package leaf

import (
	"context"
	"github.com/eclipse/paho.golang/packets"
	"github.com/eclipse/paho.golang/paho"
	"github.com/eclipse/paho.golang/paho/log"
	"sync"
)

type Router interface {
	RegisterHandler(string, ...HandlerFunc)
	UnregisterHandler(string)
	Route(*packets.Publish)
	SetDebugLogger(log.Logger)
	Use(...HandlerFunc)
}

// HandlerFunc defines the handler used by gin middleware as return value.
type HandlerFunc func(*Context)

// OptionFunc defines the function to change the default configuration
type OptionFunc func(*Engine)

// HandlersChain defines a HandlerFunc slice.
type HandlersChain []HandlerFunc

// Last returns the last handler in the chain. i.e. the last handler is the main one.
func (c HandlersChain) Last() HandlerFunc {
	if length := len(c); length > 0 {
		return c[length-1]
	}
	return nil
}

type Engine struct {
	mu      sync.RWMutex
	queueWg sync.WaitGroup

	ctx       context.Context
	cancelCtx context.CancelFunc
	done      chan struct{}

	Handlers       HandlersChain
	defaultHandler HandlersChain
	subscriptions  map[string]HandlersChain
	aliases        map[uint16]string
	debug          log.Logger
}

func New(ctx context.Context) *Engine {
	c, cancel := context.WithCancel(ctx)
	return &Engine{
		ctx:           c,
		cancelCtx:     cancel,
		done:          make(chan struct{}),
		Handlers:      make(HandlersChain, 0),
		subscriptions: make(map[string]HandlersChain),
		aliases:       make(map[uint16]string),
		debug:         log.NOOPLogger{},
	}
}

func Default(ctx context.Context) *Engine {
	c, cancel := context.WithCancel(ctx)
	engine := &Engine{
		ctx:           c,
		cancelCtx:     cancel,
		done:          make(chan struct{}),
		Handlers:      make(HandlersChain, 0),
		subscriptions: make(map[string]HandlersChain),
		aliases:       make(map[uint16]string),
		debug:         log.NOOPLogger{},
	}
	engine.Use(Recovery())
	return engine
}

func (e *Engine) RegisterHandler(topic string, handlers ...HandlerFunc) {
	e.debug.Println("registering handler for:", topic)
	e.mu.Lock()
	defer e.mu.Unlock()

	e.subscriptions[topic] = e.combineHandlers(handlers)
}

func (e *Engine) UnregisterHandler(topic string) {
	e.debug.Println("unregistering handler for:", topic)
	e.mu.Lock()
	defer e.mu.Unlock()

	delete(e.subscriptions, topic)
}

func (e *Engine) Route(pb *packets.Publish) {
	e.debug.Println("routing message for:", pb.Topic)
	e.mu.Lock()
	defer e.mu.Unlock()

	m := paho.PublishFromPacketPublish(pb)

	var topic string
	if pb.Properties.TopicAlias != nil {
		e.debug.Println("message is using topic aliasing")
		if pb.Topic != "" {
			// Register new alias
			e.debug.Printf("registering new topic alias '%d' for topic '%s'", *pb.Properties.TopicAlias, m.Topic)
			e.aliases[*pb.Properties.TopicAlias] = pb.Topic
		}
		if t, ok := e.aliases[*pb.Properties.TopicAlias]; ok {
			e.debug.Printf("aliased topic '%d' translates to '%s'", *pb.Properties.TopicAlias, m.Topic)
			topic = t
		}
	} else {
		topic = m.Topic
	}

	handlerCalled := false
	for route, handlers := range e.subscriptions {
		if match(route, topic) {
			e.debug.Println("found handler for:", route)
			e.queueWg.Add(1)
			go func() {
				defer e.queueWg.Done()
				WithLeafContext(e.ctx, m, e, handlers).Next()
			}()
			handlerCalled = true
		}
	}

	if !handlerCalled && e.defaultHandler != nil {
		e.queueWg.Add(1)
		go func() {
			defer e.queueWg.Done()
			WithLeafContext(e.ctx, m, e, e.defaultHandler).Next()
		}()
	}
}

func (e *Engine) SetDebugLogger(l log.Logger) {
	e.debug = l
}

func (e *Engine) Use(middleware ...HandlerFunc) {
	e.Handlers = append(e.Handlers, middleware...)
}

func (e *Engine) DefaultHandler(h HandlerFunc) {
	e.debug.Println("registering default handler")
	e.mu.Lock()
	defer e.mu.Unlock()

	e.defaultHandler = e.combineHandlers(HandlersChain{h})
}

func (e *Engine) Disconnect(ctx context.Context) error {
	go func() {
		e.queueWg.Wait()
		close(e.done)
	}()

	e.cancelCtx()
	select {
	case <-e.done: // wait for goroutine to exit
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (e *Engine) combineHandlers(handlers HandlersChain) HandlersChain {
	finalSize := len(e.Handlers) + len(handlers)
	assert1(finalSize < int(abortIndex), "too many handlers")
	mergedHandlers := make(HandlersChain, finalSize)
	copy(mergedHandlers, e.Handlers)
	copy(mergedHandlers[len(e.Handlers):], handlers)
	return mergedHandlers
}