Add an abstraction for hooking v1 and v2 commands

This is a step towards making command hooks work in OE, once OE is
supported.

Not the most ideal or efficient thing in the world, but it works okay
until we come up with something better, I suppose. Not a fan of the argv
copying but avoiding that would make the API a lot less ergonomic.

Not the easiest problem to solve, really...

1 files changed, 60 insertions, 0 deletions

diff --git a/src/con_.h b/src/con_.h
index c2c0cce..b67483a 100644
--- a/src/con_.h
+++ b/src/con_.h
@@ -361,6 +361,66 @@ extern struct _con_vtab_iconvar_wrap {
 #define DEF_CCMD_PLUSMINUS_UNREG DEF_CCMD_PLUSMINUS
 
 /*
+ * Defines a hook function in-place to hook a command callback, factoring in
+ * different callback ABIs used by different commands and/or different engine
+ * branches. Defines a hook_##name##_cb function to install the hook and an
+ * unhook_##name##_cb function to remove it.
+ *
+ * The hook function has the implicit arguments argc and argv, just like a
+ * command handler defined with DEF_CCMD_HERE. Calling the original command
+ * handler can be done using orig_##name##_cb, passing through argc and argv.
+ *
+ * Note that argc and argv MUST remain unmodified, as not all callback
+ * interfaces pass arguments through the callback and so attempting to change
+ * these parameters could cause unexpected or inconsistent behaviour across
+ * engine versions.
+ *
+ * In some cases, a command will be defined to take no arguments, in which case
+ * argc will be zero and argv will be null. In these cases, the parameters
+ * should still be passed through to the orig_ function, as this ensures
+ * compatibility with other game/engine versions.
+ */
+#define DEF_CCMD_COMPAT_HOOK(name) \
+	static union { \
+		con_cmdcbv1 v1; \
+		con_cmdcbv2 v2; \
+	} _orig_##name##_cb; \
+	static void _orig_##name##_cbv1(int argc, const char *const *argv) { \
+		_orig_##name##_cb.v1(); \
+	} \
+	static void _orig_##name##_cbv2(int argc, const char *const *argv) { \
+		struct con_cmdargs args; \
+		args.argc = argc; \
+		/* XXX: having to copy argv sucks, but can't see how to avoid without
+		   ruining the interface? */ \
+		for (int i = 0; i < argc; ++i) args.argv[i] = argv[i]; \
+		_orig_##name##_cb.v2(&args); \
+	} \
+	static void (*orig_##name##_cb)(int argc, const char *const *argv); \
+	static void _hook_##name##_cb(int argc, const char *const *argv); \
+	static void _hook_##name##_cbv1() { \
+		_hook_##name##_cb(0, 0); /* XXX: ??? */ \
+	} \
+	static void _hook_##name##_cbv2(const struct con_cmdargs *args) { \
+		_hook_##name##_cb(args->argc, args->argv); \
+	} \
+	static void hook_##name##_cb(struct con_cmd *cmd) { \
+		_orig_##name##_cb.v1 = cmd->cb_v1; \
+		if (cmd->use_newcb) { \
+			cmd->cb_v2 = &_hook_##name##_cbv2; \
+			orig_##name##_cb = &_orig_##name##_cbv2; \
+		} \
+		else { \
+			cmd->cb_v1 = _hook_##name##_cbv1; \
+			orig_##name##_cb = &_orig_##name##_cbv1; \
+		} \
+	} \
+	static void unhook_##name##_cb(struct con_cmd *cmd) { \
+		cmd->cb_v1 = _orig_##name##_cb.v1; \
+	} \
+	static void _hook_##name##_cb(int argc, const char *const *argv) /* ... */
+
+/*
  * These functions register a command or variable, respectively, defined with
  * the _UNREG variants of the above macros. These can be used to conditionally
  * register things. Wherever possible, it is advised to use the DEF_FEAT_*