//
//  Database.swift
//  CapCollector
//
//  Created by Christoph on 14.04.20.
//  Copyright © 2020 CH. All rights reserved.
//

import Foundation
import UIKit
import CoreML
import SQLite

protocol DatabaseDelegate: class {
    
    func database(didChangeCap cap: Int)
    
    func database(didAddCap cap: Cap)
    
    func databaseRequiresFullRefresh()
}

struct Weak {
    
  weak var value : DatabaseDelegate?
    
  init (_ value: DatabaseDelegate) {
    self.value = value
  }
}

extension Array where Element == Weak {
    
  mutating func reap () {
    self = self.filter { $0.value != nil }
    }
}

final class Database {
    
    // MARK: Variables
    
    let db: Connection
    
    let upload: Upload
    
    let download: Download
    
    private var listeners = [Weak]()
    
    // MARK: Listeners
    
    func add(listener: DatabaseDelegate) {
        listeners.append(Weak(listener))
    }
    
    init?(url: URL, server: URL) {
        guard let db = try? Connection(url.path) else {
            return nil
        }
        
        let upload = Upload(server: server)
        let download = Download(server: server)
        
        do {
            try db.run(Cap.createQuery)
            try db.run(upload.createQuery)
        } catch {
            return nil
        }

        self.db = db
        self.upload = upload
        self.download = download
        log("Database loaded with \(capCount) caps")
    }
    
    // MARK: Computed properties

    /// All caps currently in the database
    var caps: [Cap] {
        (try? db.prepare(Cap.table))?.map(Cap.init) ?? []
    }
    
    /// The ids of the caps which weren't included in the last classification
    var unmatchedCaps: [Int] {
        let query = Cap.table.select(Cap.rowId).filter(Cap.rowMatched == false)
        return (try? db.prepare(query).map { $0[Cap.rowId] }) ?? []
    }
    
    /// The number of caps which could be recognized during the last classification
    var recognizedCapCount: Int {
        (try? db.scalar(Cap.table.filter(Cap.rowMatched == true).count)) ?? 0
    }
    
    /// The number of caps currently in the database
    var capCount: Int {
        (try? db.scalar(Cap.table.count)) ?? 0
    }
    
    /// The total number of images for all caps
    var imageCount: Int {
        (try? db.prepare(Cap.table).reduce(0) { $0 + $1[Cap.rowCount] }) ?? 0
    }
    
    /// The number of caps without a downloaded image
    var capsWithoutImages: Int {
        caps.filter({ !$0.hasImage }).count
    }
    


    var pendingUploads: [(cap: Int, version: Int)] {
        do {
            return try db.prepare(upload.table).map { row in
                (cap: row[upload.rowCapId], version: row[upload.rowCapVersion])
            }
        } catch {
            log("Failed to get pending uploads")
            return []
        }
    }
    
    /// Indicate if there are any unfinished uploads
    var hasPendingUploads: Bool {
        ((try? db.scalar(upload.table.count)) ?? 0) > 0
    }
    
    var classifierVersion: Int {
        set {
            UserDefaults.standard.set(newValue, forKey: Classifier.userDefaultsKey)
            log("Classifier version set to \(newValue)")
        }
        get {
            UserDefaults.standard.integer(forKey: Classifier.userDefaultsKey)
        }
    }
    
    // MARK: Data updates
    
    /**
     Create a new cap with an image.
     
     The cap is inserted into the database, and the name and image will be uploaded to the server.
     
     - parameter image: The main image of the cap
     - parameter name: The name of the cap
     - note: Must be called on the main queue.
     - note: The registered delegates will be informed about the added cap through `database(didAddCap:)`
     - returns: `true`, if the cap was created.
     */
    func createCap(image: UIImage, name: String) -> Bool {
        guard let color = image.averageColor else {
            return false
        }
        let cap = Cap(name: name, id: capCount, color: color)
        guard insert(cap: cap) else {
            return false
        }
        guard app.storage.save(image: image, for: cap.id) else {
            return false
        }
        listeners.forEach { $0.value?.database(didAddCap: cap) }
        upload.upload(name: name, for: cap.id) { success in
            guard success else {
                return
            }
            self.update(uploaded: true, for: cap.id)
            self.upload.uploadImage(for: cap.id, version: 0) { count in
                guard let count = count else {
                    self.log("Failed to upload first image for cap \(cap.id)")
                    return
                }
                self.log("Uploaded first image for cap \(cap.id)")
                self.update(count: count, for: cap.id)
            }
        }
        return true
    }
    
    /**
     Insert a new cap.
     
