;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2020 Katherine Cox-Buday <cox.katherine.e@gmail.com>
;;; Copyright © 2020 Helio Machado <0x2b3bfa0+guix@googlemail.com>
;;; Copyright © 2021 François Joulaud <francois.joulaud@radiofrance.com>
;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix 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 Guix 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 Guix.  If not, see <http://www.gnu.org/licenses/>.

;;; (guix import golang) attempts to make it easier to create Guix package
;;; declarations for Go modules.
;;;
;;; Modules in Go are a "collection of related Go packages" which are "the
;;; unit of source code interchange and versioning".  Modules are generally
;;; hosted in a repository.
;;;
;;; At this point it should handle correctly modules which have only Go
;;; dependencies and are accessible from proxy.golang.org (or configured via
;;; GOPROXY).
;;;
;;; We want it to work more or less this way:
;;; - get latest version for the module from GOPROXY
;;; - infer VCS root repo from which we will check-out source by
;;;   + recognising known patterns (like github.com)
;;;   + or recognizing .vcs suffix
;;;   + or parsing meta tag in HTML served at the URL
;;;   + or (TODO) if nothing else works by using zip file served by GOPROXY
;;; - get go.mod from GOPROXY (which is able to synthetize one if needed)
;;; - extract list of dependencies from this go.mod
;;;
;;; The Go module paths are translated to a Guix package name under the
;;; assumption that there will be no collision.

;;; TODO list
;;; - get correct hash in vcs->origin
;;; - print partial result during recursive imports (need to catch
;;;   exceptions)

(define-module (guix import go)
  #:use-module (guix build-system go)
  #:use-module ((guix download) #:prefix download:)
  #:use-module (guix git)
  #:use-module (guix import utils)
  #:use-module (guix import json)
  #:use-module (guix packages)
  #:use-module (guix upstream)
  #:use-module (guix utils)
  #:use-module ((guix licenses) #:prefix license:)
  #:use-module (guix base16)
  #:use-module (guix base32)
  #:use-module (guix memoization)
  #:use-module ((guix build download) #:prefix build-download:)
  #:use-module (htmlprag)
  #:use-module (ice-9 match)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 receive)
  #:use-module (ice-9 regex)
  #:use-module (json)
  #:use-module (rnrs io ports)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-11)
  #:use-module (srfi srfi-26)
  #:use-module (sxml xpath)
  #:use-module (web client)
  #:use-module (web response)
  #:use-module (web uri)

  #:export (go-module->guix-package
            go-module-recursive-import))

;;; Parameterize htmlprag to parse valid HTML more reliably.
(%strict-tokenizer? #t)

(define (go-path-escape path)
  "Escape a module path by replacing every uppercase letter with an
exclamation mark followed with its lowercase equivalent, as per the module
Escaped Paths specification (see:
https://godoc.org/golang.org/x/mod/module#hdr-Escaped_Paths)."
  (define (escape occurrence)
    (string-append "!" (string-downcase (match:substring occurrence))))
  (regexp-substitute/global #f "[A-Z]" path 'pre escape 'post))

(define (go-module-latest-version goproxy-url module-path)
  "Fetch the version number of the latest version for MODULE-PATH from the
given GOPROXY-URL server."
  (assoc-ref (json-fetch (format #f "~a/~a/@latest" goproxy-url
                                 (go-path-escape module-path)))
             "Version"))

(define (go-package-licenses name)
  "Retrieve the list of licenses that apply to NAME, a Go package or module
name (e.g. \"github.com/golang/protobuf/proto\").  The data is scraped from
the https://pkg.go.dev/ web site."
  (let*-values (((url) (string-append "https://pkg.go.dev/" name
                                      "?tab=licenses"))
                ((response body) (http-get url))
                ;; Extract the text contained in a h2 child node of any
                ;; element marked with a "License" class attribute.
                ((select) (sxpath `(// (* (@ (equal? (class "License"))))
                                        h2 // *text*))))
    (and (eq? (response-code response) 200)
         (match (select (html->sxml body))
           (() #f)                      ;nothing selected
           (licenses licenses)))))

(define (go-package-description name)
  "Retrieve a short description for NAME, a Go package name,
e.g. \"google.golang.org/protobuf/proto\".  The data is scraped from the
https://pkg.go.dev/ web site."
  (let*-values (((url) (string-append "https://pkg.go.dev/" name))
                ((response body) (http-get url))
                ;; Extract the text contained in a h2 child node of any
                ;; element marked with a "License" class attribute.
                ((select) (sxpath
                           `(// (section
                                 (@ (equal? (class "Documentation-overview"))))
                                (p 1)))))
    (and (eq? (response-code response) 200)
         (match (select (html->sxml body))
           (() #f)                      ;nothing selected
           (((p . strings))
            ;; The paragraph text is returned as a list of strings embedding
            ;; newline characters.  Join them and strip the newline
            ;; characters.
            (string-delete #\newline (string-join strings)))))))

