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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.

    //! Parser and serializer for the [`application/x-www-form-urlencoded` syntax](
    //! http://url.spec.whatwg.org/#application/x-www-form-urlencoded),
    //! as used by HTML forms.
    //!
    //! Converts between a string (such as an URL’s query string)
    //! and a sequence of (name, value) pairs.

    #[macro_use]
    extern crate matches;

    use percent_encoding::{percent_decode, percent_encode_byte};
    use std::borrow::{Borrow, Cow};
    use std::str;

    /// Convert a byte string in the `application/x-www-form-urlencoded` syntax
    /// into a iterator of (name, value) pairs.
    ///
    /// Use `parse(input.as_bytes())` to parse a `&str` string.
    ///
    /// The names and values are percent-decoded. For instance, `%23first=%25try%25` will be
    /// converted to `[("#first", "%try%")]`.
    #[inline]
    pub fn parse(input: &[u8]) -> Parse<'_> {
        Parse { input }
    }
    /// The return type of `parse()`.
    #[derive(Copy, Clone)]
    pub struct Parse<'a> {
        input: &'a [u8],
    }

    impl<'a> Iterator for Parse<'a> {
        type Item = (Cow<'a, str>, Cow<'a, str>);

        fn next(&mut self) -> Option<Self::Item> {
            loop {
                if self.input.is_empty() {
                    return None;
                }
                let mut split2 = self.input.splitn(2, |&b| b == b'&');
                let sequence = split2.next().unwrap();
                self.input = split2.next().unwrap_or(&[][..]);
                if sequence.is_empty() {
                    continue;
                }
                let mut split2 = sequence.splitn(2, |&b| b == b'=');
                let name = split2.next().unwrap();
                let value = split2.next().unwrap_or(&[][..]);
                return Some((decode(name), decode(value)));
            }
        }
    }

    fn decode(input: &[u8]) -> Cow<'_, str> {
        let replaced = replace_plus(input);
        decode_utf8_lossy(match percent_decode(&replaced).into() {
            Cow::Owned(vec) => Cow::Owned(vec),
            Cow::Borrowed(_) => replaced,
        })
    }

    /// Replace b'+' with b' '
    fn replace_plus(input: &[u8]) -> Cow<'_, [u8]> {
        match input.iter().position(|&b| b == b'+') {
            None => Cow::Borrowed(input),
            Some(first_position) => {
                let mut replaced = input.to_owned();
                replaced[first_position] = b' ';
                for byte in &mut replaced[first_position + 1..] {
                    if *byte == b'+' {
                        *byte = b' ';
                    }
                }
                Cow::Owned(replaced)
            }
        }
    }

    impl<'a> Parse<'a> {
        /// Return a new iterator that yields pairs of `String` instead of pairs of `Cow<str>`.
        pub fn into_owned(self) -> ParseIntoOwned<'a> {
            ParseIntoOwned { inner: self }
        }
    }

    /// Like `Parse`, but yields pairs of `String` instead of pairs of `Cow<str>`.
    pub struct ParseIntoOwned<'a> {
        inner: Parse<'a>,
    }

    impl<'a> Iterator for ParseIntoOwned<'a> {
        type Item = (String, String);

        fn next(&mut self) -> Option<Self::Item> {
            self.inner
                .next()
                .map(|(k, v)| (k.into_owned(), v.into_owned()))
        }
    }

    /// The [`application/x-www-form-urlencoded` byte serializer](
    /// https://url.spec.whatwg.org/#concept-urlencoded-byte-serializer).
    ///
    /// Return an iterator of `&str` slices.
    pub fn byte_serialize(input: &[u8]) -> ByteSerialize<'_> {
        ByteSerialize { bytes: input }
    }

    /// Return value of `byte_serialize()`.
    #[derive(Debug)]
    pub struct ByteSerialize<'a> {
        bytes: &'a [u8],
    }

    fn byte_serialized_unchanged(byte: u8) -> bool {
        matches!(byte, b'*' | b'-' | b'.' | b'0' ..= b'9' | b'A' ..= b'Z' | b'_' | b'a' ..= b'z')
    }

