;;; nix-flake.el --- Transient interface to Nix flake commands -*- lexical-binding: t -*-

;; Keywords: nix, languages, tools, unix
;; Package-Requires: ((emacs "27.1") (transient "0.3"))
;; Homepage: https://github.com/NixOS/nix-mode

;;; Commentary:

;; This library provides transient interface to experimental commands in Nix.
;; See the Nix manual for more information available at
;; https://nixos.org/manual/nix/unstable/command-ref/experimental-commands.html

;;; Code:

(require 'nix)
(require 'transient)

(defgroup nix-flake nil
  "Nix flake commands."
  :group 'nix)

;;;; Custom variables

(defcustom nix-flake-init-post-action 'open-flake-nix
  "Action to run after successfully initializing a flake.

This action is run after a flake is successfully initialized by
`nix-flake-init` (or generally `nix-flake-dispatch`).

You can also specify a function, which should take no arguments.
It is called in the directory of the flake."
  :type '(choice (const :tag "Open flake.nix" open-flake-nix)
		 (const :tag "Do nothing" nil)
		 (function :tag "User-defined function")))

(defcustom nix-flake-add-to-registry t
  "Whether to add a new flake to registry.

When this variable is non-nil, every flake reference from the
interactive input is added to the flake registry, unless it is
already registered in either the user or the global registry."
  :type 'boolean)

;;;; Transient classes

;;;;; flake-ref

(defclass nix-flake-ref-variable (transient-variable)
  ((constant-value :initarg :constant-value :initform nil)
   (on-change :initarg :on-change)
   (reader :initarg :reader :initform nil)))

(cl-defmethod transient-init-value ((_obj nix-flake-ref-variable))
  "Set the initial value of the object.")

(cl-defmethod transient-infix-read ((obj nix-flake-ref-variable))
  "Determine the new value of the infix object OBJ."
  (if-let (value (oref obj constant-value))
      (if (symbolp value)
          (symbol-value value)
        value)
    (if-let (reader (oref obj reader))
	(funcall reader "Flake directory: " (oref obj value))
      (nix-flake--read-flake-ref nil (oref obj value)))))

(cl-defmethod transient-infix-set ((obj nix-flake-ref-variable) value)
  "Set the value of infix object OBJ to VALUE."
  (oset obj value value)
  (when-let (func (oref obj on-change))
    (funcall func value)))

(cl-defmethod transient-format-value ((_obj nix-flake-ref-variable))
  "Format the object's value for display and return the result."
  ;; Don't show the value
  "")

;;;; Utility functions

(defun nix-flake--to-list (x)
  "If X is not a list, make a singleton list containing it."
  (if (listp x)
      x
    (list x)))

;;;; Registry
;; Maybe we'll move these functions to a separate library named nix-registry.el.

(defun nix-flake--registry-list ()
  "Return a list of entries from the registry."
  (cl-flet
      ((split-entry
        (s)
        (split-string s "[[:space:]]+")))
    (thread-last (nix--process-lines "registry" "list")
      (mapcar #'split-entry))))

(defun nix-flake--registry-refs ()
  "Return a list of flake refs in the registry."
  (thread-last (nix-flake--registry-list)
    ;; I don't know if I should include flakes in the
    ;; system registry. It's ugly to display full
    ;; checksums, so I won't include them for now.
    (cl-remove-if-not (pcase-lambda (`(,type . ,_))
                        (member type '("user" "global"))))
    (mapcar (lambda (cells)
	      ;; Both references and referees are included in the output.
	      ;; It may be better to pick only one and show others as
	      ;; decoration, e.g. using marginalia, but it is not supported
	      ;; for now.
              (list (nth 1 cells)
                    (nth 2 cells))))
    (flatten-list)))

(defun nix-flake--registry-add-1 (flake-ref)
  "Add FLAKE-REF to the registry with a new name."
  (let ((name (read-string (format-message "Enter the registry name for %s: "
                                           flake-ref))))
    (unless (or (not name)
                (string-empty-p name))
      (start-process "nix registry add" "*nix registry add*"
                     nix-executable
                     "registry" "add" name flake-ref))))

;; This argument complies the standard reader interface of transient
;; just in case, but it may not be necessary.
(defun nix-flake--read-flake-ref (&optional prompt initial-input history)
  "Select a flake from the registry.

