;;; project.el --- Operations on the current project  -*- lexical-binding: t; -*-

;; Copyright (C) 2015 Free Software Foundation, Inc.

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This file contains generic infrastructure for dealing with
;; projects, some utility functions, and commands using that
;; infrastructure.
;;
;; The goal is to make it easier for Lisp programs to operate on the
;; current project, without having to know which package handles
;; detection of that project type, parsing its config files, etc.
;;
;; Infrastructure:
;;
;; Function `project-current', to determine the current project
;; instance, and 3 (at the moment) generic functions that act on it.
;; This list is to be extended in future versions.
;;
;; Utils:
;;
;; `project-combine-directories' and `project-subtract-directories',
;; mainly for use in the aborementioned generics' implementations.
;;
;; Commands:
;;
;; `project-find-regexp' and `project-or-external-find-regexp' use the
;; current API, and thus will work in any project that has an adapter.

;;; TODO:

;; * Commands `project-find-file' and `project-or-external-find-file'.
;;   Currently blocked on adding a new completion style that would let
;;   the user enter just the base file name (or a part of it), and get
;;   it expanded to the absolute file name.
;;
;; * Build tool related functionality.  Start with a `project-build'
;;   command, which should provide completions on tasks to run, and
;;   maybe allow entering some additional arguments.  This might
;;   be handled better with a separate API, though.  Then we won't
;;   force every project backend to be aware of the build tool(s) the
;;   project is using.
;;
;; * Command to (re)build the tag files in all project roots.  To that
;;   end, we might need to add a way to limit etags to certain files
;;   (e.g. have a whitelist, in addition to the blacklist provided by
;;   ignores), and/or allow specifying additional tag regexps.
;;
;; * UI for the user to be able to pick the current project for the
;;   whole Emacs session, independent of the current directory.  Or,
;;   in the more advanced case, open a set of projects, and have some
;;   project-related commands to use them all.  E.g., have a command
;;   to search for a regexp across all open projects.  Provide a
;;   history of projects that were opened in the past (storing it as a
;;   list of directories should suffice).

;;; Code:

(require 'cl-generic)

(defvar project-find-functions (list #'project-try-vc)
  "Special hook to find the project containing a given directory.
Each functions on this hook is called in turn with one
argument (the directory) and should return either nil to mean
that it is not applicable, or a project instance.")

;;;###autoload
(defun project-current (&optional maybe-prompt dir)
  "Return the project instance in DIR or `default-directory'.
When no project found in DIR, and MAYBE-PROMPT is non-nil, ask
the user for a different directory to look in."
  (unless dir (setq dir default-directory))
  (let ((pr (project--find-in-directory dir)))
    (cond
     (pr)
     (maybe-prompt
      (setq dir (read-directory-name "Choose the project directory: " dir nil t)
            pr (project--find-in-directory dir))
      (unless pr
        (user-error "No project found in `%s'" dir))))
    pr))

(defun project--find-in-directory (dir)
  (run-hook-with-args-until-success 'project-find-functions dir))

(cl-defgeneric project-roots (project)
  "Return the list of directory roots of the current project.

Most often it's just one directory which contains the project
build file and everything else in the project.  But in more
advanced configurations, a project can span multiple directories.

The directory names should be absolute.")

;; FIXME: Add MODE argument, like in `ede-source-paths'?
(cl-defgeneric project-external-roots (_project)
  "Return the list of external roots for PROJECT.

It's the list of directories outside of the project that are
still related to it.  If the project deals with source code then,
depending on the languages used, this list should include the
headers search path, load path, class path, and so on.

The rule of thumb for whether to include a directory here, and
not in `project-roots', is whether its contents are meant to be
edited together with the rest of the project."
  nil)

(cl-defgeneric project-ignores (_project _dir)
  "Return the list of glob patterns to ignore inside DIR.
Patterns can match both regular files and directories.
To root an entry, start it with `./'.  To match directories only,
end it with `/'.  DIR must be one of `project-roots' or
`project-external-roots'."
  (require 'grep)
  (defvar grep-find-ignored-files)
  (nconc
   (mapcar
    (lambda (dir)
      (concat dir "/"))
    vc-directory-exclusion-list)
   grep-find-ignored-files))

(defgroup project-vc nil
  "Project implementation using the VC package."
  :group 'tools)

(defcustom project-vc-ignores nil
  "List ot patterns to include in `project-ignores'."
  :type '(repeat string)
  :safe 'listp)

