(internal): simplify db update operations (#1212)

Instead of maintaining a file queue to process for updating the Org-roam
database, we instead simply call `org-roam-db-build-cache` to rebuild
the db. `org-roam-db-build-cache` feels Fast Enough(TM), and basically
runs instantly if no files are modified. This greatly simplifies the
code, basically allowing to maintaining a single code path for db
operations.

This PR should also address the slowness wrt to ID links. Org-roam now
builds the headline information first, so there is no need to read the
file to check if the headline is there. The downside to this is that
this only works for IDs in Org-roam files.

org-roam-db.el

@@ -84,6 +84,9 @@ value like `most-positive-fixnum'."
 (defvar org-roam-db--connection (make-hash-table :test #'equal)
   "Database connection to Org-roam database.")
 
+(defvar org-roam-db-dirty nil
+  "Whether the org-roam database is dirty and requires an update.")
+
 ;;;; Core Functions
 
 (defun org-roam-db--get-connection ()
@@ -191,6 +194,10 @@ the current `org-roam-directory'."
   (dolist (conn (hash-table-values org-roam-db--connection))
     (org-roam-db--close conn)))
 
+(defun org-roam-db--mark-dirty ()
+  "Mark the Org-roam database as dirty."
+  (setq org-roam-db-dirty t))
+
 ;;;; Database API
 ;;;;; Initialization
 (defun org-roam-db--initialized-p ()
@@ -494,8 +501,11 @@ If FORCE, force a rebuild of the cache from scratch."
         (setq deleted-count (1+ deleted-count)))
     (pcase-dolist (`(,file . _) modified-files)
       (org-roam-db--clear-file file))
+    ;; Process all the files for IDs first
+    ;;
+    ;; We do this so that link extraction is cheaper: this eliminates the need
+    ;; to read the file to check if the ID really exists
     (pcase-dolist (`(,file . ,contents-hash) modified-files)
-      (org-roam-message "Processed %s/%s modified files..." modified-count (length modified-files))
       (let* ((attr (file-attributes file))
              (atime (file-attribute-access-time attr))
              (mtime (file-attribute-modification-time attr)))
@@ -505,9 +515,18 @@ If FORCE, force a rebuild of the cache from scratch."
                [:insert :into files
                 :values $v1]
                (vector file contents-hash (list :atime atime :mtime mtime)))
-              (setq modified-count (1+ modified-count))
               (when org-roam-enable-headline-linking
-                (setq id-count (+ id-count (org-roam-db--insert-ids))))
+                (setq id-count (+ id-count (org-roam-db--insert-ids)))))
+          (file-error
+           (setq org-roam-files (remove file org-roam-files))
+           (org-roam-db--clear-file file)
+           (lwarn '(org-roam) :warning
+                  "Skipping unreadable file while building cache: %s" file)))))
+    (pcase-dolist (`(,file . _) modified-files)
+      (org-roam-message "Processed %s/%s modified files..." modified-count (length modified-files))
+      (condition-case nil
+            (org-roam--with-temp-buffer file
+              (setq modified-count (1+ modified-count))
               (setq link-count (+ link-count (org-roam-db--insert-links)))
               (setq tag-count (+ tag-count (org-roam-db--insert-tags)))
               (setq title-count (+ title-count (org-roam-db--insert-titles)))
@@ -516,7 +535,7 @@ If FORCE, force a rebuild of the cache from scratch."
            (setq org-roam-files (remove file org-roam-files))
            (org-roam-db--clear-file file)
            (lwarn '(org-roam) :warning
-                  "Skipping unreadable file while building cache: %s" file)))))
+                  "Skipping unreadable file while building cache: %s" file))))
     (org-roam-message "total: Δ%s, files-modified: Δ%s, ids: Δ%s, links: Δ%s, tags: Δ%s, titles: Δ%s, refs: Δ%s, deleted: Δ%s"
                       (length org-roam-files)
                       modified-count
@@ -527,6 +546,12 @@ If FORCE, force a rebuild of the cache from scratch."
                       ref-count
                       deleted-count)))
 
+(defun org-roam-db-update-cache ()
+  "Update the cache if the database is dirty."
+  (when org-roam-db-dirty
+    (org-roam-db-build-cache)
+    (setq org-roam-db-dirty nil)))
+
 (provide 'org-roam-db)
 
 ;;; org-roam-db.el ends here