(library (sph web atom)
  (export
    atom-author
    atom-category
    atom-content-source
    atom-content-text
    atom-content-xhtml
    atom-contributor
    atom-entry
    atom-feed
    atom-link
    atom-person
    atom-text
    atom-text-xhtml
    atom-title
    sph-web-atom-description)
  (import
    (rnrs base)
    (sph)
    (sph time rfc3339)
    (only (guile) filter identity)
    (only (sph other) remove-keyword-associations))

  (define sph-web-atom-description "create atom syndication feeds with sxml")
  ;for creating the sxml for atom syndication feeds
  ;https://en.wikipedia.org/wiki/Atom_%28standard%29#Atom_compared_to_RSS_2.0
  ;http://atomenabled.org/developers/syndication/
  ;https://tools.ietf.org/html/rfc4287
  (define-syntax-rule (if-pass-string a proc) (if (string? a) (proc a) a))
  (define (integer/string->rfc3339 a) (if (string? a) a (utc->rfc3339 a)))

  (define-syntax-rules sxml-element ((name value) (list (q name) value))
    ((name-and-value) (list (q name-and-value) name-and-value)))

  (define-syntax-rules sxml-element-optional ((name value) (and value (sxml-element name value)))
    ((name-and-value) (and name-and-value (sxml-element name-and-value))))

  (define* (atom-person author? name #:key email uri)
    "boolean [#:email string #:uri string] -> sxml
     author or contributor"
    (pairs (if author? (q author) (q contributor)) (sxml-element name)
      (filter identity (list (sxml-element-optional email) (sxml-element-optional uri)))))

  (define (atom-author . a) "name [#:email string #:uri string] -> sxml" (apply atom-person #t a))

  (define (atom-contributor . a) "name [#:email string #:uri string] -> sxml"
    (apply atom-person #f a))

  (define* (atom-category term #:key label scheme)
    "string [#:scheme string #:label string] -> sxml"
    (list (q category)
      (pairs (q @) (sxml-element term)
        (filter identity (list (sxml-element-optional scheme) (sxml-element-optional label))))))

  (define* (atom-text tag #:key (type "text") . content)
    "symbol [#:type string] sxml ... -> sxml
     examples for type are \"text\", \"html\", \"xhtml\""
    (qq
      ( (unquote tag) (@ (type (unquote type)))
        (unquote-splicing (remove-keyword-associations content)))))

  (define* (atom-text-xhtml tag . content)
    "symbol sxml ... -> sxml
     wraps content in a div as required and sets the type appropriately"
    (qq
      ( (unquote tag) (@ (type "xhtml"))
        (div (@ (xmlns "http://www.w3.org/1999/xhtml")) (unquote-splicing content)))))

  (define* (atom-link href #:key hreflang length title type rel)
    "string [#:rel string #:type string #:hreflang string #:title string #:length integer] -> sxml"
    (list (q link)
      (pairs (q @) (sxml-element href)
        (filter identity
          (list (sxml-element-optional rel) (sxml-element-optional type)
            (sxml-element-optional hreflang) (sxml-element-optional title)
            (sxml-element-optional length))))))

  (define* (atom-content-source src #:key type) "string [#:type string] -> sxml"
    (list (q content)
      (pairs (q @) (sxml-element src) (filter identity (list (sxml-element-optional type))))))

  (define* (atom-content-text . a) "[#:type string] sxml ... -> sxml"
    (apply atom-text (q content) a))

  (define* (atom-content-xhtml . a)
    "sxml ... -> sxml
     wraps content in a div as required and sets the type appropriately"
    (apply atom-text-xhtml (q content) a))

  (define* (atom-rights . atom-text-arguments) "[#:type string] string/sxml ... -> sxml"
    (apply atom-text (q rights) atom-text-arguments))

  (define* (atom-summary . atom-text-arguments) "[#:type string] string/sxml ... -> sxml"
    (apply atom-text (q summary) atom-text-arguments))

  (define* (atom-subtitle . atom-text-arguments) "[#:type string] string/sxml ... -> sxml"
    (apply atom-text (q subtitle) atom-text-arguments))

  (define*
    (atom-entry id title updated #:key authors categories content contributors link published
      rights
      source
      summary)
    "::
     string string integer:utc-posix-time/string
     [#:authors string/atom-author/(atom-author ...)
     #:categories string/atom-category/(atom-category ...)
     #:contributors string/atom-contributor/(atom-contributor ...)
     #:link string/atom-link
     #:published integer:utc-posix-time/string
     #:source sxml
     #:summary text/atom-summary]
     ->
     sxml"
    (pairs (q entry) (sxml-element title)
      (sxml-element updated (integer/string->rfc3339 updated)) (sxml-element id)
      (filter identity
        (list (sxml-element-optional published (and published (integer/string->rfc3339 published)))
          (if-pass-string link atom-link) (if-pass-string authors atom-author)
          (if-pass-string contributors atom-contributor) (if-pass-string categories atom-category)
          (if-pass-string summary atom-summary) (if-pass-string rights atom-rights) source content))))

  (define*
    (atom-feed id title updated #:key categories contributors generator icon link logo rights
      subtitle
      authors
      .
      content)
    "::
     string/number string integer:utc-posix-time/string
     [#:authors string/atom-author/(atom-author ...)
     #:link string/atom-link
     #:categories string/atom-category/(atom-category ...)
     #:contributors string/atom-contributor/(atom-contributor ...) #:generator string
     #:icon string #:logo string #:rights string/atom-rights/(atom-rights ...)
     #:subtitle string/atom-subtitle/(atom-subtitles ...)]
     ->
     sxml"
    (pairs (q feed) (q (@ (xmlns "http://www.w3.org/2005/Atom")))
      (sxml-element title) (sxml-element updated (integer/string->rfc3339 updated))
      (sxml-element id)
      (append
        (filter identity
          (list (if-pass-string link atom-link) (if-pass-string authors atom-author)
            (if-pass-string categories atom-category) (if-pass-string contributors atom-contributor)
            (if-pass-string rights atom-rights) (if-pass-string subtitle atom-subtitle)
            (sxml-element-optional icon) (sxml-element-optional logo)
            (sxml-element-optional generator)))
        (remove-keyword-associations content)))))