package handlers

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"log"
	"net/http"
	"time"

	"task-dashboard/internal/config"
	"task-dashboard/internal/models"
)

// -----------------------------------------------------------------------------
// Constants
// -----------------------------------------------------------------------------

const (
	AgentRequestExpiry = 5 * time.Minute
	AgentSessionTTL    = 1 * time.Hour
	TokenBytes         = 32
)

// Context key for agent session in request context
type contextKey string

const agentSessionContextKey contextKey = "agent_session"

// -----------------------------------------------------------------------------
// Types
// -----------------------------------------------------------------------------

// AgentRequestPayload is sent via WebSocket when an agent requests access
type AgentRequestPayload struct {
	RequestToken string                 `json:"request_token"`
	AgentName    string                 `json:"agent_name"`
	AgentID      string                 `json:"agent_id"`
	TrustLevel   models.AgentTrustLevel `json:"trust_level"`
	ExpiresAt    time.Time              `json:"expires_at"`
}

// agentContextItem is the JSON-serializable timeline item for agent context API
type agentContextItem struct {
	ID          string     `json:"id"`
	Source      string     `json:"source"`
	Type        string     `json:"type"`
	Title       string     `json:"title"`
	Description string     `json:"description,omitempty"`
	Due         *time.Time `json:"due,omitempty"`
	Priority    int        `json:"priority,omitempty"`
	Completable bool       `json:"completable"`
	URL         string     `json:"url,omitempty"`
	DaySection  string     `json:"day_section,omitempty"` // "overdue", "today", "tomorrow", "later"
}

// agentCompletedItem represents a completed task in the log
type agentCompletedItem struct {
	Source      string     `json:"source"`
	Title       string     `json:"title"`
	DueDate     *time.Time `json:"due_date,omitempty"`
	CompletedAt time.Time  `json:"completed_at"`
}

// -----------------------------------------------------------------------------
// Helpers
// -----------------------------------------------------------------------------

// generateToken creates a cryptographically random token
func generateToken() (string, error) {
	b := make([]byte, TokenBytes)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(b), nil
}

// isSessionExpired checks if a pending session has expired
func isSessionExpired(session *models.AgentSession) bool {
	return time.Now().After(session.ExpiresAt) && session.Status == "pending"
}

// timelineItemToAgentItem converts a TimelineItem to the agent API format
func timelineItemToAgentItem(item models.TimelineItem) agentContextItem {
	t := item.Time
	return agentContextItem{
		ID:          item.ID,
		Source:      item.Source,
		Type:        string(item.Type),
		Title:       item.Title,
		Description: item.Description,
		Due:         &t,
		Completable: item.Type == models.TimelineItemTypeTask || item.Type == models.TimelineItemTypeCard || item.Type == models.TimelineItemTypeGTask,
		URL:         item.URL,
		DaySection:  string(item.DaySection),
	}
}

// renderAgentTemplate renders an agent template with common error handling
func (h *Handler) renderAgentTemplate(w http.ResponseWriter, templateName string, data interface{}) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if h.renderer == nil {
		h.renderAgentError(w, "Renderer not configured", http.StatusInternalServerError)
		return
	}
	if err := h.renderer.Render(w, templateName, data); err != nil {
		h.renderAgentError(w, "Template error", http.StatusInternalServerError)
	}
}

// -----------------------------------------------------------------------------
// Auth Handlers
// -----------------------------------------------------------------------------

// HandleAgentAuthRequest handles POST /agent/auth/request
func (h *Handler) HandleAgentAuthRequest(w http.ResponseWriter, r *http.Request) {
	var req models.AgentAuthRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Invalid request body", http.StatusBadRequest)
		return
	}

	if req.Name == "" || req.AgentID == "" {
		http.Error(w, "name and agent_id are required", http.StatusBadRequest)
		return
	}

	// Invalidate any previous sessions for this agent
	if err := h.store.InvalidatePreviousAgentSessions(req.AgentID); err != nil {
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	// Generate request token
	requestToken, err := generateToken()
	if err != nil {
		http.Error(w, "Failed to generate token", http.StatusInternalServerError)
		return
	}

	// Create pending session
	session := &models.AgentSession{
		RequestToken: requestToken,
		AgentName:    req.Name,
		AgentID:      req.AgentID,
		ExpiresAt:    time.Now().Add(AgentRequestExpiry),
	}
	if err := h.store.CreateAgentSession(session); err != nil {
		http.Error(w, "Failed to create session", http.StatusInternalServerError)
		return
	}

	// Check trust level for WebSocket notification
	trustLevel, err := h.store.CheckAgentTrust(req.Name, req.AgentID)
	if err != nil {
		trustLevel = models.AgentTrustNew
	}

