import Foundation
import Cocoa
import CreateML

struct Configuration: Codable {
    
    let imageDirectory: String
    
    let classifierModelPath: String

    let trainingIterations: Int
    
    let serverPath: String
    
    let authenticationToken: String
    
    init?(at url: URL) {
        do {
            let configData = try Data(contentsOf: url)
            self = try JSONDecoder().decode(Configuration.self, from: configData)
        } catch {
            print("[ERROR] Failed to load configuration at \(url.absoluteURL.path): \(error)")
            return nil
        }
    }
}

struct Cap: Codable {

    let id: Int

    let count: Int

    enum CodingKeys: String, CodingKey {
        case id = "i"
        case count = "c"
    }
}

final class ClassifierCreator {
    
    static let configurationFileUrl = URL(fileURLWithPath: "config.json")
    
    let server: URL
    
    let configuration: Configuration
    
    let imageDirectory: URL
    
    let classifierUrl: URL
    
    let df = DateFormatter()
    
    
    // MARK: Step 1: Load configuration
    
    init?() {
        guard let configuration = Configuration(at: ClassifierCreator.configurationFileUrl) else {
            return nil
        }
        self.configuration = configuration
        guard let serverUrl = URL(string: configuration.serverPath) else {
            print("[ERROR] Configuration: Invalid server path \(configuration.serverPath)")
            return nil
        }
        self.server = serverUrl
        self.imageDirectory = URL(fileURLWithPath: configuration.imageDirectory)
        self.classifierUrl = URL(fileURLWithPath: configuration.classifierModelPath)
        df.dateFormat = "yy-MM-dd-HH-mm-ss"
    }
    
    // MARK: Main function
    
    func run() async {
        let imagesSnapshotDate = Date()
        guard let (classes, changedImageCount) = await loadImages() else {
            return
        }

        guard !classes.isEmpty else {
            return
        }
        
        guard changedImageCount > 0 else {
            print("[INFO] No changed images, so no new classifier trained")
            return
        }

        guard let classifierVersion = await getClassifierVersion() else {
            return
        }
        let newVersion = classifierVersion + 1

        print("[INFO] Image directory: \(imageDirectory.absoluteURL.path)")
        print("[INFO] Model path: \(configuration.classifierModelPath)")
        print("[INFO] Version: \(newVersion)")
        print("[INFO] Classes: \(classes.count)")
        print("[INFO] Iterations: \(configuration.trainingIterations)")

        guard trainModel() else {
            return
        }

        guard await upload(version: newVersion) else {
            return
        }

        guard await upload(classes: classes, lastUpdate: imagesSnapshotDate) else {
            return
        }

        print("[INFO] Done")
    }
    
    // MARK: Step 2: Load changed images
    
    func loadImages() async -> (classes: [Int], changedImages: Int)? {
        guard createImageFolderIfMissing() else {
            return nil
        }
        let imageCounts = await getImageCounts()
        let missingImageList: [(cap: Int, image: Int)] = imageCounts
            .sorted { $0.key < $1.key }
            .reduce(into: []) { list, pair in
                let missingImagesForCap: [(cap: Int, image: Int)] = (0..<pair.value).compactMap { image in
                    let url = imageUrl(base: imageDirectory, cap: pair.key, image: image)
                    guard !FileManager.default.fileExists(atPath: url.path) else {
                        return nil
                    }
                    return (cap: pair.key, image: image)
                }
                list.append(contentsOf: missingImagesForCap)
            }
        if missingImageList.isEmpty {
            print("[INFO] No missing images to load")
        } else {
            print("[INFO] Loading \(missingImageList.count) missing images...")
        }
        guard await loadImages(missingImageList) else {
            return nil
        }
        let changedImageList = await getChangedImageList()
        
        if changedImageList.isEmpty {
            print("[INFO] No changed images to load")
        } else {
            print("[INFO] Loading \(changedImageList.count) changed images...")
        }
        guard await loadImages(changedImageList) else {
            return nil
        }
        let classes = imageCounts.keys.sorted()
        return (classes, missingImageList.count + changedImageList.count)
    }
    
    private func createImageFolderIfMissing() -> Bool {
        guard !FileManager.default.fileExists(atPath: imageDirectory.path) else {
            return true
        }
        do {
            try FileManager.default.createDirectory(at: imageDirectory, withIntermediateDirectories: true)
            return true
        } catch {
            print("[ERROR] Failed to create image directory: \(error)")
            return false
        }
    }
    
    private func getImageCounts() async -> [Int : Int] {
        guard let data: Data = await get(server.appendingPathComponent("caps.json")) else {
            return [:]
        }
        do {
            return try JSONDecoder().decode([Cap].self, from: data)
                .reduce(into: [:]) { $0[$1.id] = $1.count }
        } catch {
            print("[ERROR] Failed to decode cap database: \(error)")
            return [:]
        }
    }
    
    private func imageUrl(base: URL, cap: Int, image: Int) -> URL {
        base.appendingPathComponent(String(format: "%04d/%04d-%02d.jpg", cap, cap, image))
    }
    
