// © 2016 and later: Unicode, Inc. and others.

// License & terms of use: http://www.unicode.org/copyright.html

/*

*******************************************************************************

*   Copyright (C) 2010-2012, International Business Machines

*   Corporation and others.  All Rights Reserved.

*******************************************************************************

*   file name:  bytestrie.h

*   encoding:   UTF-8

*   tab size:   8 (not used)

*   indentation:4

*

*   created on: 2010sep25

*   created by: Markus W. Scherer

*/

#ifndef __BYTESTRIE_H__

#define __BYTESTRIE_H__

/**

 * \file

 * \brief C++ API: Trie for mapping byte sequences to integer values.

 */

#include "unicode/utypes.h"

#if U_SHOW_CPLUSPLUS_API

#include "unicode/stringpiece.h"

#include "unicode/uobject.h"

#include "unicode/ustringtrie.h"

class BytesTrieTest;

U_NAMESPACE_BEGIN

class ByteSink;

class BytesTrieBuilder;

class CharString;

class UVector32;

/**

 * Light-weight, non-const reader class for a BytesTrie.

 * Traverses a byte-serialized data structure with minimal state,

 * for mapping byte sequences to non-negative integer values.

 *

 * This class owns the serialized trie data only if it was constructed by

 * the builder's build() method.

 * The public constructor and the copy constructor only alias the data (only copy the pointer).

 * There is no assignment operator.

 *

 * This class is not intended for public subclassing.

 * @stable ICU 4.8

 */

class U_COMMON_API BytesTrie : public UMemory {

public:

    /**

     * Constructs a BytesTrie reader instance.

     *

     * The trieBytes must contain a copy of a byte sequence from the BytesTrieBuilder,

     * starting with the first byte of that sequence.

     * The BytesTrie object will not read more bytes than

     * the BytesTrieBuilder generated in the corresponding build() call.

     *

     * The array is not copied/cloned and must not be modified while

     * the BytesTrie object is in use.

     *

     * @param trieBytes The byte array that contains the serialized trie.

     * @stable ICU 4.8

     */

    BytesTrie(const void* trieBytes U_LIFETIME_BOUND)

            : ownedArray_(nullptr), bytes_(static_cast<const uint8_t *>(trieBytes)),

              pos_(bytes_), remainingMatchLength_(-1) {}

    /**

     * Destructor.

     * @stable ICU 4.8

     */

    ~BytesTrie();

    /**

     * Copy constructor, copies the other trie reader object and its state,

     * but not the byte array which will be shared. (Shallow copy.)

     * @param other Another BytesTrie object.

     * @stable ICU 4.8

     */

    BytesTrie(const BytesTrie &other)

            : ownedArray_(nullptr), bytes_(other.bytes_),

              pos_(other.pos_), remainingMatchLength_(other.remainingMatchLength_) {}

    /**

     * Resets this trie to its initial state.

     * @return *this

     * @stable ICU 4.8

     */

    BytesTrie& reset() U_LIFETIME_BOUND {

        pos_=bytes_;

        remainingMatchLength_=-1;

        return *this;

    }

    /**

     * Returns the state of this trie as a 64-bit integer.

     * The state value is never 0.

     *

     * @return opaque state value

     * @see resetToState64

     * @stable ICU 65

     */

    uint64_t getState64() const {

        return (static_cast<uint64_t>(remainingMatchLength_ + 2) << kState64RemainingShift) |

            static_cast<uint64_t>(pos_ - bytes_);

    }

    /**

     * Resets this trie to the saved state.

     * Unlike resetToState(State), the 64-bit state value

     * must be from getState64() from the same trie object or

     * from one initialized the exact same way.

     * Because of no validation, this method is faster.

     *

     * @param state The opaque trie state value from getState64().

     * @return *this

     * @see getState64

     * @see resetToState

     * @see reset

     * @stable ICU 65

     */

    BytesTrie& resetToState64(uint64_t state) U_LIFETIME_BOUND {

        remainingMatchLength_ = static_cast<int32_t>(state >> kState64RemainingShift) - 2;

        pos_ = bytes_ + (state & kState64PosMask);

        return *this;

    }

    /**

     * BytesTrie state object, for saving a trie's current state

     * and resetting the trie back to this state later.

