#!/bin/sh
#| -*- scheme -*-
exec csi -R r7rs -s "$0" "$@"
boudin --- a little static site generator
|#

(import (chicken file)
        (chicken file posix)
        (chicken irregex)
        (chicken pathname)
        (chicken port)
        (chicken process-context)
        (chicken random)
        (chicken string)
        (chicken time posix)
        (chicanery)
        (atom)
        (html-parser)
        (scss)
        (srfi 37)
        (srfi 152)
        (sxpath))

;;; Transformations
;; A static site generator can be thought of largely as two sets of
;; transformations: one transforming given input content to output content, and
;; another transforming source paths to destination paths.  Since both, for my
;; purposes, are strings, I have a generic function that can perform both
;; transformations.

(define (transform str . procs) #| string (string ->string) ... -> string
  Apply PROCS to STR, left-to-right, and return the result.
  Each PROC will be called with its predecessor's output, and should take a
  string as input and return a string. |#
  (if (null? procs)
      str
      (apply transform ((car procs) str) (cdr procs))))

;;; Path transformations

(define (indexify path) #| path -> path
  Replace the PATH's extension with "/index.html".
  |#
  (make-pathname (pathname-strip-extension path)
                 "index"
                 "html"))

(define (transform-path path outdir) #| path => path
  Transform PATH according to boudin's needs. |#
  (transform path
             normalize-pathname
             (lambda (p) (pathname-replace-directory p outdir))
             indexify))

;;; Content transformations

(define (split-paragraphs str) #| string -> (list string ...)
  Split STR into paragraphs.
  A paragraph is a contiguous series of text lines separated from other
  paragraphs by at least 2 newline \n characters.  This procedure collapses
  inter-paragraph space. |#
  (let loop ((lines (string-split str "\n"))
             (par '())
             (acc '()))
    (cond
     ((and (null? lines)                ; base case: no more lines
           (null? par))                 ; ... or pending paragraph
      (reverse acc))
     ((null? lines)                     ; add the final paragraph
      (loop '() '() (cons (apply string-append (reverse par)) acc)))
     ((equal? (car lines) "")           ; paragraph break
      (loop (cdr lines)
            '()
            (cons (apply string-append (reverse par)) acc)))
     (else                              ; line break
      (loop (cdr lines)
            (cons (string-append (car lines) "\n") par)
            acc)))))

(define (wrap-paragraphs str) #| string -> string
  Wrap naked paragraphs of STR in <p> tags.
  A 'naked' paragraph is one that doesn't begin with '<' (after optional
  beginning whitespace). |#
  (let loop ((pars (map string-trim (split-paragraphs str)))
             (acc '()))
    (cond
     ((null? pars)
      (apply string-append (reverse acc)))
     ((zero? (string-length (car pars)))
      (loop (cdr pars)
            acc))
     ((eq? #\< (string-ref (car pars) 0))
      (loop (cdr pars)
            (cons (car pars)
                  acc)))
     (else
      (loop (cdr pars)
            (cons (string-append "<p>" (car pars) "</p>\n")
                  acc))))))

(define (preprocess-text str) #| string -> string
  Preprocess STR before passing it to `expand-string'.
  For example, replace all '#' with '##' unless followed by a '{' or '('.
  |#
  (set! str (irregex-replace/all
             '(or (: #\# #\# (look-ahead (or #\{ #\()))
                  (: #\# (look-ahead (~ #\{ #\()))
                  (: #\# eos))
             str
             "##"))
  #;  (set! str (irregex-replace/all ; XXX: missing end paren
  '(: #\@ #\()
  str
  "#(sxml->html `("))
  ;; Return transformed string
  str)

(define (expand-string str) #| string -> string
  Expand STR by passing it in a port to CHICKEN's #<# string interpolation.
  Yes, this is as cursed as it sounds.

