import { API_ENDPOINTS } from "@/lib/api_urls";
import { getStoredTokens } from "./auth";
import type {
  CreateAppointmentInput,
  ScheduleAppointmentInput,
  RejectAppointmentInput,
  UpdateAvailabilityInput,
} from "@/lib/schema/appointments";
import type {
  Appointment,
  AppointmentResponse,
  AppointmentsListResponse,
  AvailableDatesResponse,
  AdminAvailability,
  AppointmentStats,
  UserAppointmentStats,
  JitsiMeetingInfo,
  ApiError,
  WeeklyAvailabilityResponse,
  AvailabilityConfig,
  CheckDateAvailabilityResponse,
  AvailabilityOverview,
  SelectedSlot,
} from "@/lib/models/appointments";

// Helper function to extract error message from API response
function extractErrorMessage(error: ApiError): string {
  if (error.detail) {
    if (Array.isArray(error.detail)) {
      return error.detail.join(", ");
    }
    return String(error.detail);
  }
  
  if (error.message) {
    if (Array.isArray(error.message)) {
      return error.message.join(", ");
    }
    return String(error.message);
  }
  
  if (typeof error === "string") {
    return error;
  }
  
  return "An error occurred while creating the appointment";
}

// Create appointment
export async function createAppointment(
  input: CreateAppointmentInput
): Promise<Appointment> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required. Please log in to book an appointment.");
  }

  // Validate required fields
  if (!input.first_name || !input.last_name || !input.email) {
    throw new Error("First name, last name, and email are required");
  }
  
  // New API format: use selected_slots
  if (!input.selected_slots || input.selected_slots.length === 0) {
    throw new Error("At least one time slot must be selected");
  }

  // Validate and clean selected_slots to ensure all have day and time_slot
  // This filters out any invalid slots and ensures proper format
  const validSlots: SelectedSlot[] = input.selected_slots
    .filter((slot, index) => {
      // Check if slot exists and is an object
      if (!slot || typeof slot !== 'object') {
        return false;
      }
      // Check if both day and time_slot properties exist
      if (typeof slot.day === 'undefined' || typeof slot.time_slot === 'undefined') {
        return false;
      }
      // Validate day is a number between 0-6
      const dayNum = Number(slot.day);
      if (isNaN(dayNum) || dayNum < 0 || dayNum > 6) {
        return false;
      }
      // Validate time_slot is a valid string (normalize to lowercase)
      const timeSlot = String(slot.time_slot).toLowerCase().trim();
      if (!['morning', 'afternoon', 'evening'].includes(timeSlot)) {
        return false;
      }
      return true;
    })
    .map(slot => ({
      day: Number(slot.day),
      time_slot: String(slot.time_slot).toLowerCase().trim() as "morning" | "afternoon" | "evening",
    }));

  if (validSlots.length === 0) {
    throw new Error("At least one valid time slot must be selected. Each slot must have both 'day' (0-6) and 'time_slot' (morning, afternoon, or evening).");
  }

  // Limit field lengths to prevent database errors (100 char limit for all string fields)
  // Truncate all string fields BEFORE trimming to handle edge cases
  const firstName = input.first_name ? String(input.first_name).trim().substring(0, 100) : '';
  const lastName = input.last_name ? String(input.last_name).trim().substring(0, 100) : '';
  const email = input.email ? String(input.email).trim().toLowerCase().substring(0, 100) : '';
  const phone = input.phone ? String(input.phone).trim().substring(0, 100) : undefined;
  const reason = input.reason ? String(input.reason).trim().substring(0, 100) : undefined;

  // Build payload with only the fields the API expects - no extra fields
  const payload: {
    first_name: string;
    last_name: string;
    email: string;
    selected_slots: Array<{ day: number; time_slot: string }>;
    phone?: string;
    reason?: string;
  } = {
    first_name: firstName,
    last_name: lastName,
    email: email,
    selected_slots: validSlots.map(slot => ({
      day: Number(slot.day),
      time_slot: String(slot.time_slot).toLowerCase().trim(),
    })),
  };

