Zoned date time

README.md

@@ -16,7 +16,7 @@ as well as the logic to recommend the cheapest price plan for a particular house
 
 >Unfortunately, as the codebase has evolved, it has gathered tech debt in the form of a number of code smells and some 
 questionable design decisions. Our goal for the upcoming exercise would be to deliver value by implementing a new 
-feature using _Test Driven Development_ (TDD), while refactoring away the code smells we see. 
+feature using _[Test Driven Development](https://martinfowler.com/bliki/TestDrivenDevelopment.html)_ (TDD), while refactoring away the code smells we see. 
 > 
 >In preparation for this, please take some time to go through the code and identify any improvements, big or small, 
 that would improve its maintainability, testability, and design.
@@ -46,7 +46,9 @@ The project requires [Java 21](https://adoptium.net/) or higher.
 
 ## Useful commands
 
-Compile the project, run the tests and creates an executable JAR file
+### Build the project
+
+Compile the project, run the tests and creates an executable JAR file:
 
 ```console
 ./gradlew build
@@ -67,11 +69,10 @@ You can run it with the following command:
 
 ## API Documentation
 
-The codebase contains two service classes, _MeterReadingManager_ and _PricePlanComparator_, that serve as entry points to
-the implemented features.
+The codebase contains two service classes, `MeterReadingManager` and `PricePlanComparator` that serve as entry points to the implemented features.
 
 ### MeterReadingManager
-Provides methods to store and fetch the energy consumption readings from a given Smart Meter
+Provides methods to store and fetch the energy consumption readings from a given Smart Meter.
 
 > #### _public void_ storeReadings(_String smartMeterId, List<ElectricityReading> electricityReadings_)
 Stores the provided _ElectricityReading_ collection in the indicated _SmartMeter_. If no 
@@ -91,13 +92,13 @@ An _ElectricityReading_ record consists of the following fields:
 
 Example readings
 
-| Date (`GMT`)      | Epoch timestamp | Reading (kWh) |
-|-------------------|----------------:|--------------:|
-| `2020-11-29 8:00` |      1606636800 |        600.05 |
-| `2020-11-29 9:00` |      1606640400 |        602.06 |
-| `2020-11-30 7:30` |      1606721400 |        610.09 |
-| `2020-12-01 8:30` |      1606811400 |        627.12 |
-| `2020-12-02 8:30` |      1606897800 |        635.14 |
+| Date (`GMT`)      | Epoch timestamp (seconds) | Reading (kWh) |
+|-------------------|--------------------------:|--------------:|
+| `2020-11-29 8:00` |                1606636800 |        600.05 |
+| `2020-11-29 9:00` |                1606640400 |        602.06 |
+| `2020-11-30 7:30` |                1606721400 |        610.09 |
+| `2020-12-01 8:30` |                1606811400 |        627.12 |
+| `2020-12-02 8:30` |                1606897800 |        635.14 |
 
 Thee above table shows some readings sampled by a smart meter over multiple days. Note that since the smart 
 meter is reporting the total energy consumed up to that point in time, a reading's value will always be higher or the same as 

build.gradle.kts

@@ -29,7 +29,7 @@ application {
     mainClass = "tw.joi.energy.App"
 }
 
-tasks.withType<JavaCompile>() {
+tasks.withType<JavaCompile> {
     this.options.isDeprecation = true
 }
 

src/main/java/tw/joi/energy/App.java

@@ -25,7 +25,8 @@ public static void main(String[] args) {
         printAllAvailablePricePlans(pricePlanRepository);
 
         printSmartMeterInformation(smartMeterRepository, "Before storing readings...");
-        var readingsToSave = ElectricityReadingsGenerator.generate(3);
+        var readingsToSave =