     Only inserts the cap into the database, and optionally notifies the delegates.
     - note: When a new cap is created, use `createCap(image:name:)` instead
     */
    @discardableResult
    private func insert(cap: Cap, notifyDelegate: Bool = true) -> Bool {
        do {
            try db.run(cap.insertQuery)
            if notifyDelegate {
                listeners.forEach { $0.value?.database(didAddCap: cap) }
            }
            return true
        } catch {
            log("Failed to insert cap \(cap.id): \(error)")
            return false
        }
    }
    
    func add(image: UIImage, for cap: Int) -> Bool {
        guard let version = count(for: cap) else {
            log("Failed to get count for cap \(cap)")
            return false
        }
        guard app.storage.save(image: image, for: cap, version: version) else {
            log("Failed to save image \(version) for cap \(cap) to disk")
            return false
        }
        guard update(count: version + 1, for: cap) else {
            log("Failed update count \(version) for cap \(cap)")
            return false
        }
        listeners.forEach { $0.value?.database(didChangeCap: cap) }
        
        guard addPendingUpload(for: cap, version: version) else {
            log("Failed to add cap \(cap) version \(version) to upload queue")
            return false
        }
        upload.uploadImage(for: cap, version: version) { count in
            guard let _ = count else {
                self.log("Failed to upload image \(version) for cap \(cap)")
                return
            }
            guard self.removePendingUpload(of: cap, version: version) else {
                self.log("Failed to remove version \(version) for cap \(cap) from upload queue")
                return
            }
            self.log("Uploaded version \(version) for cap \(cap)")
        }
        return true
    }
    
    // MARK: Updating cap properties
    
    private func update(_ property: String, for cap: Int, setter: Setter...) -> Bool {
        do {
            let query = updateQuery(for: cap).update(setter)
            try db.run(query)
            listeners.forEach { $0.value?.database(didChangeCap: cap) }
            return true
        } catch {
            log("Failed to update \(property) for cap \(cap): \(error)")
            return false
        }
    }
    
    @discardableResult
    private func update(uploaded: Bool, for cap: Int) -> Bool {
        update("uploaded", for: cap, setter: Cap.rowUploaded <- uploaded)
    }
    
    @discardableResult
    func update(name: String, for cap: Int) -> Bool {
        update("name", for: cap, setter: Cap.rowName <- name)
    }
    
    @discardableResult
    func update(color: UIColor, for cap: Int) -> Bool {
        let (red, green, blue) = color.rgb
        return update("color", for: cap, setter: Cap.rowRed <- red, Cap.rowGreen <- green, Cap.rowBlue <- blue)
    }
    
    @discardableResult
    func update(tile: Int, for cap: Int) -> Bool {
        update("tile", for: cap, setter: Cap.rowTile <- tile)
    }
    
    @discardableResult
    func update(count: Int, for cap: Int) -> Bool {
        update("count", for: cap, setter: Cap.rowCount <- count)
    }
    
    @discardableResult
    func update(matched: Bool, for cap: Int) -> Bool {
        update("matched", for: cap, setter: Cap.rowMatched <- matched)
    }
    
    func update(recognizedCaps: Set<Int>) {
        let unrecognized = self.unmatchedCaps
        // Update caps which haven't been recognized before
        let newlyRecognized = recognizedCaps.intersection(unrecognized)
        let logIndividualMessages = newlyRecognized.count < 10
        if !logIndividualMessages {
            log("Marking \(newlyRecognized.count) caps as matched")
        }
        for cap in newlyRecognized {
            if logIndividualMessages {
                log("Marking cap \(cap) as matched")
            }
            update(matched: true, for: cap)
        }
        // Update caps which are no longer recognized
        let missing = Set(1...capCount).subtracting(recognizedCaps).subtracting(unrecognized)
        for cap in missing {
            log("Marking cap \(cap) as not matched")
            update(matched: false, for: cap)
        }
    }
    
    func addPendingUpload(for cap: Int, version: Int) -> Bool {
        do {
            try db.run(upload.insertQuery(for: cap, version: version))
            return true
        } catch {
            log("Failed to add pending upload of cap \(cap) version \(version): \(error)")
            return false
        }
    }
    
    func removePendingUpload(for cap: Int, version: Int) -> Bool {
        do {
            try db.run(upload.deleteQuery(for: cap, version: version))
            return true
        } catch {
            log("Failed to remove pending upload of cap \(cap) version \(version): \(error)")
            return false
        }
    }
    