  // Only add optional fields if they have values (and are within length limits)
  if (phone && phone.length > 0 && phone.length <= 100) {
    payload.phone = phone;
  }
  if (reason && reason.length > 0 && reason.length <= 100) {
    payload.reason = reason;
  }

  // Final validation: ensure all string fields in payload are exactly 100 chars or less
  // This is a safety check to prevent any encoding or serialization issues
  const finalPayload = {
    first_name: payload.first_name.substring(0, 100),
    last_name: payload.last_name.substring(0, 100),
    email: payload.email.substring(0, 100),
    selected_slots: payload.selected_slots,
    ...(payload.phone && { phone: payload.phone.substring(0, 100) }),
    ...(payload.reason && { reason: payload.reason.substring(0, 100) }),
  };

  const response = await fetch(API_ENDPOINTS.meetings.createAppointment, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
    body: JSON.stringify(finalPayload),
  });

  // Read response text first (can only be read once)
  const responseText = await response.text();
  
  // Check content type before parsing
  const contentType = response.headers.get("content-type");
  let data: any;

  if (contentType && contentType.includes("application/json")) {
    try {
      if (!responseText) {
        throw new Error(`Server returned empty response (${response.status})`);
      }
      data = JSON.parse(responseText);
    } catch (e) {
      throw new Error(`Server error (${response.status}): ${response.statusText || 'Invalid response format'}`);
    }
  } else {
    // Response is not JSON (likely HTML error page)
    // Try to extract error message from HTML if possible
    let errorMessage = `Server error (${response.status}): ${response.statusText || 'Internal Server Error'}`;
    
    // Try to find error details in HTML
    // Use [\s\S] instead of . with s flag for better compatibility
    const errorMatch = responseText.match(/<pre[^>]*>([\s\S]*?)<\/pre>/i) || 
                      responseText.match(/<h1[^>]*>([\s\S]*?)<\/h1>/i) ||
                      responseText.match(/<title[^>]*>([\s\S]*?)<\/title>/i);
    
    if (errorMatch && errorMatch[1]) {
      const htmlError = errorMatch[1].replace(/<[^>]*>/g, '').trim();
      if (htmlError) {
        errorMessage += `. ${htmlError}`;
      }
    }
    
    throw new Error(errorMessage);
  }

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  // Handle API response format: { appointment_id, message }
  // According to API docs, response includes appointment_id and message
  if (data.appointment_id) {
    // Construct a minimal Appointment object from the response
    // We'll use the input data plus the appointment_id from response
    const appointment: Appointment = {
      id: data.appointment_id,
      first_name: input.first_name.trim(),
      last_name: input.last_name.trim(),
      email: input.email.trim().toLowerCase(),
      phone: input.phone?.trim(),
      reason: input.reason?.trim(),
      selected_slots: validSlots,
      status: "pending_review",
      created_at: new Date().toISOString(),
      updated_at: new Date().toISOString(),
    };
    return appointment;
  }

  // Handle different response formats for backward compatibility
  if (data.appointment) {
    return data.appointment;
  }
  if ((data as any).data) {
    return (data as any).data;
  }
  
  // If appointment is returned directly
  return data as unknown as Appointment;
}

// Get available dates (optional endpoint - may fail if admin hasn't set availability)
export async function getAvailableDates(): Promise<AvailableDatesResponse> {
  try {
  const response = await fetch(API_ENDPOINTS.meetings.availableDates, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
    },
  });

    // Handle different response formats
    const contentType = response.headers.get("content-type");
    let data: any;

    if (contentType && contentType.includes("application/json")) {
      const responseText = await response.text();
      if (!responseText) {
        throw new Error(`Server returned empty response (${response.status})`);
      }
      try {
        data = JSON.parse(responseText);
      } catch (parseError) {
        throw new Error(`Invalid response format (${response.status})`);
      }
    } else {
      throw new Error(`Server error (${response.status}): ${response.statusText || 'Invalid response'}`);
    }

  if (!response.ok) {
      // Return empty response instead of throwing - this endpoint is optional
      return {
        dates: [],
      };
  }

  // If API returns array directly, wrap it in response object
  if (Array.isArray(data)) {
    return {
      dates: data,
    };
  }
  
  return data as AvailableDatesResponse;
  } catch (error) {
    // Return empty response - don't break the app
    return {
      dates: [],
    };
  }
}