For PROMPT, INITIAL-INPUT, and HISTORY, see the documentation of
readers in transient.el."
  (let* ((registered-flakes (nix-flake--registry-refs))
         (input (string-trim
                 (completing-read (or prompt "Flake URL: ")
				  registered-flakes
                                  nil nil nil history initial-input))))
    (prog1 input
      (when (and nix-flake-add-to-registry
                 (not (member input registered-flakes)))
	(nix-flake--registry-add-1 input)))))

;;;; nix-flake command

;;;;; Variables

(defvar nix-flake-ref nil)

;;;;; Setting the flake
(transient-define-infix nix-flake:from-registry ()
  :class 'nix-flake-ref-variable
  :on-change
  (lambda (flake-ref)
    (nix-flake--set-flake flake-ref :remote t)
    (transient-update))
  :description "Select a flake from the registry")

(transient-define-infix nix-flake:flake-directory ()
  :class 'nix-flake-ref-variable
  :reader 'nix-flake--read-directory
  :on-change
  (lambda (flake-ref)
    (nix-flake--set-flake flake-ref)
    (transient-update))
  :description "Select a directory")

(defun nix-flake--read-directory (prompt &optional initial-input _history)
  "Select a directory containing a flake.

For PROMPT and INITIAL-INPUT, see the documentation of transient.el."
  (let ((input (string-remove-suffix "/" (read-directory-name prompt initial-input nil t))))
    (prog1 (expand-file-name input)
      (unless (file-exists-p (expand-file-name "flake.nix" input))
        (user-error "The selected directory does not contain flake.nix"))
      (when (and nix-flake-add-to-registry
                 (not (member (concat "path:" input)
			      (nix-flake--registry-refs))))
        (nix-flake--registry-add-1 input)))))

;;;;; --update-input

(defclass nix-flake--update-input-class (transient-option)
  ())

(transient-define-infix nix-flake-arg:update-input ()
  :class 'nix-flake--update-input-class
  :argument "--update-input"
  :reader 'nix-flake--read-input-path
  :prompt "Input: "
  :description "Update a specific flake path")

(cl-defmethod transient-format-value ((obj nix-flake--update-input-class))
  "Format --update-input arguments from OBJ."
  (let ((value (oref obj value)))
    (propertize (concat (oref obj argument)
                        (when value
                          (concat " " value)))
                'face (if value
                          'transient-value
                        'transient-inactive-value))))

(cl-defmethod transient-infix-value ((obj nix-flake--update-input-class))
  "Return the value of the suffix object OBJ."
  (when-let ((value (oref obj value)))
    (list (oref obj argument) value)))

(defun nix-flake--input-names ()
  "Return a list of inputs to the flake."
  (thread-last (nix--process-json "flake" "info" nix-flake-ref "--json")
    (alist-get 'locks)
    (alist-get 'nodes)
    (alist-get 'root)
    (alist-get 'inputs)
    (mapcar #'cdr)))

(defun nix-flake--read-input-path (prompt initial-input _history)
  "Read an input name of a flake from the user.

For PROMPT and INITIAL-INPUT, see the documentation of :reader in
transient.el."
  (completing-read prompt (nix-flake--input-names)
		   nil nil initial-input))

;;;;; Attribute names

(defvar nix-flake-outputs nil)

(defun nix-flake-system-attribute-names (types)
  "Return a list of output attributes of particular TYPES."
  (let ((system (intern (nix-system))))
    (thread-last nix-flake-outputs
      (mapcar (pcase-lambda (`(,type . ,alist))
		(when (memq type types)
		  (mapcar #'car (alist-get system alist)))))
      (apply #'append)
      (cl-remove-duplicates)
      (mapcar #'symbol-name))))

(defun nix-flake--run-attribute-names ()
  "Return possible attribute names for run command."
  (nix-flake-system-attribute-names '(apps packages)))

(defun nix-flake--build-attribute-names ()
  "Return possible attribute names for build command."
  (nix-flake-system-attribute-names '(packages)))

