Meter detail: lead with periods and change, not register totals

The headline tiles were lifetime consumption, a raw reading count and the
register span. None of those answer why someone opens a meter: how much this
month, more or less than last, where the year lands, what it costs. A
cumulative counter's register value is an accident of when the meter was
installed.

MeterPeriodService buckets consumption by calendar month in the instance
timezone -- via date_trunc(... AT TIME ZONE) rather than EF grouping, because a
reading at 00:30 local on 1 January is 23:30 on 31 December in UTC and would be
booked to the wrong month (SDD §10). It reports generation for a generation
counter and consumption otherwise, so a PV meter stops claiming it consumed
0 kWh.

Month- and year-to-date are compared against a projection of the current period
rather than its running total. Three days into a month, "12 kWh vs 340 kWh last
month" reads as a collapse in usage when nothing has changed. The projection is
straight-line on elapsed days -- wrong for anything seasonal, but the honest
reading of "at this rate" -- and the UI marks it with a leading ~.

A 12-month bar strip gives the shape at a glance. A meter with nothing
normalized yet returns an empty history rather than a flat line, which would
look like a meter reading zero.

Register span, reading count and lifetime total move into a collapsed panel.
Still there when needed for an audit, no longer the first thing you see.

Claude-Session: https://claude.ai/code/session_01V6joyergfvVLFEizH1hJLd

src/App/Components/Pages/MeterDetail.razor

@@ -1,5 +1,6 @@
 @page "/meters/{Id:int}"
 @inject MeterDetailService Details
+@inject MeterPeriodService Periods
 @inject Microsoft.EntityFrameworkCore.IDbContextFactory<MeterVault.Infrastructure.Persistence.MeterVaultDbContext> DbFactory
 @inject ISnackbar Snackbar
 @inject IDialogService DialogService
@@ -34,43 +35,99 @@ else
         }
     </div>
 
-    <MudGrid Class="mb-2">
-        <MudItem xs="6" sm="3">
-            <MudPaper Class="pa-3" Elevation="2">
-                <MudText Typo="Typo.overline" Color="Color.Secondary">Consumption</MudText>
-                <MudText Typo="Typo.h6">@Format.Number(_detail.TotalConsumption, 0) @_detail.Unit</MudText>
-            </MudPaper>
-        </MudItem>
-        @if (_detail.TotalGeneration != 0)
+    @if (_periods is { } p)
     {
-            <MudItem xs="6" sm="3">
+        <MudGrid Class="mb-2">
+            <MudItem xs="12" sm="6" md="3">
                 <MudPaper Class="pa-3" Elevation="2">
-                    <MudText Typo="Typo.overline" Color="Color.Secondary">Generation</MudText>
-                    <MudText Typo="Typo.h6">@Format.Number(_detail.TotalGeneration, 0) @_detail.Unit</MudText>
-                </MudPaper>
-            </MudItem>
-        }
-        <MudItem xs="6" sm="3">
-            <MudPaper Class="pa-3" Elevation="2">
-                <MudText Typo="Typo.overline" Color="Color.Secondary">Readings</MudText>
-                <MudText Typo="Typo.h6">@_detail.ReadingCount</MudText>
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">@p.Label this month</MudText>
+                    <MudText Typo="Typo.h6">@Format.Number(p.MonthToDate, 0) @p.Unit</MudText>
+                    @if (p.MonthIsPartial)
+                    {
                         <MudText Typo="Typo.caption" Color="Color.Secondary">
-                    @(_detail.FirstReadingTime?.ToString("yyyy-MM") ?? "—") … @(_detail.LastReadingTime?.ToString("yyyy-MM") ?? "—")
+                            ≈ @Format.Number(p.MonthProjected, 0) @p.Unit by month end
+                        </MudText>
+                    }
+                </MudPaper>
+            </MudItem>
+            <MudItem xs="12" sm="6" md="3">
+                <MudPaper Class="pa-3" Elevation="2">
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">vs last month</MudText>
+                    <MudText Typo="Typo.h6">@ChangeText(p.MonthChange)</MudText>
+                    <MudText Typo="Typo.caption" Color="Color.Secondary">
+                        last month @Format.Number(p.LastMonth, 0) @p.Unit
                     </MudText>
                 </MudPaper>
             </MudItem>
-        <MudItem xs="6" sm="3">
+            <MudItem xs="12" sm="6" md="3">
                 <MudPaper Class="pa-3" Elevation="2">
-                <MudText Typo="Typo.overline" Color="Color.Secondary">Register span</MudText>
-                <MudText Typo="Typo.h6">
-                    @(_detail.FirstReadingValue is { } f ? Format.Number(f, 0) : "—") →
-                    @(_detail.LastReadingValue is { } l ? Format.Number(l, 0) : "—")
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">This year</MudText>
+                    <MudText Typo="Typo.h6">@Format.Number(p.YearToDate, 0) @p.Unit</MudText>
+                    <MudText Typo="Typo.caption" Color="Color.Secondary">
+                        @ChangeText(p.YearChange) vs @Format.Number(p.LastYear, 0) last year
+                    </MudText>
+                </MudPaper>
+            </MudItem>
+            <MudItem xs="12" sm="6" md="3">
+                <MudPaper Class="pa-3" Elevation="2">
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">Cost this year</MudText>
+                    <MudText Typo="Typo.h6">@Format.Number(p.YearToDateCost, 2) @p.Currency</MudText>
+                    <MudText Typo="Typo.caption" Color="Color.Secondary">
+                        ≈ @Format.Number(p.YearProjectedCost, 0) @p.Currency full year
+                        @(p.LastYearCost > 0 ? $"· {Format.Number(p.LastYearCost, 0)} last year" : "")
                     </MudText>
-                <MudText Typo="Typo.caption" Color="Color.Secondary">baseline @Format.Number(_detail.InitialBaseline, 0)</MudText>
                 </MudPaper>
             </MudItem>
         </MudGrid>
 
