Codechange: Template DoCommand to automagically reflect the parameters of the command proc.

When finished, this will allow each command handler to take individually
different parameters, obliviating the need for bit-packing.

1 files changed, 71 insertions, 2 deletions

diff --git a/src/command_func.h b/src/command_func.h
index 2a6f0c68a..1c24221cd 100644
--- a/src/command_func.h
+++ b/src/command_func.h
@@ -13,6 +13,7 @@
 #include "command_type.h"
 #include "company_type.h"
 #include <vector>
+#include "tile_map.h"
 
 /**
  * Define a default return value for a failed command.
@@ -36,7 +37,6 @@ static const CommandCost CMD_ERROR = CommandCost(INVALID_STRING_ID);
 /** Storage buffer for serialized command data. */
 typedef std::vector<byte> CommandDataBuffer;
 
-CommandCost DoCommand(DoCommandFlag flags, Commands cmd, TileIndex tile, uint32 p1, uint32 p2, const std::string &text = {});
 
 bool DoCommandP(Commands cmd, StringID err_message, CommandCallback *callback, TileIndex tile, uint32 p1, uint32 p2, const std::string &text = {});
 bool DoCommandP(Commands cmd, StringID err_message, TileIndex tile, uint32 p1, uint32 p2, const std::string &text = {});
@@ -58,12 +58,18 @@ const char *GetCommandName(Commands cmd);
 Money GetAvailableMoneyForCommand();
 bool IsCommandAllowedWhilePaused(Commands cmd);
 
+template <Commands Tcmd>
+constexpr CommandFlags GetCommandFlags()
+{
+	return CommandTraits<Tcmd>::flags;
+}
+
 /**
  * Extracts the DC flags needed for DoCommand from the flags returned by GetCommandFlags
  * @param cmd_flags Flags from GetCommandFlags
  * @return flags for DoCommand
  */
-static inline DoCommandFlag CommandFlagsToDCFlags(CommandFlags cmd_flags)
+static constexpr inline DoCommandFlag CommandFlagsToDCFlags(CommandFlags cmd_flags)
 {
 	DoCommandFlag flags = DC_NONE;
 	if (cmd_flags & CMD_NO_WATER) flags |= DC_NO_WATER;
@@ -83,4 +89,67 @@ private:
 	static int _counter;
 };
 
+
+template<Commands TCmd, typename T> struct CommandHelper;
+
+class CommandHelperBase {
+protected:
+	static void InternalDoBefore(bool top_level, bool test);
+	static void InternalDoAfter(CommandCost &res, DoCommandFlag flags, bool top_level, bool test);
+};
+
+/**
+ * Templated wrapper that exposes the command parameter arguments
+ * for the various Command::Do/Post calls.
+ * @tparam Tcmd The command-id to execute.
+ * @tparam Targs The command parameter types.
+ */
+template <Commands Tcmd, typename... Targs>
+struct CommandHelper<Tcmd, CommandCost(*)(DoCommandFlag, Targs...)> : protected CommandHelperBase {
+public:
+	/**
+	 * This function executes a given command with the parameters from the #CommandProc parameter list.
+	 * Depending on the flags parameter it executes or tests a command.
+	 *
+	 * @note This function is to be called from the StateGameLoop or from within the execution of a Command.
+	 * This function must not be called from the context of a "player" (real person, AI, game script).
+	 * Use ::Post for commands directly triggered by "players".
+	 *
+	 * @param flags Flags for the command and how to execute the command
+	 * @param args Parameters for the command
+	 * @see CommandProc
+	 * @return the cost
+	 */
+	static CommandCost Do(DoCommandFlag flags, Targs... args)
+	{
+		if constexpr (std::is_same_v<TileIndex, std::tuple_element_t<0, std::tuple<Targs...>>>) {
+			/* Do not even think about executing out-of-bounds tile-commands. */
+			TileIndex tile = std::get<0>(std::make_tuple(args...));
+			if (tile != 0 && (tile >= MapSize() || (!IsValidTile(tile) && (flags & DC_ALL_TILES) == 0))) return CMD_ERROR;
+		}
+
+		RecursiveCommandCounter counter{};
+
+		/* Only execute the test call if it's toplevel, or we're not execing. */
+		if (counter.IsTopLevel() || !(flags & DC_EXEC)) {
+			InternalDoBefore(counter.IsTopLevel(), true);
+			CommandCost res = CommandTraits<Tcmd>::proc(flags & ~DC_EXEC, args...);
+			InternalDoAfter(res, flags, counter.IsTopLevel(), true); // Can modify res.
+
+			if (res.Failed() || !(flags & DC_EXEC)) return res;
+		}
+
+		/* Execute the command here. All cost-relevant functions set the expenses type
+		 * themselves to the cost object at some point. */
+		InternalDoBefore(counter.IsTopLevel(), false);
+		CommandCost res = CommandTraits<Tcmd>::proc(flags, args...);
+		InternalDoAfter(res, flags, counter.IsTopLevel(), false);
+
+		return res;
+	}
+};
+
+template <Commands Tcmd>
+using Command = CommandHelper<Tcmd, typename CommandTraits<Tcmd>::ProcType>;
+
 #endif /* COMMAND_FUNC_H */