+                ElectricityReadingsGenerator.generateElectricityReadingStream(3).toList();
         meterReadingManager.storeReadings(TEST_SMART_METER, readingsToSave);
         printSmartMeterInformation(smartMeterRepository, "After storing readings...");
 

src/main/java/tw/joi/energy/config/ElectricityReadingsGenerator.java

@@ -1,35 +1,43 @@
 package tw.joi.energy.config;
 
 import java.math.BigDecimal;
-import java.math.RoundingMode;
-import java.time.Instant;
-import java.util.ArrayList;
-import java.util.Comparator;
-import java.util.List;
+import java.time.Clock;
+import java.time.temporal.ChronoUnit;
 import java.util.Random;
+import java.util.stream.Stream;
 import tw.joi.energy.domain.ElectricityReading;
 
 public class ElectricityReadingsGenerator {
 
-    public static List<ElectricityReading> generate(int number) {
-        List<ElectricityReading> readings = new ArrayList<>();
-        Instant now = Instant.now();
-        BigDecimal previousReading = BigDecimal.ONE;
-        Instant previousReadingTime = now.minusSeconds(2 * number * 60L);
+    public static final double AVG_HOURLY_USAGE = 0.3;
+    public static final double VARIANCE = 0.2;
+    public static final double MIN_HOURLY_USAGE = AVG_HOURLY_USAGE - VARIANCE;
+    public static final double MAX_HOURLY_USAGE = AVG_HOURLY_USAGE + VARIANCE;
 
-        Random readingRandomiser = new Random();
+    private ElectricityReadingsGenerator() {}
 
-        for (int i = 0; i < number; i++) {
-            double positiveIncrement = Math.abs(readingRandomiser.nextGaussian());
-            BigDecimal currentReading =
-                    previousReading.add(BigDecimal.valueOf(positiveIncrement)).setScale(4, RoundingMode.CEILING);
-            ElectricityReading electricityReading =
-                    new ElectricityReading(previousReadingTime.plusSeconds(i * 60L), currentReading);
-            readings.add(electricityReading);
-            previousReading = currentReading;
-        }
+    public static Stream<ElectricityReading> generateElectricityReadingStream(int days) {
+        return generateElectricityReadingStream(Clock.systemDefaultZone(), BigDecimal.ZERO, days);
+    }
+
+    // we'll provide hourly readings for the specified number of days assuming 24 hours a day
+    // we'll assume that a house consumes ca 2700 kWh a year, so about 0.3 kWh per hour
 
-        readings.sort(Comparator.comparing(ElectricityReading::time));
-        return readings;
+    // the assumed starting point is the time on the clock, the ending point 24 hours later - so for 1 day, we'll get 25
+    // readings
+    public static Stream<ElectricityReading> generateElectricityReadingStream(
+            Clock clock, BigDecimal initialReading, int days) {
+        var now = clock.instant();
+        var readingRandomiser = new Random();
+        var seed = new ElectricityReading(now, initialReading);
+        var lastTimeToBeSupplied = now.plus(days * 24L, ChronoUnit.HOURS);
+        return Stream.iterate(
+                seed, er -> er.time().equals(lastTimeToBeSupplied) || er.time().isBefore(lastTimeToBeSupplied), er -> {
+                    var hoursWorthOfEnergy =
+                            BigDecimal.valueOf(readingRandomiser.nextDouble(MIN_HOURLY_USAGE, MAX_HOURLY_USAGE));
+                    return new ElectricityReading(
+                            er.time().plus(1, ChronoUnit.HOURS),
+                            er.readingInKwH().add(hoursWorthOfEnergy));
+                });
     }
 }

src/main/java/tw/joi/energy/config/TestData.java

@@ -1,6 +1,7 @@
 package tw.joi.energy.config;
 
 import static java.util.Collections.emptyList;
+import static java.util.Collections.emptySet;
 
