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    // Copyright 2013-2016 The rust-url developers.
    //
    // 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.

    //! URLs use special chacters to indicate the parts of the request.
    //! For example, a `?` question mark marks the end of a path and the start of a query string.
    //! In order for that character to exist inside a path, it needs to be encoded differently.
    //!
    //! Percent encoding replaces reserved characters with the `%` escape character
    //! followed by a byte value as two hexadecimal digits.
    //! For example, an ASCII space is replaced with `%20`.
    //!
    //! When encoding, the set of characters that can (and should, for readability) be left alone
    //! depends on the context.
    //! The `?` question mark mentioned above is not a separator when used literally
    //! inside of a query string, and therefore does not need to be encoded.
    //! The [`AsciiSet`] parameter of [`percent_encode`] and [`utf8_percent_encode`]
    //! lets callers configure this.
    //!
    //! This crate delibarately does not provide many different sets.
    //! Users should consider in what context the encoded string will be used,
    //! real relevant specifications, and define their own set.
    //! This is done by using the `add` method of an existing set.
    //!
    //! # Examples
    //!
    //! ```
    //! use percent_encoding::{utf8_percent_encode, AsciiSet, CONTROLS};
    //!
    //! /// https://url.spec.whatwg.org/#fragment-percent-encode-set
    //! const FRAGMENT: &AsciiSet = &CONTROLS.add(b' ').add(b'"').add(b'<').add(b'>').add(b'`');
    //!
    //! assert_eq!(utf8_percent_encode("foo <bar>", FRAGMENT).to_string(), "foo%20%3Cbar%3E");
    //! ```

    use std::borrow::Cow;
    use std::fmt;
    use std::slice;
    use std::str;

    /// Represents a set of characters or bytes in the ASCII range.
    ///
    /// This used in [`percent_encode`] and [`utf8_percent_encode`].
    /// This is simlar to [percent-encode sets](https://url.spec.whatwg.org/#percent-encoded-bytes).
    ///
    /// Use the `add` method of an existing set to define a new set. For example:
    ///
    /// ```
    /// use percent_encoding::{AsciiSet, CONTROLS};
    ///
    /// /// https://url.spec.whatwg.org/#fragment-percent-encode-set
    /// const FRAGMENT: &AsciiSet = &CONTROLS.add(b' ').add(b'"').add(b'<').add(b'>').add(b'`');
    /// ```
    pub struct AsciiSet {
        mask: [Chunk; ASCII_RANGE_LEN / BITS_PER_CHUNK],
    }

    type Chunk = u32;

    const ASCII_RANGE_LEN: usize = 0x80;

    const BITS_PER_CHUNK: usize = 8 * std::mem::size_of::<Chunk>();

    impl AsciiSet {
        /// Called with UTF-8 bytes rather than code points.
        /// Not used for non-ASCII bytes.
        const fn contains(&self, byte: u8) -> bool {
            let chunk = self.mask[byte as usize / BITS_PER_CHUNK];
            let mask = 1 << (byte as usize % BITS_PER_CHUNK);
            (chunk & mask) != 0
        }

        fn should_percent_encode(&self, byte: u8) -> bool {
            !byte.is_ascii() || self.contains(byte)
        }

        pub const fn add(&self, byte: u8) -> Self {
            let mut mask = self.mask;
            mask[byte as usize / BITS_PER_CHUNK] |= 1 << (byte as usize % BITS_PER_CHUNK);
            AsciiSet { mask }
        }

        pub const fn remove(&self, byte: u8) -> Self {
            let mut mask = self.mask;
            mask[byte as usize / BITS_PER_CHUNK] &= !(1 << (byte as usize % BITS_PER_CHUNK));
            AsciiSet { mask }
        }
    }

