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 saveImmediatelly = true

    private var writers: Set<String>

    private var caps = [Int: Cap]() {
        didSet {
            guard saveImmediatelly else {
                return
            }
            try? saveCaps()
        }
    }

    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 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 {
        saveImmediatelly = false
        caps = try caps.mapValues {
            var cap = $0
            cap.count = try count(of: $0.id)
            return cap
        }
        saveImmediatelly = true
        try? saveCaps()
    }

    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.
     - Returns: The new image count for 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 -> Int {
        guard var count = caps[cap]?.count 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)
        count += 1
        caps[cap]!.count = count
        log("Added image \(id) for cap \(cap)")
        return count
    }
    
    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)")
    }
}