package calendar

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	"bookra/apps/backend/internal/db"
	"bookra/apps/backend/internal/domain"
)

var (
	ErrFeedNotFound     = errors.New("calendar feed not found")
	ErrTenantMembership = errors.New("tenant membership not found")
	ErrInvalidScope     = errors.New("invalid feed scope")
)

const (
	feedLookbackDays  = 30
	feedLookaheadDays = 180
)

type Service struct {
	repo db.Repository
	now  func() time.Time
}

func NewService(repo db.Repository) *Service {
	return &Service{repo: repo, now: time.Now}
}

type FeedEntry struct {
	Token    string `json:"token"`
	FeedPath string `json:"feedPath"`
}

type StaffFeedEntry struct {
	StaffID     string `json:"staffId"`
	DisplayName string `json:"displayName"`
	Token       string `json:"token"`
	FeedPath    string `json:"feedPath"`
}

type FeedInfo struct {
	Tenant FeedEntry        `json:"tenant"`
	Staff  []StaffFeedEntry `json:"staff"`
}

func feedPath(token string) string {
	return "/v1/public/calendar/" + token + ".ics"
}

func (s *Service) tenantFor(ctx context.Context, principal domain.Principal) (db.TenantRecord, error) {
	membership, err := s.repo.GetTenantMembershipBySubject(ctx, principal.Subject)
	if err != nil {
		return db.TenantRecord{}, ErrTenantMembership
	}
	return membership.Tenant, nil
}

// FeedInfo returns the current feed tokens for the tenant and every staff
// member. Tokens are secrets — this stays behind auth.
func (s *Service) FeedInfo(ctx context.Context, principal domain.Principal) (FeedInfo, error) {
	tenant, err := s.tenantFor(ctx, principal)
	if err != nil {
		return FeedInfo{}, err
	}
	tenantToken, err := s.repo.GetTenantFeedToken(ctx, tenant.ID)
	if err != nil {
		return FeedInfo{}, err
	}
	staffTokens, err := s.repo.ListStaffFeedTokens(ctx, tenant.ID)
	if err != nil {
		return FeedInfo{}, err
	}
	info := FeedInfo{
		Tenant: FeedEntry{Token: tenantToken, FeedPath: feedPath(tenantToken)},
		Staff:  []StaffFeedEntry{},
	}
	for _, entry := range staffTokens {
		info.Staff = append(info.Staff, StaffFeedEntry{
			StaffID:     entry.StaffID,
			DisplayName: entry.DisplayName,
			Token:       entry.FeedToken,
			FeedPath:    feedPath(entry.FeedToken),
		})
	}
	return info, nil
}

// RotateToken issues a fresh feed token, invalidating the previous URL.
// Scope is "tenant" or "staff"; staff rotation requires staffID.
func (s *Service) RotateToken(ctx context.Context, principal domain.Principal, scope string, staffID string) (string, error) {
	tenant, err := s.tenantFor(ctx, principal)
	if err != nil {
		return "", err
	}
	switch scope {
	case "tenant":
		return s.repo.RotateTenantFeedToken(ctx, tenant.ID)
	case "staff":
		staffID = strings.TrimSpace(staffID)
		if staffID == "" {
			return "", ErrInvalidScope
		}
		member, err := s.repo.GetStaffByID(ctx, staffID)
		if err != nil || member.TenantID != tenant.ID {
			return "", ErrInvalidScope
		}
		return s.repo.RotateStaffFeedToken(ctx, staffID)
	default:
		return "", ErrInvalidScope
	}
}