// Get weekly availability (Public)
export async function getWeeklyAvailability(): Promise<WeeklyAvailabilityResponse> {
  const response = await fetch(API_ENDPOINTS.meetings.weeklyAvailability, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
    },
  });

  const data: any = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  // Handle different response formats - API might return array directly or wrapped
  if (Array.isArray(data)) {
    return data;
  }
  
  // If wrapped in an object, return as is (our interface supports it)
  return data;
}

// Get availability configuration (Public)
export async function getAvailabilityConfig(): Promise<AvailabilityConfig> {
  const response = await fetch(API_ENDPOINTS.meetings.availabilityConfig, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
    },
  });

  const data: AvailabilityConfig = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  return data;
}

// Check date availability (Public)
export async function checkDateAvailability(date: string): Promise<CheckDateAvailabilityResponse> {
  const response = await fetch(API_ENDPOINTS.meetings.checkDateAvailability, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ date }),
  });

  const data: CheckDateAvailabilityResponse = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  return data;
}

// Get availability overview (Public)
export async function getAvailabilityOverview(): Promise<AvailabilityOverview> {
  const response = await fetch(API_ENDPOINTS.meetings.availabilityOverview, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
    },
  });

  const data: AvailabilityOverview = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  return data;
}

// List appointments (Admin sees all, users see their own)
export async function listAppointments(email?: string): Promise<Appointment[]> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const url = email 
    ? `${API_ENDPOINTS.meetings.listAppointments}?email=${encodeURIComponent(email)}`
    : API_ENDPOINTS.meetings.listAppointments;

  const response = await fetch(url, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
  });

  const responseText = await response.text();

  if (!response.ok) {
    let errorData: any;
    try {
      errorData = JSON.parse(responseText);
    } catch {
      throw new Error(`Server error (${response.status}): ${response.statusText || 'Internal Server Error'}`);
    }
    const errorMessage = extractErrorMessage(errorData as unknown as ApiError);
    throw new Error(errorMessage);
  }

  // Parse JSON response
  let data: any;
  try {
    if (!responseText || responseText.trim().length === 0) {
      return [];
    }
    data = JSON.parse(responseText);
  } catch (error) {
    throw new Error(`Failed to parse response: Invalid JSON format`);
  }

  // Handle different response formats
  // API returns array directly: [{ id, first_name, ... }, ...]
  if (Array.isArray(data)) {
    return data;
  }
  // Handle wrapped responses (if any)
  if (data && typeof data === 'object') {
  if (data.appointments && Array.isArray(data.appointments)) {
    return data.appointments;
  }
  if (data.results && Array.isArray(data.results)) {
    return data.results;
    }
    // If data is an object but not an array and doesn't have appointments/results, return empty
    // This shouldn't happen but handle gracefully
    if (data.id || data.first_name) {
      // Single appointment object, wrap in array
      return [data];
    }
  }
  
  return [];
}

// Get user appointments
export async function getUserAppointments(): Promise<Appointment[]> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(API_ENDPOINTS.meetings.userAppointments, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
  });

  const data = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  // Handle different response formats
  // API might return array directly or wrapped in an object
  if (Array.isArray(data)) {
    return data;
  }
  if (data.appointments && Array.isArray(data.appointments)) {
    return data.appointments;
  }
  if (data.results && Array.isArray(data.results)) {
    return data.results;
  }
  
  return [];
}

// Get appointment detail
export async function getAppointmentDetail(id: string): Promise<Appointment> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(`${API_ENDPOINTS.meetings.listAppointments}${id}/`, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
  });

  const data: AppointmentResponse = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  if (data.appointment) {
    return data.appointment;
  }
  
  return data as unknown as Appointment;
}

// Schedule appointment (Admin only)
export async function scheduleAppointment(
  id: string,
  input: ScheduleAppointmentInput
): Promise<Appointment> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(`${API_ENDPOINTS.meetings.listAppointments}${id}/schedule/`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
    body: JSON.stringify(input),
  });

