vim-patch:9.1.1109: cmdexpand.c hard to read (neovim#32437)

Problem:  cmdexpand.c hard to read
Solution: refactor the file slightly (glepnir)

closes: vim/vim#16621

vim/vim@977561a

Co-authored-by: glepnir <[email protected]>

Author: zeertzjq

src/nvim/cmdexpand.c

@@ -645,74 +645,78 @@ static void redraw_wildmenu(expand_T *xp, int num_matches, char **matches, int m
 /// in "xp->xp_selected"
 static char *get_next_or_prev_match(int mode, expand_T *xp)
 {
+  // When no files found, return NULL
   if (xp->xp_numfiles <= 0) {
     return NULL;
   }
 
   int findex = xp->xp_selected;
 
   if (mode == WILD_PREV) {
+    // Select last file if at start
     if (findex == -1) {
       findex = xp->xp_numfiles;
     }
     findex--;
   } else if (mode == WILD_NEXT) {
-    findex++;
-  } else if (mode == WILD_PAGEUP) {
-    if (findex == 0) {
-      // at the first entry, don't select any entries
-      findex = -1;
-    } else if (findex == -1) {
-      // no entry is selected. select the last entry
-      findex = xp->xp_numfiles - 1;
-    } else {
-      // go up by the pum height
-      int ht = pum_get_height();
-      if (ht > 3) {
-        ht -= 2;
-      }
-      findex -= ht;
-      findex = MAX(findex, 0);  // few entries left, select the first entry
-    }
-  } else if (mode == WILD_PAGEDOWN) {
-    if (findex == xp->xp_numfiles - 1) {
-      // at the last entry, don't select any entries
-      findex = -1;
-    } else if (findex == -1) {
-      // no entry is selected. select the first entry
-      findex = 0;
-    } else {
-      // go down by the pum height
-      int ht = pum_get_height();
-      if (ht > 3) {
-        ht -= 2;
-      }
-      findex += ht;
-      if (findex >= xp->xp_numfiles) {
-        // few entries left, select the last entry
+    // Select next file
+    findex = findex + 1;
+  } else if (mode == WILD_PAGEUP || mode == WILD_PAGEDOWN) {
+    // Get the height of popup menu (used for both PAGEUP and PAGEDOWN)
+    int ht = pum_get_height();
+    if (ht > 3) {
+      ht -= 2;
+    }
+
+    if (mode == WILD_PAGEUP) {
+      if (findex == 0) {
+        // at the first entry, don't select any entries
+        findex = -1;
+      } else if (findex == -1) {
+        // no entry is selected. select the last entry
         findex = xp->xp_numfiles - 1;
+      } else {
+        // go up by the pum height
+        findex = MAX(findex - ht, 0);
+      }
+    } else {  // mode == WILD_PAGEDOWN
+      if (findex < 0) {
+        // no entry is selected. select the first entry
+        findex = 0;
+      } else if (findex == xp->xp_numfiles - 1) {
+        // at the last entry, don't select any entries
+        findex = -1;
+      } else {
+        // go down by the pum height
+        findex = MIN(findex + ht, xp->xp_numfiles - 1);
       }
     }
   } else {  // mode == WILD_PUM_WANT
     assert(pum_want.active);
     findex = pum_want.item;
   }
 
-  // When wrapping around, return the original string, set findex to -1.
-  if (findex < 0) {
-    findex = xp->xp_orig == NULL ? xp->xp_numfiles - 1 : -1;
-  }
-  if (findex >= xp->xp_numfiles) {
-    findex = xp->xp_orig == NULL ? 0 : -1;
+  // Handle wrapping around
+  if (findex < 0 || findex >= xp->xp_numfiles) {
+    // If original string exists, return to it when wrapping around
+    if (xp->xp_orig != NULL) {
+      findex = -1;
+    } else {
+      // Wrap around to opposite end
+      findex = (findex < 0) ? xp->xp_numfiles - 1 : 0;
+    }
   }
+
+  // Display matches on screen
   if (compl_match_array) {
     compl_selected = findex;
     cmdline_pum_display(false);
   } else if (p_wmnu) {
     redraw_wildmenu(xp, xp->xp_numfiles, xp->xp_files, findex, cmd_showtail);
   }
-  xp->xp_selected = findex;
 
+  xp->xp_selected = findex;
+  // Return the original string or the selected match
   return xstrdup(findex == -1 ? xp->xp_orig : xp->xp_files[findex]);
 }