import Foundation
import Vapor

final class CapServer {
    
    // MARK: Paths
    
    private let imageFolder: URL

    /// The file where the database of caps is stored
    private let dbFile: URL
    
    private let fm = FileManager.default
    
    // MARK: Caps

    private var writers: Set<String>

    /**
     The time to wait for changes to be written to disk.

     This delay is used to prevent file writes for each small update to the caps.
     */
    private let saveDelay: TimeInterval = 1

    /**
     The time when a save should occur.

     No save is necessary if this property is `nil`.
     */
    private var nextSaveTime: Date?

    private var caps = [Int: Cap]() {
        didSet { scheduleSave() }
    }

    var nextClassifierVersion: Int {
        caps.values.compactMap { $0.classifierVersion }.max() ?? 1
    }
    
    init(in folder: URL, writers: [String]) throws {
        self.imageFolder = folder.appendingPathComponent("images")
        self.dbFile = folder.appendingPathComponent("caps.json")
        self.writers = Set(writers)
        
        var isDirectory: ObjCBool = false
        guard fm.fileExists(atPath: folder.path, isDirectory: &isDirectory),
              isDirectory.boolValue else {
            log("Public directory \(folder.path) is not a folder, or doesn't exist")
            throw CapError.invalidConfiguration
        }

        try loadCaps()
        try updateCounts()
    }

    private func loadCaps() throws {
        let data = try Data(contentsOf: dbFile)
        caps = try JSONDecoder().decode([Cap].self, from: data)
            .reduce(into: [:]) { $0[$1.id] = $1 }
        log("\(caps.count) caps loaded")
    }

    private func scheduleSave() {
        nextSaveTime = Date().addingTimeInterval(saveDelay)
        DispatchQueue.main.asyncAfter(deadline: .now() + saveDelay) {
            self.performScheduledSave()
        }
    }

    private func performScheduledSave() {
        guard let date = nextSaveTime else {
            // No save necessary, or already saved
            return
        }
        guard date < Date() else {
            // Save pushed to future
            return
        }
        do {
            try saveCaps()
            nextSaveTime = nil
        } catch {
            // Attempt save again
            scheduleSave()
        }
    }

    private func saveCaps() throws {
        let data = try JSONEncoder().encode(caps.values.sorted())
        try data.write(to: dbFile)
    }

    // MARK: Paths

    func folder(of cap: Int) -> URL {
        imageFolder.appendingPathComponent(String(format: "%04d", cap))
    }

    func file(of cap: Int, version: Int) -> URL {
        folder(of: cap).appendingPathComponent(String(format: "%04d-%02d.jpg", cap, version))
    }

    // MARK: Authentication

    func hasAuthorization(for key: String) -> Bool {
        // Note: This is not a constant-time compare, so there may be an opportunity
        // for timing attack here. Sets perform hashed lookups, so this may be less of an issue,
        // and we're not doing anything critical in this application.
        // Worst case, an unauthorized person with a lot of free time and energy to hack this system
        // is able to change contents of the database, which are backed up in any case.
        writers.contains(key)
    }
    
    // MARK: Counts

    private func updateCounts() throws {
        caps = try caps.mapValues {
            var cap = $0
            cap.count = try count(of: $0.id)
            return cap
        }
    }

    func countImages(in folder: URL) throws -> Int {
        try fm.contentsOfDirectory(at: folder, includingPropertiesForKeys: nil)
            .filter({ $0.pathExtension == "jpg" }).count
    }

    /**
     Get the image count of a cap.
     */
    func count(of cap: Int) throws -> Int {
        let f = folder(of: cap)
        guard fm.fileExists(atPath: f.path) else {
            return 0
        }
        return try countImages(in: f)
    }
    
    // MARK: Names

    func set(name: String, for capId: Int) throws {
        guard var cap = caps[capId] else {
            let url = server.folder(of: capId)
            if !fm.fileExists(atPath: url.path) {
                try fm.createDirectory(at: url, withIntermediateDirectories: false)
            }
            caps[capId] = Cap(id: capId, name: name, count: 0, mainImage: 0, classifierVersion: nextClassifierVersion)
            log("Added cap \(capId)")
            return
        }
        cap.name = name
        caps[capId] = cap
        log("Set name for cap \(capId)")
    }

    // MARK: Images
    
    /**
     Save a cap image to disk.
     
     Automatically creates the image name with the current image count.
     - Parameter data: The image data
     - Parameter cap: The id of the cap.
     - Throws: `CapError.unknownId`, if the cap doesn't exist. `CapError.dataInconsistency` if an image already exists for the current count.
     */
    func save(image data: Data, for cap: Int) throws {
        guard caps[cap] != nil else {
            throw CapError.unknownId
        }
        var id = 0
        var f = file(of: cap, version: id)
        while fm.fileExists(atPath: f.path) {
            id += 1
            f = file(of: cap, version: id)
        }
        try data.write(to: f)
        caps[cap]!.count += 1
        log("Added image \(id) for cap \(cap)")
    }
    
    func switchMainImage(to version: Int, for cap: Int) throws {
        let file2 = file(of: cap, version: version)
        guard fm.fileExists(atPath: file2.path) else {
            log("No image \(version) for cap \(cap)")
            throw CapError.invalidFile
        }
        caps[cap]?.mainImage = version
        log("Switched cap \(cap) to version \(version)")
    }

    func addOrUpdate(_ cap: Cap) throws {
        if let existingCap = caps[cap.id] {
            try update(existingCap, with: cap)
        } else {
            try add(cap)
        }
    }

    private func add(_ cap: Cap) throws {
        guard cap.mainImage == 0, cap.count == 0 else {
            throw CapError.invalidData
        }
        caps[cap.id] = cap
        log("Added cap \(cap.id) '\(cap.name)'")
    }

    private func update(_ existingCap: Cap, with cap: Cap) throws {
        var updatedCap = existingCap
        if cap.name != "" {
            updatedCap.name = cap.name
        }
        let url = file(of: existingCap.id, version: cap.mainImage)
        if fm.fileExists(atPath: url.path) {
            updatedCap.mainImage = cap.mainImage
        }
        if let color = cap.color {
            updatedCap.color = color
        }
        caps[existingCap.id] = updatedCap
        log("Updated cap \(existingCap.id)")
    }
}