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    // Copyright 2014-2015 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.

    use std::borrow::Cow;
    use std::collections::HashMap;
    use std::fmt;
    use std::ops::Index;
    use std::str::FromStr;
    use std::sync::Arc;

    use syntax;

    use error::Error;
    use exec::{Exec, ExecNoSyncStr};
    use re_builder::unicode::RegexBuilder;
    use re_plugin::Plugin;
    use re_trait::{self, RegularExpression, Slot};

    /// Escapes all regular expression meta characters in `text`.
    ///
    /// The string returned may be safely used as a literal in a regular
    /// expression.
    pub fn quote(text: &str) -> String {
        syntax::quote(text)
    }

    /// Tests if the given regular expression matches somewhere in the text given.
    ///
    /// If there was a problem compiling the regular expression, an error is
    /// returned.
    ///
    /// To find submatches, split or replace text, you'll need to compile an
    /// expression first.
    pub fn is_match(regex: &str, text: &str) -> Result<bool, Error> {
        Regex::new(regex).map(|r| r.is_match(text))
    }

    /// A compiled regular expression for matching Unicode strings.
    ///
    /// It is represented as either a sequence of bytecode instructions (dynamic)
    /// or as a specialized Rust function (native). It can be used to search, split
    /// or replace text. All searching is done with an implicit `.*?` at the
    /// beginning and end of an expression. To force an expression to match the
    /// whole string (or a prefix or a suffix), you must use an anchor like `^` or
    /// `$` (or `\A` and `\z`).
    ///
    /// While this crate will handle Unicode strings (whether in the regular
    /// expression or in the search text), all positions returned are **byte
    /// indices**. Every byte index is guaranteed to be at a Unicode code point
    /// boundary.
    ///
    /// The lifetimes `'r` and `'t` in this crate correspond to the lifetime of a
    /// compiled regular expression and text to search, respectively.
    ///
    /// The only methods that allocate new strings are the string replacement
    /// methods. All other methods (searching and splitting) return borrowed
    /// pointers into the string given.
    ///
    /// # Examples
    ///
    /// Find the location of a US phone number:
    ///
    /// ```rust
    /// # use regex::Regex;
    /// let re = Regex::new("[0-9]{3}-[0-9]{3}-[0-9]{4}").unwrap();
    /// assert_eq!(re.find("phone: 111-222-3333"), Some((7, 19)));
    /// ```
    ///
    /// # Using the `std::str::StrExt` methods with `Regex`
    ///
    /// > **Note**: This section requires that this crate is currently compiled with
    /// >           the `pattern` Cargo feature enabled.
    ///
    /// Since `Regex` implements `Pattern`, you can use regexes with methods
    /// defined on `std::str::StrExt`. For example, `is_match`, `find`, `find_iter`
    /// and `split` can be replaced with `StrExt::contains`, `StrExt::find`,
    /// `StrExt::match_indices` and `StrExt::split`.
    ///
    /// Here are some examples:
    ///
    /// ```rust,ignore
    /// # use regex::Regex;
    /// let re = Regex::new(r"\d+").unwrap();
    /// let haystack = "a111b222c";
    ///
    /// assert!(haystack.contains(&re));
    /// assert_eq!(haystack.find(&re), Some(1));
    /// assert_eq!(haystack.match_indices(&re).collect::<Vec<_>>(),
    ///            vec![(1, 4), (5, 8)]);
    /// assert_eq!(haystack.split(&re).collect::<Vec<_>>(), vec!["a", "b", "c"]);
    /// ```
    #[derive(Clone)]
    pub struct Regex(#[doc(hidden)] pub _Regex);

    #[derive(Clone)]
    #[doc(hidden)]
    pub enum _Regex {
        // The representation of `Regex` is exported to support the `regex!`
        // syntax extension. Do not rely on it.
        //
        // See the comments for the `program` module in `lib.rs` for a more
        // detailed explanation for what `regex!` requires.
        #[doc(hidden)]
        Dynamic(Exec),
        #[doc(hidden)]
        Plugin(Plugin),
    }

    impl fmt::Display for Regex {
        /// Shows the original regular expression.
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", self.as_str())
        }
    }

    impl fmt::Debug for Regex {
        /// Shows the original regular expression.
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Display::fmt(self, f)
        }
    }

    #[doc(hidden)]
    impl From<Exec> for Regex {
        fn from(exec: Exec) -> Regex {
            Regex(_Regex::Dynamic(exec))
        }
    }

    /// Equality comparison is based on the original string. It is possible that
    /// different regular expressions have the same matching behavior, but are
    /// still compared unequal. For example, `\d+` and `\d\d*` match the same set
    /// of strings, but are not considered equal.
    impl PartialEq for Regex {
        fn eq(&self, other: &Regex) -> bool {
            self.as_str() == other.as_str()
        }
    }

    impl Eq for Regex {}

    impl FromStr for Regex {
        type Err = Error;

