Abstract binding configuration to bindings.[ch]

Create files bindings.[ch] to contain functions for configuring,
finding, and running bindings.

Use the new function `configure_binding` for binding configuration. This
function adds a binding from config parameters.

Export the function `modifiers_from_str` from config_directives.h.

This change is made in preparation for the new bindmouse functionality.

src/bindings.c

@@ -0,0 +1,71 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ * © 2009-2014 Michael Stapelberg and contributors (see also: LICENSE)
+ *
+ * bindings.c: Functions for configuring, finding and, running bindings.
+ */
+#include "all.h"
+
+/*
+ * The name of the default mode.
+ *
+ */
+const char *DEFAULT_BINDING_MODE = "default";
+
+/*
+ * Returns the mode specified by `name` or creates a new mode and adds it to
+ * the list of modes.
+ *
+ */
+static struct Mode *mode_from_name(const char *name) {
+    struct Mode *mode;
+
+    /* Try to find the mode in the list of modes and return it */
+    SLIST_FOREACH(mode, &modes, modes) {
+        if (strcmp(mode->name, name) == 0)
+            return mode;
+    }
+
+    /* If the mode was not found, create a new one */
+    mode = scalloc(sizeof(struct Mode));
+    mode->name = sstrdup(name);
+    mode->bindings = scalloc(sizeof(struct bindings_head));
+    TAILQ_INIT(mode->bindings);
+    SLIST_INSERT_HEAD(&modes, mode, modes);
+
+    return mode;
+}
+
+/*
+ * Adds a binding from config parameters given as strings and returns a
+ * pointer to the binding structure. Returns NULL if the input code could not
+ * be parsed.
+ *
+ */
+Binding *configure_binding(const char *bindtype, const char *modifiers, const char *input_code,
+        const char *release, const char *command, const char *modename) {
+    Binding *new_binding = scalloc(sizeof(Binding));
+    DLOG("bindtype %s, modifiers %s, input code %s, release %s\n", bindtype, modifiers, input_code, release);
+    new_binding->release = (release != NULL ? B_UPON_KEYRELEASE : B_UPON_KEYPRESS);
+    if (strcmp(bindtype, "bindsym") == 0) {
+        new_binding->symbol = sstrdup(input_code);
+    } else {
+        // TODO: strtol with proper error handling
+        new_binding->keycode = atoi(input_code);
+        if (new_binding->keycode == 0) {
+            ELOG("Could not parse \"%s\" as an input code, ignoring this binding.\n", input_code);
+            FREE(new_binding);
+            return NULL;
+        }
+    }
+    new_binding->mods = modifiers_from_str(modifiers);
+    new_binding->command = sstrdup(command);
+    new_binding->input_type = B_KEYBOARD;
+
+    struct Mode *mode = mode_from_name(modename);
+    TAILQ_INSERT_TAIL(mode->bindings, new_binding, bindings);
+
+    return new_binding;
+}