add trend for avg mpg

Gas Man/Stats/MPGTrendChartView.swift

@@ -0,0 +1,63 @@
+//
+//  MPGTrendChartView.swift
+//  Gas Man
+//
+//  Created by Kameron Kenny on 3/19/25.
+//
+
+import SwiftUI
+import Charts
+import CoreData
+
+struct MPGTrendChartView: View {
+    let fuelLogs: [FuelLog]
+    
+    // Compute trend data by sorting logs by date ascending
+    // and calculating MPG for each interval where fullTank is true.
+    var trendData: [(date: Date, mpg: Double)] {
+        let sortedLogs = fuelLogs.sorted { ($0.date ?? Date()) < ($1.date ?? Date()) }
+        var data: [(Date, Double)] = []
+        // Start from index 1 because we need a previous log to compute the difference.
+        for i in 1..<sortedLogs.count {
+            let previous = sortedLogs[i - 1]
+            let current = sortedLogs[i]
+            if current.fullTank, let date = current.date,
+               current.odometer > previous.odometer,
+               current.fuelVolume > 0 {
+                let mpg = (current.odometer - previous.odometer) / current.fuelVolume
+                data.append((date, mpg))
+            }
+        }
+        return data
+    }
+    
+    var body: some View {
+        VStack {
+            if trendData.isEmpty {
+                Text("No MPG trend data available.")
+                    .foregroundColor(.secondary)
+            } else {
+                Chart {
+                    ForEach(trendData, id: \.date) { point in
+                        LineMark(
+                            x: .value("Date", point.date),
+                            y: .value("MPG", point.mpg)
+                        )
+                        PointMark(
+                            x: .value("Date", point.date),
+                            y: .value("MPG", point.mpg)
+                        )
+                    }
+                }
+                .chartXAxis {
+                    AxisMarks(values: .automatic(desiredCount: 4))
+                }
+                .chartYAxis {
+                    AxisMarks(values: .automatic(desiredCount: 5))
+                }
+            }
+        }
+        .padding()
+        .navigationTitle("MPG Trend")
+    }
+}

Gas Man/Stats/StatsView.swift

@@ -5,7 +5,6 @@
 //  Created by Kameron Kenny on 3/19/25.
 //
 
-
 import SwiftUI
 import CoreData
 
@@ -18,7 +17,7 @@ struct StatsView: View {
         animation: .default)
     private var fuelLogs: FetchedResults<FuelLog>
     
-    // Fetch all vehicles sorted by make (or any preferred order)
+    // Fetch all vehicles sorted by make
     @FetchRequest(
         sortDescriptors: [NSSortDescriptor(keyPath: \Vehicle.make, ascending: true)],
         animation: .default)
@@ -60,7 +59,7 @@ struct StatsView: View {
         return sum / Double(mpgValues.count)
     }
     
-    // Price per gallon stats: lowest, highest, average.
+    // Price per gallon stats.
     private var pricePerGallonStats: (min: Double?, max: Double?, avg: Double?) {
         let prices = filteredFuelLogs.map { $0.pricePerGalon }
         guard !prices.isEmpty else { return (nil, nil, nil) }
@@ -70,7 +69,7 @@ struct StatsView: View {
         return (minPrice, maxPrice, avgPrice)
     }
     
-    // Distance between fill-ups stats: lowest, highest, average.
+    // Distance between fill-ups stats.
     private var distanceStats: (min: Double?, max: Double?, avg: Double?) {
         let logs = filteredFuelLogs
         guard logs.count > 1 else { return (nil, nil, nil) }
@@ -103,7 +102,7 @@ struct StatsView: View {
     var body: some View {
         NavigationView {
             Form {
-                // Vehicle Selector
+                // Vehicle Selector Section
                 Section(header: Text("Select Vehicle")) {
                     Picker("Vehicle", selection: $selectedVehicleID) {
                         ForEach(vehicles, id: \.id) { vehicle in
@@ -114,20 +113,36 @@ struct StatsView: View {
                     .pickerStyle(MenuPickerStyle())
                 }
                 
-                // Stats for Fuel Logs
-                Section(header: Text("Fill-Up Count")) {
-                    Text("\(fillUpCount)")
-                }
-                
-                Section(header: Text("Average MPG")) {
-                    if let avgMPG = averageMPG {
-                        Text("\(avgMPG, specifier: "%.1f") MPG")
-                    } else {
-                        Text("N/A")
-                            .foregroundColor(.secondary)
+                // Fill-Up Count Section
+                Section {
+                    HStack {
+                        Text("Fill-Up Count:")
+                        Spacer()
+                        Text("\(fillUpCount)")
+                            .bold()
                     }
                 }
                 
+                // Average MPG Section with NavigationLink to chart.
+                Section {
+                    NavigationLink(destination: MPGTrendChartView(fuelLogs: filteredFuelLogs)) {
+                        HStack {
+                            Text("Average MPG:")
+                            Spacer()
+                            if let avgMPG = averageMPG {
+                                Text("\(avgMPG, specifier: "%.1f") MPG")
+                                    .bold()
+                            } else {
+                                Text("N/A")
+                                    .foregroundColor(.secondary)
+                            }
+                            Image(systemName: "chart.bar.fill")
+                                .foregroundColor(.blue)
+                        }
+                    }
+                }
+                
+                // Price per Gallon Stats
                 Section(header: Text("Price per Gallon")) {
                     let stats = pricePerGallonStats
                     HStack {
@@ -191,6 +206,7 @@ struct StatsView: View {
                     }
                 }
                 
+                // Gallons per Fill-Up Stats
                 Section(header: Text("Gallons per Fill-Up")) {
                     let gStats = gallonsStats
                     HStack {