/**
 * Copyright 2024-2026 Wingify Software Pvt. Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { SettingsModel } from '../models/settings/SettingsModel';
import { findGroupsFeaturePartOf } from './CampaignUtil';
import { isNaN } from './DataTypeUtil';
import { getFeatureKeysFromGroup } from './MegUtil';

/**
 * Feature keys that must be evaluated sequentially within one getFlags worker.
 */
export interface EvaluationBatch {
  featureKeys: string[];
}

/**
 * Partitions requested keys into evaluation batches for getFlags().
 * MEG-linked keys share a batch; independent keys form single-key batches.
 *
 * @param requestedFeatureKeys - Distinct feature keys requested by the caller.
 * @param settings - Account settings used to resolve MEG group membership.
 * @returns Batches where MEG-linked keys share a batch and independent keys are alone.
 */
export function getFeatureFlagBatches(requestedFeatureKeys: string[], settings: SettingsModel): EvaluationBatch[] {
  if (!requestedFeatureKeys.length) {
    return [];
  }

  const evaluationBatches: EvaluationBatch[] = [];
  // Tracks feature keys already placed into a batch.
  const assignedFeatureKeys = new Set<string>();

  for (const featureKey of requestedFeatureKeys) {
    if (assignedFeatureKeys.has(featureKey)) {
      // Skip duplicates while preserving caller order for the first occurrence.
      continue;
    }

    const megGroups = findGroupsFeaturePartOf(settings, featureKey);
    const rawMegGroupId = megGroups[0]?.groupId;
    const megGroupId = rawMegGroupId != null ? Number(rawMegGroupId) : NaN;

    if (!isNaN(megGroupId)) {
      const megGroupFeatureKeys = getFeatureKeysFromGroup(settings, megGroupId).featureKeys ?? [];
      const requestedMegFeatureKeys = requestedFeatureKeys.filter(
        (requestedFeatureKey) =>
          megGroupFeatureKeys.includes(requestedFeatureKey) && !assignedFeatureKeys.has(requestedFeatureKey),
      );
      // Never drop a requested key when group lookup is empty or mismatched.
      const megBatchFeatureKeys = requestedMegFeatureKeys.length > 0 ? requestedMegFeatureKeys : [featureKey];

      // One batch per MEG group present in this request.
      evaluationBatches.push({ featureKeys: megBatchFeatureKeys });
      megBatchFeatureKeys.forEach((assignedFeatureKey) => assignedFeatureKeys.add(assignedFeatureKey));
      continue;
    }

    // Independent flags become their own parallelizable batch.
    evaluationBatches.push({ featureKeys: [featureKey] });
    assignedFeatureKeys.add(featureKey);
  }

  return evaluationBatches;
}