◊(Local Yarn Code "Diff")

         racket/system
         racket/string)

;; 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
         set-meta!
         here-output-path
         here-source-path
         here-id
         listing-context
         current-series-noun    ; Retrieve noun-singular from current 'series meta, or #f
         current-series-title   ; Retrieve title of series in current 'series meta, or #f
         current-series-pagenode

(define (default-title body-txprs)
  (format "“~a…”" (first-words body-txprs 5)))

(define (maybe-meta m [missing ""])
  (cond [(current-metas) (or (select-from-metas m (current-metas)) missing)]
        [else missing]))

(define (set-meta! key v)
  (define cur-metas (current-metas))
  (and cur-metas
       (current-metas (hash-set! cur-metas key v))))

;; Return the current source path, relative to (current-project-root)
(define (here-source-path)
  (match (current-metas)
    [(? hash? m)
     (define-values (_ rel-path-parts)
       (drop-common-prefix (explode-path (current-project-root))
                           (explode-path (string->path (hash-ref m 'here-path)))))