dashboards/apps/business/src/utils/monthlyActivity.ts

import type { DailyActivityPoint } from '../services/dailyActivityService'
import { buildLast12MonthKeys, formatMonthLabel } from './productActivity'

export interface MonthActivityPoint {
  monthKey: string
  label: string
  primary: number
  secondary: number
}

function toMonthKey(dateKey: string): string {
  return dateKey.slice(0, 7)
}

/** Roll daily dual series into the last 12 calendar months. */
export function aggregateDailyActivityByMonth(
  primaryItems: DailyActivityPoint[],
  secondaryItems: DailyActivityPoint[],
  locale: string,
): MonthActivityPoint[] {
  const monthKeys = buildLast12MonthKeys()
  const primaryByMonth = new Map(monthKeys.map((key) => [key, 0]))
  const secondaryByMonth = new Map(monthKeys.map((key) => [key, 0]))

  for (const item of primaryItems) {
    const key = toMonthKey(item.date)
    if (primaryByMonth.has(key)) {
      primaryByMonth.set(key, (primaryByMonth.get(key) ?? 0) + item.count)
    }
  }

  for (const item of secondaryItems) {
    const key = toMonthKey(item.date)
    if (secondaryByMonth.has(key)) {
      secondaryByMonth.set(key, (secondaryByMonth.get(key) ?? 0) + item.count)
    }
  }

  return monthKeys.map((monthKey) => ({
    monthKey,
    label: formatMonthLabel(monthKey, locale),
    primary: primaryByMonth.get(monthKey) ?? 0,
    secondary: secondaryByMonth.get(monthKey) ?? 0,
  }))
}