/**
 * Meta WhatsApp Cloud API helpers.
 *
 * Every function takes a single options object (named parameters) instead
 * of positional arguments. This was a deliberate choice after the same
 * swapped-args bug was found four times in a row with the positional form
 * (e.g. `(accessToken, phoneNumberId)` vs `(phoneNumberId, accessToken)`).
 * With named params, a typo surfaces immediately as a TypeScript error
 * instead of a runtime rejection from Meta.
 */

const META_API_VERSION = 'v21.0'
const META_API_BASE = `https://graph.facebook.com/${META_API_VERSION}`

export interface MetaSendResult {
  messageId: string
}

export interface MetaPhoneInfo {
  id: string
  display_phone_number: string
  verified_name?: string
  quality_rating?: string
}

interface MetaErrorResponse {
  error?: { message?: string; code?: number; type?: string }
}

async function throwMetaError(response: Response, fallback: string): Promise<never> {
  let message = fallback
  try {
    const data = (await response.json()) as MetaErrorResponse
    if (data.error?.message) message = data.error.message
  } catch {
    // response body wasn't JSON — keep the fallback
  }
  throw new Error(message)
}

// ============================================================
// Phone number / account
// ============================================================

export interface VerifyPhoneNumberArgs {
  phoneNumberId: string
  accessToken: string
}

/**
 * Verify a Meta phone number ID by fetching its public metadata
 * (display_phone_number, verified_name, quality_rating).
 */
export async function verifyPhoneNumber(
  args: VerifyPhoneNumberArgs
): Promise<MetaPhoneInfo> {
  const { phoneNumberId, accessToken } = args
  const url = `${META_API_BASE}/${phoneNumberId}?fields=id,display_phone_number,verified_name,quality_rating`
  const response = await fetch(url, {
    headers: { Authorization: `Bearer ${accessToken}` },
  })
  if (!response.ok) {
    await throwMetaError(response, `Meta API error: ${response.status}`)
  }
  return response.json()
}

// ============================================================
// Sending
// ============================================================

export interface SendTextMessageArgs {
  phoneNumberId: string
  accessToken: string
  to: string
  text: string
  /** Meta's message_id of the message being replied to. Adds a `context` field
   *  so WhatsApp renders the new message as a reply with a quote preview. */
  contextMessageId?: string
}

/**
 * Send a free-form WhatsApp text message.
 * Only works inside the 24-hour customer service window.
 */
export async function sendTextMessage(
  args: SendTextMessageArgs
): Promise<MetaSendResult> {
  const { phoneNumberId, accessToken, to, text, contextMessageId } = args
  const url = `${META_API_BASE}/${phoneNumberId}/messages`
  const body: Record<string, unknown> = {
    messaging_product: 'whatsapp',
    recipient_type: 'individual',
    to,
    type: 'text',
    text: { body: text },
  }
  if (contextMessageId) {
    body.context = { message_id: contextMessageId }
  }
  const response = await fetch(url, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${accessToken}`,
    },
    body: JSON.stringify(body),
  })
  if (!response.ok) {
    await throwMetaError(response, `Meta API error: ${response.status}`)
  }
  const data = await response.json()
  return { messageId: data.messages[0].id }
}

export interface SendTemplateMessageArgs {
  phoneNumberId: string
  accessToken: string
  to: string
  templateName: string
  language?: string
  params?: string[]
  /** Meta's message_id of the message being replied to. */
  contextMessageId?: string
}

/**
 * Send a pre-approved WhatsApp message template. Required outside
 * the 24-hour window and for any first-touch messaging.
 */
export async function sendTemplateMessage(
  args: SendTemplateMessageArgs
): Promise<MetaSendResult> {
  const {
    phoneNumberId,
    accessToken,
    to,
    templateName,
    language = 'en_US',
    params,
    contextMessageId,
  } = args
  const url = `${META_API_BASE}/${phoneNumberId}/messages`

  const template: Record<string, unknown> = {
    name: templateName,
    language: { code: language },
  }

  if (params && params.length > 0) {
    template.components = [
      {
        type: 'body',
        parameters: params.map((p) => ({ type: 'text', text: String(p) })),
      },
    ]
  }

  const body: Record<string, unknown> = {
    messaging_product: 'whatsapp',
    recipient_type: 'individual',
    to,
    type: 'template',
    template,
  }
  if (contextMessageId) {
    body.context = { message_id: contextMessageId }
  }

  const response = await fetch(url, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${accessToken}`,
    },
    body: JSON.stringify(body),
  })
  if (!response.ok) {
    await throwMetaError(response, `Meta API error: ${response.status}`)
  }
  const data = await response.json()
  return { messageId: data.messages[0].id }
}

