Implement playlist shuffle.

    - Triggered by `script-message jftui-playlist-shuffle`.
    - Does not touch currently playing item.
    - Starts addressing #17.

src/disk.c

@@ -179,6 +179,7 @@ void jf_disk_refresh()
 }
 
 
+////////// PAYLOAD ///////////
 void jf_disk_payload_add_item(const jf_menu_item *item)
 {
     if (item == NULL) return;
@@ -192,25 +193,6 @@ jf_menu_item *jf_disk_payload_get_item(const size_t n)
 }
 
 
-const char *jf_disk_playlist_get_item_name(const size_t n)
-{
-
-    if (n == 0 || n > s_playlist.count) {
-        return "Warning: requesting item out of bounds. This is a bug.";
-    }
-
-    jf_disk_align_to(&s_playlist, n);
-    assert(fseek(s_playlist.body,
-                // let him who hath understanding reckon the number of the beast!
-                sizeof(jf_item_type) + sizeof(((jf_menu_item *)666)->id),
-                SEEK_CUR) == 0);
-
-    jf_disk_read_to_null_to_buffer(&s_playlist);
-
-    return (const char *)s_buffer->buf;
-}
-
-
 jf_item_type jf_disk_payload_get_type(const size_t n)
 {
     jf_item_type item_type;
@@ -232,8 +214,10 @@ size_t jf_disk_payload_item_count()
 {
     return s_payload.count;
 }
+//////////////////////////////
 
 
+////////// PLAYLIST ///////////
 void jf_disk_playlist_add_item(const jf_menu_item *item)
 {
     if (item == NULL || JF_ITEM_TYPE_IS_FOLDER(item->type)) return;
@@ -247,6 +231,47 @@ jf_menu_item *jf_disk_playlist_get_item(const size_t n)
 }
 
 
+const char *jf_disk_playlist_get_item_name(const size_t n)
+{
+
+    if (n == 0 || n > s_playlist.count) {
+        return "Warning: requesting item out of bounds. This is a bug.";
+    }
+
+    jf_disk_align_to(&s_playlist, n);
+    assert(fseek(s_playlist.body,
+        // let him who hath understanding reckon the number of the beast!
+        sizeof(jf_item_type) + sizeof(((jf_menu_item *)666)->id),
+        SEEK_CUR) == 0);
+
+    jf_disk_read_to_null_to_buffer(&s_playlist);
+
+    return (const char *)s_buffer->buf;
+}
+
+
+void jf_disk_playlist_swap_items(const size_t a, const size_t b)
+{
+    long old_a_value;
+    long old_b_value;
+
+    if (a > s_playlist.count || b > s_playlist.count || a == b) return;
+
+    // read offset a
+    assert(fseek(s_playlist.header, (long)((a - 1) * sizeof(long)), SEEK_SET) == 0);
+    assert(fread(&old_a_value, sizeof(long), 1, s_playlist.header) == 1);
+    // read offset b
+    assert(fseek(s_playlist.header, (long)((b - 1) * sizeof(long)), SEEK_SET) == 0);
+    assert(fread(&old_b_value, sizeof(long), 1, s_playlist.header) == 1);
+    // overwrite b
+    assert(fseek(s_playlist.header, (long)((b - 1) * sizeof(long)), SEEK_SET) == 0);
+    assert(fwrite(&old_a_value, sizeof(long), 1, s_playlist.header) == 1);
+    // overwrite a
+    assert(fseek(s_playlist.header, (long)((a - 1) * sizeof(long)), SEEK_SET) == 0);
+    assert(fwrite(&old_b_value, sizeof(long), 1, s_playlist.header) == 1);
+}
+
+
 void jf_disk_playlist_replace_item(const size_t n, const jf_menu_item *item)
 {
     long starting_body_offset;
@@ -268,3 +293,4 @@ size_t jf_disk_playlist_item_count()
 {
     return s_playlist.count;
 }
+///////////////////////////////

src/disk.h

@@ -36,6 +36,7 @@ size_t jf_disk_payload_item_count(void);
 
 void jf_disk_playlist_add_item(const jf_menu_item *item);
 void jf_disk_playlist_replace_item(const size_t n, const jf_menu_item *item);
+void jf_disk_playlist_swap_items(const size_t a, const size_t b);
 jf_menu_item *jf_disk_playlist_get_item(const size_t n);
 const char *jf_disk_playlist_get_item_name(const size_t n);
 size_t jf_disk_playlist_item_count(void);

src/main.c

@@ -15,6 +15,7 @@
 #include <errno.h>
 #include <locale.h>
 #include <assert.h>
+#include <time.h>
 #include <mpv/client.h>
 #include <yajl/yajl_version.h>
 
@@ -97,6 +98,9 @@ static inline void jf_mpv_event_dispatch(const mpv_event *event)
                     jf_term_clear_bottom(NULL);
                     jf_playback_print_playlist(0);
                     JF_MPV_ASSERT(mpv_set_property(g_mpv_ctx, "terminal", MPV_FORMAT_FLAG, &mpv_flag_yes));
+                } else if (strcmp(((mpv_event_client_message *)event->data)->args[0],
+                            "jftui-playlist-shuffle") == 0) {
+                    jf_playback_shuffle_playlist();
                 }
             }
             break;
@@ -272,6 +276,7 @@ int main(int argc, char *argv[])
     // SETUP GLOBAL STATE
     g_state = (jf_global_state){ 0 };
     assert((g_state.session_id = jf_generate_random_id(0)) != NULL);
+    srandom((unsigned)time(NULL));
     /////////////////////
 
 

src/playback.c

@@ -517,6 +517,23 @@ void jf_playback_end()
 }
 
 
+void jf_playback_shuffle_playlist()
+{
+    size_t pos = g_state.playlist_position - 1;
+    size_t item_count_no_curr = jf_disk_playlist_item_count() - 1;
+    size_t i;
+    size_t j;
+
+    for (i = 0; i < item_count_no_curr - 1; i++) {
+        if (i == pos) continue;
+        if ((j = (size_t)random() % (item_count_no_curr - i - 1) + i + 1) >= pos) {
+            j++;
+        }
+        jf_disk_playlist_swap_items(i + 1, j + 1);
+    }
+}
+
+
 static void jf_playback_playlist_window(size_t window_size, size_t window[2])
 {
     size_t pos = g_state.playlist_position;

src/playback.h

@@ -38,6 +38,8 @@ void jf_playback_play_video(const jf_menu_item *item);
 bool jf_playback_next(void);
 bool jf_playback_previous(void);
 void jf_playback_end(void);
+// won't move item currently playing
+void jf_playback_shuffle_playlist(void);
 
 // Will print part or the entirety of the current jftui playback playlist to
 // stdout.

src/shared.c

@@ -378,9 +378,8 @@ char *jf_generate_random_id(size_t len)
 
     assert((rand_id = malloc(len + 1)) != NULL);
     rand_id[len] = '\0';
-    srand((unsigned int)time(NULL));
     for (; len > 0; len--) {
-        rand_id[len - 1] = '0' + rand() % 10;
+        rand_id[len - 1] = '0' + random() % 10;
     }
     return rand_id;
 }