import Foundation

/// The in-band SPS (type 7) and PPS (type 8) NAL units extracted from an
/// access unit. The sender repeats both ahead of every keyframe, so any
/// keyframe carries them; they are the source for the VideoToolbox format
/// description.
struct NalSets {
    let sps: [UInt8]
    let pps: [UInt8]
}

/// Extracts parameter sets from an Annex-B access unit.
enum NalExtractor {
    static func parameterSets(_ annexB: [UInt8]) -> NalSets? {
        var sps: [UInt8]?
        var pps: [UInt8]?
        for nal in AvccConverter.nalUnits(annexB) {
            guard !nal.isEmpty else { continue }
            let type = Int(nal[0]) & 0x1F
            if type == 7 && sps == nil {
                sps = nal
            } else if type == 8 && pps == nil {
                pps = nal
            }
        }
        guard let s = sps, let p = pps else { return nil }
        return NalSets(sps: s, pps: p)
    }
}