From 7b1e482530c76dcf856ec4a20aee6586eb2e8ccf Mon Sep 17 00:00:00 2001
From: Matus Goljer <matus.goljer@gmail.com>
Date: Wed, 1 Mar 2023 16:02:43 +0100
Subject: [PATCH] feat(core): add setup for outline-minor-mode

Fixes #20
---
 README.md         | 38 +++++++++++++++++++++++++++++++++++++-
 terraform-mode.el | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 352974b..8f66c3a 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,24 @@ You can install `terraform-mode.el` from [MELPA](https://melpa.org/) by `package
 - Indentation
 - imenu
 - Formatting using `terraform fmt`
+- Block folding
 
+### Block folding
+
+`terraform-mode` sets up `outline-mode` variables for block folding.
+To use `outline-mode` for block folding, enable `outline-minor-mode`
+in `terraform-mode-hook`:
+
+``` emacs-lisp
+(add-hook 'terraform-mode-hook #'outline-minor-mode)
+```
+
+You can use `outline-toggle-children` bound to `C-c C-f` to toggle
+visibility of a block at point.
+
+We also provide function `terraform-toggle-or-indent` which
+folds-or-indents.  It is not bound by default, but you can bind it to
+`TAB` or any other key.
 
 ## Customize Variables
 
@@ -36,11 +53,30 @@ Set to `t` to automatically format the buffer on save.
 
 ## Sample Configuration
 
-```lisp
+```emacs-lisp
 (custom-set-variables
  '(terraform-indent-level 4))
 ```
 
+With `use-package`
+
+``` emacs-lisp
+(use-package terraform-mode
+  ;; if using straight
+  ;; :straight t
+
+  ;; if using package.el
+  ;; :ensure t
+  :custom (terraform-indent-level 4)
+  :config
+  (defun my-terraform-mode-init ()
+    ;; if you want to use outline-minor-mode
+    ;; (outline-minor-mode 1)
+    )
+
+  (add-hook 'terraform-mode-hook 'my-terraform-mode-init))
+```
+
 ## See Also
 
 - [hcl-mode](https://github.com/syohex/emacs-hcl-mode)
diff --git a/terraform-mode.el b/terraform-mode.el
index 4793278..4a06fa1 100644
--- a/terraform-mode.el
+++ b/terraform-mode.el
@@ -36,6 +36,7 @@
 (require 'hcl-mode)
 (require 'dash)
 (require 'thingatpt)
+(require 'outline)
 
 (defgroup terraform nil
   "Major mode of Terraform configuration file."
@@ -276,9 +277,45 @@
   (interactive)
   (browse-url (terraform--resource-url-at-point)))
 
+(defun terraform--outline-level ()
+  "Return the depth to which a statement is nested in the outline.
+
+See also `outline-level'."
+  (or (cdr (assoc (match-string 1) outline-heading-alist))
+      (- (match-end 1) (match-beginning 1))))
+
+(defun terraform--setup-outline-mode ()
+  (set (make-local-variable 'outline-level) #'terraform--outline-level)
+
+  (let ((terraform-keywords
+         (list "terraform" "locals" "required_providers" "atlas" "connection"
+               "backend" "provider" "provisioner"
+               "variable" "module" "output"
+               "data" "resource")))
+    (set (make-local-variable 'outline-regexp)
+         (concat
+          "^"
+          (regexp-opt terraform-keywords 'symbols)
+          "[[:blank:]].*{[[:blank:]]*$"))
+    (set (make-local-variable 'outline-heading-alist)
+         (mapcar
+          (lambda (item) (cons item 2))
+          terraform-keywords))))
+
+(defun terraform-toggle-or-indent (&optional arg)
+  "Toggle visibility of block under point or indent.
+
+If the point is not at the heading, call
+`indent-for-tab-command'."
+  (interactive)
+  (if (and outline-minor-mode (outline-on-heading-p))
+      (outline-toggle-children)
+    (indent-for-tab-command arg)))
+
 (defvar terraform-mode-map
   (let ((map (make-sparse-keymap)))
     (define-key map (kbd "C-c C-h") #'terraform-open-doc)
+    (define-key map (kbd "C-c C-f") #'outline-toggle-children)
     map))
 
 ;;;###autoload
@@ -293,6 +330,9 @@
   (make-local-variable 'terraform-indent-level)
   (setq hcl-indent-level terraform-indent-level)
 
+  ;; outline
+  (terraform--setup-outline-mode)
+
   ;; imenu
   (setq imenu-sort-function 'imenu--sort-by-name)
   (setq imenu-create-index-function 'terraform--generate-imenu)