     * @stable ICU 4.8

     */

    class State : public UMemory {

    public:

        /**

         * Constructs an empty State.

         * @stable ICU 4.8

         */

        State() { bytes=nullptr; }

    private:

        friend class BytesTrie;

        const uint8_t *bytes;

        const uint8_t *pos;

        int32_t remainingMatchLength;

    };

    /**

     * Saves the state of this trie.

     * @param state The State object to hold the trie's state.

     * @return *this

     * @see resetToState

     * @stable ICU 4.8

     */

    const BytesTrie& saveState(State& state) const U_LIFETIME_BOUND {

        state.bytes=bytes_;

        state.pos=pos_;

        state.remainingMatchLength=remainingMatchLength_;

        return *this;

    }

    /**

     * Resets this trie to the saved state.

     * If the state object contains no state, or the state of a different trie,

     * then this trie remains unchanged.

     * @param state The State object which holds a saved trie state.

     * @return *this

     * @see saveState

     * @see reset

     * @stable ICU 4.8

     */

    BytesTrie& resetToState(const State& state) U_LIFETIME_BOUND {

        if(bytes_==state.bytes && bytes_!=nullptr) {

            pos_=state.pos;

            remainingMatchLength_=state.remainingMatchLength;

        }

        return *this;

    }

    /**

     * Determines whether the byte sequence so far matches, whether it has a value,

     * and whether another input byte can continue a matching byte sequence.

     * @return The match/value Result.

     * @stable ICU 4.8

     */

    UStringTrieResult current() const;

    /**

     * Traverses the trie from the initial state for this input byte.

     * Equivalent to reset().next(inByte).

     * @param inByte Input byte value. Values -0x100..-1 are treated like 0..0xff.

     *               Values below -0x100 and above 0xff will never match.

     * @return The match/value Result.

     * @stable ICU 4.8

     */

    inline UStringTrieResult first(int32_t inByte) {

        remainingMatchLength_=-1;

        if(inByte<0) {

            inByte+=0x100;

        }

        return nextImpl(bytes_, inByte);

    }

    /**

     * Traverses the trie from the current state for this input byte.

     * @param inByte Input byte value. Values -0x100..-1 are treated like 0..0xff.

     *               Values below -0x100 and above 0xff will never match.

     * @return The match/value Result.

     * @stable ICU 4.8

     */

    UStringTrieResult next(int32_t inByte);

    /**

     * Traverses the trie from the current state for this byte sequence.

     * Equivalent to

     * \code

     * Result result=current();

     * for(each c in s)

     *   if(!USTRINGTRIE_HAS_NEXT(result)) return USTRINGTRIE_NO_MATCH;

     *   result=next(c);

     * return result;

     * \endcode

     * @param s A string or byte sequence. Can be nullptr if length is 0.

     * @param length The length of the byte sequence. Can be -1 if NUL-terminated.

     * @return The match/value Result.

     * @stable ICU 4.8

     */

    UStringTrieResult next(const char *s, int32_t length);

    /**

     * Returns a matching byte sequence's value if called immediately after

     * current()/first()/next() returned USTRINGTRIE_INTERMEDIATE_VALUE or USTRINGTRIE_FINAL_VALUE.

     * getValue() can be called multiple times.

     *

     * Do not call getValue() after USTRINGTRIE_NO_MATCH or USTRINGTRIE_NO_VALUE!

     * @return The value for the byte sequence so far.

     * @stable ICU 4.8

     */

    inline int32_t getValue() const {

        const uint8_t *pos=pos_;

        int32_t leadByte=*pos++;

        // U_ASSERT(leadByte>=kMinValueLead);

        return readValue(pos, leadByte>>1);

    }

    /**

     * Determines whether all byte sequences reachable from the current state

     * map to the same value.

     * @param uniqueValue Receives the unique value, if this function returns true.

     *                    (output-only)

     * @return true if all byte sequences reachable from the current state

     *         map to the same value.

