import { createBatteriesResponse, createDashboardSnapshot } from '@/domain/battery'
import { os } from '@/server/api/server'
import {
  getBatteryHistory,
  getBatteryPredictionHistories,
  getLatestBatteryPage,
  getLatestBatteryPerDevice,
} from '@/server/battery/mysql'
import { isPredictionEnabled, predictSoh } from '@/server/prediction/client'

const dashboardPredictionConcurrency = 5

async function mapWithConcurrency<T, R>(
  items: T[],
  concurrency: number,
  handler: (item: T) => Promise<R>,
): Promise<R[]> {
  const results: R[] = []
  let nextIndex = 0

  async function worker() {
    while (nextIndex < items.length) {
      const index = nextIndex
      nextIndex += 1
      const item = items[index]
      if (item !== undefined) results[index] = await handler(item)
    }
  }

  await Promise.all(Array.from({ length: Math.min(concurrency, items.length) }, worker))

  return results
}

export const dashboard = os.battery.dashboard.handler(async () => {
  const items = await getLatestBatteryPerDevice()
  const predictionHistories = isPredictionEnabled()
    ? await getBatteryPredictionHistories(items.map((item) => item.mac))
    : new Map()
  const predictionEntries = isPredictionEnabled()
    ? await mapWithConcurrency(items, dashboardPredictionConcurrency, async (item) => {
        const prediction = await predictSoh(item, predictionHistories.get(item.mac) ?? [])

        return prediction ? ([item.mac, prediction] as const) : null
      })
    : []
  const predictions = new Map(predictionEntries.filter((entry) => entry !== null))

  return createDashboardSnapshot(items, new Date(), predictions)
})

export const batteries = os.battery.batteries.handler(async ({ input }) => {
  const page = await getLatestBatteryPage(input)

  return createBatteriesResponse(
    page.items,
    new Date(),
    { total: page.total, lowPower: page.lowPower, charging: page.charging },
    page.nextCursor,
  )
})

export const history = os.battery.history.handler(async ({ input }) => {
  const items = await getBatteryHistory(input.mac)

  return createBatteriesResponse(items)
})