typesetting/quad/quadwriter/font.rkt

#lang debug racket/base
(require racket/runtime-path
         racket/string
         racket/path
         racket/match
         "attrs.rkt")
(provide (all-defined-out))

(define-runtime-path quadwriter-fonts-dir "fonts")
(define-runtime-path default-font-face "fonts/default/SourceSerifPro-Regular.otf")
(define default-font-family "text")
(define default-font-size 12)
(define default-line-height 16)
(define default-font-color "black")
(define default-font-features (list (cons #"tnum" 1)))

(define font-paths (make-hash))

(define top-font-directory "fonts")
(define font-file-extensions '(#".otf" #".ttf" #".woff"))

(define (setup-font-path-table! base-path)
  ;; create a table of font paths that we can use to resolve references to font names.
  
  ;; rules for font naming
  ;; "fonts" subdirectory on top
  ;; family directories inside: each named with font family name
  ;; this makes it possible to give font families generic names (e.g., "body-text")
  ;; and change the font files without disturbing anything else.
  (hash-clear! font-paths)
  (define doc-fonts-dir
    (simple-form-path
     (build-path (match/values (split-path base-path)
                               [(base name #true) (build-path base name)]
                               [(dir _ _) dir]) top-font-directory)))
  ;; run doc-fonts-dir first because earlier fonts take precedence (using hash-ref! below)
  (for* ([fonts-dir (in-list (list doc-fonts-dir quadwriter-fonts-dir))]
         #:when (directory-exists? fonts-dir)
         [font-family-subdir (in-directory fonts-dir)]
         #:when (directory-exists? font-family-subdir)
         [font-path (in-directory font-family-subdir)]
         #:when (member (path-get-extension font-path) font-file-extensions))
    (match-define (list font-path-string family-name)
      (for/list ([x (list font-path font-family-subdir)])
        (path->string (find-relative-path fonts-dir x))))
    (define path-parts (for/list ([part (in-list (explode-path (string->path (string-downcase font-path-string))))])
                         (path->string part)))
    (define key
      (cons (string-downcase family-name)
            (cond
              [(member "bold-italic" path-parts) 'bi]
              [(member "bold" path-parts) 'b]
              [(member "italic" path-parts) 'i]
              [else 'r])))
    ;; only set value if there's not one there already.
    ;; this means that we only use the first eligible font we find.
    (hash-ref! font-paths key font-path)))

(define (font-attrs->path font-family bold italic)
  ;; find the font-path corresponding to a certain family name and style.
  (define key (cons (string-downcase font-family)
                    (cond
                      [(and bold italic) 'bi]
                      [bold 'b]
                      [italic 'i]
                      [else 'r])))
  (define regular-key (cons font-family 'r))
  (cond
    [(hash-ref font-paths key #false)]
    [(hash-ref font-paths regular-key #false)]
    [else default-font-face]))

(define (resolve-font-path! attrs)
  ;; convert references to a font family and style to an font path on disk
  ;; we trust it exists because we used `setup-font-path-table!` earlier,
  ;; but if not, fallback fonts will kick in, on the idea that a missing font shouldn't stop the show
  (define this-font-family (hash-ref! attrs :font-family default-font-family))
  (unless (complete-path? this-font-family)
    (define this-bold (hash-ref! attrs :font-bold #false))
    (define this-italic (hash-ref! attrs :font-italic #false))
    (hash-set! attrs :font-path (font-attrs->path this-font-family this-bold this-italic))))

(define (parse-adjustment pstr suffix)
  (and
   pstr
   (string? pstr)
   (string-suffix? pstr suffix)
   (string->number (string-trim pstr suffix))))

(define (parse-percentage pstr)
  (match (parse-adjustment pstr "%")
    [#false #false]
    [res (/ res 100.0)]))

(define (parse-percentage-or-em str)
  (or (parse-percentage str) (parse-adjustment str "em")))

(define (resolve-font-size! attrs)
  ;; convert font-size attributes into a simple font size
  ;; we stashed the previous size in private key 'font-size-previous
  (define prev-font-size-key 'font-size-previous)
  (define val (hash-ref attrs :font-size default-font-size))
  (define adjustment (parse-percentage-or-em val))
  ;; if our value represents an adjustment, we apply the adjustment to the previous value
  ;; otherwise we use our value directly
  (define base-size (if adjustment (hash-ref attrs prev-font-size-key default-font-size) val))
  (define base-size-adjusted (and base-size (* base-size (or adjustment 1))))
  ;; we write our new value into both font-size and font-size-previous
  ;; because as we cascade down, we're likely to come across superseding values
  ;; of font-size (but font-size-previous will persist)
  (hash-set! attrs :font-size base-size-adjusted)
  (hash-set! attrs prev-font-size-key base-size-adjusted))

(define (resolve-line-height! attrs)
  ;; convert line-height attributes into a simple line height
  (hash-update! attrs :line-height
                (λ (val)
                  (define adjustment (parse-percentage-or-em val))
                  (define base-height (if adjustment (hash-ref attrs :font-size) val))
                  (and base-height (* base-height (or adjustment 1))))
                default-line-height))

(define (resolve-font-tracking! attrs)
  (hash-update! attrs :font-tracking
                (λ (val)
                  (define adjustment (parse-percentage-or-em val))
                  (define base-tracking (if adjustment (hash-ref attrs :font-size) val))
                  (and base-tracking (* base-tracking (or adjustment 1))))
                0))