@@ -19,26 +19,114 @@
 ;; Author contact information:
 ;;   joel@jdueck.net
 ;;   https://joeldueck.com
 ;; -------------------------------------------------------------------------
 
-;; Convenience functions for YYYY-MM-DD date strings
-
-(require gregor
+(require pollen/core
+         pollen/pagetree
+         net/uri-codec
+         gregor
+         txexpr
+         racket/list
          racket/string)
 
-(provide (all-defined-out))
+;; Provides common helper functions used throughout the project
+
+(provide maybe-meta     ; Select from (current-metas) or default value ("") if not available
+         maybe-attr     ; Return an attribute’s value or a default ("") if not available
+         series-noun    ; Retrieve noun-singular from current 'series meta, or ""
+         attr-present?  ; Test if an attribute is present
+         disposition-values
+         ymd->english
+         ymd->dateformat
+         default-authorname
+         default-title
+         tx-strs
+         build-note-id
+         notes->last-disposition-values
+         )
+
+(define default-authorname "Joel Dueck")
+
+(define (default-title date)
+  (format "Entry of ~a" (ymd->dateformat date "d MMM YYYY")))
+
+(define (maybe-meta m [missing ""])
+  (or (select-from-metas m (current-metas)) missing))
+
+(define (series-noun)
+  (define series-pagenode (->pagenode (or (select-from-metas 'series (current-metas)) "")))
+  (case series-pagenode
+    ['|| ""] ; no series specified
+    [else (or (select-from-metas 'noun-singular series-pagenode) "")]))
+
+(define (attr-present? name attrs)
+  (for/or ([attr-pair (in-list attrs)])
+          (equal? name (car attr-pair))))
+
+(define (maybe-attr name attrs [missing ""])
+  (define result (assoc name attrs))
+  (cond
+    [(pair? result) (cadr result)]
+    [else missing]))
+
+(define (tx-strs xpr)
+  (cond
+    [(txexpr? xpr) (apply string-append (map tx-strs (get-elements xpr)))]
+    [(string? xpr) xpr]
+    [else ""]))
+
+(module+ test
+  (require rackunit)
+  (define test-metas (hash 'name "Fiver" 'size "Small"))
+  (define test-attrs '([name "Hazel"] [rank "Chief"]))
+
+  (parameterize ([current-metas test-metas])
+    (check-equal? (maybe-meta 'name) "Fiver") ; present meta
+    (check-equal? (maybe-meta 'age) "")       ; missing meta
+    (check-equal? (maybe-meta 'age 2) 2))      ; alternate default value
+  
+  (check-equal? (attr-present? 'name test-attrs) #t)
+  (check-equal? (attr-present? 'dingus test-attrs) #f)
+  (check-equal? (maybe-attr 'rank test-attrs) "Chief")
+  (check-equal? (maybe-attr 'dingus test-attrs) "")
+  (check-equal? (maybe-attr 'dingus test-attrs "zippy") "zippy"))
+                
+;; Convert, e.g., "* thoroughly recanted" into (values "*" "thoroughly recanted")
+(define (disposition-values str)
+  (cond [(string=? "" str) (values "" "")]
+        [else (let ([splut (string-split str)])
+                (values (car splut) (string-join (cdr splut))))]))
+
+;; The format of a note’s ID is “HTML-driven” (used as an anchor link) but is included
+;; here since it also serves as a primary key in the DB.
+(define (build-note-id txpr)
+  (string-append "#"
+                 (maybe-attr 'date (get-attrs txpr))
+                 "_"
+                 (uri-encode (maybe-attr 'author (get-attrs txpr) default-authorname))))
+
+;; Extract the last disposition (if any), and the ID of the disposing note, out of a list of notes
+(define (notes->last-disposition-values txprs)
+  (define (contains-disposition? tx) (attr-present? 'disposition (get-attrs tx)))
+  (define disp-notes (filter contains-disposition? txprs))
+  (cond [(not (empty? disp-notes))
+         (define latest-disposition-note (last disp-notes))
+         (values (attr-ref latest-disposition-note 'disposition)
+                 (build-note-id latest-disposition-note))]
+        [else (values "" "")]))
+        
+;; ~~~ Convenience functions for YYYY-MM-DD date strings ~~~
 
-;; These functions ignore everything after the first space!
+;; These functions ignore everything after the first space in the input!
 (define (ymd->dateformat ymd-string dateformat)
   (~t (iso8601->date (car (string-split ymd-string))) dateformat))
 
 (define (ymd->english ymd-string)
   (ymd->dateformat ymd-string "MMMM d, yyyy"))
 
 (module+ test
-  (require rackunit)
   (check-equal? (ymd->english "2018-08-12") "August 12, 2018")
   (check-equal? (ymd->dateformat "2018-08-12" "d MMM YYYY") "12 Aug 2018")
 
   ;; How we handle weird input
   (check-equal? (ymd->english "2018-08-12 everything after 1st space ignored") "August 12, 2018")