 import java.math.BigDecimal;
 import java.util.List;
@@ -12,23 +13,39 @@
 public final class TestData {
 
     private static final PricePlan MOST_EVIL_PRICE_PLAN =
-            new PricePlan("price-plan-0", "Dr Evil's Dark Energy", BigDecimal.TEN, emptyList());
+            new PricePlan("price-plan-0", "Dr Evil's Dark Energy", BigDecimal.TEN, emptySet());
     private static final PricePlan RENEWABLES_PRICE_PLAN =
-            new PricePlan("price-plan-1", "The Green Eco", BigDecimal.valueOf(2), null);
+            new PricePlan("price-plan-1", "The Green Eco", BigDecimal.valueOf(2), emptySet());
     private static final PricePlan STANDARD_PRICE_PLAN =
-            new PricePlan("price-plan-2", "Power for Everyone", BigDecimal.ONE, emptyList());
+            new PricePlan("price-plan-2", "Power for Everyone", BigDecimal.ONE, emptySet());
 
     public static SmartMeterRepository smartMeterRepository() {
         var smartMeterRepository = new SmartMeterRepository();
         smartMeterRepository.save("smart-meter-0", new SmartMeter(MOST_EVIL_PRICE_PLAN, emptyList()));
         smartMeterRepository.save(
-                "smart-meter-1", new SmartMeter(RENEWABLES_PRICE_PLAN, ElectricityReadingsGenerator.generate(7)));
+                "smart-meter-1",
+                new SmartMeter(
+                        RENEWABLES_PRICE_PLAN,
+                        ElectricityReadingsGenerator.generateElectricityReadingStream(7)
+                                .toList()));
         smartMeterRepository.save(
-                "smart-meter-2", new SmartMeter(MOST_EVIL_PRICE_PLAN, ElectricityReadingsGenerator.generate(20)));
+                "smart-meter-2",
+                new SmartMeter(
+                        MOST_EVIL_PRICE_PLAN,
+                        ElectricityReadingsGenerator.generateElectricityReadingStream(20)
+                                .toList()));
         smartMeterRepository.save(
-                "smart-meter-3", new SmartMeter(STANDARD_PRICE_PLAN, ElectricityReadingsGenerator.generate(12)));
+                "smart-meter-3",
+                new SmartMeter(
+                        STANDARD_PRICE_PLAN,
+                        ElectricityReadingsGenerator.generateElectricityReadingStream(12)
+                                .toList()));
         smartMeterRepository.save(
-                "smart-meter-4", new SmartMeter(RENEWABLES_PRICE_PLAN, ElectricityReadingsGenerator.generate(3)));
+                "smart-meter-4",
+                new SmartMeter(
+                        RENEWABLES_PRICE_PLAN,
+                        ElectricityReadingsGenerator.generateElectricityReadingStream(3)
+                                .toList()));
         return smartMeterRepository;
     }
 

src/main/java/tw/joi/energy/domain/ElectricityReading.java

@@ -1,9 +1,16 @@
 package tw.joi.energy.domain;
 
 import java.math.BigDecimal;
+import java.time.Clock;
 import java.time.Instant;
 
 /**
- * @param reading kWh
+ * @param time point in time
+ * @param readingInKwH energy consumed in total to this point in time in kWh
  */
-public record ElectricityReading(Instant time, BigDecimal reading) {}
+public record ElectricityReading(Instant time, BigDecimal readingInKwH) {
+
+    public ElectricityReading(Clock clock, double readingInKwH) {
+        this(clock.instant(), BigDecimal.valueOf(readingInKwH));
+    }
+}

src/main/java/tw/joi/energy/domain/PeakTimeMultiplier.java

@@ -0,0 +1,6 @@
+package tw.joi.energy.domain;
+
+import java.math.BigDecimal;
+import java.time.DayOfWeek;
+
+public record PeakTimeMultiplier(DayOfWeek dayOfWeek, BigDecimal multiplier) {}

src/main/java/tw/joi/energy/domain/PricePlan.java

@@ -1,64 +1,46 @@
 package tw.joi.energy.domain;
 
