LegendOfEffectiveDate.java

import java.math.BigDecimal;
import java.time.LocalDate;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.temporal.TemporalAdjusters;
import java.util.*;

public class LegendOfEffectiveDate {

    private static final TamsDb tamsDb = initialize();

    private static TamsDb initialize() {
        final var constant = new Constant();
        constant.id = 1L;
        constant.name = "Heat Rate 10%";
        constant.val = new BigDecimal("10.83302");
        tamsDb.constants.add(constant);

        final var constantAud = new ConstantAud();
        constantAud.id = constant.id;
        constantAud.name = constant.name;
        constantAud.rev = 1L;
        constantAud.timestamp = ZonedDateTime.parse("2020-06-31T23:59:59+01:00[Europe/Amsterdam]");
        tamsDb.constantsWithEffectiveDates.put(constantAud.timestamp, constantAud);

        return tamsDb;
    }
    
    public static void main(String... args) {
        BigDecimal monthlyReport = generateMonthlyReport();
        System.out.println("SCENARIO #1 Time: 2021-02-04, Result: " + monthlyReport);

        List<BigDecimal> reportssByMonthDefault = generate2020LastQuarterReport();
    }

    private static BigDecimal generateMonthlyReport() {
        final var endOfLastMonth = LocalDate.now()
                .minusMonths(1)
                .with(TemporalAdjusters.lastDayOfMonth())
                .atTime(LocalTime.of(23, 45))
                .atZone(ZoneId.of("Europe/Amsterdam"));
        return generateMonthlyReport(endOfLastMonth, tamsDb);
    }


    private static List<BigDecimal> generate2020LastQuarterReport() {
        final var effectiveDate2020Dec = ZonedDateTime.parse("2020-12-31T23:59:59+01:00[Europe/Amsterdam]");
        BigDecimal report2020December = generateMonthlyReport(effectiveDate2020Dec, tamsDb);

        final var effectiveDate2020Nov = ZonedDateTime.parse("2020-11-31T23:59:59+01:00[Europe/Amsterdam]");
        BigDecimal report2020November = generateMonthlyReport(effectiveDate2020Nov, tamsDb);

        final var effectiveDate2020Oct = ZonedDateTime.parse("2020-10-31T23:59:59+01:00[Europe/Amsterdam]");
        BigDecimal report2020October = generateMonthlyReport(effectiveDate2020Oct, tamsDb);

        return List.of(report2020December, report2020November, report2020October);
    }

    private static BigDecimal generateMonthlyReport(ZonedDateTime effectiveDate, TamsDb tamsDb) {
        return BigDecimal.TEN.multiply(tamsDb.findValByEffectiveDate(effectiveDate));
    }
}

class TamsDb {
    List<Constant> constants = new ArrayList<>();
    Map<ZonedDateTime, ConstantAud> constantsWithEffectiveDates = new TreeMap<>();


    public BigDecimal findValByEffectiveDate(ZonedDateTime effectiveDate) {

        return constantsWithEffectiveDates.entrySet()
                .stream()
                .filter(entry -> entry.getKey().isBefore(effectiveDate))
                .findFirst()
                .get()
                .getValue()
                .val;
    }
}

class Constant {
    Long id;
    String name;
    BigDecimal val;
}

// REVINFO joined
class ConstantAud {
    Long rev;
    //Data snapshot instant
    ZonedDateTime timestamp;
    Long id;
    String name;
    BigDecimal val;
}