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+// Copyright (c) 2014-2017, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include "syncobj.h"
+#include "cryptonote_basic/cryptonote_basic.h"
+
+namespace cryptonote
+{
+  class BlockchainDB;
+
+  class HardFork
+  {
+  public:
+    typedef enum {
+      LikelyForked,
+      UpdateNeeded,
+      Ready,
+    } State;
+
+    static const uint64_t DEFAULT_ORIGINAL_VERSION_TILL_HEIGHT = 0; // <= actual height
+    static const time_t DEFAULT_FORKED_TIME = 31557600; // a year in seconds
+    static const time_t DEFAULT_UPDATE_TIME = 31557600 / 2;
+    static const uint64_t DEFAULT_WINDOW_SIZE = 10080; // supermajority window check length - a week
+    static const uint8_t DEFAULT_THRESHOLD_PERCENT = 80;
+
+    /**
+     * @brief creates a new HardFork object
+     *
+     * @param original_version the block version for blocks 0 through to the first fork
+     * @param forked_time the time in seconds before thinking we're forked
+     * @param update_time the time in seconds before thinking we need to update
+     * @param window_size the size of the window in blocks to consider for version voting
+     * @param default_threshold_percent the size of the majority in percents
+     */
+    HardFork(cryptonote::BlockchainDB &db, uint8_t original_version = 1, uint64_t original_version_till_height = DEFAULT_ORIGINAL_VERSION_TILL_HEIGHT, time_t forked_time = DEFAULT_FORKED_TIME, time_t update_time = DEFAULT_UPDATE_TIME, uint64_t window_size = DEFAULT_WINDOW_SIZE, uint8_t default_threshold_percent = DEFAULT_THRESHOLD_PERCENT);
+
+    /**
+     * @brief add a new hardfork height
+     *
+     * returns true if no error, false otherwise
+     *
+     * @param version the major block version for the fork
+     * @param height The height the hardfork takes effect
+     * @param threshold The threshold of votes needed for this fork (0-100)
+     * @param time Approximate time of the hardfork (seconds since epoch)
+     */
+    bool add_fork(uint8_t version, uint64_t height, uint8_t threshold, time_t time);
+
+    /**
+     * @brief add a new hardfork height
+     *
+     * returns true if no error, false otherwise
+     *
+     * @param version the major block version for the fork
+     * @param voting_version the minor block version for the fork, used for voting
+     * @param height The height the hardfork takes effect
+     * @param time Approximate time of the hardfork (seconds since epoch)
+     */
+    bool add_fork(uint8_t version, uint64_t height, time_t time);
+
+    /**
+     * @brief initialize the object
+     *
+     * Must be done after adding all the required hardforks via add above
+     */
+    void init();
+
+    /**
+     * @brief check whether a new block would be accepted
+     *
+     * returns true if the block is accepted, false otherwise
+     *
+     * @param block the new block
+     *
+     * This check is made by add. It is exposed publicly to allow
+     * the caller to inexpensively check whether a block would be
+     * accepted or rejected by its version number. Indeed, if this
+     * check could only be done as part of add, the caller would
+     * either have to add the block to the blockchain first, then
+     * call add, then have to pop the block from the blockchain if
+     * its version did not satisfy the hard fork requirements, or
+     * call add first, then, if the hard fork requirements are met,
+     * add the block to the blockchain, upon which a failure (the
+     * block being invalid, double spending, etc) would cause the
+     * hardfork object to reorganize.
+     */
+    bool check(const cryptonote::block &block) const;
+
+    /**
+     * @brief same as check, but for a particular height, rather than the top
+     *
+     * NOTE: this does not play well with voting, and relies on voting to be
+     * disabled (that is, forks happen on the scheduled date, whether or not
+     * enough blocks have voted for the fork).
