require 'net/http'
require 'net/https'
require 'delegate'
require 'thread'
require 'logger'

Seahorse::Client::NetHttp::Patches.apply!

module Seahorse
  module Client
    module NetHttp

      class ConnectionPool

        @pools_mutex = Mutex.new
        @pools = {}

        OPTIONS = {
          http_proxy: nil,
          http_open_timeout: 15,
          http_read_timeout: 60,
          http_idle_timeout: 5,
          http_continue_timeout: 1,
          http_wire_trace: false,
          logger: nil,
          ssl_verify_peer: true,
          ssl_ca_bundle: nil,
          ssl_ca_directory: nil,
          ssl_ca_store: nil,
        }

        # @api private
        def initialize(options = {})
          OPTIONS.each_pair do |opt_name, default_value|
            value = options[opt_name].nil? ? default_value : options[opt_name]
            instance_variable_set("@#{opt_name}", value)
          end
          @pool_mutex = Mutex.new
          @pool = Hash.new do |pool, endpoint|
            pool[endpoint] = []
            pool[endpoint]
          end
        end

        OPTIONS.keys.each do |attr_name|
          attr_reader(attr_name)
        end

        alias http_wire_trace? http_wire_trace
        alias ssl_verify_peer? ssl_verify_peer

        # Makes an HTTP request, yielding a Net::HTTPResponse object.
        #
        #   pool.request('http://domain', Net::HTTP::Get.new('/')) do |resp|
        #     puts resp.code # status code
        #     puts resp.to_h.inspect # dump the headers
        #     puts resp.body
        #   end
        #
        # @param [String] endpoint The HTTP(S) endpoint to
        #    connect to (e.g. 'https://domain.com').
        #
        # @param [Net::HTTPRequest] request The request to make.  This can be
        #   any request object from Net::HTTP (e.g. Net::HTTP::Get,
        #   Net::HTTP::POST, etc).
        #
        # @yieldparam [Net::HTTPResponse] net_http_response
        #
        # @return (see #session_for)
        def request(endpoint, request, &block)
          session_for(endpoint) do |http|
            yield(http.request(request))
          end
        end

        # @param [URI::HTTP, URI::HTTPS] endpoint The HTTP(S) endpoint
        #    to connect to (e.g. 'https://domain.com').
        #
        # @yieldparam [Net::HTTPSession] session
        #
        # @return [nil]
        def session_for(endpoint, &block)
          endpoint = remove_path_and_query(endpoint)
          session = nil

          # attempt to recycle an already open session
          @pool_mutex.synchronize do
            _clean
            session = @pool[endpoint].shift
          end

          begin
            session ||= start_session(endpoint)
            session.read_timeout = http_read_timeout
            session.continue_timeout = http_continue_timeout if
              session.respond_to?(:continue_timeout=)
            yield(session)
          rescue
            session.finish if session
            raise
          else
            # No error raised? Good, check the session into the pool.
            @pool_mutex.synchronize { @pool[endpoint] << session }
          end
          nil
        end

        # @return [Integer] Returns the count of sessions currently in the
        #   pool, not counting those currently in use.
        def size
          @pool_mutex.synchronize do
            size = 0
            @pool.each_pair do |endpoint,sessions|
              size += sessions.size
            end
            size
          end
        end

        # Removes stale http sessions from the pool (that have exceeded
        # the idle timeout).
        # @return [nil]
        def clean!
          @pool_mutex.synchronize { _clean }
          nil
        end

        # Closes and removes removes all sessions from the pool.
        # If empty! is called while there are outstanding requests they may
        # get checked back into the pool, leaving the pool in a non-empty
        # state.
        # @return [nil]
        def empty!
          @pool_mutex.synchronize do
            @pool.each_pair do |endpoint,sessions|
              sessions.each(&:finish)
            end
            @pool.clear
          end
          nil
        end

        private

        def remove_path_and_query(endpoint)
          endpoint.dup.tap do |e|
            e.path = ''
            e.query = nil
          end.to_s
        end

