namespace WorldSim;

/// <summary>
/// Trade evaluation and execution (SPEC §9). South MVP: generous, voluntary,
/// no currency — a gift economy where the ratio favors the receiver.
///
/// Soul consequences: a generous completed exchange eases both parties'
/// imprints (external perception — the world pressed kindly on them).
/// Later soul types change the ratio logic only; the mechanism is shared.
/// </summary>
public static class TradeSystem
{
    /// <summary>Trades since the last daily stats snapshot.</summary>
    public static int TradesToday;

    /// <summary>
    /// Need-based: the trigger is a person in need, not an inventory gap.
    /// Food flows to the hungry first; raw material surplus vs. genuine
    /// lack remains as a fallback.
    /// </summary>
    public static bool CanTrade(Npc giver, Npc receiver, out MaterialKind material)
    {
        material = MaterialKind.Food;

        // The ungenerous do not give. Not from an empty pack — from a full one.
        if (giver.Soul.Generosity < 0.3f) return false;

        giver.Inventory.TryGetValue(MaterialKind.Food, out float giverFood);
        receiver.Inventory.TryGetValue(MaterialKind.Food, out float receiverFood);
        if (receiver.Nourishment < 0.6f && receiverFood < 2f && giverFood > 3f)
            return true;

        foreach (var kv in giver.Inventory)
        {
            bool receiverLacks = !receiver.Inventory.TryGetValue(kv.Key, out float has) || has < 2f;
            if (kv.Value > 5f && receiverLacks) { material = kv.Key; return true; }
        }
        return false;
    }

    public static void Execute(Npc giver, Npc receiver, MaterialKind material)
    {
        TradesToday++;

        // Generosity decides how much of the surplus is given.
        float surplus = giver.Inventory[material] - 2f;
        float given = surplus * giver.Soul.Generosity;

        giver.Inventory[material] -= given;
        receiver.Inventory.TryGetValue(material, out float has);
        receiver.Inventory[material] = has + given;

        StatsLogger.LogGift(giver, receiver, material, given);

        // The kindness lands on both atmospheres — gently.
        giver.Imprint.ExternalPerception    -= 0.002f;
        receiver.Imprint.ExternalPerception -= 0.002f;
        giver.Imprint.Clamp();
        receiver.Imprint.Clamp();

        // TODO(Week 3): soul-imprint-weighted PARTNER selection (trusted vs
        // tainted history) — the constrained-emergence reference pattern (SPEC §7).
    }
}