+     *
+     * returns true if no error, false otherwise
+     *
+     * @param block the new block
+     * @param height which height to check for
+     */
+    bool check_for_height(const cryptonote::block &block, uint64_t height) const;
+
+    /**
+     * @brief add a new block
+     *
+     * returns true if no error, false otherwise
+     *
+     * @param block the new block
+     */
+    bool add(const cryptonote::block &block, uint64_t height);
+
+    /**
+     * @brief called when the blockchain is reorganized
+     *
+     * This will rescan the blockchain to determine which hard forks
+     * have been triggered
+     *
+     * returns true if no error, false otherwise
+     *
+     * @param blockchain the blockchain
+     * @param height of the last block kept from the previous blockchain
+     */
+    bool reorganize_from_block_height(uint64_t height);
+    bool reorganize_from_chain_height(uint64_t height);
+
+    /**
+     * @brief returns current state at the given time
+     *
+     * Based on the approximate time of the last known hard fork,
+     * estimate whether we need to update, or if we're way behind
+     *
+     * @param t the time to consider
+     */
+    State get_state(time_t t) const;
+    State get_state() const;
+
+    /**
+     * @brief returns the hard fork version for the given block height
+     *
+     * @param height height of the block to check
+     */
+    uint8_t get(uint64_t height) const;
+
+    /**
+     * @brief returns the latest "ideal" version
+     *
+     * This is the latest version that's been scheduled
+     */
+    uint8_t get_ideal_version() const;
+
+    /**
+     * @brief returns the "ideal" version for a given height
+     *
+     * @param height height of the block to check
+     */
+    uint8_t get_ideal_version(uint64_t height) const;
+
+    /**
+     * @brief returns the next version
+     *
+     * This is the version which will we fork to next
+     */
+    uint8_t get_next_version() const;
+
+    /**
+     * @brief returns the current version
+     *
+     * This is the latest version that's past its trigger date and had enough votes
+     * at one point in the past.
+     */
+    uint8_t get_current_version() const;
+
+    /**
+     * @brief returns the earliest block a given version may activate
+     */
+    uint64_t get_earliest_ideal_height_for_version(uint8_t version) const;
+
+    /**
+     * @brief returns information about current voting state
+     *
+     * returns true if the given version is enabled (ie, the current version
+     * is at least the passed version), false otherwise
+     *
+     * @param version the version to check voting for
+     * @param window the number of blocks considered in voting
+     * @param votes number of votes for next version
+     * @param threshold number of votes needed to switch to next version
+     * @param earliest_height earliest height at which the version can take effect
+     */
+    bool get_voting_info(uint8_t version, uint32_t &window, uint32_t &votes, uint32_t &threshold, uint64_t &earliest_height, uint8_t &voting) const;
+
+    /**
+     * @brief returns the size of the voting window in blocks
+     */
+    uint64_t get_window_size() const { return window_size; }
+
+  private:
+
+    uint8_t get_block_version(uint64_t height) const;
+    bool do_check(uint8_t block_version, uint8_t voting_version) const;
+    bool do_check_for_height(uint8_t block_version, uint8_t voting_version, uint64_t height) const;
+    int get_voted_fork_index(uint64_t height) const;
+    uint8_t get_effective_version(uint8_t voting_version) const;
+    bool add(uint8_t block_version, uint8_t voting_version, uint64_t height);
+
+    bool rescan_from_block_height(uint64_t height);
+    bool rescan_from_chain_height(uint64_t height);
+
+  private:
+
+    BlockchainDB &db;
+
+    time_t forked_time;
+    time_t update_time;
+    uint64_t window_size;
+    uint8_t default_threshold_percent;
+
+    uint8_t original_version;
+    uint64_t original_version_till_height;
+
+    struct Params {
+      uint8_t version;
+      uint8_t threshold;
+      uint64_t height;
+      time_t time;
+      Params(uint8_t version, uint64_t height, uint8_t threshold, time_t time): version(version), threshold(threshold), height(height), time(time) {}
+    };
+    std::vector<Params> heights;
+
+    std::deque<uint8_t> versions; /* rolling window of the last N blocks' versions */
+    unsigned int last_versions[256]; /* count of the block versions in the last N blocks */
+    uint32_t current_fork_index;
+
+    mutable epee::critical_section lock;
+  };
+
+}  // namespace cryptonote
+