package ssh

import (
	"errors"
	"log"
	"sync"
	"time"
)

type SessionID string

type SessionType int

const (
	TypeServiceUnknown SessionType = iota
	TypeServiceProvider
	TypeServiceConsumer
)

type SessionData struct {
	Type  SessionType
	Token string
}

type SessionManager struct {
	sessions      map[SessionID]SessionData
	sessionsMutex sync.Mutex

	tokenIndex map[string]SessionID

	updates      map[SessionID][]chan SessionData
	updatesMutex sync.Mutex

	updateReadTimeout time.Duration
}

func (m *SessionManager) Get(sessID SessionID, defaultValue SessionData) SessionData {
	log.Println("reading session", sessID)

	m.sessionsMutex.Lock()
	defer m.sessionsMutex.Unlock()

	session, exists := m.sessions[sessID]
	if !exists {
		session = defaultValue
		m.sessions[sessID] = session

		m.updatesMutex.Lock()
		m.dispatchUpdate(sessID, session)
		m.updatesMutex.Unlock()
	}

	return session
}

func (m *SessionManager) FindByToken(token string) SessionID {
	m.sessionsMutex.Lock()
	defer m.sessionsMutex.Unlock()

	sessID, exists := m.tokenIndex[token]
	if !exists {
		return ""
	}

	return sessID
}

func (m *SessionManager) Set(sessID SessionID, sess SessionData) {
	log.Println("updating session", sessID, sess)

	m.sessionsMutex.Lock()
	oldSess, ok := m.sessions[sessID]
	if ok {
		m.updateTokenIndex(sessID, sess.Token, oldSess.Token)
	} else {
		m.updateTokenIndex(sessID, sess.Token, "")
	}
	m.sessions[sessID] = sess
	m.sessionsMutex.Unlock()

	m.updatesMutex.Lock()
	m.dispatchUpdate(sessID, sess)
	m.updatesMutex.Unlock()
}

func (m *SessionManager) Remove(sessID SessionID) {
	m.sessionsMutex.Lock()
	oldSess, ok := m.sessions[sessID]
	if ok {
		m.updateTokenIndex(sessID, "", oldSess.Token)
	}
	delete(m.sessions, sessID)
	m.sessionsMutex.Unlock()

	m.updatesMutex.Lock()
	m.closeAllUpdates(sessID)
	m.updatesMutex.Unlock()
}

func (m *SessionManager) OnUpdate(sessID SessionID) (<-chan SessionData, func()) {
	update := make(chan SessionData)

	close := func() {
		m.updatesMutex.Lock()
		m.closeUpdate(sessID, update)
		m.updatesMutex.Unlock()
	}

	m.updatesMutex.Lock()
	defer m.updatesMutex.Unlock()

	channels, exists := m.updates[sessID]
	if !exists {
		channels = make([]chan SessionData, 0, 1)
	}

	channels = append(channels, update)
	m.updates[sessID] = channels

	return update, close
}

func (m *SessionManager) closeAllUpdates(sessID SessionID) {
	channels, exists := m.updates[sessID]
	if !exists {
		return
	}

	for _, ch := range channels {
		m.closeUpdate(sessID, ch)
	}
}

func (m *SessionManager) closeUpdate(sessID SessionID, update chan SessionData) {
	channels, exists := m.updates[sessID]
	if !exists {
		return
	}

	for idx, ch := range channels {
		if ch != update {
			continue
		}

		close(ch)
		m.updates[sessID] = append(channels[:idx], channels[idx+1:]...)
	}
}

func (m *SessionManager) dispatchUpdate(sessID SessionID, sess SessionData) {
	channels, exists := m.updates[sessID]
	if !exists {
		return
	}

	for _, ch := range channels {
		timeout := time.After(m.updateReadTimeout)
		select {
		case ch <- sess:
		case <-timeout:
			err := errors.New("session update read timed out")
			log.Printf("[ERROR] %+v", err)
		}
	}
}

func (m *SessionManager) updateTokenIndex(sessID SessionID, addedToken, deletedToken string) {
	if addedToken != "" {
		m.tokenIndex[addedToken] = sessID
	}

	if deletedToken != "" {
		delete(m.tokenIndex, deletedToken)
	}
}

func NewSessionManager(updateReadTimeout time.Duration) *SessionManager {
	return &SessionManager{
		sessions:          make(map[SessionID]SessionData),
		tokenIndex:        make(map[string]SessionID),
		updates:           make(map[SessionID][]chan SessionData),
		updateReadTimeout: updateReadTimeout,
	}
}