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+;;; entr.el --- Working with terminals and entr -*- lexical-binding: t -*-
+;; Author: William Carroll <wpcarro@gmail.com>
+
+;;; Commentary:
+;; Help make watch commands easier.
+;;
+;; This should be entirely temporary because in reality we should be able to use
+;; Emacs's buffer watching abilities to run commands.
+;; TODO: Explore Emacs integration that obviates `entr`.
+
+;;; Code:
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Dependencies
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(require 'f)
+(require 'buffer)
+(require 'prelude)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Library
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; TODO: Support a generic file-watcher for commonly used languages.
+(defconst entr/major-mode->save-handler
+  '((python-mode . entr/handle-python3))
+  "Mapping of language to the `after-save-hook' function it should register.")
+
+(defun entr/shell-command-to-buffer (cmd name)
+  "Run CMD in a shell and output to the buffer NAME.
+The buffer is a find-or-create operation.
+The buffer is erased between runs with `erase-buffer'."
+  (let ((b (buffer/find-or-create name)))
+    (with-current-buffer b (erase-buffer))
+    (shell-command cmd b)
+    (buffer/show b)))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Python
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; TODO: This should be a top-level function.
+(defconst entr/handle-python3
+  (lambda ()
+    (entr/shell-command-to-buffer
+     (format "python3 %s" (buffer-file-name))
+     "*python3*"))
+  "Function that is registered as the `after-save-hook' for python3.")
+
+(defun entr/register-python3 ()
+  "Register a buffer-local `after-save-hook' for calling python3 with filename."
+  (interactive)
+  (add-hook 'after-save-hook entr/handle-python3 nil t))
+
+(defun entr/deregister-python3 ()
+  "Remove the buffer-local `after-save-hook' for python3."
+  (interactive)
+  (remove-hook 'after-save-hook entr/handle-python3 t))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Protobuf
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defun entr/format-protobuf ()
+  "Formats a protobuf buffer."
+  (call-interactively #'clang-format))
+
+;; TODO: Run this automatically with .proto file extensions.  Do this after
+;; verifying that `clang-format' complies with Google's style guide.
+(defun entr/register-protobuf ()
+  "Register a buffer-local `before-save-hook' for formatting protobuf buffers."
+  (interactive)
+  (add-hook
+   'before-save-hook
+   #'entr/format-protobuf
+   nil
+   t))
+
+;; TODO: Is there an interactive way to remove hooks in Emacs?
+(defun entr/deregister-protobuf ()
+  "Remove the buffer-local `before-save-hook' for protobuf."
+  (interactive)
+  (remove-hook
+   'before-save-hook
+   #'entr/format-protobuf
+   t))
+
+;; TODO: Support this.  Currently the `intern' call is the problem.
+;; (defun entr/ivy-remove-hook (hook)
+;;   "Use Counsel to remove a handler from HOOK."
+;;   (interactive)
+;;   (ivy-read
+;;    "Remove hook: "
+;;    (intern (prelude/prompt "Hook name: "))
+;;    :action (lambda (x) (message x))))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Miscellaneous
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defun entr/command (command)
+  "Create a terminal instance with entr running COMMAND.
+COMMAND is a function that is called with the current filename."
+  ;; Algorithm:
+  ;; - Get buffer's filename.
+  ;; - Open terminator running: `echo entr <filename> | entr <command>`.
+  (interactive)
+  (with-current-buffer (current-buffer)
+      (let ((filename (buffer-file-name)))
+        (prelude/inspect
+         (format "echo %s | entr %s" filename (funcall command filename))))))
+
+(provide 'entr)
+;;; entr.el ends here