From 02fbf1686565ace00df5af938d95fbe18783fc37 Mon Sep 17 00:00:00 2001
From: Mattes D <github@xoft.cz>
Date: Fri, 23 Aug 2019 16:17:05 +0200
Subject: Added BlockState implementation for 1.13 support.

---
 src/BlockState.h | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 src/BlockState.h

(limited to 'src/BlockState.h')

diff --git a/src/BlockState.h b/src/BlockState.h
new file mode 100644
index 000000000..3b0575f0e
--- /dev/null
+++ b/src/BlockState.h
@@ -0,0 +1,90 @@
+#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);
+
+	/** 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);
+};
-- 
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