/** Back office ↔ store-server client; session token survives reloads. */
import type { Gstr1, Gstr3b, HsnRow, Reconciliation, TaxAmounts } from '@sims/billing-engine'

let token = sessionStorage.getItem('bo.token') ?? ''

export function hasSession(): boolean {
  return token !== ''
}

export function clearSession(): void {
  token = ''
  sessionStorage.removeItem('bo.token')
}

async function call<T>(path: string, init?: RequestInit): Promise<T> {
  const res = await fetch(`/api${path}`, {
    ...init,
    headers: {
      'content-type': 'application/json',
      ...(token !== '' ? { authorization: `Bearer ${token}` } : {}),
    },
  }).catch(() => undefined)
  if (res === undefined) throw new Error('Store-server unreachable (E-3301)')
  if (res.status === 401) clearSession()
  const body = (await res.json().catch(() => ({}))) as T & { error?: string }
  if (!res.ok) throw new Error(body.error ?? `Server error HTTP ${res.status}`)
  return body
}

export async function login(username: string, password: string): Promise<string> {
  const s = await call<{ token: string; displayName: string }>('/auth/login', {
    method: 'POST',
    body: JSON.stringify({ username, password }),
  })
  token = s.token
  sessionStorage.setItem('bo.token', s.token)
  return s.displayName
}

/** End the session server-side (M4) then clear it locally. Best-effort on the network call. */
export async function logout(): Promise<void> {
  try { await call('/auth/logout', { method: 'POST' }) } catch { /* server down: clear locally anyway */ }
  clearSession()
}

export const getItems = (q?: string): Promise<Record<string, unknown>[]> =>
  call(`/items${q !== undefined && q !== '' ? `?q=${encodeURIComponent(q)}` : ''}`)
export const createItem = (body: Record<string, unknown>): Promise<Record<string, unknown>> =>
  call('/items', { method: 'POST', body: JSON.stringify(body) })
export const getParties = (kind?: string): Promise<Record<string, unknown>[]> =>
  call(`/parties${kind !== undefined ? `?kind=${kind}` : ''}`)
export const getBills = (date?: string, limit?: number, offset?: number): Promise<Record<string, unknown>[]> => {
  const qs = new URLSearchParams()
  if (date !== undefined) qs.set('date', date)
  if (limit !== undefined) qs.set('limit', String(limit))
  if (offset !== undefined) qs.set('offset', String(offset))
  return call(`/bills${qs.toString() !== '' ? `?${qs}` : ''}`)
}
export const getStock = (): Promise<Record<string, unknown>[]> => call('/stock')
/** Credit notes (SALE_RETURN docs) — tenant-scoped, paginated; feeds the Returns page. */
export const getReturns = (limit?: number, offset?: number): Promise<Record<string, unknown>[]> => {
  const qs = new URLSearchParams()
  if (limit !== undefined) qs.set('limit', String(limit))
  if (offset !== undefined) qs.set('offset', String(offset))
  return call(`/returns${qs.toString() !== '' ? `?${qs}` : ''}`)
}
/** S5: per-batch on-hand + value inputs joined to the item — feeds the expiry
 *  dashboard and the Stock page's batch breakdown. */
export const getExpiry = (): Promise<Record<string, unknown>[]> => call('/expiry')
export const getAudit = (limit?: number, offset?: number): Promise<Record<string, unknown>[]> => {
  const qs = new URLSearchParams()
  if (limit !== undefined) qs.set('limit', String(limit))
  if (offset !== undefined) qs.set('offset', String(offset))
  return call(`/audit${qs.toString() !== '' ? `?${qs}` : ''}`)
}

export const getPurchases = (): Promise<Record<string, unknown>[]> => call('/purchases')
export const getLastCosts = (supplierId?: string): Promise<Record<string, { last?: number; supplierLast?: number }>> =>
  call(`/purchases/last-costs${supplierId !== undefined ? `?supplierId=${supplierId}` : ''}`)
export const postPurchase = (body: Record<string, unknown>): Promise<{ id: string; totalPaise: number }> =>
  call('/purchases', { method: 'POST', body: JSON.stringify(body) })
export const getCostHistory = (itemId: string, supplierId?: string): Promise<{ cost: number; date: string; supplier: string }[]> =>
  call(`/purchases/cost-history?itemId=${itemId}${supplierId !== undefined ? `&supplierId=${supplierId}` : ''}`)
export const getBootstrapPublic = (): Promise<{ taxClasses: { classCode: string; ratePctBp: number; cessPctBp: number; effectiveFrom: string; effectiveTo?: string }[] }> =>
  call('/bootstrap?counter=C1')

export interface Seller { id: string; name: string; storeCode: string; stateCode: string; gstin?: string }
/** Seller header for GST invoices/labels — store name, GSTIN, state (from bootstrap). */
export const getSeller = (): Promise<Seller> =>
  call<{ store: Seller }>('/bootstrap?counter=C1').then((b) => b.store)

// GST returns — READ-ONLY reporting over a period's immutable documents. The server folds them
// through the shared engine and returns each section plus a reconciliation proof (see repos-gst).
export interface Gstr1Response extends Gstr1 { period: string; storeStateCode: string; reconciliation: Reconciliation }
export interface Gstr3bResponse extends Gstr3b { period: string; storeStateCode: string; reconciliation: Reconciliation }
export interface HsnResponse { period: string; storeStateCode: string; rows: HsnRow[]; totals: TaxAmounts; reconciliation: Reconciliation }

export const getGstr1 = (period: string): Promise<Gstr1Response> => call(`/gst/gstr1?period=${encodeURIComponent(period)}`)
export const getGstr3b = (period: string): Promise<Gstr3bResponse> => call(`/gst/gstr3b?period=${encodeURIComponent(period)}`)
export const getGstHsn = (period: string): Promise<HsnResponse> => call(`/gst/hsn?period=${encodeURIComponent(period)}`)
/** The pragmatic GSTN-shaped JSON export (documented in-payload as NOT a certified filing). */
export const getGstr1Json = (period: string): Promise<Record<string, unknown>> => call(`/gst/gstr1.json?period=${encodeURIComponent(period)}`)