// parseConsistency is used to parse the ?stale and ?consistent query params.
// Returns true on error
func parseConsistency(resp http.ResponseWriter, req *http.Request, b *structs.QueryOptions) bool {
	query := req.URL.Query()
	if _, ok := query["stale"]; ok {
		b.AllowStale = true
	}
	if _, ok := query["consistent"]; ok {
		b.RequireConsistent = true
	}
	if b.AllowStale && b.RequireConsistent {
		resp.WriteHeader(400)
		resp.Write([]byte("Cannot specify ?stale with ?consistent, conflicting semantics."))
		return true
	}
	return false
}

// parseWait is used to parse the ?wait and ?index query params
// Returns true on error
func parseWait(resp http.ResponseWriter, req *http.Request, b *structs.QueryOptions) bool {
	query := req.URL.Query()
	if wait := query.Get("wait"); wait != "" {
		dur, err := time.ParseDuration(wait)
		if err != nil {
			resp.WriteHeader(400)
			resp.Write([]byte("Invalid wait time"))
			return true
		}
		b.MaxQueryTime = dur
	}
	if idx := query.Get("index"); idx != "" {
		index, err := strconv.ParseUint(idx, 10, 64)
		if err != nil {
			resp.WriteHeader(400)
			resp.Write([]byte("Invalid index"))
			return true
		}
		b.MinQueryIndex = index
	}
	return false
}

// blockingRPC is used for queries that need to wait for a
// minimum index. This is used to block and wait for changes.
func (s *Server) blockingRPC(b *structs.QueryOptions, m *structs.QueryMeta,
	tables MDBTables, run func() error) error {
	var timeout <-chan time.Time
	var notifyCh chan struct{}

	// Fast path non-blocking
	if b.MinQueryIndex == 0 {
		goto RUN_QUERY
	}

	// Sanity check that we have tables to block on
	if len(tables) == 0 {
		panic("no tables to block on")
	}

	// Restrict the max query time
	if b.MaxQueryTime > maxQueryTime {
		b.MaxQueryTime = maxQueryTime
	}

	// Ensure a time limit is set if we have an index
	if b.MinQueryIndex > 0 && b.MaxQueryTime == 0 {
		b.MaxQueryTime = maxQueryTime
	}

	// Setup a query timeout
	if b.MaxQueryTime > 0 {
		timeout = time.After(b.MaxQueryTime)
	}

	// Setup a notification channel for changes
SETUP_NOTIFY:
	if b.MinQueryIndex > 0 {
		notifyCh = make(chan struct{}, 1)
		s.fsm.State().Watch(tables, notifyCh)
	}

RUN_QUERY:
	// Update the query meta data
	s.setQueryMeta(m)

	// Check if query must be consistent
	if b.RequireConsistent {
		if err := s.consistentRead(); err != nil {
			return err
		}
	}

	// Run the query function
	err := run()

	// Check for minimum query time
	if err == nil && m.Index > 0 && m.Index <= b.MinQueryIndex {
		select {
		case <-notifyCh:
			goto SETUP_NOTIFY
		case <-timeout:
		}
	}
	return err
}

// EventList is used to retrieve the recent list of events
func (s *HTTPServer) EventList(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
	// Parse the query options, since we simulate a blocking query
	var b structs.QueryOptions
	if parseWait(resp, req, &b) {
		return nil, nil
	}

	// Look for a name filter
	var nameFilter string
	if filt := req.URL.Query().Get("name"); filt != "" {
		nameFilter = filt
	}

	// Lots of this logic is borrowed from consul/rpc.go:blockingRPC
	// However we cannot use that directly since this code has some
	// slight semantics differences...
	var timeout <-chan time.Time
	var notifyCh chan struct{}

	// Fast path non-blocking
	if b.MinQueryIndex == 0 {
		goto RUN_QUERY
	}

	// Restrict the max query time
	if b.MaxQueryTime > maxQueryTime {
		b.MaxQueryTime = maxQueryTime
	}

	// Ensure a time limit is set if we have an index
	if b.MinQueryIndex > 0 && b.MaxQueryTime == 0 {
		b.MaxQueryTime = maxQueryTime
	}

	// Setup a query timeout
	if b.MaxQueryTime > 0 {
		timeout = time.After(b.MaxQueryTime)
	}

	// Setup a notification channel for changes
SETUP_NOTIFY:
	if b.MinQueryIndex > 0 {
		notifyCh = make(chan struct{}, 1)
		s.agent.eventNotify.Wait(notifyCh)
	}

RUN_QUERY:
	// Get the recent events
	events := s.agent.UserEvents()

	// Filter the events if necessary
	if nameFilter != "" {
		n := len(events)
		for i := 0; i < n; i++ {
			if events[i].Name == nameFilter {
				continue
			}
			events[i], events[n-1] = events[n-1], nil
			i--
			n--
		}
		events = events[:n]
	}

	// Determine the index
	var index uint64
	if len(events) == 0 {
		// Return a non-zero index to prevent a hot query loop. This
		// can be caused by a watch for example when there is no matching
		// events.
		index = 1
	} else {
		last := events[len(events)-1]
		index = uuidToUint64(last.ID)
	}
	setIndex(resp, index)

	// Check for exact match on the query value. Because
	// the index value is not monotonic, we just ensure it is
	// not an exact match.
	if index > 0 && index == b.MinQueryIndex {
		select {
		case <-notifyCh:
			goto SETUP_NOTIFY
		case <-timeout:
		}
	}
	return events, nil
}

// blockingRPC is used for queries that need to wait for a minimum index. This
// is used to block and wait for changes.
func (s *Server) blockingRPC(queryOpts *structs.QueryOptions, queryMeta *structs.QueryMeta,
	watch state.Watch, run func() error) error {
	var timeout *time.Timer
	var notifyCh chan struct{}

	// Fast path right to the non-blocking query.
	if queryOpts.MinQueryIndex == 0 {
		goto RUN_QUERY
	}

	// Make sure a watch was given if we were asked to block.
	if watch == nil {
		panic("no watch given for blocking query")
	}

	// Restrict the max query time, and ensure there is always one.
	if queryOpts.MaxQueryTime > maxQueryTime {
		queryOpts.MaxQueryTime = maxQueryTime
	} else if queryOpts.MaxQueryTime <= 0 {
		queryOpts.MaxQueryTime = defaultQueryTime
	}

	// Apply a small amount of jitter to the request.
	queryOpts.MaxQueryTime += lib.RandomStagger(queryOpts.MaxQueryTime / jitterFraction)

	// Setup a query timeout.
	timeout = time.NewTimer(queryOpts.MaxQueryTime)

	// Setup the notify channel.
	notifyCh = make(chan struct{}, 1)

	// Ensure we tear down any watches on return.
	defer func() {
		timeout.Stop()
		watch.Clear(notifyCh)
	}()

REGISTER_NOTIFY:
	// Register the notification channel. This may be done multiple times if
	// we haven't reached the target wait index.
	watch.Wait(notifyCh)

RUN_QUERY:
	// Update the query metadata.
	s.setQueryMeta(queryMeta)

	// If the read must be consistent we verify that we are still the leader.
	if queryOpts.RequireConsistent {
		if err := s.consistentRead(); err != nil {
			return err
		}
	}

	// Run the query.
	metrics.IncrCounter([]string{"consul", "rpc", "query"}, 1)
	err := run()

	// Check for minimum query time.
	if err == nil && queryMeta.Index > 0 && queryMeta.Index <= queryOpts.MinQueryIndex {
		select {
		case <-notifyCh:
			goto REGISTER_NOTIFY
		case <-timeout.C:
		}
	}
	return err
}