// ============================================================
// Reactions
// ============================================================

export interface SendReactionMessageArgs {
  phoneNumberId: string
  accessToken: string
  to: string
  /** Meta's message_id of the message being reacted to. */
  targetMessageId: string
  /** Single emoji, or empty string to remove an existing reaction. */
  emoji: string
}

/**
 * Send a reaction (or removal) to a previously-exchanged message.
 * Empty `emoji` removes the reaction per Meta's spec.
 */
export async function sendReactionMessage(
  args: SendReactionMessageArgs
): Promise<MetaSendResult> {
  const { phoneNumberId, accessToken, to, targetMessageId, emoji } = args
  const url = `${META_API_BASE}/${phoneNumberId}/messages`
  const response = await fetch(url, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${accessToken}`,
    },
    body: JSON.stringify({
      messaging_product: 'whatsapp',
      recipient_type: 'individual',
      to,
      type: 'reaction',
      reaction: { message_id: targetMessageId, emoji },
    }),
  })
  if (!response.ok) {
    await throwMetaError(response, `Meta API error: ${response.status}`)
  }
  const data = await response.json()
  return { messageId: data.messages[0].id }
}

// ============================================================
// Interactive (button replies + list messages)
// ============================================================
//
// Meta's two flavours of interactive message — used by the Flows
// engine to drive scripted chatbot menus. Caller passes plain
// JS values; helpers shape the Meta payload and enforce Meta's
// limits BEFORE the network call so the failure mode is a
// developer-facing error rather than a customer-facing one.

/**
 * Meta limits for interactive messages, hard-coded so violations
 * fail at build/save time rather than as a 400 from the Meta API
 * mid-conversation. See:
 *   https://developers.facebook.com/docs/whatsapp/cloud-api/messages/interactive-reply-buttons-messages
 *   https://developers.facebook.com/docs/whatsapp/cloud-api/messages/interactive-list-messages
 */
export const INTERACTIVE_LIMITS = {
  maxButtons: 3,
  buttonTitleMaxLength: 20,
  maxListSections: 10,
  maxListRowsTotal: 10,
  listRowTitleMaxLength: 24,
  listRowDescriptionMaxLength: 72,
  bodyMaxLength: 1024,
  footerMaxLength: 60,
  headerTextMaxLength: 60,
} as const

export interface InteractiveButton {
  /** Stable id sent back in the webhook when tapped (≤ 256 chars). */
  id: string
  /** Visible label (≤ 20 chars per Meta). */
  title: string
}

export interface SendInteractiveButtonsArgs {
  phoneNumberId: string
  accessToken: string
  to: string
  /** The body text — what the customer reads above the buttons. */
  bodyText: string
  /** Optional plain-text header (≤ 60 chars). */
  headerText?: string
  /** Optional grey footer line under the buttons (≤ 60 chars). */
  footerText?: string
  /** 1–3 buttons. Validated against Meta's limits before sending. */
  buttons: InteractiveButton[]
  /** Meta's message_id of the message being replied to (quote preview). */
  contextMessageId?: string
}

/**
 * Send an interactive message with up to 3 inline reply buttons. The
 * customer taps one and Meta delivers a webhook with
 * `messages[0].interactive.button_reply.id` set to the matching button.id.
 *
 * Validation throws BEFORE the network call so misconfigured flows
 * fail at save time, not during a live conversation.
 */
export async function sendInteractiveButtons(
  args: SendInteractiveButtonsArgs
): Promise<MetaSendResult> {
  const {
    phoneNumberId, accessToken, to,
    bodyText, headerText, footerText, buttons, contextMessageId,
  } = args
  validateInteractiveBody(bodyText)
  validateInteractiveHeaderFooter(headerText, footerText)
  if (buttons.length < 1 || buttons.length > INTERACTIVE_LIMITS.maxButtons) {
    throw new Error(
      `Interactive button message requires 1-${INTERACTIVE_LIMITS.maxButtons} buttons (got ${buttons.length}).`
    )
  }
  for (const btn of buttons) {
    if (!btn.id) throw new Error('Interactive button missing id.')
    if (!btn.title) throw new Error(`Interactive button "${btn.id}" missing title.`)
    if (btn.title.length > INTERACTIVE_LIMITS.buttonTitleMaxLength) {
      throw new Error(
        `Interactive button title "${btn.title}" exceeds ${INTERACTIVE_LIMITS.buttonTitleMaxLength} chars.`
      )
    }
  }