+        @if (p.HasHistory)
+        {
+            <MudPaper Class="pa-3 mb-2" Elevation="2">
+                <MudText Typo="Typo.overline" Color="Color.Secondary">Last 12 months</MudText>
+                <div class="d-flex align-end mt-2" style="gap:.35rem; height:110px">
+                    @foreach (var m in p.Last12Months)
+                    {
+                        <div class="d-flex flex-column align-center" style="flex:1; height:100%">
+                            <div style="flex:1; display:flex; align-items:flex-end; width:100%">
+                                <div title="@($"{m.Month:yyyy-MM}: {Format.Number(m.Amount, 0)} {p.Unit}")"
+                                     style="@BarStyle(m.Amount, p.Last12Months)"></div>
+                            </div>
+                            <MudText Typo="Typo.caption" Color="Color.Secondary">@m.Month.ToString("MMM")</MudText>
+                        </div>
+                    }
+                </div>
+            </MudPaper>
+        }
+    }
+
+    <MudExpansionPanels Elevation="0" Class="mb-2">
+        <MudExpansionPanel Text="Meter register details">
+            <div class="d-flex flex-wrap" style="gap:2rem">
+                <div>
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">Register span</MudText>
+                    <MudText Typo="Typo.body1">
+                        @(_detail.FirstReadingValue is { } f ? Format.Number(f, 0) : "—") →
+                        @(_detail.LastReadingValue is { } l ? Format.Number(l, 0) : "—")
+                        (baseline @Format.Number(_detail.InitialBaseline, 0))
+                    </MudText>
+                </div>
+                <div>
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">Readings</MudText>
+                    <MudText Typo="Typo.body1">
+                        @_detail.ReadingCount ·
+                        @(_detail.FirstReadingTime?.ToString("yyyy-MM") ?? "—") … @(_detail.LastReadingTime?.ToString("yyyy-MM") ?? "—")
+                    </MudText>
+                </div>
+                <div>
+                    <MudText Typo="Typo.overline" Color="Color.Secondary">Lifetime total</MudText>
+                    <MudText Typo="Typo.body1">
+                        @Format.Number(_detail.TotalGeneration != 0 ? _detail.TotalGeneration : _detail.TotalConsumption, 0) @_detail.Unit
+                    </MudText>
+                </div>
+            </div>
+        </MudExpansionPanel>
+    </MudExpansionPanels>
+
     <MudTabs Elevation="2" Rounded="true" ApplyEffectsToContainer="true" Class="mt-2">
         <MudTabPanel Text="@($"Readings ({_detail.ReadingCount})")">
             @if (_detail.RecentReadings.Count == 0)
@@ -279,6 +336,7 @@ else
     public int Id { get; set; }
 
     private MeterDetailView? _detail;
+    private MeterPeriodView? _periods;
     private bool _notFound;
     private List<MeterSource> _sources = [];
     private List<IngestionEndpoint> _endpoints = [];
@@ -289,15 +347,43 @@ else
     protected override async Task OnParametersSetAsync()
     {
         _detail = null;
+        _periods = null;
         _notFound = false;
         _detail = await Details.GetAsync(Id);
         _notFound = _detail is null;
         if (_detail is not null)
         {
+            _periods = await Periods.GetAsync(Id);
             await LoadSourcesAsync();
         }
     }
 
