// ── The map's picture: noticing a new map and fetching it ─────────────────
//
// R9's first half, as the rig rewrote it (PLAN.md §30.0). The picture is not
// extracted from anything: the game's Rust+ service already holds a JPEG of the
// map in memory, and the plugin hands it over in 512 KiB slices. That changes
// the one rule R9 carried over from the asset bridge, where a fetch was an
// expensive extraction:
//
// **D110 — the site fetches the picture BY ITSELF the first time it sees a map
// it does not have**, because reading the cache costs the game nothing. It is
// triggered off the board poll (`boot.js`): a new boot, wipe, seed or world
// size, or a server with no row at all, is a reason to ask `map.info`, and a
// key or hash that differs from the row is a reason to fetch.
//
// **D109 — a render is never automatic.** A server with no Rust+ cache has no
// picture until an admin presses Render now, which stalls that game for seconds
// and is said so beside the button. The render answers at once and happens on a
// later frame; this file then polls `map.info` until the picture exists and
// fetches it like any other.
//
// Three rules the fetch keeps:
//
//   • **One fetch per server at a time**, held here. A second trigger while one
//     runs is dropped, and an admin's Fetch again is told one is running.
//   • **A fetch that straddles a map change is abandoned whole.** The plugin
//     refuses a slice with `stale` when the key or hash moved, and the bytes are
//     checked against the hash before anything is written: two maps are never
//     spliced, and a half-fetched picture is never stored.
//   • **A failure keeps the old row** and retries on a backoff. The page keeps
//     drawing the last picture it had, which is still the right map until the
//     key says otherwise.

const crypto = require('crypto')

const core = require('./core')

const db = require('./model/map/map.db')
const model = require('./model/map/map.model')
const sidecar = require('./sidecarClient')

const log = core.logger('map')

/** Backoff after a failed fetch: 30 s doubling to 10 minutes. */
const BACKOFF_MIN_MS = 30 * 1000
const BACKOFF_MAX_MS = 10 * 60 * 1000

/** How soon to ask again when the plugin is still hashing, or the world still loading. */
const SOON_MS = 3000

/** How long a render is watched for before this side gives up on it (a 6000 map stalls ~40 s). */
const RENDER_WATCH_MS = 5 * 60 * 1000
const RENDER_POLL_MS = 3000

/** The first protocol whose plugin knows the map verbs. */
const MAP_PROTOCOL = 11

/** The most slices one picture may have: 16 MiB, MEDIUMBLOB's ceiling. */
const MAX_CHUNKS = 32

/**
 * Per server: the observation last acted on, whether a fetch is running, and
 * when the next try may happen. In memory, deliberately — a restart of the
 * website forgets it and asks once more, which costs one `map.info`.
 */
const state = new Map()

function stateOf(serverId) {
  if (!state.has(serverId)) {
    state.set(serverId, { sig: null, running: null, nextTryAt: 0, failures: 0, rendering: null, lastError: null })
  }
  return state.get(serverId)
}

/** What about a server makes its map worth asking about again. */
const signature = ({ bootId, wipeId, seed, worldSize }) => [bootId, wipeId, seed, worldSize].map((v) => (v == null ? '' : String(v))).join('|')

/**
 * Called by every board poll for a CONNECTED server whose world is ready. Cheap
 * when nothing moved: one map lookup and a string compare. When something did,
 * it starts a fetch in the background and returns — the poll never waits on a
 * picture.
 */
function observe(server, frame, now = Date.now()) {
  if (!server || !frame || frame.worldReady === false) return
  // The game link has no version handshake: a plugin older than protocol 11
  // never answers `map.info`, and asking would cost a full reply timeout a try.
  if (!(Number(frame.protocol) >= MAP_PROTOCOL)) return
  const s = stateOf(server.id)
  const sig = signature(frame)

  if (s.running || now < s.nextTryAt) return
  if (s.sig === sig) return

  run(server, sig).catch((err) => log.warn('map fetch failed', { server: server.id, error: err.message }))
}