     * @stable ICU 4.8

     */

    inline UBool hasUniqueValue(int32_t &uniqueValue) const {

        const uint8_t *pos=pos_;

        // Skip the rest of a pending linear-match node.

        return pos!=nullptr && findUniqueValue(pos+remainingMatchLength_+1, false, uniqueValue);

    }

    /**

     * Finds each byte which continues the byte sequence from the current state.

     * That is, each byte b for which it would be next(b)!=USTRINGTRIE_NO_MATCH now.

     * @param out Each next byte is appended to this object.

     *            (Only uses the out.Append(s, length) method.)

     * @return the number of bytes which continue the byte sequence from here

     * @stable ICU 4.8

     */

    int32_t getNextBytes(ByteSink &out) const;

    /**

     * Iterator for all of the (byte sequence, value) pairs in a BytesTrie.

     * @stable ICU 4.8

     */

    class U_COMMON_API Iterator : public UMemory {

    public:

        /**

         * Iterates from the root of a byte-serialized BytesTrie.

         * @param trieBytes The trie bytes.

         * @param maxStringLength If 0, the iterator returns full strings/byte sequences.

         *                        Otherwise, the iterator returns strings with this maximum length.

         * @param errorCode Standard 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.)

         * @stable ICU 4.8

         */

        Iterator(const void* trieBytes U_LIFETIME_BOUND,

                 int32_t maxStringLength,

                 UErrorCode& errorCode);

        /**

         * Iterates from the current state of the specified BytesTrie.

         * @param trie The trie whose state will be copied for iteration.

         * @param maxStringLength If 0, the iterator returns full strings/byte sequences.

         *                        Otherwise, the iterator returns strings with this maximum length.

         * @param errorCode Standard 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.)

         * @stable ICU 4.8

         */

        Iterator(const BytesTrie &trie, int32_t maxStringLength, UErrorCode &errorCode);

        /**

         * Destructor.

         * @stable ICU 4.8

         */

        ~Iterator();

        /**

         * Resets this iterator to its initial state.

         * @return *this

         * @stable ICU 4.8

         */

        Iterator& reset() U_LIFETIME_BOUND;

        /**

         * @return true if there are more elements.

         * @stable ICU 4.8

         */

        UBool hasNext() const;

        /**

         * Finds the next (byte sequence, value) pair if there is one.

         *

         * If the byte sequence is truncated to the maximum length and does not

         * have a real value, then the value is set to -1.

         * In this case, this "not a real value" is indistinguishable from

         * a real value of -1.

         * @param errorCode Standard 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 element.

         * @stable ICU 4.8

         */

        UBool next(UErrorCode &errorCode);

        /**

         * @return The NUL-terminated byte sequence for the last successful next().

         * @stable ICU 4.8

         */

        StringPiece getString() const U_LIFETIME_BOUND;

        /**

         * @return The value for the last successful next().

         * @stable ICU 4.8

         */

        int32_t getValue() const { return value_; }

    private:

        UBool truncateAndStop();

        const uint8_t* branchNext(const uint8_t* pos U_LIFETIME_BOUND,

                                  int32_t length,

                                  UErrorCode& errorCode);

        const uint8_t *bytes_;

        const uint8_t *pos_;

        const uint8_t *initialPos_;

        int32_t remainingMatchLength_;

        int32_t initialRemainingMatchLength_;

        CharString *str_;

        int32_t maxLength_;

        int32_t value_;

        // The stack stores pairs of integers for backtracking to another

        // outbound edge of a branch node.

        // The first integer is an offset from bytes_.

        // The second integer has the str_->length() from before the node in bits 15..0,

        // and the remaining branch length in bits 24..16. (Bits 31..25 are unused.)

        // (We could store the remaining branch length minus 1 in bits 23..16 and not use bits 31..24,

        // but the code looks more confusing that way.)

        UVector32 *stack_;

    };

private:

    friend class BytesTrieBuilder;

    friend class ::BytesTrieTest;

    /**

     * Constructs a BytesTrie reader instance.

     * Unlike the public constructor which just aliases an array,

     * this constructor adopts the builder's array.

     * This constructor is only called by the builder.

