/*
**********************************************************************
*   Copyright (C) 1999, International Business Machines
*   Corporation and others.  All Rights Reserved.
**********************************************************************
*   Date        Name        Description
*   10/20/99    alan        Creation.
**********************************************************************
*/

#include "unicode/uniset.h"
#include "unicode/parsepos.h"
#include "rbt_data.h"

// N.B.: This mapping is different in ICU and Java
const UnicodeString UnicodeSet::CATEGORY_NAMES(
    "CnLuLlLtLmLoMnMeMcNdNlNoZsZlZpCcCfCoCsPdPsPePcPoSmScSkSoPiPf", "");

/**
 * A cache mapping character category integers, as returned by
 * Unicode::getType(), to pairs strings.  Entries are initially
 * zero length and are filled in on demand.
 */
UnicodeString* UnicodeSet::CATEGORY_PAIRS_CACHE =
     new UnicodeString[Unicode::GENERAL_TYPES_COUNT];

/**
 * Delimiter string used in patterns to close a category reference:
 * ":]".  Example: "[:Lu:]".
 */
const UnicodeString UnicodeSet::CATEGORY_CLOSE = UNICODE_STRING(":]", 2);

/**
 * Delimiter char beginning a variable reference:
 * "{".  Example: "{var}".
 */
const UChar UnicodeSet::VARIABLE_REF_OPEN = '{';

/**
 * Delimiter char ending a variable reference:
 * "}".  Example: "{var}".
 */
const UChar UnicodeSet::VARIABLE_REF_CLOSE = '}';

//----------------------------------------------------------------
// Debugging and testing
//----------------------------------------------------------------

/**
 * Return the representation of this set as a list of character
 * ranges.  Ranges are listed in ascending Unicode order.  For
 * example, the set [a-zA-M3] is represented as "33AMaz".
 */
const UnicodeString& UnicodeSet::getPairs(void) const {
    return pairs;
}

//----------------------------------------------------------------
// Constructors &c
//----------------------------------------------------------------

/**
 * Constructs an empty set.
 */
UnicodeSet::UnicodeSet() : pairs() {}

/**
 * Constructs a set from the given pattern, optionally ignoring
 * white space.  See the class description for the syntax of the
 * pattern language.
 * @param pattern a string specifying what characters are in the set
 * @exception <code>IllegalArgumentException</code> if the pattern
 * contains a syntax error.
 */
UnicodeSet::UnicodeSet(const UnicodeString& pattern,
                       UErrorCode& status) : pairs() {
    applyPattern(pattern, status);
}

UnicodeSet::UnicodeSet(const UnicodeString& pattern, ParsePosition& pos,
                       const TransliterationRuleData* data,
                       UErrorCode& status) {
    parse(pairs, pattern, pos, data, status);
}

/**
 * Constructs a set from the given Unicode character category.
 * @param category an integer indicating the character category as
 * returned by <code>Character.getType()</code>.
 * @exception <code>IllegalArgumentException</code> if the given
 * category is invalid.
 */
UnicodeSet::UnicodeSet(int8_t category, UErrorCode& status) : pairs() {
    if (U_SUCCESS(status)) {
        if (category < 0 || category >= Unicode::GENERAL_TYPES_COUNT) {
            status = U_ILLEGAL_ARGUMENT_ERROR;
        } else {
            pairs = getCategoryPairs(category);
        }
    }
}

/**
 * Constructs a set that is identical to the given UnicodeSet.
 */
UnicodeSet::UnicodeSet(const UnicodeSet& o) : pairs(o.pairs) {}

/**
 * Destructs the set.
 */
UnicodeSet::~UnicodeSet() {}

/**
 * Assigns this object to be a copy of another.
 */
UnicodeSet& UnicodeSet::operator=(const UnicodeSet& o) {
    pairs = o.pairs;
    return *this;
}

/**
 * Compares the specified object with this set for equality.  Returns
 * <tt>true</tt> if the two sets
 * have the same size, and every member of the specified set is
 * contained in this set (or equivalently, every member of this set is
 * contained in the specified set).
 *
 * @param o set to be compared for equality with this set.
 * @return <tt>true</tt> if the specified set is equal to this set.
 */
bool_t UnicodeSet::operator==(const UnicodeSet& o) const {
    return pairs == o.pairs;
}

/**
 * Returns a copy of this object.  All UnicodeFilter objects have
 * to support cloning in order to allow classes using
 * UnicodeFilters, such as Transliterator, to implement cloning.
 */
UnicodeFilter* UnicodeSet::clone() const {
    return new UnicodeSet(*this);
}

/**
 * Returns the hash code value for this set.
 *
 * @return the hash code value for this set.
 * @see Object#hashCode()
 */
int32_t UnicodeSet::hashCode(void) const {
    return pairs.hashCode();
}

//----------------------------------------------------------------
// Public API
//----------------------------------------------------------------

