# frozen_string_literal: true

require 'openssl'
require 'active_support/security_utils'

module StrikeMe
  module API
    # Verifies the X-Webhook-Signature header Strike attaches to every
    # webhook POST — HMAC-SHA256 of the raw request body, keyed by the
    # secret set at webhook-subscription creation time. See
    # https://docs.strike.me/webhooks/signature-verification — this
    # mirrors Strike's own documented reference implementation exactly
    # (hex digest, timing-safe compare), just in Ruby.
    #
    # `raw_body` must be the exact bytes Strike sent, before any
    # JSON-parsing round-trip — re-serializing a parsed body can reorder
    # keys or change whitespace and silently break verification.
    module Webhook
      SIGNATURE_HEADER = 'X-Webhook-Signature'

      def self.valid_signature?(raw_body:, signature:, secret:)
        return false if signature.blank? || raw_body.blank?

        expected = OpenSSL::HMAC.hexdigest('SHA256', secret, raw_body)
        # Strike sends X-Webhook-Signature in UPPERCASE hex — confirmed
        # live against a real webhook delivery (payment.updated, a real
        # executed Lightning send) 2026-09-22. OpenSSL::HMAC.hexdigest
        # always returns lowercase. Without downcasing both sides here,
        # secure_compare's case-sensitive byte comparison rejected every
        # genuine Strike webhook as an invalid signature — silently: a
        # rejected webhook looks identical to an actual forgery attempt
        # from the outside, so this would have broken settlement in
        # production with no visible error at all. Their own docs'
        # reference implementation (docs.strike.me/webhooks/
        # signature-verification) doesn't mention this case difference.
        secure_compare(expected.downcase, signature.downcase)
      end

      # ActiveSupport::SecurityUtils.secure_compare raises on a length
      # mismatch rather than returning false — a garbled/truncated header
      # from a malformed request should fail closed, not raise.
      def self.secure_compare(expected, actual)
        return false unless expected.bytesize == actual.bytesize

        ActiveSupport::SecurityUtils.secure_compare(expected, actual)
      end
    end
  end
end