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    use std::borrow::Borrow;
    use std::collections::HashMap;
    use std::error;
    use std::fmt;
    use std::io;
    use std::result;

    use super::{TrieSetSlice, CHUNK_SIZE};

    // This implementation was pretty much cribbed from raphlinus' contribution
    // to the standard library: https://github.com/rust-lang/rust/pull/33098/files
    //
    // The fundamental principle guiding this implementation is to take advantage
    // of the fact that similar Unicode codepoints are often grouped together, and
    // that most boolean Unicode properties are quite sparse over the entire space
    // of Unicode codepoints.
    //
    // To do this, we represent sets using something like a trie (which gives us
    // prefix compression). The "final" states of the trie are embedded in leaves
    // or "chunks," where each chunk is a 64 bit integer. Each bit position of the
    // integer corresponds to whether a particular codepoint is in the set or not.
    // These chunks are not just a compact representation of the final states of
    // the trie, but are also a form of suffix compression. In particular, if
    // multiple ranges of 64 contiguous codepoints map have the same set membership
    // ordering, then they all map to the exact same chunk in the trie.
    //
    // We organize this structure by partitioning the space of Unicode codepoints
    // into three disjoint sets. The first set corresponds to codepoints
    // [0, 0x800), the second [0x800, 0x1000) and the third [0x10000, 0x110000).
    // These partitions conveniently correspond to the space of 1 or 2 byte UTF-8
    // encoded codepoints, 3 byte UTF-8 encoded codepoints and 4 byte UTF-8 encoded
    // codepoints, respectively.
    //
    // Each partition has its own tree with its own root. The first partition is
    // the simplest, since the tree is completely flat. In particular, to determine
    // the set membership of a Unicode codepoint (that is less than `0x800`), we
    // do the following (where `cp` is the codepoint we're testing):
    //
    //     let chunk_address = cp >> 6;
    //     let chunk_bit = cp & 0b111111;
    //     let chunk = tree1[cp >> 6];
    //     let is_member = 1 == ((chunk >> chunk_bit) & 1);
    //
    // We do something similar for the second partition:
    //
    //     // we subtract 0x20 since (0x800 >> 6) == 0x20.
    //     let child_address = (cp >> 6) - 0x20;
    //     let chunk_address = tree2_level1[child_address];
    //     let chunk_bit = cp & 0b111111;
    //     let chunk = tree2_level2[chunk_address];
    //     let is_member = 1 == ((chunk >> chunk_bit) & 1);
    //
    // And so on for the third partition.
    //
    // Note that as a special case, if the second or third partitions are empty,
    // then the trie will store empty slices for those levels. The `contains`
    // check knows to return `false` in those cases.

    const CHUNKS: usize = 0x110000 / CHUNK_SIZE;

    /// A type alias that maps to `std::result::Result<T, ucd_trie::Error>`.
    pub type Result<T> = result::Result<T, Error>;

    /// An error that can occur during construction of a trie.
    #[derive(Clone, Debug)]
    pub enum Error {
        /// This error is returned when an invalid codepoint is given to
        /// `TrieSetOwned::from_codepoints`. An invalid codepoint is a `u32` that
        /// is greater than `0x10FFFF`.
        InvalidCodepoint(u32),
        /// This error is returned when a set of Unicode codepoints could not be
        /// sufficiently compressed into the trie provided by this crate. There is
        /// no work-around for this error at this time.
        GaveUp,
    }

    impl error::Error for Error {}

    impl fmt::Display for Error {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match *self {
                Error::InvalidCodepoint(cp) => write!(
                    f,
                    "could not construct trie set containing an \
                     invalid Unicode codepoint: 0x{:X}",
                    cp
                ),
                Error::GaveUp => {
                    write!(f, "could not compress codepoint set into a trie")
                }
            }
        }
    }

    impl From<Error> for io::Error {
        fn from(err: Error) -> io::Error {
            io::Error::new(io::ErrorKind::Other, err)
        }
    }

    /// An owned trie set.
    #[derive(Clone)]
    pub struct TrieSetOwned {
        tree1_level1: Vec<u64>,
        tree2_level1: Vec<u8>,
        tree2_level2: Vec<u64>,
        tree3_level1: Vec<u8>,
        tree3_level2: Vec<u8>,
        tree3_level3: Vec<u64>,
    }

    impl fmt::Debug for TrieSetOwned {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "TrieSetOwned(...)")
        }
    }

    impl TrieSetOwned {
        fn new(all: &[bool]) -> Result<TrieSetOwned> {
            let mut bitvectors = Vec::with_capacity(CHUNKS);
            for i in 0..CHUNKS {
                let mut bitvector = 0u64;
                for j in 0..CHUNK_SIZE {
                    if all[i * CHUNK_SIZE + j] {
                        bitvector |= 1 << j;
                    }
                }
                bitvectors.push(bitvector);
            }