/**
 * Modifies this set to represent the set specified by the given
 * pattern, optionally ignoring white space.  See the class
 * description for the syntax of the pattern language.
 * @param pattern a string specifying what characters are in the set
 * @param ignoreSpaces if <code>true</code>, all spaces in the
 * pattern are ignored.  Spaces are those characters for which
 * <code>Character.isSpaceChar()</code> is <code>true</code>.
 * Characters preceded by '\\' are escaped, losing any special
 * meaning they otherwise have.  Spaces may be included by
 * escaping them.
 * @exception <code>IllegalArgumentException</code> if the pattern
 * contains a syntax error.
 */
void UnicodeSet::applyPattern(const UnicodeString& pattern,
                              UErrorCode& status) {
    if (U_FAILURE(status)) {
        return;
    }

    ParsePosition pos(0);
    parse(pairs, pattern, pos, NULL, status);

    // Skip over trailing whitespace
    int32_t i = pos.getIndex();
    int32_t n = pattern.length();
    while (i<n && Unicode::isWhitespace(pattern.charAt(i))) {
        ++i;
    }

    if (i != n) {
        status = U_ILLEGAL_ARGUMENT_ERROR;
    }
}

/**
 * Returns a string representation of this set.  If the result of
 * calling this function is passed to a UnicodeSet constructor, it
 * will produce another set that is equal to this one.
 */
UnicodeString& UnicodeSet::toPattern(UnicodeString& result) const {
    result.remove().append((UChar)'[');
    
    // iterate through the ranges in the UnicodeSet
    for (int32_t i=0; i<pairs.length(); i+=2) {
        // for a range with the same beginning and ending point,
        // output that character, otherwise, output the start and
        // end points of the range separated by a dash
        result.append(pairs.charAt(i));
        if (pairs.charAt(i) != pairs.charAt(i+1)) {
            result.append((UChar)'-').append(pairs.charAt(i+1));
        }
    }
    
    return result.append((UChar)']');
}

/**
 * Returns the number of elements in this set (its cardinality),
 * <em>n</em>, where <code>0 <= </code><em>n</em><code> <= 65536</code>.
 *
 * @return the number of elements in this set (its cardinality).
 */
int32_t UnicodeSet::size(void) const {
    int32_t n = 0;
    for (int32_t i=0; i<pairs.length(); i+=2) {
        n += pairs.charAt(i+1) - pairs.charAt(i) + 1;
    }
    return n;
}

/**
 * Returns <tt>true</tt> if this set contains no elements.
 *
 * @return <tt>true</tt> if this set contains no elements.
 */
bool_t UnicodeSet::isEmpty(void) const {
    return pairs.length() == 0;
}

/**
 * Returns <tt>true</tt> if this set contains the specified range
 * of chars.
 *
 * @return <tt>true</tt> if this set contains the specified range
 * of chars.
 */
bool_t UnicodeSet::contains(UChar first, UChar last) const {
    // Set i to the end of the smallest range such that its end
    // point >= last, or pairs.length() if no such range exists.
    int32_t i = 1;
    while (i<pairs.length() && last>pairs.charAt(i)) i+=2;
    return i<pairs.length() && first>=pairs.charAt(i-1);
}

/**
 * Returns <tt>true</tt> if this set contains the specified char.
 *
 * @return <tt>true</tt> if this set contains the specified char.
 */
bool_t UnicodeSet::contains(UChar c) const {
    return contains(c, c);
}

/**
 * Returns <tt>true</tt> if this set contains any character whose low byte
 * is the given value.  This is used by <tt>RuleBasedTransliterator</tt> for
 * indexing.
 */
bool_t UnicodeSet::containsIndexValue(uint8_t v) const {
    /* The index value v, in the range [0,255], is contained in this set if
     * it is contained in any pair of this set.  Pairs either have the high
     * bytes equal, or unequal.  If the high bytes are equal, then we have
     * aaxx..aayy, where aa is the high byte.  Then v is contained if xx <=
     * v <= yy.  If the high bytes are unequal we have aaxx..bbyy, bb>aa.
     * Then v is contained if xx <= v || v <= yy.  (This is identical to the
     * time zone month containment logic.)
     */
    for (int32_t i=0; i<pairs.length(); i+=2) {
        UChar low = pairs.charAt(i);
        UChar high = pairs.charAt(i+1);
        if ((low & 0xFF00) == (high & 0xFF00)) {
            if (uint8_t(low) <= v && v <= uint8_t(high)) {
                return TRUE;
            }
        } else if (uint8_t(low) <= v || v <= uint8_t(high)) {
            return TRUE;
        }
    }
    return FALSE;
}

/**
 * Adds the specified range to this set if it is not already
 * present.  If this set already contains the specified range,
 * the call leaves this set unchanged.  If <code>last > first</code>
 * then an empty range is added, leaving the set unchanged.
 *
 * @param first first character, inclusive, of range to be added
 * to this set.
 * @param last last character, inclusive, of range to be added
 * to this set.
 */
void UnicodeSet::add(UChar first, UChar last) {
    if (first <= last) {
        addPair(pairs, first, last);
    }
}

