// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT

// file at the top-level directory of this distribution and at

// http://rust-lang.org/COPYRIGHT.

//

// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or

// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license

// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your

// option. This file may not be copied, modified, or distributed

// except according to those terms.

//

// Original authors: alexchrichton, bluss

// UTF-8 ranges and tags for encoding characters

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;

/// Placeholder

pub struct EncodeUtf8Error;

/// Encode a char into buf using UTF-8.

///

/// On success, return the byte length of the encoding (1, 2, 3 or 4).<br>

/// On error, return `EncodeUtf8Error` if the buffer was too short for the char.

///

/// Safety: `ptr` must be writable for `len` bytes.

#[inline]

pub unsafe fn encode_utf8(ch: char, ptr: *mut u8, len: usize) -> Result<usize, EncodeUtf8Error>

{

    let code = ch as u32;

    if code < MAX_ONE_B && len >= 1 {

        ptr.add(0).write(code as u8);

        return Ok(1);

    } else if code < MAX_TWO_B && len >= 2 {

        ptr.add(0).write((code >> 6 & 0x1F) as u8 | TAG_TWO_B);

        ptr.add(1).write((code & 0x3F) as u8 | TAG_CONT);

        return Ok(2);

    } else if code < MAX_THREE_B && len >= 3 {

        ptr.add(0).write((code >> 12 & 0x0F) as u8 | TAG_THREE_B);

        ptr.add(1).write((code >>  6 & 0x3F) as u8 | TAG_CONT);

        ptr.add(2).write((code & 0x3F) as u8 | TAG_CONT);

        return Ok(3);

    } else if len >= 4 {

        ptr.add(0).write((code >> 18 & 0x07) as u8 | TAG_FOUR_B);

        ptr.add(1).write((code >> 12 & 0x3F) as u8 | TAG_CONT);

        ptr.add(2).write((code >>  6 & 0x3F) as u8 | TAG_CONT);

        ptr.add(3).write((code & 0x3F) as u8 | TAG_CONT);

        return Ok(4);

    };

    Err(EncodeUtf8Error)

}

#[test]

#[cfg_attr(miri, ignore)] // Miri is too slow

fn test_encode_utf8() {

    // Test that all codepoints are encoded correctly

    let mut data = [0u8; 16];

    for codepoint in 0..=(std::char::MAX as u32) {

        if let Some(ch) = std::char::from_u32(codepoint) {

            for elt in &mut data { *elt = 0; }

            let ptr = data.as_mut_ptr();

            let len = data.len();

            unsafe {

                let res = encode_utf8(ch, ptr, len).ok().unwrap();

                assert_eq!(res, ch.len_utf8());

            }

            let string = std::str::from_utf8(&data).unwrap();

            assert_eq!(string.chars().next(), Some(ch));

        }

    }

}

#[test]

fn test_encode_utf8_oob() {

    // test that we report oob if the buffer is too short

    let mut data = [0u8; 16];

    let chars = ['a', 'α', '�', '𐍈'];

    for (len, &ch) in (1..=4).zip(&chars) {

        assert_eq!(len, ch.len_utf8(), "Len of ch={}", ch);

        let ptr = data.as_mut_ptr();

        unsafe {

            assert!(matches::matches!(encode_utf8(ch, ptr, len - 1), Err(_)));

            assert!(matches::matches!(encode_utf8(ch, ptr, len), Ok(_)));

        }

    }

}