  let data: any;
  const contentType = response.headers.get("content-type");
  
  if (contentType && contentType.includes("application/json")) {
    try {
      const text = await response.text();
      data = text ? JSON.parse(text) : {};
    } catch (e) {
      data = {};
    }
  } else {
    const text = await response.text();
    data = text || {};
  }

  if (!response.ok) {
    // Try to extract detailed error information
    let errorMessage = `Failed to schedule appointment (${response.status})`;
    
    if (data && Object.keys(data).length > 0) {
      // Check for common error formats
      if (data.detail) {
        errorMessage = Array.isArray(data.detail) ? data.detail.join(", ") : String(data.detail);
      } else if (data.message) {
        errorMessage = Array.isArray(data.message) ? data.message.join(", ") : String(data.message);
      } else if (data.error) {
        errorMessage = Array.isArray(data.error) ? data.error.join(", ") : String(data.error);
      } else if (typeof data === "string") {
        errorMessage = data;
      } else {
        // Check for field-specific errors
        const fieldErrors: string[] = [];
        Object.keys(data).forEach((key) => {
          if (key !== "detail" && key !== "message" && key !== "error") {
            const fieldError = data[key];
            if (Array.isArray(fieldError)) {
              fieldErrors.push(`${key}: ${fieldError.join(", ")}`);
            } else if (typeof fieldError === "string") {
              fieldErrors.push(`${key}: ${fieldError}`);
            }
          }
        });
        if (fieldErrors.length > 0) {
          errorMessage = fieldErrors.join(". ");
        } else {
          // If we have data but can't parse it, show the status
          errorMessage = `Server error: ${response.status} ${response.statusText}`;
        }
      }
    } else {
      // No data in response
      errorMessage = `Server error: ${response.status} ${response.statusText || 'Unknown error'}`;
    }
    
    throw new Error(errorMessage);
  }

  if (data.appointment) {
    return data.appointment;
  }
  
  return data as unknown as Appointment;
}

// Reject appointment (Admin only)
export async function rejectAppointment(
  id: string,
  input: RejectAppointmentInput
): Promise<Appointment> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(`${API_ENDPOINTS.meetings.listAppointments}${id}/reject/`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
    body: JSON.stringify(input),
  });

  const data: AppointmentResponse = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  if (data.appointment) {
    return data.appointment;
  }
  
  return data as unknown as Appointment;
}

// Get admin availability (public version - uses weekly availability endpoint instead)
export async function getPublicAvailability(): Promise<AdminAvailability | null> {
  try {
    // Use weekly availability endpoint which is public
    const weeklyAvailability = await getWeeklyAvailability();
    
    // Normalize to array format
    const weekArray = Array.isArray(weeklyAvailability) 
      ? weeklyAvailability 
      : (weeklyAvailability as any).week || [];
    
    if (!weekArray || weekArray.length === 0) {
      return null;
    }

    // Convert weekly availability to AdminAvailability format
    const availabilitySchedule: Record<string, string[]> = {};
    const availableDays: number[] = [];
    const availableDaysDisplay: string[] = [];

    weekArray.forEach((day: any) => {
      if (day.is_available && day.available_slots && day.available_slots.length > 0) {
        availabilitySchedule[day.day.toString()] = day.available_slots;
        availableDays.push(day.day);
        availableDaysDisplay.push(day.day_name);
      }
    });

    return {
      available_days: availableDays,
      available_days_display: availableDaysDisplay,
      availability_schedule: availabilitySchedule,
      all_available_slots: weekArray
        .filter((d: any) => d.is_available)
        .flatMap((d: any) => d.available_slots.map((slot: string) => ({ day: d.day, time_slot: slot as "morning" | "afternoon" | "evening" }))),
    } as AdminAvailability;
  } catch (error) {
    return null;
  }
}

// Get admin availability
export async function getAdminAvailability(): Promise<AdminAvailability> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(API_ENDPOINTS.meetings.adminAvailability, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
  });

  const data: any = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  // Handle new format with availability_schedule
  // API returns availability_schedule, which may be a JSON string or object
  // Time slots are strings: "morning", "afternoon", "evening"
  if (data.availability_schedule) {
    let availabilitySchedule: Record<string, string[]>;
    