/**
 * Adds the specified character to this set if it is not already
 * present.  If this set already contains the specified character,
 * the call leaves this set unchanged.
 */
void UnicodeSet::add(UChar c) {
    add(c, c);
}

/**
 * Removes the specified range from this set if it is present.
 * The set will not contain the specified range once the call
 * returns.  If <code>last > first</code> then an empty range is
 * removed, leaving the set unchanged.
 * 
 * @param first first character, inclusive, of range to be removed
 * from this set.
 * @param last last character, inclusive, of range to be removed
 * from this set.
 */
void UnicodeSet::remove(UChar first, UChar last) {
    if (first <= last) {
        removePair(pairs, first, last);
    }
}

/**
 * Removes the specified character from this set if it is present.
 * The set will not contain the specified range once the call
 * returns.
 */
void UnicodeSet::remove(UChar c) {
    remove(c, c);
}

/**
 * Returns <tt>true</tt> if the specified set is a <i>subset</i>
 * of this set.
 *
 * @param c set to be checked for containment in this set.
 * @return <tt>true</tt> if this set contains all of the elements of the
 * 	       specified set.
 */
bool_t UnicodeSet::containsAll(const UnicodeSet& c) const {
    // The specified set is a subset if all of its pairs are contained
    // in this set.
    int32_t i = 1;
    for (int32_t j=0; j<c.pairs.length(); j+=2) {
        UChar last = c.pairs.charAt(j+1);
        // Set i to the end of the smallest range such that its
        // end point >= last, or pairs.length() if no such range
        // exists.
        while (i<pairs.length() && last>pairs.charAt(i)) i+=2;
        if (i>pairs.length() || c.pairs.charAt(j) < pairs.charAt(i-1)) {
            return FALSE;
        }
    }
    return TRUE;
}

/**
 * Adds all of the elements in the specified set to this set if
 * they're not already present.  This operation effectively
 * modifies this set so that its value is the <i>union</i> of the two
 * sets.  The behavior of this operation is unspecified if the specified
 * collection is modified while the operation is in progress.
 *
 * @param c set whose elements are to be added to this set.
 * @see #add(char, char)
 */
void UnicodeSet::addAll(const UnicodeSet& c) {
    doUnion(pairs, c.pairs);
}

/**
 * Retains only the elements in this set that are contained in the
 * specified set.  In other words, removes from this set all of
 * its elements that are not contained in the specified set.  This
 * operation effectively modifies this set so that its value is
 * the <i>intersection</i> of the two sets.
 *
 * @param c set that defines which elements this set will retain.
 */
void UnicodeSet::retainAll(const UnicodeSet& c) {
    doIntersection(pairs, c.pairs);
}

/**
 * Removes from this set all of its elements that are contained in the
 * specified set.  This operation effectively modifies this
 * set so that its value is the <i>asymmetric set difference</i> of
 * the two sets.
 *
 * @param c set that defines which elements will be removed from
 *          this set.
 */
void UnicodeSet::removeAll(const UnicodeSet& c) {
    doDifference(pairs, c.pairs);
}

/**
 * Inverts this set.  This operation modifies this set so that
 * its value is its complement.  This is equivalent to the pseudo code:
 * <code>this = new UnicodeSet("[\u0000-\uFFFF]").removeAll(this)</code>.
 */
void UnicodeSet::complement(void) {
    doComplement(pairs);
}

/**
 * Removes all of the elements from this set.  This set will be
 * empty after this call returns.
 */
void UnicodeSet::clear(void) {
    pairs.remove();
}

//----------------------------------------------------------------
// Implementation: Pattern parsing
//----------------------------------------------------------------

/**
 * Parses the given pattern, starting at the given position.  The
 * character at pattern.charAt(pos.getIndex()) must be '[', or the
 * parse fails.  Parsing continues until the corresponding closing
 * ']'.  If a syntax error is encountered between the opening and
 * closing brace, the parse fails.  Upon return from a U_SUCCESSful
 * parse, the ParsePosition is updated to point to the character
 * following the closing ']', and a StringBuffer containing a
 * pairs list for the parsed pattern is returned.  This method calls
 * itself recursively to parse embedded subpatterns.
 *
 * @param pattern the string containing the pattern to be parsed.
 * The portion of the string from pos.getIndex(), which must be a
 * '[', to the corresponding closing ']', is parsed.
 * @param pos upon entry, the position at which to being parsing.
 * The character at pattern.charAt(pos.getIndex()) must be a '['.
 * Upon return from a U_SUCCESSful parse, pos.getIndex() is either
 * the character after the closing ']' of the parsed pattern, or
 * pattern.length() if the closing ']' is the last character of
 * the pattern string.
 * @return a StringBuffer containing a pairs list for the parsed
 * substring of <code>pattern</code>
 * @exception IllegalArgumentException if the parse fails.
 */
UnicodeString& UnicodeSet::parse(UnicodeString& pairsBuf /*result*/,
                                 const UnicodeString& pattern,
                                 ParsePosition& pos,
                                 const TransliterationRuleData* data,
                                 UErrorCode& status) {
    if (U_FAILURE(status)) {
        return pairsBuf;
    }

    bool_t invert = FALSE;
    pairsBuf.remove();

    int32_t lastChar = -1; // This is either a char (0..FFFF) or -1
    UChar lastOp = 0;

