import { goto } from '$app/navigation'

export type HttpMethod = 'GET' | 'POST' | 'PUT' | 'PATCH' | 'DELETE'

export interface RequestOptions<TBody = unknown> {
  method?: HttpMethod
  body?: TBody
  signal?: AbortSignal
  headers?: Record<string, string>
}

export interface ApiError extends Error {
  status: number
  details?: unknown
}

function getAuthHeader() {
  return {}
}

async function handleResponse(res: Response) {
  if (res.status === 401) {
    // Redirect to login for unauthorized requests
    try {
      goto('/admin/login')
    } catch {
      // Ignore navigation errors (e.g., if already on login page)
    }
  }

  const contentType = res.headers.get('content-type') || ''
  const isJson = contentType.includes('application/json')
  const data = isJson ? await res.json().catch(() => undefined) : undefined

  if (!res.ok) {
    const err: ApiError = Object.assign(new Error('Request failed'), {
      status: res.status,
      details: data
    })
    throw err
  }
  return data
}

export async function request<TResponse = unknown, TBody = unknown>(
  url: string,
  opts: RequestOptions<TBody> = {}
): Promise<TResponse> {
  const { method = 'GET', body, signal, headers } = opts

  const isFormData = typeof FormData !== 'undefined' && body instanceof FormData
  const mergedHeaders: Record<string, string> = {
    ...(isFormData ? {} : { 'Content-Type': 'application/json' }),
    ...getAuthHeader(),
    ...(headers || {})
  }

  const res = await fetch(url, {
    method,
    headers: mergedHeaders,
    body: body ? (isFormData ? (body as any) : JSON.stringify(body)) : undefined,
    signal,
    credentials: 'same-origin'
  })

  return handleResponse(res) as Promise<TResponse>
}

export const api = {
  get: <T = unknown>(url: string, opts: Omit<RequestOptions, 'method' | 'body'> = {}) =>
    request<T>(url, { ...opts, method: 'GET' }),
  post: <T = unknown, B = unknown>(url: string, body: B, opts: Omit<RequestOptions<B>, 'method' | 'body'> = {}) =>
    request<T, B>(url, { ...opts, method: 'POST', body }),
  put: <T = unknown, B = unknown>(url: string, body: B, opts: Omit<RequestOptions<B>, 'method' | 'body'> = {}) =>
    request<T, B>(url, { ...opts, method: 'PUT', body }),
  patch: <T = unknown, B = unknown>(url: string, body: B, opts: Omit<RequestOptions<B>, 'method' | 'body'> = {}) =>
    request<T, B>(url, { ...opts, method: 'PATCH', body }),
  delete: <T = unknown>(url: string, opts: Omit<RequestOptions, 'method' | 'body'> = {}) =>
    request<T>(url, { ...opts, method: 'DELETE' })
}

export function createAbortable() {
  let controller: AbortController | null = null
  return {
    nextSignal() {
      if (controller) controller.abort()
      controller = new AbortController()
      return controller.signal
    },
    abort() {
      if (controller) controller.abort()
    }
  }
}