    // Map numeric indices to string names (in case API returns numeric indices)
    const numberToTimeSlot: Record<number, string> = {
      0: 'morning',
      1: 'afternoon',
      2: 'evening',
    };
    
    // Parse if it's a string, otherwise use as-is
    let rawSchedule: Record<string, number[] | string[]>;
    if (typeof data.availability_schedule === 'string') {
      try {
        rawSchedule = JSON.parse(data.availability_schedule);
      } catch (parseError) {
        rawSchedule = {};
      }
    } else {
      rawSchedule = data.availability_schedule;
    }
    
    // Convert to string format, handling both numeric indices and string values
    availabilitySchedule = {};
    Object.keys(rawSchedule).forEach(day => {
      const slots = rawSchedule[day];
      if (Array.isArray(slots) && slots.length > 0) {
        // Check if slots are numbers (indices) or already strings
        if (typeof slots[0] === 'number') {
          // Convert numeric indices to string names
          availabilitySchedule[day] = (slots as number[])
            .map((num: number) => numberToTimeSlot[num])
            .filter((slot: string | undefined) => slot !== undefined) as string[];
        } else {
          // Already strings, validate and use as-is
          availabilitySchedule[day] = (slots as string[]).filter(slot => 
            ['morning', 'afternoon', 'evening'].includes(slot)
          );
        }
      }
    });
    
    const availableDays = Object.keys(availabilitySchedule).map(Number);
    
    // Generate available_days_display if not provided
    const dayNames = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'];
    const availableDaysDisplay = availableDays.map(day => dayNames[day] || `Day ${day}`);

    return {
      available_days: availableDays,
      available_days_display: data.availability_schedule_display ? [data.availability_schedule_display] : availableDaysDisplay,
      availability_schedule: availabilitySchedule,
      availability_schedule_display: data.availability_schedule_display,
      all_available_slots: data.all_available_slots || [],
    } as AdminAvailability;
  }

  // Handle legacy format
  let availableDays: number[] = [];
  if (typeof data.available_days === 'string') {
    try {
      availableDays = JSON.parse(data.available_days);
    } catch {
      // If parsing fails, try splitting by comma
      availableDays = data.available_days.split(',').map((d: string) => parseInt(d.trim())).filter((d: number) => !isNaN(d));
    }
  } else if (Array.isArray(data.available_days)) {
    availableDays = data.available_days;
  }

  return {
    available_days: availableDays,
    available_days_display: data.available_days_display || [],
  } as AdminAvailability;
}

// Update admin availability
export async function updateAdminAvailability(
  input: UpdateAvailabilityInput
): Promise<AdminAvailability> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  // Prepare payload using new format (availability_schedule)
  // API expects availability_schedule as an object with string keys (day numbers) and string arrays (time slot names)
  // Format: { "0": ["morning", "afternoon"], "1": ["evening"], ... }
  const payload: any = {};
  
  if (input.availability_schedule) {
    // Validate and clean the schedule object
    // API expects: { "0": ["morning", "evening"], "1": ["afternoon"], ... }
    // Time slots are strings: "morning", "afternoon", "evening"
    const cleanedSchedule: Record<string, string[]> = {};
    Object.keys(input.availability_schedule).forEach(key => {
      // Ensure key is a valid day (0-6)
      const dayNum = parseInt(key);
      if (isNaN(dayNum) || dayNum < 0 || dayNum > 6) {
        return;
      }
      
      const slots = input.availability_schedule[key];
      if (Array.isArray(slots) && slots.length > 0) {
        // Filter to only valid time slot strings and remove duplicates
        const validSlots = slots
          .filter((slot: string) => 
            typeof slot === 'string' && ['morning', 'afternoon', 'evening'].includes(slot)
          )
          .filter((slot: string, index: number, self: string[]) => 
            self.indexOf(slot) === index
          ); // Remove duplicates
        
        if (validSlots.length > 0) {
          // Ensure day key is a string (as per API spec)
          cleanedSchedule[key.toString()] = validSlots;
        }
      }
    });
    
    if (Object.keys(cleanedSchedule).length === 0) {
      throw new Error("At least one day with valid time slots must be provided");
    }
    