    /* This loop iterates over the characters in the pattern.  We start at
     * the position specified by pos.  We exit the loop when either a
     * matching closing ']' is seen, or we read all characters of the
     * pattern.  In the latter case an error will be thrown.
     */

    /* Pattern syntax:
     *  pat := '[' '^'? elem* ']'
     *  elem := a | a '-' a | set | set op set
     *  set := pat | (a set variable)
     *  op := '&' | '-'
     *  a := (a character, possibly defined by a var)
     */

    // mode 0: No chars parsed yet; next must be '['
    // mode 1: '[' seen; if next is '^' or ':' then special
    // mode 2: '[' '^'? seen; parse pattern and close with ']'
    // mode 3: '[:' seen; parse category and close with ':]'
    int8_t mode = 0;
    int32_t openPos = 0; // offset to opening '['
    int32_t i = pos.getIndex();
    int32_t limit = pattern.length();
    UnicodeString nestedAux;
    UnicodeString* nestedPairs;
    UnicodeString scratch;
    for (; i<limit; ++i) {
        /* If the next element is a single character, c will be set to it,
         * and nestedPairs will be null.  In this case isLiteral indicates
         * whether the character should assume special meaning if it has
         * one.  If the next element is a nested set, either via a variable
         * reference, or via an embedded "[..]"  or "[:..:]" pattern, then
         * nestedPairs will be set to the pairs list for the nested set, and
         * c's value should be ignored.
         */
        UChar c = pattern.charAt(i);
        nestedPairs = NULL;
        bool_t isLiteral = FALSE;

        // Ignore whitespace.  This is not Unicode whitespace, but Java
        // whitespace, a subset of Unicode whitespace.
        if (Unicode::isWhitespace(c)) {
            continue;
        }

        // Parse the opening '[' and optional following '^'
        switch (mode) {
        case 0:
            if (c == '[') {
                mode = 1; // Next look for '^'
                openPos = i;
                continue;
            } else {
                // throw new IllegalArgumentException("Missing opening '['");
                status = U_ILLEGAL_ARGUMENT_ERROR;
                return pairsBuf;
            }
        case 1:
            mode = 2;
            switch (c) {
            case '^':
                invert = TRUE;
                continue; // Back to top to fetch next character
            case ':':
                if (i == openPos+1) {
                    // '[:' cannot have whitespace in it
                    --i;
                    c = '[';
                    mode = 3;
                    // Fall through and parse category normally
                }
                break; // Fall through
            case '-':
                isLiteral = TRUE; // Treat leading '-' as a literal
                break; // Fall through
            }
            // else fall through and parse this character normally
        }

        // After opening matter is parsed ("[", "[^", or "[:"), the mode
        // will be 2 if we want a closing ']', or 3 if we should parse a
        // category and close with ":]".

        /* Handle escapes.  If a character is escaped, then it assumes its
         * literal value.  This is true for all characters, both special
         * characters and characters with no special meaning.  We also
         * interpret '\\uxxxx' Unicode escapes here (as literals).
         */
        if (c == '\\') {
            ++i;
            if (i < pattern.length()) {
                c = pattern.charAt(i);
                isLiteral = TRUE;
                if (c == 'u') {
                    if ((i+4) >= pattern.length()) {
						status = U_ILLEGAL_ARGUMENT_ERROR;
						return pairsBuf;
                    }
                    c = (UChar)0x0000;
                    for (int32_t j=(++i)+4; i<j; ++i) { // [sic]
                        int32_t digit = Unicode::digit(pattern.charAt(i), 16);
                        if (digit<0) {
                            status = U_ILLEGAL_ARGUMENT_ERROR;
                            return pairsBuf;
                        }
                        c = (UChar) ((c << 4) | digit);
                    }
                    --i; // Move i back to last parsed character
                }
            } else {
                status = U_ILLEGAL_ARGUMENT_ERROR;
                return pairsBuf;
            }
        }

        /* Parse variable references.  These are treated as literals.  If a
         * variable refers to a UnicodeSet, nestedPairs is assigned here.
         * Variable names are only parsed if varNameToChar is not null.
         * Set variables are only looked up if varCharToSet is not null.
         */
        else if (data != NULL && !isLiteral && c == VARIABLE_REF_OPEN) {
            ++i;
            int32_t j = pattern.indexOf(VARIABLE_REF_CLOSE, i);
            if (i == j || j < 0) { // empty or unterminated
                // throw new IllegalArgumentException("Illegal variable reference");
                status = U_ILLEGAL_ARGUMENT_ERROR;
            } else {
                scratch.truncate(0);
                pattern.extractBetween(i, j, scratch);
                ++j;
                c = data->lookupVariable(scratch, status);
            }
            if (U_FAILURE(status)) {
                // Either the reference was ill-formed (empty name, or no
                // closing '}', or the specified name is not defined.
                return pairsBuf;
            }
            isLiteral = TRUE;

