Implement NIP-19 bech32-encoded private and public keys

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

spec/nostr/key_spec.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Key do
+  let(:subclass) do
+    Class.new(Nostr::Key) do
+      def self.hrp
+        'npub'
+      end
+
+      protected
+
+      def validate_hex_value(_hex_value) = nil
+    end
+  end
+
+  let(:valid_hex) { 'a' * 64 }
+
+  describe '.new' do
+    it 'raises an error because this is an abstract class' do
+      expect { described_class.new(valid_hex) }.to raise_error(/Subclasses must implement this method/)
+    end
+  end
+
+  describe '.from_bech32' do
+    context 'when given a valid Bech32 value' do
+      let(:valid_bech32) { 'npub10elfcs4fr0l0r8af98jlmgdh9c8tcxjvz9qkw038js35mp4dma8qzvjptg' }
+
+      it 'creates a new key' do
+        expect { subclass.from_bech32(valid_bech32) }.not_to raise_error
+      end
+    end
+
+    context 'when given an invalid Bech32 value' do
+      let(:invalid_bech32) { 'this is obviously not valid' }
+
+      it 'raises an error' do
+        expect { subclass.from_bech32(invalid_bech32) }.to raise_error(ArgumentError, /Invalid nip19 string\./)
+      end
+    end
+  end
+
+  describe '.hrp' do
+    context 'when called on the abstract class' do
+      it 'raises an error because this is an abstract method' do
+        expect { described_class.hrp }.to raise_error(/Subclasses must implement this method/)
+      end
+    end
+
+    context 'when called on a subclass' do
+      it 'returns the human readable part of a Bech32 string' do
+        expect(subclass.hrp).to eq('npub')
+      end
+    end
+  end
+
+  describe '#to_bech32' do
+    let(:key) { subclass.new(valid_hex) }
+
+    it 'returns a bech32 string representation of the key' do
+      expect(key.to_bech32).to match(/^npub[0-9a-z]+$/)
+    end
+  end
+
+  describe '#validate_hex_value' do
+    let(:invalid_hex) { 'g' * 64 }
+
+    it 'raises an error because this is an abstract method' do
+      expect { described_class.new(invalid_hex) }.to raise_error(/Subclasses must implement this method/)
+    end
+  end
+end