(import (Alpha Core))
(import (Alpha String))
(import (only (Alpha String) replace))
(import (only (ice-9 ftw) scandir))
(import (only (srfi srfi-1) remove))

;; general functions

(define (os.listdir path)
  (scandir path))

(define (os.path.expanduser path)
  (let ([home (getenv "HOME")])
    (replace path "~" home)))

(define (rm ls item)
  (remove (/. x (eq? x item)) ls))

(define (set.difference s1 s2)
  (cond [(null? s1) '()]
        [(not (member? (first s1) s2))
         (cons (first s1) (set.difference (rest s1) s2))]
        [else
         (set.difference (rest s1) s2)]))

;; z program

(define *zdir* (os.path.expanduser "~/test-z-wiki"))

;; A node 'id' is a monotonically increasing number.

;; It can be represented as a string, in which case it is encoded in
;; base 36.

(define (id->string id)
  (number->string id 36))

(define (string->id s)
  (string->number s 36))

;; It can be represented as a path, in which case it is
;; `<*zdir*>/<string>.md'

(define (path->id fname)
  "Given a path, parse out the node id."
  (-> fname
      (replace ".md" "")
      (replace *zdir* "")
      (string->id)))

(define (id->path id)
  "Given an id, return the absolute path to the file."
  (fmt "~a/~a.md"
       *zdir*
       (id->string id)))

;; Manipulating nodes

(define (list-nodes dir)
  (->> dir
       (os.listdir)
       ;; remove '.' and '..'
       ((/. s (set.difference s '("." ".."))))
       (map path->id)))

(define (latest-node ls)
  (if (eq? ls '())
      0
      (apply max ls)))

(define (make-node title)
  (let ([id (inc (-> *zdir* list-nodes latest-node))])
    (call-with-output-file (id->path id)
      (fn [file]
          (format file "title: ~a" title)
          (newline file)))))