block-parser: Add support for custom block functions

Similar to replace-table custom functions, this brings an ability
to register custom block functions that can be called from templates
with variable arguments.

The syntax is as follows:

<!-- $(if (function_name(arg1, "arg2", 'arg3'))) -->
...
<!-- $(endif (function_name(arg1, "arg2", 'arg3'))) -->

An optional exclamation mark before the function name reverts the result
(negates) the predicate.

This allows template flexibility with respect to the currently processed image.

1 files changed, 56 insertions, 27 deletions

diff --git a/src/replace-table.c b/src/replace-table.c
index 3398bae..9c1b254 100644
--- a/src/replace-table.c
+++ b/src/replace-table.c
@@ -209,38 +209,64 @@ parse_function_args (const char *str, GPtrArray *a)
     add_arg (a, str_start, str + i - str_start);
 }
 
-static gboolean
-parse_registered_function (const char *token, gchar **out_fname, gchar ***args)
+/*
+ *   parse_function: returns name of the function or NULL if token is invalid. Parsed arguments are stored in *args.
+ *                   - in case an exclamation mark is present before the function name, the *negation argument is set to TRUE
+ *
+ */
+gchar *
+parse_function (const char *token, gchar ***args, gboolean *negation)
 {
   char *opening_p, *closing_p;
   GPtrArray *a;
+  gchar *tok;
   gchar *s;
+  gchar *fname;
 
-  g_return_val_if_fail (token != NULL, FALSE);
-  g_return_val_if_fail (out_fname != NULL, FALSE);
+  if (args)
+    *args = NULL;
+  if (negation)
+    *negation = FALSE;
 
-  opening_p = strchr (token, '(');
-  closing_p = strchr (token, ')');
+  g_return_val_if_fail (token != NULL, NULL);
+
+  tok = g_strdup (token);
+  g_strstrip (tok);
+  opening_p = strchr (tok, '(');
+  closing_p = strrchr (tok, ')');
 
   /*  every function call should contain an opening and closing parenthesis  */
-  if (opening_p == NULL || closing_p == NULL || closing_p <= opening_p)
-    return FALSE;
+  if (opening_p == NULL || closing_p == NULL || closing_p <= opening_p) {
+    g_free (tok);
+    return NULL;
+  }
+
+  /*  find a possible exclamation mark  */
+  if (*tok == '!') {
+    if (negation)
+      *negation = TRUE;
+    *tok = ' ';
+  }
 
   /*  find function name  */
-  s = g_strndup (token, opening_p - token);
-  *out_fname = g_strdup (g_strstrip (s));
+  s = g_strndup (tok, opening_p - tok);
+  fname = g_strdup (g_strstrip (s));
   g_free (s);
 
   /*  parse arguments  */
-  a = g_ptr_array_new ();
-  s = g_strndup (opening_p + 1, closing_p - opening_p - 1);
-  parse_function_args (s, a);
-  g_free (s);
+  if (args) {
+    a = g_ptr_array_new ();
+    s = g_strndup (opening_p + 1, closing_p - opening_p - 1);
+    parse_function_args (s, a);
+    g_free (s);
 
-  g_ptr_array_add (a, NULL);
-  *args = (gchar **) g_ptr_array_free (a, FALSE);
+    g_ptr_array_add (a, NULL);
+    *args = (gchar **) g_ptr_array_free (a, FALSE);
+  }
+
+  g_free (tok);
 
-  return TRUE;
+  return fname;
 }
 
 /*
@@ -289,15 +315,18 @@ replace_table_process (gchar **buffer, ReplaceTable *table)
     }
 
     /*  check registered functions  */
-    if (! replace_value && parse_registered_function (token, &s, &args)) {
-      func_data = g_hash_table_lookup (table->functions, s);
-      g_free (s);
-      if (func_data) {
-        replace_value = func_data->callback (args, func_data->user_data);
-        if (replace_value == NULL)
-          replace_value = g_strdup ("");
+    if (! replace_value) {
+      s = parse_function (token, &args, NULL);
+      if (s) {
+        func_data = g_hash_table_lookup (table->functions, s);
+        if (func_data) {
+          replace_value = func_data->callback (args, func_data->user_data);
+          if (replace_value == NULL)
+            replace_value = g_strdup ("");
+        }
+        g_strfreev (args);
+        g_free (s);
       }
-      g_strfreev (args);
     }
 
     /*  lookup in the replace table  */
@@ -437,12 +466,12 @@ extract_token_arg (const gchar *str)
   const gchar *start;
   const gchar *end;
 
-  start = strstr (str, "(");
+  start = strchr (str, '(');
   if (start == NULL)
     return NULL;
   start++;
 
-  end = strstr (str, ")");
+  end = strrchr (str, ')');
   if (end == NULL)
     return NULL;
   end++;