(define (go-package-synopsis module-name)
  "Retrieve a short synopsis for a Go module named MODULE-NAME,
e.g. \"google.golang.org/protobuf\".  The data is scraped from
the https://pkg.go.dev/ web site."
  ;; Note: Only the *module* (rather than package) page has the README title
  ;; used as a synopsis on the https://pkg.go.dev web site.
  (let*-values (((url) (string-append "https://pkg.go.dev/" module-name))
                ((response body) (http-get url))
                ;; Extract the text contained in a h2 child node of any
                ;; element marked with a "License" class attribute.
                ((select) (sxpath
                           `(// (div (@ (equal? (class "UnitReadme-content"))))
                                // h3 *text*))))
    (and (eq? (response-code response) 200)
         (match (select (html->sxml body))
           (() #f)                      ;nothing selected
           ((title more ...)            ;title is the first string of the list
            (string-trim-both title))))))

(define (list->licenses licenses)
  "Given a list of LICENSES mostly following the SPDX conventions, return the
corresponding Guix license or 'unknown-license!"
  (filter-map (lambda (license)
                (and (not (string-null? license))
                     (not (any (cut string=? <> license)
                               '("AND" "OR" "WITH")))
                     ;; Adjust the license names scraped from
                     ;; https://pkg.go.dev to an equivalent SPDX identifier,
                     ;; if they differ (see: https://github.com/golang/pkgsite
                     ;; /internal/licenses/licenses.go#L174).
                     (or (spdx-string->license
                          (match license
                            ("BlueOak-1.0" "BlueOak-1.0.0")
                            ("BSD-0-Clause" "0BSD")
                            ("BSD-2-Clause" "BSD-2-Clause-FreeBSD")
                            ("GPL2" "GPL-2.0")
                            ("GPL3" "GPL-3.0")
                            ("NIST" "NIST-PD")
                            (_ license)))
                         'unknown-license!)))
              licenses))

(define (fetch-go.mod goproxy-url module-path version)
  "Fetch go.mod from the given GOPROXY-URL server for the given MODULE-PATH
and VERSION and return an input port."
  (let ((url (format #f "~a/~a/@v/~a.mod" goproxy-url
                     (go-path-escape module-path)
                     (go-path-escape version))))
    (build-download:http-fetch (string->uri url))))

(define (parse-go.mod port)
  "Parse the go.mod file accessible via the input PORT, returning a list of
requirements."
  ;; We parse only a subset of https://golang.org/ref/mod#go-mod-file-grammar
  ;; which we think necessary for our use case.
  (define (toplevel results)
    "Main parser, RESULTS is a pair of alist serving as accumulator for
     all encountered requirements and replacements."
    (let ((line (read-line)))
      (cond
       ((eof-object? line)
        ;; parsing ended, give back the result
        results)
       ((string=? line "require (")
        ;; a require block begins, delegate parsing to IN-REQUIRE
        (in-require results))
       ((string=? line "replace (")
        ;; a replace block begins, delegate parsing to IN-REPLACE
        (in-replace results))
       ((string-prefix? "require " line)
        ;; a require directive by itself
        (let* ((stripped-line (string-drop line 8))
               (new-results (require-directive results stripped-line)))
          (toplevel new-results)))
       ((string-prefix? "replace " line)
        ;; a replace directive by itself
        (let* ((stripped-line (string-drop line 8))
               (new-results (replace-directive results stripped-line)))
          (toplevel new-results)))
       (#t
        ;; unrecognised line, ignore silently
        (toplevel results)))))

  (define (in-require results)
    (let ((line (read-line)))
      (cond
       ((eof-object? line)
        ;; this should never happen here but we ignore silently
        results)
       ((string=? line ")")
        ;; end of block, coming back to toplevel
        (toplevel results))
       (#t
        (in-require (require-directive results line))))))

  (define (in-replace results)
    (let ((line (read-line)))
      (cond
       ((eof-object? line)
        ;; this should never happen here but we ignore silently
        results)
       ((string=? line ")")
        ;; end of block, coming back to toplevel
        (toplevel results))
       (#t
        (in-replace (replace-directive results line))))))