    // MARK: Information retrieval
    
    func cap(for id: Int) -> Cap? {
        do {
            guard let row = try db.pluck(updateQuery(for: id)) else {
                log("No cap with id \(id) in database")
                return nil
            }
            return Cap(row: row)
        } catch {
            log("Failed to get cap \(id): \(error)")
            return nil
        }
    }
    
    private func count(for cap: Int) -> Int? {
        do {
            let row = try db.pluck(updateQuery(for: cap).select(Cap.rowCount))
            return row?[Cap.rowCount]
        } catch {
            log("Failed to get count for cap \(cap)")
            return nil
        }
    }
    
    func countOfCaps(withImageCountLessThan limit: Int) -> Int {
        do {
            return try db.scalar(Cap.table.filter(Cap.rowCount < limit).count)
        } catch {
            log("Failed to get caps with less than \(limit) images")
            return 0
        }
    }
    
    func lowestImageCountForCaps(startingAt start: Int) -> (count: Int, numberOfCaps: Int) {
        do {
            var currentCount = start - 1
            var capsFound = 0
            repeat {
                currentCount += 1
                capsFound = try db.scalar(Cap.table.filter(Cap.rowCount == currentCount).count)
            } while capsFound == 0
            
            return (currentCount, capsFound)
        } catch {
            return (0,0)
        }
    }
    
    func updateQuery(for cap: Int) -> Table {
        Cap.table.filter(Cap.rowId == cap)
    }
    
    // MARK: Downloads
    
    @discardableResult
    func downloadMainImage(for cap: Int, completion: @escaping (_ image: UIImage?) -> Void) -> Bool {
        return download.image(for: cap, version: 0) { image in
            // Guaranteed to be on the main queue
            guard let image = image else {
                completion(nil)
                return
            }
            
            defer {
                completion(image)
            }
            if !app.storage.save(thumbnail: Cap.thumbnail(for: image), for: cap) {
                self.log("Failed to save thumbnail for cap \(cap)")
            }
            guard let color = image.averageColor else {
                self.log("Failed to calculate color for cap \(cap)")
                return
            }
            self.update(color: color, for: cap)
        }
    }
    
    @discardableResult
    func downloadImage(for cap: Int, version: Int, completion: @escaping (_ image: UIImage?) -> Void) -> Bool {
        return download.image(for: cap, version: version, completion: completion)
    }
    
    func getServerDatabaseSize(completion: @escaping (_ size: Int64?) -> Void) {
        download.databaseSize(completion: completion)
    }
    
    func downloadServerDatabase(progress: Download.Delegate.ProgressHandler? = nil, completion: @escaping (_ success: Bool) -> Void, processed: (() -> Void)? = nil) {
        download.database(progress: progress) { tempUrl in
            guard let url = tempUrl else {
                self.log("Failed to download database")
                completion(false)
                return
            }
            completion(true)
            self.processServerDatabase(at: url)
            processed?()
        }
    }
    
    func downloadMainCapImages(progress: @escaping (_ current: Int, _ total: Int) -> Void) {
        let caps = self.caps.filter { !$0.hasImage }.map { $0.id }
        
        var downloaded = 0
        let total = caps.count
        
        func update() {
            DispatchQueue.main.async {
                progress(downloaded, total)
            }
        }
        update()
        
        guard total > 0 else {
            log("No images to download")
            return
        }
        log("Starting to download \(total) images")
        
        let group = DispatchGroup()
        let split = 50
        DispatchQueue.global(qos: .userInitiated).async {
            for part in caps.split(intoPartsOf: split) {
                for id in part {
                    let downloading = self.downloadMainImage(for: id) { _ in
                        group.leave()
                    }
                    if downloading {
                        group.enter()
                    }
                }
                if group.wait(timeout: .now() + .seconds(30)) != .success {
                    self.log("Timed out waiting for images to be downloaded")
                }
                downloaded += part.count
                self.log("Finished \(downloaded) of \(total) image downloads")
                update()
            }
            self.log("Finished all image downloads")
        }
        