    /// The set of 0x00 to 0x1F (C0 controls), and 0x7F (DEL).
    ///
    /// Note that this includes the newline and tab characters, but not the space 0x20.
    ///
    /// <https://url.spec.whatwg.org/#c0-control-percent-encode-set>
    pub const CONTROLS: &AsciiSet = &AsciiSet {
        mask: [
            !0_u32, // C0: 0x00 to 0x1F (32 bits set)
            0,
            0,
            1 << (0x7F_u32 % 32), // DEL: 0x7F (one bit set)
        ],
    };

    macro_rules! static_assert {
        ($( $bool: expr, )+) => {
            fn _static_assert() {
                $(
                    let _ = std::mem::transmute::<[u8; $bool as usize], u8>;
                )+
            }
        }
    }

    static_assert! {
        CONTROLS.contains(0x00),
        CONTROLS.contains(0x1F),
        !CONTROLS.contains(0x20),
        !CONTROLS.contains(0x7E),
        CONTROLS.contains(0x7F),
    }

    /// Everything that is not an ASCII letter or digit.
    ///
    /// This is probably more eager than necessary in any context.
    pub const NON_ALPHANUMERIC: &AsciiSet = &CONTROLS
        .add(b' ')
        .add(b'!')
        .add(b'"')
        .add(b'#')
        .add(b'$')
        .add(b'%')
        .add(b'&')
        .add(b'\'')
        .add(b'(')
        .add(b')')
        .add(b'*')
        .add(b'+')
        .add(b',')
        .add(b'-')
        .add(b'.')
        .add(b'/')
        .add(b':')
        .add(b';')
        .add(b'<')
        .add(b'=')
        .add(b'>')
        .add(b'?')
        .add(b'@')
        .add(b'[')
        .add(b'\\')
        .add(b']')
        .add(b'^')
        .add(b'_')
        .add(b'`')
        .add(b'{')
        .add(b'|')
        .add(b'}')
        .add(b'~');

    /// Return the percent-encoding of the given byte.
    ///
    /// This is unconditional, unlike `percent_encode()` which has an `AsciiSet` parameter.
    ///
    /// # Examples
    ///
    /// ```
    /// use percent_encoding::percent_encode_byte;
    ///
    /// assert_eq!("foo bar".bytes().map(percent_encode_byte).collect::<String>(),
    ///            "%66%6F%6F%20%62%61%72");
    /// ```
    pub fn percent_encode_byte(byte: u8) -> &'static str {
        let index = usize::from(byte) * 3;
        &"\
          %00%01%02%03%04%05%06%07%08%09%0A%0B%0C%0D%0E%0F\
          %10%11%12%13%14%15%16%17%18%19%1A%1B%1C%1D%1E%1F\
          %20%21%22%23%24%25%26%27%28%29%2A%2B%2C%2D%2E%2F\
          %30%31%32%33%34%35%36%37%38%39%3A%3B%3C%3D%3E%3F\
          %40%41%42%43%44%45%46%47%48%49%4A%4B%4C%4D%4E%4F\
          %50%51%52%53%54%55%56%57%58%59%5A%5B%5C%5D%5E%5F\
          %60%61%62%63%64%65%66%67%68%69%6A%6B%6C%6D%6E%6F\
          %70%71%72%73%74%75%76%77%78%79%7A%7B%7C%7D%7E%7F\
          %80%81%82%83%84%85%86%87%88%89%8A%8B%8C%8D%8E%8F\
          %90%91%92%93%94%95%96%97%98%99%9A%9B%9C%9D%9E%9F\
          %A0%A1%A2%A3%A4%A5%A6%A7%A8%A9%AA%AB%AC%AD%AE%AF\
          %B0%B1%B2%B3%B4%B5%B6%B7%B8%B9%BA%BB%BC%BD%BE%BF\
          %C0%C1%C2%C3%C4%C5%C6%C7%C8%C9%CA%CB%CC%CD%CE%CF\
          %D0%D1%D2%D3%D4%D5%D6%D7%D8%D9%DA%DB%DC%DD%DE%DF\
          %E0%E1%E2%E3%E4%E5%E6%E7%E8%E9%EA%EB%EC%ED%EE%EF\
          %F0%F1%F2%F3%F4%F5%F6%F7%F8%F9%FA%FB%FC%FD%FE%FF\
          "[index..index + 3]
    }

