using System;
using System.Collections.Generic;
using Godot;

namespace WorldSim;

public enum MaterialKind { Wood, Stone, Clay, Water, Food, Ore, Herb }

/// <summary>
/// A harvestable resource node on the grid (SPEC §6).
/// Wood regenerates; stone is static; clay sits near water; water is unlimited.
/// </summary>
public class ResourceNode
{
    public MaterialKind Kind;
    public Vector2I Cell;
    public float Amount;
    public float MaxAmount;
    public float RegenPerDay;   // 0 for stone; water ignores Amount entirely

    public bool IsDepleted => Kind != MaterialKind.Water && Amount <= 0f;
}

/// <summary>
/// World generation, resource placement, and the shared resource pool (SPEC §9).
/// Grid is 256×256 (SPEC §9 performance target). No scripted town layout —
/// NPCs are dropped in and the community forms where it forms.
/// </summary>
public class World
{
    public const int GridSize = 1280;

    public List<ResourceNode> Nodes { get; } = new();

    /// <summary>Units harvested since the last daily stats snapshot.</summary>
    public float HarvestedToday;

    private readonly Random _rng;

    // Node cell index (built once — nodes never move). Only the sensing sweep
    // uses it, but that runs per-NPC constantly, so it's the one place a node
    // index genuinely pays (unlike nearest-of-kind, which stays a linear scan).
    private const int NodeCell = 32;
    private readonly Dictionary<(int, int), List<ResourceNode>> _nodeCells = new();

    private void IndexNode(ResourceNode n)
    {
        var key = ((int)(n.Cell.X / NodeCell), (int)(n.Cell.Y / NodeCell));
        if (!_nodeCells.TryGetValue(key, out var list))
            _nodeCells[key] = list = new List<ResourceNode>();
        list.Add(n);
    }

    public World(int seed)
    {
        _rng = new Random(seed);
    }

    /// <summary>
    /// Place resources: water source tiles first, clay near water,
    /// wood in clusters (groves), stone in a few deposits.
    /// TODO(Week 1): replace uniform scatter with noise-based clustering.
    /// </summary>
    public void Generate()
    {
        // Resource counts scale with area (1280² ≈ 1.23× the 1152² world) so
        // density holds across the boundless globe.
        PlaceMany(MaterialKind.Water, count: 110,  amount: float.PositiveInfinity, regen: 0f);
        PlaceMany(MaterialKind.Clay,  count: 220,  amount: 40f, regen: 0.5f);
        PlaceMany(MaterialKind.Wood,  count: 1330, amount: 30f, regen: 2f);
        PlaceMany(MaterialKind.Stone, count: 390,  amount: 80f, regen: 0f);
        PlaceMany(MaterialKind.Food,  count: 1000, amount: 20f, regen: 4f);
        PlaceMany(MaterialKind.Ore,   count: 110,  amount: 60f, regen: 0f);
        PlaceMany(MaterialKind.Herb,  count: 330,  amount: 15f, regen: 3f);
    }

    private void PlaceMany(MaterialKind kind, int count, float amount, float regen)
    {
        for (int i = 0; i < count; i++)
        {
            var node = new ResourceNode
            {
                Kind = kind,
                Cell = new Vector2I(_rng.Next(GridSize), _rng.Next(GridSize)),
                Amount = amount,
                MaxAmount = amount,
                RegenPerDay = regen,
            };
            Nodes.Add(node);
            IndexNode(node);
        }
    }

    /// <summary>
    /// Harvest respecting the harvester's sustainability weight:
    /// a South soul stops at ~50% of the node (SPEC §10) so nodes stay healthy.
    /// Taking from below the commons line marks the taker's soul — it is
    /// taking from everyone, whether anyone sees it or not.
    /// Returns the amount actually taken.
    /// </summary>
    public float Harvest(ResourceNode node, float requested, Npc npc)
    {
        if (node.Kind == MaterialKind.Water) return requested; // unlimited at source

        // Reciprocity is with the living land: floors and the commons line
        // apply only to what regrows. Minerals quarry to depletion, for
        // every soul equally, with no mark on anyone.
        bool living = node.RegenPerDay > 0f;

        float floorFraction = living ? npc.Soul.Sustainability * 0.5f : 0f;
        float takeable = Math.Max(0f, node.Amount - node.MaxAmount * floorFraction);
        float taken = Math.Min(requested, takeable);
        node.Amount -= taken;
        HarvestedToday += taken;