    }
    
    func hasNewClassifier(completion: @escaping (_ version: Int?, _ size: Int64?) -> Void) {
        download.classifierVersion { version in
            guard let version = version else {
                self.log("Failed to download server model version")
                completion(nil, nil)
                return
            }
            let ownVersion = self.classifierVersion
            guard ownVersion < version else {
                self.log("Not updating classifier: Own version \(ownVersion), server version \(version)")
                completion(nil, nil)
                return
            }
            self.log("Getting classifier size: Own version \(ownVersion), server version \(version)")
            self.download.classifierSize { size in
                completion(version, size)
            }
        }
    }
    
    func downloadClassifier(progress: Download.Delegate.ProgressHandler? = nil, completion: @escaping (_ success: Bool) -> Void) {
        download.classifier(progress: progress) { url in
            guard let url = url else {
                self.log("Failed to download classifier")
                completion(false)
                return
            }
            let compiledUrl: URL
            do {
                compiledUrl = try MLModel.compileModel(at: url)
            } catch {
                self.log("Failed to compile downloaded classifier: \(error)")
                completion(false)
                return
            }
            
            guard app.storage.save(recognitionModelAt: compiledUrl) else {
                self.log("Failed to save classifier")
                completion(false)
                return
            }
            completion(true)
            self.download.classifierVersion { version in
                guard let version = version else {
                    self.log("Failed to download classifier version")
                    return
                }
                self.classifierVersion = version
            }
        }
    }
    
    func downloadImageCounts() {
        guard !hasPendingUploads else {
            log("Waiting to refresh server image counts (uploads pending)")
            return
        }
        log("Refreshing server image counts")
        app.database.download.imageCounts { counts in
            guard let counts = counts else {
                self.log("Failed to download server image counts")
                return
            }
            self.didDownload(imageCounts: counts)
            
        }
    }
    
    private func didDownload(imageCounts newCounts: [(cap: Int, count: Int)]) {
        let capsCounts = self.caps.reduce(into: [:]) { $0[$1.id] = $1.count }
        if newCounts.count != capsCounts.count {
            log("Downloaded \(newCounts.count) image counts, but \(app.database.capCount) caps stored locally")
            return
        }
        let changed = newCounts.compactMap { id, newCount -> Int? in
            guard let oldCount = capsCounts[id] else {
                log("Received count \(newCount) for unknown cap \(id)")
                return nil
            }
            guard oldCount != newCount else {
                return nil
            }
            app.database.update(count: newCount, for: id)
            return id
        }
        switch changed.count {
        case 0:
            log("Refreshed image counts for all caps without changes")
        case 1:
            log("Refreshed image counts for caps, changed cap \(changed[0])")
        case 2...10:
            log("Refreshed image counts for caps \(changed.map(String.init).joined(separator: ", ")).")
        default:
            log("Refreshed image counts for all caps (\(changed.count) changed)")
        }
    }

    private func processServerDatabase(at url: URL) {
        guard let db = ServerDatabase(downloadedTo: url) else {
            log("Failed to open downloaded server database")
            return
        }
        for (id, count, name) in db.caps {
            let cap = Cap(id: id, name: name, count: count)
            insert(cap: cap, notifyDelegate: false)
        }
        listeners.forEach { $0.value?.databaseRequiresFullRefresh() }
    }
    
    func uploadRemainingImages() {
        guard pendingUploads.count > 0 else {
            log("No pending uploads")
            return
        }
        log("\(pendingUploads.count) image uploads pending")
        
        for (cap, version) in pendingUploads {
            upload.uploadImage(for: cap, version: version) { count in
                guard let _ = count else {
                    self.log("Failed to upload version \(version) of cap \(cap)")
                    return
                }
                self.log("Uploaded version \(version) of cap \(cap)")
                self.removePendingUpload(of: cap, version: version)
            }
        }
    }
    
    @discardableResult
    func removePendingUpload(of cap: Int, version: Int) -> Bool {
        do {
            let query = upload.table.filter(upload.rowCapId == cap && upload.rowCapVersion == version).delete()
            try db.run(query)
            log("Deleted pending upload of cap \(cap) version \(version)")
            return true
        } catch {
            log("Failed to delete pending upload of cap \(cap) version \(version)")
            return false
        }
    }
    
    func setMainImage(of cap: Int, to version: Int) {
        guard version != 0 else {
            log("No need to switch main image with itself for cap \(cap)")
            return
        }
        upload.setMainImage(for: cap, to: version) { color in
            guard let color = color else {
                self.log("Could not make \(version) the main image for cap \(cap)")
                return
            }
            self.update(color: color, for: cap)
            self.listeners.forEach { $0.value?.database(didChangeCap: cap) }
        }
    }
}

extension Database: Logger { }