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 // © 2016 and later: Unicode, Inc. and others.
 // License & terms of use: http://www.unicode.org/copyright.html
 
 // edits.h
 // created: 2016dec30 Markus W. Scherer
 
 #ifndef __EDITS_H__
 #define __EDITS_H__
 
 #include "unicode/utypes.h"
 
 #if U_SHOW_CPLUSPLUS_API
 
 #include "unicode/uobject.h"
 
 /**
  * \file
  * \brief C++ API: C++ class Edits for low-level string transformations on styled text.
  */
 
 U_NAMESPACE_BEGIN
 
 class UnicodeString;
 
 /**
  * Records lengths of string edits but not replacement text. Supports replacements, insertions, deletions
  * in linear progression. Does not support moving/reordering of text.
  *
  * There are two types of edits: <em>change edits</em> and <em>no-change edits</em>. Add edits to
  * instances of this class using {@link #addReplace(int32_t, int32_t)} (for change edits) and
  * {@link #addUnchanged(int32_t)} (for no-change edits). Change edits are retained with full granularity,
  * whereas adjacent no-change edits are always merged together. In no-change edits, there is a one-to-one
  * mapping between code points in the source and destination strings.
  *
  * After all edits have been added, instances of this class should be considered immutable, and an
  * {@link Edits::Iterator} can be used for queries.
  *
  * There are four flavors of Edits::Iterator:
  *
  * <ul>
  * <li>{@link #getFineIterator()} retains full granularity of change edits.
  * <li>{@link #getFineChangesIterator()} retains full granularity of change edits, and when calling
  * next() on the iterator, skips over no-change edits (unchanged regions).
  * <li>{@link #getCoarseIterator()} treats adjacent change edits as a single edit. (Adjacent no-change
  * edits are automatically merged during the construction phase.)
  * <li>{@link #getCoarseChangesIterator()} treats adjacent change edits as a single edit, and when
  * calling next() on the iterator, skips over no-change edits (unchanged regions).
  * </ul>
  *
  * For example, consider the string "abcßDeF", which case-folds to "abcssdef". This string has the
  * following fine edits:
  * <ul>
  * <li>abc ⇨ abc (no-change)
  * <li>ß ⇨ ss (change)
  * <li>D ⇨ d (change)
  * <li>e ⇨ e (no-change)
  * <li>F ⇨ f (change)
  * </ul>
  * and the following coarse edits (note how adjacent change edits get merged together):
  * <ul>
  * <li>abc ⇨ abc (no-change)
  * <li>ßD ⇨ ssd (change)
  * <li>e ⇨ e (no-change)
  * <li>F ⇨ f (change)
  * </ul>
  *
  * The "fine changes" and "coarse changes" iterators will step through only the change edits when their
  * `Edits::Iterator::next()` methods are called. They are identical to the non-change iterators when
  * their `Edits::Iterator::findSourceIndex()` or `Edits::Iterator::findDestinationIndex()`
  * methods are used to walk through the string.
  *
  * For examples of how to use this class, see the test `TestCaseMapEditsIteratorDocs` in
  * UCharacterCaseTest.java.
  *
  * An Edits object tracks a separate UErrorCode, but ICU string transformation functions
  * (e.g., case mapping functions) merge any such errors into their API's UErrorCode.
  *
  * @stable ICU 59
  */
 class U_COMMON_API Edits final : public UMemory {
 public:
     /**
      * Constructs an empty object.
      * @stable ICU 59
      */
     Edits() :
             array(stackArray), capacity(STACK_CAPACITY), length(0), delta(0), numChanges(0),
             errorCode_(U_ZERO_ERROR) {}
     /**
      * Copy constructor.
      * @param other source edits
      * @stable ICU 60
      */
     Edits(const Edits &other) :
             array(stackArray), capacity(STACK_CAPACITY), length(other.length),
             delta(other.delta), numChanges(other.numChanges),
             errorCode_(other.errorCode_) {
         copyArray(other);
     }
     /**
      * Move constructor, might leave src empty.
      * This object will have the same contents that the source object had.
      * @param src source edits
      * @stable ICU 60
      */
     Edits(Edits &&src) noexcept :
             array(stackArray), capacity(STACK_CAPACITY), length(src.length),
             delta(src.delta), numChanges(src.numChanges),
             errorCode_(src.errorCode_) {
         moveArray(src);
     }
 
     /**
      * Destructor.
      * @stable ICU 59
      */
     ~Edits();
 
     /**
      * Assignment operator.
      * @param other source edits
      * @return *this
      * @stable ICU 60
      */
     Edits &operator=(const Edits &other);
 