            let tree1_level1 =
                bitvectors.iter().cloned().take(0x800 / CHUNK_SIZE).collect();

            let (mut tree2_level1, mut tree2_level2) = compress_postfix_leaves(
                &bitvectors[0x800 / CHUNK_SIZE..0x10000 / CHUNK_SIZE],
            )?;
            if tree2_level2.len() == 1 && tree2_level2[0] == 0 {
                tree2_level1.clear();
                tree2_level2.clear();
            }

            let (mid, mut tree3_level3) = compress_postfix_leaves(
                &bitvectors[0x10000 / CHUNK_SIZE..0x110000 / CHUNK_SIZE],
            )?;
            let (mut tree3_level1, mut tree3_level2) =
                compress_postfix_mid(&mid, 64)?;
            if tree3_level3.len() == 1 && tree3_level3[0] == 0 {
                tree3_level1.clear();
                tree3_level2.clear();
                tree3_level3.clear();
            }

            Ok(TrieSetOwned {
                tree1_level1,
                tree2_level1,
                tree2_level2,
                tree3_level1,
                tree3_level2,
                tree3_level3,
            })
        }

        /// Create a new trie set from a set of Unicode scalar values.
        ///
        /// This returns an error if a set could not be sufficiently compressed to
        /// fit into a trie.
        pub fn from_scalars<I, C>(scalars: I) -> Result<TrieSetOwned>
        where
            I: IntoIterator<Item = C>,
            C: Borrow<char>,
        {
            let mut all = vec![false; 0x110000];
            for s in scalars {
                all[*s.borrow() as usize] = true;
            }
            TrieSetOwned::new(&all)
        }

        /// Create a new trie set from a set of Unicode scalar values.
        ///
        /// This returns an error if a set could not be sufficiently compressed to
        /// fit into a trie. This also returns an error if any of the given
        /// codepoints are greater than `0x10FFFF`.
        pub fn from_codepoints<I, C>(codepoints: I) -> Result<TrieSetOwned>
        where
            I: IntoIterator<Item = C>,
            C: Borrow<u32>,
        {
            let mut all = vec![false; 0x110000];
            for cp in codepoints {
                let cp = *cp.borrow();
                if cp > 0x10FFFF {
                    return Err(Error::InvalidCodepoint(cp));
                }
                all[cp as usize] = true;
            }
            TrieSetOwned::new(&all)
        }

        /// Return this set as a slice.
        #[inline(always)]
        pub fn as_slice(&self) -> TrieSetSlice<'_> {
            TrieSetSlice {
                tree1_level1: &self.tree1_level1,
                tree2_level1: &self.tree2_level1,
                tree2_level2: &self.tree2_level2,
                tree3_level1: &self.tree3_level1,
                tree3_level2: &self.tree3_level2,
                tree3_level3: &self.tree3_level3,
            }
        }

        /// Returns true if and only if the given Unicode scalar value is in this
        /// set.
        pub fn contains_char(&self, c: char) -> bool {
            self.as_slice().contains_char(c)
        }

        /// Returns true if and only if the given codepoint is in this set.
        ///
        /// If the given value exceeds the codepoint range (i.e., it's greater
        /// than `0x10FFFF`), then this returns false.
        pub fn contains_u32(&self, cp: u32) -> bool {
            self.as_slice().contains_u32(cp)
        }
    }

    fn compress_postfix_leaves(chunks: &[u64]) -> Result<(Vec<u8>, Vec<u64>)> {
        let mut root = vec![];
        let mut children = vec![];
        let mut bychild = HashMap::new();
        for &chunk in chunks {
            if !bychild.contains_key(&chunk) {
                let start = bychild.len();
                if start > ::std::u8::MAX as usize {
                    return Err(Error::GaveUp);
                }
                bychild.insert(chunk, start as u8);
                children.push(chunk);
            }
            root.push(bychild[&chunk]);
        }
        Ok((root, children))
    }

    fn compress_postfix_mid(
        chunks: &[u8],
        chunk_size: usize,
    ) -> Result<(Vec<u8>, Vec<u8>)> {
        let mut root = vec![];
        let mut children = vec![];
        let mut bychild = HashMap::new();
        for i in 0..(chunks.len() / chunk_size) {
            let chunk = &chunks[i * chunk_size..(i + 1) * chunk_size];
            if !bychild.contains_key(chunk) {
                let start = bychild.len();
                if start > ::std::u8::MAX as usize {
                    return Err(Error::GaveUp);
                }
                bychild.insert(chunk, start as u8);
                children.extend(chunk);
            }
            root.push(bychild[chunk]);
        }
        Ok((root, children))
    }

