Add a conversion method for different formats

lib/ksuid.rb

@@ -75,6 +75,28 @@ module KSUID
   # @return [String]
   MAX_STRING_ENCODED = 'aWgEPTl1tmebfsQzFP4bxwgy80V'
 
+  # Converts a KSUID-compatible value into an actual KSUID
+  #
+  # @api public
+  #
+  # @example Converts a base 62 KSUID string into a KSUID
+  #   KSUID.call('15Ew2nYeRDscBipuJicYjl970D1')
+  #
+  # @param ksuid [String, Array<Integer>, KSUID::Type] the KSUID-compatible value
+  # @return [KSUID::Type] the converted KSUID
+  # @raise [ArgumentError] if the value is not KSUID-compatible
+  def self.call(ksuid)
+    return unless ksuid
+
+    case ksuid
+    when KSUID::Type then ksuid
+    when Array then KSUID.from_bytes(ksuid)
+    when String then cast_string(ksuid)
+    else
+      raise ArgumentError, "Cannot convert #{ksuid.inspect} to KSUID"
+    end
+  end
+
   # The configuration for creating new KSUIDs
   #
   # @api private
@@ -167,4 +189,19 @@ def self.max
   def self.new(payload: nil, time: Time.now)
     Type.new(payload: payload, time: time)
   end
+
+  # Casts a string into a KSUID
+  #
+  # @api private
+  #
+  # @param ksuid [String] the string to convert into a KSUID
+  # @return [KSUID::Type] the converted KSUID
+  def self.cast_string(ksuid)
+    if Base62.compatible?(ksuid)
+      KSUID.from_base62(ksuid)
+    else
+      KSUID.from_bytes(ksuid)
+    end
+  end
+  private_class_method :cast_string
 end

spec/ksuid_spec.rb

@@ -12,4 +12,48 @@
 
     expect(KSUID.config.random_generator).to eq(generator)
   end
+
+  describe '.call' do
+    it 'returns KSUIDs in tact' do
+      ksuid = KSUID.new
+
+      result = KSUID.call(ksuid)
+
+      expect(result).to eq(ksuid)
+    end
+
+    it 'converts byte strings to KSUIDs' do
+      ksuid = KSUID.new
+
+      result = KSUID.call(ksuid.to_bytes)
+
+      expect(result).to eq(ksuid)
+    end
+
+    it 'converts byte arrays to KSUIDs' do
+      ksuid = KSUID.new
+
+      result = KSUID.call(ksuid.__send__(:uid))
+
+      expect(result).to eq(ksuid)
+    end
+
+    it 'converts base 62 strings to KSUIDs' do
+      ksuid = KSUID.new
+
+      result = KSUID.call(ksuid.to_s)
+
+      expect(result).to eq(ksuid)
+    end
+
+    it 'returns nil if passed nil' do
+      result = KSUID.call(nil)
+
+      expect(result).to be_nil
+    end
+
+    it 'raise an ArgumentError upon an unknown value' do
+      expect { KSUID.call(1) }.to raise_error(ArgumentError)
+    end
+  end
 end