Org-Roam multiple directories workaround hack

org-roam-multi-dir.el

(defvar org-roam-directories nil
  "Paths to org-roam files. List where CAR is name and CDR is path.")

;; Example:
;; (setq org-roam-directories '(("Home roam" . "~/Documents/home-roam")
;;                              ("Work roam" . "~/Documents/work-roam")))

;; Set first directory
(setq org-roam-directory (cdar org-roam-directories))

;; This buffer hook updates org-roam-directory on switching buffers.
(add-hook 'buffer-list-update-hook #'org-roam--buffer-change-hook)

(defvar org-roam--multi-dir-cache nil
  "Alist keyed by name of wiki from org-roam-directories containing built cache data.")

(defun org-roam--multi-name-from-path (path)
  (car (--first (f-same? path (cdr it)) org-roam-directories)))

(defun org-roam--multi-path-from-name (name)
  (cdr (assoc name org-roam-directories)))

(defun org-roam--switch-cache (roam-dir-name)
  "Switch cache by name from org-roam-directories."
  ;; Save current cache if good.
  (when org-roam-cache-initialized
    ;; Extra checking due to async build cache
    (when-let* (((< 0 (hash-table-count org-roam-titles-cache)))
                (name (org-roam--multi-name-from-path org-roam-directory))
                (a-file-path (block nil
                               (maphash (lambda (k v) (return k))
                                        org-roam-titles-cache)))
                ((f-parent-of? org-roam-directory a-file-path)))
      (setf (alist-get name org-roam--multi-dir-cache)
            (list org-roam-forward-links-cache
                  org-roam-backward-links-cache
                  org-roam-titles-cache
                  org-roam-directory))))
  ;; Retrieve existing cache, else clear and build cache.
  (if-let* ((cached (alist-get roam-dir-name org-roam--multi-dir-cache)))
      (progn
        (setq org-roam-cache-initialized t
              org-roam-forward-links-cache (elt cached 0)
              org-roam-backward-links-cache (elt cached 1)
              org-roam-titles-cache (elt cached 2)
              org-roam-directory (elt cached 3)))
    (org-roam--clear-cache)
    (setq org-roam-directory (org-roam--multi-path-from-name roam-dir-name))
    (org-roam--build-cache-async)
    nil))

(defun org-roam--multi-dir-helm-select (description)
  "Helm selector to pick wiki directory."
  (let ((max-len (--reduce-from (max acc (length (car it)))
                                0 org-roam-directories)))
    (helm :sources (helm-build-sync-source description
                     :candidates (--map
                                  (cons (format (format "%%-%ds  %%s" max-len)
                                                (car it) (cdr it))
                                        it)
                                  org-roam-directories)))))

(defun org-roam-multi-switch-and-find-file ()
  "Switch to another roam directory defined in
  org-roam-directories and find file within."
  (interactive)
  (when-let ((pair (org-roam--multi-dir-helm-select "Pick dir to roam:")))
    (org-roam--switch-cache (car pair))
    (org-roam--after-cache-initialized #'org-roam-find-file (car pair))))

(defun org-roam--buffer-change-hook ()
  "To be triggered when buffers are entered.  Switches the
    org-roam cache if the buffer belongs to a different org-roam directory."
  (when-let* ((not-minibuffer (not (active-minibuffer-window)))
              ((get-buffer-window nil (selected-frame)))
              (path (buffer-file-name))
              (wiki-pair (--first (f-parent-of? (cdr it) path)
                                  org-roam-directories))
              (is-different-wiki (not (equal (cdr wiki-pair)
                                             org-roam-directory))))
    (org-roam--switch-cache (car wiki-pair))
    (when (get-buffer org-roam-buffer)
      (org-roam--after-cache-initialized (lambda () (org-roam-update path))
                                         (car wiki-pair)))))

(defun org-roam--after-cache-initialized (f multi-name)
  "Execute a function when cache becomes initialized with expected multi-name."
  (if (and org-roam-cache-initialized
           (f-same? (org-roam--multi-path-from-name multi-name)
                    org-roam-directory))
      (funcall f)
    (run-at-time 0.2 nil
                 (lambda () (org-roam--after-cache-initialized f multi-name)))))

Extended on-init-cache hack since it wasn't working with new minor mode.