// RenderFeed resolves a public feed token to an ICS body. Staff tokens take
// precedence; a miss on both lookups is a 404.
func (s *Service) RenderFeed(ctx context.Context, token string) (string, error) {
	if member, err := s.repo.GetStaffByFeedToken(ctx, token); err == nil {
		return s.render(ctx, member.TenantID, &member)
	}
	if tenant, err := s.repo.GetTenantByFeedToken(ctx, token); err == nil {
		return s.render(ctx, tenant.ID, nil)
	}
	return "", ErrFeedNotFound
}

func (s *Service) render(ctx context.Context, tenantID string, member *db.StaffRecord) (string, error) {
	tenant, err := s.repo.GetTenantByID(ctx, tenantID)
	if err != nil {
		return "", err
	}
	now := s.now()
	bookings, err := s.repo.ListBookingsByTenantBetween(ctx, tenantID, now.AddDate(0, 0, -feedLookbackDays), now.AddDate(0, 0, feedLookaheadDays))
	if err != nil {
		return "", err
	}
	services, err := s.repo.ListServicesByTenant(ctx, tenantID)
	if err != nil {
		return "", err
	}
	staffList, err := s.repo.ListStaffByTenant(ctx, tenantID)
	if err != nil {
		return "", err
	}
	locations, err := s.repo.ListLocationsByTenant(ctx, tenantID)
	if err != nil {
		return "", err
	}
	sessions, err := s.repo.ListClassSessionsByTenant(ctx, tenantID, now.AddDate(0, 0, -feedLookbackDays), 500)
	if err != nil {
		return "", err
	}

	serviceNames := map[string]string{}
	for _, service := range services {
		serviceNames[service.ID] = service.Name
	}
	staffNames := map[string]string{}
	for _, staff := range staffList {
		staffNames[staff.ID] = staff.DisplayName
	}
	locationNames := map[string]string{}
	for _, location := range locations {
		locationNames[location.ID] = location.Name
	}
	sessionTitles := map[string]string{}
	for _, session := range sessions {
		sessionTitles[session.ID] = session.Title
	}

	czech := strings.HasPrefix(tenant.Locale, "cs")
	labels := map[bool][3]string{
		true:  {"Telefon", "E-mail", "Poznámky"},
		false: {"Phone", "Email", "Notes"},
	}[czech]
	waitlistLabel := map[bool]string{true: "čekací listina", false: "waitlist"}[czech]

	var events []Event
	for _, booking := range bookings {
		if member != nil {
			if booking.StaffID == nil || *booking.StaffID != member.ID {
				continue
			}
		}
		title := ""
		if booking.ServiceID != nil {
			title = serviceNames[*booking.ServiceID]
		}
		if title == "" && booking.ClassSessionID != nil {
			title = sessionTitles[*booking.ClassSessionID]
		}
		if title == "" {
			title = "Bookra"
		}

		summary := title + " · " + booking.CustomerName
		if member == nil && booking.StaffID != nil {
			if name := staffNames[*booking.StaffID]; name != "" {
				summary += " · " + name
			}
		}

		var description []string
		if booking.CustomerPhone != "" {
			description = append(description, labels[0]+": "+booking.CustomerPhone)
		}
		if booking.CustomerEmail != "" {
			description = append(description, labels[1]+": "+booking.CustomerEmail)
		}
		if booking.Notes != "" {
			description = append(description, labels[2]+": "+booking.Notes)
		}

		location := ""
		if booking.LocationID != nil {
			location = locationNames[*booking.LocationID]
		}

		event := Event{
			UID:         booking.ID + "@bookra",
			StartsAt:    booking.StartsAt,
			EndsAt:      booking.EndsAt,
			Stamp:       booking.CreatedAt,
			Summary:     summary,
			Description: strings.Join(description, "\n"),
			Location:    location,
			Status:      "confirmed",
		}
		switch booking.Status {
		case "cancelled":
			event.Status = "cancelled"
		case "pending", "waitlisted":
			event.Status = "tentative"
			event.Transparent = true
		}
		if booking.Status == "waitlisted" {
			event.Summary += " (" + waitlistLabel + ")"
		}
		events = append(events, event)
	}
	sort.Slice(events, func(i, j int) bool { return events[i].StartsAt.Before(events[j].StartsAt) })

	name := fmt.Sprintf("Bookra — %s", tenant.Name)
	if member != nil {
		name = fmt.Sprintf("Bookra — %s · %s", tenant.Name, member.DisplayName)
	}
	return RenderCalendar(name, tenant.Timezone, events), nil
}