    /// Percent-encode the given bytes with the given set.
    ///
    /// Non-ASCII bytes and bytes in `ascii_set` are encoded.
    ///
    /// The return type:
    ///
    /// * Implements `Iterator<Item = &str>` and therefore has a `.collect::<String>()` method,
    /// * Implements `Display` and therefore has a `.to_string()` method,
    /// * Implements `Into<Cow<str>>` borrowing `input` when none of its bytes are encoded.
    ///
    /// # Examples
    ///
    /// ```
    /// use percent_encoding::{percent_encode, NON_ALPHANUMERIC};
    ///
    /// assert_eq!(percent_encode(b"foo bar?", NON_ALPHANUMERIC).to_string(), "foo%20bar%3F");
    /// ```
    #[inline]
    pub fn percent_encode<'a>(input: &'a [u8], ascii_set: &'static AsciiSet) -> PercentEncode<'a> {
        PercentEncode {
            bytes: input,
            ascii_set,
        }
    }

    /// Percent-encode the UTF-8 encoding of the given string.
    ///
    /// See [`percent_encode`] regarding the return type.
    ///
    /// # Examples
    ///
    /// ```
    /// use percent_encoding::{utf8_percent_encode, NON_ALPHANUMERIC};
    ///
    /// assert_eq!(utf8_percent_encode("foo bar?", NON_ALPHANUMERIC).to_string(), "foo%20bar%3F");
    /// ```
    #[inline]
    pub fn utf8_percent_encode<'a>(input: &'a str, ascii_set: &'static AsciiSet) -> PercentEncode<'a> {
        percent_encode(input.as_bytes(), ascii_set)
    }

    /// The return type of [`percent_encode`] and [`utf8_percent_encode`].
    #[derive(Clone)]
    pub struct PercentEncode<'a> {
        bytes: &'a [u8],
        ascii_set: &'static AsciiSet,
    }

    impl<'a> Iterator for PercentEncode<'a> {
        type Item = &'a str;

        fn next(&mut self) -> Option<&'a str> {
            if let Some((&first_byte, remaining)) = self.bytes.split_first() {
                if self.ascii_set.should_percent_encode(first_byte) {
                    self.bytes = remaining;
                    Some(percent_encode_byte(first_byte))
                } else {
                    for (i, &byte) in remaining.iter().enumerate() {
                        if self.ascii_set.should_percent_encode(byte) {
                            // 1 for first_byte + i for previous iterations of this loop
                            let (unchanged_slice, remaining) = self.bytes.split_at(1 + i);
                            self.bytes = remaining;
                            return Some(unsafe { str::from_utf8_unchecked(unchanged_slice) });
                        }
                    }
                    let unchanged_slice = self.bytes;
                    self.bytes = &[][..];
                    Some(unsafe { str::from_utf8_unchecked(unchanged_slice) })
                }
            } else {
                None
            }
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            if self.bytes.is_empty() {
                (0, Some(0))
            } else {
                (1, Some(self.bytes.len()))
            }
        }
    }

    impl<'a> fmt::Display for PercentEncode<'a> {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            for c in (*self).clone() {
                formatter.write_str(c)?
            }
            Ok(())
        }
    }

    impl<'a> From<PercentEncode<'a>> for Cow<'a, str> {
        fn from(mut iter: PercentEncode<'a>) -> Self {
            match iter.next() {
                None => "".into(),
                Some(first) => match iter.next() {
                    None => first.into(),
                    Some(second) => {
                        let mut string = first.to_owned();
                        string.push_str(second);
                        string.extend(iter);
                        string.into()
                    }
                },
            }
        }
    }

    /// Percent-decode the given string.
    ///
    /// <https://url.spec.whatwg.org/#string-percent-decode>
    ///
    /// See [`percent_decode`] regarding the return type.
    #[inline]
    pub fn percent_decode_str(input: &str) -> PercentDecode {
        percent_decode(input.as_bytes())
    }

    /// Percent-decode the given bytes.
    ///
    /// <https://url.spec.whatwg.org/#percent-decode>
    ///
    /// Any sequence of `%` followed by two hexadecimal digits is decoded.
    /// The return type:
    ///
    /// * Implements `Into<Cow<u8>>` borrowing `input` when it contains no percent-encoded sequence,
    /// * Implements `Iterator<Item = u8>` and therefore has a `.collect::<Vec<u8>>()` method,
    /// * Has `decode_utf8()` and `decode_utf8_lossy()` methods.
    ///
    /// # Examples
    ///
    /// ```
    /// use percent_encoding::percent_decode;
    ///
    /// assert_eq!(percent_decode(b"foo%20bar%3f").decode_utf8().unwrap(), "foo bar?");
    /// ```
    #[inline]
    pub fn percent_decode(input: &[u8]) -> PercentDecode {
        PercentDecode {
            bytes: input.iter(),
        }
    }

