/**
 * Resend Email Service Implementation
 *
 * Implements EmailService using the Resend API.
 */

import { Resend } from 'resend'
import { createLogger } from '@/lib/logger'
import { getBranding } from '@/lib/branding/service'
import type { EmailService, SendEmailOptions, SendEmailResult } from '@/lib/email/service'

const log = createLogger('email')

const DEFAULT_FROM_EMAIL = process.env.RESEND_FROM_EMAIL || 'noreply@localhost'

function sanitizeHeaderPart(s: string): string {
  return s.replace(/[\r\n<>]/g, '').trim()
}

function optionalAddressList(addresses: string | string[] | undefined): string[] | undefined {
  if (!addresses) return undefined
  const list = Array.isArray(addresses) ? addresses : [addresses]
  return list.length > 0 ? list : undefined
}

let resendClient: Resend | null = null

function getResendClient(): Resend {
  if (!resendClient) {
    if (!process.env.RESEND_API_KEY) {
      throw new Error('RESEND_API_KEY is not configured')
    }
    resendClient = new Resend(process.env.RESEND_API_KEY)
  }
  return resendClient
}

function isResendConfigured(): boolean {
  return !!process.env.RESEND_API_KEY && !!process.env.RESEND_FROM_EMAIL && process.env.RESEND_FROM_EMAIL !== 'noreply@localhost'
}

export class ResendEmailService implements EmailService {
  async sendEmail(options: SendEmailOptions): Promise<SendEmailResult> {
    const { to, cc, bcc, subject, html, text, replyTo, fromName, attachments } = options

    if (!this.isConfigured()) {
      return { success: false, error: 'Email service is not configured' }
    }

    // Strip CRLF and angle brackets from name parts to prevent header injection.
    // Resend's API does its own validation, but defense in depth: both fromName
    // (user-controlled, from company settings) and appName (admin-controlled,
    // from branding) flow into the From header.
    const safeAppName = sanitizeHeaderPart(getBranding().appName)
    const safeFromName = fromName ? sanitizeHeaderPart(fromName) : null
    const from = safeFromName
      ? `${safeFromName} via ${safeAppName} <${DEFAULT_FROM_EMAIL}>`
      : `${safeAppName} <${DEFAULT_FROM_EMAIL}>`

    try {
      const resend = getResendClient()
      const response = await resend.emails.send({
        from,
        to: Array.isArray(to) ? to : [to],
        cc: optionalAddressList(cc),
        bcc: optionalAddressList(bcc),
        subject,
        html,
        text,
        replyTo,
        attachments: attachments?.map(att => ({
          filename: att.filename,
          content: typeof att.content === 'string'
            ? Buffer.from(att.content, 'base64')
            : Buffer.from(att.content),
          contentType: att.contentType,
        })),
      })

      if (response.error) {
        log.error('Resend error:', response.error)
        return { success: false, provider: 'resend', error: response.error.message }
      }

      return { success: true, provider: 'resend', messageId: response.data?.id }
    } catch (error) {
      log.error('Failed to send email:', error)
      return {
        success: false,
        provider: 'resend',
        error: error instanceof Error ? error.message : 'Unknown error',
      }
    }
  }

  isConfigured(): boolean {
    return isResendConfigured()
  }
}