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

        fn next(&mut self) -> Option<&'a str> {
            if let Some((&first, tail)) = self.bytes.split_first() {
                if !byte_serialized_unchanged(first) {
                    self.bytes = tail;
                    return Some(if first == b' ' {
                        "+"
                    } else {
                        percent_encode_byte(first)
                    });
                }
                let position = tail.iter().position(|&b| !byte_serialized_unchanged(b));
                let (unchanged_slice, remaining) = match position {
                    // 1 for first_byte + i unchanged in tail
                    Some(i) => self.bytes.split_at(1 + i),
                    None => (self.bytes, &[][..]),
                };
                self.bytes = remaining;
                // This unsafe is appropriate because we have already checked these
                // bytes in byte_serialized_unchanged, which checks for a subset
                // of UTF-8. So we know these bytes are valid UTF-8, and doing
                // another UTF-8 check would be wasteful.
                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()))
            }
        }
    }

    /// The [`application/x-www-form-urlencoded` serializer](
    /// https://url.spec.whatwg.org/#concept-urlencoded-serializer).
    pub struct Serializer<'a, T: Target> {
        target: Option<T>,
        start_position: usize,
        encoding: EncodingOverride<'a>,
    }

    pub trait Target {
        fn as_mut_string(&mut self) -> &mut String;
        fn finish(self) -> Self::Finished;
        type Finished;
    }

    impl Target for String {
        fn as_mut_string(&mut self) -> &mut String {
            self
        }
        fn finish(self) -> Self {
            self
        }
        type Finished = Self;
    }

    impl<'a> Target for &'a mut String {
        fn as_mut_string(&mut self) -> &mut String {
            &mut **self
        }
        fn finish(self) -> Self {
            self
        }
        type Finished = Self;
    }

    impl<'a, T: Target> Serializer<'a, T> {
        /// Create a new `application/x-www-form-urlencoded` serializer for the given target.
        ///
        /// If the target is non-empty,
        /// its content is assumed to already be in `application/x-www-form-urlencoded` syntax.
        pub fn new(target: T) -> Self {
            Self::for_suffix(target, 0)
        }

        /// Create a new `application/x-www-form-urlencoded` serializer
        /// for a suffix of the given target.
        ///
        /// If that suffix is non-empty,
        /// its content is assumed to already be in `application/x-www-form-urlencoded` syntax.
        pub fn for_suffix(mut target: T, start_position: usize) -> Self {
            if target.as_mut_string().len() < start_position {
                panic!(
                    "invalid length {} for target of length {}",
                    start_position,
                    target.as_mut_string().len()
                );
            }

            Serializer {
                target: Some(target),
                start_position,
                encoding: None,
            }
        }

        /// Remove any existing name/value pair.
        ///
        /// Panics if called after `.finish()`.
        pub fn clear(&mut self) -> &mut Self {
            string(&mut self.target).truncate(self.start_position);
            self
        }

        /// Set the character encoding to be used for names and values before percent-encoding.
        pub fn encoding_override(&mut self, new: EncodingOverride<'a>) -> &mut Self {
            self.encoding = new;
            self
        }

        /// Serialize and append a name/value pair.
        ///
        /// Panics if called after `.finish()`.
        pub fn append_pair(&mut self, name: &str, value: &str) -> &mut Self {
            append_pair(
                string(&mut self.target),
                self.start_position,
                self.encoding,
                name,
                value,
            );
            self
        }

        /// Serialize and append a name of parameter without any value.
        ///
        /// Panics if called after `.finish()`.
        pub fn append_key_only(&mut self, name: &str) -> &mut Self {
            append_key_only(
                string(&mut self.target),
                self.start_position,
                self.encoding,
                name,
            );
            self
        }

        /// Serialize and append a number of name/value pairs.
        ///
        /// This simply calls `append_pair` repeatedly.
        /// This can be more convenient, so the user doesn’t need to introduce a block
        /// to limit the scope of `Serializer`’s borrow of its string.
        ///
        /// Panics if called after `.finish()`.
        pub fn extend_pairs<I, K, V>(&mut self, iter: I) -> &mut Self
        where
            I: IntoIterator,
            I::Item: Borrow<(K, V)>,
            K: AsRef<str>,
            V: AsRef<str>,
        {
            {
                let string = string(&mut self.target);
                for pair in iter {
                    let &(ref k, ref v) = pair.borrow();
                    append_pair(
                        string,
                        self.start_position,
                        self.encoding,
                        k.as_ref(),
                        v.as_ref(),
                    );
                }
            }
            self
        }

