import Foundation

final class MetadataInfoLogger {

    private let input: URL

    private var numberOfMetadataFiles = 0

    private var unusedProperties: [(name: String, source: String)] = []

    private var invalidProperties: [(name: String, source: String, reason: String)] = []

    private var unknownProperties: [(name: String, source: String)] = []

    private var missingProperties: [(name: String, source: String)] = []

    private var unreadableMetadata: [(source: String, error: Error)] = []

    private var warnings: [(source: String, message: String)] = []

    private var errors: [(source: String, message: String)] = []

    init(input: URL) {
        self.input = input
    }

    /**
     Adds an info message if a value is set for an unused property.
     - Note: Unused properties do not cause an element to be skipped.
     */
    @discardableResult
    func unused<T>(_ value: Optional<T>, _ name: String, source: String) -> T where T: DefaultValueProvider {
        if let value {
            unusedProperties.append((name, source))
            return value
        }
        return T.defaultValue
    }

    /**
     Cast a string value to another value, and using a default in case of errors.
     - Note: Invalid string values do not cause an element to be skipped.
     */
    func cast<T>(_ value: String, _ name: String, source: String) -> T where T: DefaultValueProvider, T: StringProperty {
        guard let result = T.init(value) else {
            invalidProperties.append((name: name, source: source, reason: T.castFailureReason))
            return T.defaultValue
        }
        return result
    }

    /**
     Cast a string value to another value, and using a default in case of errors or missing values.
     - Note: Invalid string values do not cause an element to be skipped.
     */
    func cast<T>(_ value: String?, _ name: String, source: String) -> T where T: DefaultValueProvider, T: StringProperty {
        guard let value else {
            return T.defaultValue
        }
        guard let result = T.init(value) else {
            invalidProperties.append((name: name, source: source, reason: T.castFailureReason))
            return T.defaultValue
        }
        return result
    }

    /**
     Cast the string value of an unused property to another value, and using a default in case of errors.
     - Note: Invalid string values do not cause an element to be skipped.
     */
    func castUnused<R>(_ value: String?, _ name: String, source: String) -> R where R: DefaultValueProvider, R: StringProperty {
        unused(value.unwrapped { cast($0, name, source: source) }, name, source: source)
    }

    /**
     Note an unknown property.
     - Note: Unknown properties do not cause an element to be skipped.
     */
    func unknown(property: String, source: String) {
        unknownProperties.append((name: property, source: source))
    }

    /**
     Ensure that a property is set, and aborting metadata decoding.
     - Note: Missing required properties cause an element to be skipped.
     */
    func required<T>(_ value: T?, name: String, source: String, _ valid: inout Bool) -> T where T: DefaultValueProvider {
        guard let value = value else {
            missingProperties.append((name, source))
            valid = false
            return T.defaultValue
        }
        return value
    }

    func warning(_ message: String, source: String) {
        warnings.append((source, message))
    }

    func error(_ message: String, source: String) {
        errors.append((source, message))
    }

    func failedToDecodeMetadata(source: String, error: Error) {
        unreadableMetadata.append((source, error))
    }

    func readPotentialMetadata(atPath path: String, source: String) -> Data? {
        let url = input.appendingPathComponent(path)
        guard url.exists else {
            return nil
        }

        numberOfMetadataFiles += 1
        printMetadataScanUpdate()
        do {
            return try Data(contentsOf: url)
        } catch {
            unreadableMetadata.append((source, error))
            return nil
        }
    }

    // MARK: Printing

    private func printMetadataScanUpdate() {
        print("           Pages found: \(numberOfMetadataFiles)   \r", terminator: "")
    }

    func printMetadataScanOverview(languages: Int) {
        var notes = [String]()
        func addIfNotZero<S>(_ sequence: Array<S>, _ name: String) {
            guard sequence.count > 0 else {
                return
            }
            notes.append("\(sequence.count) \(name)")
        }
        addIfNotZero(warnings, "warnings")
        addIfNotZero(errors, "errors")
        addIfNotZero(unreadableMetadata, "unreadable files")
        addIfNotZero(unusedProperties, "unused properties")
        addIfNotZero(invalidProperties, "invalid properties")
        addIfNotZero(unknownProperties, "unknown properties")
        addIfNotZero(missingProperties, "missing properties")

        print("           Pages found: \(numberOfMetadataFiles)        ")
        print("             Languages: \(languages)")
        if !notes.isEmpty {
            print("                 Notes: " + notes.joined(separator: ", "))
        }
    }

    func writeResults(to file: URL) {
        guard !errors.isEmpty || !warnings.isEmpty || !unreadableMetadata.isEmpty || !unusedProperties.isEmpty || !invalidProperties.isEmpty || !unknownProperties.isEmpty || !missingProperties.isEmpty else {
            do {
                if FileManager.default.fileExists(atPath: file.path) {
                    try FileManager.default.removeItem(at: file)
                }
            } catch {
                print("    Failed to delete metadata log: \(error)")
            }
            return
        }
        var lines: [String] = []
        func add<S>(_ name: String, _ property: S, convert: (S.Element) -> String) where S: Sequence {
            let elements = property.map { "  " + convert($0) }.sorted()
            guard !elements.isEmpty else {
                return
            }
            lines.append("\(name):")
            lines.append(contentsOf: elements)
        }
        add("Errors", errors) { "\($0.source): \($0.message)" }
        add("Warnings", warnings) { "\($0.source): \($0.message)" }
        add("Unreadable files", unreadableMetadata) { "\($0.source): \($0.error)" }
        add("Unused properties", unusedProperties) { "\($0.source): \($0.name)" }
        add("Invalid properties", invalidProperties) { "\($0.source): \($0.name) (\($0.reason))" }
        add("Unknown properties", unknownProperties) { "\($0.source): \($0.name)" }
        add("Missing properties", missingProperties) { "\($0.source): \($0.name)" }

        let data = lines.joined(separator: "\n").data(using: .utf8)!
        do {
            try data.createFolderAndWrite(to: file)
        } catch {
            print("    Failed to save metadata log: \(error)")
        }
    }
}