     /**
      * Move assignment operator, might leave src empty.
      * This object will have the same contents that the source object had.
      * The behavior is undefined if *this and src are the same object.
      * @param src source edits
      * @return *this
      * @stable ICU 60
      */
     Edits &operator=(Edits &&src) noexcept;
 
     /**
      * Resets the data but may not release memory.
      * @stable ICU 59
      */
     void reset() noexcept;
 
     /**
      * Adds a no-change edit: a record for an unchanged segment of text.
      * Normally called from inside ICU string transformation functions, not user code.
      * @stable ICU 59
      */
     void addUnchanged(int32_t unchangedLength);
     /**
      * Adds a change edit: a record for a text replacement/insertion/deletion.
      * Normally called from inside ICU string transformation functions, not user code.
      * @stable ICU 59
      */
     void addReplace(int32_t oldLength, int32_t newLength);
     /**
      * Sets the UErrorCode if an error occurred while recording edits.
      * Preserves older error codes in the outErrorCode.
      * Normally called from inside ICU string transformation functions, not user code.
      * @param outErrorCode Set to an error code if it does not contain one already
      *                  and an error occurred while recording edits.
      *                  Otherwise unchanged.
      * @return true if U_FAILURE(outErrorCode)
      * @stable ICU 59
      */
     UBool copyErrorTo(UErrorCode &outErrorCode) const;
 
     /**
      * How much longer is the new text compared with the old text?
      * @return new length minus old length
      * @stable ICU 59
      */
     int32_t lengthDelta() const { return delta; }
     /**
      * @return true if there are any change edits
      * @stable ICU 59
      */
     UBool hasChanges() const { return numChanges != 0; }
 
     /**
      * @return the number of change edits
      * @stable ICU 60
      */
     int32_t numberOfChanges() const { return numChanges; }
 
     /**
      * Access to the list of edits.
      *
      * At any moment in time, an instance of this class points to a single edit: a "window" into a span
      * of the source string and the corresponding span of the destination string. The source string span
      * starts at {@link #sourceIndex()} and runs for {@link #oldLength()} chars; the destination string
      * span starts at {@link #destinationIndex()} and runs for {@link #newLength()} chars.
      *
      * The iterator can be moved between edits using the `next()`, `findSourceIndex(int32_t, UErrorCode &)`,
      * and `findDestinationIndex(int32_t, UErrorCode &)` methods.
      * Calling any of these methods mutates the iterator to make it point to the corresponding edit.
      *
      * For more information, see the documentation for {@link Edits}.
      *
      * @see getCoarseIterator
      * @see getFineIterator
      * @stable ICU 59
      */
     struct U_COMMON_API Iterator final : public UMemory {
         /**
          * Default constructor, empty iterator.
          * @stable ICU 60
          */
         Iterator() :
                 array(nullptr), index(0), length(0),
                 remaining(0), onlyChanges_(false), coarse(false),
                 dir(0), changed(false), oldLength_(0), newLength_(0),
                 srcIndex(0), replIndex(0), destIndex(0) {}
         /**
          * Copy constructor.
          * @stable ICU 59
          */
         Iterator(const Iterator &other) = default;
         /**
          * Assignment operator.
          * @stable ICU 59
          */
         Iterator &operator=(const Iterator &other) = default;
 
         /**
          * Advances the iterator to the next edit.
          * @param errorCode ICU error code. Its input value must pass the U_SUCCESS() test,
          *                  or else the function returns immediately. Check for U_FAILURE()
          *                  on output or use with function chaining. (See User Guide for details.)
          * @return true if there is another edit
          * @stable ICU 59
          */
         UBool next(UErrorCode &errorCode) { return next(onlyChanges_, errorCode); }
 
         /**
          * Moves the iterator to the edit that contains the source index.
          * The source index may be found in a no-change edit
          * even if normal iteration would skip no-change edits.
          * Normal iteration can continue from a found edit.
          *
          * The iterator state before this search logically does not matter.
          * (It may affect the performance of the search.)
          *
          * The iterator state after this search is undefined
          * if the source index is out of bounds for the source string.
          *
          * @param i source index
          * @param errorCode ICU error code. Its input value must pass the U_SUCCESS() test,
          *                  or else the function returns immediately. Check for U_FAILURE()
          *                  on output or use with function chaining. (See User Guide for details.)
          * @return true if the edit for the source index was found
          * @stable ICU 59
          */
         UBool findSourceIndex(int32_t i, UErrorCode &errorCode) {
             return findIndex(i, true, errorCode) == 0;
         }
 
