/**
 * Trace → policy association.
 *
 * For each high-V trace, we try to attach it to an existing L2 policy:
 *
 *   1. Pull the top-K nearest policies (cosine on `trace.vecSummary`).
 *   2. Score each candidate via `tracePolicySimilarity` (cosine + signature
 *      overlap).
 *   3. Pick the best whose score ≥ `minSimilarity` (algorithm.l2Induction).
 *   4. Emit an event, push the trace id into the policy's source episodes.
 *
 * If nothing meets the threshold, the trace is handed off to the candidate
 * pool for later induction.
 *
 * This module does NOT mutate policy.support / gain / status — that's the
 * gain step's job (we want one coherent write per policy per episode).
 */

import type { Logger } from "../../logger/types.js";
import type { EmbeddingVector, PolicyId, PolicyRow, TraceRow } from "../../types.js";
import type { Repos } from "../../storage/repos/index.js";
import { tracePolicySimilarity } from "./similarity.js";
import type { AssociationResult } from "./types.js";

interface AssociateDeps {
  repos: Pick<Repos, "policies">;
  log: Logger;
  config: { minSimilarity: number; poolFactor: number };
}

/**
 * Attempt to associate each trace with an existing `active` or `candidate`
 * L2 policy. Returns one result per input trace (null `matchedPolicyId`
 * when nothing matched).
 */
export function associateTraces(
  traces: readonly TraceRow[],
  deps: AssociateDeps,
): AssociationResult[] {
  const { repos, log, config } = deps;
  const results: AssociationResult[] = [];

  for (const tr of traces) {
    const vec = tr.vecSummary ?? tr.vecAction ?? null;
    if (!vec) {
      results.push(emptyResult(tr));
      continue;
    }

    const poolSize = Math.max(4, Math.floor(config.poolFactor * 4));
    let hits: Array<{ id: PolicyId }>;
    try {
      hits = repos.policies.searchByVector(vec as EmbeddingVector, poolSize, {
        statusIn: ["active", "candidate"],
      });
    } catch (err) {
      log.warn("associate.search_failed", {
        traceId: tr.id,
        err: err instanceof Error ? err.message : String(err),
      });
      results.push(emptyResult(tr));
      continue;
    }
    if (hits.length === 0) {
      results.push(emptyResult(tr));
      continue;
    }

    let best: { score: number; cosine: number; policy: PolicyRow } | null = null;
    for (const h of hits) {
      const p = repos.policies.getById(h.id);
      if (!p) continue;
      const s = tracePolicySimilarity(tr, p, null);
      if (!best || s.score > best.score) best = { score: s.score, cosine: s.cosine, policy: p };
    }
    if (!best || best.score < config.minSimilarity) {
      results.push(emptyResult(tr));
      continue;
    }

    results.push({
      traceId: tr.id,
      signature: "",
      matchedPolicyId: best.policy.id,
      matchSimilarity: best.cosine,
      addedToCandidatePool: false,
    });
  }
  return results;
}

function emptyResult(tr: TraceRow): AssociationResult {
  return {
    traceId: tr.id,
    signature: "",
    matchedPolicyId: null,
    matchSimilarity: 0,
    addedToCandidatePool: false,
  };
}