New slash command parser

Source/Integration/SlashCommand.h

@@ -0,0 +1,121 @@
+////////////////////////////////////////////////////////////
+//
+// SlashCommand.h
+//
+// A command line plus a cursor, exposed to blueprint.
+//
+////////////////////////////////////////////////////////////
+
+#pragma once
+
+#include "Containers/Array.h"
+#include "Containers/Set.h"
+#include "Containers/UnrealString.h"
+#include "Containers/StringFwd.h"
+#include "Common.h"
+#include "SlashCommand.generated.h"
+
+////////////////////////////////////////////////////////////
+//
+// UlxSlashCommand
+//
+// Holds a command line (a string the user has typed) together
+// with a cursor marking the current position within it.  This
+// is the object that wraps Unreal's FParse facilities so that
+// blueprint can parse a typed command piece by piece, with the
+// cursor advancing as each token is consumed.
+//
+////////////////////////////////////////////////////////////
+
+UCLASS(BlueprintType)
+class UlxSlashCommand : public UObject
+{
+	GENERATED_BODY()
+
+private:
+	// The full command line that we are parsing.
+	//
+	FString CommandLine;
+
+	// The current parse position: an index into CommandLine.
+	//
+	int32 Cursor = 0;
+
+	// Known command names that have been registered while exploring
+	// possible parses for this line.
+	//
+	TSet<FString> KnownCommands;
+
+	// Prototypes whose command name matches this line.
+	//
+	TArray<FString> MatchingPrototypes;
+
+	// Skip leading whitespace at the cursor, then read characters up
+	// to (but not including) the next whitespace.  The token is
+	// returned as a view into CommandLine, and the cursor is advanced
+	// past it.
+	//
+	// Returns an empty view if there is no nonwhitespace input left.
+	//
+	FStringView FetchToken();
+
+public:
+	// Construct a slash command from a command line string.
+	// The cursor starts at the beginning.
+	//
+	UFUNCTION(BlueprintCallable)
+	static UlxSlashCommand* MakeSlashCommand(const FString& CommandLine);
+
+	// Return true if the string is a slash followed by one or more
+	// alphanumeric characters, and nothing else (e.g. "/foo").
+	//
+	static bool IsSlashCommand(const FString& Command);
+
+	// Reset the cursor to the start, then read the first token and
+	// check whether it matches the given literal, case-insensitively.
+	// The command name is recorded in KnownCommands either way.  If it
+	// matched, the prototype is added to MatchingPrototypes.  The token
+	// is consumed either way.  Returns Success if it matched, Error
+	// otherwise.
+	//
+	UFUNCTION(BlueprintCallable, meta = (ExpandEnumAsExecs = "ReturnValue"))
+	ElxSuccessOrError CheckCommand(const FString& Literal, const FString& Prototype);
+
+	// Read the next whitespace-delimited word from the command line.
+	//
+	// This is the blueprint-callable form of FetchToken: it returns
+	// the token as an FString.  Returns Error (with an empty Result)
+	// if there is no nonwhitespace input left, Success otherwise.
+	//
+	UFUNCTION(BlueprintCallable, meta = (ExpandEnumAsExecs = "ReturnValue"))
+	ElxSuccessOrError ReadToken(FString& Result);
+
+	// Read the next token and interpret it as an integer, using C++
+	// number syntax (optional sign; decimal, 0x hex, or leading-0
+	// octal).  The whole token must be valid; "12abc" is rejected.
+	// Returns Error (with Result 0) on failure, Success otherwise.
+	//
+	UFUNCTION(BlueprintCallable, meta = (ExpandEnumAsExecs = "ReturnValue"))
+	ElxSuccessOrError ReadInteger(int32& Result);
+
+	// Read the next token and interpret it as a floating-point number,
+	// using C++ number syntax (optional sign, digits, dot, e/E
+	// exponent, trailing f).  The whole token must be valid; "12abc"
+	// is rejected.  Returns Error (with Result 0) on failure, Success
+	// otherwise.
+	//
+	UFUNCTION(BlueprintCallable, meta = (ExpandEnumAsExecs = "ReturnValue"))
+	ElxSuccessOrError ReadFloat(double& Result);
+
+	// Read the rest of the command line, from the cursor to the end,
+	// trimmed of leading and trailing whitespace.  The cursor is
+	// advanced to the end.  Always returns Success.
+	//
+	UFUNCTION(BlueprintCallable, meta = (ExpandEnumAsExecs = "ReturnValue"))
+	ElxSuccessOrError ReadRest(FString& Result);
+
+	// Return a user-facing error message describing why parsing failed.
+	//
+	UFUNCTION(BlueprintCallable)
+	FString GetErrorMessage() const;
+};