Refine trends and debug harness; clean up warnings

FuelBoard/TrendsView.swift

@@ -13,6 +13,8 @@ struct TrendsView: View {
     /// All favourites (fuel-scoped entries) — the sheet derives the active
     /// fuel's stations and which fuels have favourites.
     let favourites: [FavouriteEntry]
+    /// The fuel the Favourites tab is showing when the Trends button is
+    /// tapped — the sheet must open on the same fuel, not always .e10.
     let selectedFuel: FuelType
     let priceDisplayStyle: PriceDisplayStyle
 
@@ -32,6 +34,21 @@ struct TrendsView: View {
     @State private var loadFailed = false
     @State private var firstSnapshot: String?
 
+    /// Seeded from `selectedFuel` (the fuel the tab was on) so the sheet
+    /// opens where the user was — same pattern as FavouritesView.
+    init(favourites: [FavouriteEntry],
+         selectedFuel: FuelType,
+         priceDisplayStyle: PriceDisplayStyle,
+         onHistoryUnavailable: (() -> Void)? = nil,
+         onHistoryRecovered: (() -> Void)? = nil) {
+        self.favourites = favourites
+        self.selectedFuel = selectedFuel
+        self.priceDisplayStyle = priceDisplayStyle
+        self.onHistoryUnavailable = onHistoryUnavailable
+        self.onHistoryRecovered = onHistoryRecovered
+        _fuel = State(initialValue: selectedFuel)
+    }
+
     enum TrendsMode: String, CaseIterable, Identifiable {
         case price
         case vsCheapest
@@ -85,7 +102,34 @@ struct TrendsView: View {
         }
     }
 
+    /// Y-domain hugging the displayed data (RevenueCat-style tight scale).
+    /// Without it Swift Charts pads a sparse series (e.g. 3 days of ~150.7p)
+    /// out to a 0→200 axis, wasting the plot area. Pad by ~4% of the range
+    /// (min 0.5p) so the line doesn't kiss the top edge.
+    private var yDomain: ClosedRange<Double> {
+        let values = displaySeries.flatMap { $0.points.map(\.pence) }
+        guard let lo = values.min(), let hi = values.max() else {
+            return 0...1
+        }
+        let pad = max((hi - lo) * 0.04, 0.5)
+        return (lo - pad)...(hi + pad)
+    }
+
+    /// Depth of each series' gradient fill band, in pence. Band instead of
+    /// fill-to-axis: with 2+ favourites, full-height unstacked fills overlap
+    /// and wash out the lower lines (observed on device 2026-08-17). A band
+    /// of ~18% of the y-range under each line keeps every area visible and
+    /// gives the RevenueCat "fade under the line" look.
+    private var fillBand: Double {
+        let values = displaySeries.flatMap { $0.points.map(\.pence) }
+        guard let lo = values.min(), let hi = values.max(), hi > lo else {
+            return 1.0
+        }
+        return max((hi - lo) * 0.18, 0.8)
+    }
+
     private func load() async {
+#if DEBUG
         // QA hook: force the unreachable state for screenshots (same pattern
         // as -showTrends / -forceConnectionProblem). Runs before the fetch so
         // the retry state renders immediately with no spinner flash.
@@ -95,6 +139,7 @@ struct TrendsView: View {
             onHistoryUnavailable?()
             return
         }
+#endif
         isLoading = true
         loadFailed = false
         defer { isLoading = false }
@@ -132,6 +177,38 @@ struct TrendsView: View {
         }
     }
 
