import {
  buildCsvDownloadItem,
  buildPngDownloadItem,
  type DownloadItem,
} from '../actions/download'
import type { TimeseriesWidgetData } from './types'

/**
 * Download menu items for the Timeseries widget. Always includes a CSV
 * item with `time, series_1, series_2, …` columns (one row per unique time
 * across all series; ISO-8601 strings for `Date`/numeric times). When
 * `getCaptureEl` is supplied, prepends a PNG item that rasterises the
 * captured element via `html2canvas`.
 */
export function createTimeseriesDownloadConfig(args: {
  filename: string
  getData: () => TimeseriesWidgetData
  seriesNames?: readonly string[]
  getCaptureEl?: () => HTMLElement | null
  pngPixelRatio?: number
  pngBackgroundColor?: string | null
}): DownloadItem[] {
  const items: DownloadItem[] = []
  if (args.getCaptureEl) {
    items.push(
      buildPngDownloadItem({
        filename: args.filename,
        getCaptureEl: args.getCaptureEl,
        pixelRatio: args.pngPixelRatio,
        backgroundColor: args.pngBackgroundColor,
      }),
    )
  }
  items.push(
    buildCsvDownloadItem({
      filename: args.filename,
      getRows: () => {
        const data = args.getData()
        const seriesCount = data.length

        // Collect every unique time, preserving insertion order.
        const timeKeys: (Date | number | string)[] = []
        const seenKeys = new Set<string>()
        for (const series of data) {
          for (const point of series) {
            const key = String(point.name)
            if (!seenKeys.has(key)) {
              seenKeys.add(key)
              timeKeys.push(point.name)
            }
          }
        }

        // Build a quick lookup per series for O(rows × series) emit.
        const lookups = data.map(
          (series) => new Map(series.map((p) => [String(p.name), p.value])),
        )

        const header: unknown[] = ['time']
        for (let i = 0; i < seriesCount; i++) {
          header.push(args.seriesNames?.[i] ?? `series_${i + 1}`)
        }
        const rows: unknown[][] = [header]
        for (const key of timeKeys) {
          const row: unknown[] = [formatTime(key)]
          const lookupKey = String(key)
          for (const lookup of lookups) row.push(lookup.get(lookupKey) ?? '')
          rows.push(row)
        }

        return rows
      },
    }),
  )
  return items
}

function formatTime(v: Date | number | string): string {
  if (v instanceof Date) return v.toISOString()
  if (typeof v === 'number') return new Date(v).toISOString()
  return v
}