use crate::enc::floatX;

fn parse_as_utf8(input: &[u8], size: usize) -> (usize, i32) {

    if (input[0] & 0x80) == 0 {

        if input[0] > 0 {

            return (1, i32::from(input[0]));

        }

    }

    if size > 1 && (input[0] & 0xe0) == 0xc0 && (input[1] & 0xc0) == 0x80 {

        let symbol = (input[0] as i32 & 0x1f) << 6 | input[1] as i32 & 0x3f;

        if symbol > 0x7f {

            return (2, symbol);

        }

    }

    if size > 2

        && (input[0] & 0xf0) == 0xe0

        && (input[1] & 0xc0) == 0x80

        && (input[2] & 0xc0) == 0x80

    {

        let symbol = (i32::from(input[0]) & 0x0f) << 12

            | (i32::from(input[1]) & 0x3f) << 6

            | i32::from(input[2]) & 0x3f;

        if symbol > 0x7ff {

            return (3, symbol);

        }

    }

    if size > 3

        && (input[0] & 0xf8) == 0xf0

        && (input[1] & 0xc0) == 0x80

        && (input[2] & 0xc0) == 0x80

        && (input[3] & 0xc0) == 0x80

    {

        let symbol = (i32::from(input[0]) & 0x07) << 18

            | (i32::from(input[1]) & 0x3f) << 12

            | (i32::from(input[2]) & 0x3f) << 6

            | i32::from(input[3]) & 0x3f;

        if symbol > 0xffff && symbol <= 0x10_ffff {

            return (4, symbol);

        }

    }

    (1, 0x11_0000 | i32::from(input[0]))

}

pub(crate) fn is_mostly_utf8(

    data: &[u8],

    pos: usize,

    mask: usize,

    length: usize,

    min_fraction: floatX,

) -> bool {

    let mut size_utf8: usize = 0;

    let mut i: usize = 0;

    while i < length {

        let (bytes_read, symbol) = parse_as_utf8(&data[(pos.wrapping_add(i) & mask)..], length - i);

        i = i.wrapping_add(bytes_read);

        if symbol < 0x11_0000 {

            size_utf8 = size_utf8.wrapping_add(bytes_read);

        }

    }

    size_utf8 as floatX > min_fraction * length as floatX

}