/// Finds the connected screen a `ScreenRef` means.
public enum ScreenMatching {
    /// - Parameter names: names of the connected screens in system order.
    /// - Returns: index into `names`, or nil if the screen is not connected.
    public static func index(of ref: ScreenRef, in names: [String]) -> Int? {
        let sameName = names.indices.filter { names[$0] == ref.name }
        switch sameName.count {
        case 1:
            return sameName[0]
        case 0:
            // Renamed or different monitor model: only trust the position if the count still fits.
            return nil
        default:
            // Identical monitors: prefer the remembered position, else the first free match.
            return sameName.contains(ref.index) ? ref.index : sameName.first
        }
    }

    /// Resolves all assignments; screens claimed twice keep the first assignment.
    public static func resolve(_ assignments: [VideoAssignment], in names: [String]) -> [Int: Source] {
        var result: [Int: Source] = [:]
        for assignment in assignments {
            guard let index = index(of: assignment.screen, in: names), result[index] == nil else { continue }
            result[index] = assignment.source
        }
        return result
    }
}

/// What to stop and start to get from the current state to the desired one.
public enum Reconcile {
    public struct Plan<Key: Hashable, Value: Equatable> {
        public var stop: [Key]
        public var start: [Key: Value]
    }

    public static func plan<Key: Hashable, Value: Equatable>(current: [Key: Value], desired: [Key: Value]) -> Plan<Key, Value> {
        let stop = current.keys.filter { desired[$0] == nil }
        let start = desired.filter { current[$0.key] != $0.value }
        return Plan(stop: stop, start: start)
    }
}