+    /// <summary>
+    /// "+12%" / "−4%" against the previous period. Less is better for consumption and worse for
+    /// generation, so colour is left to the caller's context rather than hardcoded green/red here.
+    /// </summary>
+    private static string ChangeText(double? change)
+    {
+        if (change is not { } c)
+        {
+            return "no basis yet";
+        }
+
+        return Math.Abs(c) < 0.005
+            ? "about the same"
+            : $"{(c > 0 ? "+" : "−")}{Format.Number(Math.Abs(c) * 100, 0)}%";
+    }
+
+    private static string BarStyle(double amount, IReadOnlyList<MeterMonthPoint> history)
+    {
+        var peak = history.Max(h => Math.Abs(h.Amount));
+        var fraction = peak < 1e-9 ? 0 : Math.Abs(amount) / peak;
+        // Floor at 2% so a month with a little usage is still visibly distinct from an empty one.
+        var height = amount == 0 ? 0 : Math.Max(2, fraction * 100);
+        return $"width:100%; height:{height.ToString("0.#", System.Globalization.CultureInfo.InvariantCulture)}%; "
+            + "background:var(--mud-palette-primary); border-radius:2px 2px 0 0";
+    }
+
     private async Task LoadSourcesAsync()
     {
         await using var db = await DbFactory.CreateDbContextAsync();

src/Infrastructure/Dashboard/MeterDetailModels.cs

@@ -8,6 +8,47 @@ public sealed record ReadingRow(DateTimeOffset Time, double Value, ReadingQualit
 /// <summary>A normalized consumption row for the meter-detail table.</summary>
 public sealed record ConsumptionDetailRow(DateTimeOffset Time, double Amount, ConsumptionKind Kind, ReadingQuality Quality);
 
+/// <summary>One calendar month of a meter's normalized history, bucketed in the instance timezone.</summary>
+public sealed record MeterMonthPoint(DateOnly Month, double Amount, double Cost);
+
+/// <summary>
+/// A meter framed the way it is actually read: what it used this period, how that compares with the
+/// last one, and where the year is heading. Amounts are generation for a generation counter and
+/// consumption otherwise, so <see cref="Label"/> says which.
+/// </summary>
+/// <remarks>
+/// Month- and year-to-date are compared against a <em>projection</em> of the current period rather
+/// than its raw running total: three days into a month, "12 kWh vs 340 kWh last month" reads as a
+/// collapse in usage when nothing has changed. Projections are flagged so the UI can mark them.
+/// </remarks>
+public sealed record MeterPeriodView(
+    string Label,
+    string Unit,
+    string Currency,
+    double MonthToDate,
+    double MonthProjected,
+    double LastMonth,
+    double YearToDate,
+    double YearProjected,
+    double LastYear,
+    double YearToDateCost,
+    double YearProjectedCost,
+    double LastYearCost,
+    bool MonthIsPartial,
+    IReadOnlyList<MeterMonthPoint> Last12Months)
+{
+    /// <summary>Projected month against last month, as a fraction (+0.12 = 12% more). Null if no basis.</summary>
+    public double? MonthChange => Ratio(MonthProjected, LastMonth);
+
+    /// <summary>Projected year against last year, as a fraction. Null if no basis.</summary>
+    public double? YearChange => Ratio(YearProjected, LastYear);
+
+    public bool HasHistory => Last12Months.Count > 0;
+
+    private static double? Ratio(double current, double previous) =>
+        Math.Abs(previous) < 1e-9 ? null : (current - previous) / previous;
+}
+
 /// <summary>A meter lifecycle/correction event row.</summary>
 public sealed record EventRow(DateTimeOffset Time, MeterEventType Type, double? Amount, double? PrevValue, double? NewValue, string? Unit, string? Notes);
 

