module Sprockets::DigestUtils

def detect_digest_class(bytes)

Returns Digest::Base or nil.

While not elegant, all the supported digests have a unique bytesize.

Internal: Detect digest class hash algorithm for digest bytes. 
def detect_digest_class(bytes)
  DIGEST_SIZES[bytes.bytesize]
end

def digest(obj)

Returns a String digest of the object.

obj - A JSON serializable object.

wicked fast. Microbenchmarks away!
This is used for generating cache keys, so its pretty important its

Internal: Generate a hexdigest for a nested JSON serializable object. 
def digest(obj)
  digest = digest_class.new
  ADD_VALUE_TO_DIGEST[obj.class].call(obj, digest)
  digest.digest
end

def digest_class

Returns a Digest::Base subclass.

Internal: Default digest class. 
def digest_class
  Digest::SHA256
end

def hexdigest_integrity_uri(hexdigest)

Returns a String or nil if hash algorithm is incompatible.

digest - The String hexbyte digest of the asset content.

as per the subresource integrity specification.
Public: Generate hash for use in the `integrity` attribute of an asset tag 
def hexdigest_integrity_uri(hexdigest)
  integrity_uri(unpack_hexdigest(hexdigest))
end

def integrity_uri(digest)

Returns a String or nil if hash algorithm is incompatible.

digest - The String byte digest of the asset content.

as per the subresource integrity specification.
Public: Generate hash for use in the `integrity` attribute of an asset tag 
def integrity_uri(digest)
  case digest
  when Digest::Base
    digest_class = digest.class
    digest = digest.digest
  when String
    digest_class = DIGEST_SIZES[digest.bytesize]
  else
    raise TypeError, "unknown digest: #{digest.inspect}"
  end
  if hash_name = HASH_ALGORITHMS[digest_class]
    "#{hash_name}-#{pack_base64digest(digest)}"
  end
end

def pack_base64digest(bin)

Returns base64 String.

bin - String bytes

Internal: Pack a binary digest to a base64 encoded string. 
def pack_base64digest(bin)
  [bin].pack('m0')
end

def pack_hexdigest(bin)

Returns hex String.

bin - String bytes

Internal: Pack a binary digest to a hex encoded string. 
def pack_hexdigest(bin)
  bin.unpack('H*').first
end

def pack_urlsafe_base64digest(bin)

Returns urlsafe base64 String.

bin - String bytes

Internal: Pack a binary digest to a urlsafe base64 encoded string. 
def pack_urlsafe_base64digest(bin)
  str = pack_base64digest(bin)
  str.tr!('+/'.freeze, '-_'.freeze)
  str.tr!('='.freeze, ''.freeze)
  str
end

def unpack_hexdigest(hex)

Returns binary String.

hex - String hex

Internal: Unpack a hex encoded digest string into binary bytes. 
def unpack_hexdigest(hex)
  [hex].pack('H*')
end