import Foundation

/// A one-tap stem mix. [build] returns nil when the track lacks the stems it needs.
struct MixPreset: Identifiable, Equatable {
    let label: String
    let build: ([String]) -> [String: StemSetting]?
    var id: String { label }
    static func == (a: MixPreset, b: MixPreset) -> Bool { a.label == b.label }
}

enum MixPresets {
    static let full = MixPreset(label: "Full Mix") { _ in [:] }
    static let karaoke = MixPreset(label: "Karaoke") { n in n.contains("vocals") ? ["vocals": StemSetting(muted: true)] : nil }

    static let all: [MixPreset] = [
        full,
        karaoke,
        MixPreset(label: "A Cappella") { n in n.contains("vocals") ? ["vocals": StemSetting(solo: true)] : nil },
        MixPreset(label: "No Drums") { n in n.contains("drums") ? ["drums": StemSetting(muted: true)] : nil },
        MixPreset(label: "Rhythm") { n in
            n.contains("drums") && n.contains("bass") ? ["drums": StemSetting(solo: true), "bass": StemSetting(solo: true)] : nil
        },
        MixPreset(label: "No Guitar") { n in n.contains("guitar") ? ["guitar": StemSetting(muted: true)] : nil },
        MixPreset(label: "No Bass") { n in n.contains("bass") ? ["bass": StemSetting(muted: true)] : nil },
    ]

    /// Drops stems left at their defaults, so mixes compare by what they actually change.
    static func normalized(_ m: [String: StemSetting]) -> [String: StemSetting] { m.filter { $0.value != StemSetting() } }

    /// The preset [mix] matches for these stems, or nil for a hand-made mix.
    static func current(_ names: [String], _ mix: [String: StemSetting]) -> MixPreset? {
        let m = normalized(mix)
        return all.first { p in p.build(names).map { normalized($0) == m } ?? false }
    }

    /// The preset after the current one (a custom mix goes back to Full), skipping ones these stems can't do.
    static func next(_ names: [String], _ mix: [String: StemSetting]) -> MixPreset {
        let usable = all.filter { $0.build(names) != nil }
        guard let cur = current(names, mix), let i = usable.firstIndex(of: cur) else { return full }
        return usable[(i + 1) % usable.count]
    }

    /// True when the vocals stem can't be heard (muted, or another stem soloed).
    static func vocalsSilent(_ names: [String], _ mix: [String: StemSetting]) -> Bool {
        if !names.contains("vocals") { return false }
        let v = mix["vocals"] ?? StemSetting()
        let anySolo = names.contains { mix[$0]?.solo == true }
        return v.muted || anySolo && !v.solo || v.level <= 0
    }
}