//
//  StatsView.swift
//  Gas Man
//
//  Created by Kameron Kenny on 3/19/25.
//


import SwiftUI
import CoreData

struct StatsView: View {
    @Environment(\.managedObjectContext) private var viewContext
    
    // Fetch all fuel logs sorted by date (descending)
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \FuelLog.date, ascending: false)],
        animation: .default)
    private var fuelLogs: FetchedResults<FuelLog>
    
    // Fetch all vehicles sorted by make (or any preferred order)
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Vehicle.make, ascending: true)],
        animation: .default)
    private var vehicles: FetchedResults<Vehicle>
    
    @State private var selectedVehicleID: UUID? = nil
    
    // Filter fuel logs by the selected vehicle.
    private var filteredFuelLogs: [FuelLog] {
        if let vehicleID = selectedVehicleID {
            return fuelLogs.filter { log in
                log.vehicle?.id == vehicleID
            }
        } else {
            return Array(fuelLogs)
        }
    }
    
    // Total number of fill-ups.
    private var fillUpCount: Int {
        filteredFuelLogs.count
    }
    
    // Average MPG computed only for full-tank logs.
    private var averageMPG: Double? {
        let logs = filteredFuelLogs
        guard logs.count > 1 else { return nil }
        var mpgValues: [Double] = []
        for i in 0..<logs.count - 1 {
            let current = logs[i]
            let next = logs[i + 1]
            if current.fullTank, current.fuelVolume > 0, current.odometer > next.odometer {
                let mpg = (current.odometer - next.odometer) / current.fuelVolume
                mpgValues.append(mpg)
            }
        }
        guard !mpgValues.isEmpty else { return nil }
        let sum = mpgValues.reduce(0, +)
        return sum / Double(mpgValues.count)
    }
    
    // Price per gallon stats: lowest, highest, average.
    private var pricePerGallonStats: (min: Double?, max: Double?, avg: Double?) {
        let prices = filteredFuelLogs.map { $0.pricePerGalon }
        guard !prices.isEmpty else { return (nil, nil, nil) }
        let minPrice = prices.min()
        let maxPrice = prices.max()
        let avgPrice = prices.reduce(0, +) / Double(prices.count)
        return (minPrice, maxPrice, avgPrice)
    }
    
    // Distance between fill-ups stats: lowest, highest, average.
    private var distanceStats: (min: Double?, max: Double?, avg: Double?) {
        let logs = filteredFuelLogs
        guard logs.count > 1 else { return (nil, nil, nil) }
        var distances: [Double] = []
        for i in 0..<logs.count - 1 {
            let current = logs[i]
            let next = logs[i + 1]
            let dist = current.odometer - next.odometer
            if dist > 0 {
                distances.append(dist)
            }
        }
        guard !distances.isEmpty else { return (nil, nil, nil) }
        let minDistance = distances.min()!
        let maxDistance = distances.max()!
        let avgDistance = distances.reduce(0, +) / Double(distances.count)
        return (minDistance, maxDistance, avgDistance)
    }
    
    // Gallons per fill-up stats.
    private var gallonsStats: (min: Double?, max: Double?, avg: Double?) {
        let gallons = filteredFuelLogs.map { $0.fuelVolume }
        guard !gallons.isEmpty else { return (nil, nil, nil) }
        let minGallons = gallons.min()
        let maxGallons = gallons.max()
        let avgGallons = gallons.reduce(0, +) / Double(gallons.count)
        return (minGallons, maxGallons, avgGallons)
    }
    
    var body: some View {
        NavigationView {
            Form {
                // Vehicle Selector
                Section(header: Text("Select Vehicle")) {
                    Picker("Vehicle", selection: $selectedVehicleID) {
                        ForEach(vehicles, id: \.id) { vehicle in
                            Text("\(vehicle.year ?? "") \(vehicle.make ?? "") \(vehicle.model ?? "")")
                                .tag(vehicle.id)
                        }
                    }
                    .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)
                    }
                }
                
                Section(header: Text("Price per Gallon")) {
                    let stats = pricePerGallonStats
                    HStack {
                        Text("Lowest:")
                        Spacer()
                        if let minPrice = stats.min {
                            Text("$\(minPrice, specifier: "%.3f")")
                        } else {
                            Text("N/A")
                        }
                    }
                    HStack {
                        Text("Highest:")
                        Spacer()
                        if let maxPrice = stats.max {
                            Text("$\(maxPrice, specifier: "%.3f")")
                        } else {
                            Text("N/A")
                        }
                    }
                    HStack {
                        Text("Average:")
                        Spacer()
                        if let avgPrice = stats.avg {
                            Text("$\(avgPrice, specifier: "%.3f")")
                        } else {
                            Text("N/A")
                        }
                    }
                }
                
                // Distance Between Fill-Ups Stats
                Section(header: Text("Distance Between Fill-Ups")) {
                    let dStats = distanceStats
                    HStack {
                        Text("Lowest:")
                        Spacer()
                        if let minDistance = dStats.min {
                            Text("\(minDistance, specifier: "%.0f") miles")
                        } else {
                            Text("N/A")
                        }
                    }
                    HStack {
                        Text("Highest:")
                        Spacer()
                        if let maxDistance = dStats.max {
                            Text("\(maxDistance, specifier: "%.0f") miles")
                        } else {
                            Text("N/A")
                        }
                    }
                    HStack {
                        Text("Average:")
                        Spacer()
                        if let avgDistance = dStats.avg {
                            Text("\(avgDistance, specifier: "%.0f") miles")
                        } else {
                            Text("N/A")
                        }
                    }
                }
                
                Section(header: Text("Gallons per Fill-Up")) {
                    let gStats = gallonsStats
                    HStack {
                        Text("Lowest:")
                        Spacer()
                        if let minGallons = gStats.min {
                            Text("\(minGallons, specifier: "%.3f") gallons")
                        } else {
                            Text("N/A")
                        }
                    }
                    HStack {
                        Text("Highest:")
                        Spacer()
                        if let maxGallons = gStats.max {
                            Text("\(maxGallons, specifier: "%.3f") gallons")
                        } else {
                            Text("N/A")
                        }
                    }
                    HStack {
                        Text("Average:")
                        Spacer()
                        if let avgGallons = gStats.avg {
                            Text("\(avgGallons, specifier: "%.3f") gallons")
                        } else {
                            Text("N/A")
                        }
                    }
                }
            }
            .navigationTitle("Stats")
        }
        .onAppear {
            if selectedVehicleID == nil {
                selectedVehicleID = vehicles.first?.id
            }
        }
    }
}