//
//  AddFuelLogView.swift
//  Gas Man
//
//  Created by Kameron Kenny on 3/17/25.
//

import SwiftUI
import CoreData

struct AddFuelLogView: View {
    @Environment(\.managedObjectContext) private var viewContext
    @Environment(\.dismiss) var dismiss

    // Form fields
    @State private var date = Date()
    @State private var odometer = ""
    @State private var fuelVolume = ""
    @State private var cost = ""
    @State private var locationCoordinates = ""
    @State private var locationName = ""
    @State private var selectedOctane: Int = 87  // Default or from previous record
    @State private var pricePerGalon = ""
    
    // Allowed octane options
    let octaneOptions = [87, 89, 91, 92, 93, 95]
    
    // Location manager for automatic location updates
    @StateObject private var locationManager = LocationManager()
    
    // For tracking the previous odometer reading
    @State private var previousOdometer: Double? = nil
    @State private var showOdometerAlert = false
    
    // Flag to avoid update loops in our calculation logic
    @State private var isUpdatingCalculation = false
    
    // Computed property for formatted previous odometer value
    private var previousOdometerString: String {
        previousOdometer.map { String(format: "%.0f", $0) } ?? "N/A"
    }
    
    // Computed property for the odometer alert
    var odometerAlert: Alert {
        let messageString = "Odometer reading must be greater than the previous record (\(previousOdometerString))."
        return Alert(
            title: Text("Odometer Reading Error"),
            message: Text(messageString),
            dismissButton: .default(Text("OK"))
        )
    }
    
    var body: some View {
        NavigationView {
            Form {
                fuelLogDetailsSection
            }
            .navigationTitle("Add Fuel Log")
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    Button("Save") { saveFuelLog() }
                }
                ToolbarItem(placement: .navigationBarLeading) {
                    Button("Cancel") { dismiss() }
                }
            }
            .onChange(of: locationManager.location) { newLocation in
                if let loc = newLocation {
                    locationCoordinates = "\(loc.coordinate.latitude), \(loc.coordinate.longitude)"
                }
            }
            .onChange(of: locationManager.placemark) { newPlacemark in
                if let placemark = newPlacemark {
                    locationName = placemark.name ?? ""
                }
            }
            .onAppear(perform: loadPreviousData)
            .alert(isPresented: $showOdometerAlert) { odometerAlert }
        }
    }
    
    // MARK: - Subviews
    
    private var fuelLogDetailsSection: some View {
        Section(header: Text("Fuel Log Details")) {
            DatePicker("Date", selection: $date, displayedComponents: [.date, .hourAndMinute])
            
            // Odometer field
            HStack(spacing: 4) {
                Text("Odometer: ")
                    .font(.caption)
                    .foregroundColor(.secondary)
                TextField("", text: $odometer)
                    .keyboardType(.decimalPad)
                    .textFieldStyle(RoundedBorderTextFieldStyle())
            }
            
            // Fuel Volume field
            HStack(spacing: 4) {
                Text("Gallons: ")
                    .font(.caption)
                    .foregroundColor(.secondary)
                TextField("", text: $fuelVolume)
                    .keyboardType(.decimalPad)
                    .textFieldStyle(RoundedBorderTextFieldStyle())
                    .onChange(of: fuelVolume) { _ in updateCalculatedValues() }
            }
            
            // Price per Gallon field
            HStack(spacing: 4) {
                Text("Price/Gal: $")
                    .font(.caption)
                    .foregroundColor(.secondary)
                TextField("", text: $pricePerGalon)
                    .keyboardType(.decimalPad)
                    .textFieldStyle(RoundedBorderTextFieldStyle())
                    .onChange(of: pricePerGalon) { _ in updateCalculatedValues() }
            }
            
            // Cost field
            HStack(spacing: 4) {
                Text("Cost: $")
                    .font(.caption)
                    .foregroundColor(.secondary)
                TextField("", text: $cost)
                    .keyboardType(.decimalPad)
                    .textFieldStyle(RoundedBorderTextFieldStyle())
                    .onChange(of: cost) { _ in updateCalculatedValues() }
            }
            
