using System.Collections.Generic;

namespace InteractiveVideo
{
    /// <summary>
    /// A whole tracking file, ready for lookup: object identities, and tracked frames sorted by frame number.
    /// Built by <see cref="VideoTrackingLoader"/>; the raw JSON is parsed exactly once.
    /// </summary>
    public sealed class TrackingData
    {
        public string Video;
        public int Width;
        public int Height;
        public float Fps;

        /// <summary>Object identities in file order.</summary>
        public readonly List<TrackedObject> Objects = new List<TrackedObject>();
        public readonly Dictionary<string, TrackedObject> ObjectsById = new Dictionary<string, TrackedObject>();

        /// <summary>Tracked frames sorted ascending by <see cref="TrackingFrame.Frame"/>, no duplicates.</summary>
        public readonly List<TrackingFrame> Frames = new List<TrackingFrame>();
        /// <summary>Parallel array of frame numbers for binary search (kept in sync with <see cref="Frames"/>).</summary>
        public long[] FrameNumbers = System.Array.Empty<long>();

        public long FirstFrame => Frames.Count > 0 ? Frames[0].Frame : -1;
        public long LastFrame => Frames.Count > 0 ? Frames[Frames.Count - 1].Frame : -1;

        /// <summary>
        /// Index of the last tracked frame whose number is &lt;= videoFrame, or -1 when videoFrame precedes all data.
        /// O(log n).
        /// </summary>
        public int FindFrameIndexAtOrBefore(long videoFrame)
        {
            int lo = 0, hi = FrameNumbers.Length - 1, result = -1;
            while (lo <= hi)
            {
                int mid = lo + ((hi - lo) >> 1);
                if (FrameNumbers[mid] <= videoFrame)
                {
                    result = mid;
                    lo = mid + 1;
                }
                else
                {
                    hi = mid - 1;
                }
            }
            return result;
        }

        /// <summary>Exact match lookup; -1 when the video frame has no tracked frame of its own.</summary>
        public int FindExactFrameIndex(long videoFrame)
        {
            int i = FindFrameIndexAtOrBefore(videoFrame);
            return i >= 0 && FrameNumbers[i] == videoFrame ? i : -1;
        }

        /// <summary>Called by the loader after frames are appended; sorts and builds the lookup array.</summary>
        public void RebuildIndex()
        {
            Frames.Sort((a, b) => a.Frame.CompareTo(b.Frame));
            // Drop duplicate frame numbers (keep the first); duplicates would break binary search semantics.
            for (int i = Frames.Count - 1; i > 0; i--)
                if (Frames[i].Frame == Frames[i - 1].Frame) Frames.RemoveAt(i);

            FrameNumbers = new long[Frames.Count];
            for (int i = 0; i < Frames.Count; i++) FrameNumbers[i] = Frames[i].Frame;
        }
    }
}