            UnicodeSet* set = data->lookupSet(c);
            if (set != NULL) {
                nestedPairs = &set->pairs;
            }
        }

        /* An opening bracket indicates the first bracket of a nested
         * subpattern, either a normal pattern or a category pattern.  We
         * recognize these here and set nestedPairs accordingly.
         */
        else if (!isLiteral && c == '[') {
            // Handle "[:...:]", representing a character category
            UChar d = charAfter(pattern, i);
            if (d == ':') {
                i += 2;
                int32_t j = pattern.indexOf(CATEGORY_CLOSE, i);
                if (j < 0) {
                    // throw new IllegalArgumentException("Missing \":]\"");
                    status = U_ILLEGAL_ARGUMENT_ERROR;
                    return pairsBuf;
                }
                scratch.truncate(0);
                pattern.extractBetween(i, j, scratch);
                nestedPairs = &getCategoryPairs(nestedAux, scratch, status);
                if (U_FAILURE(status)) {
                    return pairsBuf;
                }
                i = j+1; // Make i point to ']'
                if (mode == 3) {
                    // Entire pattern is a category; leave parse loop
                    pairsBuf.append(*nestedPairs);
                    break;
                }
            } else {
                // Recurse to get the pairs for this nested set.
                pos.setIndex(i);
                nestedPairs = &parse(nestedAux, pattern, pos, data, status);
                if (U_FAILURE(status)) {
                    return pairsBuf;
                }
                i = pos.getIndex() - 1; // - 1 to point at ']'
            }
        }

        /* At this point we have either a character c, or a nested set.  If
         * we have encountered a nested set, either embedded in the pattern,
         * or as a variable, we have a non-null nestedPairs, and c should be
         * ignored.  Otherwise c is the current character, and isLiteral
         * indicates whether it is an escaped literal (or variable) or a
         * normal unescaped character.  Unescaped characters '-', '&', and
         * ']' have special meanings.
         */
        if (nestedPairs != NULL) {
            if (lastChar >= 0) {
                if (lastOp != 0) {
                    // throw new IllegalArgumentException("Illegal rhs for " + lastChar + lastOp);
                    status = U_ILLEGAL_ARGUMENT_ERROR;
                    return pairsBuf;
                }
                addPair(pairsBuf, (UChar)lastChar, (UChar)lastChar);
                lastChar = -1;
            }
            switch (lastOp) {
            case '-':
                doDifference(pairsBuf, *nestedPairs);
                break;
            case '&':
                doIntersection(pairsBuf, *nestedPairs);
                break;
            case 0:
                doUnion(pairsBuf, *nestedPairs);
                break;
            }
            lastOp = 0;
        } else if (!isLiteral && c == ']') {
            // Final closing delimiter.  This is the only way we leave this
            // loop if the pattern is well-formed.
            break;
        } else if (lastOp == 0 && !isLiteral && (c == '-' || c == '&')) {
            lastOp = c;
        } else if (lastOp == '-') {
            addPair(pairsBuf, (UChar)lastChar, c);
            lastOp = 0;
            lastChar = -1;
        } else if (lastOp != 0) {
            // We have <set>&<char> or <char>&<char>
            // throw new IllegalArgumentException("Unquoted " + lastOp);
            status = U_ILLEGAL_ARGUMENT_ERROR;
            return pairsBuf;
        } else {
            if (lastChar >= 0) {
                // We have <char><char>
                addPair(pairsBuf, (UChar)lastChar, (UChar)lastChar);
            }
            lastChar = c;
        }
    }

    // Handle unprocessed stuff preceding the closing ']'
    if (lastOp == '-') {
        // Trailing '-' is treated as literal
        addPair(pairsBuf, lastOp, lastOp);
    } else if (lastOp == '&') {
        // throw new IllegalArgumentException("Unquoted trailing " + lastOp);
        status = U_ILLEGAL_ARGUMENT_ERROR;
        return pairsBuf;
    }
    if (lastChar >= 0) {
        addPair(pairsBuf, (UChar)lastChar, (UChar)lastChar);                    
    }

    /**
     * If we saw a '^' after the initial '[' of this pattern, then perform
     * the complement.  (Inversion after '[:' is handled elsewhere.)
     */
    if (invert) {
        doComplement(pairsBuf);
    }

    /**
     * i indexes the last character we parsed or is pattern.length().  In
     * the latter case, we have run off the end without finding a closing
     * ']'.  Otherwise, we know i < pattern.length(), and we set the
     * ParsePosition to the next character to be parsed.
     */
    if (i == limit) {
        // throw new IllegalArgumentException("Missing ']'");
        status = U_ILLEGAL_ARGUMENT_ERROR;
        return pairsBuf;
    }

    pos.setIndex(i+1);

    return pairsBuf;
}

//----------------------------------------------------------------
// Implementation: Efficient in-place union & difference
//----------------------------------------------------------------

