import Foundation

final class ValidationLog {

    private enum LogLevel: String {
        case error = "ERROR"
        case warning = "WARNING"
        case info = "INFO"
    }

    init() {

    }

    private func add(_ type: LogLevel, item: ContentError) {
        let errorText: String
        if let err = item.error {
            errorText = ", Error: \(err.localizedDescription)"
        } else {
            errorText = ""
        }
        print("[\(type.rawValue)][\(item.source)] \(item.reason)\(errorText)")
    }

    func add(error: ContentError) {
        add(.error, item: error)
    }

    func add(error reason: String, source: String, error: Error? = nil) {
        add(error: .init(reason: reason, source: source, error: error))
    }

    func add(warning: ContentError) {
        add(.warning, item: warning)
    }

    func add(warning reason: String, source: String, error: Error? = nil) {
        add(warning: .init(reason: reason, source: source, error: error))
    }

    func add(info: ContentError) {
        add(.info, item: info)
    }

    func add(info reason: String, source: String, error: Error? = nil) {
        add(info: .init(reason: reason, source: source, error: error))
    }

    @discardableResult
    func unused<T, R>(_ value: Optional<T>, _ name: String, source: String) -> Optional<R> {
        if value != nil {
            add(info: "Unused property '\(name)'", source: source)
        }
        return nil
    }

    func unknown(property: String, source: String) {
        add(info: "Unknown property '\(property)'", source: source)
    }

    func required<T>(_ value: Optional<T>, name: String, source: String) -> Optional<T> {
        guard let value = value else {
            add(error: "Missing property '\(name)'", source: source)
            return nil
        }
        return value
    }

    func unexpected<T>(_ value: Optional<T>, name: String, source: String) -> Optional<T> {
        if let value = value {
            add(error: "Unexpected property '\(name)' = '\(value)'", source: source)
            return nil
        }
        return nil
    }

    func missing(_ file: String, requiredBy source: String) {
        print("[ERROR] Missing file '\(file)' required by \(source)")
    }

    func failedToOpen(_ file: String, requiredBy source: String, error: Error?) {
        print("[ERROR] Failed to open file '\(file)' required by \(source): \(error?.localizedDescription ?? "No error provided")")
    }

    func state(_ raw: String?, source: String) -> PageState {
        guard let raw = raw else {
            return .standard
        }
        guard let state = PageState(rawValue: raw) else {
            add(warning: "Invalid 'state' '\(raw)', using 'standard'", source: source)
            return .standard
        }
        return state
    }

    func headerType(_ raw: String?, source: String) -> HeaderType {
        guard let raw = raw else {
            return .left
        }
        guard let type = HeaderType(rawValue: raw) else {
            add(warning: "Invalid 'headerType' '\(raw)', using 'left'", source: source)
            return .left
        }
        return type
    }

    func thumbnailStyle(_ raw: String?, source: String) -> ThumbnailStyle {
        guard let raw = raw else {
            return .large
        }
        guard let style = ThumbnailStyle(rawValue: raw) else {
            add(warning: "Invalid 'thumbnailStyle' '\(raw)', using 'large'", source: source)
            return .large
        }
        return style
    }

    func linkPreviewThumbnail(customFile: String?, for language: String, in folder: URL, source: String) -> String? {
        if let customFile = customFile {
            let customFileUrl: URL
            if customFile.starts(with: "/") {
                customFileUrl = URL(fileURLWithPath: customFile)
            } else {
                customFileUrl = folder.appendingPathComponent(customFile)
            }
            guard customFileUrl.exists else {
                missing(customFile, requiredBy: "property 'linkPreviewImage' in metadata of \(source)")
                return nil
            }
            return customFile
        }
        guard let thumbnail = Element.findThumbnail(for: language, in: folder) else {
            // Link preview images are not necessarily required
            return nil
        }
        return thumbnail
    }

    func moreLinkText(_ elementText: String?, parent parentText: String?, source: String) -> String {
        if let elementText = elementText {
            return elementText
        }
        let standard = Element.LocalizedMetadata.moreLinkDefaultText
        guard let parentText = parentText, parentText != standard else {
            add(error: "Missing property 'moreLinkText'", source: source)
            return standard
        }

        return parentText
    }

    func date(from string: String?, property: String, source: String) -> Date? {
        guard let string = string else {
            return nil
        }
        guard let date = ValidationLog.metadataDate.date(from: string) else {
            add(warning: "Invalid date string '\(string)' for property '\(property)'", source: source)
            return nil
        }
        return date
    }

    private static let metadataDate: DateFormatter = {
        let df = DateFormatter()
        df.dateFormat = "dd.MM.yy"
        return df
    }()
}