import Foundation

/// Generates filenames from audio metadata using configurable templates.
///
/// Template variables (enclosed in `{}`):
///   {artist}      - Track artist
///   {album}       - Album name
///   {title}       - Track title
///   {genre}       - Genre
///   {bpm}         - BPM (rounded)
///   {key}         - Musical key
///   {year}        - Release year from metadata
///   {track}       - Track number in playlist (zero-padded)
///   {duration}    - Duration as M:SS
///   {format}      - File format extension
///   {samplerate}  - Sample rate
///   {bitdepth}    - Bit depth
///
/// Example: "{artist} - {album} - {title}" → "Raekwon - Only Built 4 Cuban Linx - Spot Rusherz"
struct FileNameTemplate {

    /// Default template
    static let defaultTemplate = "{artist} - {album} - {title}"

    /// All available template variables with descriptions.
    static let availableVariables: [(token: String, description: String)] = [
        ("{track}", "Track number in playlist (zero-padded)"),
        ("{artist}", "Artist name"),
        ("{album}", "Album name"),
        ("{title}", "Track title"),
        ("{genre}", "Genre"),
        ("{bpm}", "BPM (rounded)"),
        ("{key}", "Musical key"),
        ("{year}", "Release year"),
        ("{duration}", "Duration (M:SS)"),
        ("{format}", "File format (MP3, WAV, etc.)"),
        ("{samplerate}", "Sample rate (e.g. 44100)"),
        ("{bitdepth}", "Bit depth (e.g. 16)"),
    ]

    /// Some common presets.
    static let presets: [(name: String, template: String)] = [
        ("Artist - Album - Title", "{artist} - {album} - {title}"),
        ("## Artist - Title", "{track} {artist} - {title}"),
        ("## Title", "{track} {title}"),
        ("Artist - Title [BPM Key]", "{artist} - {title} [{bpm} {key}]"),
        ("Album - ## Title", "{album} - {track} {title}"),
        ("Artist - Title (Format)", "{artist} - {title} ({format})"),
    ]

    /// Generate a filename from a template string and track metadata.
    static func generate(
        template: String,
        track: Track,
        playlistIndex: Int,
        totalTracks: Int
    ) -> String {
        let padWidth = totalTracks >= 100 ? 3 : 2

        var result = template
        result = result.replacingOccurrences(of: "{track}", with: String(format: "%0\(padWidth)d", playlistIndex + 1))
        result = result.replacingOccurrences(of: "{artist}", with: track.artist.isEmpty ? "Unknown Artist" : track.artist)
        result = result.replacingOccurrences(of: "{album}", with: track.album.isEmpty ? "Unknown Album" : track.album)
        result = result.replacingOccurrences(of: "{title}", with: track.title)
        result = result.replacingOccurrences(of: "{genre}", with: track.genre.isEmpty ? "Unknown" : track.genre)
        result = result.replacingOccurrences(of: "{bpm}", with: track.bpm.map { String(format: "%.0f", $0) } ?? "")
        result = result.replacingOccurrences(of: "{key}", with: track.musicalKey ?? "")
        result = result.replacingOccurrences(of: "{year}", with: track.year.map { String($0) } ?? "")
        result = result.replacingOccurrences(of: "{duration}", with: track.formattedDuration)
        result = result.replacingOccurrences(of: "{format}", with: track.fileFormat)
        result = result.replacingOccurrences(of: "{samplerate}", with: "\(Int(track.sampleRate))")
        result = result.replacingOccurrences(of: "{bitdepth}", with: "\(track.bitDepth)")

        // Clean up: remove double separators from empty fields, trim
        result = result.replacingOccurrences(of: "  ", with: " ")
        result = result.replacingOccurrences(of: " - - ", with: " - ")
        result = result.replacingOccurrences(of: "- -", with: "-")
        result = result.replacingOccurrences(of: "[]", with: "")
        result = result.replacingOccurrences(of: "()", with: "")
        result = result.trimmingCharacters(in: .whitespaces)
        result = result.trimmingCharacters(in: CharacterSet(charactersIn: "- "))

        // Sanitize for filesystem
        return sanitizeFilename(result)
    }

    /// Preview what a filename would look like with a given template.
    static func preview(template: String) -> String {
        let fakeTrack = Track(
            title: "Spot Rusherz",
            artist: "Raekwon",
            album: "Only Built 4 Cuban Linx",
            genre: "Hip-Hop",
            filePath: "/fake.mp3",
            duration: 193,
            fileFormat: "MP3"
        )
        fakeTrack.bpm = 95
        fakeTrack.musicalKey = "Dm"
        fakeTrack.year = 1995
        return generate(template: template, track: fakeTrack, playlistIndex: 0, totalTracks: 18)
    }

    // MARK: - Helpers

    private static func sanitizeFilename(_ name: String) -> String {
        let illegal = CharacterSet(charactersIn: "/\\:*?\"<>|")
        return name.components(separatedBy: illegal).joined(separator: "_")
    }
}