;;; repro-preview-cache.el --- Does dirvish's text preview disturb an org buffer's element cache? -*- lexical-binding: t -*-

;; Replays `dirvish--preview-file-maybe-truncate' (dirvish.el:653-684) against an
;; org file that is ALSO open for real, then kills the preview buffer the way
;; dirvish does (`dirvish--kill-buffer', dirvish.el:416).  The kill is the step
;; that matters: killing an org-mode buffer with a `buffer-file-name' is when
;; org-persist writes that file's cache.

(require 'org)
(require 'org-element)
(require 'org-persist)

(setq org-element-use-cache t
      org-element-cache-persistent t
      org-element--cache-self-verify t
      org-element--cache-self-verify-frequency 1.0)

(defun repro--build-cache (buf)
  "Actually populate the element cache of BUF by walking it."
  (with-current-buffer buf
    (org-element-cache-map (lambda (_el) nil) :granularity 'element)
    (and org-element--cache (avl-tree-size org-element--cache))))

(defun repro--warnings ()
  (when (get-buffer "*Warnings*")
    (with-current-buffer "*Warnings*" (string-trim (buffer-string)))))

(let* ((src (expand-file-name "todo.org" default-directory))
       (file (make-temp-file "repro-" nil ".org"))
       (threshold 1048576))
  (copy-file src file t)
  (let ((size (nth 7 (file-attributes file))))
    (message "== fixture %s (%d bytes, %s threshold) =="
             (file-name-nondirectory file) size
             (if (>= size threshold) "over" "under")))

  (let ((real (find-file-noselect file)))
    (message "real buffer cache after full walk: %S" (repro--build-cache real))

    ;; --- dirvish text preview of the same file ---
    (with-current-buffer (get-buffer-create "*preview-temp*")
      (let (jka-compr-verbose)
        (with-silent-modifications
          (setq buffer-read-only t)
          (insert-file-contents file nil 0 threshold)
          (when (>= (nth 7 (file-attributes file)) threshold)
            (goto-char (point-max))
            (insert "\n\nFile truncated. End of partial preview.\n"))
          (setq buffer-file-name file)
          (goto-char (point-min))
          (rename-buffer (format "PREVIEW :: %s" (file-name-nondirectory file))))
        (let ((enable-dir-local-variables nil)
              (enable-local-variables :safe)
              (non-essential t))
          (set-auto-mode)
          (font-lock-mode 1)))
      (message "preview buffer: mode=%s claims=%s cache=%S"
               major-mode (file-name-nondirectory (or buffer-file-name "none"))
               (repro--build-cache (current-buffer))))

    (message "-- both buffers live: real=%S claiming-file=%d --"
             (with-current-buffer real (avl-tree-size org-element--cache))
             (length (seq-filter (lambda (b) (equal (buffer-local-value 'buffer-file-name b) file))
                                 (buffer-list))))

    ;; --- dirvish kills the preview buffer when the session ends ---
    (let ((kill-buffer-query-functions nil)
          (preview (format "PREVIEW :: %s" (file-name-nondirectory file))))
      (kill-buffer preview)
      (message "preview buffer %S killed" preview))

    ;; --- is the real buffer still coherent? ---
    (with-current-buffer real
      ;; Edit it the way Craig would after stepping back from dirvish.
      (goto-char (point-max))
      (condition-case err
          (let ((inhibit-read-only t)) (insert "\n* Repro edit\n"))
        (error (message "RESULT: insert into real buffer SIGNALLED %S" (car err))))
      (condition-case err
          (progn (org-element-cache-map (lambda (_el) nil) :granularity 'element)
                 (message "post-kill cache-map: clean (size=%S)"
                          (avl-tree-size org-element--cache)))
        (error (message "post-kill cache-map: ERROR %S" err)))
      (set-buffer-modified-p nil))

    (message "warnings=%s" (or (repro--warnings) "none")))

  (delete-file file))