-import java.io.*;
 import java.math.BigDecimal;
-import java.text.*;
 import java.time.DayOfWeek;
-import java.time.LocalDateTime;
-import java.util.List;
+import java.time.ZonedDateTime;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 public class PricePlan {
 
-    private String energySupplier;
-    private String planName;
+    private final String energySupplier;
+    private final String planName;
     private final BigDecimal unitRate; // unit price per kWh
-    private final List<PeakTimeMultiplier> peakTimeMultipliers;
+    private final Map<DayOfWeek, BigDecimal> peakTimeMultipliers;
 
     public PricePlan(
-            String planName, String energySupplier, BigDecimal unitRate, List<PeakTimeMultiplier> peakTimeMultipliers) {
+            String planName, String energySupplier, BigDecimal unitRate, Set<PeakTimeMultiplier> peakTimeMultipliers) {
         this.planName = planName;
         this.energySupplier = energySupplier;
         this.unitRate = unitRate;
-        this.peakTimeMultipliers = peakTimeMultipliers;
+        this.peakTimeMultipliers = peakTimeMultipliers.stream()
+                .collect(Collectors.toUnmodifiableMap(PeakTimeMultiplier::dayOfWeek, PeakTimeMultiplier::multiplier));
     }
 
     public String getEnergySupplier() {
         return energySupplier;
     }
 
-    public void setEnergySupplier(String supplierName) {
-        this.energySupplier = supplierName;
-    }
-
     public String getPlanName() {
         return planName;
     }
 
-    public void setPlanName(String name) {
-        this.planName = name;
-    }
-
     public BigDecimal getUnitRate() {
         return unitRate;
     }
 
-    public BigDecimal getPrice(LocalDateTime dateTime) {
+    public BigDecimal getPrice(ZonedDateTime dateTime) {
         return unitRate;
     }
 
     @Override
     public String toString() {
         return "Name: '" + planName + "', Unit Rate: " + unitRate + ", Supplier: '" + energySupplier + "'";
     }
-
-    static class PeakTimeMultiplier {
-
-        DayOfWeek dayOfWeek;
-        BigDecimal multiplier;
-
-        public PeakTimeMultiplier(DayOfWeek dayOfWeek, BigDecimal multiplier) {
-            this.dayOfWeek = dayOfWeek;
-            this.multiplier = multiplier;
-        }
-    }
 }

src/main/java/tw/joi/energy/domain/SmartMeter.java

@@ -8,6 +8,7 @@
 import java.util.stream.Collectors;
 
 public class SmartMeter {
+
     private final PricePlan pricePlan;
     private final List<ElectricityReading> electricityReadings;
 

src/main/java/tw/joi/energy/repository/PricePlanRepository.java

@@ -1,14 +1,13 @@
 package tw.joi.energy.repository;
 
-import static java.util.Comparator.*;
-import static java.util.stream.Collectors.*;
+import static java.util.Comparator.comparing;
+import static java.util.stream.Collectors.toMap;
 
 import java.math.BigDecimal;
-import java.time.LocalDateTime;
+import java.time.ZonedDateTime;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.regex.*;
 import tw.joi.energy.domain.ElectricityReading;
 import tw.joi.energy.domain.PricePlan;
 import tw.joi.energy.domain.SmartMeter;
@@ -34,8 +33,8 @@ private BigDecimal calculateCost(Collection<ElectricityReading> electricityReadi
                 .max(comparing(ElectricityReading::time))
                 .get();
 
-        BigDecimal energyConsumed = latest.reading().subtract(oldest.reading());
-        return energyConsumed.multiply(pricePlan.getPrice(LocalDateTime.now()));
+        BigDecimal energyConsumed = latest.readingInKwH().subtract(oldest.readingInKwH());
+        return energyConsumed.multiply(pricePlan.getPrice(ZonedDateTime.now()));
     }
 
     public List<PricePlan> getAllPricePlans() {