  const interactive: Record<string, unknown> = {
    type: 'button',
    body: { text: bodyText },
    action: {
      buttons: buttons.map((b) => ({
        type: 'reply',
        reply: { id: b.id, title: b.title },
      })),
    },
  }
  if (headerText) interactive.header = { type: 'text', text: headerText }
  if (footerText) interactive.footer = { text: footerText }

  const body: Record<string, unknown> = {
    messaging_product: 'whatsapp',
    recipient_type: 'individual',
    to,
    type: 'interactive',
    interactive,
  }
  if (contextMessageId) body.context = { message_id: contextMessageId }

  const url = `${META_API_BASE}/${phoneNumberId}/messages`
  const response = await fetch(url, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${accessToken}`,
    },
    body: JSON.stringify(body),
  })
  if (!response.ok) {
    await throwMetaError(response, `Meta API error: ${response.status}`)
  }
  const data = await response.json()
  return { messageId: data.messages[0].id }
}

export interface InteractiveListRow {
  /** Stable id sent back in the webhook when tapped (≤ 200 chars). */
  id: string
  /** Visible row title (≤ 24 chars per Meta). */
  title: string
  /** Optional secondary line shown under the title (≤ 72 chars). */
  description?: string
}

export interface InteractiveListSection {
  /** Optional section header shown above its rows. */
  title?: string
  rows: InteractiveListRow[]
}

export interface SendInteractiveListArgs {
  phoneNumberId: string
  accessToken: string
  to: string
  bodyText: string
  /** Label of the tap-to-expand button on the message bubble. */
  buttonLabel: string
  headerText?: string
  footerText?: string
  /**
   * 1–10 rows TOTAL across all sections. Meta caps the *total*, not
   * per-section. Validation enforces this before send.
   */
  sections: InteractiveListSection[]
  contextMessageId?: string
}

/**
 * Send an interactive message with a tap-to-expand list of selectable
 * rows. Use when there are more options than the 3-button limit allows.
 * Webhook arrives with `messages[0].interactive.list_reply.id` set to
 * the matching row.id.
 */
export async function sendInteractiveList(
  args: SendInteractiveListArgs
): Promise<MetaSendResult> {
  const {
    phoneNumberId, accessToken, to,
    bodyText, buttonLabel, headerText, footerText, sections, contextMessageId,
  } = args
  validateInteractiveBody(bodyText)
  validateInteractiveHeaderFooter(headerText, footerText)
  if (!buttonLabel) throw new Error('Interactive list requires a buttonLabel.')
  if (buttonLabel.length > INTERACTIVE_LIMITS.buttonTitleMaxLength) {
    throw new Error(
      `Interactive list buttonLabel "${buttonLabel}" exceeds ${INTERACTIVE_LIMITS.buttonTitleMaxLength} chars.`
    )
  }
  if (sections.length < 1 || sections.length > INTERACTIVE_LIMITS.maxListSections) {
    throw new Error(
      `Interactive list requires 1-${INTERACTIVE_LIMITS.maxListSections} sections (got ${sections.length}).`
    )
  }
  const totalRows = sections.reduce((sum, s) => sum + s.rows.length, 0)
  if (totalRows < 1 || totalRows > INTERACTIVE_LIMITS.maxListRowsTotal) {
    throw new Error(
      `Interactive list requires 1-${INTERACTIVE_LIMITS.maxListRowsTotal} rows total across all sections (got ${totalRows}).`
    )
  }
  const seenIds = new Set<string>()
  for (const section of sections) {
    for (const row of section.rows) {
      if (!row.id) throw new Error('Interactive list row missing id.')
      if (seenIds.has(row.id)) {
        throw new Error(`Interactive list has duplicate row id "${row.id}".`)
      }
      seenIds.add(row.id)
      if (!row.title) throw new Error(`Interactive list row "${row.id}" missing title.`)
      if (row.title.length > INTERACTIVE_LIMITS.listRowTitleMaxLength) {
        throw new Error(
          `Interactive list row title "${row.title}" exceeds ${INTERACTIVE_LIMITS.listRowTitleMaxLength} chars.`
        )
      }
      if (
        row.description &&
        row.description.length > INTERACTIVE_LIMITS.listRowDescriptionMaxLength
      ) {
        throw new Error(
          `Interactive list row description for "${row.id}" exceeds ${INTERACTIVE_LIMITS.listRowDescriptionMaxLength} chars.`
        )
      }
    }
  }