         /**
          * Moves the iterator to the edit that contains the destination index.
          * The destination index may be found in a no-change edit
          * even if normal iteration would skip no-change edits.
          * Normal iteration can continue from a found edit.
          *
          * The iterator state before this search logically does not matter.
          * (It may affect the performance of the search.)
          *
          * The iterator state after this search is undefined
          * if the source index is out of bounds for the source string.
          *
          * @param i destination index
          * @param errorCode ICU error code. Its input value must pass the U_SUCCESS() test,
          *                  or else the function returns immediately. Check for U_FAILURE()
          *                  on output or use with function chaining. (See User Guide for details.)
          * @return true if the edit for the destination index was found
          * @stable ICU 60
          */
         UBool findDestinationIndex(int32_t i, UErrorCode &errorCode) {
             return findIndex(i, false, errorCode) == 0;
         }
 
         /**
          * Computes the destination index corresponding to the given source index.
          * If the source index is inside a change edit (not at its start),
          * then the destination index at the end of that edit is returned,
          * since there is no information about index mapping inside a change edit.
          *
          * (This means that indexes to the start and middle of an edit,
          * for example around a grapheme cluster, are mapped to indexes
          * encompassing the entire edit.
          * The alternative, mapping an interior index to the start,
          * would map such an interval to an empty one.)
          *
          * This operation will usually but not always modify this object.
          * The iterator state after this search is undefined.
          *
          * @param i source index
          * @param errorCode ICU error code. Its input value must pass the U_SUCCESS() test,
          *                  or else the function returns immediately. Check for U_FAILURE()
          *                  on output or use with function chaining. (See User Guide for details.)
          * @return destination index; undefined if i is not 0..string length
          * @stable ICU 60
          */
         int32_t destinationIndexFromSourceIndex(int32_t i, UErrorCode &errorCode);
 
         /**
          * Computes the source index corresponding to the given destination index.
          * If the destination index is inside a change edit (not at its start),
          * then the source index at the end of that edit is returned,
          * since there is no information about index mapping inside a change edit.
          *
          * (This means that indexes to the start and middle of an edit,
          * for example around a grapheme cluster, are mapped to indexes
          * encompassing the entire edit.
          * The alternative, mapping an interior index to the start,
          * would map such an interval to an empty one.)
          *
          * This operation will usually but not always modify this object.
          * The iterator state after this search is undefined.
          *
          * @param i destination index
          * @param errorCode ICU error code. Its input value must pass the U_SUCCESS() test,
          *                  or else the function returns immediately. Check for U_FAILURE()
          *                  on output or use with function chaining. (See User Guide for details.)
          * @return source index; undefined if i is not 0..string length
          * @stable ICU 60
          */
         int32_t sourceIndexFromDestinationIndex(int32_t i, UErrorCode &errorCode);
 
         /**
          * Returns whether the edit currently represented by the iterator is a change edit.
          *
          * @return true if this edit replaces oldLength() units with newLength() different ones.
          *         false if oldLength units remain unchanged.
          * @stable ICU 59
          */
         UBool hasChange() const { return changed; }
 
         /**
          * The length of the current span in the source string, which starts at {@link #sourceIndex}.
          *
          * @return the number of units in the original string which are replaced or remain unchanged.
          * @stable ICU 59
          */
         int32_t oldLength() const { return oldLength_; }
 
         /**
          * The length of the current span in the destination string, which starts at
          * {@link #destinationIndex}, or in the replacement string, which starts at
          * {@link #replacementIndex}.
          *
          * @return the number of units in the modified string, if hasChange() is true.
          *         Same as oldLength if hasChange() is false.
          * @stable ICU 59
          */
         int32_t newLength() const { return newLength_; }
 
         /**
          * The start index of the current span in the source string; the span has length
          * {@link #oldLength}.
          *
          * @return the current index into the source string
          * @stable ICU 59
          */
         int32_t sourceIndex() const { return srcIndex; }
 
         /**
          * The start index of the current span in the replacement string; the span has length
          * {@link #newLength}. Well-defined only if the current edit is a change edit.
          *
          * The *replacement string* is the concatenation of all substrings of the destination
          * string corresponding to change edits.
          *
          * This method is intended to be used together with operations that write only replacement
          * characters (e.g. operations specifying the \ref U_OMIT_UNCHANGED_TEXT option).
          * The source string can then be modified in-place.
          *
          * @return the current index into the replacement-characters-only string,
          *         not counting unchanged spans
          * @stable ICU 59
          */
         int32_t replacementIndex() const {
             // TODO: Throw an exception if we aren't in a change edit?
             return replIndex;
         }
 
         /**
          * The start index of the current span in the destination string; the span has length
          * {@link #newLength}.
          *
          * @return the current index into the full destination string
          * @stable ICU 59
          */
         int32_t destinationIndex() const { return destIndex; }
 
