ltc payments

lib/invoice.rb

@@ -35,6 +35,19 @@ class Invoice < Sequel::Model(:invoices)
     (total * BigDecimal(gel_rate.to_s)).round(2)
   end
 
+  def ltc?
+    !ltc_address.to_s.strip.empty?
+  end
+
+  # The LTC amount to display / encode in the QR. Returns nil when no amount
+  # is known (address-only invoice).
+  def ltc_amount_due
+    return nil unless ltc?
+    return BigDecimal(ltc_amount.to_s) unless ltc_amount.nil?
+    return nil if ltc_rate.nil? || BigDecimal(ltc_rate.to_s).zero?
+    (total / BigDecimal(ltc_rate.to_s)).round(8)
+  end
+
   class << self
     def allocate_number(year = Date.today.year)
       prefix = "INV-#{year}-"
@@ -64,12 +77,37 @@ class Invoice < Sequel::Model(:invoices)
         pdf_key:        '',
         created_at:     Time.now.utc
       )
+      apply_ltc(invoice, params, subtotal)
       invoice.uuid = SecureRandom.uuid
       invoice
     end
 
     private
 
+    # LTC is opt-in: only populated when an address is given. Rate and amount
+    # are both optional; if amount is blank but rate is present, derive it.
+    def apply_ltc(invoice, params, subtotal)
+      address = params[:ltc_address].to_s.strip
+      return if address.empty?
+
+      invoice.ltc_address = address
+
+      rate = decimal_or_nil(params[:ltc_rate])
+      invoice.ltc_rate = rate
+
+      amount = decimal_or_nil(params[:ltc_amount])
+      amount ||= (subtotal / rate).round(8) if rate && !rate.zero?
+      invoice.ltc_amount = amount
+    end
+
+    def decimal_or_nil(raw)
+      s = raw.to_s.strip
+      return nil if s.empty?
+      BigDecimal(s)
+    rescue ArgumentError
+      nil
+    end
+
     def normalize_currency(c)
       c = c.to_s.upcase
       CURRENCIES.include?(c) or raise ArgumentError, "Unsupported currency: #{c}"

lib/invoice_pdf.rb

@@ -1,6 +1,7 @@
 require 'prawn'
 require 'prawn/table'
 require 'bigdecimal'
+require 'stringio'
 
 class InvoicePdf
   FONTS_DIR = File.join($root, 'public', 'fonts')
@@ -233,6 +234,9 @@ class InvoicePdf
       pdf.text "SWIFT: #{ISSUER[:swift]}"
       pdf.text "Beneficiary: #{ISSUER[:name_latin]}"
     end
+
+    draw_ltc(pdf) if @invoice.respond_to?(:ltc?) && @invoice.ltc?
+
     unless @invoice.notes.to_s.strip.empty?
       pdf.move_down 14
       pdf.fill_color COLOR_MUTED
@@ -243,7 +247,51 @@ class InvoicePdf
     end
   end
 
+  def draw_ltc(pdf)
+    amount  = @invoice.ltc_amount_due
+    qr_size = 78
+
+    pdf.move_down 12
+    pdf.fill_color COLOR_MUTED
+    pdf.font_size(8) { pdf.text 'PAY IN LITECOIN (LTC)', character_spacing: 1.5 }
+    pdf.fill_color COLOR_TEXT
+    pdf.move_down 4
+
+    # Fixed-height row: QR on the right (drawn with float so it doesn't advance
+    # the cursor), text column on the left. The outer bounding_box of height
+    # qr_size leaves the cursor exactly below the row when it ends.
+    qr_bytes = LtcQr.png(@invoice.ltc_address, amount)
+    pdf.bounding_box([0, pdf.cursor], width: pdf.bounds.width, height: qr_size) do
+      pdf.float do
+        pdf.bounding_box([pdf.bounds.right - qr_size, pdf.bounds.top], width: qr_size, height: qr_size) do
+          pdf.image StringIO.new(qr_bytes), width: qr_size, height: qr_size
+        end
+      end
+
+      pdf.bounding_box([0, pdf.bounds.top], width: pdf.bounds.width - qr_size - 16) do
+        pdf.font_size(9) do
+          if amount
+            pdf.text "Amount: #{fmt_ltc(amount)} LTC", style: :bold
+            if @invoice.ltc_rate
+              pdf.fill_color COLOR_MUTED
+              pdf.text "(rate 1 LTC = #{fmt_money(@invoice.ltc_rate)} #{@invoice.currency} at issue)", size: 8
+              pdf.fill_color COLOR_TEXT
+            end
+            pdf.move_down 3
+          end
+          pdf.text 'Address:'
+          pdf.font_size(8) { pdf.text @invoice.ltc_address }
+          pdf.move_down 3
+          pdf.fill_color COLOR_MUTED
+          pdf.font_size(7) { pdf.text 'Scan the QR with any Litecoin wallet to prefill the payment.' }
+          pdf.fill_color COLOR_TEXT
+        end
+      end
+    end
+  end
+
   def draw_footer(pdf)
+    # Static left-side line repeats on every page.
     pdf.repeat(:all) do
       pdf.canvas do
         pdf.fill_color COLOR_MUTED
@@ -252,17 +300,32 @@ class InvoicePdf
             "#{ISSUER[:name_latin]} · Tax ID #{ISSUER[:tax_id]} · Small Business (1% turnover tax)",
             at: [50, 25]
           )
-          pdf.draw_text("Page #{pdf.page_number}", at: [pdf.bounds.right - 50, 25])
         end
         pdf.fill_color COLOR_TEXT
       end
     end
+
+    # Page number must be stamped per page: inside repeat(:all), pdf.page_number
+    # resolves to the final page count for every page. number_pages substitutes
+    # <page>/<total> at finalization, once per actual page.
+    pdf.number_pages(
+      'Page <page> of <total>',
+      at:      [pdf.bounds.right - 90, -25],
+      width:   90,
+      align:   :right,
+      size:    8,
+      color:   COLOR_MUTED
+    )
   end
 
