Add NIP-01 compliant client code

lib/nostr/user.rb

@@ -0,0 +1,92 @@
+# frozen_string_literal: true
+
+require 'schnorr'
+require 'json'
+
+module Nostr
+  # Each user has a keypair. Signatures, public key, and encodings are done according to the
+  # Schnorr signatures standard for the curve secp256k1.
+  class User
+    # A pair of private and public keys
+    #
+    # @api public
+    #
+    # @example
+    #   user.keypair # #<Nostr::KeyPair:0x0000000107bd3550
+    #    @private_key="893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900",
+    #    @public_key="2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558">
+    #
+    # @return [KeyPair]
+    #
+    attr_reader :keypair
+
+    # Instantiates a user
+    #
+    # @api public
+    #
+    # @example Creating a user with no keypair
+    #   user = Nostr::User.new
+    #
+    # @example Creating a user with a keypair
+    #   user = Nostr::User.new(keypair: keypair)
+    #
+    # @param keypair [Keypair] A pair of private and public keys
+    # @param keygen [Keygen] A private key and public key generator
+    #
+    def initialize(keypair: nil, keygen: Keygen.new)
+      @keypair = keypair || keygen.generate_key_pair
+    end
+
+    # Builds an Event
+    #
+    # @api public
+    #
+    # @example Creating a note event
+    #   event = user.create_event(
+    #     kind: Nostr::EventKind::TEXT_NOTE,
+    #     content: 'Your feedback is appreciated, now pay $8'
+    #   )
+    #
+    # @param event_attributes [Hash]
+    # @option event_attributes [String] :pubkey 32-bytes hex-encoded public key of the event creator.
+    # @option event_attributes [Integer] :created_at Date of the creation of the vent. A UNIX timestamp, in seconds.
+    # @option event_attributes [Integer] :kind The kind of the event. An integer from 0 to 2.
+    # @option event_attributes [Array<Array>] :tags  An array of tags. Each tag is an array of strings.
+    # @option event_attributes [String] :content Arbitrary string.
+    #
+    # @return [Event]
+    #
+    def create_event(event_attributes)
+      event_fragment = EventFragment.new(**event_attributes.merge(pubkey: keypair.public_key))
+      event_sha256 = Digest::SHA256.hexdigest(JSON.dump(event_fragment.serialize))
+
+      signature = sign(event_sha256)
+
+      Event.new(
+        id: event_sha256,
+        pubkey: event_fragment.pubkey,
+        created_at: event_fragment.created_at,
+        kind: event_fragment.kind,
+        tags: event_fragment.tags,
+        content: event_fragment.content,
+        sig: signature
+      )
+    end
+
+    private
+
+    # Signs an event with the user's private key
+    #
+    # @api private
+    #
+    # @param event_sha256 [String] The SHA256 hash of the event.
+    #
+    # @return [String] The signature of the event.
+    #
+    def sign(event_sha256)
+      hex_private_key = Array(keypair.private_key).pack('H*')
+      hex_message = Array(event_sha256).pack('H*')
+      Schnorr.sign(hex_message, hex_private_key).encode.unpack1('H*')
+    end
+  end
+end