  To make it slightly less so, all # are duplicated to escape them, except for
  those before ( and {.  To escape /those/, double them. |#
  (let* ((delim (let loop ((attempt (number->string (pseudo-random-real))))
                  (if (irregex-search attempt str)
                      (loop (number->string (pseudo-random-real)))
                      attempt)))
         (template (make-concatenated-port
                    (open-input-string (string-append "#<#" delim "\n"))
                    (open-input-string (preprocess-text str))
                    (open-input-string (string-append "\n" delim "\n"))))
         (expanded (with-output-to-string
                     (lambda ()
                       (display (eval (read template)
                                      (interaction-environment)))))))
    (irregex-replace/all '(: "#<unspecified>"
                             (* whitespace))
                         expanded
                         "")))

(define (transform-content content) #| string -> string
  Transform CONTENT according to boudin's needs.
  This is the raw html, and will still need to be processed to extract metadata
  and to be further wrapped in a template. |#
  (transform content
             expand-string
             wrap-paragraphs))

;;; Pages
;; A <page> is a record type that wraps the two transformations outlined above.
;; It also includes the extracted metadata from the page for processing.

(define-record-type <page>
  (make-page url meta source dest source-path dest-path)
  page?
  (url page-url (setter page-url))
  (meta page-meta (setter page-meta))
  (source page-source)
  (dest page-dest (setter page-dest))
  (source-path page-source-path)
  (dest-path page-dest-path (setter page-dest-path)))

(define (%read-port port) #| port -> string
  Read PORT until it hits eof and return the results as a string.
  |#
  (let ((chunk-size 512))
    (let loop ((next (read-string chunk-size port))
               (blank? #f)
               (acc '()))
      (cond
       ((or (eof-object? next)
            (and blank? (equal? next "")))
        (close-input-port port)
        (apply string-append (reverse acc)))
       ((equal? next "")
        (loop (read-string chunk-size port)
              #t
              (cons next acc)))
       (else
        (loop (read-string chunk-size port)
              blank?
              (cons next acc)))))))

(define read-port #| (optional port) -> string
  Read PORT completely, returning the results as a string.
  PORT defaults to `current-input-port'.
  |#
  (case-lambda
    (() (%read-port (current-input-port)))
    ((p) (%read-port p))))

(define (file->page file) #| string -> <page>
  Convert FILE to an sxml tree after transforming it.
  This procedure returns both the sxml of the transformed content, but that
  page's metadata, too. |#
  (let* ((source (with-input-from-file file read-port))
         (dest (html->sxml (transform-content source))))
    (make-page (pathname-directory (transform-path file (site-base-url)))
               (extract-meta dest)
               source
               dest
               file
               (transform-path file (build-directory)))))

(define (extract-meta tree) #| sxml -> alist
  Extract metadata from TREE's comments.
  Returns an alist of (key . value) pairs where keys and values are strings. |#
  (let loop ((tree tree)
             (acc '()))
    (cond
     ((or (atom? tree)
          (null? tree))
      (reverse acc))
     ((and (list? (car tree))
           (eq? (caar tree) '*COMMENT*))
      (loop (cdr tree)
            (let* ((comment (string-trim-both (cadar tree)))
                   (lines (string-split comment "\n")))
              (map (lambda (l)
                     (let ((kv (string-split l ":")))
                       (cons (string-trim-both (car kv))
                             (string-trim
                              (string-intersperse (cdr kv) ":")))))
                   lines))))
     ((list? (car tree))
      (loop (cdr tree)
            (let ((subtree (loop (car tree) '())))
              (if (null? subtree)
                  acc
                  (cons subtree acc)))))
     (else (loop (cdr tree) acc)))))

(define (meta-ref meta key default) #| alist string string -> <?>
  Get KEY's value from META, or DEFAULT if it doesn't exist.
  DEFAULT is required because I think it's a good idea to require it. |#
  (let ((x (assoc key meta)))
    (if x (cdr x) default)))

(define (page-meta-ref page key default) #| <page> string string -> <?>
  Get KEY's value from PAGE's meta, or DEFAULT.
  |#
  (let ((meta (page-meta page)))
    (meta-ref meta key default)))

;;; Time
;; Time really only matters in feeds ... but it really does matter.  So I need a
;; few helper functions.