src/Infrastructure/Dashboard/MeterPeriodService.cs

@@ -0,0 +1,151 @@
+using Dapper;
+using MeterVault.Core.Domain;
+using MeterVault.Infrastructure.Options;
+using MeterVault.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
+
+namespace MeterVault.Infrastructure.Dashboard;
+
+/// <summary>
+/// Answers the questions a meter is actually read for (SDD §8.6): how much this month, how that
+/// compares with last month, where the year lands, what it costs. Register totals answer none of
+/// those — a cumulative counter's value is an accident of when the meter was installed.
+/// </summary>
+public sealed class MeterPeriodService(
+    IDbContextFactory<MeterVaultDbContext> contextFactory,
+    Costing.CostService costs,
+    IOptions<MeterVaultOptions> options)
+{
+    private readonly IDbContextFactory<MeterVaultDbContext> _contextFactory = contextFactory;
+    private readonly Costing.CostService _costs = costs;
+    private readonly MeterVaultOptions _options = options.Value;
+
+    // Monthly buckets in the instance timezone, not UTC: a reading at 00:30 local on 1 January is
+    // 23:30 on 31 December in UTC, and would otherwise be booked to the wrong month (SDD §10).
+    private const string MonthlySql = """
+        SELECT date_trunc('month', time AT TIME ZONE @tz)::date AS month,
+               sum(amount)                                     AS amount
+        FROM consumption
+        WHERE meter_id = @meterId AND kind = @kind AND time >= @from
+        GROUP BY 1
+        ORDER BY 1
+        """;
+
+    public async Task<MeterPeriodView?> GetAsync(int meterId, CancellationToken cancellationToken = default)
+    {
+        await using var db = await _contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
+
+        var meter = await db.Meters.AsNoTracking()
+            .FirstOrDefaultAsync(m => m.Id == meterId, cancellationToken).ConfigureAwait(false);
+        if (meter is null)
+        {
+            return null;
+        }
+
+        var tz = ResolveTimeZone();
+        var today = DateOnly.FromDateTime(TimeZoneInfo.ConvertTime(DateTimeOffset.UtcNow, tz).Date);
+
+        // A generation counter's output is generation, not consumption — reporting 0 kWh consumed
+        // for a working PV array is technically true and completely useless.
+        var isGeneration = meter.Mode == MeterMode.GenerationCounter;
+        var kind = isGeneration ? ConsumptionKind.Generation : ConsumptionKind.Consumption;
+
+        // From the start of last year: enough for last-year totals and a rolling 12-month history.
+        var from = new DateTimeOffset(new DateTime(today.Year - 1, 1, 1, 0, 0, 0, DateTimeKind.Utc));
+
+        var months = (await db.Database.GetDbConnection()
+            .QueryAsync<MonthlyRow>(
+                MonthlySql,
+                new { tz = _options.TimeZone, meterId, kind = (short)kind, from })
+            .ConfigureAwait(false))
+            .ToDictionary(r => r.Month, r => r.Amount);
+
+        var costs = await LoadCostsAsync(meterId, from, cancellationToken).ConfigureAwait(false);
+
+        var thisMonth = new DateOnly(today.Year, today.Month, 1);
+        var lastMonth = thisMonth.AddMonths(-1);
+
+        var monthToDate = months.GetValueOrDefault(thisMonth);
+        var daysInMonth = DateTime.DaysInMonth(today.Year, today.Month);
+        var monthPartial = today.Day < daysInMonth;
+
+        var yearToDate = SumYear(months, today.Year);