(defun nix-flake--default-run-p ()
  "Return non-nil if there is the default derivation for run command."
  (not (null (nix-flake-system-attribute-names '(defaultApp defaultPackage)))))

(defun nix-flake--default-build-p ()
  "Return non-nil if there is the default derivation for build command."
  (not (null (nix-flake-system-attribute-names '(defaultPackage)))))

;;;;; Building command lines

(defun nix-flake--options ()
  "Return a list of options for `nix-flake-dispatch'."
  (flatten-list (transient-args 'nix-flake-dispatch)))

(defun nix-flake--command (subcommand options flake-ref)
  "Build a command line for a Nix subcommand.

SUBCOMMAND is a string or a list of strings which is a subcommand of Nix.

OPTIONS is a list of options appended after FLAKE-REF.

COMMAND-ARGUMENTS is extra arguments to the
command after the flake reference."
  (concat nix-executable
          " "
          (mapconcat #'shell-quote-argument
                     `(,@(nix-flake--to-list subcommand)
                       ,flake-ref
		       ,@options)
                     " ")))

(defun nix-flake--installable-command (subcommand options flake-ref attribute
						  &optional extra-arguments)
  "Build a command line for a Nix subcommand.

This is like `nix-flake--command', but for a subcommand which
takes an installable as an argument. See the user manual of Nix
for what installable means.

SUBCOMMAND, OPTIONS, and FLAKE-REF are the same as in the
function. ATTRIBUTE is the name of a package, app, or anything
that refers to a derivation in the flake. It must be a string
that is concatenated with the sharp symbol in the installable
reference.

EXTRA-ARGUMENTS is a list of strings passed to the Nix command
after \"--\". Note that some commands such as \"nix build\" do
not take the extra arguments."
  (concat nix-executable
	  " "
          (mapconcat #'shell-quote-argument
                     `(,@(nix-flake--to-list subcommand)
		       ,(if attribute
			    (concat flake-ref "#" attribute)
			  flake-ref)
		       ,@options)
                     " ")
          (if extra-arguments
              (concat " -- " extra-arguments)
            "")))

;;;;; Individual subcommands

(defun nix-flake-run-attribute (options flake-ref attribute command-args)
  "Run an app in the current flake.

OPTIONS and FLAKE-REF are the same as in other Nix commands.
ATTRIBUTE is the name of a package or app in the flake, and
COMMAND-ARGS is an optional list of strings passed to the
application."
  (interactive (list (nix-flake--options)
                     nix-flake-ref
                     (completing-read "Nix app/package: "
                                      (nix-flake--run-attribute-names))
                     nil))
  (compile (nix-flake--installable-command "run" options flake-ref attribute
                                           command-args)))

(defun nix-flake-run-default (options flake-ref command-args)
  "Run the default app or package in the current flake.

For OPTIONS, FLAKE-REF, and COMMAND-ARGS, see the documentation of
`nix-flake-run-attribute'."
  (interactive (list (nix-flake--options)
                     nix-flake-ref
                     nil))
  (compile (nix-flake--installable-command "run" options flake-ref nil
                                           command-args)))

(defun nix-flake-build-attribute (options flake-ref attribute)
  "Build a derivation in the current flake.

For OPTIONS, FLAKE-REF, and ATTRIBUTE, see the documentation of
`nix-flake-run-attribute'."
  (interactive (list (nix-flake--options)
                     nix-flake-ref
                     (completing-read "Nix package: "
                                      (nix-flake--build-attribute-names))))
  (compile (nix-flake--installable-command "build" options flake-ref attribute)))

(defun nix-flake-build-default (options flake-ref)
  "Build the default package in the current flake.


For OPTIONS and FLAKE-REF, see the documentation of
`nix-flake-run-attribute'."
  (interactive (list (nix-flake--options)
                     nix-flake-ref))
  (compile (nix-flake--installable-command "build" options flake-ref nil)))

(defun nix-flake-check (options flake-ref)
  "Check the flake.