/**
 * Performs a union operation: adds the range 'c'-'d' to the given
 * pairs list.  The pairs list is modified in place.  The result
 * is normalized (in order and as short as possible).  For
 * example, addPair("am", 'l', 'q') => "aq".  addPair("ampz", 'n',
 * 'o') => "az".
 */
void UnicodeSet::addPair(UnicodeString& pairs, UChar c, UChar d) {
    UChar a = 0;
    UChar b = 0;
    for (int32_t i=0; i<pairs.length(); i+=2) {
        UChar e = pairs.charAt(i);
        UChar f = pairs.charAt(i+1);
        if (e <= (d+1) && c <= (f+1)) {
            // Merge with this range
            f = (UChar) uprv_max(d, f);

            // Check to see if we need to merge with the
            // subsequent range also.  This happens if we have
            // "abdf" and are merging in "cc".  We only need to
            // check on the right side -- never on the left.
            if ((i+2) < pairs.length() &&
                pairs.charAt(i+2) == (f+1)) {
                f = pairs.charAt(i+3);
                pairs.remove(i+2, 2);
            }
            pairs.setCharAt(i, (UChar) uprv_min(c, e));
            pairs.setCharAt(i+1, f);
            return;
        } else if ((b+1) < c && (d+1) < e) {
            // Insert before this range c, then d
            pairs.insert(i, d); // d gets moved to i+1 by next insert
            pairs.insert(i, c);
            return;
        }
        a = e;
        b = f;
    }
    // If nothing else, fall through and append this new range to
    // the end.
    pairs.append(c).append(d);
}

/**
 * Performs an asymmetric difference: removes the range 'c'-'d'
 * from the pairs list.  The pairs list is modified in place.  The
 * result is normalized (in order and as short as possible).  For
 * example, removePair("am", 'l', 'q') => "ak".
 * removePair("ampz", 'l', 'q') => "akrz".
 */
void UnicodeSet::removePair(UnicodeString& pairs, UChar c, UChar d) {
    // Iterate over pairs until we find a pair that overlaps
    // with the given range.
    for (int32_t i=0; i<pairs.length(); i+=2) {
        UChar b = pairs.charAt(i+1);
        if (b < c) {
            // Range at i is entirely before the given range,
            // since we have a-b < c-d.  No overlap yet...keep
            // iterating.
            continue;
        }
        UChar a = pairs.charAt(i);
        if (d < a) {
            // Range at i is entirely after the given range; c-d <
            // a-b.  Since ranges are in order, nothing else will
            // overlap.
            break;
        }
        // Once we get here, we know c <= b and d >= a.
        // rangeEdited is set to true if we have modified the
        // range a-b (the range at i) in place.
        bool_t rangeEdited = FALSE;
        if (c > a) {
            // If c is after a and before b, then we have overlap
            // of this sort: a--c==b--d or a--c==d--b, where a-b
            // and c-d are the ranges of interest.  We need to
            // add the range a,c-1.
            pairs.setCharAt(i+1, (UChar)(c-1));
            // i is already a
            rangeEdited = TRUE;
        }
        if (d < b) {
            // If d is after a and before b, we overlap like this:
            // c--a==d--b or a--c==d--b, where a-b is the range at
            // i and c-d is the range being removed.  We need to
            // add the range d+1,b.
            if (rangeEdited) {
                // Insert {d+1, b}
                pairs.insert(i+2, b); // b moves to i+3 by next insert:
                pairs.insert(i+2, (UChar)(d+1));
                i += 2;
            } else {
                pairs.setCharAt(i, (UChar)(d+1));
                // i+1 is already b
                rangeEdited = TRUE;
            }
        }
        if (!rangeEdited) {
            // If we didn't add any ranges, that means the entire
            // range a-b must be deleted, since we have
            // c--a==b--d.
            pairs.remove(i, 2);
            i -= 2;
        }
    }
}

//----------------------------------------------------------------
// Implementation: Fundamental operators
//----------------------------------------------------------------

/**
 * Changes the pairs list to represent the complement of the set it
 * currently represents.  The pairs list will be normalized (in
 * order and in shortest possible form) if the original pairs list
 * was normalized.
 */
void UnicodeSet::doComplement(UnicodeString& pairs) {
    if (pairs.length() == 0) {
        pairs.append((UChar)0x0000).append((UChar)0xffff);
        return;
    }

    // Change each end to a start and each start to an end of the
    // gaps between the ranges.  That is, 3-7 9-12 becomes x-2 8-8
    // 13-x, where 'x' represents a range that must now be fixed
    // up.
    for (int32_t i=0; i<pairs.length(); i+=2) {
        pairs.setCharAt(i,   (UChar) (pairs.charAt(i)   - 1));
        pairs.setCharAt(i+1, (UChar) (pairs.charAt(i+1) + 1));
    }