+        var lastYear = SumYear(months, today.Year - 1);
+        var dayOfYear = today.DayOfYear;
+        var daysInYear = DateTime.IsLeapYear(today.Year) ? 366 : 365;
+
+        var yearToDateCost = SumYear(costs, today.Year);
+
+        return new MeterPeriodView(
+            Label: isGeneration ? "Generation" : "Consumption",
+            Unit: meter.Unit,
+            Currency: _options.Currency,
+            MonthToDate: monthToDate,
+            MonthProjected: Project(monthToDate, today.Day, daysInMonth),
+            LastMonth: months.GetValueOrDefault(lastMonth),
+            YearToDate: yearToDate,
+            YearProjected: Project(yearToDate, dayOfYear, daysInYear),
+            LastYear: lastYear,
+            YearToDateCost: yearToDateCost,
+            YearProjectedCost: Project(yearToDateCost, dayOfYear, daysInYear),
+            LastYearCost: SumYear(costs, today.Year - 1),
+            MonthIsPartial: monthPartial,
+            Last12Months: BuildHistory(months, costs, thisMonth));
+    }
+
+    /// <summary>
+    /// Scales a partial period to its full length. Straight-line on elapsed days: it assumes the
+    /// rest of the period looks like what came before, which is wrong for anything seasonal but is
+    /// the honest reading of "at this rate". The UI marks these as projections.
+    /// </summary>
+    private static double Project(double soFar, int elapsed, int total) =>
+        elapsed <= 0 ? soFar : soFar / elapsed * total;
+
+    private static double SumYear(Dictionary<DateOnly, double> byMonth, int year) =>
+        byMonth.Where(kv => kv.Key.Year == year).Sum(kv => kv.Value);
+
+    private static IReadOnlyList<MeterMonthPoint> BuildHistory(
+        Dictionary<DateOnly, double> months, Dictionary<DateOnly, double> costs, DateOnly thisMonth)
+    {
+        var history = new List<MeterMonthPoint>(12);
+        for (var offset = 11; offset >= 0; offset--)
+        {
+            var month = thisMonth.AddMonths(-offset);
+            history.Add(new MeterMonthPoint(month, months.GetValueOrDefault(month), costs.GetValueOrDefault(month)));
+        }
+
+        // All-zero history means the meter has no normalized data yet; say nothing rather than
+        // drawing a flat line that looks like a meter reading zero.
+        return history.All(p => Math.Abs(p.Amount) < 1e-9) ? [] : history;
+    }
+
+    private async Task<Dictionary<DateOnly, double>> LoadCostsAsync(
+        int meterId, DateTimeOffset from, CancellationToken cancellationToken)
+    {
+        var buckets = await _costs.GetMeterCostsAsync(
+            meterId, from, DateTimeOffset.UtcNow, Costing.CostBucket.Month, cancellationToken).ConfigureAwait(false);
+
+        return buckets
+            .GroupBy(b => new DateOnly(b.Period.Year, b.Period.Month, 1))
+            .ToDictionary(g => g.Key, g => g.Sum(b => b.Cost));
+    }
+
+    /// <summary>
+    /// Dapper row shape — it maps by column name, so a value tuple will not do, and Npgsql surfaces
+    /// a <c>date</c> column as <see cref="DateOnly"/>.
+    /// </summary>
+    private sealed record MonthlyRow(DateOnly Month, double Amount);
+
+    private TimeZoneInfo ResolveTimeZone()
+    {
+        try
+        {
+            return TimeZoneInfo.FindSystemTimeZoneById(_options.TimeZone);
+        }
+        catch (Exception ex) when (ex is TimeZoneNotFoundException or InvalidTimeZoneException)
+        {
+            return TimeZoneInfo.Utc;
+        }
+    }
+}

