(local yaml (require :lyaml))

(local { : view } (require :fennel))

(fn basename [str ext]
  (-> str
      (string.gsub "(.*/)(.*)" "%2")
      (string.gsub (.. ext "$") "")))

(fn headline [name]
  (let [title (assert (basename name ".nix"))
        len (title:len)]
    (.. title "\n" (string.rep "=" len))))

(fn read-preamble [pathname]
  (let [pathname (if (string.match pathname ".nix$")
                     pathname
                     (.. pathname "/default.nix"))]
    (with-open [f (assert (io.open pathname :r))]
      (accumulate [lines nil
                   l (f:lines)
                   :until (not (= (string.sub l 1 2) "##"))]
        (.. (or lines "") (string.gsub l "^## *" "") "\n")))))

(fn relative-pathname [pathname]
  (let [pathname
        (if (string.match pathname ".nix$")
            pathname
            (.. pathname "/default.nix"))]
    (pick-values 1 (string.gsub pathname "^/nix/store/[^/]+/" "modules/"))))

(fn strip-newlines [text]
  (-> text
      (string.gsub "\n([^\n])" " %1")
      (string.gsub "\n\n+" "\n")))

(fn indent [n text]
  (let [margin (string.rep " " n)]
    (.. margin (string.gsub (or text "") "\n +" (.. "\n" margin )))))

(fn indent-literal [n text]
  (let [margin (string.rep " " n)]
    (.. margin (string.gsub (or text "") "\n" (.. "\n" margin )))))

(fn extract-text [description]
  (match description
    { :_type "literalExpression" : text } text
    (where s (= (type s) "string")) description
    _ nil))

(fn escape-backslash [s]
  (string.gsub s "\\" "\\\\"))

(fn print-option [o offset]
  (let [i (or offset 0)]
    (print (indent i (.. " * option ``" o.name "``")))
    (case (-?> o.description extract-text strip-newlines)
          descr (print (indent (+ 4 i) descr)))
    (print)
    (print (indent (+ 4 i) (.. "**type** " (escape-backslash o.type) "\n")))
    (when o.example
      (print (indent (+ 4 i) "**example**")) (print)
      (print (indent (+ 4 i) ".. code-block:: nix"))
      (print)
      (print (indent-literal (+ 8 i) (extract-text o.example)) "\n")
      (print))

    (when (extract-text o.default)
      (print (indent (+ 4 i) "**default**")) (print)
      (print (indent (+ 4 i) ".. code-block:: nix"))
      (print)
      (print (indent-literal (+ 8 i) (extract-text o.default)) "\n")
      (print))))

(fn print-service [o]
  (print (.. " * service ``" o.name "``"))
  (match (extract-text o.description)
    descr (print (indent 4 descr)))
  (print)
  (print (indent 4 "**Service parameters**\n"))
  (each [_ param (ipairs o.parameters)]
    (print-option param 4)))

(fn output? [option]
  (match option.loc
    ["system" "outputs" & _] true
    _ false))

(fn is-service? [o]
  (= o.type "parametrisable s6-rc service definition"))

(fn has-service? [module]
  (accumulate [found false
               _ o (ipairs module)]
    (or found (is-service? o))))

(fn sort-modules [modules]
  ;; modules containing services should sort _after_ modules
  ;; that contain only options
  (doto (icollect [n m (pairs modules)]
          { :name n :service? (has-service? m) :module m })
    (table.sort
     (fn [a b]
       (if (and a.service? (not b.service?))
           false
           (and b.service? (not a.service?))
           true
           (< a.name b.name))))))

(fn sort-options [module]
  (let [options (icollect [_ o (ipairs module)]
                  (if (not (output? o))
                      o))]
    (doto options (table.sort (fn [a b] (< a.name b.name))))))

(let [raw (yaml.load (io.read "*a"))
      modules {}]
  (each [_ option (ipairs raw)]
    (each [_ path (ipairs option.declarations)]
      (let [e (or (. modules path) [])]
        (table.insert e option)
        (tset modules path e))))
  (tset modules "lib/modules.nix" nil)
  (let [modules (sort-modules modules)]
    (each [_ {: name : module : service?} (ipairs modules)]
      (let [options (sort-options module)]
        (when (> (# options) 0)
          (print (or (read-preamble name) (headline name)))
          (when service?
            (print "**path** " (.. ":file:`" (relative-pathname name) "`")))
          (print)
          (each [_ o (ipairs options)]
            (if (is-service? o)
                (print-service o)
                (print-option o))))))))