Add display of sample rate

src/widget-sample-rate.c

@@ -0,0 +1,123 @@
+// SPDX-FileCopyrightText: 2024 Geoffrey D. Bennett <g@b4.vu>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "gtkhelper.h"
+#include "widget-boolean.h"
+
+struct sample_rate {
+  struct alsa_card *card;
+  GtkWidget        *button;
+  guint             source;
+  char             *path;
+  int               sample_rate;
+};
+
+static void button_set_text(GtkWidget *button, int value) {
+  gtk_widget_remove_css_classes_by_prefix(button, "sample-rate-");
+
+  if (!value) {
+    gtk_button_set_label(GTK_BUTTON(button), "N/A");
+    return;
+  }
+
+  char *text;
+  if (value % 1000 == 0)
+    text = g_strdup_printf("%dkHz", value / 1000);
+  else
+    text = g_strdup_printf("%.1fkHz", value / 1000.0);
+  gtk_button_set_label(GTK_BUTTON(button), text);
+  g_free(text);
+
+  char *css_class = g_strdup_printf(
+    "sample-rate-%d", value
+  );
+  gtk_widget_add_css_class(button, css_class);
+  g_free(css_class);
+}
+
+// Read the sample rate from /proc/asound/cardN/stream0
+// and return it as an integer
+//
+// Looking for a line containing:
+//   Momentary freq = 48000 Hz (0x6.0000)
+static int get_sample_rate(struct sample_rate *data) {
+  if (!data->path)
+    return 0;
+
+  FILE *file = fopen(data->path, "r");
+  if (!file) {
+    perror("fopen");
+    return 0;
+  }
+
+  char *line = NULL;
+  size_t len = 0;
+  ssize_t read;
+
+  int sample_rate = 0;
+
+  while ((read = getline(&line, &len, file)) != -1) {
+    if (strstr(line, "Momentary freq = ")) {
+      char *start = strstr(line, "Momentary freq = ") + 17;
+      char *end = strstr(start, " Hz");
+
+      if (!start || !end)
+        continue;
+
+      *end = '\0';
+      sample_rate = atoi(start);
+
+      break;
+    }
+  }
+
+  free(line);
+  fclose(file);
+
+  return sample_rate;
+}
+
+static gboolean update_sample_rate(struct sample_rate *data) {
+  int sample_rate = get_sample_rate(data);
+
+  if (sample_rate != data->sample_rate) {
+    data->sample_rate = sample_rate;
+    button_set_text(data->button, sample_rate);
+  }
+
+  return G_SOURCE_CONTINUE;
+}
+
+static void on_destroy(struct sample_rate *data, GObject *widget) {
+  if (data->source)
+    g_source_remove(data->source);
+  g_free(data->path);
+  g_free(data);
+}
+
+GtkWidget *make_sample_rate_widget(
+  struct alsa_card *card
+) {
+  struct sample_rate *data = g_malloc0(sizeof(struct sample_rate));
+  data->card = card;
+  data->button = gtk_toggle_button_new();
+  data->sample_rate = -1;
+
+  gtk_widget_add_css_class(data->button, "fixed");
+  gtk_widget_add_css_class(data->button, "sample-rate");
+
+  // can only update if it's a real card
+  if (card->num != SIMULATED_CARD_NUM) {
+    data->path = g_strdup_printf("/proc/asound/card%d/stream0", card->num);
+    data->source =
+      g_timeout_add_seconds(1, (GSourceFunc)update_sample_rate, data);
+  }
+
+  // initial update (will show "N/A" for simulated card)
+  update_sample_rate(data);
+
+  // cleanup when the button is destroyed
+  g_object_weak_ref(G_OBJECT(data->button), (GWeakNotify)on_destroy, data);
+
+  return data->button;
+}