import Foundation

/// Resolves group template strings using track metadata.
/// Supported placeholders: {Artist}, {Album}, {Genre}, {Year}, {Folder}, {Format}, {BPM}, {Key}
struct GroupTemplateResolver {

    /// Preset templates for quick selection.
    static let presets: [(name: String, template: String)] = [
        ("No Grouping", ""),
        ("Album (Date)", "{Album} ({Date})"),
        ("Artist — Album", "{Artist} — {Album}"),
        ("Artist", "{Artist}"),
        ("Album", "{Album}"),
        ("Genre", "{Genre}"),
        ("Folder", "{Folder}"),
        ("Format", "{Format}"),
        ("BPM Range", "{BPM}"),
    ]

    /// Available placeholders with descriptions.
    static let placeholders: [(token: String, description: String)] = [
        ("{Artist}", "Track artist"),
        ("{Album}", "Album name"),
        ("{Genre}", "Genre"),
        ("{Date}", "Release date/year from metadata"),
        ("{Folder}", "Parent folder name"),
        ("{Format}", "File format (FLAC, MP3, etc.)"),
        ("{BPM}", "BPM (rounded to nearest 10)"),
        ("{Key}", "Musical key"),
    ]

    /// Resolve a template string for a track, returning the group header text.
    static func resolve(template: String, for track: Track) -> String {
        guard !template.isEmpty else { return "" }

        var result = template
        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: "{Genre}", with: track.genre.isEmpty ? "Unknown Genre" : track.genre)
        let yearStr = track.year.map { String($0) } ?? ""
        result = result.replacingOccurrences(of: "{Year}", with: yearStr)
        result = result.replacingOccurrences(of: "{Date}", with: yearStr)
        result = result.replacingOccurrences(of: "{Folder}", with: folderName(for: track))
        result = result.replacingOccurrences(of: "{Format}", with: track.fileFormat.isEmpty ? "Unknown" : track.fileFormat)
        result = result.replacingOccurrences(of: "{BPM}", with: bpmRange(for: track))
        result = result.replacingOccurrences(of: "{Key}", with: track.musicalKey ?? "Unknown Key")

        // Clean up empty brackets etc.
        result = result.replacingOccurrences(of: "()", with: "")
        result = result.replacingOccurrences(of: "[]", with: "")
        result = result.replacingOccurrences(of: " — Unknown Artist", with: "")
        result = result.trimmingCharacters(in: .whitespaces)

        return result.isEmpty ? "Ungrouped" : result
    }

    private static func folderName(for track: Track) -> String {
        let components = track.filePath.split(separator: "/")
        if components.count >= 2 {
            return String(components[components.count - 2])
        }
        return "Root"
    }

    private static func bpmRange(for track: Track) -> String {
        guard let bpm = track.bpm else { return "No BPM" }
        let rounded = Int(bpm / 10) * 10
        return "\(rounded)-\(rounded + 10) BPM"
    }
}