using SeaHaven.DataServices.Models;

namespace SeaHaven.Services.Helpers
{
    public static class VendorConflictPairs
    {
        // Group by vendor so cross-vendor intervals are never compared, then sweep the
        // start-sorted windows within a vendor. Every overlapping pair is still emitted;
        // output is O(n log n + p) where p is the number of emitted pairs, so the worst
        // case stays quadratic only when a single vendor has many mutually-overlapping
        // windows, which is inherent to enumerating all such pairs.
        public static IEnumerable<(ScheduledDispatchReadModel Left, ScheduledDispatchReadModel Right)> Build(
            IReadOnlyList<ScheduledDispatchReadModel> dispatches)
        {
            foreach (var group in dispatches.GroupBy(dispatch => dispatch.VendorId))
            {
                var sorted = group.OrderBy(dispatch => dispatch.Start).ToList();
                for (var leftIndex = 0; leftIndex < sorted.Count; leftIndex++)
                {
                    var left = sorted[leftIndex];
                    for (var rightIndex = leftIndex + 1; rightIndex < sorted.Count; rightIndex++)
                    {
                        var right = sorted[rightIndex];
                        // Sorted by start: once a window starts at or after left's end, none that follow can overlap it.
                        if (right.Start >= left.End)
                            break;
                        if (left.WorkOrderId != right.WorkOrderId)
                            yield return (left, right);
                    }
                }
            }
        }
    }
}