const DEFAULT_RECENT_LIMIT = 50;

export function createAlertEngine({
  activePair,
  priceStaleMs,
  inventoryStaleMs,
  fundingCreditPendingMs,
  fundingStuckMs,
  evaluationIntervalMs,
  recentTransitionLimit = DEFAULT_RECENT_LIMIT,
}) {
  const state = {
    latest_price: null,
    latest_inventory: null,
    latest_liquidity_action: null,
    latest_trade_result: null,
    funding_observations: {},
    active_alerts: {},
    runtime_alert_keys: new Set(),
    recent_transitions: [],
    last_evaluated_at: null,
  };

  return {
    applyEvent(topic, payload, now = new Date().toISOString()) {
      switch (topic) {
        case 'ref.market_price':
          state.latest_price = payload;
          break;
        case 'state.intent_inventory':
          state.latest_inventory = payload;
          break;
        case 'ops.liquidity_action':
          state.latest_liquidity_action = payload;
          break;
        case 'ops.funding_observation':
          if (payload?.funding_observation_id) {
            state.funding_observations[payload.funding_observation_id] = payload;
          }
          break;
        case 'exec.trade_result':
          state.latest_trade_result = payload;
          break;
        default:
          break;
      }

      return evaluateAlerts({
        state,
        activePair,
        priceStaleMs,
        inventoryStaleMs,
        fundingCreditPendingMs,
        fundingStuckMs,
        recentTransitionLimit,
        now,
      });
    },
    evaluate(now = new Date().toISOString()) {
      return evaluateAlerts({
        state,
        activePair,
        priceStaleMs,
        inventoryStaleMs,
        fundingCreditPendingMs,
        fundingStuckMs,
        recentTransitionLimit,
        now,
      });
    },
    applyRuntimeAlerts(desiredAlerts = [], now = new Date().toISOString()) {
      return reconcileRuntimeAlertState({
        state,
        desiredAlerts,
        now,
        recentTransitionLimit,
      });
    },
    getState(now = new Date().toISOString()) {
      return summarizeState({
        state,
        evaluationIntervalMs,
        now,
      });
    },
  };
}

function evaluateAlerts({
  state,
  activePair,
  priceStaleMs,
  inventoryStaleMs,
  fundingCreditPendingMs,
  fundingStuckMs,
  recentTransitionLimit,
  now,
}) {
  const desired = new Map();
  const nowValue = timestampValue(now);

  const priceAgeMs = ageMs(state.latest_price?.observed_at || state.latest_price?.ingested_at, nowValue);
  if (priceAgeMs == null || priceAgeMs > priceStaleMs) {
    desired.set(
      buildAlertKey({
        alertCode: 'reference_price_stale',
        serviceScope: 'market-reference-ingest',
        pair: activePair,
      }),
      {
        alert_code: 'reference_price_stale',
        severity: 'warning',
        reason: priceAgeMs == null
          ? 'no reference price has been observed'
          : `reference price age ${priceAgeMs}ms exceeds ${priceStaleMs}ms`,
        service_scope: 'market-reference-ingest',
        pair: activePair,
        asset_id: null,
        tx_hash: null,
        details: {
          last_price_at: state.latest_price?.observed_at || state.latest_price?.ingested_at || null,
          age_ms: priceAgeMs,
          stale_after_ms: priceStaleMs,
        },
      },
    );
  }

  const inventoryAgeMs = ageMs(
    state.latest_inventory?.synced_at || state.latest_inventory?.ingested_at,
    nowValue,
  );
  if (inventoryAgeMs == null || inventoryAgeMs > inventoryStaleMs) {
    desired.set(
      buildAlertKey({
        alertCode: 'inventory_snapshot_stale',
        serviceScope: 'inventory-sync',
      }),
      {
        alert_code: 'inventory_snapshot_stale',
        severity: 'warning',
        reason: inventoryAgeMs == null
          ? 'no inventory snapshot has been observed'
          : `inventory snapshot age ${inventoryAgeMs}ms exceeds ${inventoryStaleMs}ms`,
        service_scope: 'inventory-sync',
        pair: null,
        asset_id: null,
        tx_hash: null,
        details: {
          last_inventory_at: state.latest_inventory?.synced_at || state.latest_inventory?.ingested_at || null,
          age_ms: inventoryAgeMs,
          stale_after_ms: inventoryStaleMs,
        },
      },
    );
  }