(define publish-time      ; this is a parameter so it's consistent across a run.
  (make-parameter
   (time->string (seconds->utc-time) "%FT%TZ")))

(define (page-mtime page) #| <page> -> time-string
  Grab the mtime field from PAGE's source file. |#
  (let ((file (page-source-path page)))
    (and file
         (file-exists? file)
         (time->string (seconds->utc-time
                        (file-modification-time
                         file))))))

(define (page-guess-updated page) #| <page> -> time-string
  Guess the "updated" property of PAGE. |#
  (let ((meta-date (page-meta-ref page "date" #f)))
    (if meta-date
        ;; Attempt to parse the date metadata field.
        (time->string (seconds->utc-time ; This double-conversion is /great/
                       (local-time->seconds
                        (or (string->time meta-date "%Y-%m-%d")
                            (string->time meta-date "%Y-%m-%d%n%H:%M")
                            (string->time meta-date "%Y-%m-%d%n%I:%M%n%p")
                            ;; ... more ?
                            (or (page-mtime page)
                                (publish-time))))))
        (or (page-mtime page)
            (publish-time)))))

;;; Templating
;; Templating uses sxml to define a layout for pages and indeces (index.html,
;; feed.xml).  Sxml's "stylesheets" can be used to extract metadata out of html
;; comments and to further process the document.

;; Each template has a default, but the user can override by defining templates
;; in .config.scm (see below).  All templates are function parameters that take
;; a page's sxml tree (argument PAGE) and return a string.

(define page-template
  (make-parameter
   (lambda (page)
     `(html (@ (lang "en"))
            (head (title ,(page-meta-ref page "title" "[untitled]"))
                  (link (@ (href "../style.css") ; relative
                           (rel "stylesheet")))
                  (meta (@ (name "viewport")
                           (content "initial-scale=1.0"))))
            (body ,(let ((title (page-meta-ref page "title" #f)))
                     (if title `(h1 ,title) ""))
                  ,@(cdr (page-dest page)))))))

(define index-template
  (make-parameter
   (lambda pages
     `(html (@ (lang "en"))
            (head (title ,(site-name))
                  (link (@ (href "./style.css") ; relative
                           (rel "stylesheet")))
                  (meta (@ (name "viewport")
                           (content "initial-scale=1.0"))))
            (body (h1 ,(site-name))
                  (ul
                   ,@(map (lambda (pg)
                            `(li (a (@ (href ,(page-url pg)))
                                    ,(page-meta-ref pg
                                                    "title"
                                                    (pathname-file
                                                     (page-source-path pg))))))
                          pages)))))))

(define feed-template
  (make-parameter
   (lambda pages
     (make-atom-doc
      (make-feed
       title: (make-title (site-name))
       id: (site-base-url)
       updated: (publish-time)       ; I don't like these semantics ..
       authors: (list (make-author name: (site-author)
                                   uri: (site-base-url)))
       links: (list (make-link type: 'html
                               uri-language: "en"
                               uri: (site-base-url))
                    (make-link relation: "self"
                               type: "application/atom+xml"
                               uri: (make-pathname
                                     (site-base-url) "feed" "xml")))
       rights: (make-rights (site-rights))
       generator: (make-generator "Boudin"
                                  uri: "https://git.acdw.net/boudin"
                                  version: "0.1.0")
       entries: (map (lambda (pg)
                       (make-entry
                        title: (make-title
                                (page-meta-ref pg "title" "[untitled]"))
                        links: (list (make-link type: 'html
                                                uri: (page-url pg)))
                        id: (page-url pg)
                        updated: (page-guess-updated pg)
                        ;;published:
                        content:
                        `(atom:content (@ (type "html"))
                                       ,(cdr (page-dest pg)))))
                     pages))))))

