import Foundation
import Combine
import BinaryCodable
import SwiftUI

final class TemperatureStorage: ObservableObject {

    static var documentDirectory: URL {
        try! FileManager.default.url(
        for: .documentDirectory,
        in: .userDomainMask,
        appropriateFor: nil, create: true)
    }

    @Published
    var recentMeasurements: [TemperatureMeasurement]
    
    @Published
    var dailyMeasurementCounts: [MeasurementDailyCount] = []
    
    private var unsavedMeasurements: [TemperatureMeasurement] = []
    
    private let fileNameFormatter: DateFormatter
    
    private let storageFolder: URL
    
    private let overviewFileUrl: URL
    
    private let fm: FileManager
    
    private let lastValueInterval: TimeInterval

    init(lastMeasurements: [TemperatureMeasurement] = [], lastValueInterval: TimeInterval = 3600) {
        self.recentMeasurements = lastMeasurements
        let documentDirectory = TemperatureStorage.documentDirectory
        self.storageFolder = documentDirectory.appendingPathComponent("measurements")
        self.overviewFileUrl = documentDirectory.appendingPathComponent("overview.bin")
        self.fm = .default
        self.fileNameFormatter = DateFormatter()
        self.fileNameFormatter.dateFormat = "yyyyMMdd.bin"
        self.lastValueInterval = lastValueInterval
        
        if lastMeasurements.isEmpty {
            loadLastMeasurements()
        } else {
            setDailyCounts(from: lastMeasurements)
        }
        
        ensureExistenceOfFolder()
    }
    
    private func ensureExistenceOfFolder() {
        guard !fm.fileExists(atPath: storageFolder.path) else {
            return
        }
        do {
            try fm.createDirectory(at: storageFolder, withIntermediateDirectories: true)
        } catch {
            print("Failed to create folder: \(error)")
        }
    }
    
    private func fileName(for date: Date) -> String {
        fileNameFormatter.string(from: date)
    }
    
    private func fileName(for index: Int) -> String {
        String(format: "%08d.bin", index)
    }
    
    private func fileUrl(for fileName: String) -> URL {
        storageFolder.appendingPathComponent(fileName)
    }
    
    private func loadLastMeasurements() {
        let startDate = Date().addingTimeInterval(-lastValueInterval)
        let todayIndex = Date().dateIndex
        let todayValues = loadMeasurements(for: todayIndex)
            .filter { $0.date >= startDate }
        let dateIndexOfStart = startDate.dateIndex
        guard todayIndex != dateIndexOfStart else {
            recentMeasurements = todayValues
            return
        }
        let yesterdayValues = loadMeasurements(for: dateIndexOfStart)
            .filter { $0.date >= startDate }
        recentMeasurements = yesterdayValues + todayValues
    }
    
    private func loadMeasurements(for date: Date) -> [TemperatureMeasurement] {
        loadMeasurements(from: fileName(for: date))
    }
    
    func loadMeasurements(for dateIndex: Int) -> [TemperatureMeasurement] {
        loadMeasurements(from: fileName(for: dateIndex))
    }
    
    private func loadMeasurements(from fileName: String) -> [TemperatureMeasurement] {
        let fileUrl = fileUrl(for: fileName)
        guard fm.fileExists(atPath: fileUrl.path) else {
            print("No measurements for \(fileName)")
            return []
        }
        do {
            let content = try Data(contentsOf: fileUrl)
            let points: [TemperatureMeasurement] = try BinaryDecoder.decode(from: content)
            print("Loaded \(points.count) points for \(fileName)")
            return points
        } catch {
            print("Failed to read file \(fileName): \(error)")
            return []
        }
    }
    
    func save() {
        for (dateIndex, values) in unsavedMeasurements.splitByDate() {
            let count = saveNew(values, for: dateIndex)
            print("Day \(dateIndex): \(count) of \(values.count) saved")
        }
        unsavedMeasurements = []
        saveDailyCounts()
    }
    
