require 'oauth2'
require 'faraday'
require 'faraday_middleware'
require 'base64'

# Initialize

options = {
  site: 'https://api.freee.co.jp',
  authorize_url: '/oauth/authorize',
  token_url: '/oauth/token'
}

client = OAuth2::Client.new(YOUR_APP_ID, YOUR_SECRET, options) do |conn|
  conn.request :url_encoded
  conn.request :json
  conn.response :json, content_type: /\bjson$/
  conn.adapter Faraday.default_adapter
end

# Getting authorized

AUTHORIZATION_BASE64_PACK = Base64.encode64("#{YOUR_APP_ID}:#{YOUR_SECRET}").gsub("\n", '')

params = {
  grant_type: 'authorization_code',
  code: AUTHORIZATION_CODE,
  redirect_uri: YOUR_REDIRECT_URI,
  headers: {
    'Content-Type' => 'application/json',
    'Authorization' => "Basic #{AUTHORIZATION_BASE64_PACK}"
  }
}

token = client.get_token(params).token

access_token = OAuth2::AccessToken.new(client, token)

# GET /api/1/users/me

access_token.get('/api/1/users/me?companies=true').response.env[:body]
# {
#   "user" =>
#     {
#       "email" => "freee@freee.co.jp",
#       "display_name" => "freee太郎,
#       "first_name" => "太郎",
#       "last_name" => "freee",
#       "first_name_kana" => "たろう",
#       "last_name_kana"=> "ふりー"
#       "companies" =>
#         {
#           "id" => "12345",
#           "display_name" => "freee株式会社",
#           "role" => "default"
#         }
#     }
# }

# GET /api/1/companies/:id

access_token.get('/api/1/companies/12345?details=true').response.env[:body]
# {
#   "company" =>
#     {
#       "id" => 12345,
#       "name" => "freee株式会社,
#       "name_kana" => "ふりーかぶしきがいしゃ",
#       "display_name"=> "freeeカブシキガイシャ",
#       "role" => "default",
#       "account_items" => {...},
#       "taxes" => {...},
#       "items" => {...},
#       "partners" => {...}
# }