'use strict';

/**
 * probabilityContractService — LOAD THE FROZEN ARTIFACT. DO NOT FIT.
 *
 * This used to call the fitter on every snapshot, so the active mapping changed
 * silently as outcomes settled: a user's number could move with no version, no
 * review and no rollback, and a past Read could not be reconstructed because the
 * curve that produced it no longer existed anywhere.
 *
 * The refit PROCEDURE is certified separately and offline
 * (`scripts/certify-current-era-procedure.js`), and produces ONE committed
 * artifact (`scripts/build-current-era-artifact.js`). At runtime there is no
 * fitter, no ledger read, and nothing to drift: `artifactRegistry` loads the
 * promoted JSON and the served value comes from its frozen curve.
 *
 * A consequence worth stating: new settled outcomes are FORWARD EVALUATION
 * evidence. They may inform a future candidate. They cannot alter this curve.
 */

const pc = require('./probabilityContract');
const registry = require('./artifactRegistry');

/**
 * @returns {null|{contract, artifact, resolve}} null when nothing is promoted
 *   for this sport/stat, or the promoted artifact fails to load. Null means
 *   NOTHING is served — never a fallback curve, which would be a mapping nobody
 *   certified.
 */
async function build(_sb, { sport = 'mlb', stat = 'hits', usage = 'shadow' } = {}) {
  const contract = pc.contractFor(sport, stat);
  if (!contract) return null;

  const artifact = registry.load(sport, stat);
  if (!artifact) return null;

  return {
    contract,
    artifact,
    fit_n: artifact.fit_n,
    fitted_through: artifact.training_cutoff,
    cutoff: artifact.fit_as_of,
    /** The frozen curve. Two calls return the same value, forever. */
    estimate: (p) => registry.applyCurve(artifact, p),
    /**
     * THE ROW'S IDENTITY DECIDES — never the identity this resolver was built
     * with. Stamping `{sport, stat}` here applied the mlb-hits curve to every
     * row in the batch: measured on cohort 0353c551, 513 PUBLISHED non-hits
     * rows (total_bases, runs, rbi, walks, outs, strikeouts, hits_allowed,
     * earned_runs) came back CERTIFIED_CALIBRATED with a served probability
     * from the hits artifact. A read that names no stat resolves to no
     * contract, which is UNSUPPORTED — the correct answer, not a fallback.
     */
    resolve(read) {
      return pc.resolve(read,
        { estimate: (p) => registry.applyCurve(artifact, p), artifact, usage });
    },
  };
}

module.exports = { build };