 #ifndef U_HIDE_INTERNAL_API
         /**
          * A string representation of the current edit represented by the iterator for debugging. You
          * should not depend on the contents of the return string.
          * @internal
          */
         UnicodeString& toString(UnicodeString& appendTo) const;
 #endif  // U_HIDE_INTERNAL_API
 
     private:
         friend class Edits;
 
         Iterator(const uint16_t *a, int32_t len, UBool oc, UBool crs);
 
         int32_t readLength(int32_t head);
         void updateNextIndexes();
         void updatePreviousIndexes();
         UBool noNext();
         UBool next(UBool onlyChanges, UErrorCode &errorCode);
         UBool previous(UErrorCode &errorCode);
         /** @return -1: error or i<0; 0: found; 1: i>=string length */
         int32_t findIndex(int32_t i, UBool findSource, UErrorCode &errorCode);
 
         const uint16_t *array;
         int32_t index, length;
         // 0 if we are not within compressed equal-length changes.
         // Otherwise the number of remaining changes, including the current one.
         int32_t remaining;
         UBool onlyChanges_, coarse;
 
         int8_t dir;  // iteration direction: back(<0), initial(0), forward(>0)
         UBool changed;
         int32_t oldLength_, newLength_;
         int32_t srcIndex, replIndex, destIndex;
     };
 
     /**
      * Returns an Iterator for coarse-grained change edits
      * (adjacent change edits are treated as one).
      * Can be used to perform simple string updates.
      * Skips no-change edits.
      * @return an Iterator that merges adjacent changes.
      * @stable ICU 59
      */
     Iterator getCoarseChangesIterator() const {
         return Iterator(array, length, true, true);
     }
 
     /**
      * Returns an Iterator for coarse-grained change and no-change edits
      * (adjacent change edits are treated as one).
      * Can be used to perform simple string updates.
      * Adjacent change edits are treated as one edit.
      * @return an Iterator that merges adjacent changes.
      * @stable ICU 59
      */
     Iterator getCoarseIterator() const {
         return Iterator(array, length, false, true);
     }
 
     /**
      * Returns an Iterator for fine-grained change edits
      * (full granularity of change edits is retained).
      * Can be used for modifying styled text.
      * Skips no-change edits.
      * @return an Iterator that separates adjacent changes.
      * @stable ICU 59
      */
     Iterator getFineChangesIterator() const {
         return Iterator(array, length, true, false);
     }
 
     /**
      * Returns an Iterator for fine-grained change and no-change edits
      * (full granularity of change edits is retained).
      * Can be used for modifying styled text.
      * @return an Iterator that separates adjacent changes.
      * @stable ICU 59
      */
     Iterator getFineIterator() const {
         return Iterator(array, length, false, false);
     }
 
     /**
      * Merges the two input Edits and appends the result to this object.
      *
      * Consider two string transformations (for example, normalization and case mapping)
      * where each records Edits in addition to writing an output string.<br>
      * Edits ab reflect how substrings of input string a
      * map to substrings of intermediate string b.<br>
      * Edits bc reflect how substrings of intermediate string b
      * map to substrings of output string c.<br>
      * This function merges ab and bc such that the additional edits
      * recorded in this object reflect how substrings of input string a
      * map to substrings of output string c.
      *
      * If unrelated Edits are passed in where the output string of the first
      * has a different length than the input string of the second,
      * then a U_ILLEGAL_ARGUMENT_ERROR is reported.
      *
      * @param ab reflects how substrings of input string a
      *     map to substrings of intermediate string b.
      * @param bc reflects how substrings of intermediate string b
      *     map to substrings of output string c.
      * @param errorCode ICU error code. Its input value must pass the U_SUCCESS() test,
      *                  or else the function returns immediately. Check for U_FAILURE()
      *                  on output or use with function chaining. (See User Guide for details.)
      * @return *this, with the merged edits appended
      * @stable ICU 60
      */
     Edits &mergeAndAppend(const Edits &ab, const Edits &bc, UErrorCode &errorCode);
 
 private:
     void releaseArray() noexcept;
     Edits &copyArray(const Edits &other);
     Edits &moveArray(Edits &src) noexcept;
 
     void setLastUnit(int32_t last) { array[length - 1] = (uint16_t)last; }
     int32_t lastUnit() const { return length > 0 ? array[length - 1] : 0xffff; }
 
     void append(int32_t r);
     UBool growArray();
 
     static const int32_t STACK_CAPACITY = 100;
     uint16_t *array;
     int32_t capacity;
     int32_t length;
     int32_t delta;
     int32_t numChanges;
     UErrorCode errorCode_;
     uint16_t stackArray[STACK_CAPACITY];
 };
 
 U_NAMESPACE_END
 
 #endif /* U_SHOW_CPLUSPLUS_API */
 
 #endif  // __EDITS_H__

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