adding history feature to manual (duplicates current entry on missing pages)

src/user/manual/manual.c

@@ -21,6 +21,8 @@
 
 struct file *cur_file = 0;
 
+char *name_backup = 0;
+
 uint32_t *line_offsets = 0;
 uint32_t n_lines;
 
@@ -122,6 +124,10 @@ void load_file(const char *name) {
     return;
   }
 
+  if (name_backup)
+    free_block(name_backup);
+  name_backup = strdup(name);
+
   if (cur_file)
     close_file(cur_file);
   cur_file = new_file;
@@ -182,6 +188,32 @@ void load_file(const char *name) {
   scroll_to(0);
 }
 
+struct stack_entry {
+  struct stack_entry *down;
+  char *name;
+  uint32_t line;
+};
+
+struct stack_entry *stack_top = 0;
+
+void push() {
+  struct stack_entry *new_entry = get_block(sizeof(struct stack_entry));
+  new_entry->down = stack_top;
+  new_entry->name = strdup(name_backup);
+  new_entry->line = line_on;
+  stack_top = new_entry;
+}
+
+void pop() {
+  if (stack_top) {
+    load_file(stack_top->name);
+    scroll_to(stack_top->line);
+    free_block(stack_top->name);
+    free_block(stack_top);
+    stack_top = stack_top->down;
+  }
+}
+
 void main() {
   _set_color(UI_COLOR);
   _print_at(24, 79, " ");
@@ -255,11 +287,14 @@ void main() {
     case ' ':
     case '\n':
     case _KEY_NENTER:
-      if (cur_link)
+      if (cur_link) {
+        push();
         load_file(cur_link->lto);
+      }
       break;
     case _KEY_ESC:
-      //TODO
+      if (stack_top)
+        pop();
       break;
     case 'q':
       return;