(use-modules ((gnu packages haskell-xyz) #:select (pandoc))
	     ((gnu packages python) #:select (python))
	     (guix build utils)
	     (guix gexp))

(define (build-post post)
  (computed-file (basename post ".md")
		 (with-imported-modules '((guix build utils))
		   #~(begin
		       (use-modules (guix build utils))

		       (let ((posts-directory (string-append #$output "/posts/")))
			 (mkdir-p posts-directory)
			 (invoke #$(file-append pandoc "/bin/pandoc")
				 "--from" "markdown"
				 "--to" "html"
				 "--standalone"
				 "--output" (string-append posts-directory
							   #$(basename post ".md")
							   ".html")
				 #$(local-file post)))))))

(define (build-index posts)
  (computed-file "blog-index"
		 (with-imported-modules '((guix build utils))
		   #~(begin
		       (use-modules (guix build utils))

		       (invoke #$(file-append python "/bin/python3")
			       #$(local-file "generate-index.py")
			       "index.md"
			       #$@(map (lambda (file)
					 (local-file file))
				       posts))
		       (mkdir #$output)
		       (invoke #$(file-append pandoc "/bin/pandoc")
			       "--from" "markdown"
			       "--to" "html"
			       "--standalone"
			       "--metadata" "title=My blog"
			       "--output" (string-append #$output "/index.html")
			       "index.md")))))

(let ((posts (find-files "posts" "\\.md$")))
  (directory-union "blog"
		   (cons (build-index posts)
			 (map build-post posts))))