use lib::*;

const TAG_CONT: u8 = 0b1000_0000;

const TAG_TWO_B: u8 = 0b1100_0000;

const TAG_THREE_B: u8 = 0b1110_0000;

const TAG_FOUR_B: u8 = 0b1111_0000;

const MAX_ONE_B: u32 = 0x80;

const MAX_TWO_B: u32 = 0x800;

const MAX_THREE_B: u32 = 0x10000;

#[inline]

pub fn encode(c: char) -> Encode {

    let code = c as u32;

    let mut buf = [0; 4];

    let pos = if code < MAX_ONE_B {

        buf[3] = code as u8;

        3

    } else if code < MAX_TWO_B {

        buf[2] = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;

        buf[3] = (code & 0x3F) as u8 | TAG_CONT;

        2

    } else if code < MAX_THREE_B {

        buf[1] = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;

        buf[2] = (code >> 6 & 0x3F) as u8 | TAG_CONT;

        buf[3] = (code & 0x3F) as u8 | TAG_CONT;

        1

    } else {

        buf[0] = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;

        buf[1] = (code >> 12 & 0x3F) as u8 | TAG_CONT;

        buf[2] = (code >> 6 & 0x3F) as u8 | TAG_CONT;

        buf[3] = (code & 0x3F) as u8 | TAG_CONT;

        0

    };

    Encode { buf: buf, pos: pos }

}

pub struct Encode {

    buf: [u8; 4],

    pos: usize,

}

impl Encode {

    pub fn as_str(&self) -> &str {

        str::from_utf8(&self.buf[self.pos..]).unwrap()

    }

}