        /// Attempts to parse a string into a regular expression
        fn from_str(s: &str) -> Result<Regex, Error> {
            Regex::new(s)
        }
    }

    impl Regex {
        /// Compiles a regular expression. Once compiled, it can be used repeatedly
        /// to search, split or replace text in a string.
        ///
        /// If an invalid expression is given, then an error is returned.
        pub fn new(re: &str) -> Result<Regex, Error> {
            Regex::with_size_limit(10 * (1 << 20), re)
        }

        /// Compiles a regular expression with the given size limit.
        ///
        /// The size limit is applied to the size of the *compiled* data structure.
        /// If the data structure exceeds the size given, then an error is
        /// returned.
        pub fn with_size_limit(size: usize, re: &str) -> Result<Regex, Error> {
            RegexBuilder::new(re).size_limit(size).compile()
        }

        /// Returns true if and only if the regex matches the string given.
        ///
        /// It is recommended to use this method if all you need to do is test
        /// a match, since the underlying matching engine may be able to do less
        /// work.
        ///
        /// # Example
        ///
        /// Test if some text contains at least one word with exactly 13
        /// Unicode word characters:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let text = "I categorically deny having triskaidekaphobia.";
        /// assert!(Regex::new(r"\b\w{13}\b").unwrap().is_match(text));
        /// # }
        /// ```
        pub fn is_match(&self, text: &str) -> bool {
            self.is_match_at(text, 0)
        }

        /// Returns the same as is_match, but starts the search at the given
        /// offset.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        #[doc(hidden)]
        pub fn is_match_at(&self, text: &str, start: usize) -> bool {
            self.shortest_match_at(text, start).is_some()
        }

        /// Returns the start and end byte range of the leftmost-first match in
        /// `text`. If no match exists, then `None` is returned.
        ///
        /// Note that this should only be used if you want to discover the position
        /// of the match. Testing the existence of a match is faster if you use
        /// `is_match`.
        ///
        /// # Example
        ///
        /// Find the start and end location of the first word with exactly 13
        /// Unicode word characters:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let text = "I categorically deny having triskaidekaphobia.";
        /// let pos = Regex::new(r"\b\w{13}\b").unwrap().find(text);
        /// assert_eq!(pos, Some((2, 15)));
        /// # }
        /// ```
        pub fn find(&self, text: &str) -> Option<(usize, usize)> {
            self.find_at(text, 0)
        }

        /// Returns the same as find, but starts the search at the given
        /// offset.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        #[doc(hidden)]
        pub fn find_at(&self, text: &str, start: usize) -> Option<(usize, usize)> {
            match self.0 {
                _Regex::Dynamic(ref exec) => {
                    exec.searcher_str().find_at(text, start)
                }
                _Regex::Plugin(ref plug) => plug.find_at(text, start),
            }
        }

        /// Returns an iterator for each successive non-overlapping match in
        /// `text`, returning the start and end byte indices with respect to
        /// `text`.
        ///
        /// # Example
        ///
        /// Find the start and end location of every word with exactly 13 Unicode
        /// word characters:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let text = "Retroactively relinquishing remunerations is reprehensible.";
        /// for pos in Regex::new(r"\b\w{13}\b").unwrap().find_iter(text) {
        ///     println!("{:?}", pos);
        /// }
        /// // Output:
        /// // (0, 13)
        /// // (14, 27)
        /// // (28, 41)
        /// // (45, 58)
        /// # }
        /// ```
        pub fn find_iter<'r, 't>(&'r self, text: &'t str) -> FindMatches<'r, 't> {
            match self.0 {
                _Regex::Dynamic(ref exec) => {
                    let it = exec.searcher_str().find_iter(text);
                    FindMatches(FindMatchesInner::Dynamic(it))
                }
                _Regex::Plugin(ref plug) => {
                    let it = plug.find_iter(text);
                    FindMatches(FindMatchesInner::Plugin(it))
                }
            }
        }

