'use strict'

function meshRejoinJitterMs (guildId, salt = '') {
  const max = Math.max(0, Number(process.env.PEARCORD_MESH_REJOIN_JITTER_MS) || 900)
  if (!max) return 0
  let h = 2166136261
  const key = `${guildId || ''}:${salt}`
  for (let i = 0; i < key.length; i++) {
    h ^= key.charCodeAt(i)
    h = Math.imul(h, 16777619)
  }
  return h % max
}

/**
 * Score 0–100 for selective mesh sync priority (higher is healthier).
 * @param {object} row peer seen row
 * @param {object} opts
 */
function computeMeshPeerQualityScore (row, opts = {}) {
  const now = Date.now()
  const rttMs = Math.max(0, Number(row?.rttMs) || Number(opts.fallbackRttMs) || 120)
  const staleMs = Math.max(0, now - (Number(row?.lastSeenAt) || 0))
  const drops = Math.max(0, Number(row?.dropCount) || 0)
  let score = 100
  score -= Math.min(40, Math.round(rttMs / 20))
  score -= Math.min(25, drops * 6)
  score -= Math.min(22, Math.round(staleMs / 12000))
  if (row?.sparseCursorStale) score -= 12
  return Math.max(0, Math.min(100, score))
}

function rankMeshPeersByQuality (peerMap, opts = {}) {
  const rows = []
  for (const [peerId, row] of peerMap.entries()) {
    const qualityScore = computeMeshPeerQualityScore(row, opts)
    rows.push({
      peerId,
      qualityScore,
      rttMs: Number(row.rttMs) || null,
      dropCount: Number(row.dropCount) || 0,
      lastSeenAt: Number(row.lastSeenAt) || 0,
      sparseCursorStale: !!row.sparseCursorStale
    })
  }
  rows.sort((a, b) => b.qualityScore - a.qualityScore)
  return rows
}

module.exports = {
  meshRejoinJitterMs,
  computeMeshPeerQualityScore,
  rankMeshPeersByQuality
}