#lang scheme/base
(require scheme/contract)

;; Git design, following the docs in
;;    http://eagain.net/articles/git-for-computer-scientists.
;;
;; I'm trying to straighten out my understanding of git's design
;; by trying to write equivalent data structure definitions.



;; Storage
(define-struct Blob (bytes))
(define-struct Tree (files subdirs))
(define-struct File (filename mode blob))
(define-struct Subdir (filename tree))
(define-struct Commit (tree parents body))
(define-struct Ref (ref))
(define-struct Remoteref (ref))
(define-struct Tag (commit message sig))

;; dag-node?: any -> boolean
;; Returns true if the datum is an element of the dag.
(define (dag-node? datum)
  (ormap (lambda (f) (f datum))
         (list Blob? Tree? Commit? Ref? Remoteref?)))


;; Contracts
(provide/contract
 [struct Blob ([bytes bytes?])]
 [struct Tree ([files (listof File?)]
               [subdirs (listof Subdir?)])]
 [struct File ([filename bytes?]
               [mode number?]
               [blob Blob?])]
 [struct Subdir ([filename bytes?]
                 [tree Tree?])]
 
 [struct Commit ([tree Tree?]
                 [parents (listof Tree?)]
                 [body bytes?])]
 [struct Ref ([ref dag-node?])]
 [struct Remoteref ([ref dag-node?])]
 [struct Tag ([commit Commit?]
              [message (or/c false/c bytes?)]
              [sig (or/c false/c bytes?)])])