        /// Returns the capture groups corresponding to the leftmost-first
        /// match in `text`. Capture group `0` always corresponds to the entire
        /// match. If no match is found, then `None` is returned.
        ///
        /// You should only use `captures` if you need access to submatches.
        /// Otherwise, `find` is faster for discovering the location of the overall
        /// match.
        ///
        /// # Examples
        ///
        /// Say you have some text with movie names and their release years,
        /// like "'Citizen Kane' (1941)". It'd be nice if we could search for text
        /// looking like that, while also extracting the movie name and its release
        /// year separately.
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"'([^']+)'\s+\((\d{4})\)").unwrap();
        /// let text = "Not my favorite movie: 'Citizen Kane' (1941).";
        /// let caps = re.captures(text).unwrap();
        /// assert_eq!(caps.at(1), Some("Citizen Kane"));
        /// assert_eq!(caps.at(2), Some("1941"));
        /// assert_eq!(caps.at(0), Some("'Citizen Kane' (1941)"));
        /// // You can also access the groups by index using the Index notation.
        /// // Note that this will panic on an invalid index.
        /// assert_eq!(&caps[1], "Citizen Kane");
        /// assert_eq!(&caps[2], "1941");
        /// assert_eq!(&caps[0], "'Citizen Kane' (1941)");
        /// # }
        /// ```
        ///
        /// Note that the full match is at capture group `0`. Each subsequent
        /// capture group is indexed by the order of its opening `(`.
        ///
        /// We can make this example a bit clearer by using *named* capture groups:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"'(?P<title>[^']+)'\s+\((?P<year>\d{4})\)")
        ///                .unwrap();
        /// let text = "Not my favorite movie: 'Citizen Kane' (1941).";
        /// let caps = re.captures(text).unwrap();
        /// assert_eq!(caps.name("title"), Some("Citizen Kane"));
        /// assert_eq!(caps.name("year"), Some("1941"));
        /// assert_eq!(caps.at(0), Some("'Citizen Kane' (1941)"));
        /// // You can also access the groups by name using the Index notation.
        /// // Note that this will panic on an invalid group name.
        /// assert_eq!(&caps["title"], "Citizen Kane");
        /// assert_eq!(&caps["year"], "1941");
        /// assert_eq!(&caps[0], "'Citizen Kane' (1941)");
        ///
        /// # }
        /// ```
        ///
        /// Here we name the capture groups, which we can access with the `name`
        /// method or the `Index` notation with a `&str`. Note that the named
        /// capture groups are still accessible with `at` or the `Index` notation
        /// with a `usize`.
        ///
        /// The `0`th capture group is always unnamed, so it must always be
        /// accessed with `at(0)` or `[0]`.
        pub fn captures<'t>(&self, text: &'t str) -> Option<Captures<'t>> {
            let mut slots = vec![None; 2 * self.captures_len()];
            self.read_captures_at(&mut slots, text, 0).map(|_| Captures {
                text: text,
                slots: slots,
                named_groups: NamedGroups::from_regex(self)
            })
        }

        /// Returns the same as captures, but starts the search at the given
        /// offset and populates the capture locations given.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        #[doc(hidden)]
        pub fn read_captures_at(
            &self,
            slots: &mut [Slot],
            text: &str,
            start: usize,
        ) -> Option<(usize, usize)> {
            match self.0 {
                _Regex::Dynamic(ref exec) => {
                    exec.searcher_str().read_captures_at(slots, text, start)
                }
                _Regex::Plugin(ref plug) => {
                    plug.read_captures_at(slots, text, start)
                }
            }
        }

        /// Returns an iterator over all the non-overlapping capture groups matched
        /// in `text`. This is operationally the same as `find_iter`, except it
        /// yields information about submatches.
        ///
        /// # Example
        ///
        /// We can use this to find all movie titles and their release years in
        /// some text, where the movie is formatted like "'Title' (xxxx)":
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"'(?P<title>[^']+)'\s+\((?P<year>\d{4})\)")
        ///                .unwrap();
        /// let text = "'Citizen Kane' (1941), 'The Wizard of Oz' (1939), 'M' (1931).";
        /// for caps in re.captures_iter(text) {
        ///     println!("Movie: {:?}, Released: {:?}",
        ///              caps.name("title"), caps.name("year"));
        /// }
        /// // Output:
        /// // Movie: Citizen Kane, Released: 1941
        /// // Movie: The Wizard of Oz, Released: 1939
        /// // Movie: M, Released: 1931
        /// # }
        /// ```
        pub fn captures_iter<'r, 't>(
            &'r self,
            text: &'t str,
        ) -> FindCaptures<'r, 't> {
            match self.0 {
                _Regex::Dynamic(ref exec) => {
                    let it = exec.searcher_str().captures_iter(text);
                    FindCaptures(FindCapturesInner::Dynamic(it))
                }
                _Regex::Plugin(ref plug) => {
                    let it = plug.captures_iter(text);
                    FindCaptures(FindCapturesInner::Plugin(it))
                }
            }
        }

        /// Returns an iterator of substrings of `text` delimited by a match of the
        /// regular expression. Namely, each element of the iterator corresponds to
        /// text that *isn't* matched by the regular expression.
        ///
        /// This method will *not* copy the text given.
        ///
        /// # Example
        ///
        /// To split a string delimited by arbitrary amounts of spaces or tabs:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"[ \t]+").unwrap();
        /// let fields: Vec<&str> = re.split("a b \t  c\td    e").collect();
        /// assert_eq!(fields, vec!["a", "b", "c", "d", "e"]);
        /// # }
        /// ```
        pub fn split<'r, 't>(&'r self, text: &'t str) -> RegexSplits<'r, 't> {
            RegexSplits {
                finder: self.find_iter(text),
                last: 0,
            }
        }