        /// Serialize and append a number of names without values.
        ///
        /// This simply calls `append_key_only` repeatedly.
        /// This can be more convenient, so the user doesn’t need to introduce a block
        /// to limit the scope of `Serializer`’s borrow of its string.
        ///
        /// Panics if called after `.finish()`.
        pub fn extend_keys_only<I, K>(&mut self, iter: I) -> &mut Self
        where
            I: IntoIterator,
            I::Item: Borrow<K>,
            K: AsRef<str>,
        {
            {
                let string = string(&mut self.target);
                for key in iter {
                    let k = key.borrow().as_ref();
                    append_key_only(string, self.start_position, self.encoding, k);
                }
            }
            self
        }

        /// If this serializer was constructed with a string, take and return that string.
        ///
        /// ```rust
        /// use form_urlencoded;
        /// let encoded: String = form_urlencoded::Serializer::new(String::new())
        ///     .append_pair("foo", "bar & baz")
        ///     .append_pair("saison", "Été+hiver")
        ///     .finish();
        /// assert_eq!(encoded, "foo=bar+%26+baz&saison=%C3%89t%C3%A9%2Bhiver");
        /// ```
        ///
        /// Panics if called more than once.
        pub fn finish(&mut self) -> T::Finished {
            self.target
                .take()
                .expect("url::form_urlencoded::Serializer double finish")
                .finish()
        }
    }

    fn append_separator_if_needed(string: &mut String, start_position: usize) {
        if string.len() > start_position {
            string.push('&')
        }
    }

    fn string<T: Target>(target: &mut Option<T>) -> &mut String {
        target
            .as_mut()
            .expect("url::form_urlencoded::Serializer finished")
            .as_mut_string()
    }

    fn append_pair(
        string: &mut String,
        start_position: usize,
        encoding: EncodingOverride<'_>,
        name: &str,
        value: &str,
    ) {
        append_separator_if_needed(string, start_position);
        append_encoded(name, string, encoding);
        string.push('=');
        append_encoded(value, string, encoding);
    }

    fn append_key_only(
        string: &mut String,
        start_position: usize,
        encoding: EncodingOverride,
        name: &str,
    ) {
        append_separator_if_needed(string, start_position);
        append_encoded(name, string, encoding);
    }

    fn append_encoded(s: &str, string: &mut String, encoding: EncodingOverride<'_>) {
        string.extend(byte_serialize(&encode(encoding, s)))
    }

    pub(crate) fn encode<'a>(encoding_override: EncodingOverride<'_>, input: &'a str) -> Cow<'a, [u8]> {
        if let Some(o) = encoding_override {
            return o(input);
        }
        input.as_bytes().into()
    }

    pub(crate) fn decode_utf8_lossy(input: Cow<'_, [u8]>) -> Cow<'_, str> {
        // Note: This function is duplicated in `percent_encoding/lib.rs`.
        match input {
            Cow::Borrowed(bytes) => String::from_utf8_lossy(bytes),
            Cow::Owned(bytes) => {
                match String::from_utf8_lossy(&bytes) {
                    Cow::Borrowed(utf8) => {
                        // If from_utf8_lossy returns a Cow::Borrowed, then we can
                        // be sure our original bytes were valid UTF-8. This is because
                        // if the bytes were invalid UTF-8 from_utf8_lossy would have
                        // to allocate a new owned string to back the Cow so it could
                        // replace invalid bytes with a placeholder.

                        // First we do a debug_assert to confirm our description above.
                        let raw_utf8: *const [u8];
                        raw_utf8 = utf8.as_bytes();
                        debug_assert!(raw_utf8 == &*bytes as *const [u8]);

                        // Given we know the original input bytes are valid UTF-8,
                        // and we have ownership of those bytes, we re-use them and
                        // return a Cow::Owned here.
                        Cow::Owned(unsafe { String::from_utf8_unchecked(bytes) })
                    }
                    Cow::Owned(s) => Cow::Owned(s),
                }
            }
        }
    }

    pub type EncodingOverride<'a> = Option<&'a dyn Fn(&str) -> Cow<'_, [u8]>>;