  for (const observation of Object.values(state.funding_observations)) {
    const observationAgeMs = ageMs(observation.last_seen_at, nowValue);
    const baseDetails = {
      funding_observation_id: observation.funding_observation_id,
      funding_handle: observation.funding_handle,
      confirmations: observation.confirmations,
      amount: observation.amount,
      observation_status: observation.status,
      first_seen_at: observation.first_seen_at,
      last_seen_at: observation.last_seen_at,
      age_ms: observationAgeMs,
      bridge_deposit_tx_hash: observation.bridge_deposit_tx_hash,
      bridge_status: observation.bridge_status,
    };

    if (observation.status === 'SEEN_UNCONFIRMED') {
      desired.set(
        buildAlertKey({
          alertCode: 'funding_seen_unconfirmed',
          serviceScope: 'liquidity-manager',
          assetId: observation.asset_id,
          txHash: observation.tx_hash,
        }),
        {
          alert_code: 'funding_seen_unconfirmed',
          severity: 'info',
          reason: `funding tx ${observation.tx_hash} is visible before confirmations`,
          service_scope: 'liquidity-manager',
          pair: null,
          asset_id: observation.asset_id,
          tx_hash: observation.tx_hash,
          details: baseDetails,
        },
      );
    }

    if (
      observation.status === 'CREDIT_PENDING'
      || (observation.status === 'SEEN_CONFIRMED' && observationAgeMs != null && observationAgeMs >= fundingCreditPendingMs)
    ) {
      desired.set(
        buildAlertKey({
          alertCode: 'funding_confirmed_credit_pending',
          serviceScope: 'liquidity-manager',
          assetId: observation.asset_id,
          txHash: observation.tx_hash,
        }),
        {
          alert_code: 'funding_confirmed_credit_pending',
          severity: 'warning',
          reason: `funding tx ${observation.tx_hash} is confirmed but not spendable yet`,
          service_scope: 'liquidity-manager',
          pair: null,
          asset_id: observation.asset_id,
          tx_hash: observation.tx_hash,
          details: {
            ...baseDetails,
            credit_pending_after_ms: fundingCreditPendingMs,
          },
        },
      );
    }

    if (
      observation.status === 'FAILED_OR_STUCK'
      || (
        observation.status !== 'CREDITED'
        && observation.status !== 'SEEN_UNCONFIRMED'
        && observationAgeMs != null
        && fundingStuckMs != null
        && observationAgeMs >= fundingStuckMs
      )
    ) {
      desired.set(
        buildAlertKey({
          alertCode: 'funding_stuck',
          serviceScope: 'liquidity-manager',
          assetId: observation.asset_id,
          txHash: observation.tx_hash,
        }),
        {
          alert_code: 'funding_stuck',
          severity: 'critical',
          reason: `funding tx ${observation.tx_hash} is failed or stuck before credit`,
          service_scope: 'liquidity-manager',
          pair: null,
          asset_id: observation.asset_id,
          tx_hash: observation.tx_hash,
          details: baseDetails,
        },
      );
    }
  }

  const latestTradeResult = state.latest_trade_result;
  if (latestTradeResult && isSubmissionFailure(latestTradeResult)) {
    desired.set(
      buildAlertKey({
        alertCode: 'executor_submission_failed',
        serviceScope: 'trade-executor',
        pair: latestTradeResult.pair || activePair,
      }),
      {
        alert_code: 'executor_submission_failed',
        severity: 'critical',
        reason: `executor submission failed for command ${latestTradeResult.command_id}`,
        service_scope: 'trade-executor',
        pair: latestTradeResult.pair || activePair,
        asset_id: null,
        tx_hash: null,
        details: {
          command_id: latestTradeResult.command_id,
          quote_id: latestTradeResult.quote_id,
          result_code: latestTradeResult.result_code,
          error: latestTradeResult.error || null,
          status: latestTradeResult.status,
        },
      },
    );
  }

  const transitions = reconcileAlertState({
    state,
    desired,
    now,
    recentTransitionLimit,
  });
  state.last_evaluated_at = now;
  return transitions;
}

function reconcileAlertState({ state, desired, now, recentTransitionLimit }) {
  const transitions = [];

  for (const [key, next] of desired.entries()) {
    const existing = state.active_alerts[key];
    if (!existing) {
      const raised = {
        ...next,
        status: 'raised',
        first_raised_at: now,
        raised_at: now,
        cleared_at: null,
        last_evaluated_at: now,
      };
      state.active_alerts[key] = raised;
      transitions.push(raised);
      continue;
    }