        /// Returns an iterator of at most `limit` substrings of `text` delimited
        /// by a match of the regular expression. (A `limit` of `0` will return no
        /// substrings.) Namely, each element of the iterator corresponds to text
        /// that *isn't* matched by the regular expression. The remainder of the
        /// string that is not split will be the last element in the iterator.
        ///
        /// This method will *not* copy the text given.
        ///
        /// # Example
        ///
        /// Get the first two words in some text:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"\W+").unwrap();
        /// let fields: Vec<&str> = re.splitn("Hey! How are you?", 3).collect();
        /// assert_eq!(fields, vec!("Hey", "How", "are you?"));
        /// # }
        /// ```
        pub fn splitn<'r, 't>(&'r self, text: &'t str, limit: usize)
                             -> RegexSplitsN<'r, 't> {
            RegexSplitsN {
                splits: self.split(text),
                n: limit,
            }
        }

        /// Replaces the leftmost-first match with the replacement provided.
        /// The replacement can be a regular string (where `$N` and `$name` are
        /// expanded to match capture groups) or a function that takes the matches'
        /// `Captures` and returns the replaced string.
        ///
        /// If no match is found, then a copy of the string is returned unchanged.
        ///
        /// # Examples
        ///
        /// Note that this function is polymorphic with respect to the replacement.
        /// In typical usage, this can just be a normal string:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new("[^01]+").unwrap();
        /// assert_eq!(re.replace("1078910", ""), "1010");
        /// # }
        /// ```
        ///
        /// But anything satisfying the `Replacer` trait will work. For example,
        /// a closure of type `|&Captures| -> String` provides direct access to the
        /// captures corresponding to a match. This allows one to access
        /// submatches easily:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # use regex::Captures; fn main() {
        /// let re = Regex::new(r"([^,\s]+),\s+(\S+)").unwrap();
        /// let result = re.replace("Springsteen, Bruce", |caps: &Captures| {
        ///     format!("{} {}", caps.at(2).unwrap_or(""), caps.at(1).unwrap_or(""))
        /// });
        /// assert_eq!(result, "Bruce Springsteen");
        /// # }
        /// ```
        ///
        /// But this is a bit cumbersome to use all the time. Instead, a simple
        /// syntax is supported that expands `$name` into the corresponding capture
        /// group. Here's the last example, but using this expansion technique
        /// with named capture groups:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"(?P<last>[^,\s]+),\s+(?P<first>\S+)").unwrap();
        /// let result = re.replace("Springsteen, Bruce", "$first $last");
        /// assert_eq!(result, "Bruce Springsteen");
        /// # }
        /// ```
        ///
        /// Note that using `$2` instead of `$first` or `$1` instead of `$last`
        /// would produce the same result. To write a literal `$` use `$$`.
        ///
        /// Finally, sometimes you just want to replace a literal string with no
        /// submatch expansion. This can be done by wrapping a string with
        /// `NoExpand`:
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// use regex::NoExpand;
        ///
        /// let re = Regex::new(r"(?P<last>[^,\s]+),\s+(\S+)").unwrap();
        /// let result = re.replace("Springsteen, Bruce", NoExpand("$2 $last"));
        /// assert_eq!(result, "$2 $last");
        /// # }
        /// ```
        pub fn replace<R: Replacer>(&self, text: &str, rep: R) -> String {
            self.replacen(text, 1, rep)
        }

        /// Replaces all non-overlapping matches in `text` with the replacement
        /// provided. This is the same as calling `replacen` with `limit` set to
        /// `0`.
        ///
        /// See the documentation for `replace` for details on how to access
        /// submatches in the replacement string.
        pub fn replace_all<R: Replacer>(&self, text: &str, rep: R) -> String {
            self.replacen(text, 0, rep)
        }

        /// Replaces at most `limit` non-overlapping matches in `text` with the
        /// replacement provided. If `limit` is 0, then all non-overlapping matches
        /// are replaced.
        ///
        /// See the documentation for `replace` for details on how to access
        /// submatches in the replacement string.
        pub fn replacen<R: Replacer>(
            &self,
            text: &str,
            limit: usize,
            mut rep: R,
        ) -> String {

            // If we know that the replacement doesn't have any capture expansions,
            // then we can fast path. The fast path can make a tremendous
            // difference:
            //
            //   1) We use `find_iter` instead of `captures_iter`. Not asking for
            //      captures generally makes the regex engines faster.
            //   2) We don't need to look up all of the capture groups and do
            //      replacements inside the replacement string. We just push it
            //      at each match and be done with it.
            if let Some(rep) = rep.no_expand() {
                let mut new = String::with_capacity(text.len());
                let mut last_match = 0;
                for (i, (s, e)) in self.find_iter(text).enumerate() {
                    if limit > 0 && i >= limit {
                        break
                    }
                    new.push_str(&text[last_match..s]);
                    new.push_str(&rep);
                    last_match = e;
                }
                new.push_str(&text[last_match..]);
                return new;
            }

