1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150

/*
==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--

SJ

Copyright (C) 2019-2023  Anonymous

There are several releases over multiple years,
they are listed as ranges, such as: "2019-2023".

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.

::--::--::--::--::--::--::--::--::--::--::--::--::--::--::--::--
*/

//! # Unicode character
//!
//! ## References
//!
//! - <https://en.wikipedia.org/wiki/UTF-8>

use {
    alloc::vec::Vec,
    crate::Result,
};

/// # Unicode character
#[derive(Debug)]
pub (super) struct UnicodeChar {
    bytes: [u8; 4],
    idx: usize,
}

impl UnicodeChar {

    /// # Makes new instance
    pub fn new() -> Self {
        Self {
            bytes: [0; 4],
            idx: 0,
        }
    }

    /// # Adds new byte written as a hexadecimal
    pub fn add_hex(&mut self, hex: &u8) -> Result<()> {
        match self.bytes.get_mut(self.idx) {
            Some(item) => {
                let byte = match hex {
                    b'0'..=b'9' => hex - b'0',
                    b'a'..=b'f' => hex - b'a' + 10,
                    b'A'..=b'F' => hex - b'A' + 10,
                    _ => return Err(err!("Not a hexadecimal: {:?}", char::from(*hex))),
                };
                match self.idx % 2 {
                    0 => *item = byte * 16,
                    _ => *item = byte,
                };
                self.idx += 1;
                Ok(())
            },
            None => return Err(err!("Bytes are full")),
        }
    }

    /// # Checks if data is full
    pub fn is_full(&self) -> bool {
        self.idx >= self.bytes.len()
    }

    /// # Encodes as UTF-8 bytes
    pub fn encode_as_utf8_bytes(self, out: &mut Vec<u8>) -> Result<()> {
        const MARKER: u8 = 0b_1000_0000;

        if self.is_full() {
            let first = self.bytes[0] + self.bytes[1];
            let last = self.bytes[2] + self.bytes[3];
            let byte_count = match first {
                0x00 => match last {
                    0x00..=0x7f => ByteCount::One,
                    _ => ByteCount::Two,
                },
                0x01..=0x07 => ByteCount::Two,
                _ => ByteCount::Three,
            };
            match byte_count {
                ByteCount::One => out.push(last),
                ByteCount::Two => {
                    const HEADER_OF_TWO: u8 = 0b_1100_0000;
                    out.push(HEADER_OF_TWO | (first << 5 >> 3) | (last >> 6));
                    out.push(MARKER | (last << 2 >> 2));
                },
                ByteCount::Three => {
                    const HEADER_OF_THREE: u8 = 0b_1110_0000;
                    out.push(HEADER_OF_THREE | (first >> 4));
                    out.push(MARKER | (first << 4 >> 2) | (last >> 6));
                    out.push(MARKER | (last << 2 >> 2));
                },
            };
            return Ok(());
        }

        Err(err!("Bytes are not full"))
    }

}

/// # Byte count
#[derive(Debug)]
enum ByteCount {
    One,
    Two,
    Three,
}

#[test]
fn tests() -> Result<()> {
    for (hex, chr) in &[
        ("0024", '\u{0024}'), ("00A2", '\u{00a2}'),

        ("07fF", '\u{07ff}'),

        ("0939", '\u{0939}'), ("20AC", '\u{20AC}'), ("d55c", '\u{d55c}'), ("1d2D", '\u{1d2d}'), ("0800", '\u{0800}'), ("fFFf", '\u{FFff}'),
    ] {
        let mut buf = [0; 4];
        chr.encode_utf8(&mut buf);
        let buf = &buf[..chr.len_utf8()];

        let mut uc = UnicodeChar::new();
        for b in hex.as_bytes() {
            uc.add_hex(b)?;
        }

        let mut out = Vec::with_capacity(4);
        uc.encode_as_utf8_bytes(&mut out)?;
        assert_eq!(out, buf);
    }

    Ok(())
}