using System.Security.Cryptography;
using SVSim.BattleNode.Sessions;

namespace SVSim.BattleNode.Bridge;

/// <summary>
/// In-process implementation of <see cref="IMatchingBridge"/>. The HTTP-side
/// matching queue calls <see cref="RegisterBattle"/> once it has decided "these two
/// play each other" or "this viewer is solo (bot)."
/// </summary>
public sealed class MatchingBridge : IMatchingBridge
{
    /// <summary>Battle id is two zero-padded decimal halves concatenated (e.g. "975695" + "075012").
    /// The half-width and the draw bound must stay coupled: bound == 10^digits.</summary>
    private const int BattleIdHalfDigits = 6;
    private const int BattleIdHalfExclusiveMax = 1_000_000; // 10^BattleIdHalfDigits

    private readonly IBattleSessionStore _store;
    private readonly BattleNodeOptions _options;

    public MatchingBridge(IBattleSessionStore store, BattleNodeOptions options)
    {
        _store = store;
        _options = options;
    }

    public PendingMatch RegisterBattle(BattlePlayer p1, BattlePlayer? p2, BattleType type)
    {
        ValidateContract(p1, p2, type);

        // Decimal battle id mirrors the captures (e.g. "975695075012"): two unbiased
        // BattleIdHalfDigits-wide draws concatenated. RandomNumberGenerator.GetInt32 uses
        // rejection sampling so each half is uniform on [0, BattleIdHalfExclusiveMax).
        var hi = RandomNumberGenerator.GetInt32(0, BattleIdHalfExclusiveMax);
        var lo = RandomNumberGenerator.GetInt32(0, BattleIdHalfExclusiveMax);
        var halfFormat = "D" + BattleIdHalfDigits;
        var battleId = hi.ToString(halfFormat) + lo.ToString(halfFormat);

        _store.RegisterPending(new PendingBattle(battleId, type, p1, p2));
        return new PendingMatch(battleId, _options.NodeServerUrl);
    }

    private static void ValidateContract(BattlePlayer p1, BattlePlayer? p2, BattleType type)
    {
        if (p1 is null) throw new ArgumentNullException(nameof(p1));
        switch (type)
        {
            case BattleType.Pvp:
                if (p2 is null) throw new ArgumentException("Pvp requires both p1 and p2.", nameof(p2));
                if (p1.ViewerId == p2.ViewerId)
                    throw new ArgumentException("Pvp requires distinct viewer ids.", nameof(p2));
                break;
            case BattleType.Bot:
                if (p2 is not null) throw new ArgumentException("Bot must have p2==null.", nameof(p2));
                break;
            default:
                throw new ArgumentOutOfRangeException(nameof(type), type, "Unknown BattleType.");
        }
    }
}