            // The slower path, which we use if the replacement needs access to
            // capture groups.
            let mut new = String::with_capacity(text.len());
            let mut last_match = 0;
            for (i, cap) in self.captures_iter(text).enumerate() {
                if limit > 0 && i >= limit {
                    break
                }
                // unwrap on 0 is OK because captures only reports matches
                let (s, e) = cap.pos(0).unwrap();
                new.push_str(&text[last_match..s]);
                new.push_str(&rep.reg_replace(&cap));
                last_match = e;
            }
            new.push_str(&text[last_match..]);
            new
        }

        /// Returns the end location of a match in the text given.
        ///
        /// This method may have the same performance characteristics as
        /// `is_match`, except it provides an end location for a match. In
        /// particular, the location returned *may be shorter* than the proper end
        /// of the leftmost-first match.
        ///
        /// # Example
        ///
        /// Typically, `a+` would match the entire first sequence of `a` in some
        /// text, but `shortest_match` can give up as soon as it sees the first
        /// `a`.
        ///
        /// ```rust
        /// # extern crate regex; use regex::Regex;
        /// # fn main() {
        /// let text = "aaaaa";
        /// let pos = Regex::new(r"a+").unwrap().shortest_match(text);
        /// assert_eq!(pos, Some(1));
        /// # }
        /// ```
        pub fn shortest_match(&self, text: &str) -> Option<usize> {
            self.shortest_match_at(text, 0)
        }

        /// Returns the same as shortest_match, but starts the search at the given
        /// offset.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        #[doc(hidden)]
        pub fn shortest_match_at(
            &self,
            text: &str,
            start: usize,
        ) -> Option<usize> {
            match self.0 {
                _Regex::Dynamic(ref exec) => {
                    exec.searcher_str().shortest_match_at(text, start)
                }
                _Regex::Plugin(ref plug) => plug.shortest_match_at(text, start),
            }
        }

        /// Returns the original string of this regex.
        pub fn as_str(&self) -> &str {
            match self.0 {
                _Regex::Dynamic(ref exec) => &exec.regex_strings()[0],
                _Regex::Plugin(ref plug) => &plug.original,
            }
        }

        /// Returns an iterator over the capture names.
        pub fn capture_names(&self) -> CaptureNames {
            CaptureNames(match self.0 {
                _Regex::Plugin(ref n) => _CaptureNames::Plugin(n.names.iter()),
                _Regex::Dynamic(ref d) => {
                    _CaptureNames::Dynamic(d.capture_names().iter())
                }
            })
        }

        /// Returns the number of captures.
        pub fn captures_len(&self) -> usize {
            match self.0 {
                _Regex::Plugin(ref n) => n.names.len(),
                _Regex::Dynamic(ref d) => d.capture_names().len()
            }
        }
    }

    /// An iterator over the names of all possible captures.
    ///
    /// `None` indicates an unnamed capture; the first element (capture 0, the
    /// whole matched region) is always unnamed.
    ///
    /// `'r` is the lifetime of the compiled regular expression.
    pub struct CaptureNames<'r>(_CaptureNames<'r>);

    enum _CaptureNames<'r> {
        #[doc(hidden)]
        Plugin(::std::slice::Iter<'r, Option<&'static str>>),
        #[doc(hidden)]
        Dynamic(::std::slice::Iter<'r, Option<String>>)
    }

    impl<'r> Iterator for CaptureNames<'r> {
        type Item = Option<&'r str>;

        fn next(&mut self) -> Option<Option<&'r str>> {
            match self.0 {
                _CaptureNames::Plugin(ref mut i) => i.next().cloned(),
                _CaptureNames::Dynamic(ref mut i) => {
                    i.next().as_ref().map(|o| o.as_ref().map(|s| s.as_ref()))
                }
            }
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            match self.0 {
                _CaptureNames::Plugin(ref i)  => i.size_hint(),
                _CaptureNames::Dynamic(ref i) => i.size_hint(),
            }
        }
    }

    /// NoExpand indicates literal string replacement.
    ///
    /// It can be used with `replace` and `replace_all` to do a literal
    /// string replacement without expanding `$name` to their corresponding
    /// capture groups.
    ///
    /// `'t` is the lifetime of the literal text.
    pub struct NoExpand<'t>(pub &'t str);

    /// Replacer describes types that can be used to replace matches in a string.
    pub trait Replacer {
        /// Returns a possibly owned string that is used to replace the match
        /// corresponding to the `caps` capture group.
        ///
        /// The `'a` lifetime refers to the lifetime of a borrowed string when
        /// a new owned string isn't needed (e.g., for `NoExpand`).
        fn reg_replace(&mut self, caps: &Captures) -> Cow<str>;