    // Sort the schedule keys for consistency
    const sortedSchedule: Record<string, string[]> = {};
    Object.keys(cleanedSchedule)
      .sort((a, b) => parseInt(a) - parseInt(b))
      .forEach(key => {
        sortedSchedule[key] = cleanedSchedule[key];
      });
    
    // IMPORTANT: API expects availability_schedule as an object (not stringified)
    // Format: { "0": ["morning", "afternoon"], "1": ["evening"], ... }
    payload.availability_schedule = sortedSchedule;
  } else if (input.available_days) {
    // Legacy format: available_days
    payload.available_days = Array.isArray(input.available_days) 
      ? input.available_days.map(day => Number(day))
      : input.available_days;
  } else {
    throw new Error("Either availability_schedule or available_days must be provided");
  }


  // Try PUT first, fallback to PATCH if needed
  // The payload object will be JSON stringified, including availability_schedule as an object
  let response = await fetch(API_ENDPOINTS.meetings.adminAvailability, {
    method: "PUT",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
    body: JSON.stringify(payload),
  });

  // If PUT fails with 500, try PATCH (some APIs prefer PATCH for updates)
  if (!response.ok && response.status === 500) {
    response = await fetch(API_ENDPOINTS.meetings.adminAvailability, {
      method: "PATCH",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${tokens.access}`,
      },
      body: JSON.stringify(payload),
    });
  }

  // Read response text first (can only be read once)
  const responseText = await response.text();
  let data: any;
  
  // Get content type
  const contentType = response.headers.get("content-type") || "";
  
  // Handle empty response
  if (!responseText || responseText.trim().length === 0) {
    // If successful status but empty response, refetch the availability
    if (response.ok) {
      return await getAdminAvailability();
    }
    
    throw new Error(`Server error (${response.status}): ${response.statusText || 'Empty response from server'}`);
  }
  
  // Try to parse as JSON
  if (contentType.includes("application/json")) {
      try {
        data = JSON.parse(responseText);
  } catch (parseError) {
        throw new Error(`Server error (${response.status}): Invalid JSON response format`);
      }
  } else {
    // Response is not JSON - try to extract useful information
    // Try to extract error message from HTML if it's an HTML error page
    let errorMessage = `Server error (${response.status}): ${response.statusText || 'Internal Server Error'}`;
    let actualError = '';
    let errorType = '';
    let fullTraceback = '';
    
    if (responseText) {
      // Extract Django error details from HTML
      const titleMatch = responseText.match(/<title[^>]*>(.*?)<\/title>/i);
      const h1Match = responseText.match(/<h1[^>]*>(.*?)<\/h1>/i);
      
      // Try to find the actual error traceback in <pre> tags (Django debug pages)
      const tracebackMatch = responseText.match(/<pre[^>]*class="[^"]*traceback[^"]*"[^>]*>([\s\S]*?)<\/pre>/i) ||
                            responseText.match(/<pre[^>]*>([\s\S]*?)<\/pre>/i);
      
      // Extract the actual error type and message
      const errorTypeMatch = responseText.match(/<h2[^>]*>(.*?)<\/h2>/i);
      
      if (tracebackMatch && tracebackMatch[1]) {
        // Extract the full traceback and find the actual error
        const tracebackText = tracebackMatch[1].replace(/<[^>]*>/g, ''); // Remove HTML tags
        fullTraceback = tracebackText;
        const tracebackLines = tracebackText.split('\n').filter(line => line.trim());
        
        // Look for the actual error message - Django errors usually appear at the end
        // First, try to find error patterns in the entire traceback
        const errorPatterns = [
          // Database column errors
          /column\s+[\w.]+\.(\w+)\s+(does not exist|already exists|is missing)/i,
          // Programming errors
          /(ProgrammingError|OperationalError|IntegrityError|DatabaseError|ValueError|TypeError|AttributeError|KeyError):\s*(.+?)(?:\n|$)/i,
          // Generic error patterns
          /^(\w+Error):\s*(.+)$/i,
          // Error messages without type
          /^(.+Error[:\s]+.+)$/i,
        ];
        
