/**
 * In-memory CoT store (TAK, ADS-B, AIS).
 */

import { acquire } from './asyncLock.js'
import { COT_OSINT_TTL_MS, COT_TTL_MS } from './constants.js'
import { inferSourceFromId, isInBbox, matchesLayerFilter } from './cotEntityUtils.js'

const entities = new Map()
/** @type {Set<(event: string, payload: unknown) => void>} */
const listeners = new Set()

/**
 * @param {(event: string, payload: unknown) => void} fn
 * @returns {() => void} Unsubscribe function.
 */
export function onCotChange(fn) {
  listeners.add(fn)
  return () => listeners.delete(fn)
}

function emitChange(event, payload) {
  for (const fn of listeners) {
    try {
      fn(event, payload)
    }
    catch {
      /* ignore listener errors */
    }
  }
}

function pickOptionalNumber(value, fallback) {
  if (value === undefined || value === null) return fallback
  const n = Number(value)
  return Number.isFinite(n) ? n : fallback
}

/**
 * @param {Record<string, unknown>} entity
 */
function toSnapshot(entity) {
  return {
    id: entity.id,
    lat: entity.lat,
    lng: entity.lng,
    label: entity.label ?? entity.id,
    type: entity.type ?? '',
    source: entity.source ?? 'tak',
    heading: entity.heading,
    speed: entity.speed,
    altitude: entity.altitude,
    verticalRate: entity.verticalRate,
    onGround: entity.onGround,
    originCountry: entity.originCountry,
    icao: entity.icao,
    mmsi: entity.mmsi,
    squawk: entity.squawk,
    updatedAt: entity.updatedAt,
  }
}

/**
 * @param {Record<string, unknown>} entity
 * @param {{ ttlMs?: number, osintTtlMs?: number }} opts
 */
function entityTtlMs(entity, opts) {
  const source = entity.source
  if (source === 'adsb' || source === 'ais') {
    return opts.osintTtlMs ?? COT_OSINT_TTL_MS
  }
  return opts.ttlMs ?? COT_TTL_MS
}

function isEntityExpired(entity, now, opts) {
  return now - entity.updatedAt > entityTtlMs(entity, opts)
}

/**
 * Upsert entity by id. Input is not mutated; stored value is a new object.
 * @param {{ id: string, lat: number, lng: number, label?: string, eventType?: string, type?: string, source?: string, heading?: number, speed?: number, altitude?: number }} parsed
 * @param {{ silent?: boolean }} [options]
 */
export async function updateFromCot(parsed, options = {}) {
  if (!parsed || typeof parsed.id !== 'string') return
  const lat = Number(parsed.lat)
  const lng = Number(parsed.lng)
  if (!Number.isFinite(lat) || !Number.isFinite(lng)) return

  let snapshot = null
  await acquire(`cot-${parsed.id}`, async () => {
    const now = Date.now()
    const existing = entities.get(parsed.id)
    const label = typeof parsed.label === 'string' ? parsed.label : (existing?.label ?? parsed.id)
    const type = typeof parsed.eventType === 'string'
      ? parsed.eventType
      : (typeof parsed.type === 'string' ? parsed.type : (existing?.type ?? ''))
    const explicitSource = parsed.source
    const source = explicitSource === 'adsb' || explicitSource === 'ais' || explicitSource === 'tak'
      ? explicitSource
      : inferSourceFromId(parsed.id)

    const stored = {
      id: parsed.id,
      lat,
      lng,
      label,
      type,
      source,
      heading: pickOptionalNumber(parsed.heading, existing?.heading),
      speed: pickOptionalNumber(parsed.speed, existing?.speed),
      altitude: pickOptionalNumber(parsed.altitude, existing?.altitude),
      verticalRate: pickOptionalNumber(parsed.verticalRate, existing?.verticalRate),
      onGround: typeof parsed.onGround === 'boolean' ? parsed.onGround : existing?.onGround,
      originCountry: typeof parsed.originCountry === 'string' ? parsed.originCountry : existing?.originCountry,
      icao: typeof parsed.icao === 'string' ? parsed.icao : existing?.icao,
      mmsi: typeof parsed.mmsi === 'string' ? parsed.mmsi : existing?.mmsi,
      squawk: typeof parsed.squawk === 'string' ? parsed.squawk : existing?.squawk,
      updatedAt: now,
    }
    entities.set(parsed.id, stored)
    snapshot = toSnapshot(stored)
  })