            Button("Get Current Location") {
                locationManager.requestLocation()
            }
            
            if !locationCoordinates.isEmpty {
                Text("Coordinates: \(locationCoordinates)")
                    .font(.caption)
                    .foregroundColor(.secondary)
            }
            
            TextField("Location Coordinates", text: $locationCoordinates)
            
            HStack(spacing: 4) {
                Text("Location Name:")
                    .font(.caption)
                    .foregroundColor(.secondary)
                TextField("", text: $locationName)
            }
            
            Picker("Octane", selection: $selectedOctane) {
                ForEach(octaneOptions, id: \.self) { option in
                    Text("\(option)").tag(option)
                }
            }
            .pickerStyle(MenuPickerStyle())
        }
    }
    
    // MARK: - Helper Methods
    
    private func loadPreviousData() {
        let fetchRequest: NSFetchRequest<FuelLog> = FuelLog.fetchRequest()
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: false)]
        fetchRequest.fetchLimit = 1
        if let lastFuelLog = try? viewContext.fetch(fetchRequest).first {
            selectedOctane = Int(lastFuelLog.octane)
            previousOdometer = lastFuelLog.odometer
            odometer = String(format: "%.0f", lastFuelLog.odometer)
        } else {
            selectedOctane = 87
            odometer = ""
        }
    }
    
    private func roundToThree(_ value: Double) -> Double {
        return (value * 1000).rounded() / 1000
    }
    
    private func roundToTwo(_ value: Double) -> Double {
        return (value * 100).rounded() / 100
    }
    
    private func updateCalculatedValues() {
        // Prevent recursive updates.
        guard !isUpdatingCalculation else { return }
        isUpdatingCalculation = true
        
        let fuel = Double(fuelVolume)
        let costVal = Double(cost)
        let price = Double(pricePerGalon)
        
        // 1. If fuelVolume and pricePerGalon are provided, calculate cost.
        if let f = fuel, let p = price, f > 0 {
            let computedCost = roundToTwo(f * p)
            let computedCostStr = String(format: "%.2f", computedCost)
            if cost != computedCostStr {
                cost = computedCostStr
            }
        }
        // 2. If fuelVolume and cost are provided, and pricePerGalon is empty, calculate pricePerGalon.
        else if let f = fuel, let c = costVal, f > 0, pricePerGalon.trimmingCharacters(in: .whitespaces).isEmpty {
            let computedPrice = roundToThree(c / f)
            let computedPriceStr = String(format: "%.3f", computedPrice)
            if pricePerGalon != computedPriceStr {
                pricePerGalon = computedPriceStr
            }
        }
        // 3. If pricePerGalon and cost are provided, and fuelVolume is empty, calculate fuelVolume.
        else if let p = price, let c = costVal, p > 0, fuelVolume.trimmingCharacters(in: .whitespaces).isEmpty {
            let computedFuel = roundToThree(c / p)
            let computedFuelStr = String(format: "%.3f", computedFuel)
            if fuelVolume != computedFuelStr {
                fuelVolume = computedFuelStr
            }
        }
        
        isUpdatingCalculation = false
    }
    
    private func saveFuelLog() {
        guard let newOdometer = Double(odometer) else {
            return
        }
        // Validate that the new odometer reading is greater than the previous record
        if let previous = previousOdometer, newOdometer <= previous {
            showOdometerAlert = true
            return
        }
        
        let newLog = FuelLog(context: viewContext)
        newLog.id = UUID()
        newLog.date = date
        newLog.odometer = newOdometer
        newLog.fuelVolume = Double(fuelVolume) ?? 0
        newLog.cost = Double(cost) ?? 0
        newLog.locationCoordinates = locationCoordinates
        newLog.locationName = locationName
        newLog.octane = Int16(selectedOctane)
        newLog.pricePerGalon = Double(pricePerGalon) ?? 0
        
        do {
            try viewContext.save()
            dismiss()
        } catch {
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
    }
}