        /// Returns a possibly owned string that never needs expansion.
        fn no_expand(&mut self) -> Option<Cow<str>> { None }
    }

    impl<'t> Replacer for NoExpand<'t> {
        fn reg_replace(&mut self, _: &Captures) -> Cow<str> {
            self.0.into()
        }

        fn no_expand(&mut self) -> Option<Cow<str>> {
            Some(self.0.into())
        }
    }

    impl<'t> Replacer for &'t str {
        fn reg_replace<'a>(&'a mut self, caps: &Captures) -> Cow<'a, str> {
            caps.expand(*self).into()
        }

        fn no_expand(&mut self) -> Option<Cow<str>> {
            // if there is a $ there may be an expansion
            match self.find('$') {
                Some(_) => None,
                None => Some((*self).into()),
            }
        }
    }

    impl<F> Replacer for F where F: FnMut(&Captures) -> String {
        fn reg_replace<'a>(&'a mut self, caps: &Captures) -> Cow<'a, str> {
            (*self)(caps).into()
        }
    }

    /// Yields all substrings delimited by a regular expression match.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the string being split.
    pub struct RegexSplits<'r, 't> {
        finder: FindMatches<'r, 't>,
        last: usize,
    }

    impl<'r, 't> Iterator for RegexSplits<'r, 't> {
        type Item = &'t str;

        fn next(&mut self) -> Option<&'t str> {
            let text = self.finder.text();
            match self.finder.next() {
                None => {
                    if self.last >= text.len() {
                        None
                    } else {
                        let s = &text[self.last..];
                        self.last = text.len();
                        Some(s)
                    }
                }
                Some((s, e)) => {
                    let matched = &text[self.last..s];
                    self.last = e;
                    Some(matched)
                }
            }
        }
    }

    /// Yields at most `N` substrings delimited by a regular expression match.
    ///
    /// The last substring will be whatever remains after splitting.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the string being split.
    pub struct RegexSplitsN<'r, 't> {
        splits: RegexSplits<'r, 't>,
        n: usize,
    }

    impl<'r, 't> Iterator for RegexSplitsN<'r, 't> {
        type Item = &'t str;

        fn next(&mut self) -> Option<&'t str> {
            if self.n == 0 {
                return None
            }
            self.n -= 1;
            if self.n == 0 {
                let text = self.splits.finder.text();
                Some(&text[self.splits.last..])
            } else {
                self.splits.next()
            }
        }
    }

    enum NamedGroups {
        Plugin(&'static [(&'static str, usize)]),
        Dynamic(Arc<HashMap<String, usize>>),
    }

    impl NamedGroups {
        fn from_regex(regex: &Regex) -> NamedGroups {
            match regex.0 {
                _Regex::Plugin(ref plug) => NamedGroups::Plugin(&plug.groups),
                _Regex::Dynamic(ref exec) => {
                    NamedGroups::Dynamic(exec.capture_name_idx().clone())
                }
            }
        }

        fn pos(&self, name: &str) -> Option<usize> {
            match *self {
                NamedGroups::Plugin(groups) => {
                    groups.binary_search_by(|&(n, _)| n.cmp(name))
                          .ok().map(|i| groups[i].1)
                },
                NamedGroups::Dynamic(ref groups) => {
                    groups.get(name).map(|i| *i)
                },
            }
        }

        fn iter<'n>(&'n self) -> NamedGroupsIter<'n> {
            match *self {
                NamedGroups::Plugin(g) => NamedGroupsIter::Plugin(g.iter()),
                NamedGroups::Dynamic(ref g) => NamedGroupsIter::Dynamic(g.iter()),
            }
        }
    }

    enum NamedGroupsIter<'n> {
        Plugin(::std::slice::Iter<'static, (&'static str, usize)>),
        Dynamic(::std::collections::hash_map::Iter<'n, String, usize>),
    }

    impl<'n> Iterator for NamedGroupsIter<'n> {
        type Item = (&'n str, usize);

        fn next(&mut self) -> Option<Self::Item> {
            match *self {
                NamedGroupsIter::Plugin(ref mut it) => it.next().map(|&v| v),
                NamedGroupsIter::Dynamic(ref mut it) => {
                    it.next().map(|(s, i)| (s.as_ref(), *i))
                }
            }
        }
    }

    /// Captures represents a group of captured strings for a single match.
    ///
    /// The 0th capture always corresponds to the entire match. Each subsequent
    /// index corresponds to the next capture group in the regex. If a capture
    /// group is named, then the matched string is *also* available via the `name`
    /// method. (Note that the 0th capture is always unnamed and so must be
    /// accessed with the `at` method.)
    ///
    /// Positions returned from a capture group are always byte indices.
    ///
    /// `'t` is the lifetime of the matched text.
    pub struct Captures<'t> {
        text: &'t str,
        slots: Vec<Option<usize>>,
        named_groups: NamedGroups,
    }

    impl<'t> Captures<'t> {
        /// Returns the start and end positions of the Nth capture group. Returns
        /// `None` if `i` is not a valid capture group or if the capture group did
        /// not match anything. The positions returned are *always* byte indices
        /// with respect to the original string matched.
        pub fn pos(&self, i: usize) -> Option<(usize, usize)> {
            let (s, e) = (i * 2, i * 2 + 1);
            match (self.slots.get(s), self.slots.get(e)) {
                (Some(&Some(s)), Some(&Some(e))) => Some((s, e)),
                _ => None,
            }
        }