    private func loadImage(cap: Int, image: Int) async -> Bool {
        let url = imageUrl(base: server.appendingPathComponent("images"), cap: cap, image: image)
        let tempFile: URL, response: URLResponse
        do {
            (tempFile, response) = try await URLSession.shared.download(from: url)
        } catch {
            print("[ERROR] Failed to load image \(image) of cap \(cap): \(error)")
            return false
        }
        let responseCode = (response as! HTTPURLResponse).statusCode
        guard responseCode == 200 else {
            print("[ERROR] Failed to load image \(image) of cap \(cap): Response \(responseCode)")
            return false
        }
        do {
            let localUrl = imageUrl(base: imageDirectory, cap: cap, image: image)
            if FileManager.default.fileExists(atPath: localUrl.path) {
                try FileManager.default.removeItem(at: localUrl)
            }
            try FileManager.default.moveItem(at: tempFile, to: localUrl)
            return true
        } catch {
            print("[ERROR] Failed to save image \(image) of cap \(cap): \(error)")
            return false
        }
    }
    
    private func loadImages(_ list: [(cap: Int, image: Int)]) async -> Bool {
        guard !list.isEmpty else {
            return true
        }
        var loadedImages = 0
        await withTaskGroup(of: Bool.self) { group in
            for (cap, image) in list {
                group.addTask {
                    await self.loadImage(cap: cap, image: image)
                }
            }
            for await loaded in group {
                if loaded {
                    loadedImages += 1
                }
            }
        }
        if loadedImages != list.count {
            print("[ERROR] Only \(loadedImages) of \(list.count) images loaded")
            return false
        }
        return true
    }
    
    func getChangedImageList() async -> [(cap: Int, image: Int)] {
        guard let string: String = await get(server.appendingPathComponent("changes.txt")) else {
            print("[ERROR] Failed to get list of changed images")
            return []
        }
        
        return string
            .components(separatedBy: "\n")
            .filter { $0 != "" }
            .compactMap {
                let parts = $0.components(separatedBy: ":")
                guard parts.count == 3 else {
                    return nil
                }
                /*
                guard let date = df.date(from: parts[0]) else {
                    print("[WARN] Invalid date \(parts[0]) in change list")
                    return nil
                }
                 */
                guard let cap = Int(parts[1]) else {
                    print("[WARN] Invalid cap id \(parts[1]) in change list")
                    return nil
                }
                guard let image = Int(parts[2]) else {
                    print("[WARN] Invalid image id \(parts[2]) in change list")
                    return nil
                }
                return (cap, image)
            }
    }
    
    // MARK: Step 3: Compute version
    
    func getClassifierVersion() async -> Int? {
        guard let string: String = await get(server.appendingPathComponent("version")) else {
            print("[ERROR] Failed to get classifier version")
            return nil
        }
        guard let version = Int(string) else {
            print("[ERROR] Invalid classifier version \(string)")
            return nil
        }
        return version
    }
    
    // MARK: Step 4: Train classifier
    
    func trainModel() -> Bool {
        var params = MLImageClassifier.ModelParameters(augmentation: [])
        params.maxIterations = configuration.trainingIterations
        let model: MLImageClassifier
        do {
            model = try MLImageClassifier(
                trainingData: .labeledDirectories(at: imageDirectory),
                parameters: params)
        } catch {
            print("[ERROR] Failed to create classifier: \(error)")
            return false
        }

        print("[INFO] Saving classifier...")
        do {
            try model.write(to: classifierUrl)
            return true
        } catch {
            print("[ERROR] Failed to save model to file: \(error)")
            return false
        }
    }
    
    // MARK: Step 5: Upload classifier
    
    func upload(version: Int) async -> Bool {
        print("[INFO] Uploading classifier...")
        let modelData: Data
        do {
            modelData = try Data(contentsOf: classifierUrl)
        } catch {
            print("[ERROR] Failed to read classifier data: \(error)")
            return false
        }
        
        return await post(
            url: server.appendingPathComponent("classifier/\(version)"),
            body: modelData)
    }
    
    // MARK: Step 6: Update classes
    
    func upload(classes: [Int], lastUpdate: Date) async -> Bool {
        print("[INFO] Uploading trained classes...")
        let dateString = df.string(from: lastUpdate)
        return await post(
            url: server.appendingPathComponent("classes/\(dateString)"),
            body: classes.map(String.init).joined(separator: "\n").data(using: .utf8)!,
            dateKey: lastUpdate)
    }
    
    // MARK: Requests
    
    private func post(url: URL, body: Data) async -> Bool {
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.httpBody = body
        request.addValue(configuration.authenticationToken, forHTTPHeaderField: "key")
        return await perform(request) != nil
    }
    
    private func perform(_ request: URLRequest) async -> Data? {
        let data: Data
        let response: URLResponse
        do {
            (data, response) = try await URLSession.shared.data(for: request)
        } catch {
            print("[ERROR] Request failed: \(error)")
            return nil
        }
        let code = (response as! HTTPURLResponse).statusCode
        guard code == 200 else {
            print("[ERROR] Invalid response \(code)")
            return nil
        }
        return data
    }
    
    private func get(_ url: URL) async -> Data? {
        await perform(URLRequest(url: url))
    }
    
    private func get(_ url: URL) async -> String? {
        guard let data: Data = await get(url) else {
            return nil
        }
        guard let string = String(data: data, encoding: .utf8) else {
            print("[ERROR] Invalid string response \(data)")
            return nil
        }
        return string
    }
}

await ClassifierCreator().run()