32) {
    let mut buffer = [0];
    if value == 0 {
        buf.write_all(&buffer).unwrap();
    }
    while value != 0 {
        buffer[0] = (value & 0b0111_1111) as u8;
        value = (value >> 7) & (i32::max_value() >> 6);
        if value != 0 {
            buffer[0] |= 0b1000_0000;
        }
        buf.write_all(&buffer).unwrap();
    }
}

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

    #[test]
    fn test_write_varint() {
        let mut buf = Vec::new();
        write_varint(&mut buf, 123456);
        assert_eq!(buf, vec![192, 196, 7]);

        let mut buf = Vec::new();
        write_varint(&mut buf, 0);
        assert_eq!(buf, vec![0]);
    }

    #[tokio::test]
    async fn test_read_varint() {
        let mut buf = BufReader::new(Cursor::new(vec![192, 196, 7]));
        assert_eq!(read_varint(&mut buf).await.unwrap(), (123456, 3));

        let mut buf = BufReader::new(Cursor::new(vec![0]));
        assert_eq!(read_varint(&mut buf).await.unwrap(), (0, 1));

        let mut buf = BufReader::new(Cursor::new(vec![1]));
        assert_eq!(read_varint(&mut buf).await.unwrap(), (1, 1));
    }

    #[tokio::test]
    async fn test_read_varint_longer() {
        let mut buf = BufReader::new(Cursor::new(vec![138, 56, 0, 135, 56, 123]));
        assert_eq!(read_varint(&mut buf).await.unwrap(), (7178, 2));
    }
}

pub async fn read_utf_with_len<T: AsyncRead + std::marker::Unpin>(
    buf: &mut BufReader<T>,
    max_length: u32,
) -> Result<String, String> {
    let (length, _length_varint_length) = read_varint(buf).await?;
    // i don't know why it's multiplied by 4 but it's like that in mojang's code so
    if length < 0 {
        return Err(
            "The received encoded string buffer length is less than zero! Weird string!"
                .to_string(),
        );
    }
    if length as u32 > max_length * 4 {
        return Err(format!(
            "The received encoded string buffer length is longer than maximum allowed ({} > {})",
            length,
            max_length * 4
        ));
    }

    // this is probably quite inefficient, idk how to do it better
    let mut string = String::new();
    let mut buffer = vec![0; length as usize];
    buf.read_exact(&mut buffer)
        .await
        .map_err(|_| "Invalid UTF-8".to_string())?;

    string.push_str(std::str::from_utf8(&buffer).unwrap());
    if string.len() > length as usize {
        return Err(format!(
            "The received string length is longer than maximum allowed ({} > {})",
            length, max_length
        ));
    }

    Ok(string)
}

pub fn write_utf_with_len(buf: &mut Vec<u8>, string: &str, len: usize) {
    if string.len() > len {
        panic!(
            "String too big (was {} bytes encoded, max {})",
            string.len(),
            len
        );
    }
    write_varint(buf, string.len() as i32);
    write_bytes(buf, string.as_bytes());
}

pub async fn read_utf<T: AsyncRead + std::marker::Unpin>(
    buf: &mut BufReader<T>,
) -> Result<String, String> {
    read_utf_with_len(buf, MAX_STRING_LENGTH.into()).await
}

pub fn write_utf(buf: &mut Vec<u8>, string: &str) {
    write_utf_with_len(buf, string, MAX_STRING_LENGTH.into());
}

pub fn write_short(buf: &mut Vec<u8>, n: u16) {
    WriteBytesExt::write_u16::<BigEndian>(buf, n).unwrap();
}