	// Broadcast to connected browsers via WebSocket
	h.BroadcastAgentRequest(session, trustLevel)

	// Return response
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(models.AgentAuthResponse{
		RequestToken: requestToken,
		Status:       "pending",
	})
}

// HandleAgentAuthPoll handles GET /agent/auth/poll
func (h *Handler) HandleAgentAuthPoll(w http.ResponseWriter, r *http.Request) {
	token := r.URL.Query().Get("token")
	if token == "" {
		http.Error(w, "token parameter required", http.StatusBadRequest)
		return
	}

	session, err := h.store.GetAgentSessionByRequestToken(token)
	if err != nil {
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	if session == nil {
		http.Error(w, "Session not found", http.StatusNotFound)
		return
	}

	if isSessionExpired(session) {
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(models.AgentPollResponse{Status: "expired"})
		return
	}

	resp := models.AgentPollResponse{Status: session.Status}

	if session.Status == "approved" && session.SessionToken != "" {
		resp.SessionToken = session.SessionToken
		resp.ExpiresAt = session.SessionExpiresAt
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}

// HandleAgentAuthApprove handles POST /agent/auth/approve (browser auth required)
func (h *Handler) HandleAgentAuthApprove(w http.ResponseWriter, r *http.Request) {
	var req struct {
		RequestToken string `json:"request_token"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Invalid request body", http.StatusBadRequest)
		return
	}

	if req.RequestToken == "" {
		http.Error(w, "request_token required", http.StatusBadRequest)
		return
	}

	// Verify session exists and is pending
	session, err := h.store.GetAgentSessionByRequestToken(req.RequestToken)
	if err != nil {
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	if session == nil {
		http.Error(w, "Session not found", http.StatusNotFound)
		return
	}
	if session.Status != "pending" {
		http.Error(w, "Session already processed", http.StatusConflict)
		return
	}
	if time.Now().After(session.ExpiresAt) {
		http.Error(w, "Session expired", http.StatusGone)
		return
	}

	// Generate session token
	sessionToken, err := generateToken()
	if err != nil {
		http.Error(w, "Failed to generate session token", http.StatusInternalServerError)
		return
	}

	sessionExpiresAt := time.Now().Add(AgentSessionTTL)

	// Approve the session
	if err := h.store.ApproveAgentSession(req.RequestToken, sessionToken, sessionExpiresAt); err != nil {
		http.Error(w, "Failed to approve session", http.StatusInternalServerError)
		return
	}

	// Register/update agent in the trusted agents table
	if err := h.store.CreateOrUpdateAgent(session.AgentName, session.AgentID); err != nil {
		// Don't fail - the session was approved; this just affects future trust level checks
		log.Printf("warning: failed to register agent %q: %v", session.AgentName, err)
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]string{"status": "approved"})
}

// HandleAgentAuthDeny handles POST /agent/auth/deny (browser auth required)
func (h *Handler) HandleAgentAuthDeny(w http.ResponseWriter, r *http.Request) {
	var req struct {
		RequestToken string `json:"request_token"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Invalid request body", http.StatusBadRequest)
		return
	}

	if req.RequestToken == "" {
		http.Error(w, "request_token required", http.StatusBadRequest)
		return
	}

	if err := h.store.DenyAgentSession(req.RequestToken); err != nil {
		http.Error(w, "Failed to deny session", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]string{"status": "denied"})
}

// -----------------------------------------------------------------------------
// Context Handlers
// -----------------------------------------------------------------------------

// HandleAgentContext handles GET /agent/context (agent auth required)
func (h *Handler) HandleAgentContext(w http.ResponseWriter, r *http.Request) {
	session := r.Context().Value(agentSessionContextKey).(*models.AgentSession)
	_ = h.store.UpdateAgentLastSeen(session.AgentID)

	now := config.Now()
	today := config.Today()
	// Extend range: 7 days back (overdue) to 14 days forward
	startDate := today.Add(-7 * 24 * time.Hour)
	endDate := today.Add(14 * 24 * time.Hour)

	ctx := r.Context()
	timeline := h.buildAgentContext(ctx, startDate, endDate)
	completedLog := h.buildCompletedLog(50) // Last 50 completed tasks

	resp := map[string]interface{}{
		"generated_at": now.Format(time.RFC3339),
		"range": map[string]string{
			"start": startDate.Format("2006-01-02"),
			"end":   endDate.Format("2006-01-02"),
		},
		"timeline":      timeline,
		"completed_log": completedLog,
		"summary":       h.buildContextSummary(timeline, today),
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}

// buildAgentContext builds the context timeline by reusing BuildTimeline
func (h *Handler) buildAgentContext(ctx context.Context, start, end time.Time) []agentContextItem {
	// Reuse the main BuildTimeline function (excludes live API calls for Google services)
	timelineItems, err := BuildTimeline(ctx, h.store, nil, start, end)
	if err != nil {
		return nil
	}