+    // MARK: - RevenueCat-style headline metric
+
+    /// Overall average across displayed series (mean of per-station means) —
+    /// the big figure in the card header, Price and vs-cheapest mode both.
+    private var headlineAverage: Double? {
+        let avgs = displaySeries.compactMap { FuelHistoryStore.averagePence($0.points) }
+        guard !avgs.isEmpty else { return nil }
+        return avgs.reduce(0, +) / Double(avgs.count)
+    }
+
+    /// Change over the window: mean of each series' (last − first) point.
+    /// Positive = prices/gaps rose; negative = fell. Hidden while loading or
+    /// when any displayed series lacks two points.
+    private var headlineDelta: Double? {
+        let deltas = displaySeries.compactMap { history -> Double? in
+            guard let first = history.points.first?.pence,
+                  let last = history.points.last?.pence else { return nil }
+            return last - first
+        }
+        guard deltas.count == displaySeries.count else { return nil }
+        return deltas.reduce(0, +) / Double(deltas.count)
+    }
+
+    /// Good = prices fell (saving money) or the gap to cheapest narrowed.
+    private var deltaIsGood: Bool {
+        (headlineDelta ?? 0) <= 0
+    }
+
+    private var periodLabel: String {
+        "Last \(rangeDays) days"
+    }
+
     var body: some View {
         NavigationStack {
             VStack(spacing: 14) {
@@ -195,11 +272,7 @@ struct TrendsView: View {
             } else if !hasEnoughData {
                 emptyState // single point — nothing to draw yet
             } else {
-                VStack(spacing: 12) {
-                    chart
-                    legend
-                    legendFooter
-                }
+                revenueCatCard
             }
         }
         .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .top)
@@ -228,21 +301,103 @@ struct TrendsView: View {
         .padding(.vertical, 24)
     }
 
+    /// RevenueCat-style card: rounded surface with a headline metric (period
+    /// average + change), the multi-series area chart, then the key. Mirrors
+    /// the mockup approved after the dashboard reference screenshot.
+    private var revenueCatCard: some View {
+        VStack(alignment: .leading, spacing: 10) {
+            metricHeader
+            metricFooter
+            chart
+            legend
+            legendFooter
+        }
+        .padding(16)
+        .background(
+            RoundedRectangle(cornerRadius: 16, style: .continuous)
+                .fill(Color(.secondarySystemGroupedBackground))
+        )
+    }
+
+    /// Headline row: big average figure, signed change, right-aligned period.
+    /// Colours stay on the app palette — green when the move is good
+    /// (prices fell / gap narrowed), the accent tint when it rose.
+    @ViewBuilder
+    private var metricHeader: some View {
+        HStack(alignment: .firstTextBaseline, spacing: 8) {
+            if let headAvg = headlineAverage {
+                Text(yLabel(headAvg))
+                    .font(.system(size: 30, weight: .bold, design: .default))
+                    .monospacedDigit()
+                    .foregroundStyle(.primary)
+                if let delta = headlineDelta, delta != 0 {
+                    Label(
+                        "\(deltaIsGood ? "−" : "+")\(abs(delta), specifier: "%.1f")p",
+                        systemImage: deltaIsGood ? "arrow.down.right" : "arrow.up.right"
+                    )
+                    .font(.system(size: 13, weight: .semibold))
+                    .labelStyle(.titleAndIcon)
+                    .foregroundStyle(deltaIsGood ? Color(red: 48/255.0, green: 209/255.0, blue: 88/255.0) : Color.accentColor)
+                }
+            }
+            Spacer()
+            Text(periodLabel)
+                .font(.footnote)
+                .foregroundStyle(.secondary)
+        }
+    }
+
+    /// One-line descriptor under the headline so the big figure (period
+    /// average across favourites) and the arrowed delta (change over the
+    /// window) are self-explanatory.
+    private var metricFooter: some View {
+        Text(chartFooterText)
+            .font(.caption2)
+            .foregroundStyle(.secondary)
+    }
+
+    private var chartFooterText: String {
+        switch mode {
+        case .price:
+            return "Average across favourites · change since the first day"
+        case .vsCheapest:
+            return "Average gap above the day's cheapest · change since the first day"
+        }
+    }
+
     private var chart: some View {
         // NOTE: each LineMark MUST carry an explicit `series:` — without it
         // Swift Charts merges every station's points into ONE polyline
         // (points connect across stations, so only the first station's line
         // is recognisable). The outer ForEach keeps one chart with N series;
         // per-mark foregroundStyle then colours each series from the palette.
+        // The AreaMark under each LineMark adds the gradient fill.
+        //
+        // stacking: .unstacked is essential — the standard stacking mode
+        // piles each series' area ON TOP of the previous series' area, so