    /**
     - Returns: The number of new points
     */
    private func saveNew(_ measurements: [TemperatureMeasurement], for dateIndex: Int) -> Int {
        let fileName = fileName(for: dateIndex)
        var existing = loadMeasurements(from: fileName)
        guard !existing.isEmpty else {
            save(measurements, for: fileName)
            setDailyCount(measurements.count, for: dateIndex)
            return measurements.count
        }
        var inserted = 0
        for value in measurements {
            if existing.insert(value) {
                inserted += 1
            }
        }
        save(existing, for: fileName)
        setDailyCount(existing.count, for: dateIndex)
        return inserted
    }
    
    private func save(_ measurements: [TemperatureMeasurement], for fileName: String) {
        let fileUrl = fileUrl(for: fileName)
        do {
            let data = try BinaryEncoder.encode(measurements.sorted())
            try data.write(to: fileUrl)
        } catch {
            print("Failed to save \(fileName): \(error)")
        }
    }
    
    // MARK: Daily counts
    
    private func setDailyCount(_ count: Int, for dateIndex: Int) {
        guard let index = dailyMeasurementCounts.firstIndex(where: { $0.dateIndex == dateIndex }) else {
            add(dailyCount: count, for: dateIndex)
            return
        }
        dailyMeasurementCounts[index].count = count
    }
    
    private func add(dailyCount count: Int, for dateIndex: Int) {
        let entry = MeasurementDailyCount(dateIndex: dateIndex, count: count)
        guard let index = dailyMeasurementCounts.firstIndex(where: { $0.dateIndex < dateIndex }) else {
            dailyMeasurementCounts.append(entry)
            return
        }
        dailyMeasurementCounts.insert(entry, at: index)
    }
    
    private func incrementCount(for dateIndex: Int, by increment: Int = 1) {
        guard let index = dailyMeasurementCounts.firstIndex(where: { $0.dateIndex == dateIndex }) else {
            add(dailyCount: increment, for: dateIndex)
            return
        }
        dailyMeasurementCounts[index].count += increment
    }
    
    private func loadDailyCounts() {
        do {
            let data = try Data(contentsOf: overviewFileUrl)
            dailyMeasurementCounts = try BinaryDecoder.decode(from: data)
        } catch {
            print("Failed to load overview: \(error)")
        }
    }
    
    private func saveDailyCounts() {
        do {
            let data = try BinaryEncoder.encode(dailyMeasurementCounts)
            try data.write(to: overviewFileUrl)
        } catch {
            print("Failed to write overview: \(error)")
        }
    }
    
    private func setDailyCounts(from measurements: [TemperatureMeasurement]) {
        self.dailyMeasurementCounts = measurements.reduce(into: [Int: Int]()) { counts, value in
            let index = value.date.dateIndex
            counts[index] = (counts[index] ?? 0) + 1
        }.map { MeasurementDailyCount(dateIndex: $0.key, count: $0.value) }
            .sorted()
    }
    
    func recalculateDailyCounts() {
        do {
            let newValues: [Int: Int] = try fm.contentsOfDirectory(atPath: storageFolder.path)
                .reduce(into: [:]) { counts, fileName in
                    guard let dateIndex = Int(fileName) else {
                        return
                    }
                    counts[dateIndex] = loadMeasurements(from: fileName).count
                }
            DispatchQueue.main.async {
                self.dailyMeasurementCounts = newValues
                    .map { .init(dateIndex: $0.key, count: $0.value) }
                    .sorted()
            }
        } catch {
            print("Failed to load daily counts: \(error)")
        }
    }
    
}

extension TemperatureStorage: TemperatureDataTransferDelegate {
    
    func didReceiveRecording(_ measurement: TemperatureMeasurement) {
        // Add to unsaved measurements
        if unsavedMeasurements.insert(measurement) {
            incrementCount(for: measurement.date.dateIndex)
        }
        
        // Add to last measurements
        recentMeasurements.insert(measurement)
    }
    
    func saveAfterTransfer() {
        save()
    }
}

private extension Array where Element == TemperatureMeasurement {
    
    @discardableResult
    mutating func insert(_ measurement: TemperatureMeasurement) -> Bool {
        guard !contains(measurement) else {
            return false
        }
        guard let index = self.firstIndex(where: { $0.date > measurement.date }) else {
            append(measurement)
            return true
        }
        insert(measurement, at: index)
        return true
    }
    
    func splitByDate() -> [Int : [TemperatureMeasurement]] {
        reduce(into: [:]) { result, value in
            let dateIndex = value.date.dateIndex
            result[dateIndex] = (result[dateIndex] ?? []) + [value]
        }
    }
}

extension TemperatureStorage {
    
    static var mock: TemperatureStorage {
        .init(lastMeasurements: TemperatureMeasurement.mockData)
    }
}