        /// Returns the matched string for the capture group `i`.  If `i` isn't
        /// a valid capture group or didn't match anything, then `None` is
        /// returned.
        pub fn at(&self, i: usize) -> Option<&'t str> {
            match self.pos(i) {
                None => None,
                Some((s, e)) => Some(&self.text[s..e])
            }
        }

        /// Returns the matched string for the capture group named `name`.  If
        /// `name` isn't a valid capture group or didn't match anything, then
        /// `None` is returned.
        pub fn name(&self, name: &str) -> Option<&'t str> {
            self.named_groups.pos(name).and_then(|i| self.at(i))
        }

        /// Creates an iterator of all the capture groups in order of appearance
        /// in the regular expression.
        pub fn iter(&'t self) -> SubCaptures<'t> {
            SubCaptures { idx: 0, caps: self, }
        }

        /// Creates an iterator of all the capture group positions in order of
        /// appearance in the regular expression. Positions are byte indices
        /// in terms of the original string matched.
        pub fn iter_pos(&'t self) -> SubCapturesPos<'t> {
            SubCapturesPos { idx: 0, slots: &self.slots }
        }

        /// Creates an iterator of all named groups as an tuple with the group
        /// name and the value. The iterator returns these values in arbitrary
        /// order.
        pub fn iter_named(&'t self) -> SubCapturesNamed<'t> {
            SubCapturesNamed {
                caps: self,
                names: self.named_groups.iter()
            }
        }

        /// Expands all instances of `$name` in `text` to the corresponding capture
        /// group `name`.
        ///
        /// `name` may be an integer corresponding to the index of the
        /// capture group (counted by order of opening parenthesis where `0` is the
        /// entire match) or it can be a name (consisting of letters, digits or
        /// underscores) corresponding to a named capture group.
        ///
        /// If `name` isn't a valid capture group (whether the name doesn't exist or
        /// isn't a valid index), then it is replaced with the empty string.
        ///
        /// To write a literal `$` use `$$`.
        pub fn expand(&self, text: &str) -> String {
            const REPLACE_EXPAND: &'static str = r"(?x)
              (?P<before>^|\b|[^$]) # Ignore `$$name`.
              \$
              (?P<name> # Match the actual capture name. Can be...
                [0-9]+  # A sequence of digits (for indexed captures), or...
                |
                [_a-zA-Z][_0-9a-zA-Z]* # A name for named captures.
              )
            ";
            // How evil can you get?
            let re = Regex::new(REPLACE_EXPAND).unwrap();
            let text = re.replace_all(text, |refs: &Captures| -> String {
                let before = refs.name("before").unwrap_or("");
                let name = refs.name("name").unwrap_or("");
                format!("{}{}", before, match name.parse::<usize>() {
                    Err(_) => self.name(name).unwrap_or("").to_owned(),
                    Ok(i) => self.at(i).unwrap_or("").to_owned(),
                })
            });
            let re = Regex::new(r"\$\$").unwrap();
            re.replace_all(&text, NoExpand("$"))
        }

        /// Returns the number of captured groups.
        #[inline]
        pub fn len(&self) -> usize {
            self.slots.len() / 2
        }

        /// Returns true if and only if there are no captured groups.
        #[inline]
        pub fn is_empty(&self) -> bool {
            self.len() == 0
        }
    }

    impl<'t> fmt::Debug for Captures<'t> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_tuple("Captures").field(&CapturesDebug(self)).finish()
        }
    }

    struct CapturesDebug<'c, 't: 'c>(&'c Captures<'t>);

    impl<'c, 't> fmt::Debug for CapturesDebug<'c, 't> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            // We'd like to show something nice here, even if it means an
            // allocation to build a reverse index.
            let slot_to_name: HashMap<usize, &str> =
                self.0.named_groups.iter().map(|(a, b)| (b, a)).collect();
            let mut map = f.debug_map();
            for (slot, m) in self.0.iter_pos().enumerate() {
                let m = m.map(|(s, e)| &self.0.text[s..e]);
                if let Some(ref name) = slot_to_name.get(&slot) {
                    map.entry(&name, &m);
                } else {
                    map.entry(&slot, &m);
                }
            }
            map.finish()
        }
    }

    /// Get a group by index.
    ///
    /// `'t` is the lifetime of the matched text.
    ///
    /// The text can't outlive the `Captures` object if this method is
    /// used, because of how `Index` is defined (normally `a[i]` is part
    /// of `a` and can't outlive it); to do that, use `at()` instead.
    ///
    /// # Panics
    ///
    /// If there is no group at the given index.
    impl<'t> Index<usize> for Captures<'t> {
        type Output = str;

        fn index(&self, i: usize) -> &str {
            self.at(i).unwrap_or_else(|| panic!("no group at index '{}'", i))
        }
    }