  if (snapshot && !options.silent) emitChange('update', { entity: snapshot })
}

/**
 * @param {number} now
 * @param {{ ttlMs?: number, osintTtlMs?: number }} opts
 */
function pruneExpired(now, opts) {
  const expired = []
  for (const entity of entities.values()) {
    if (isEntityExpired(entity, now, opts)) expired.push(entity.id)
  }
  for (const id of expired) {
    entities.delete(id)
    emitChange('remove', { id })
  }
}

/**
 * @param {{ ttlMs?: number, osintTtlMs?: number }} [opts]
 */
export async function pruneStaleEntities(opts = {}) {
  const ttlMs = opts.ttlMs ?? COT_TTL_MS
  const osintTtlMs = opts.osintTtlMs ?? COT_OSINT_TTL_MS
  await acquire('cot-prune', async () => {
    pruneExpired(Date.now(), { ttlMs, osintTtlMs })
  })
}

/**
 * @param {Record<string, unknown>} entity
 * @param {{ west: number, south: number, east: number, north: number } | null | undefined} bbox
 * @param {boolean} takFilterBbox
 */
function passesBboxFilter(entity, bbox, takFilterBbox) {
  if (!bbox) return true
  const inBox = isInBbox(entity, bbox)
  if (entity.source === 'tak' && !takFilterBbox) return true
  return inBox
}

/**
 * Active entities (updated within ttlMs). Prunes expired. Returns new array of new objects.
 * @param {{ ttlMs?: number, osintTtlMs?: number }} [opts]
 */
export async function getActiveEntities(opts = {}) {
  const ttlMs = opts.ttlMs ?? COT_TTL_MS
  const osintTtlMs = opts.osintTtlMs ?? COT_OSINT_TTL_MS
  return acquire('cot-prune', async () => {
    const now = Date.now()
    pruneExpired(now, { ttlMs, osintTtlMs })
    return [...entities.values()].map(toSnapshot)
  })
}

/**
 * Active entities filtered by viewport bbox and layer set.
 * @param {{ west: number, south: number, east: number, north: number } | null} bbox
 * @param {{ ttlMs?: number, osintTtlMs?: number, layers?: Set<string>, takFilterBbox?: boolean, maxEntities?: number }} [opts]
 */
export async function getActiveEntitiesInBbox(bbox, opts = {}) {
  const ttlMs = opts.ttlMs ?? COT_TTL_MS
  const osintTtlMs = opts.osintTtlMs ?? COT_OSINT_TTL_MS
  const layers = opts.layers
  const takFilterBbox = Boolean(opts.takFilterBbox)
  const ttlOpts = { ttlMs, osintTtlMs }

  return acquire('cot-prune', async () => {
    const now = Date.now()
    pruneExpired(now, ttlOpts)
    const active = []
    for (const entity of entities.values()) {
      if (isEntityExpired(entity, now, ttlOpts)) continue
      const snap = toSnapshot(entity)
      if (!passesBboxFilter(snap, bbox, takFilterBbox)) continue
      if (!matchesLayerFilter(layers, snap)) continue
      active.push(snap)
    }
    const maxEntities = opts.maxEntities
    if (maxEntities != null && active.length > maxEntities) {
      active.sort((a, b) => (b.updatedAt ?? 0) - (a.updatedAt ?? 0))
      active.length = maxEntities
    }
    return active
  })
}

/** Clear store (tests only). */
export function clearCotStore() {
  entities.clear()
}