;;; perga-mode.el --- major mode for perga  -*- lexical-binding: t; -*-

;; Author: William Ball <wball@ballcloud.cc>
;; Maintainer: William Ball <wball@ballcloud.cc>
;; Version: 0.1
;; Package-Requires: ((emacs "29.1"))
;; Homepage: https://forgejo.ballcloud.cc/wball/perga-mode
;; Keywords: languages, tree-sitter

;; This file is not part of GNU Emacs.

;;; Commentary:

;; Major mode for editing perga code, with Tree-sitter-based
;; font-lock support.  Requires Emacs 29 or newer.

;;; Code:

(require 'treesit)

(defun perga--ensure-treesit-grammar ()
  "Ensure the perga Tree-sitter grammar is installed."
  (unless (treesit-ready-p 'perga)
    (add-to-list 'treesit-language-source-alist
                 '(perga . ("https://forgejo.ballcloud.cc/wball/tree-sitter-perga")))
    (when (yes-or-no-p "Tree-sitter grammar for perga not found. Install it now? ")
      (treesit-install-language-grammar 'perga))))

(defvar perga--font-lock-rules
    '(:language perga
      :override t
      :feature keyword
      ([ "fun" "λ" "forall" "∏" "let" "in" "end" "def" "axiom" "variable" "hypothesis" "section" "infixl" "infixr" "[" "]" ] @font-lock-keyword-face)

      :language perga
      :override t
      :feature preprocessor
      ((preprocess
	(command) @font-lock-preprocessor-face
	(post_command) @font-lock-string-face))

      :language perga
      :override t
      :feature delimiter
      ([ "=>" "→" "⇒" "," ":=" ";" ":" ] @font-lock-delimiter-face)

      :language perga
      :override t
      :feature operator
      ((symbol) @font-lock-operator-face)

      :language perga
      :override t
      :feature constant
      ([(star) (square)] @font-lock-constant-face)

      :language perga
      :override t
      :feature comment
      ((comment) @font-lock-comment-face)

      :language perga
      :override t
      :feature definition
      ((definition
	name: (identifier) @font-lock-function-name-face))

      :language perga
      :override t
      :feature definition
      ((axiom
	name: (identifier) @font-lock-function-name-face))

      :language perga
      :override t
      :feature assignment
      ((binding
	(identifier) @font-lock-function-name-face))

      :language perga
      :override t
      :feature parameter
      ((param_block
	param: (identifier)+ @font-lock-variable-name-face))

      :language perga
      :override t
      :feature type
      ((param_block
	type: (expr) @font-lock-type-face))

      :language perga
      :override t
      :feature type
      ((labs_alt
	type: (expr) @font-lock-type-face))

      :language perga
      :override t
      :feature parameter
      ((labs_alt
	param: (identifier)+ @font-lock-variable-name-face))

      :language perga
      :override t
      :feature type
      ((ascription
	type: (expr) @font-lock-type-face))))

(defun perga--setup ()
  "Setup treesit for perga-mode."
  (setq-local treesit-font-lock-settings
               (apply #'treesit-font-lock-rules
                      perga--font-lock-rules))

  (setq-local font-lock-defaults nil)
  
  (setq-local treesit-font-lock-feature-list
	      '((comment definition)
		(keyword type constant preprocessor)
		(assignment parameter delimiter operator)))

  (setq-local treesit-font-lock-level 3)

  ;; (setq-local treesit-simple-indent-rules
  ;; 	      `((perga
  ;; 		 ((parent-is "program") column-0 0)
  ;; 		 ((node-is ":=") parent 4)
  ;; 		 ((parent-is "definition") parent 4)
  ;; 		 ((parent-is "labs") parent 4)
  ;; 		 (no-node parent 0))))

  (treesit-major-mode-setup))

;;;###autoload
(define-derived-mode perga-mode prog-mode "perga"
  "Major mode for perga files."
  (perga--ensure-treesit-grammar)
  (when (treesit-ready-p 'perga)
    (treesit-parser-create 'perga)
    (perga--setup)))

(defun perga-typecheck-current-file ()
  "Typecheck the current file using the `perga` executable"
  (interactive))

(defvar perga-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map "C-c c" #'do-stuff)
    map))

(provide 'perga-mode)

;;;###autoload
(add-to-list 'auto-mode-alist '("\\.pg" . perga-mode))

;;; perga-mode.el ends here