        if (living)
        {
            // The moral line sits below any respectful harvest floor (nature
            // souls stop at 45%) — ordinary sustainable taking never grazes
            // it, while strip-harvesting (selfish ~10%) lives deep inside it.
            float commons = node.MaxAmount * 0.4f;
            if (node.Amount < commons)
            {
                float takenBelow = Math.Min(taken, commons - node.Amount);
                npc.Imprint.OthersRegard =
                    Math.Clamp(npc.Imprint.OthersRegard + takenBelow * 0.004f, 0f, 1f);
            }
        }

        return taken;
    }

    /// <summary>Invoke action for every node within radius — used by NPCs to
    /// discover nearby nodes (addendum §4 sensing). Cell-indexed: scans only
    /// the buckets the radius touches, not all ~1,260 nodes.</summary>
    public void ForEachNodeNear(Vector2 position, float radius, System.Action<ResourceNode> action)
    {
        float r2 = radius * radius;
        int reach = (int)(radius / NodeCell) + 1;
        int cols = (GridSize + NodeCell - 1) / NodeCell;   // cells per axis
        int cx = (int)(position.X / NodeCell);
        int cy = (int)(position.Y / NodeCell);
        for (int dx = -reach; dx <= reach; dx++)
        for (int dy = -reach; dy <= reach; dy++)
        {
            int gx = ((cx + dx) % cols + cols) % cols;   // wrap at the seam
            int gy = ((cy + dy) % cols + cols) % cols;
            if (!_nodeCells.TryGetValue((gx, gy), out var list)) continue;
            foreach (var node in list)
                if (Toroidal.DistanceSquared(position, node.Cell) <= r2)
                    action(node);
        }
    }

    /// <summary>Seed a town's founders with the resources around their home,
    /// so they begin with a working local map instead of blind.</summary>
    public IEnumerable<ResourceNode> NodesWithin(Vector2 center, float radius)
    {
        float r2 = radius * radius;
        foreach (var node in Nodes)
            if (Toroidal.DistanceSquared(center, node.Cell) <= r2)
                yield return node;
    }

    /// <summary>Nearest node of a kind regardless of amount — for returning
    /// unneeded minerals to the quarry rather than carrying them forever.</summary>
    public ResourceNode? FindNearestAny(MaterialKind kind, Vector2 position)
    {
        ResourceNode? best = null;
        float bestDist = float.MaxValue;
        foreach (var node in Nodes)
        {
            if (node.Kind != kind) continue;
            float d = Toroidal.DistanceSquared(position, node.Cell);
            if (d < bestDist) { best = node; bestDist = d; }
        }
        return best;
    }

    /// <summary>
    /// Called once per in-game day by GameManager. Season multipliers throttle
    /// regeneration — winter is when the granary earns its clay.
    /// </summary>
    public void RegenerateDaily(float foodMult = 1f, float woodMult = 1f)
    {
        bool frost = foodMult < 0.1f;   // deep winter

        foreach (var node in Nodes)
        {
            // Frost kills standing food — the wild larder rots on the stem.
            // Without this, the sustainability floors act as a huge hidden
            // savings account and winter never reaches an actual villager.
            if (frost && node.Kind == MaterialKind.Food)
            {
                node.Amount = Math.Max(node.Amount * 0.93f, node.MaxAmount * 0.15f);
                continue;
            }

            if (node.RegenPerDay <= 0f) continue;
            float mult = node.Kind switch
            {
                MaterialKind.Food => foodMult,
                MaterialKind.Wood => woodMult,
                _ => 1f,
            };
            node.Amount = Math.Min(node.MaxAmount, node.Amount + node.RegenPerDay * mult);
        }
    }

    /// <summary>
    /// Nearest node this particular soul considers harvestable. What counts
    /// as "worth taking" is a moral judgment, not a world fact: a nature
    /// soul walks past a node at half strength; a selfish soul strips it to
    /// the stem. The commons' savings account only exists for those who
    /// honor it.
    /// </summary>
    public ResourceNode? FindNearest(MaterialKind kind, Vector2 position, float minFraction = 0.5f)
    {
        ResourceNode? best = null;
        float bestDist = float.MaxValue;
        foreach (var node in Nodes)
        {
            if (node.Kind != kind || node.IsDepleted) continue;
            // The harvest floor is an ethic of regrowth — it applies only to
            // living, regenerating things. Leaving half a berry bush lets it
            // live; leaving half a stone deposit protects nobody, and once
            // stranded it homelessly, we learned that the hard way (run 9).
            if (node.Kind != MaterialKind.Water && node.RegenPerDay > 0f &&
                node.Amount <= node.MaxAmount * minFraction)
                continue;
            float d = Toroidal.DistanceSquared(position, node.Cell);
            if (d < bestDist) { best = node; bestDist = d; }
        }
        return best;
    }
}