  (define (replace-directive results line)
    "Extract replaced modules and new requirements from replace directive
    in LINE and add to RESULTS."
    ;; ReplaceSpec = ModulePath [ Version ] "=>" FilePath newline
    ;;             | ModulePath [ Version ] "=>" ModulePath Version newline .
    (let* ((requirements (car results))
           (replaced (cdr results))
           (re (string-concatenate
                '("([^[:blank:]]+)([[:blank:]]+([^[:blank:]]+))?"
                  "[[:blank:]]+" "=>" "[[:blank:]]+"
                  "([^[:blank:]]+)([[:blank:]]+([^[:blank:]]+))?")))
           (match (string-match re line))
           (module-path (match:substring match 1))
           (version (match:substring match 3))
           (new-module-path (match:substring match 4))
           (new-version (match:substring match 6))
           (new-replaced (acons module-path version replaced))
           (new-requirements
            (if (string-match "^\\.?\\./" new-module-path)
                requirements
                (acons new-module-path new-version requirements))))
      (cons new-requirements new-replaced)))

  (define (require-directive results line)
    "Extract requirement from LINE and add it to RESULTS."
    (let* ((requirements (car results))
           (replaced (cdr results))
           ;; A line in a require directive is composed of a module path and
           ;; a version separated by whitespace and an optionnal '//' comment at
           ;; the end.
           (re (string-concatenate
                '("^[[:blank:]]*"
                  "([^[:blank:]]+)[[:blank:]]+([^[:blank:]]+)"
                  "([[:blank:]]+//.*)?")))
           (match (string-match re line))
           (module-path (match:substring match 1))
           ;; we saw double-quoted string in the wild without escape
           ;; sequences so we just trim the quotes
           (module-path (string-trim-both module-path #\"))
           (version (match:substring match 2)))
      (cons (acons module-path version requirements) replaced)))

  (with-input-from-port port
    (lambda ()
      (let* ((results (toplevel '(() . ())))
             (requirements (car results))
             (replaced (cdr results)))
        ;; At last we remove replaced modules from the requirements list
        (fold
         (lambda (replacedelem requirements)
           (alist-delete! (car replacedelem) requirements))
         requirements
         replaced)))))

(define (module-path->repository-root module-path)
  "Infer the repository root from a module path.  Go modules can be
defined at any level of a repository tree, but querying for the meta tag
usually can only be done from the web page at the root of the repository,
hence the need to derive this information."
  ;; See the following URL for the official Go equivalent:
  ;; https://github.com/golang/go/blob/846dce9d05f19a1f53465e62a304dea21b99f910/src/cmd/go/internal/vcs/vcs.go#L1026-L1087

  (define-record-type <vcs>
    (make-vcs url-prefix root-regex type)
    vcs?
    (url-prefix vcs-url-prefix)
    (root-regex vcs-root-regex)
    (type vcs-type))

  (define known-vcs
    (list
     (make-vcs
      "github.com"
      "^(github\\.com/[A-Za-z0-9_.\\-]+/[A-Za-z0-9_.\\-]+)(/[A-Za-z0-9_.\\-]+)*$"
      'git)
     (make-vcs
      "bitbucket.org"
      "^(bitbucket\\.org/([A-Za-z0-9_.\\-]+/[A-Za-z0-9_.\\-]+))(/[A-Za-z0-9_.\\-]+)*$"
      'unknown)
     (make-vcs
      "hub.jazz.net/git/"
      "^(hub\\.jazz\\.net/git/[a-z0-9]+/[A-Za-z0-9_.\\-]+)(/[A-Za-z0-9_.\\-]+)*$"
      'git)
     (make-vcs
      "git.apache.org"
      "^(git\\.apache\\.org/[a-z0-9_.\\-]+\\.git)(/[A-Za-z0-9_.\\-]+)*$"
      'git)
     (make-vcs
      "git.openstack.org"
      "^(git\\.openstack\\.org/[A-Za-z0-9_.\\-]+/[A-Za-z0-9_.\\-]+)(\\.git)?\
(/[A-Za-z0-9_.\\-]+)*$"
      'git)))

  ;; For reference, see: https://golang.org/ref/mod#vcs-find.
  (define vcs-qualifiers '(".bzr" ".fossil" ".git" ".hg" ".svn"))

  (define (vcs-qualified-module-path->root-repo-url module-path)
    (let* ((vcs-qualifiers-group (string-join vcs-qualifiers "|"))
           (pattern (format #f "^(.*(~a))(/|$)" vcs-qualifiers-group))
           (m (string-match pattern module-path)))
      (and=> m (cut match:substring <> 1))))

  (or (and=> (find (lambda (vcs)
                     (string-prefix? (vcs-url-prefix vcs) module-path))
                   known-vcs)
             (lambda (vcs)
               (match:substring (string-match (vcs-root-regex vcs)
                                              module-path) 1)))
      (vcs-qualified-module-path->root-repo-url module-path)
      module-path))