     */

    BytesTrie(void *adoptBytes, const void *trieBytes)

            : ownedArray_(static_cast<uint8_t *>(adoptBytes)),

              bytes_(static_cast<const uint8_t *>(trieBytes)),

              pos_(bytes_), remainingMatchLength_(-1) {}

    // No assignment operator.

    BytesTrie &operator=(const BytesTrie &other) = delete;

    inline void stop() {

        pos_=nullptr;

    }

    // Reads a compact 32-bit integer.

    // pos is already after the leadByte, and the lead byte is already shifted right by 1.

    static int32_t readValue(const uint8_t *pos, int32_t leadByte);

    static inline const uint8_t* skipValue(const uint8_t* pos U_LIFETIME_BOUND, int32_t leadByte) {

        // U_ASSERT(leadByte>=kMinValueLead);

        if(leadByte>=(kMinTwoByteValueLead<<1)) {

            if(leadByte<(kMinThreeByteValueLead<<1)) {

                ++pos;

            } else if(leadByte<(kFourByteValueLead<<1)) {

                pos+=2;

            } else {

                pos+=3+((leadByte>>1)&1);

            }

        }

        return pos;

    }

    static inline const uint8_t* skipValue(const uint8_t* pos U_LIFETIME_BOUND) {

        int32_t leadByte=*pos++;

        return skipValue(pos, leadByte);

    }

    // Reads a jump delta and jumps.

    static const uint8_t* jumpByDelta(const uint8_t* pos U_LIFETIME_BOUND);

    static inline const uint8_t* skipDelta(const uint8_t* pos U_LIFETIME_BOUND) {

        int32_t delta=*pos++;

        if(delta>=kMinTwoByteDeltaLead) {

            if(delta<kMinThreeByteDeltaLead) {

                ++pos;

            } else if(delta<kFourByteDeltaLead) {

                pos+=2;

            } else {

                pos+=3+(delta&1);

            }

        }

        return pos;

    }

    static inline UStringTrieResult valueResult(int32_t node) {

        return static_cast<UStringTrieResult>(USTRINGTRIE_INTERMEDIATE_VALUE - (node & kValueIsFinal));

    }

    // Handles a branch node for both next(byte) and next(string).

    UStringTrieResult branchNext(const uint8_t *pos, int32_t length, int32_t inByte);

    // Requires remainingLength_<0.

    UStringTrieResult nextImpl(const uint8_t *pos, int32_t inByte);

    // Helper functions for hasUniqueValue().

    // Recursively finds a unique value (or whether there is not a unique one)

    // from a branch.

    static const uint8_t* findUniqueValueFromBranch(const uint8_t* pos U_LIFETIME_BOUND,

                                                    int32_t length,

                                                    UBool haveUniqueValue,

                                                    int32_t& uniqueValue);

    // Recursively finds a unique value (or whether there is not a unique one)

    // starting from a position on a node lead byte.

    static UBool findUniqueValue(const uint8_t *pos, UBool haveUniqueValue, int32_t &uniqueValue);

    // Helper functions for getNextBytes().

    // getNextBytes() when pos is on a branch node.

    static void getNextBranchBytes(const uint8_t *pos, int32_t length, ByteSink &out);

    static void append(ByteSink &out, int c);

    // BytesTrie data structure

    //

    // The trie consists of a series of byte-serialized nodes for incremental

    // string/byte sequence matching. The root node is at the beginning of the trie data.

    //

    // Types of nodes are distinguished by their node lead byte ranges.

    // After each node, except a final-value node, another node follows to

    // encode match values or continue matching further bytes.

    //

    // Node types:

    //  - Value node: Stores a 32-bit integer in a compact, variable-length format.

    //    The value is for the string/byte sequence so far.

    //    One node bit indicates whether the value is final or whether

    //    matching continues with the next node.

    //  - Linear-match node: Matches a number of bytes.

    //  - Branch node: Branches to other nodes according to the current input byte.

    //    The node byte is the length of the branch (number of bytes to select from)

    //    minus 1. It is followed by a sub-node:

    //    - If the length is at most kMaxBranchLinearSubNodeLength, then

    //      there are length-1 (key, value) pairs and then one more comparison byte.

