adding the citarn minimal experiment

citarn.el

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+;;; citarn.el --- Stripped down test of alt citar -*- lexical-binding: t; -*-
+;;
+;; Copyright (C) 2022 Bruce D'Arcus
+;;
+;; Author: Bruce D'Arcus <bdarcus@gmail.com>
+;; Maintainer: Bruce D'Arcus <bdarcus@gmail.com>
+;; Created: June 06, 2022
+;; Modified: June 06, 2022
+;; Version: 0.0.1
+;; Package-Requires: ((emacs "28.1"))
+;;
+;; This file is not part of GNU Emacs.
+;;
+;;; Commentary:
+;;
+;;  A minimal experiment in an alternative structure for citar caching and the
+;;  API.
+;;
+;;  Code is commented.
+;;
+;;; Code:
+
+(require 'parsebib)
+(require 'citar)
+
+;; Internal variables
+
+;; Most of this design is adapted from org-mode 'oc-basic',
+;; written by Nicolas Goaziou.
+
+(defvar citarn--bibliography-cache nil
+  "Cache for parsed bibliography files.
+This is an association list following the pattern:
+  (FILE-ID . ENTRIES)
+FILE-ID is a cons cell (FILE . HASH), with FILE being the absolute file name of
+the bibliography file, and HASH a hash of its contents.
+ENTRIES is a hash table with citation references as keys and fields alist as
+values.")
+
+(defvar citarn--completion-cache (make-hash-table :test #'equal)
+  "Hash with key as completion string, value as citekey.")
+
+;; Internal functions
+
+(defun citarn--all-keys ()
+  "List all keys available in current bibliography."
+  (seq-mapcat (pcase-lambda (`(,_ . ,entries))
+                (map-keys entries))
+              (citarn--parse-bibliography)))
+
+(defun citarn--ref-completion-table ()
+  "Return completion table for cite keys, as a hash table.
+In this hash table, keys are a strings with author, date, and
+title of the reference.  Values are the cite keys.
+Return nil if there are no bibliography files or no entries."
+  ;; Populate bibliography cache.
+  (let ((entries (citarn--parse-bibliography)))
+    (cond
+     ((null entries) nil)  ; no bibliography files
+     ((gethash entries citarn--completion-cache)
+      citarn--completion-cache) ; REVIEW ?
+     (t
+      (clrhash citarn--completion-cache)
+      (dolist (key (citarn--all-keys))
+        (let ((completion (citarn--get-value key "title"))) ; TODO hook up string formatting
+          (puthash completion key citarn--completion-cache)))
+      (unless (map-empty-p citarn--completion-cache) ; no key
+        (puthash entries t citarn--completion-cache) ; REVIEW ?
+        citarn--completion-cache)))))
+
+;; adapted from 'org-cite-basic--parse-bibliography'
+(defvar citarn--file-id-cache nil
+   "Hash table linking files to their hash.")
+
+(defun citarn--parse-bibliography ()
+  "List all entries available in the buffer.
+Each association follows the pattern
+  (FILE . ENTRIES)
+where FILE is the absolute file name of the bibliography file,
+and ENTRIES is a hash table where keys are references and values
+are association lists between fields, as symbols, and values as
+strings or nil."
+  (unless (hash-table-p citarn--file-id-cache)
+    (setq citarn--file-id-cache (make-hash-table :test #'equal)))
+  (let ((results nil))
+    ;; FIX the files to parse needs to be a function that returns the right
+    ;; local and/or global bibliography files for the current buffer.
+    (dolist (file citar-bibliography)
+      (when (file-readable-p file)
+        (with-temp-buffer
+          (when (or (file-has-changed-p file)
+                    (not (gethash file citarn--file-id-cache)))
+            (insert-file-contents file)
+            (puthash file (md5 (current-buffer)) citarn--file-id-cache))
+	  (let* ((file-id (cons file (gethash file citarn--file-id-cache)))
+                 (entries
+                  (or (cdr (assoc file-id citarn--bibliography-cache))
+                      (let ((table (parsebib-parse file)))
+                        (push (cons file-id table) citarn--bibliography-cache)
+                        table))))
+            (push (cons file entries) results)))))
+    results))
+
+(defun citarn--get-entry (key)
+  "Return entry for KEY, as an association list."
+  (catch :found
+    ;; Iterate through the cached bibliography hashes and find a key.
+    (pcase-dolist (`(,_ . ,entries) (citarn--parse-bibliography))
+      (let ((entry (gethash key entries)))
+        (when entry (throw :found entry))))
+    nil))
+
+(defun citarn--get-value (key-or-entry field)
+  "Return FIELD value for KEY-OR-ENTRY."
+  (let ((entry (if (stringp key-or-entry)
+                   (citarn--get-entry key-or-entry)
+                 key-or-entry)))
+    (cdr (assoc-string field entry))))
+
+(defun citarn-select-ref ()
+  "Select reference, return citekey."
+  (let* ((table
+          (or (citarn--ref-completion-table)
+              (user-error "No bibliography set")))
+         (choice (completing-read "Ref: " table)))
+    (gethash choice table)))
+
+;; Interactive commands
+
+(defun citarn-example ()
+  "Return title as message."
+  (interactive)
+  (let* ((choice (citarn-select-ref))
+         (title (citarn--get-value choice "title")))
+  (message title)))
+
+(citarn-example)
+
+(provide 'citarn)
+;;; citarn.el ends here