   def fmt_money(value)
     BigDecimal(value.to_s).round(2).to_s('F').then { |s| with_thousands(s) }
   end
 
+  def fmt_ltc(value)
+    BigDecimal(value.to_s).round(8).to_s('F').sub(/(\.\d*?)0+$/, '\\1').sub(/\.$/, '')
+  end
+
   def fmt_qty(value)
     bd = BigDecimal(value.to_s)
     bd.frac.zero? ? bd.to_i.to_s : bd.to_s('F')

lib/ltc_qr.rb

@@ -0,0 +1,30 @@
+require 'rqrcode'
+
+# Renders a Litecoin payment QR as PNG bytes for embedding in the PDF.
+# Encodes a BIP21-style URI: litecoin:<address>?amount=<ltc>
+module LtcQr
+  module_function
+
+  # `amount` is a BigDecimal LTC amount or nil (address-only QR).
+  def uri(address, amount)
+    base = "litecoin:#{address}"
+    return base if amount.nil?
+    # Trim trailing zeros so the wallet shows a clean amount; keep up to 8 dp.
+    amt = amount.round(8).to_s('F').sub(/\.?0+$/, '')
+    "#{base}?amount=#{amt}"
+  end
+
+  # Returns PNG bytes (binary string), sized for a crisp ~120pt PDF placement.
+  def png(address, amount, size: 480)
+    data = uri(address, amount)
+    qr = RQRCode::QRCode.new(data, level: :m)
+    qr.as_png(
+      bit_depth:    1,
+      border_modules: 2,
+      color:        'black',
+      fill:         'white',
+      module_px_size: 6,
+      resize_exactly_to: size
+    ).to_s
+  end
+end

lib/ltc_rate.rb

@@ -0,0 +1,57 @@
+require 'net/http'
+require 'json'
+require 'uri'
+require 'bigdecimal'
+
+# Fetches the current Litecoin price from CoinGecko (free, no API key).
+#
+# CoinGecko's simple/price supports usd and eur directly. GEL is not a
+# CoinGecko vs_currency we rely on, so GEL is derived from the invoice's own
+# captured gel_rate (USD->GEL): ltc_in_gel = ltc_in_usd * gel_rate.
+module LtcRate
+  ENDPOINT = 'https://api.coingecko.com/api/v3/simple/price'.freeze
+  SUPPORTED = %w[USD EUR].freeze
+  TIMEOUT = 6 # seconds
+
+  class Error < StandardError; end
+
+  module_function
+
+  # Returns a BigDecimal: the price of 1 LTC in `currency`.
+  # `gel_rate` (USD->GEL) is required only when currency == 'GEL'.
+  def fetch(currency, gel_rate: nil)
+    currency = currency.to_s.upcase
+
+    if currency == 'GEL'
+      raise Error, 'gel_rate required to derive LTC/GEL' if gel_rate.nil?
+      usd = fetch_simple('usd')
+      (usd * BigDecimal(gel_rate.to_s)).round(8)
+    elsif SUPPORTED.include?(currency)
+      fetch_simple(currency.downcase).round(8)
+    else
+      raise Error, "Unsupported currency: #{currency}"
+    end
+  end
+
+  def fetch_simple(vs)
+    uri = URI(ENDPOINT)
+    uri.query = URI.encode_www_form(ids: 'litecoin', vs_currencies: vs)
+
+    res = Net::HTTP.start(uri.host, uri.port, use_ssl: true,
+                          open_timeout: TIMEOUT, read_timeout: TIMEOUT) do |http|
+      http.get(uri.request_uri, 'Accept' => 'application/json')
+    end
+
+    raise Error, "CoinGecko HTTP #{res.code}" unless res.is_a?(Net::HTTPSuccess)
+
+    data = JSON.parse(res.body)
+    price = data.dig('litecoin', vs)
+    raise Error, "No price for #{vs} in response" if price.nil?
+
+    BigDecimal(price.to_s)
+  rescue JSON::ParserError => e
+    raise Error, "Bad JSON from CoinGecko: #{e.message}"
+  rescue Net::OpenTimeout, Net::ReadTimeout
+    raise Error, 'CoinGecko timed out'
+  end
+end