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authorTiger Wang <ziwei.tiger@outlook.com>2020-09-08 10:46:16 +0200
committerTiger Wang <ziwei.tiger@outlook.com>2020-12-21 01:11:34 +0100
commit742e27ad2f037205285e475be487ec9ed874ca91 (patch)
tree3218d3c2791e823c88a294ba7fdb10035c8fbb9b /src/Bindings/BlockState.h
parentEnable LOS checks for Hostile Mobs. (diff)
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diff --git a/src/Bindings/BlockState.h b/src/Bindings/BlockState.h
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+#pragma once
+
+#include <initializer_list>
+
+
+
+
+
+/** Represents the state of a single block (previously known as "block meta").
+The state consists of a map of string -> string, plus a mechanism for fast equality checks between two BlockState instances.
+Once a BlockState instance is created, it is then immutable - there's no way of changing it, only by creating a (modified) copy.
+A BlockState instance can be created from hard-coded data or from dynamic data:
+ BlockState bs({{"key1", "value1"}, {key2", "value2"}}); // Hard-coded
+ - or -
+ std::map<AString, AString> map({{"key1", "value1"}, {key2", "value2"}});
+ map["key3"] = "value3";
+ BlockState bs(map); // From dynamic data
+*/
+class BlockState
+{
+public:
+
+ /** Creates a new instance with an empty map. */
+ BlockState();
+
+ /** Creates a new instance consisting of a single key-value pair.
+ If the value is empty, it is not stored wihin the map. */
+ BlockState(const AString & aKey, const AString & aValue);
+
+ /** Creates a new instance initialized with several (hard-coded) key-value pairs.
+ Any key with an empty value is not stored within the map. */
+ BlockState(std::initializer_list<std::pair<const AString, AString>> aKeysAndValues);
+
+ /** Creates a new instance initialized with several (dynamic) key-value pairs.
+ Makes a copy of aKeysAndValues for this object.
+ Any key with an empty value is not stored within the map. */
+ BlockState(const std::map<AString, AString> & aKeysAndValues);
+
+ /** Creates a new instance initialized with several (dynamic) key-value pairs.
+ Any key with an empty value is not stored within the map. */
+ BlockState(std::map<AString, AString> && aKeysAndValues);
+
+ /** Creates a copy of the specified BlockState with the (hard-coded) additional keys and values added to it.
+ Any key in aAdditionalKeysAndValues that is already present in aCopyFrom is overwritten with the aAdditionalKeysAndValues' one.
+ Any key with an empty value is not stored in the map.
+ (it's possible to erase a key from aCopyFrom by setting it to empty string in aAdditionalKeysAndValues). */
+ BlockState(const BlockState & aCopyFrom, std::initializer_list<std::pair<const AString, AString>> aAdditionalKeysAndValues);
+
+ /** Creates a copy of the specified BlockState with the (dynamic) additional keys and values added to it.
+ Any key in aAdditionalKeysAndValues that is already present in aCopyFrom is overwritten with the aAdditionalKeysAndValues' one.
+ Any key with an empty value is not stored in the map.
+ (it's possible to erase a key from aCopyFrom by setting it to empty string in aAdditionalKeysAndValues). */
+ BlockState(const BlockState & aCopyFrom, const std::map<AString, AString> & aAdditionalKeysAndValues);
+
+ /** Less-than comparison. */
+ bool operator <(const BlockState & aOther) const;
+
+ /** Fast equality check. */
+ bool operator ==(const BlockState & aOther) const;
+
+ /** Fast inequality check. */
+ bool operator !=(const BlockState & aOther) const
+ {
+ return !(operator ==(aOther));
+ }
+
+ /** Returns the value at the specified key.
+ If the key is not present, returns an empty string. */
+ const AString & value(const AString & aKey) const;
+
+
+protected:
+
+ /** The state, represented as a string->string map. */
+ std::map<AString, AString> mState;
+
+ /** The checksum used for the fast equality check.
+ This is calculated upon creation. */
+ UInt32 mChecksum;
+
+
+ /** Normalizes mState and calculates the checksum from it.
+ Removes all the empty values from mState.
+ Used only from constructors. */
+ UInt32 initializeChecksum();
+
+ /** Removes all the keys from mState that have an empty value. */
+ void removeEmptyKeys();
+
+ /** Calculates the partial checksum of a single string.
+ Used from within initializeChecksum(). */
+ UInt32 partialChecksum(const AString & aString);
+};