+As different bibtex types share common keys, it is advantageous to separate data extraction from json, and the formatting of the bibtex entry.
+
+#+BEGIN_SRC emacs-lisp :tangle doi-utils.el
+(setq doi-utils-json-metadata-extract
+ '((type (plist-get results :type))
+ (author (mapconcat (lambda (x) (concat (plist-get x :given) " " (plist-get x :family)))
+ (plist-get results :author) " and "))
+ (title (plist-get results :title))
+ (subtitle (plist-get results :subtitle))
+ (journal (plist-get results :container-title))
+ (series (plist-get results :container-title))
+ (publisher (plist-get results :publisher))
+ (volume (plist-get results :volume))
+ (issue (plist-get results :issue))
+ (number (plist-get results :issue))
+ (year (elt (elt (plist-get (plist-get results :issued) :date-parts) 0) 0))
+ (month (elt (elt (plist-get (plist-get results :issued) :date-parts) 0) 1))
+ (pages (plist-get results :page))
+ (doi (plist-get results :DOI))
+ (url (plist-get results :URL))
+ (booktitle (plist-get results :container-title))))
+#+END_SRC
+
+Next, we need to define the different bibtex types. Each type has a bibtex type (for output) and the type as provided in the doi record. Finally, we have to declare the fields we want to output.
+
+#+BEGIN_SRC emacs-lisp :tangle doi-utils.el :results none
+(setq doi-utils-bibtex-type-generators nil)
+
+(defun doi-utils-concat-prepare (lst &optional acc)
+ "Given a list `lst' of strings and other expressions, which are
+intented to passed to `concat', concat any subsequent strings,
+minimising the number of arguments being passed to `concat'
+without changing the results."
+ (cond ((null lst) (nreverse acc))
+ ((and (stringp (car lst))
+ (stringp (car acc)))
+ (doi-utils-concat-prepare (cdr lst) (cons (concat (car acc) (car lst))
+ (cdr acc))))
+ (t (doi-utils-concat-prepare (cdr lst) (cons (car lst) acc)))))
+
+(defmacro doi-utils-def-bibtex-type (name matching-types &rest fields)
+ "Define a BibTeX type identified by (symbol) `name' with
+`fields' (given as symbols), matching to retrieval expressions in
+`doi-utils-json-metadata-extract'. This type will only be used
+when the `:type' parameter in the JSON metadata is contained in
+`matching-types' - a list of strings."
+ `(push (lambda (type results)
+ (when (or ,@(mapcar (lambda (match-type) `(string= type ,match-type)) matching-types))
+ (let ,(mapcar (lambda (field)
+ (let ((field-expr (assoc field doi-utils-json-metadata-extract)))
+ (if field-expr
+ ;; need to convert to string first
+ `(,(car field-expr) (format "%s" ,(cadr field-expr)))
+ (error "unknown bibtex field type %s" field))))
+ fields)
+ (concat
+ ,@(doi-utils-concat-prepare
+ (-flatten
+ (list (concat "@" (symbol-name name) "{,\n")
+ ;; there seems to be some bug with mapcan,
+ ;; so we fall back to flatten
+ (mapcar (lambda (field)
+ `(" " ,(symbol-name field) " = {" ,field "},\n"))
+ fields)
+ "}\n")))))))
+ doi-utils-bibtex-type-generators))
+
+(doi-utils-def-bibtex-type article ("journal-article" "article-journal")
+ author title journal year volume number pages doi url)
+
+(doi-utils-def-bibtex-type inproceedings ("proceedings-article")
+ author title booktitle year month pages doi url)
+
+(doi-utils-def-bibtex-type book ("book")
+ author title series publisher year pages doi url)
+#+END_SRC
+
+With the code generating the bibtex entry in place, we can glue it to the json retrieval code.