A not-crazy Paypal REST API interface.

paypal.rb

# Everything else was worse...
# https://developer.paypal.com/docs/api/
require 'rest_client'
require 'addressable/uri'
require 'thread'

class Paypal
  OAUTH2_IS_INCREDIBLY_SHITTY_COMEDY_TIME_PADDING = 10
  SANDBOX_URI = Addressable::URI.parse 'https://api.sandbox.paypal.com/v1'
  LIVE_URI = Addressable::URI.parse 'https://api.paypal.com/v1'

  def initialize(client_id, client_secret, mode='live')
    @client_id = client_id
    @client_secret = client_secret
    @uri = (mode == 'live' ? LIVE_URI : SANDBOX_URI)
    @semaphore = Mutex.new
  end

  def uri_for(path)
    uri = @uri.clone
    uri.path = uri.path + path
    uri
  end

  def refresh_token
    uri = uri_for '/oauth2/token'
    uri.user = @client_id
    uri.password = @client_secret
    res = execute :post, uri, grant_type: 'client_credentials'

    @semaphore.synchronize {
      @access_token = res[:access_token]
      @access_token_expiration = Time.now + res[:expires_in] - OAUTH2_IS_INCREDIBLY_SHITTY_COMEDY_TIME_PADDING
    }
  end

  def access_token_expired?
    return true if @access_token_expiration.nil? || Time.now > @access_token_expiration
    false
  end

  def execute(meth, uri, args={}, headers={}, &block)
    request_args = {
      method: meth,
      headers: headers.merge(accept: 'application/json', accept_language: 'en_US')
    }

    if meth == :get
      uri.query_values = args
    elsif meth == :post
      request_args[:payload] = args
    end

    request_args[:url] = uri.to_s

    JSON.parse RestClient::Request.execute(request_args, &block), symbolize_names: true
  end

  def execute_with_token(meth, uri, args=nil, headers={}, &block)
    refresh_token if access_token_expired?
    headers.merge! authorization: "Bearer #{@access_token}"
    execute meth, uri, args, headers, &block
  end

  def get(path, args=nil, headers={}, &block)
    execute_with_token :get, uri_for(path), headers, &block
  end

  def post(path, args, headers)
    execute_with_token :post, uri_for(path), args, headers, &block
  end
end