;; FIXME: Using the current approach, major modes are supposed to set
;; this variable to a buffer-local value.  So we don't have access to
;; the "external roots" of language A from buffers of language B, which
;; seems desirable in multi-language projects, at least for some
;; potential uses, like "jump to a file in project or external dirs".
;;
;; We could add a second argument to this function: a file extension,
;; or a language name.  Some projects will know the set of languages
;; used in them; for others, like VC-based projects, we'll need
;; auto-detection.  I see two options:
;;
;; - That could be implemented as a separate second hook, with a
;;   list of functions that return file extensions.
;;
;; - This variable will be turned into a hook with "append" semantics,
;;   and each function in it will perform auto-detection when passed
;;   nil instead of an actual file extension.  Then this hook will, in
;;   general, be modified globally, and not from major mode functions.
;;
;; The second option seems simpler, but the first one has the
;; advantage that the user could override the list of languages used
;; in a project via a directory-local variable, thus skipping
;; languages they're not working on personally (in a big project), or
;; working around problems in language detection (the detection logic
;; might be imperfect for the project in question, or it might work
;; too slowly for the user's taste).
(defvar project-vc-external-roots-function (lambda () tags-table-list)
  "Function that returns a list of external roots.

It should return a list of directory roots that contain source
files related to the current buffer.

The directory names should be absolute.  Used in the VC project
backend implementation of `project-external-roots'.")

(defun project-try-vc (dir)
  (let* ((backend (ignore-errors (vc-responsible-backend dir)))
         (root (and backend (ignore-errors
                              (vc-call-backend backend 'root dir)))))
    (and root (cons 'vc root))))

(cl-defmethod project-roots ((project (head vc)))
  (list (cdr project)))

(cl-defmethod project-external-roots ((project (head vc)))
  (project-subtract-directories
   (project-combine-directories
    (mapcar
     #'file-name-as-directory
     (funcall project-vc-external-roots-function)))
   (project-roots project)))

(cl-defmethod project-ignores ((project (head vc)) dir)
  (let* ((root (cdr project))
          backend)
    (append
     (when (file-equal-p dir root)
       (setq backend (vc-responsible-backend root))
       (mapcar
        (lambda (entry)
          (if (string-match "\\`/" entry)
              (replace-match "./" t t entry)
            entry))
        (vc-call-backend backend 'ignore-completion-table root)))
     (project--value-in-dir 'project-vc-ignores root)
     (cl-call-next-method))))

(defun project-combine-directories (&rest lists-of-dirs)
  "Return a sorted and culled list of directory names.
Appends the elements of LISTS-OF-DIRS together, removes
non-existing directories, as well as directories a parent of
whose is already in the list."
  (let* ((dirs (sort
                (mapcar
                 (lambda (dir)
                   (file-name-as-directory (expand-file-name dir)))
                 (apply #'append lists-of-dirs))
                #'string<))
         (ref dirs))
    ;; Delete subdirectories from the list.
    (while (cdr ref)
      (if (string-prefix-p (car ref) (cadr ref))
          (setcdr ref (cddr ref))
        (setq ref (cdr ref))))
    (cl-delete-if-not #'file-exists-p dirs)))

(defun project-subtract-directories (files dirs)
  "Return a list of elements from FILES that are outside of DIRS.
DIRS must contain directory names."
  ;; Sidestep the issue of expanded/abbreviated file names here.
  (cl-set-difference files dirs :test #'file-in-directory-p))

(defun project--value-in-dir (var dir)
  (with-temp-buffer
    (setq default-directory dir)
    (hack-dir-local-variables-non-file-buffer)
    (symbol-value var)))

(declare-function grep-read-files "grep")
(declare-function xref-collect-matches "xref")
(declare-function xref--show-xrefs "xref")
(declare-function xref-backend-identifier-at-point "xref")

;;;###autoload
(defun project-find-regexp (regexp)
  "Find all matches for REGEXP in the current project's roots.
With \\[universal-argument] prefix, you can specify the directory
to search in, and the file name pattern to search for."
  (interactive (list (project--read-regexp)))
  (let* ((pr (project-current t))
         (dirs (if current-prefix-arg
                   (list (read-directory-name "Base directory: "
                                              nil default-directory t))
                 (project-roots pr))))
    (project--find-regexp-in dirs regexp pr)))

;;;###autoload
(defun project-or-external-find-regexp (regexp)
  "Find all matches for REGEXP in the project roots or external roots.
With \\[universal-argument] prefix, you can specify the file name
pattern to search for."
  (interactive (list (project--read-regexp)))
  (let* ((pr (project-current t))
         (dirs (append
                (project-roots pr)
                (project-external-roots pr))))
    (project--find-regexp-in dirs regexp pr)))

(defun project--read-regexp ()
  (read-regexp "Find regexp"
               (xref-backend-identifier-at-point (xref-find-backend))))

(defun project--find-regexp-in (dirs regexp project)
  (require 'grep)
  (let* ((files (if current-prefix-arg
                    (grep-read-files regexp)
                  "*"))
         (xrefs (cl-mapcan
                 (lambda (dir)
                   (xref-collect-matches regexp files dir
                                         (project-ignores project dir)))
                 dirs)))
    (unless xrefs
      (user-error "No matches for: %s" regexp))
    (xref--show-xrefs xrefs nil)))

(provide 'project)
;;; project.el ends here