/**
 * One fetch cycle. Resolves `{ ok, outcome, detail }`, never rejects in normal
 * operation; the outcome words are what the admin card shows.
 *
 *   fetched    a new picture is stored
 *   current    the stored picture is already this map's
 *   none       the game has no picture; geometry stored so layers can be drawn
 *   busy       another fetch is running (admin only)
 *   failed     something did not answer; the old row is kept
 */
function run(server, sig = null, { force = false } = {}) {
  const s = stateOf(server.id)
  if (s.running) return Promise.resolve({ ok: false, outcome: 'busy', detail: 'a fetch is already running for this server' })

  s.running = (async () => {
    try {
      const result = await fetchOnce(server, { force })
      if (result.retrySoon) {
        s.nextTryAt = Date.now() + SOON_MS
        return result
      }
      if (result.ok) {
        s.sig = sig
        s.failures = 0
        s.nextTryAt = 0
        s.lastError = null
      } else {
        s.failures += 1
        s.nextTryAt = Date.now() + Math.min(BACKOFF_MAX_MS, BACKOFF_MIN_MS * 2 ** (s.failures - 1))
        s.lastError = result.detail || result.outcome
      }
      return result
    } finally {
      s.running = null
    }
  })()

  return s.running
}

/** The plugin's refusal, as a sentence, or null when the answer was not one. */
function refusal(res) {
  if (!res.ok) return `the sidecar did not answer (${res.status})`
  if (res.data && res.data.kind === 'map.error') return res.data.message || res.data.reason || 'refused'
  return null
}

async function fetchOnce(server, { force }) {
  const info = await sidecar.mapInfo(server)
  const why = refusal(info)

  if (why) {
    // A world still loading is not a failure worth backing off for.
    if (info.ok && info.data && info.data.reason === 'not-ready') return { ok: false, retrySoon: true, outcome: 'failed', detail: why }
    return { ok: false, outcome: 'failed', detail: why }
  }

  const data = info.data || {}
  if (data.hashing) return { ok: false, retrySoon: true, outcome: 'failed', detail: 'the plugin is still hashing the picture' }

  const row = model.derive(server.id, data)
  if (!row.mapKey) return { ok: false, outcome: 'failed', detail: 'map.info named no map' }

  const stored = await db.getMeta(server.id)

  if (row.source === 'none') {
    // The same map with a picture already stored keeps it: nothing about the map
    // changed, only where a picture would come from now. A different map, or no
    // row at all, stores the geometry so the page can draw the layers.
    if (stored && stored.mapKey === row.mapKey && stored.sha256) {
      await db.putGeometry({ ...row, source: stored.source, width: Number(stored.width), height: Number(stored.height), background: stored.background })
      return { ok: true, outcome: 'current', detail: 'the game has no picture now; the stored one is the same map' }
    }
    await db.putImage(row)
    return { ok: true, outcome: 'none', detail: 'the game has no picture of its map; an admin can render one' }
  }

  if (!force && stored && stored.mapKey === row.mapKey && stored.sha256 === row.sha256) {
    if (Number(stored.derivation) !== model.DERIVATION_VERSION || stored.source !== row.source) await db.putGeometry(row)
    return { ok: true, outcome: 'current', detail: 'the stored picture is this map' }
  }

  const chunks = Number(data.chunks)
  if (!Number.isInteger(chunks) || chunks < 1 || chunks > MAX_CHUNKS) {
    return { ok: false, outcome: 'failed', detail: `the plugin described ${data.chunks} slices` }
  }