        // Search from the end backwards (errors are usually at the end)
        for (let i = tracebackLines.length - 1; i >= 0; i--) {
          const line = tracebackLines[i];
          
          // Check each pattern
          for (const pattern of errorPatterns) {
            const match = line.match(pattern);
            if (match) {
              // For database column errors, capture the full message
              if (pattern.source.includes('column')) {
                actualError = match[0];
                errorType = 'DatabaseError';
              } else if (match[1] && match[2]) {
                errorType = match[1];
                actualError = match[2].trim();
              } else {
                actualError = match[0];
              }
              break;
            }
          }
          if (actualError) break;
        }
        
        // If no pattern match, look for lines containing "Error" or common error keywords
        if (!actualError) {
          for (let i = tracebackLines.length - 1; i >= Math.max(0, tracebackLines.length - 10); i--) {
            const line = tracebackLines[i];
            if (line.match(/(Error|Exception|Failed|Invalid|Missing|does not exist|already exists)/i)) {
              actualError = line;
              break;
            }
          }
        }
        
        // Last resort: get the last line
        if (!actualError && tracebackLines.length > 0) {
          actualError = tracebackLines[tracebackLines.length - 1];
        }
        
        // Clean up the error message
        if (actualError) {
          actualError = actualError.trim();
          // Remove common prefixes
          actualError = actualError.replace(/^(Traceback|File|Error|Exception):\s*/i, '');
        }
      } else if (errorTypeMatch && errorTypeMatch[1]) {
        errorType = errorTypeMatch[1].replace(/<[^>]*>/g, '').trim();
        actualError = errorType;
        if (errorType && errorType.length < 200) {
          errorMessage += `. ${errorType}`;
        }
      } else if (h1Match && h1Match[1]) {
        actualError = h1Match[1].replace(/<[^>]*>/g, '').trim();
        if (actualError && actualError.length < 200) {
          errorMessage += `. ${actualError}`;
        }
      } else if (titleMatch && titleMatch[1]) {
        actualError = titleMatch[1].replace(/<[^>]*>/g, '').trim();
        if (actualError && actualError.length < 200) {
          errorMessage += `. ${actualError}`;
        }
      }
    }
    
    // Update error message with the extracted error
    if (actualError) {
      errorMessage = `Server error (${response.status}): ${actualError}`;
    }
    
    throw new Error(errorMessage);
  }

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    
    // Build detailed error message
    let detailedError = `Server error (${response.status}): `;
    if (data && typeof data === 'object') {
      if (data.detail) {
        detailedError += Array.isArray(data.detail) ? data.detail.join(", ") : String(data.detail);
      } else if (data.error) {
        detailedError += Array.isArray(data.error) ? data.error.join(", ") : String(data.error);
      } else if (data.message) {
        detailedError += Array.isArray(data.message) ? data.message.join(", ") : String(data.message);
      } else {
        detailedError += response.statusText || 'Failed to update availability';
      }
    } else if (responseText && responseText.length > 0) {
      // Try to extract error from HTML response if it's not JSON
      detailedError += responseText.substring(0, 200);
    } else {
      detailedError += response.statusText || 'Failed to update availability';
    }
    
    throw new Error(detailedError);
  }

  // Handle new format with availability_schedule in response
  // API returns availability_schedule, which may be a JSON string or object
  // Time slots may be strings or numeric indices
  if (data && data.availability_schedule) {
    let availabilitySchedule: Record<string, string[]>;
    
    // Map numeric indices to string names (in case API returns numeric indices)
    const numberToTimeSlot: Record<number, string> = {
      0: 'morning',
      1: 'afternoon',
      2: 'evening',
    };
    
    // Parse if it's a string, otherwise use as-is
    let rawSchedule: Record<string, number[] | string[]>;
    if (typeof data.availability_schedule === 'string') {
      try {
        rawSchedule = JSON.parse(data.availability_schedule);
      } catch (parseError) {
        rawSchedule = {};
      }
    } else if (typeof data.availability_schedule === 'object') {
      rawSchedule = data.availability_schedule;
    } else {
      rawSchedule = {};
    }
    