+        // with 2+ favourites the fills land in the wrong place (seen on
+        // device 2026-08-17: fills shifted/overlapping vs the lines).
+        // .unstacked draws each area from its own line down to the axis,
+        // the RevenueCat look.
+        // Two passes: ALL AreaMarks first, then ALL LineMarks. Same-series
+        // marks composite in insertion order — if fills and lines interleave,
+        // a later series' fill paints OVER an earlier series' line (the
+        // bottom favourite's line vanished under the next fill; seen on
+        // device 2026-08-17). Drawing every fill before every line keeps all
+        // lines on top of all fills, RevenueCat style. (Mark builders are
+        // extracted into small helpers — the inline expression grew past the
+        // type-checker's budget.)
         Chart {
             ForEach(displaySeries) { history in
                 ForEach(history.points) { point in
-                    LineMark(
-                        x: .value("Date", point.date),
-                        y: .value("Price", point.pence),
-                        series: .value("Station", history.name)
-                    )
-                    .foregroundStyle(seriesColor(index(of: history.stationID)))
+                    areaMark(point, series: history.name,
+                             color: seriesColor(index(of: history.stationID)))
+                }
+            }
+            ForEach(displaySeries) { history in
+                ForEach(history.points) { point in
+                    lineMark(point, series: history.name,
+                             color: seriesColor(index(of: history.stationID)))
                 }
             }
         }
@@ -251,31 +406,83 @@ struct TrendsView: View {
                 AxisGridLine()
                 AxisTick()
                 AxisValueLabel(format: .dateTime.month().day())
+                    .font(.caption2)
+                    .foregroundStyle(.secondary)
             }
         }
+        .chartYScale(domain: yDomain)
         .chartYAxis {
             AxisMarks { value in
                 AxisGridLine()
                 AxisValueLabel {
                     if let pence = value.as(Double.self) {
                         Text(yLabel(pence))
+                            .font(.caption2)
+                            .foregroundStyle(.secondary)
                     }
                 }
             }
         }
-        .frame(height: 260)
+        .frame(height: 190)
+    }
+
+    /// One gradient-filled area band under a single point of a series.
+    /// yStart/yEnd bound the fill to `fillBand` pence under the line
+    /// instead of to the axis: full-height fills overlap and bury lower
+    /// lines when several favourites overlap (observed on device
+    /// 2026-08-17).
+    private func areaMark(_ point: PricePoint, series: String,
+                          color: Color) -> some ChartContent {
+        AreaMark(
+            x: .value("Date", point.date),
+            yStart: .value("Price start", point.pence),
+            yEnd: .value("Price end", point.pence - fillBand),
+            series: .value("Station", series)
+        )
+        .foregroundStyle(
+            LinearGradient(
+                colors: [color.opacity(0.30), color.opacity(0.02)],
+                startPoint: .top,
+                endPoint: .bottom
+            )
+        )
+        .interpolationMethod(.monotone)
+    }
+
+    /// One line segment point for a series, drawn above every fill.
+    private func lineMark(_ point: PricePoint, series: String,
+                          color: Color) -> some ChartContent {
+        LineMark(
+            x: .value("Date", point.date),
+            y: .value("Price", point.pence),
+            series: .value("Station", series)
+        )
+        .foregroundStyle(color)
+        .lineStyle(StrokeStyle(lineWidth: 2.5, lineCap: .round, lineJoin: .round))
+        .interpolationMethod(.monotone)
     }
 
     private func index(of stationID: String) -> Int {
         orderedStations.firstIndex(where: { $0.id == stationID }) ?? 0
     }
 
+    /// Key rows in the same vertical order as the chart: most expensive at the
+    /// top working down to cheapest at the bottom (the chart's y-axis puts
+    /// the cheapest line lowest). Sorts by average price — the bracketed
+    /// figure — descending, so the first key row matches the top line.
+    private var legendSeries: [StationHistory] {
+        displaySeries.sorted {
+            (FuelHistoryStore.averagePence($0.points) ?? 0)
+                > (FuelHistoryStore.averagePence($1.points) ?? 0)
+        }
+    }
+
     private var legend: some View {
         VStack(alignment: .leading, spacing: 4) {
-            ForEach(Array(displaySeries.enumerated()), id: \.element.stationID) { index, history in
+            ForEach(legendSeries, id: \.stationID) { history in
                 HStack(spacing: 8) {
                     Circle()
-                        .fill(seriesColor(index))
+                        .fill(seriesColor(index(of: history.stationID)))
                         .frame(width: 8, height: 8)
                     Text(history.name)
                         .font(.caption)