    /// The return type of [`percent_decode`].
    #[derive(Clone, Debug)]
    pub struct PercentDecode<'a> {
        bytes: slice::Iter<'a, u8>,
    }

    fn after_percent_sign(iter: &mut slice::Iter<u8>) -> Option<u8> {
        let mut cloned_iter = iter.clone();
        let h = char::from(*cloned_iter.next()?).to_digit(16)?;
        let l = char::from(*cloned_iter.next()?).to_digit(16)?;
        *iter = cloned_iter;
        Some(h as u8 * 0x10 + l as u8)
    }

    impl<'a> Iterator for PercentDecode<'a> {
        type Item = u8;

        fn next(&mut self) -> Option<u8> {
            self.bytes.next().map(|&byte| {
                if byte == b'%' {
                    after_percent_sign(&mut self.bytes).unwrap_or(byte)
                } else {
                    byte
                }
            })
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            let bytes = self.bytes.len();
            (bytes / 3, Some(bytes))
        }
    }

    impl<'a> From<PercentDecode<'a>> for Cow<'a, [u8]> {
        fn from(iter: PercentDecode<'a>) -> Self {
            match iter.if_any() {
                Some(vec) => Cow::Owned(vec),
                None => Cow::Borrowed(iter.bytes.as_slice()),
            }
        }
    }

    impl<'a> PercentDecode<'a> {
        /// If the percent-decoding is different from the input, return it as a new bytes vector.
        fn if_any(&self) -> Option<Vec<u8>> {
            let mut bytes_iter = self.bytes.clone();
            while bytes_iter.any(|&b| b == b'%') {
                if let Some(decoded_byte) = after_percent_sign(&mut bytes_iter) {
                    let initial_bytes = self.bytes.as_slice();
                    let unchanged_bytes_len = initial_bytes.len() - bytes_iter.len() - 3;
                    let mut decoded = initial_bytes[..unchanged_bytes_len].to_owned();
                    decoded.push(decoded_byte);
                    decoded.extend(PercentDecode { bytes: bytes_iter });
                    return Some(decoded);
                }
            }
            // Nothing to decode
            None
        }

        /// Decode the result of percent-decoding as UTF-8.
        ///
        /// This is return `Err` when the percent-decoded bytes are not well-formed in UTF-8.
        pub fn decode_utf8(self) -> Result<Cow<'a, str>, str::Utf8Error> {
            match self.clone().into() {
                Cow::Borrowed(bytes) => match str::from_utf8(bytes) {
                    Ok(s) => Ok(s.into()),
                    Err(e) => Err(e),
                },
                Cow::Owned(bytes) => match String::from_utf8(bytes) {
                    Ok(s) => Ok(s.into()),
                    Err(e) => Err(e.utf8_error()),
                },
            }
        }

        /// Decode the result of percent-decoding as UTF-8, lossily.
        ///
        /// Invalid UTF-8 percent-encoded byte sequences will be replaced � U+FFFD,
        /// the replacement character.
        pub fn decode_utf8_lossy(self) -> Cow<'a, str> {
            decode_utf8_lossy(self.clone().into())
        }
    }

    fn decode_utf8_lossy(input: Cow<[u8]>) -> Cow<str> {
        match input {
            Cow::Borrowed(bytes) => String::from_utf8_lossy(bytes),
            Cow::Owned(bytes) => {
                let raw_utf8: *const [u8];
                match String::from_utf8_lossy(&bytes) {
                    Cow::Borrowed(utf8) => raw_utf8 = utf8.as_bytes(),
                    Cow::Owned(s) => return s.into(),
                }
                // from_utf8_lossy returned a borrow of `bytes` unchanged.
                debug_assert!(raw_utf8 == &*bytes as *const [u8]);
                // Reuse the existing `Vec` allocation.
                unsafe { String::from_utf8_unchecked(bytes) }.into()
            }
        }
    }