/**
 * enforce.ts — Quota Share enforcement for the hot path.
 *
 * Two entry points:
 *   - enforceQuotaShare(input): EnforceDecision — PRE-request check.
 *   - recordConsumption(input): void — POST-response tracker (fire-and-forget via spendRecorder).
 *
 * Design principles (Group B decisions):
 *   - B16: fail-open — any error from store/plan/saturation is caught and treated as "allow".
 *   - B25: 429 message is sanitized (routed through buildErrorBody in chatCore hook, not here).
 *   - B29: recordConsumption failures never propagate to the caller (drift is acceptable).
 *
 * Part of: Group B — Quota Sharing Engine (plan 22, frente F7).
 */

import type { EnforceDecision, EnforceInput, RecordConsumptionInput } from "./types";
import type { QuotaUnit } from "./dimensions";
import { dimensionKeyToString } from "./dimensions";
import { decideFairShare } from "./fairShare";
import { resolvePlan } from "./planResolver";
import { getSaturation } from "./saturationSignals";
import { getQuotaStore } from "./QuotaStore";
import { listAllocationsForApiKey, getPool } from "@/lib/db/quotaPools";

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

const SATURATION_THRESHOLD = Number(process.env.QUOTA_SATURATION_THRESHOLD ?? "0.5");

/**
 * Units for which the store tracks a real pool-wide aggregate (sum of per-key
 * consumption via quota_consumption rows). For these units, globalUsedPercent
 * (the saturation signal from the upstream provider) is always 0 because no
 * external API reports a "percent used" for raw request/token/usd counters.
 *
 * Using globalUsedPercent × effectiveLimit for countable units would always
 * yield consumedTotal = 0, meaning the pool never saturates and per-key
 * overage is never blocked. We use store.poolConsumedTotal() instead, which
 * sums the actual consumption across all keys in the pool window.
 *
 * "percent" dimensions remain driven by the saturation signal because that IS
 * the authoritative consumption measure (the upstream provider percentage).
 */
const COUNTABLE_UNITS = new Set(["requests", "tokens", "usd"]);

// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------

/**
 * PRE-request enforcement gate.
 *
 * Returns "allow" (optionally with deprioritize=true for soft policy) or
 * "block" (429, with reason and optional retryAfterSeconds).
 *
 * Always fail-open per B16: errors from the store, plan resolver, or saturation
 * signals result in { kind: "allow" } so a transient quota infra failure never
 * blocks legitimate traffic.
 */
export async function enforceQuotaShare(input: EnforceInput): Promise<EnforceDecision> {
  // 1. Find pools that contain this apiKeyId.
  let allocations: Array<{ poolId: string; allocation: import("@/lib/db/quotaPools").PoolAllocation }>;
  try {
    allocations = listAllocationsForApiKey(input.apiKeyId);
  } catch {
    // DB not available or migration not run — fail-open
    return { kind: "allow" };
  }

  if (!allocations.length) {
    // No pool assignment → no restriction
    return { kind: "allow" };
  }

  // 2. Filter to pool that belongs to the same connectionId.
  let pool: import("@/lib/db/quotaPools").QuotaPool | null = null;
  let poolAllocation: import("@/lib/db/quotaPools").PoolAllocation | null = null;
  for (const { poolId, allocation } of allocations) {
    let p: import("@/lib/db/quotaPools").QuotaPool | null = null;
    try {
      p = getPool(poolId);
    } catch {
      continue;
    }
    // D2: match if the input connectionId is ANY member of the pool, not only
    // the legacy primary. Fall back to connectionId equality for rows that
    // have not yet been backfilled (connectionIds empty/undefined).
    if (
      p &&
      (Array.isArray(p.connectionIds)
        ? p.connectionIds.includes(input.connectionId)
        : p.connectionId === input.connectionId)
    ) {
      pool = p;
      poolAllocation = allocation;
      break;
    }
  }

  if (!pool || !poolAllocation) {
    // API key is in pools but none matches this connection → no restriction
    return { kind: "allow" };
  }

  // 3. Resolve the provider plan (dimensions).
  const plan = resolvePlan(input.connectionId, input.provider);
  if (!plan.dimensions.length) {
    // No dimensions configured → nothing to enforce
    return { kind: "allow" };
  }

  // 3a. Compute the account multiplier: a pool with N same-type connections has an
  // effective budget of perAccountLimit × N per dimension. Consumption is already
  // pool-keyed (shared bucket) — only the limit scales, never the consumption.
  const accountCount =
    Array.isArray(pool.connectionIds) && pool.connectionIds.length > 0
      ? pool.connectionIds.length
      : 1;

  // 4. For each active dimension, peek consumption and saturation.
  const store = await getQuotaStore();
  const dimensionsInfo: Array<{
    key: { poolId: string; unit: QuotaUnit; window: import("./dimensions").QuotaWindow };
    limit: number;
    consumedTotal: number;
    globalUsedPercent: number;
  }> = [];
  const consumedByThisKey: Record<string, number> = {};

  for (const dim of plan.dimensions) {
    const dimKey = { poolId: pool.id, unit: dim.unit, window: dim.window };
    const dimKeyStr = dimensionKeyToString(dimKey);

    const consumedThisKey = await store.peek(input.apiKeyId, dimKey).catch(() => 0);
    consumedByThisKey[dimKeyStr] = consumedThisKey;

    // Global saturation signal — fail-open: 0 (generous mode)
    const globalUsedPercent = await getSaturation(input.connectionId, input.provider, dim).catch(
      () => 0
    );