    //      If one of the key bytes matches, then the value is either a final value for

    //      the string/byte sequence so far, or a "jump" delta to the next node.

    //      If the last byte matches, then matching continues with the next node.

    //      (Values have the same encoding as value nodes.)

    //    - If the length is greater than kMaxBranchLinearSubNodeLength, then

    //      there is one byte and one "jump" delta.

    //      If the input byte is less than the sub-node byte, then "jump" by delta to

    //      the next sub-node which will have a length of length/2.

    //      (The delta has its own compact encoding.)

    //      Otherwise, skip the "jump" delta to the next sub-node

    //      which will have a length of length-length/2.

    // Node lead byte values.

    // 00..0f: Branch node. If node!=0 then the length is node+1, otherwise

    // the length is one more than the next byte.

    // For a branch sub-node with at most this many entries, we drop down

    // to a linear search.

    static const int32_t kMaxBranchLinearSubNodeLength=5;

    // 10..1f: Linear-match node, match 1..16 bytes and continue reading the next node.

    static const int32_t kMinLinearMatch=0x10;

    static const int32_t kMaxLinearMatchLength=0x10;

    // 20..ff: Variable-length value node.

    // If odd, the value is final. (Otherwise, intermediate value or jump delta.)

    // Then shift-right by 1 bit.

    // The remaining lead byte value indicates the number of following bytes (0..4)

    // and contains the value's top bits.

    static const int32_t kMinValueLead=kMinLinearMatch+kMaxLinearMatchLength;  // 0x20

    // It is a final value if bit 0 is set.

    static const int32_t kValueIsFinal=1;

    // Compact value: After testing bit 0, shift right by 1 and then use the following thresholds.

    static const int32_t kMinOneByteValueLead=kMinValueLead/2;  // 0x10

    static const int32_t kMaxOneByteValue=0x40;  // At least 6 bits in the first byte.

    static const int32_t kMinTwoByteValueLead=kMinOneByteValueLead+kMaxOneByteValue+1;  // 0x51

    static const int32_t kMaxTwoByteValue=0x1aff;

    static const int32_t kMinThreeByteValueLead=kMinTwoByteValueLead+(kMaxTwoByteValue>>8)+1;  // 0x6c

    static const int32_t kFourByteValueLead=0x7e;

    // A little more than Unicode code points. (0x11ffff)

    static const int32_t kMaxThreeByteValue=((kFourByteValueLead-kMinThreeByteValueLead)<<16)-1;

    static const int32_t kFiveByteValueLead=0x7f;

    // Compact delta integers.

    static const int32_t kMaxOneByteDelta=0xbf;

    static const int32_t kMinTwoByteDeltaLead=kMaxOneByteDelta+1;  // 0xc0

    static const int32_t kMinThreeByteDeltaLead=0xf0;

    static const int32_t kFourByteDeltaLead=0xfe;

    static const int32_t kFiveByteDeltaLead=0xff;

    static const int32_t kMaxTwoByteDelta=((kMinThreeByteDeltaLead-kMinTwoByteDeltaLead)<<8)-1;  // 0x2fff

    static const int32_t kMaxThreeByteDelta=((kFourByteDeltaLead-kMinThreeByteDeltaLead)<<16)-1;  // 0xdffff

    // For getState64():

    // The remainingMatchLength_ is -1..14=(kMaxLinearMatchLength=0x10)-2

    // so we need at least 5 bits for that.

    // We add 2 to store it as a positive value 1..16=kMaxLinearMatchLength.

    static constexpr int32_t kState64RemainingShift = 59;

    static constexpr uint64_t kState64PosMask = (UINT64_C(1) << kState64RemainingShift) - 1;

    uint8_t *ownedArray_;

    // Fixed value referencing the BytesTrie bytes.

    const uint8_t *bytes_;

    // Iterator variables.

    // Pointer to next trie byte to read. nullptr if no more matches.

    const uint8_t *pos_;

    // Remaining length of a linear-match node, minus 1. Negative if not in such a node.

    int32_t remainingMatchLength_;

};

U_NAMESPACE_END

#endif /* U_SHOW_CPLUSPLUS_API */

#endif  // __BYTESTRIE_H__