import { formatINR } from '@sims/domain'

/** Templated reminder emails — one place so WhatsApp can reuse them later (spec §7). */

export type ReminderRuleKind =
  | 'invoice_overdue' | 'renewal_due' | 'amc_expiring'
  | 'follow_up' | 'recurring_generated' | 'email_bounced'

export interface ReminderContext {
  clientName: string; companyName: string
  docNo?: string; amountPaise?: number; dueDate?: string
  daysOverdue?: number; coverage?: string; period?: string
}

export interface ReminderMail { subject: string; bodyText: string }

const signOff = (ctx: ReminderContext): string => `Warm regards,\n${ctx.companyName}`

export function reminderEmail(kind: ReminderRuleKind, ctx: ReminderContext): ReminderMail {
  switch (kind) {
    case 'invoice_overdue': {
      const amt = ctx.amountPaise !== undefined ? formatINR(ctx.amountPaise) : ''
      return {
        subject: `Payment reminder — Invoice ${ctx.docNo} (${ctx.companyName})`,
        bodyText:
          `Dear ${ctx.clientName},\n\n`
          + `This is a gentle reminder that Invoice ${ctx.docNo}${amt !== '' ? ` for ${amt}` : ''} is outstanding`
          + (ctx.daysOverdue !== undefined ? ` and is now ${ctx.daysOverdue} day(s) past due` : '')
          + `. We would be grateful if you could arrange payment at your earliest convenience.\n\n`
          + `If payment has already been made, kindly ignore this message.\n\n`
          + signOff(ctx),
      }
    }
    case 'recurring_generated': {
      const amt = ctx.amountPaise !== undefined ? formatINR(ctx.amountPaise) : ''
      const forPeriod = ctx.period !== undefined ? ` for ${ctx.period}` : ''
      return {
        subject: `Invoice ${ctx.docNo}${forPeriod} (${ctx.companyName})`,
        bodyText:
          `Dear ${ctx.clientName},\n\n`
          + `Please find attached Invoice ${ctx.docNo}${forPeriod}${amt !== '' ? `, amounting to ${amt}` : ''}.\n\n`
          + `Kindly arrange payment as per the agreed terms. Thank you for your continued association.\n\n`
          + signOff(ctx),
      }
    }
    case 'renewal_due':
      return {
        subject: `Subscription renewal reminder (${ctx.companyName})`,
        bodyText:
          `Dear ${ctx.clientName},\n\n`
          + `Your subscription is due for renewal${ctx.dueDate !== undefined ? ` on ${ctx.dueDate}` : ' shortly'}. `
          + `Please let us know if you would like us to raise the renewal invoice.\n\n`
          + `We value your continued association and look forward to serving you.\n\n`
          + signOff(ctx),
      }
    case 'amc_expiring':
      return {
        subject: `AMC renewal reminder${ctx.coverage !== undefined && ctx.coverage !== '' ? ` — ${ctx.coverage}` : ''} (${ctx.companyName})`,
        bodyText:
          `Dear ${ctx.clientName},\n\n`
          + `Your Annual Maintenance Contract${ctx.coverage !== undefined && ctx.coverage !== '' ? ` (${ctx.coverage})` : ''} `
          + `is due to expire${ctx.dueDate !== undefined ? ` on ${ctx.dueDate}` : ' soon'}. `
          + `To ensure uninterrupted support, please confirm the renewal at your convenience.\n\n`
          + signOff(ctx),
      }
    case 'follow_up':
    case 'email_bounced':
      // Internal dashboard items — never emailed to the client. A neutral value
      // exists so callers can't crash; repos-reminders refuses to send these kinds.
      return { subject: '(internal reminder)', bodyText: '' }
  }
}