	// Convert to agent API format, filtering completed items
	var items []agentContextItem
	for _, item := range timelineItems {
		if item.IsCompleted {
			continue
		}
		items = append(items, timelineItemToAgentItem(item))
	}
	return items
}

// buildContextSummary builds summary statistics for the agent context
func (h *Handler) buildContextSummary(items []agentContextItem, today time.Time) map[string]interface{} {
	bySource := make(map[string]int)
	bySection := make(map[string]int)
	endOfToday := today.Add(24 * time.Hour)

	for _, item := range items {
		bySource[item.Source]++
		if item.DaySection != "" {
			bySection[item.DaySection]++
		} else if item.Due != nil {
			if item.Due.Before(today) {
				bySection["overdue"]++
			} else if item.Due.Before(endOfToday) {
				bySection["today"]++
			}
		}
	}

	return map[string]interface{}{
		"total_items": len(items),
		"by_source":   bySource,
		"by_section":  bySection,
	}
}

// buildCompletedLog retrieves recently completed tasks
func (h *Handler) buildCompletedLog(limit int) []agentCompletedItem {
	completed, err := h.store.GetCompletedTasks(limit)
	if err != nil {
		return nil
	}

	items := make([]agentCompletedItem, len(completed))
	for i, c := range completed {
		items[i] = agentCompletedItem{
			Source:      c.Source,
			Title:       c.Title,
			DueDate:     c.DueDate,
			CompletedAt: c.CompletedAt,
		}
	}
	return items
}

// -----------------------------------------------------------------------------
// Middleware
// -----------------------------------------------------------------------------

// AgentAuthMiddleware verifies agent session token
func (h *Handler) AgentAuthMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		authHeader := r.Header.Get("Authorization")
		if authHeader == "" || len(authHeader) < 8 || authHeader[:7] != "Bearer " {
			http.Error(w, "Authorization header required", http.StatusUnauthorized)
			return
		}

		token := authHeader[7:]

		session, err := h.store.GetAgentSessionBySessionToken(token)
		if err != nil || session == nil {
			http.Error(w, "Invalid session token", http.StatusUnauthorized)
			return
		}

		// Check session expiry
		if session.SessionExpiresAt != nil && time.Now().After(*session.SessionExpiresAt) {
			http.Error(w, "Session expired", http.StatusUnauthorized)
			return
		}

		// Add session to context
		ctx := context.WithValue(r.Context(), agentSessionContextKey, session)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// -----------------------------------------------------------------------------
// Web Handlers (HTML pages for browser-only agents)
// -----------------------------------------------------------------------------

// HandleAgentWebRequest handles GET /agent/web/request for browser-only agents
func (h *Handler) HandleAgentWebRequest(w http.ResponseWriter, r *http.Request) {
	name := r.URL.Query().Get("name")
	agentID := r.URL.Query().Get("agent_id")

	if name == "" || agentID == "" {
		h.renderAgentError(w, "name and agent_id query parameters are required", http.StatusBadRequest)
		return
	}

	// Check for existing pending session
	existingSession, err := h.store.GetPendingAgentSessionByAgentID(agentID)
	if err != nil {
		h.renderAgentError(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	if existingSession != nil {
		// Return existing pending session
		h.renderAgentRequest(w, existingSession)
		return
	}

	// Invalidate any previous sessions for this agent
	if err := h.store.InvalidatePreviousAgentSessions(agentID); err != nil {
		h.renderAgentError(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	// Generate request token
	requestToken, err := generateToken()
	if err != nil {
		h.renderAgentError(w, "Failed to generate token", http.StatusInternalServerError)
		return
	}

	// Create pending session
	session := &models.AgentSession{
		RequestToken: requestToken,
		AgentName:    name,
		AgentID:      agentID,
		ExpiresAt:    time.Now().Add(AgentRequestExpiry),
	}
	if err := h.store.CreateAgentSession(session); err != nil {
		h.renderAgentError(w, "Failed to create session", http.StatusInternalServerError)
		return
	}

	// Check trust level for WebSocket notification
	trustLevel, err := h.store.CheckAgentTrust(name, agentID)
	if err != nil {
		trustLevel = models.AgentTrustNew
	}