(define (go-module->guix-package-name module-path)
  "Converts a module's path to the canonical Guix format for Go packages."
  (string-downcase (string-append "go-" (string-replace-substring
                                         (string-replace-substring
                                          module-path
                                          "." "-")
                                         "/" "-"))))

(define-record-type <module-meta>
  (make-module-meta import-prefix vcs repo-root)
  module-meta?
  (import-prefix module-meta-import-prefix)
  (vcs module-meta-vcs)                 ;a symbol
  (repo-root module-meta-repo-root))

(define (fetch-module-meta-data module-path)
  "Retrieve the module meta-data from its landing page.  This is necessary
because goproxy servers don't currently provide all the information needed to
build a package."
  ;; <meta name="go-import" content="import-prefix vcs repo-root">
  (let* ((port (build-download:http-fetch
                (string->uri (format #f "https://~a?go-get=1" module-path))))
         (select (sxpath `(// head (meta (@ (equal? (name "go-import"))))
                              // content))))
    (match (select (call-with-port port html->sxml))
      (() #f)                         ;nothing selected
      (((content content-text))
       (match (string-split content-text #\space)
         ((root-path vcs repo-url)
          (make-module-meta root-path (string->symbol vcs) repo-url)))))))

(define (module-meta-data-repo-url meta-data goproxy-url)
  "Return the URL where the fetcher which will be used can download the
source."
  (if (member (module-meta-vcs meta-data) '(fossil mod))
      goproxy-url
      (module-meta-repo-root meta-data)))

(define (vcs->origin vcs-type vcs-repo-url version)
  "Generate the `origin' block of a package depending on what type of source
control system is being used."
  (case vcs-type
    ((git)
     `(origin
        (method git-fetch)
        (uri (git-reference
              (url ,vcs-repo-url)
              (commit (go-version->git-ref version))))
        (file-name (git-file-name name version))
        (sha256
         (base32
          ;; FIXME: populate hash for git repo checkout
          "0000000000000000000000000000000000000000000000000000"))))
    ((hg)
     `(origin
        (method hg-fetch)
        (uri (hg-reference
              (url ,vcs-repo-url)
              (changeset ,version)))
        (file-name (string-append name "-" version "-checkout"))
        (sha256
         (base32
          ;; FIXME: populate hash for hg repo checkout
          "0000000000000000000000000000000000000000000000000000"))))
    ((svn)
     `(origin
        (method svn-fetch)
        (uri (svn-reference
              (url ,vcs-repo-url)
              (revision (string->number version))))
        (file-name (string-append name "-" version "-checkout"))
        (sha256
         (base32
          ;; FIXME: populate hash for svn repo checkout
          "0000000000000000000000000000000000000000000000000000"))))
    (else
     (raise-exception (format #f "unsupported vcs type: ~a" vcs-type)))))

(define* (go-module->guix-package module-path #:key
                                  (goproxy-url "https://proxy.golang.org"))
  (let* ((latest-version (go-module-latest-version goproxy-url module-path))
         (port (fetch-go.mod goproxy-url module-path latest-version))
         (dependencies (map car (call-with-port port parse-go.mod)))
         (guix-name (go-module->guix-package-name module-path))
         (root-module-path (module-path->repository-root module-path))
         ;; The VCS type and URL are not included in goproxy information. For
         ;; this we need to fetch it from the official module page.
         (meta-data (fetch-module-meta-data root-module-path))
         (vcs-type (module-meta-vcs meta-data))
         (vcs-repo-url (module-meta-data-repo-url meta-data goproxy-url))
         (synopsis (go-package-synopsis root-module-path))
         (description (go-package-description module-path))
         (licenses (go-package-licenses module-path)))
    (values
     `(package
        (name ,guix-name)
        ;; Elide the "v" prefix Go uses
        (version ,(string-trim latest-version #\v))
        (source
         ,(vcs->origin vcs-type vcs-repo-url latest-version))
        (build-system go-build-system)
        (arguments
         '(#:import-path ,root-module-path))
        ,@(maybe-inputs (map go-module->guix-package-name dependencies))
        (home-page ,(format #f "https://~a" root-module-path))
        (synopsis ,synopsis)
        (description ,description)
        (license ,(and=> licenses list->licenses)))
     dependencies)))

(define go-module->guix-package* (memoize go-module->guix-package))

(define* (go-module-recursive-import package-name
                                     #:key (goproxy-url "https://proxy.golang.org"))
  (recursive-import
   package-name
   #:repo->guix-package (lambda* (name . _)
                          (go-module->guix-package*
                           name
                           #:goproxy-url goproxy-url))
   #:guix-name go-module->guix-package-name))