    // Fix up the initial range, either by adding a start point of
    // U+0000, or by deleting the range altogether, if the
    // original range was U+0000 - x.
    if (pairs.charAt(0) == (UChar)0xFFFF) {
        pairs.remove(0, 1);
    } else {
        pairs.insert(0, (UChar)0x0000);
    }

    // Fix up the final range, either by adding an end point of
    // U+FFFF, or by deleting the range altogether, if the
    // original range was x - U+FFFF.
    if (pairs.charAt(pairs.length() - 1) == (UChar)0x0000) {
        pairs.remove(pairs.length() - 1);
    } else {
        pairs.append((UChar)0xFFFF);
    }
}

/**
 * Given two pairs lists, changes the first in place to represent
 * the union of the two sets.
 */
void UnicodeSet::doUnion(UnicodeString& c1, const UnicodeString& c2) {
    UnicodeString result;

    int32_t i = 0;
    int32_t j = 0;

    // consider all the characters in both strings
    while (i < c1.length() && j < c2.length()) {
        UChar ub;
        
        // the first character in the result is the lower of the
        // starting characters of the two strings, and "ub" gets
        // set to the upper bound of that range
        if (c1.charAt(i) < c2.charAt(j)) {
            result.append(c1.charAt(i));
            ub = c1.charAt(++i);
        }
        else {
            result.append(c2.charAt(j));
            ub = c2.charAt(++j);
        }
        
        // for as long as one of our two pointers is pointing to a range's
        // end point, or i is pointing to a character that is less than
        // "ub" plus one (the "plus one" stitches touching ranges together)...
        while (i % 2 == 1 || j % 2 == 1 || (i < c1.length() && c1.charAt(i)
                        <= ub + 1)) {
            // advance i to the first character that is greater than
            // "ub" plus one
            while (i < c1.length() && c1.charAt(i) <= ub + 1)
                ++i;
                
            // if i points to the endpoint of a range, update "ub"
            // to that character, or if i points to the start of
            // a range and the endpoint of the preceding range is
            // greater than "ub", update "up" to _that_ character
            if (i % 2 == 1)
                ub = c1.charAt(i);
            else if (i > 0 && c1.charAt(i - 1) > ub)
                ub = c1.charAt(i - 1);

            // now advance j to the first character that is greater
            // that "ub" plus one
            while (j < c2.length() && c2.charAt(j) <= ub + 1)
                ++j;
                
            // if j points to the endpoint of a range, update "ub"
            // to that character, or if j points to the start of
            // a range and the endpoint of the preceding range is
            // greater than "ub", update "up" to _that_ character
            if (j % 2 == 1)
                ub = c2.charAt(j);
            else if (j > 0 && c2.charAt(j - 1) > ub)
                ub = c2.charAt(j - 1);
        }
        // when we finally fall out of this loop, we will have stitched
        // together a series of ranges that overlap or touch, i and j
        // will both point to starting points of ranges, and "ub" will
        // be the endpoint of the range we're working on.  Write "ub"
        // to the result
        result.append(ub);
        
    // loop back around to create the next range in the result
    }
    
    // we fall out to here when we've exhausted all the characters in
    // one of the operands.  We can append all of the remaining characters
    // in the other operand without doing any extra work.
    if (i < c1.length())
        result.append(c1, i, LONG_MAX);
    if (j < c2.length())
        result.append(c2, j, LONG_MAX);

    c1 = result;
}

/**
 * Given two pairs lists, changes the first in place to represent
 * the asymmetric difference of the two sets.
 */
void UnicodeSet::doDifference(UnicodeString& pairs, const UnicodeString& pairs2) {
    UnicodeString p2(pairs2);
    doComplement(p2);
    doIntersection(pairs, p2);
}

/**
 * Given two pairs lists, changes the first in place to represent
 * the intersection of the two sets.
 */
void UnicodeSet::doIntersection(UnicodeString& c1, const UnicodeString& c2) {
    UnicodeString result;

    int32_t i = 0;
    int32_t j = 0;
    int32_t oldI;
    int32_t oldJ;

    // iterate until we've exhausted one of the operands
    while (i < c1.length() && j < c2.length()) {
        
        // advance j until it points to a character that is larger than
        // the one i points to.  If this is the beginning of a one-
        // character range, advance j to point to the end
        if (i < c1.length() && i % 2 == 0) {
            while (j < c2.length() && c2.charAt(j) < c1.charAt(i))
                ++j;
            if (j < c2.length() && j % 2 == 0 && c2.charAt(j) == c1.charAt(i))
                ++j;
        }

        // if j points to the endpoint of a range, save the current
        // value of i, then advance i until it reaches a character
        // which is larger than the character pointed at
        // by j.  All of the characters we've advanced over (except
        // the one currently pointed to by i) are added to the result
        oldI = i;
        while (j % 2 == 1 && i < c1.length() && c1.charAt(i) <= c2.charAt(j))
            ++i;
        result.append(c1, oldI, i-oldI);

