// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: MIT-0

import {
  CostExplorerClient,
  GetCostAndUsageCommand
} from '@aws-sdk/client-cost-explorer'

const client = new CostExplorerClient()
const today = new Date()
const yesterday = new Date(new Date().setDate(new Date().getDate() - 1))

const params = {
  Metrics: [
    'USAGE_QUANTITY'
  ],
  Filter: {
    Dimensions: {
      Key: 'SERVICE',
      MatchOptions: ['EQUALS'],
      Values: ['Amazon Elastic Compute Cloud - Compute']
    }
  },
  TimePeriod: {
    End: today.toISOString().split('T')[0],
    Start: yesterday.toISOString().split('T')[0]
  },
  Granularity: 'DAILY',
  GroupBy: [{
    Key: 'REGION',
    Type: 'DIMENSION'
  }]
}

export const handler = async (event) => {
  const regions = new Set()
  let res
  do {
    if (res && res.NextToken) {
      params.NextToken = res.NextToken
    }
    // https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/clients/client-cost-explorer/classes/getcostandusagecommand.html
    const command = new GetCostAndUsageCommand(params)
    res = await client.send(command)

    for (const result of res.ResultsByTime) {
      for (const group of result.Groups) {
        for (const key of group.Keys) {
          regions.add(key)
        }
      }
    }
  } while (res.NextToken)
  return [...regions]
}