  const parts = []
  for (let n = 0; n < chunks; n += 1) {
    // eslint-disable-next-line no-await-in-loop
    const res = await sidecar.mapChunk(server, { mapKey: row.mapKey, sha256: row.sha256, n })
    const no = refusal(res)
    if (no) {
      // `stale` means the map moved under the fetch: start again soon rather
      // than back off, because the next `map.info` describes the new one.
      if (res.ok && res.data && res.data.reason === 'stale') return { ok: false, retrySoon: true, outcome: 'failed', detail: no }
      return { ok: false, outcome: 'failed', detail: `slice ${n}: ${no}` }
    }
    if (!res.data || res.data.kind !== 'map.chunk' || Number(res.data.chunk) !== n || typeof res.data.data !== 'string') {
      return { ok: false, outcome: 'failed', detail: `slice ${n} was not the slice asked for` }
    }
    parts.push(Buffer.from(res.data.data, 'base64'))
  }

  const bytes = Buffer.concat(parts)
  const hash = crypto.createHash('sha256').update(bytes).digest('hex')

  if (hash !== row.sha256 || (Number(data.bytes) > 0 && bytes.length !== Number(data.bytes))) {
    return { ok: false, outcome: 'failed', detail: 'the picture did not match its own hash; nothing was stored' }
  }

  await db.putImage({ ...row, bytes })
  log.info('map picture stored', { server: server.id, mapKey: row.mapKey, source: row.source, bytes: bytes.length })
  return { ok: true, outcome: 'fetched', detail: `${bytes.length} bytes from ${row.source}` }
}

/**
 * An admin's Render now (D109). Refused here when a render is already being
 * watched; the plugin refuses the rest (a picture exists, the world is loading).
 * On `accepted` the render is watched in the background: `map.info` is polled
 * until its source is `rendered` — through a stall that makes the game answer
 * nothing at all for its duration — and then fetched like any picture.
 */
async function render(server, actor) {
  const s = stateOf(server.id)
  if (s.rendering) return { ok: false, status: 409, message: 'A render is already running for this server.' }

  const res = await sidecar.mapRender(server, { actor: actor || null })
  const no = refusal(res)
  if (no) {
    const reason = res.ok && res.data ? res.data.reason : null
    return { ok: false, status: reason === 'has-picture' || reason === 'busy' ? 409 : 502, message: no, reason }
  }

  s.rendering = { startedAt: Date.now() }
  watchRender(server).catch((err) => log.warn('render watch failed', { server: server.id, error: err.message }))
  return { ok: true, worldSize: res.data && res.data.worldSize, stallSeconds: model.renderStallSeconds(res.data && res.data.worldSize) }
}

async function watchRender(server) {
  const s = stateOf(server.id)
  const until = Date.now() + RENDER_WATCH_MS
  try {
    while (Date.now() < until) {
      // eslint-disable-next-line no-await-in-loop
      await new Promise((resolve) => {
        const t = setTimeout(resolve, RENDER_POLL_MS)
        if (typeof t.unref === 'function') t.unref()
      })
      // eslint-disable-next-line no-await-in-loop
      const info = await sidecar.mapInfo(server)
      const data = info.ok && info.data ? info.data : null
      if (!data || data.kind !== 'map.info') continue // the game is mid-stall and answering nothing
      if (data.rendering) continue
      if (data.source === 'none') {
        s.lastError = 'the render finished without a picture — see rg.map on the server console'
        return
      }
      // eslint-disable-next-line no-await-in-loop
      await run(server, null, { force: false })
      return
    }
    s.lastError = 'the render did not finish within five minutes'
  } finally {
    s.rendering = null
  }
}

/** For the admin card: what this side is doing about each server's picture. */
function statusOf(serverId) {
  const s = state.get(serverId)
  if (!s) return { fetching: false, rendering: false, lastError: null }
  return { fetching: Boolean(s.running), rendering: Boolean(s.rendering), lastError: s.lastError }
}

/** Test seam: forget everything. */
function _reset() {
  state.clear()
}

module.exports = { observe, run, render, statusOf, signature, MAX_CHUNKS, _reset }