#lang racket/base

; No external crypto package dependency: sha256-bytes is provided by racket/base.
(require file/sha1
         file/md5)

(provide file-digest)

(define (digest->string v)
  (cond [(bytes? v) (bytes->hex-string v)]
        [(string? v) v]
        [else (format "~a" v)]))

(define (file-digest path [algorithm "sha256"])
  (define alg (string-downcase (format "~a" algorithm)))
  (call-with-input-file path
    (lambda (in)
      (cond [(member alg '("sha256" "sha-256" "sha2")) (digest->string (sha256-bytes in))]
            [(member alg '("md5")) (digest->string (md5 in))]
            [else (error 'file-digest "unsupported digest algorithm: ~a" algorithm)]))
    #:mode 'binary))