        // if i points to the endpoint of a range, save the current
        // value of j, then advance j until it reaches a character
        // which is larger than the character pointed at
        // by i.  All of the characters we've advanced over (except
        // the one currently pointed to by i) are added to the result
        oldJ = j;
        while (i % 2 == 1 && j < c2.length() && c2.charAt(j) <= c1.charAt(i))
            ++j;
        result.append(c2, oldJ, j-oldJ);

        // advance i until it points to a character larger than j
        // If it points at the beginning of a one-character range,
        // advance it to the end of that range
        if (j < c2.length() && j % 2 == 0) {
            while (i < c1.length() && c1.charAt(i) < c2.charAt(j))
                ++i;
            if (i < c1.length() && i % 2 == 0 && c2.charAt(j) == c1.charAt(i))
                ++i;
        }
    }

    c1 = result;
}

//----------------------------------------------------------------
// Implementation: Generation of pairs for Unicode categories
//----------------------------------------------------------------

/**
 * Returns a pairs string for the given category, given its name.
 * The category name must be either a two-letter name, such as
 * "Lu", or a one letter name, such as "L".  One-letter names
 * indicate the logical union of all two-letter names that start
 * with that letter.  Case is significant.  If the name starts
 * with the character '^' then the complement of the given
 * character set is returned.
 *
 * Although individual categories such as "Lu" are cached, we do
 * not currently cache single-letter categories such as "L" or
 * complements such as "^Lu" or "^L".  It would be easy to cache
 * these as well in a hashtable should the need arise.
 */
UnicodeString& UnicodeSet::getCategoryPairs(UnicodeString& result,
                                            const UnicodeString& catName,
                                            UErrorCode& status) {
    if (U_FAILURE(status)) {
        return result;
    }

	// The temporary cat is only really needed if invert is true.
	// TO DO: Allocate cat on the heap only if needed.
	UnicodeString cat(catName);
    bool_t invert = (catName.length() > 1 &&
                     catName.charAt(0) == '^');
    if (invert) {
        cat.remove(0, 1);
    }

    result.remove();
    
    // if we have two characters, search the category map for that
    // code and either construct and return a UnicodeSet from the
    // data in the category map or throw an exception
    if (cat.length() == 2) {
        int32_t i = CATEGORY_NAMES.indexOf(cat);
        if (i>=0 && i%2==0) {
            i /= 2;
            result = getCategoryPairs((int8_t)i);
            if (!invert) {
                return result;
            }
        }
    } else if (cat.length() == 1) {
        // if we have one character, search the category map for
        // codes beginning with that letter, and union together
        // all of the matching sets that we find (or throw an
        // exception if there are no matches)
        for (int32_t i=0; i<Unicode::GENERAL_TYPES_COUNT; ++i) {
            if (CATEGORY_NAMES.charAt(2*i) == cat.charAt(0)) {
                const UnicodeString& pairs = getCategoryPairs((int8_t)i);
                if (result.length() == 0) {
                    result = pairs;
                } else {
                    doUnion(result, pairs);
                }
            }
        }
    }

    if (result.length() == 0) {
        status = U_ILLEGAL_ARGUMENT_ERROR;
        return result;
    }

    if (invert) {
        doComplement(result);
    }
    return result;
}

/**
 * Returns a pairs string for the given category.  This string is
 * cached and returned again if this method is called again with
 * the same parameter.
 */
const UnicodeString& UnicodeSet::getCategoryPairs(int8_t cat) {
    // In order to tell what cache entries are empty, we assume
    // every category specifies at least one character.  Thus
    // pair lists in the cache that are empty are uninitialized.
    if (CATEGORY_PAIRS_CACHE[cat].length() == 0) {
        // Walk through all Unicode characters, noting the start
        // and end of each range for which Character.getType(c)
        // returns the given category integer.  Since we are
        // iterating in order, we can simply append the resulting
        // ranges to the pairs string.
        UnicodeString& pairs = CATEGORY_PAIRS_CACHE[cat];
        int32_t first = -1;
        int32_t last = -2;
        for (int32_t i=0; i<=0xFFFF; ++i) {
            if (Unicode::getType((UChar)i) == cat) {
                if ((last+1) == i) {
                    last = i;
                } else {
                    if (first >= 0) {
                        pairs.append((UChar)first).append((UChar)last);
                    }
                    first = last = i;
                }
            }
        }
        if (first >= 0) {
            pairs.append((UChar)first).append((UChar)last);
        }
    }
    return CATEGORY_PAIRS_CACHE[cat];
}

//----------------------------------------------------------------
// Implementation: Utility methods
//----------------------------------------------------------------

/**
 * Returns the character after the given position, or '\uFFFF' if
 * there is none.
 */
UChar UnicodeSet::charAfter(const UnicodeString& str, int32_t i) {
    return ((++i) < str.length()) ? str.charAt(i) : (UChar)0xFFFF;
}