        class << self

          # Returns a connection pool constructed from the given options.
          # Calling this method twice with the same options will return
          # the same pool.
          #
          # @option options [URI::HTTP,String] :http_proxy A proxy to send
          #   requests through.  Formatted like 'http://proxy.com:123'.
          #
          # @option options [Float] :http_open_timeout (15) The number of
          #   seconds to wait when opening a HTTP session before rasing a
          #   `Timeout::Error`.
          #
          # @option options [Integer] :http_read_timeout (60) The default
          #   number of seconds to wait for response data.  This value can
          #   safely be set
          #   per-request on the session yeidled by {#session_for}.
          #
          # @option options [Float] :http_idle_timeout (5) The number of
          #   seconds a connection is allowed to sit idble before it is
          #   considered stale.  Stale connections are closed and removed
          #   from the pool before making a request.
          #
          # @option options [Float] :http_continue_timeout (1) The number of
          #   seconds to wait for a 100-continue response before sending the
          #   request body.  This option has no effect unless the request has
          #   "Expect" header set to "100-continue".  Defaults to `nil` which
          #   disables this behaviour.  This value can safely be set per
          #   request on the session yeidled by {#session_for}.
          #
          # @option options [Boolean] :http_wire_trace (false) When `true`,
          #   HTTP debug output will be sent to the `:logger`.
          #
          # @option options [Logger] :logger Where debug output is sent.
          #    Defaults to `nil` when `:http_wire_trace` is `false`.
          #    Defaults to `Logger.new($stdout)` when `:http_wire_trace` is
          #    `true`.
          #
          # @option options [Boolean] :ssl_verify_peer (true) When `true`,
          #   SSL peer certificates are verified when establishing a
          #   connection.
          #
          # @option options [String] :ssl_ca_bundle Full path to the SSL
          #   certificate authority bundle file that should be used when
          #   verifying peer certificates.  If you do not pass
          #   `:ssl_ca_bundle` or `:ssl_ca_directory` the the system default
          #   will be used if available.
          #
          # @option options [String] :ssl_ca_directory Full path of the
          #   directory that contains the unbundled SSL certificate
          #   authority files for verifying peer certificates.  If you do
          #   not pass `:ssl_ca_bundle` or `:ssl_ca_directory` the the
          #   system default will be used if available.
          #
          # @return [ConnectionPool]
          def for options = {}
            options = pool_options(options)
            @pools_mutex.synchronize do
              @pools[options] ||= new(options)
            end
          end

          # @return [Array<ConnectionPool>] Returns a list of of the
          #   constructed connection pools.
          def pools
            @pools.values
          end

          private

          # Filters an option hash, merging in default values.
          # @return [Hash]
          def pool_options options
            wire_trace = !!options[:http_wire_trace]
            logger = options[:logger] || Logger.new($stdout) if wire_trace
            verify_peer = options.key?(:ssl_verify_peer) ?
              !!options[:ssl_verify_peer] : true
            {
              :http_proxy => URI.parse(options[:http_proxy].to_s),
              :http_continue_timeout => options[:http_continue_timeout],
              :http_open_timeout => options[:http_open_timeout] || 15,
              :http_idle_timeout => options[:http_idle_timeout] || 5,
              :http_read_timeout => options[:http_read_timeout] || 60,
              :http_wire_trace => wire_trace,
              :logger => logger,
              :ssl_verify_peer => verify_peer,
              :ssl_ca_bundle => options[:ssl_ca_bundle],
              :ssl_ca_directory => options[:ssl_ca_directory],
              :ssl_ca_store => options[:ssl_ca_store],
            }
          end

        end

        private

        # Starts and returns a new HTTP(S) session.
        # @param [String] endpoint
        # @return [Net::HTTPSession]
        def start_session endpoint

          endpoint = URI.parse(endpoint)

          args = []
          args << endpoint.host
          args << endpoint.port
          args << http_proxy.host
          args << http_proxy.port
          args << http_proxy.user
          args << http_proxy.password

          http = ExtendedSession.new(Net::HTTP.new(*args.compact))
          http.set_debug_output(logger) if http_wire_trace?
          http.open_timeout = http_open_timeout

          if endpoint.scheme == 'https'
            http.use_ssl = true
            if ssl_verify_peer?
              http.verify_mode = OpenSSL::SSL::VERIFY_PEER
              http.ca_file = ssl_ca_bundle if ssl_ca_bundle
              http.ca_path = ssl_ca_directory if ssl_ca_directory
              http.cert_store = ssl_ca_store if ssl_ca_store
            else
              http.verify_mode = OpenSSL::SSL::VERIFY_NONE
            end
          else
            http.use_ssl = false
          end

          http.start
          http
        end

        # Removes stale sessions from the pool.  This method *must* be called
        # @note **Must** be called behind a `@pool_mutex` synchronize block.
        def _clean
          now = Time.now
          @pool.each_pair do |endpoint,sessions|
            sessions.delete_if do |session|
              if
                session.last_used.nil? or
                now - session.last_used > http_idle_timeout
              then
                session.finish
                true
              end
            end
          end
        end

        # Helper methods extended onto Net::HTTPSession objects opend by the
        # connection pool.
        # @api private
        class ExtendedSession < Delegator

          def initialize(http)
            super(http)
            @http = http
          end

          # @return [Time,nil]
          attr_reader :last_used

          def __getobj__
            @http
          end

          def __setobj__(obj)
            @http = obj
          end

          # Sends the request and tracks that this session has been used.
          def request(*args, &block)
            @last_used = Time.now
            @http.request(*args, &block)
          end

          # Attempts to close/finish the session without raising an error.
          def finish
            @http.finish
          rescue IOError
            nil
          end

        end
      end
    end
  end
end