    /// Get a group by name.
    ///
    /// `'t` is the lifetime of the matched text and `'i` is the lifetime
    /// of the group name (the index).
    ///
    /// The text can't outlive the `Captures` object if this method is
    /// used, because of how `Index` is defined (normally `a[i]` is part
    /// of `a` and can't outlive it); to do that, use `name` instead.
    ///
    /// # Panics
    ///
    /// If there is no group named by the given value.
    impl<'t, 'i> Index<&'i str> for Captures<'t> {
        type Output = str;

        fn index<'a>(&'a self, name: &'i str) -> &'a str {
            self.name(name).unwrap_or_else(|| panic!("no group named '{}'", name))
        }
    }

    /// An iterator over capture groups for a particular match of a regular
    /// expression.
    ///
    /// `'c` is the lifetime of the captures.
    pub struct SubCaptures<'c> {
        idx: usize,
        caps: &'c Captures<'c>,
    }

    impl<'c> Iterator for SubCaptures<'c> {
        type Item = Option<&'c str>;

        fn next(&mut self) -> Option<Option<&'c str>> {
            if self.idx < self.caps.len() {
                self.idx += 1;
                Some(self.caps.at(self.idx - 1))
            } else {
                None
            }
        }
    }

    /// An iterator over capture group positions for a particular match of a
    /// regular expression.
    ///
    /// Positions are byte indices in terms of the original string matched.
    ///
    /// `'c` is the lifetime of the captures.
    pub struct SubCapturesPos<'c> {
        idx: usize,
        slots: &'c [Option<usize>]
    }

    impl<'c> Iterator for SubCapturesPos<'c> {
        type Item = Option<(usize, usize)>;

        fn next(&mut self) -> Option<Option<(usize, usize)>> {
            if self.idx >= self.slots.len() {
                return None
            }
            let r = match (self.slots[self.idx], self.slots[self.idx + 1]) {
                (Some(s), Some(e)) => Some((s, e)),
                (None, None) => None,
                _ => unreachable!()
            };
            self.idx += 2;
            Some(r)
        }
    }

    /// An Iterator over named capture groups as a tuple with the group
    /// name and the value.
    ///
    /// `'c` is the lifetime of the captures.
    pub struct SubCapturesNamed<'c> {
        caps: &'c Captures<'c>,
        names: NamedGroupsIter<'c>,
    }

    impl<'c> Iterator for SubCapturesNamed<'c> {
        type Item = (&'c str, Option<&'c str>);

        fn next(&mut self) -> Option<(&'c str, Option<&'c str>)> {
            self.names.next().map(|(name, pos)| (name, self.caps.at(pos)))
        }
    }

    /// An iterator that yields all non-overlapping capture groups matching a
    /// particular regular expression.
    ///
    /// The iterator stops when no more matches can be found.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the matched string.
    pub struct FindCaptures<'r, 't>(FindCapturesInner<'r, 't>);

    enum FindCapturesInner<'r, 't> {
        Dynamic(re_trait::FindCaptures<'t, ExecNoSyncStr<'r>>),
        Plugin(re_trait::FindCaptures<'t, Plugin>),
    }

    impl<'r, 't> Iterator for FindCaptures<'r, 't> {
        type Item = Captures<'t>;

        fn next(&mut self) -> Option<Captures<'t>> {
            match self.0 {
                FindCapturesInner::Dynamic(ref mut it) => {
                    let named = it.regex().capture_name_idx().clone();
                    it.next().map(|slots| Captures {
                        text: it.text(),
                        slots: slots,
                        named_groups: NamedGroups::Dynamic(named),
                    })
                }
                FindCapturesInner::Plugin(ref mut it) => {
                    it.next().map(|slots| Captures {
                        text: it.text(),
                        slots: slots,
                        named_groups: NamedGroups::Plugin(it.regex().groups),
                    })
                }
            }
        }
    }

    /// An iterator over all non-overlapping matches for a particular string.
    ///
    /// The iterator yields a tuple of integers corresponding to the start and end
    /// of the match. The indices are byte offsets. The iterator stops when no more
    /// matches can be found.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the matched string.
    pub struct FindMatches<'r, 't>(FindMatchesInner<'r, 't>);

    enum FindMatchesInner<'r, 't> {
        Dynamic(re_trait::FindMatches<'t, ExecNoSyncStr<'r>>),
        Plugin(re_trait::FindMatches<'t, Plugin>),
    }

    impl<'r, 't> FindMatches<'r, 't> {
        fn text(&self) -> &'t str {
            match self.0 {
                FindMatchesInner::Dynamic(ref it) => it.text(),
                FindMatchesInner::Plugin(ref it) => it.text(),
            }
        }
    }

    impl<'r, 't> Iterator for FindMatches<'r, 't> {
        type Item = (usize, usize);

        fn next(&mut self) -> Option<(usize, usize)> {
            match self.0 {
                FindMatchesInner::Dynamic(ref mut it) => it.next(),
                FindMatchesInner::Plugin(ref mut it) => it.next(),
            }
        }
    }

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