/**
 * AI module — usage ledger sink (Phase 12, TASK-0121).
 *
 * The gateway's usage sink: called (fire-and-forget, never awaited by the
 * request path) after EVERY completed or failed-after-consume gateway call.
 *
 * **Why this is a logger, not a writer (recorded decision):** the durable
 * `ai_messages` rows are written by the feature services on the request
 * path — the chat service persists the visible assistant message (content +
 * token counts + tool calls) in the user's conversation; the feature
 * services (writing / RAG / generate) persist their hidden per-call
 * conversation row. If the sink ALSO wrote a row, every call would be
 * double-counted in the monthly rollup (the budget guard sums
 * `ai_messages` — a double ledger would 402 workspaces twice as fast).
 *
 * The sink therefore gives the gateway's metering an observability home
 * (AGENTS rule 26 — usage of the AI surface is an important operation): a
 * structured line per call (capability, model, provider, tokens, status,
 * latency). The durable ledger is `ai_messages` (one row per call, written
 * by the services); the nightly `usage.rollup` worker job reconciles it for
 * dashboards.
 */
import { Inject, Injectable } from "@nestjs/common";
import type { UsageRecord } from "@factory/ai";
import { PrismaService } from "../../common/prisma.service.js";
import { logger } from "../../common/logger.js";

export const AI_LEDGER = "AI_LEDGER";

@Injectable()
export class AiLedgerService {
  constructor(@Inject(PrismaService) private readonly prisma: PrismaService) {}

  /**
   * The gateway's sink (see module doc). Observability only — the durable
   * row is the service's own `ai_messages` write for the same call.
   */
  async record(record: UsageRecord): Promise<void> {
    logger.info(
      `ai usage ${record.kind} ${record.model}/${record.provider} in=${record.tokensIn} out=${record.tokensOut} ${record.latencyMs}ms ${record.status} (gateway metering; the durable row is the service's ai_messages write)`,
      {
        event: "ai.usage",
        workspaceId: record.workspaceId,
        ...(record.userId ? { userId: record.userId } : {}),
        ...(record.capability ? { capability: record.capability } : {}),
        kind: record.kind,
        model: record.model,
        provider: record.provider,
        tokensIn: record.tokensIn,
        tokensOut: record.tokensOut,
        latencyMs: record.latencyMs,
        status: record.status
      }
    );
  }
}