  const interactive: Record<string, unknown> = {
    type: 'list',
    body: { text: bodyText },
    action: {
      button: buttonLabel,
      sections: sections.map((s) => ({
        ...(s.title ? { title: s.title } : {}),
        rows: s.rows.map((r) => ({
          id: r.id,
          title: r.title,
          ...(r.description ? { description: r.description } : {}),
        })),
      })),
    },
  }
  if (headerText) interactive.header = { type: 'text', text: headerText }
  if (footerText) interactive.footer = { text: footerText }

  const body: Record<string, unknown> = {
    messaging_product: 'whatsapp',
    recipient_type: 'individual',
    to,
    type: 'interactive',
    interactive,
  }
  if (contextMessageId) body.context = { message_id: contextMessageId }

  const url = `${META_API_BASE}/${phoneNumberId}/messages`
  const response = await fetch(url, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${accessToken}`,
    },
    body: JSON.stringify(body),
  })
  if (!response.ok) {
    await throwMetaError(response, `Meta API error: ${response.status}`)
  }
  const data = await response.json()
  return { messageId: data.messages[0].id }
}

function validateInteractiveBody(bodyText: string): void {
  if (!bodyText) throw new Error('Interactive message requires bodyText.')
  if (bodyText.length > INTERACTIVE_LIMITS.bodyMaxLength) {
    throw new Error(
      `Interactive bodyText exceeds ${INTERACTIVE_LIMITS.bodyMaxLength} chars.`
    )
  }
}

function validateInteractiveHeaderFooter(
  headerText: string | undefined,
  footerText: string | undefined,
): void {
  if (headerText && headerText.length > INTERACTIVE_LIMITS.headerTextMaxLength) {
    throw new Error(
      `Interactive headerText exceeds ${INTERACTIVE_LIMITS.headerTextMaxLength} chars.`
    )
  }
  if (footerText && footerText.length > INTERACTIVE_LIMITS.footerMaxLength) {
    throw new Error(
      `Interactive footerText exceeds ${INTERACTIVE_LIMITS.footerMaxLength} chars.`
    )
  }
}

// ============================================================
// Media
// ============================================================

export interface GetMediaUrlArgs {
  mediaId: string
  accessToken: string
}

/**
 * Resolve a media ID to Meta's (short-lived, authenticated) CDN URL
 * plus the MIME type. Step one of the media-proxy flow.
 */
export async function getMediaUrl(
  args: GetMediaUrlArgs
): Promise<{ url: string; mimeType: string }> {
  const { mediaId, accessToken } = args
  const response = await fetch(`${META_API_BASE}/${mediaId}`, {
    headers: { Authorization: `Bearer ${accessToken}` },
  })
  if (!response.ok) {
    await throwMetaError(response, `Media fetch failed: ${response.status}`)
  }
  const data = await response.json()
  if (!data.url) throw new Error('Media URL not found in Meta response')
  return { url: data.url, mimeType: data.mime_type || 'application/octet-stream' }
}

export interface DownloadMediaArgs {
  downloadUrl: string
  accessToken: string
}

/**
 * Fetch the binary bytes for a media URL obtained from getMediaUrl.
 * Step two of the media-proxy flow.
 */
export async function downloadMedia(
  args: DownloadMediaArgs
): Promise<{ buffer: Buffer; contentType: string }> {
  const { downloadUrl, accessToken } = args
  const response = await fetch(downloadUrl, {
    headers: { Authorization: `Bearer ${accessToken}` },
  })
  if (!response.ok) {
    throw new Error(`Media download failed: ${response.status}`)
  }
  const contentType =
    response.headers.get('content-type') || 'application/octet-stream'
  const buffer = Buffer.from(await response.arrayBuffer())
  return { buffer, contentType }
}