init.el

;; ============================================================
;; Emacs 30.2 — Scala IDE Configuration (Clean Test Config)
;; Approach: lsp-mode + Metals (official recommendation)
;; ============================================================

;; ---- Package Management Setup ----

(require 'package)

(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t)
(add-to-list 'package-archives '("melpa-stable" . "https://stable.melpa.org/packages/") t)

(package-initialize)

;; Refresh package list on first run
(unless package-archive-contents
  (package-refresh-contents))

;; Install use-package if not already installed
(unless (package-installed-p 'use-package)
  (package-install 'use-package))

(require 'use-package)

(setq use-package-always-ensure t)
(setq use-package-always-defer t)

;; ---- General Settings ----

;; Keep auto-save/backup files out of project directories
;; (Metals is sensitive to stray files in the project tree)
(setq backup-directory-alist `((".*" . ,temporary-file-directory)))
(setq auto-save-file-name-transforms `((".*" ,temporary-file-directory t)))

(add-hook 'prog-mode-hook 'display-line-numbers-mode)
(column-number-mode 1)
(show-paren-mode 1)
(setq inhibit-startup-screen t)
(setq-default indent-tabs-mode nil)
(setq-default tab-width 2)

;; which-key is built into Emacs 30 — shows available keybindings after a prefix
(which-key-mode 1)

;; ---- Performance Tuning for LSP ----
;; These are critical for Metals. Without them, large projects will lag.

;; Increase GC threshold to 100MB (default 800KB causes constant GC pauses)
(setq gc-cons-threshold 100000000)

;; Increase process read size to 1MB (default 4KB too small for LSP JSON)
(setq read-process-output-max (* 1024 1024))

;; ---- scala-mode — Syntax Highlighting & Indentation ----

(use-package scala-mode
  :interpreter ("scala" . scala-mode)
  :mode "\\.s\\(cala\\|bt\\)$")

;; ---- sbt-mode — Run sbt Commands from Emacs ----

(use-package sbt-mode
  :commands sbt-start sbt-command
  :config
  ;; Allow SPACE in minibuffer (without this, space triggers completion)
  (substitute-key-definition
   'minibuffer-complete-word
   'self-insert-command
   minibuffer-local-completion-map)
  ;; Disable sbt supershell (breaks sbt-mode output parsing)
  (setq sbt:program-options '("-Dsbt.supershell=false")))

;; ---- flycheck — Real-time Error Highlighting ----

(use-package flycheck
  :init (global-flycheck-mode))

;; ---- company — Auto-completion Framework ----

(use-package company
  :hook (scala-mode . company-mode)
  :config
  (setq company-idle-delay 0.2)
  (setq company-minimum-prefix-length 1)
  (setq lsp-completion-provider :capf))

;; ---- yasnippet — Code Snippets ----

(use-package yasnippet
  :hook (scala-mode . yas-minor-mode))

;; ---- posframe — Pop-up Framework (needed by dap-mode) ----

(use-package posframe)

;; ---- lsp-mode — The Core LSP Client ----

(use-package lsp-mode
  :hook
  (scala-mode . lsp)
  (lsp-mode . lsp-lens-mode)
  :config
  (setq lsp-prefer-flymake nil)
  (setq lsp-keep-workspace-alive nil)
  (setq lsp-headerline-breadcrumb-enable t)
  (setq lsp-semantic-tokens-enable t)
  (setq lsp-log-io nil))

;; ---- lsp-metals — Scala-specific LSP Features ----

(use-package lsp-metals
  :ensure t
  :custom
  (lsp-metals-server-args '(
    "-J-Dmetals.allow-multiline-string-formatting=off"
    "-J-Dmetals.icons=unicode"))
  (lsp-metals-enable-semantic-highlighting t)
  :hook (scala-mode . lsp))

;; ---- lsp-ui — Enhanced UI ----

(use-package lsp-ui
  :after lsp-mode
  :config
  (setq lsp-ui-doc-enable t)
  (setq lsp-ui-doc-position 'at-point)
  (setq lsp-ui-sideline-enable t)
  (setq lsp-ui-sideline-show-code-actions t)
  (setq lsp-ui-sideline-show-hover nil)
  (setq lsp-ui-peek-enable t))

;; ---- dap-mode — Debugging ----

(use-package dap-mode
  :hook
  (lsp-mode . dap-mode)
  (lsp-mode . dap-ui-mode))

;; ---- Scala Keybindings ----
;; Russ will have his own — these are for verification in the test VM

(with-eval-after-load 'scala-mode
  (define-key scala-mode-map (kbd "C-c C-t") 'lsp-describe-thing-at-point)
  (define-key scala-mode-map (kbd "C-c C-d") 'lsp-ui-doc-show)
  (define-key scala-mode-map (kbd "C-c C-r") 'lsp-rename)
  (define-key scala-mode-map (kbd "C-c C-a") 'lsp-execute-code-action)
  (define-key scala-mode-map (kbd "C-c C-f") 'lsp-format-buffer)
  (define-key scala-mode-map (kbd "C-c C-o") 'lsp-organize-imports)
  (define-key scala-mode-map (kbd "C-c C-b") 'lsp-metals-build-import))

(provide 'init)