package agent

import (
	"bytes"
	"fmt"
	"regexp"

	"github.com/ugorji/go/codec"
)

const (
	// userEventMaxVersion is the maximum protocol version we understand
	userEventMaxVersion = 1
)

// UserEventParam is used to parameterize a user event
type UserEvent struct {
	// ID of the user event. Automatically generated.
	ID string

	// Name of the event
	Name string `codec:"n"`

	// Optional payload
	Payload []byte `codec:"p,omitempty"`

	// NodeFilter is a regular expression to filter on nodes
	NodeFilter string `codec:"nf,omitempty"`

	// ServiceFilter is a regular expression to filter on services
	ServiceFilter string `codec:"sf,omitempty"`

	// TagFilter is a regular expression to filter on tags of a service,
	// must be provided with ServiceFilter
	TagFilter string `codec:"tf,omitempty"`

	// Version of the user event. Automatically generated.
	Version int `codec:"v"`
}

// validateUserEventParams is used to sanity check the inputs
func validateUserEventParams(params *UserEvent) error {
	// Validate the inputs
	if params.Name == "" {
		return fmt.Errorf("User event missing name")
	}
	if params.TagFilter != "" && params.ServiceFilter == "" {
		return fmt.Errorf("Cannot provide tag filter without service filter")
	}
	if params.NodeFilter != "" {
		if _, err := regexp.Compile(params.NodeFilter); err != nil {
			return fmt.Errorf("Invalid node filter: %v", err)
		}
	}
	if params.ServiceFilter != "" {
		if _, err := regexp.Compile(params.ServiceFilter); err != nil {
			return fmt.Errorf("Invalid service filter: %v", err)
		}
	}
	if params.TagFilter != "" {
		if _, err := regexp.Compile(params.TagFilter); err != nil {
			return fmt.Errorf("Invalid tag filter: %v", err)
		}
	}
	return nil
}

// UserEvent is used to fire an event via the Serf layer on the LAN
func (a *Agent) UserEvent(params *UserEvent) error {
	// Validate the params
	if err := validateUserEventParams(params); err != nil {
		return err
	}

	// Format message
	params.ID = generateUUID()
	params.Version = userEventMaxVersion
	payload, err := encodeUserEvent(&params)
	if err != nil {
		return fmt.Errorf("UserEvent encoding failed: %v", err)
	}
	if a.server != nil {
		return a.server.UserEvent(params.Name, payload)
	} else {
		return a.client.UserEvent(params.Name, payload)
	}
}

// handleEvents is used to process incoming user events
func (a *Agent) handleEvents() {
	for {
		select {
		case e := <-a.eventCh:
			// Decode the event
			msg := new(UserEvent)
			if err := decodeUserEvent(e.Payload, msg); err != nil {
				a.logger.Printf("[ERR] agent: Failed to decode event: %v", err)
				continue
			}

			// Skip if we don't pass filtering
			if !a.shouldProcessUserEvent(msg) {
				continue
			}

			// Ingest the event
			a.ingestUserEvent(msg)

		case <-a.shutdownCh:
			return
		}
	}
}

// shouldProcessUserEvent checks if an event makes it through our filters
func (a *Agent) shouldProcessUserEvent(msg *UserEvent) bool {
	// Check the version
	if msg.Version > userEventMaxVersion {
		a.logger.Printf("[WARN] agent: Event version %d may have unsupported features (%s)",
			msg.Version, msg.Name)
	}

	// Apply the filters
	if msg.NodeFilter != "" {
		re, err := regexp.Compile(msg.NodeFilter)
		if err != nil {
			a.logger.Printf("[ERR] agent: Failed to parse node filter '%s' for event '%s': %v",
				msg.NodeFilter, msg.Name, err)
			return false
		}
		if !re.MatchString(a.config.NodeName) {
			return false
		}
	}

	if msg.ServiceFilter != "" {
		re, err := regexp.Compile(msg.ServiceFilter)
		if err != nil {
			a.logger.Printf("[ERR] agent: Failed to parse service filter '%s' for event '%s': %v",
				msg.ServiceFilter, msg.Name, err)
			return false
		}

		var tagRe *regexp.Regexp
		if msg.TagFilter != "" {
			re, err := regexp.Compile(msg.TagFilter)
			if err != nil {
				a.logger.Printf("[ERR] agent: Failed to parse tag filter '%s' for event '%s': %v",
					msg.TagFilter, msg.Name, err)
				return false
			}
			tagRe = re
		}

		// Scan for a match
		services := a.state.Services()
		found := false
	OUTER:
		for name, info := range services {
			// Check the service name
			if !re.MatchString(name) {
				continue
			}
			if tagRe == nil {
				found = true
				break
			}

			// Look for a matching tag
			for _, tag := range info.Tags {
				if !tagRe.MatchString(tag) {
					continue
				}
				found = true
				break OUTER
			}
		}

		// No matching services
		if !found {
			return false
		}
	}
	return true
}

// ingestUserEvent is used to process an event that passes filtering
func (a *Agent) ingestUserEvent(msg *UserEvent) {
	a.eventLock.Lock()
	defer func() {
		a.eventLock.Unlock()
		a.eventNotify.Notify()
	}()

	idx := a.eventIndex
	a.eventBuf[idx] = msg
	a.eventIndex = (idx + 1) % len(a.eventBuf)
}

// Decode is used to decode a MsgPack encoded object
func decodeUserEvent(buf []byte, out interface{}) error {
	return codec.NewDecoder(bytes.NewReader(buf), msgpackHandle).Decode(out)
}

// encodeUserEvent is used to encode user event
func encodeUserEvent(msg interface{}) ([]byte, error) {
	var buf bytes.Buffer
	err := codec.NewEncoder(&buf, msgpackHandle).Encode(msg)
	return buf.Bytes(), err
}