Implement NIP-19 bech32-encoded private and public keys

https://github.com/nostr-protocol/nips/blob/master/19.md

lib/nostr/key.rb

@@ -0,0 +1,102 @@
+# frozen_string_literal: true
+
+require 'bech32'
+
+module Nostr
+  # Abstract class for all keys
+  #
+  # @api private
+  #
+  class Key < String
+    # The regular expression for hexadecimal lowercase characters
+    #
+    # @return [Regexp] The regular expression for hexadecimal lowercase characters
+    #
+    FORMAT = /^[a-f0-9]+$/
+
+    # The length of the key in hex format
+    #
+    # @return [Integer] The length of the key in hex format
+    #
+    LENGTH = 64
+
+    # Instantiates a new key. Can't be used directly because this is an abstract class. Raises a +ValidationError+
+    #
+    # @see Nostr::PrivateKey
+    # @see Nostr::PublicKey
+    #
+    # @param [String] hex_value Hex-encoded value of the key
+    #
+    # @raise [ValidationError]
+    #
+    def initialize(hex_value)
+      validate_hex_value(hex_value)
+
+      super(hex_value)
+    end
+
+    # Instantiates a key from a bech32 string
+    #
+    # @api public
+    #
+    # @example
+    #   bech32_key = 'nsec1vl029mgpspedva04g90vltkh6fvh240zqtv9k0t9af8935ke9laqsnlfe5'
+    #   bech32_key.to_key # => #<Nostr::PublicKey:0x000000010601e3c8 @hex_value="...">
+    #
+    # @raise [Nostr::InvalidHRPError] if the bech32 string is invalid.
+    #
+    # @param [String] bech32_value The bech32 string representation of the key.
+    #
+    # @return [Key] the key.
+    #
+    def self.from_bech32(bech32_value)
+      entity = Bech32::Nostr::NIP19.decode(bech32_value)
+
+      raise InvalidHRPError.new(entity.hrp, hrp) unless entity.hrp == hrp
+
+      new(entity.data)
+    end
+
+    # Abstract method to be implemented by subclasses to provide the HRP (npub, nsec)
+    #
+    # @api private
+    #
+    # @return [String] The HRP
+    #
+    def self.hrp
+      raise 'Subclasses must implement this method'
+    end
+
+    # Converts the key to a bech32 string representation
+    #
+    # @api public
+    #
+    # @example Converting a private key to a bech32 string
+    #   public_key = Nostr::PrivateKey.new('67dea2ed018072d675f5415ecfaed7d2597555e202d85b3d65ea4e58d2d92ffa')
+    #   public_key.to_bech32 # => 'nsec1vl029mgpspedva04g90vltkh6fvh240zqtv9k0t9af8935ke9laqsnlfe5'
+    #
+    # @example Converting a public key to a bech32 string
+    #   public_key = Nostr::PublicKey.new('7e7e9c42a91bfef19fa929e5fda1b72e0ebc1a4c1141673e2794234d86addf4e')
+    #   public_key.to_bech32 # => 'npub10elfcs4fr0l0r8af98jlmgdh9c8tcxjvz9qkw038js35mp4dma8qzvjptg'
+    #
+    # @return [String] The bech32 string representation of the key
+    #
+    def to_bech32 = Bech32::Nostr::BareEntity.new(self.class.hrp, self).encode
+
+    protected
+
+    # Validates the hex value during initialization
+    #
+    # @api private
+    #
+    # @param [String] _hex_value The hex value of the key
+    #
+    # @raise [KeyValidationError] When the hex value is invalid
+    #
+    # @return [void]
+    #
+    def validate_hex_value(_hex_value)
+      raise 'Subclasses must implement this method'
+    end
+  end
+end