    // Convert to string format, handling both numeric indices and string values
    availabilitySchedule = {};
    Object.keys(rawSchedule).forEach(day => {
      const slots = rawSchedule[day];
      if (Array.isArray(slots) && slots.length > 0) {
        // Check if slots are numbers (indices) or already strings
        if (typeof slots[0] === 'number') {
          // Convert numeric indices to string names
          availabilitySchedule[day] = (slots as number[])
            .map((num: number) => numberToTimeSlot[num])
            .filter((slot: string | undefined) => slot !== undefined) as string[];
        } else {
          // Already strings, validate and use as-is
          availabilitySchedule[day] = (slots as string[]).filter(slot => 
            ['morning', 'afternoon', 'evening'].includes(slot)
          );
        }
      }
    });
    
    const availableDays = Object.keys(availabilitySchedule).map(Number);
    const dayNames = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'];
    const availableDaysDisplay = availableDays.map(day => dayNames[day] || `Day ${day}`);

    return {
      available_days: availableDays,
      available_days_display: data.availability_schedule_display ? 
        (Array.isArray(data.availability_schedule_display) ? 
          data.availability_schedule_display : 
          [data.availability_schedule_display]) : 
        availableDaysDisplay,
      availability_schedule: availabilitySchedule,
      availability_schedule_display: data.availability_schedule_display,
      all_available_slots: data.all_available_slots || [],
    } as AdminAvailability;
  }
  
  // If response is empty but successful (200), return empty availability
  // This might happen if the server doesn't return data on success
  if (response.ok && (!data || Object.keys(data).length === 0)) {
    // Refetch the availability to get the updated data
    return getAdminAvailability();
  }

  // Handle legacy format
  let availableDays: number[] = [];
  if (typeof data.available_days === 'string') {
    try {
      availableDays = JSON.parse(data.available_days);
    } catch {
      // If parsing fails, try splitting by comma
      availableDays = data.available_days.split(',').map((d: string) => parseInt(d.trim())).filter((d: number) => !isNaN(d));
    }
  } else if (Array.isArray(data.available_days)) {
    availableDays = data.available_days;
  }

  return {
    available_days: availableDays,
    available_days_display: data.available_days_display || [],
  } as AdminAvailability;
}

// Get appointment stats (Admin only)
export async function getAppointmentStats(): Promise<AppointmentStats> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(`${API_ENDPOINTS.meetings.listAppointments}stats/`, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
  });

  const data: AppointmentStats = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  return data;
}

// Get user appointment stats
export async function getUserAppointmentStats(email: string): Promise<UserAppointmentStats> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  if (!email) {
    throw new Error("Email is required to fetch user appointment stats.");
  }

  const response = await fetch(API_ENDPOINTS.meetings.userAppointmentStats, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
    body: JSON.stringify({ email }),
  });

  const responseText = await response.text();

  if (!response.ok) {
    let errorData: any;
    try {
      errorData = JSON.parse(responseText);
    } catch {
      throw new Error(`Server error (${response.status}): ${response.statusText || 'Internal Server Error'}`);
    }
    const errorMessage = extractErrorMessage(errorData as unknown as ApiError);
    throw new Error(errorMessage);
  }

  let data: UserAppointmentStats;
  try {
    if (!responseText || responseText.trim().length === 0) {
      throw new Error("Empty response from server");
    }
    data = JSON.parse(responseText);
  } catch (error) {
    throw new Error(`Failed to parse response: Invalid JSON format`);
  }

  return data;
}

// Get Jitsi meeting info
export async function getJitsiMeetingInfo(id: string): Promise<JitsiMeetingInfo> {
  const tokens = getStoredTokens();
  
  if (!tokens.access) {
    throw new Error("Authentication required.");
  }

  const response = await fetch(`${API_ENDPOINTS.meetings.listAppointments}${id}/jitsi-meeting/`, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${tokens.access}`,
    },
  });

  const data: JitsiMeetingInfo = await response.json();

  if (!response.ok) {
    const errorMessage = extractErrorMessage(data as unknown as ApiError);
    throw new Error(errorMessage);
  }

  return data;
}