'use strict';

const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

// A/B 实验：按 conversationId 稳定分桶（旧 bridge config/experiments.js 精简版）。
function createExperimentManager(cfg = {}) {
  const file = cfg.experimentsPath || path.resolve(__dirname, '..', 'config', 'experiments.json');
  let experiments = [];
  try {
    const data = JSON.parse(fs.readFileSync(file, 'utf8'));
    experiments = Array.isArray(data.experiments) ? data.experiments : [];
  } catch {
    experiments = [];
  }

  function getVariant(convId, experimentId) {
    const exp = experiments.find((e) => e.active && (!experimentId || e.id === experimentId));
    if (!exp) return { experiment_id: null, variant: null, overriddenParams: null };
    const hash = crypto.createHash('md5').update(`${convId}:${exp.id}`).digest('hex');
    const bucket = parseInt(hash.slice(0, 8), 16) % 100;
    let cumulative = 0;
    for (const v of exp.variants || []) {
      cumulative += v.weight || 50;
      if (bucket < cumulative) return { experiment_id: exp.id, variant: v.name, overriddenParams: v.overriddenParams || null };
    }
    return { experiment_id: exp.id, variant: (exp.variants && exp.variants[0] && exp.variants[0].name) || null, overriddenParams: null };
  }

  function getActiveExperiments() {
    return experiments.filter((e) => e.active);
  }

  return { getVariant, getActiveExperiments };
}

module.exports = { createExperimentManager };