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+;;; fonts.el --- Font preferences -*- lexical-binding: t -*-
+;; Author: William Carroll <wpcarro@gmail.com>
+
+;;; Commentary:
+;; Control my font preferences with ELisp.
+
+;;; Code:
+
+;; TODO: `defcustom' font-size.
+;; TODO: `defcustom' fonts.
+;; TODO: Remove wpc/ namespace.
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Dependencies
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(require 'prelude)
+(require 'cycle)
+(require 'device)
+(require 'maybe)
+(require 'general)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Constants
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; TODO: Troubleshoot why "8" appears so large on my desktop.
+
+;; TODO: Consider having a different font size when I'm using my 4K monitor.
+
+(defconst fonts/size
+  (pcase (device/classify)
+    ('work-laptop  "9")
+    ('work-desktop "8"))
+  "My preferred default font-size, which is device specific.")
+
+(defconst fonts/keybindings? t
+  "Install the keybindings when non-nil.")
+
+(defconst fonts/size-step 10
+  "The amount (%) by which to increase or decrease a font.")
+
+(defconst fonts/hacker-news-recommendations
+  '("APL385 Unicode"
+    "Go Mono"
+    "Sudo"
+    "Monoid"
+    "Input Mono Medium" ;; NOTE: Also "Input Mono Thin" is nice.
+    )
+  "List of fonts optimized for programming I found in a HN article.")
+
+(defconst fonts/whitelist
+  (cycle/from-list
+   (list/concat
+    fonts/hacker-news-recommendations
+    '("JetBrainsMono"
+      "Mononoki Medium"
+      "Monospace"
+      "Operator Mono Light"
+      "Courier"
+      "Andale Mono"
+      "Source Code Pro"
+      "Terminus")))
+  "This is a list of my preferred fonts.")
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Functions
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; TODO: fonts and fonts/whitelist make it difficult to name functions like
+;; fonts/set as a generic Emacs function vs choosing a font from the whitelist.
+
+(cl-defun fonts/cycle (&key forward?)
+  "Cycle forwards when `FORWARD?' non-nil."
+  (let ((font (if forward?
+                  (cycle/next fonts/whitelist)
+                (cycle/prev fonts/whitelist))))
+    (message (s-concat "Active font: " font))
+    (fonts/set font)))
+
+(defun fonts/next ()
+  "Quickly cycle through preferred fonts."
+  (interactive)
+  (fonts/cycle :forward? t))
+
+(defun fonts/prev ()
+  "Quickly cycle through preferred fonts."
+  (interactive)
+  (fonts/cycle :forward? nil))
+
+(defun fonts/set (font &optional size)
+  "Change the font to `FONT' with option integer, SIZE, in pixels."
+  (if (maybe/some? size)
+      (set-frame-font (string/format "%s %s" font size) nil t)
+    (set-frame-font font nil t)))
+
+(defun fonts/whitelist-set (font)
+  "Focuses the FONT in the `fonts/whitelist' cycle.
+The size of the font is determined by `fonts/size'."
+  (prelude/assert (cycle/contains? font fonts/whitelist))
+  (cycle/focus (lambda (x) (equal x font)) fonts/whitelist)
+  (fonts/set (fonts/current) fonts/size))
+
+(defun fonts/ivy-select ()
+  "Select a font from an ivy prompt."
+  (interactive)
+  (fonts/whitelist-set
+   (ivy-read "Font: " (cycle/to-list fonts/whitelist))))
+
+(defun fonts/print-current ()
+  "Message the currently enabled font."
+  (interactive)
+  (message
+   (string/format "[fonts] Current font: \"%s\""
+                  (fonts/current))))
+
+(defun fonts/current ()
+  "Return the currently enabled font."
+  (cycle/current fonts/whitelist))
+
+(defun fonts/increase-size ()
+  "Increase font size."
+  (interactive)
+  (->> (face-attribute 'default :height)
+       (+ fonts/size-step)
+       (set-face-attribute 'default (selected-frame) :height)))
+
+(defun fonts/decrease-size ()
+  "Decrease font size."
+  (interactive)
+  (->> (face-attribute 'default :height)
+       (+ (- fonts/size-step))
+       (set-face-attribute 'default (selected-frame) :height)))
+
+(defun fonts/reset-size ()
+  "Restore font size to its default value."
+  (interactive)
+  (fonts/whitelist-set (fonts/current)))
+
+(when fonts/keybindings?
+  (progn
+    (general-define-key
+     :prefix "<SPC>"
+     :states '(normal)
+     "Ff" #'fonts/next
+     "Pf" #'fonts/prev)
+    (general-define-key "s-9" #'fonts/ivy-select)
+    (general-define-key "s-0" #'fonts/reset-size)
+    (general-define-key "s-j" #'fonts/decrease-size)
+    (general-define-key "s-k" #'fonts/increase-size)))
+
+(provide 'fonts)
+;;; fonts.el ends here