emergency-call-types: Allow to lookup emergency numbers by country code

We build a hash as cache to speed up lookups. As this is a one time
thing we just do it once and don't bother to free it up.

We currently assume that all numbers can be used for the location based
lookups. Should that change we want to add a flag indicating that.

src/calls-emergency-call-types.c

@@ -26,10 +26,12 @@ typedef struct {
 } CallsEmergencyNumber;
 
 typedef struct {
-  char *country_code;
-  CallsEmergencyNumber numbers[3];
+  char                 *country_code;
+  CallsEmergencyNumber  numbers[3];
 } CallsEmergencyNumberTypes;
 
+GHashTable *by_mcc;
+
 CallsEmergencyNumberTypes emergency_number_types[] = {
   { "CH",
     {
@@ -55,6 +57,22 @@ CallsEmergencyNumberTypes emergency_number_types[] = {
 };
 
 
+static void
+init_hash (void)
+{
+  if (g_once_init_enter (&by_mcc)) {
+    GHashTable *table = g_hash_table_new (g_str_hash, g_str_equal);
+
+    for (int i = 0; i < G_N_ELEMENTS (emergency_number_types); i++) {
+      CallsEmergencyNumberTypes *numbers = &emergency_number_types[i];
+
+      g_hash_table_insert (table, numbers->country_code, numbers);
+    }
+    g_once_init_leave (&by_mcc, table);
+  }
+}
+
+
 static char *
 flags_to_string (CallsEmergencyCallTypeFlags flags)
 {
@@ -105,3 +123,36 @@ calls_emergency_call_type_get_name (const char *lookup, const char *country_code
 
   return NULL;
 }
+
+/**
+ * calls_emergency_call_types_get_numbers_by_country_code:
+ * @mcc: The country code
+ *
+ * Get the valid emergency numbers for this country code
+ *
+ * Returns:(transfer full): A string array of emergency numbers
+ */
+GStrv
+calls_emergency_call_types_get_numbers_by_country_code (const char *country_code)
+{
+  g_autoptr (GPtrArray) ret = g_ptr_array_new_with_free_func (g_free);
+  CallsEmergencyNumberTypes *match;
+
+ if (country_code == NULL)
+    return NULL;
+
+  init_hash ();
+
+  match = g_hash_table_lookup (by_mcc, country_code);
+  if (!match)
+    return NULL;
+
+  /* Can use g_strv_builder with glib > 2.68 */
+  for (int i = 0; i < G_N_ELEMENTS (match->numbers); i++) {
+    char *number = g_strdup (match->numbers[i].number);
+    g_ptr_array_add (ret, number);
+  }
+  g_ptr_array_add (ret, NULL);
+
+  return (GStrv) g_ptr_array_steal (ret, NULL);
+}

src/calls-emergency-call-types.h

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
+#include <glib.h>
+
 # pragma once
 
 typedef enum {
@@ -22,3 +24,4 @@ typedef enum {
 } CallsEmergencyCallTypeFlags;
 
 char *calls_emergency_call_type_get_name (const char *number, const char *country_code);
+GStrv calls_emergency_call_types_get_numbers_by_country_code (const char *country_code);