merge(PR#11): Move bits of Emacs configuration into local packages r/156

As requested by @wpcarro, some bits of my Emacs configuration are now in separate local packages (located at `//depot/tools/emacs-pkgs/`).

Specifically this change introduces:

* `tools.emacs-pkgs.dottime`: A package to render time in the modeline as [dottime](https://dotti.me)
* `tools.emacs-pkgs.term-switcher`: A package to quickly switch between and open new terminal instances in EXWM using ivy

My Emacs configuration is updated to accomodate these refactorings.

2 files changed, 66 insertions, 0 deletions

diff --git a/tools/emacs-pkgs/dottime/default.nix b/tools/emacs-pkgs/dottime/default.nix
new file mode 100644
index 000000000000..b09756dea560
--- /dev/null
+++ b/tools/emacs-pkgs/dottime/default.nix
@@ -0,0 +1,7 @@
+{ pkgs, ... }:
+
+pkgs.third_party.emacsPackagesNg.trivialBuild rec {
+  pname = "dottime";
+  version = "1.0";
+  src = ./dottime.el;
+}
diff --git a/tools/emacs-pkgs/dottime/dottime.el b/tools/emacs-pkgs/dottime/dottime.el
new file mode 100644
index 000000000000..7caeb2f2c440
--- /dev/null
+++ b/tools/emacs-pkgs/dottime/dottime.el
@@ -0,0 +1,59 @@
+;;; dottime.el --- use dottime in the modeline
+;;
+;; Copyright (C) 2019 Google Inc.
+;;
+;; Author: Vincent Ambo <tazjin@google.com>
+;; Version: 1.0
+;; Package-Requires: (cl-lib)
+;;
+;;; Commentary:
+;;
+;; This package changes the display of time in the modeline to use
+;; dottime (see https://dotti.me/) instead of the standard time
+;; display.
+;;
+;; Modeline dottime display is enabled by calling
+;; `dottime-display-mode' and dottime can be used in Lisp code via
+;; `dottime-format'.
+
+(require 'cl-lib)
+(require 'time)
+
+(defun dottime--format-string ()
+  "Creates the dottime format string for `format-time-string'
+  based on the local timezone."
+
+  (let* ((offset-sec (car (current-time-zone)))
+         (offset-hours (/ offset-sec 60 60)))
+    (if (/= offset-hours 0)
+        (concat "%m-%dT%H·%M" (format "%0+3d" offset-hours))
+      "%m-%dT%H·%M")))
+
+(defun dottime--display-time-update-advice (orig)
+  "Function used as advice to `display-time-update' with a
+  rebound definition of `format-time-string' that renders all
+  timestamps as dottime."
+
+  (cl-letf* ((format-orig (symbol-function 'format-time-string))
+             ((symbol-function 'format-time-string)
+              (lambda (&rest _)
+                (funcall format-orig (dottime--format-string) nil t))))
+    (funcall orig)))
+
+(defun dottime-format (&optional time)
+  "Format the given TIME in dottime. If TIME is nil, the current
+  time will be used."
+
+  (format-time-string (dottime--format-string) time t))
+
+(defun dottime-display-mode (arg)
+  "Enable time display as dottime. Disables dottime if called
+  with prefix 0 or nil."
+
+  (interactive "p")
+  (if (or (eq arg 0) (eq arg nil))
+      (advice-remove 'display-time-update #'dottime--display-time-update-advice)
+    (advice-add 'display-time-update :around #'dottime--display-time-update-advice))
+  (display-time-update))
+
+(provide 'dottime)