	// Broadcast to connected browsers via WebSocket
	h.BroadcastAgentRequest(session, trustLevel)

	h.renderAgentRequest(w, session)
}

// HandleAgentWebStatus handles GET /agent/web/status for browser-only agents
// Returns HTML page with approval status and session token if approved
func (h *Handler) HandleAgentWebStatus(w http.ResponseWriter, r *http.Request) {
	token := r.URL.Query().Get("token")
	if token == "" {
		h.renderAgentError(w, "token query parameter required", http.StatusBadRequest)
		return
	}

	session, err := h.store.GetAgentSessionByRequestToken(token)
	if err != nil {
		h.renderAgentError(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	if session == nil {
		h.renderAgentError(w, "Session not found", http.StatusNotFound)
		return
	}

	h.renderAgentStatus(w, session)
}

// HandleAgentWebContext handles GET /agent/web/context for browser-only agents
func (h *Handler) HandleAgentWebContext(w http.ResponseWriter, r *http.Request) {
	sessionToken := r.URL.Query().Get("session")
	if sessionToken == "" {
		h.renderAgentError(w, "session query parameter required", http.StatusBadRequest)
		return
	}

	session, err := h.store.GetAgentSessionBySessionToken(sessionToken)
	if err != nil || session == nil {
		h.renderAgentError(w, "Invalid session token", http.StatusUnauthorized)
		return
	}

	if session.SessionExpiresAt != nil && time.Now().After(*session.SessionExpiresAt) {
		h.renderAgentError(w, "Session expired", http.StatusUnauthorized)
		return
	}

	_ = h.store.UpdateAgentLastSeen(session.AgentID)

	now := config.Now()
	today := config.Today()
	startDate := today.Add(-7 * 24 * time.Hour)
	endDate := today.Add(14 * 24 * time.Hour)

	ctx := r.Context()
	timeline := h.buildAgentContext(ctx, startDate, endDate)
	completedLog := h.buildCompletedLog(50)

	h.renderAgentContextFull(w, session, timeline, completedLog, today, startDate, endDate, now)
}

// renderAgentError renders an error page for agent web endpoints
func (h *Handler) renderAgentError(w http.ResponseWriter, message string, status int) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if h.renderer != nil {
		_ = h.renderer.Render(w, "agent-error.html", map[string]interface{}{
			"Error":  message,
			"Status": status,
		})
	} else {
		// Fallback if renderer not configured
		w.Write([]byte(`<!DOCTYPE html><html><head><title>Error</title></head><body><h1>Error</h1><p>` + message + `</p></body></html>`))
	}
}

// renderAgentRequest renders the request page with token info
func (h *Handler) renderAgentRequest(w http.ResponseWriter, session *models.AgentSession) {
	h.renderAgentTemplate(w, "agent-request.html", map[string]interface{}{
		"RequestToken": session.RequestToken,
		"AgentName":    session.AgentName,
		"AgentID":      session.AgentID,
		"Status":       "pending",
		"PollURL":      "/agent/web/status?token=" + session.RequestToken,
		"ExpiresAt":    session.ExpiresAt.Format(time.RFC3339),
	})
}

// renderAgentStatus renders the status page
func (h *Handler) renderAgentStatus(w http.ResponseWriter, session *models.AgentSession) {
	status := session.Status
	if isSessionExpired(session) {
		status = "expired"
	}

	data := map[string]interface{}{
		"RequestToken": session.RequestToken,
		"AgentName":    session.AgentName,
		"Status":       status,
	}

	if status == "approved" && session.SessionToken != "" {
		data["SessionToken"] = session.SessionToken
		data["ContextURL"] = "/agent/web/context?session=" + session.SessionToken
		if session.SessionExpiresAt != nil {
			data["SessionExpiresAt"] = session.SessionExpiresAt.Format(time.RFC3339)
		}
	}

	h.renderAgentTemplate(w, "agent-status.html", data)
}

// renderAgentContextFull renders the context page with full timeline data and completed log
func (h *Handler) renderAgentContextFull(w http.ResponseWriter, session *models.AgentSession, timeline []agentContextItem, completedLog []agentCompletedItem, today, startDate, endDate, now time.Time) {
	// Separate today's items for calendar view
	var todayItems []agentContextItem
	var otherItems []agentContextItem
	endOfToday := today.Add(24 * time.Hour)

	for _, item := range timeline {
		if item.Due != nil && !item.Due.Before(today) && item.Due.Before(endOfToday) {
			todayItems = append(todayItems, item)
		} else {
			otherItems = append(otherItems, item)
		}
	}

	h.renderAgentTemplate(w, "agent-context.html", map[string]interface{}{
		"AgentName":    session.AgentName,
		"GeneratedAt":  now.Format(time.RFC3339),
		"Today":        today.Format("2006-01-02"),
		"RangeStart":   startDate.Format("2006-01-02"),
		"RangeEnd":     endDate.Format("2006-01-02"),
		"TodayItems":   todayItems,
		"Timeline":     otherItems,
		"CompletedLog": completedLog,
		"Summary":      h.buildContextSummary(timeline, today),
	})
}