    // Effective limit = per-account plan limit × number of accounts in the pool.
    // This is the summed budget: N accounts contribute N × L capacity to the shared bucket.
    const effectiveLimit = dim.limit * accountCount;

    // Derive consumedTotal based on the unit type:
    //   - Countable units (requests/tokens/usd): use the real store aggregate so the
    //     pool can actually saturate and block per-key overage. The saturation signal
    //     (globalUsedPercent) is always 0 for these units — using it would permanently
    //     keep consumedTotal at 0 and never trigger the block path.
    //   - percent dimensions: the saturation signal IS the consumed signal (the upstream
    //     provider returns a utilisation percentage, not raw counts).
    let consumedTotal: number;
    if (COUNTABLE_UNITS.has(dim.unit)) {
      // Real pool-wide aggregate (sum of per-key consumption across all apiKeyIds).
      consumedTotal = await store.poolConsumedTotal(pool.id, dimKey).catch(() => 0);
    } else {
      // percent (account-quota window): the saturation signal is authoritative.
      consumedTotal = globalUsedPercent * effectiveLimit;
    }

    dimensionsInfo.push({
      key: dimKey,
      limit: effectiveLimit,
      consumedTotal,
      globalUsedPercent,
    });
  }

  // 5. Apply the fair-share algorithm across all dimensions.
  // Equal-split fallback: when ALL allocations in the pool have weight 0 (e.g. newly
  // added keys whose weight was never set), treat each as an equal share so the pool
  // is usable without requiring a re-save. Original non-zero weights are kept as-is.
  const poolTotalWeight = Array.isArray(pool.allocations)
    ? pool.allocations.reduce((s, a) => s + (Number.isFinite(a.weight) ? a.weight : 0), 0)
    : 0;
  const allocCount = Array.isArray(pool.allocations) ? pool.allocations.length : 0;
  const effectiveWeight =
    poolTotalWeight > 0 ? poolAllocation.weight : allocCount > 0 ? 100 / allocCount : 0;

  const decision = decideFairShare({
    dimensions: dimensionsInfo,
    allocation: { ...poolAllocation, weight: effectiveWeight },
    consumedByThisKey,
    saturationThreshold: SATURATION_THRESHOLD,
  });

  if (decision.kind === "block") {
    // Fire webhook (fire-and-forget, never blocks the response)
    try {
      const { notifyWebhookEvent } = await import("@/lib/webhookDispatcher");
      notifyWebhookEvent("quota.exceeded", {
        apiKeyId: input.apiKeyId,
        provider: input.provider,
        connectionId: input.connectionId,
        reason: decision.reason,
      });
    } catch {
      // webhook dispatch is best-effort
    }

    return {
      kind: "block",
      reason: messageForReason(decision.reason, input.provider),
      httpStatus: 429,
      retryAfterSeconds: decision.retryAfterMs
        ? Math.ceil(decision.retryAfterMs / 1000)
        : undefined,
    };
  }

  // "allow" — may be penalized (soft policy overage)
  return {
    kind: "allow",
    deprioritize: decision.penalized === true,
  };
}

/**
 * POST-response consumption recorder.
 *
 * Increments the quota counter for each active dimension.
 * Errors are swallowed (B29): the LLM response has already been delivered.
 */
export async function recordConsumption(input: RecordConsumptionInput): Promise<void> {
  let allocations: Array<{ poolId: string; allocation: import("@/lib/db/quotaPools").PoolAllocation }>;
  try {
    allocations = listAllocationsForApiKey(input.apiKeyId);
  } catch {
    return; // DB not available — silent no-op
  }

  if (!allocations.length) return;

  // Find the pool matching this connection
  let poolId: string | null = null;
  for (const { poolId: pid } of allocations) {
    let p: import("@/lib/db/quotaPools").QuotaPool | null = null;
    try {
      p = getPool(pid);
    } catch {
      continue;
    }
    // D2: membership check — same logic as enforceQuotaShare above.
    if (
      p &&
      (Array.isArray(p.connectionIds)
        ? p.connectionIds.includes(input.connectionId)
        : p.connectionId === input.connectionId)
    ) {
      poolId = pid;
      break;
    }
  }

  if (!poolId) return;

  const plan = resolvePlan(input.connectionId, input.provider);
  if (!plan.dimensions.length) return;

  const store = await getQuotaStore();
  for (const dim of plan.dimensions) {
    const dimKey = { poolId, unit: dim.unit, window: dim.window };
    const cost = costForUnit(input.cost, dim.unit);
    if (cost > 0) {
      await store.consume(input.apiKeyId, dimKey, cost).catch(() => {
        // Fail-open per B29 — drift expected; teto global do fetcher corrige
      });
    }
  }
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

function messageForReason(reason: string, provider: string): string {
  switch (reason) {
    case "fair-share":
      return `Quota share limit reached for your API key on ${provider}`;
    case "cap-absolute":
      return `Absolute quota cap reached for your API key on ${provider}`;
    case "global-saturated":
      return `Provider ${provider} quota window is saturated; no shared capacity available`;
    default:
      return "Quota share enforcement blocked the request";
  }
}

function costForUnit(
  cost: RecordConsumptionInput["cost"],
  unit: QuotaUnit
): number {
  switch (unit) {
    case "tokens":
      return cost.tokens ?? 0;
    case "usd":
      return cost.usd ?? 0;
    case "requests":
      return cost.requests ?? 1;
    case "percent":
      // percent is a global signal; not incremented locally
      return 0;
    default:
      return 0;
  }
}