import Foundation
import PDFKit

/// Whether an output format can actually be produced on this Mac, and why not
/// when it cannot. The wheel uses this to mark options as unavailable instead
/// of failing after the user has already committed to a drop.
struct Availability {
    let isAvailable: Bool
    let reason: String?

    static let ok = Availability(isAvailable: true, reason: nil)

    static func unavailable(_ reason: String) -> Availability {
        Availability(isAvailable: false, reason: reason)
    }
}

/// Front door for format conversions: picks the engine, handles formats that
/// produce more than one file, and reports a useful reason when nothing can.
enum Converter {
    @discardableResult
    static func convert(
        source: URL,
        to format: Format,
        at destination: URL,
        quality: Double = 0.9,
        mediaQuality: String = "Medium",
        audioBitrate: String = "192",
        cancellation: Cancellation? = nil,
        progress: ((Double) -> Void)? = nil
    ) throws -> [URL] {
        try cancellation?.check()
        let category = FileKind.category(of: source)

        switch category {
        case .image:
            try ImageConverter.convert(
                source: source,
                to: format,
                at: destination,
                quality: quality,
                cancellation: cancellation
            )
            progress?(1)
            return [destination]

        case .video, .audio:
            try AVConverter.convert(
                source: source,
                to: format,
                at: destination,
                quality: mediaQuality,
                bitrate: audioBitrate,
                cancellation: cancellation,
                progress: progress
            )
            return [destination]

        case .pdf:
            switch format {
            case .jpg, .png:
                let directory = OutputNaming.artifactDirectory(for: source, suffix: " \(format.displayName)")
                return try PDFConverter.renderPages(
                    source,
                    to: format,
                    into: directory,
                    dpi: 300,
                    cancellation: cancellation,
                    progress: progress
                )
            case .pptx, .xlsx:
                try Office.convert(source, to: format, at: destination, cancellation: cancellation)
                progress?(1)
                return [destination]
            case .pdf:
                guard let document = PDFDocument(url: source) else {
                    throw ConversionError.unreadable(source.lastPathComponent)
                }
                guard document.write(to: destination) else {
                    throw ConversionError.failed("Could not rewrite the PDF.")
                }
                progress?(1)
                return [destination]
            default:
                try DocumentConverter.convert(
                    source: source,
                    to: format,
                    at: destination,
                    cancellation: cancellation,
                    progress: progress
                )
                return [destination]
            }

        case .document, .spreadsheet:
            try DocumentConverter.convert(
                source: source,
                to: format,
                at: destination,
                cancellation: cancellation,
                progress: progress
            )
            return [destination]

        case .slides:
            try SlidesConverter.convert(
                source: source,
                to: format,
                at: destination,
                cancellation: cancellation,
                progress: progress
            )
            if format == .png || format == .jpg {
                let directory = OutputNaming.artifactDirectory(for: source, suffix: " \(format.displayName)")
                let files = (try? FileManager.default.contentsOfDirectory(at: directory, includingPropertiesForKeys: nil)) ?? []
                return files.sorted { $0.lastPathComponent < $1.lastPathComponent }
            }
            return [destination]

        case .ebook:
            try EbookConverter.convert(
                source: source,
                to: format,
                at: destination,
                cancellation: cancellation,
                progress: progress
            )
            return [destination]

        case .subtitle:
            try SubtitleConverter.convert(source: source, to: format, at: destination, cancellation: cancellation)
            progress?(1)
            return [destination]

        case .archive:
            try ArchiveConverter.convert(
                source: source,
                to: format,
                at: destination,
                cancellation: cancellation,
                progress: progress
            )
            return [destination]

        case .folder, .unknown:
            throw ConversionError.unsupported("\(source.lastPathComponent) has no conversion options.")
        }
    }

    // MARK: - Availability

    static func availability(target: Format, source: FileCategory) -> Availability {
        if let offered = ConversionCatalog.targets[source], !offered.contains(target) {
            return .unavailable("\(source.title) cannot become \(target.displayName).")
        }
        if target.requiresFFmpeg, !Toolchain.hasFFmpeg {
            return .unavailable("Needs ffmpeg — brew install ffmpeg")
        }
        if target.requiresLibreOffice, !Toolchain.hasLibreOffice {
            return .unavailable("Needs LibreOffice — brew install --cask libreoffice")
        }
        if !Settings.shared.useExternalTools, target.requiresFFmpeg || target.requiresLibreOffice {
            return .unavailable("External tools are turned off in Settings.")
        }
        if target.category == .image, !Raster.canEncode(target) {
            if target == .webp, WebPEncoder.isAvailable {
                return .ok
            }
            return .unavailable("This Mac cannot write \(target.displayName) files.")
        }
        if source == .spreadsheet, !["xlsx", "ods", "csv", "tsv"].contains(target.ext), target != .pdf {
            return .unavailable("Spreadsheets cannot become \(target.displayName).")
        }
        return .ok
    }
}