;;; Publishing

(define (write-style)
  (print-log "writing style")
  (with-output-to-file (make-pathname (build-directory) "style" "css")
    (lambda () (write-css (site-style)))))

(define (write-page page)
  (print-log "writing " (or (page-meta-ref page "title" #f)
                            (page-source-path page)))
  (create-directory (pathname-directory (page-dest-path page)) 'parents)
  (with-output-to-file (page-dest-path page)
    (lambda () (sxml-display-as-html ((page-template) page)))))

(define (write-index pages)
  (print-log "writing index")
  (with-output-to-file (make-pathname (build-directory) "index" "html")
    (lambda () (sxml-display-as-html (apply (index-template) pages)))))

(define (write-feed pages)
  (print-log "writing feed")
  (with-output-to-file (make-pathname (build-directory) "feed" "xml")
    (lambda () (write-atom-doc (apply (feed-template) pages)))))

;;; Configuration

;; Build configuration

(define build-directory
  (make-parameter "out/"))

(define build-config
  (make-parameter "config.scm"))

;; Site configuration

(define site-name
  (make-parameter "[A boudin web site]"))

(define site-base-url
  (make-parameter "https://example.com/"))

(define site-author
  (make-parameter "nobody"))

(define site-rights
  (make-parameter (string-append "(C) " (site-author))))

(define site-style
  (make-parameter
   `(css+ (body (font "20px/1.4 sans-serif")
                (max-width "48em")
                (padding "1em")
                (margin auto)))))

;;; Options & Operands (SRFI 37)

(define (print-log . xs)
  (with-output-to-port (current-error-port)
    (lambda () (apply print xs))))

(define (die error-code . xs)
  (apply print-log xs)
  (exit error-code))

(define usage
  (string-append
   "Usage: boudin [OPTIONS] FILE ...\n"
   "Options:\n"
   "-h, --help            show this help and exit\n"
   "-o DIR, --output DIR  build site to DIR (default: out/)\n"
   "Operands:\n"
   "FILE ...              files to build\n"))

(define opt/help
  (option '(#\h "help")                 ; Names
          #f                            ; Required arg?
          #f                            ; Optional arg?
          (lambda _                          ; Option proc (opt name arg seeds ...)
            (die 0 usage))))

(define opt/build-directory
  (option '(#\o "output") #t #f
          (lambda (opt name arg seeds)
            (build-directory arg)
            seeds)))

(define opt/build-config
  (option '(#\c "config") #t #f
          (lambda (opt name arg seeds)
            (build-config arg)
            seeds)))

(define (process-args args)
  (let ((pages '()))
    (args-fold args
               ;; Options
               (list opt/help
                     opt/build-directory
                     opt/build-config)
               ;; Unrecognized option proc (option name arg seeds ...)
               (lambda (_ name _ _)
                 (die 1 "Unrecognized option: -" name "\n" usage))
               ;; Operand proc (operand seeds ...)
               (lambda (name seeds)
                 (if (file-exists? name)
                     (set! pages (cons (file->page name) pages))
                     (die 2 "Page not found: " name))
                 seeds)
               ;; Seeds
               '())
    pages))

;;; Main entry point

(define pages (make-parameter #f))

(define (main args)
  (parameterize ((pages (process-args args)))
    (unless (pages)
      (die 0 "No pages to process.  Abort."))
    ;; Check for files, create directories
    (if (file-exists? (build-config))
        (load (build-config))
        (print-log "No config.scm found; using default config"))
    (create-directory (build-directory) 'parents)
    ;; Build the site
    (write-style)                       ; TODO: copy static assets (?)
    (for-each write-page (pages))
    (write-index (pages))
    (write-feed (pages))))

(cond-expand
  ((or chicken-script compiling)
   (main (command-line-arguments)))
  (else))