    #[cfg(test)]
    mod tests {
        use super::TrieSetOwned;
        use crate::general_category;
        use std::collections::HashSet;

        fn mk(scalars: &[char]) -> TrieSetOwned {
            TrieSetOwned::from_scalars(scalars).unwrap()
        }

        fn ranges_to_set(ranges: &[(u32, u32)]) -> Vec<u32> {
            let mut set = vec![];
            for &(start, end) in ranges {
                for cp in start..end + 1 {
                    set.push(cp);
                }
            }
            set
        }

        #[test]
        fn set1() {
            let set = mk(&['a']);
            assert!(set.contains_char('a'));
            assert!(!set.contains_char('b'));
            assert!(!set.contains_char('β'));
            assert!(!set.contains_char('☃'));
            assert!(!set.contains_char('😼'));
        }

        #[test]
        fn set_combined() {
            let set = mk(&['a', 'b', 'β', '☃', '😼']);
            assert!(set.contains_char('a'));
            assert!(set.contains_char('b'));
            assert!(set.contains_char('β'));
            assert!(set.contains_char('☃'));
            assert!(set.contains_char('😼'));

            assert!(!set.contains_char('c'));
            assert!(!set.contains_char('θ'));
            assert!(!set.contains_char('⛇'));
            assert!(!set.contains_char('🐲'));
        }

        // Basic tests on all of the general category sets. We check that
        // membership is correct on every Unicode codepoint... because we can.

        macro_rules! category_test {
            ($name:ident, $ranges:ident) => {
                #[test]
                fn $name() {
                    let set = ranges_to_set(general_category::$ranges);
                    let hashset: HashSet<u32> = set.iter().cloned().collect();
                    let trie = TrieSetOwned::from_codepoints(&set).unwrap();
                    for cp in 0..0x110000 {
                        assert!(trie.contains_u32(cp) == hashset.contains(&cp));
                    }
                    // Test that an invalid codepoint is treated correctly.
                    assert!(!trie.contains_u32(0x110000));
                    assert!(!hashset.contains(&0x110000));
                }
            };
        }

        category_test!(gencat_cased_letter, CASED_LETTER);
        category_test!(gencat_close_punctuation, CLOSE_PUNCTUATION);
        category_test!(gencat_connector_punctuation, CONNECTOR_PUNCTUATION);
        category_test!(gencat_control, CONTROL);
        category_test!(gencat_currency_symbol, CURRENCY_SYMBOL);
        category_test!(gencat_dash_punctuation, DASH_PUNCTUATION);
        category_test!(gencat_decimal_number, DECIMAL_NUMBER);
        category_test!(gencat_enclosing_mark, ENCLOSING_MARK);
        category_test!(gencat_final_punctuation, FINAL_PUNCTUATION);
        category_test!(gencat_format, FORMAT);
        category_test!(gencat_initial_punctuation, INITIAL_PUNCTUATION);
        category_test!(gencat_letter, LETTER);
        category_test!(gencat_letter_number, LETTER_NUMBER);
        category_test!(gencat_line_separator, LINE_SEPARATOR);
        category_test!(gencat_lowercase_letter, LOWERCASE_LETTER);
        category_test!(gencat_math_symbol, MATH_SYMBOL);
        category_test!(gencat_mark, MARK);
        category_test!(gencat_modifier_letter, MODIFIER_LETTER);
        category_test!(gencat_modifier_symbol, MODIFIER_SYMBOL);
        category_test!(gencat_nonspacing_mark, NONSPACING_MARK);
        category_test!(gencat_number, NUMBER);
        category_test!(gencat_open_punctuation, OPEN_PUNCTUATION);
        category_test!(gencat_other, OTHER);
        category_test!(gencat_other_letter, OTHER_LETTER);
        category_test!(gencat_other_number, OTHER_NUMBER);
        category_test!(gencat_other_punctuation, OTHER_PUNCTUATION);
        category_test!(gencat_other_symbol, OTHER_SYMBOL);
        category_test!(gencat_paragraph_separator, PARAGRAPH_SEPARATOR);
        category_test!(gencat_private_use, PRIVATE_USE);
        category_test!(gencat_punctuation, PUNCTUATION);
        category_test!(gencat_separator, SEPARATOR);
        category_test!(gencat_space_separator, SPACE_SEPARATOR);
        category_test!(gencat_spacing_mark, SPACING_MARK);
        category_test!(gencat_surrogate, SURROGATE);
        category_test!(gencat_symbol, SYMBOL);
        category_test!(gencat_titlecase_letter, TITLECASE_LETTER);
        category_test!(gencat_unassigned, UNASSIGNED);
        category_test!(gencat_uppercase_letter, UPPERCASE_LETTER);
    }