    state.active_alerts[key] = {
      ...existing,
      ...next,
      status: 'raised',
      raised_at: existing.raised_at || existing.first_raised_at || now,
      first_raised_at: existing.first_raised_at || existing.raised_at || now,
      cleared_at: null,
      last_evaluated_at: now,
    };
  }

  for (const [key, existing] of Object.entries(state.active_alerts)) {
    if (desired.has(key)) continue;

    const cleared = {
      ...existing,
      status: 'cleared',
      raised_at: existing.raised_at || existing.first_raised_at || now,
      cleared_at: now,
      last_evaluated_at: now,
    };
    delete state.active_alerts[key];
    transitions.push(cleared);
  }

  if (transitions.length > 0) {
    state.recent_transitions.unshift(...transitions);
    state.recent_transitions = state.recent_transitions.slice(0, recentTransitionLimit);
  }

  return transitions;
}

function reconcileRuntimeAlertState({
  state,
  desiredAlerts,
  now,
  recentTransitionLimit,
}) {
  const transitions = [];
  const desired = new Map();
  const nextRuntimeKeys = new Set();

  for (const alert of desiredAlerts || []) {
    const key = buildAlertKey({
      alertCode: alert.alert_code,
      serviceScope: alert.service_scope,
      pair: alert.pair,
      assetId: alert.asset_id,
      txHash: alert.tx_hash,
    });
    desired.set(key, alert);
    nextRuntimeKeys.add(key);
  }

  for (const key of state.runtime_alert_keys) {
    if (desired.has(key)) continue;
    const existing = state.active_alerts[key];
    if (!existing) continue;
    const cleared = {
      ...existing,
      status: 'cleared',
      raised_at: existing.raised_at || existing.first_raised_at || now,
      cleared_at: now,
      last_evaluated_at: now,
    };
    delete state.active_alerts[key];
    transitions.push(cleared);
  }

  for (const [key, alert] of desired.entries()) {
    const existing = state.active_alerts[key];
    if (!existing) {
      const raised = {
        ...alert,
        status: 'raised',
        first_raised_at: now,
        raised_at: now,
        cleared_at: null,
        last_evaluated_at: now,
      };
      state.active_alerts[key] = raised;
      transitions.push(raised);
      continue;
    }

    state.active_alerts[key] = {
      ...existing,
      ...alert,
      status: 'raised',
      raised_at: existing.raised_at || existing.first_raised_at || now,
      first_raised_at: existing.first_raised_at || existing.raised_at || now,
      cleared_at: null,
      last_evaluated_at: now,
    };
  }

  state.runtime_alert_keys = nextRuntimeKeys;
  if (transitions.length > 0) {
    state.recent_transitions.unshift(...transitions);
    state.recent_transitions = state.recent_transitions.slice(0, recentTransitionLimit);
  }
  state.last_evaluated_at = now;
  return transitions;
}

function summarizeState({ state, evaluationIntervalMs, now }) {
  const activeAlerts = Object.values(state.active_alerts)
    .sort((left, right) => timestampValue(right.first_raised_at) - timestampValue(left.first_raised_at));
  const nowValue = timestampValue(now);

  return {
    active_alerts: activeAlerts,
    recent_transitions: state.recent_transitions,
    last_evaluated_at: state.last_evaluated_at,
    stale: ageMs(state.last_evaluated_at, nowValue) > (evaluationIntervalMs * 2),
    latest_inputs: {
      market_price_at: state.latest_price?.observed_at || state.latest_price?.ingested_at || null,
      inventory_at: state.latest_inventory?.synced_at || state.latest_inventory?.ingested_at || null,
      liquidity_action_at: state.latest_liquidity_action?.observed_at || null,
      trade_result_at: state.latest_trade_result?.ingested_at || null,
      funding_observation_count: Object.keys(state.funding_observations).length,
    },
  };
}

function buildAlertKey({ alertCode, serviceScope, pair = null, assetId = null, txHash = null }) {
  return [alertCode, serviceScope, pair || '', assetId || '', txHash || ''].join('|');
}

function isSubmissionFailure(result) {
  return result?.status === 'failed' || result?.result_code === 'submission_failed';
}

function ageMs(value, nowValue) {
  const start = timestampValue(value);
  if (!Number.isFinite(start) || !Number.isFinite(nowValue)) return null;
  return Math.max(0, nowValue - start);
}

function timestampValue(value) {
  if (!value) return NaN;
  const parsed = Date.parse(value);
  return Number.isFinite(parsed) ? parsed : NaN;
}