For OPTIONS and FLAKE-REF, see the documentation of
`nix-flake-run-attribute'."
  (interactive (list (nix-flake--options) nix-flake-ref))
  (compile (nix-flake--command '("flake" "check") options flake-ref)))

(defun nix-flake-lock (options flake-ref)
  "Create missing lock file entries.

For OPTIONS and FLAKE-REF, see the documentation of
`nix-flake-run-attribute'."
  (interactive (list (nix-flake--options) nix-flake-ref))
  (compile (nix-flake--command '("flake" "lock") options flake-ref)))

(defun nix-flake-update (options flake-ref)
  "Update the lock file.

For OPTIONS and FLAKE-REF, see the documentation of
`nix-flake-run-attribute'."
  (interactive (list (nix-flake--options) nix-flake-ref))
  (compile (nix-flake--command '("flake" "update") options flake-ref)))

;;;###autoload (autoload 'nix-flake-dispatch "nix-flake" nil t)
(transient-define-prefix nix-flake-dispatch (flake-ref &optional remote)
  "Run a command on a Nix flake."
  :value '("--print-build-logs")
  [:description
   nix-flake--description
   ("=r" nix-flake:from-registry)
   ("=d" nix-flake:flake-directory)]
  ["Arguments"
   ("-i" "Allow access to mutable paths and repositories" "--impure")
   ("-ui" nix-flake-arg:update-input)
   ("-nu" "Do not allow any updates to the flake's lock file" "--no-update-lock-file")
   ("-cl" "Commit changes to the flake's lock file" "--commit-lock-file")
   ("-L" "Print build logs" "--print-build-logs")]
  ["Installable commands"
   ("r" "Run attribute" nix-flake-run-attribute)
   ("R" "Run default" nix-flake-run-default :if nix-flake--default-run-p)
   ("b" "Build attribute" nix-flake-build-attribute)
   ("B" "Build default" nix-flake-build-default :if nix-flake--default-build-p)]
  ["Flake commands"
   ("c" "flake check" nix-flake-check)
   ("l" "flake lock" nix-flake-lock)
   ("u" "flake update" nix-flake-update)]
  (interactive (list (convert-standard-filename default-directory)))
  (nix-flake--set-flake flake-ref :remote remote)
  (transient-setup 'nix-flake-dispatch))

(cl-defun nix-flake--set-flake (flake-ref &key remote)
  "Set the flake of the transient interface.

FLAKE-REF and REMOTE should be passed down from `nix-flake-dispatch'."
  (setq nix-flake-ref flake-ref)
  (setq nix-flake-outputs
        (if remote
	    (nix--process-json "flake" "show" "--json" nix-flake-ref)
	  (let ((default-directory flake-ref))
            (nix--process-json "flake" "show" "--json")))))

(defun nix-flake--description ()
  "Describe the current flake."
  (concat "Flake: " nix-flake-ref))

;; A wrapper function for ensuring existence of flake.nix and flake.lock
;; in the project directory.
;;;###autoload
(cl-defun nix-flake (dir &key flake-ref)
  "Dispatch a transient interface for Nix commands.

DIR is a directory on the file system in which flake.nix resides.

Alternatively, you can specify FLAKE-REF which follows the syntax
of flake-url. It can refer to a remote url, a local file path, or
whatever supported by Nix."
  (interactive (pcase current-prefix-arg
                 ('(4) (list nil :flake-ref (nix-flake--read-flake-ref)))
		 ('(16) (if nix-flake-ref
			    (list nil :flake-ref nix-flake-ref)
			  (user-error "Last flake is unavailable")))
                 (_ (list default-directory))))
  (cl-assert (or (and (stringp dir) (file-directory-p dir))
                 flake-ref)
             nil
             "DIR or FLAKE-REF must be specified")
  (cond
   (flake-ref
    (nix-flake-dispatch flake-ref t))
   ((file-exists-p (expand-file-name "flake.lock" dir))
    (nix-flake-dispatch (nix-flake--directory-ref dir)))
   ((file-exists-p (expand-file-name "flake.nix" dir))
    (message "You have not created flake.lock yet, so creating it...")
    (let ((default-directory dir))
      (nix-flake--command '("flake" "lock") nil
                          (nix-flake--directory-ref dir))))
   (t
    (nix-flake-init-dispatch))))

(defun nix-flake--directory-ref (dir)
  "Return the flake ref for a local DIR."
  (expand-file-name dir))

;;;; nix flake init

;;;;; Setting the template repository

(defvar nix-flake-template-repository nil
  "Flake reference to the current template sets.")