src/Infrastructure/DependencyInjection.cs

@@ -43,6 +43,7 @@ public static class DependencyInjection
         services.AddScoped<Costing.CostService>();
         services.AddScoped<Dashboard.DashboardService>();
         services.AddScoped<Dashboard.SolarService>();
+        services.AddScoped<Dashboard.MeterPeriodService>();
         services.AddScoped<Dashboard.ConsumableService>();
         services.AddScoped<Dashboard.MeterDetailService>();
         services.AddScoped<Dashboard.FlowService>();

tests/Integration.Tests/MeterPeriodServiceTests.cs

@@ -0,0 +1,124 @@
+using MeterVault.Core.Domain;
+using MeterVault.Infrastructure.Costing;
+using MeterVault.Infrastructure.Dashboard;
+using MeterVault.Infrastructure.Options;
+using MeterVault.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
+
+namespace MeterVault.Integration.Tests;
+
+/// <summary>
+/// The meter-detail headline numbers: month/year totals bucketed in the instance timezone, and the
+/// generation-vs-consumption split that decides which of the two a meter reports.
+/// </summary>
+[Collection("Timescale")]
+public sealed class MeterPeriodServiceTests(TimescaleFixture fx)
+{
+    [Fact]
+    public async Task Buckets_by_local_month_and_compares_with_the_previous_one()
+    {
+        await using var db = fx.CreateContext();
+        var meterId = await SetupAsync(db, MeterMode.CumulativeCounter);
+        var today = DateOnly.FromDateTime(DateTime.UtcNow);
+        var thisMonth = new DateOnly(today.Year, today.Month, 1);
+        var lastMonth = thisMonth.AddMonths(-1);
+
+        await AddConsumptionAsync(db, meterId, ConsumptionKind.Consumption, thisMonth.AddDays(1), 30);
+        await AddConsumptionAsync(db, meterId, ConsumptionKind.Consumption, lastMonth.AddDays(3), 100);
+
+        var view = await NewService().GetAsync(meterId);
+
+        Assert.NotNull(view);
+        Assert.Equal("Consumption", view!.Label);
+        Assert.Equal(30d, view.MonthToDate, 3);
+        Assert.Equal(100d, view.LastMonth, 3);
+        Assert.Equal(130d, view.YearToDate, 3);
+
+        // Projection scales the partial month up, so it must be at least what has already happened.
+        Assert.True(view.MonthProjected >= view.MonthToDate);
+
+        await CleanupAsync(db, meterId);
+    }
+
+    [Fact]
+    public async Task A_generation_counter_reports_generation_not_consumption()
+    {
+        // Regression: a PV meter showed "0 kWh consumption", which is true and useless.
+        await using var db = fx.CreateContext();
+        var meterId = await SetupAsync(db, MeterMode.GenerationCounter);
+        var today = DateOnly.FromDateTime(DateTime.UtcNow);
+
+        await AddConsumptionAsync(
+            db, meterId, ConsumptionKind.Generation, new DateOnly(today.Year, today.Month, 1).AddDays(1), 42);
+
+        var view = await NewService().GetAsync(meterId);
+
+        Assert.NotNull(view);
+        Assert.Equal("Generation", view!.Label);
+        Assert.Equal(42d, view.MonthToDate, 3);
+
+        await CleanupAsync(db, meterId);
+    }
+
+    [Fact]
+    public async Task A_meter_with_no_consumption_yields_an_empty_history_rather_than_a_flat_line()
+    {
+        await using var db = fx.CreateContext();
+        var meterId = await SetupAsync(db, MeterMode.CumulativeCounter);
+
+        var view = await NewService().GetAsync(meterId);
+
+        Assert.NotNull(view);
+        Assert.False(view!.HasHistory);
+        Assert.Empty(view.Last12Months);
+        Assert.Null(view.MonthChange); // no previous month to divide by
+
+        await CleanupAsync(db, meterId);
+    }
+
+    private MeterPeriodService NewService()
+    {
+        var options = Microsoft.Extensions.Options.Options.Create(
+            new MeterVaultOptions { TimeZone = "Europe/Berlin", Currency = "EUR" });
+        return new MeterPeriodService(fx, new CostService(fx), options);
+    }
+
+    private static async Task<int> SetupAsync(MeterVaultDbContext db, MeterMode mode)
+    {
+        await DatabaseSeeder.SeedAsync(db);
+        var type = await db.EnergyTypes.FirstAsync(t => t.Key == "electricity");
+
+        var meter = new Meter
+        {
+            Name = $"period-{Guid.NewGuid():N}",
+            EnergyTypeId = type.Id,
+            Mode = mode,
+            Unit = "kWh",
+        };
+        db.Meters.Add(meter);
+        await db.SaveChangesAsync();
+        return meter.Id;
+    }
+
+    private static async Task AddConsumptionAsync(
+        MeterVaultDbContext db, int meterId, ConsumptionKind kind, DateOnly day, double amount)
+    {
+        db.Consumption.Add(new Consumption
+        {
+            MeterId = meterId,
+            // Midday local, so the row cannot drift into an adjacent month through the UTC offset.
+            Time = new DateTimeOffset(day.Year, day.Month, day.Day, 12, 0, 0, TimeSpan.Zero),
+            Kind = kind,
+            Amount = amount,
+            Quality = ReadingQuality.Measured,
+        });
+        await db.SaveChangesAsync();
+    }
+
+    private static async Task CleanupAsync(MeterVaultDbContext db, int meterId)
+    {
+        await db.Consumption.Where(c => c.MeterId == meterId).ExecuteDeleteAsync();
+        await db.Meters.Where(m => m.Id == meterId).ExecuteDeleteAsync();
+    }
+}