namespace HSchool.People;

internal readonly record struct FamilyPlan(int FamilyIndex, IReadOnlyList<PupilSeat> Seats);

/// <summary>
/// Walks seats in order and groups them into families of 1–3. A short remainder becomes
/// singleton families rather than shrinking an earlier family's intended size, so a longer
/// seat list only appends families.
/// </summary>
internal static class FamilyPlanner
{
    public static IReadOnlyList<FamilyPlan> Plan(int schoolSeed, IReadOnlyList<PupilSeat> seats, int startIndex = 0)
    {
        var plans = new List<FamilyPlan>();
        var offset = 0;
        var index = startIndex;
        while (offset < seats.Count)
        {
            var remaining = seats.Count - offset;
            var want = ChildCount(schoolSeed, index);
            var take = want <= remaining ? want : 1;
            var slice = new PupilSeat[take];
            for (var i = 0; i < take; i++)
            {
                slice[i] = seats[offset + i];
            }

            plans.Add(new FamilyPlan(index, slice));
            offset += take;
            index++;
        }

        return plans;
    }

    public static int ChildCount(int schoolSeed, int familyIndex)
    {
        var rng = new Random(Seed.Mix(schoolSeed, familyIndex, Seed.ChildCountSalt));
        var roll = rng.Next(100);
        if (roll < 50)
        {
            return 1;
        }

        return roll < 85 ? 2 : 3;
    }
}