(defvar nix-flake-template-name nil
  "Attribute name of the last used template.")

(defun nix-flake--init-source ()
  "Describe the current template repository for init command."
  (format "Template repository: %s" nix-flake-template-repository))

(transient-define-infix nix-flake-init:from-registry ()
  :class 'nix-flake-ref-variable
  :variable 'nix-flake-template-repository
  :description "Select from the registry")

(transient-define-infix nix-flake-init:default-templates ()
  :class 'nix-flake-ref-variable
  :variable 'nix-flake-template-repository
  :constant-value "flake:templates"
  :description "Use the default template set")

;;;;; Running the command

(defun nix-flake--init (flake-ref template-name)
  "Initialize a flake from a template.

FLAKE-REF must be a reference to a flake which contains the
template, TEMPLATE-NAME is the name of the template."
  ;; Save the selection state for later use.
  (setq nix-flake-template-repository flake-ref
        nix-flake-template-name template-name)
  (let ((proc (start-process "nix flake init"
                             "*nix flake init*"
                             nix-executable
                             "flake"
                             "init"
                             "-t"
                             (concat flake-ref "#" template-name))))
    (set-process-sentinel proc
			  (lambda (process _event)
			    (when (eq 'exit (process-status process))
			      (if (= 0 (process-exit-status process))
				  (nix-flake-init-post-action)
				(message "Returned non-zero from nix flake init")))))
    proc))

(defun nix-flake-init-post-action ()
  "Perform an post-process action depending on the configuration.

See `nix-flake-init-post-action' variable for details."
  (pcase nix-flake-init-post-action
    ('open-flake-nix
     (find-file "flake.nix"))
    ((pred functionp)
     (funcall nix-flake-init-post-action))))

;;;;; Selecting a template

(defun nix-flake--templates (flake-ref)
  "Return a list of templates in FLAKE-REF."
  (thread-last (nix--process-json "flake" "show" "--json" flake-ref)
    (alist-get 'templates)
    (mapcar #'car)
    (mapcar #'symbol-name)))

;; It might be better to use `transient-define-suffix', but I don't know for
;; sure.
(defun nix-flake-init-select-template ()
  "Select a template and initialize a flake."
  (interactive)
  (let* ((flake-ref (or nix-flake-template-repository
                        (nix-flake--read-flake-ref "Template repository: ")))
         (template-name (completing-read
                         (format-message "Select a template from %s: " flake-ref)
                         (nix-flake--templates flake-ref))))
    (nix-flake--init flake-ref template-name)))

;;;;; The transient interface

;;;###autoload (autoload 'nix-flake-init "nix-flake" nil t)
(transient-define-prefix nix-flake-init-dispatch (&optional flake-ref)
  "Scaffold a project from a template."
  [:description "Initialize a flake"]
  [:description
   nix-flake--init-source
   ("=r" nix-flake-init:from-registry)
   ("=d" nix-flake-init:default-templates)]
  ["Initialize a flake"
   ("t" "Select template" nix-flake-init-select-template)]
  (interactive (list nil))
  (when flake-ref
    (setq nix-flake-template-repository flake-ref))
  (transient-setup 'nix-flake-init-dispatch))

;;;###autoload
(defun nix-flake-init ()
  "Run \"nix flake init\" command via a transient interface."
  (interactive)
  (let* ((root (locate-dominating-file default-directory ".git"))
         (default-directory
           (if (and root
                    (not (file-equal-p root default-directory))
                    (yes-or-no-p (format-message
                                  "The directory %s is not the repository root. Change to %s?"
                                  default-directory root)))
               root
             default-directory)))
    (if (file-exists-p "flake.nix")
        (user-error "The directory already contains a flake")
      (nix-flake-init-dispatch))))

(provide 'nix-flake)
;;; nix-flake.el ends here