using UnityEngine;
using UnityEditor;
using System.Collections.Generic;
using System.Linq;

// Simple DAG data model
[System.Serializable]
public class DagNode {
    public int id;
    public string title;
    public Vector2 position;
    public float radius = 20f; // circle radius
}

[System.Serializable]
public class DagEdge {
    public int fromId;
    public int toId;
}

public class BrainEditorWindow : EditorWindow {
    readonly List<DagNode> nodes = new();
    readonly List<DagEdge> edges = new();

    Vector2 pan = Vector2.zero;
    float zoom = 1.0f;
    const float minZoom = 0.5f;
    const float maxZoom = 2.0f;

    // Vector2 dragStart;
    // bool draggingNode = false;
    // int draggingNodeId = -1;

    private readonly System.Type acceptedType = typeof(ClusterPrefab);

    [MenuItem("Window/Brain Viewer")]
    public static void ShowWindow() {
        var w = GetWindow<BrainEditorWindow>("Brain Viewer");
        w.minSize = new Vector2(500, 300);
    }

    void OnEnable() {
        // if (nodes.Count == 0)
        //     CreateSampleGraph();


        // Register callback so window updates when selection changes
        Selection.selectionChanged += OnSelectionChanged;
        RefreshSelection();
        ComputeLeftToRightLayout();
    }

    private void OnDisable() {
        Selection.selectionChanged -= OnSelectionChanged;
    }

    private void OnSelectionChanged() {
        RefreshSelection();
        ComputeLeftToRightLayout();
        Repaint();
    }

    private void RefreshSelection() {
        ClusterPrefab prefab = Selection.activeObject as ClusterPrefab;
        if (prefab != null && acceptedType.IsAssignableFrom(prefab.GetType())) {
            GenerateGraph(prefab);
        }
    }

    private void GenerateGraph(ClusterPrefab prefab) {
        nodes.Clear();
        edges.Clear();

        int ix = 0;
        foreach (Nucleus nucleus in prefab.nuclei) {
            nodes.Add(new DagNode() { id = ix, title = nucleus.name });
            if (nucleus is Neuron neuron) {
                foreach (Nucleus receiver in neuron.receivers) {
                    int receiverIx = prefab.GetNucleusIndex(receiver);
                    edges.Add(new DagEdge() { fromId = ix, toId = receiverIx });
                }
            }
            ix++;
        }
    }


    // void CreateSampleGraph() {
    //     nodes.Clear();
    //     edges.Clear();

    //     nodes.Add(new DagNode() { id = 0, title = "In1" });
    //     nodes.Add(new DagNode() { id = 1, title = "In2" });
    //     nodes.Add(new DagNode() { id = 2, title = "A" });
    //     nodes.Add(new DagNode() { id = 3, title = "B" });
    //     nodes.Add(new DagNode() { id = 4, title = "C" });
    //     nodes.Add(new DagNode() { id = 5, title = "Out1" });
    //     nodes.Add(new DagNode() { id = 6, title = "Out2" });

    //     edges.Add(new DagEdge() { fromId = 0, toId = 2 });
    //     edges.Add(new DagEdge() { fromId = 1, toId = 2 });
    //     edges.Add(new DagEdge() { fromId = 2, toId = 3 });
    //     edges.Add(new DagEdge() { fromId = 2, toId = 4 });
    //     edges.Add(new DagEdge() { fromId = 3, toId = 5 });
    //     edges.Add(new DagEdge() { fromId = 4, toId = 6 });
    // }

    void OnGUI() {
        HandleInput();

        Rect rect = new(0, 0, position.width, position.height);
        EditorGUI.DrawRect(rect, new Color(0.11f, 0.11f, 0.11f));

        // compute window center
        Vector2 windowCenter = new(position.width / 2f, position.height / 2f);

        // compute graph bounds center (in graph space)
        Rect bounds = GetGraphBounds();
        Vector2 graphCenter = bounds.center;

        // compute autoPan that recenters the graph (does not modify node positions)
        Vector2 autoPan = -graphCenter; // moves graph center to origin
                                        // total translation = windowCenter + autoPan + user pan
        Matrix4x4 oldMatrix = GUI.matrix;
        GUI.matrix = Matrix4x4.TRS(windowCenter + autoPan + pan, Quaternion.identity, Vector3.one * zoom) *
                     Matrix4x4.TRS(-windowCenter, Quaternion.identity, Vector3.one);


        // Draw edges first
        foreach (DagEdge e in edges) {
            DagNode from = GetNodeById(e.fromId);
            DagNode to = GetNodeById(e.toId);
            if (from == null || to == null) continue;
            DrawEdgeCircleNodes(from, to);
        }

        // Draw nodes (circles)
        foreach (DagNode n in nodes)
            DrawNucleus(n);

        GUI.matrix = oldMatrix;

        // Footer toolbar
        GUILayout.FlexibleSpace();
        EditorGUILayout.BeginHorizontal(EditorStyles.toolbar);
        if (GUILayout.Button("Fit", EditorStyles.toolbarButton)) FitToView();
        if (GUILayout.Button("Layout LR", EditorStyles.toolbarButton)) ComputeLeftToRightLayout();
        EditorGUILayout.EndHorizontal();
    }

    void HandleInput() {
        Event e = Event.current;

        // Zoom with scroll
        if (e.type == EventType.ScrollWheel) {
            float oldZoom = zoom;
            float delta = -e.delta.y * 0.01f;
            zoom = Mathf.Clamp(zoom + delta, minZoom, maxZoom);
            Vector2 mouse = e.mousePosition;
            pan += (mouse - new Vector2(position.width / 2, position.height / 2)) * (1 - zoom / oldZoom);
            e.Use();
        }

        // Pan with middle or right+ctrl drag
        if (e.type == EventType.MouseDrag && (e.button == 2 || (e.button == 1 && e.control))) {
            pan += e.delta;
            e.Use();
        }
    }

    DagNode GetNodeById(int id) => nodes.FirstOrDefault(x => x.id == id);
    List<DagEdge> GetIncomingEdges(DagNode node) {
        List<DagEdge> incoming = new();
        foreach (DagEdge e in edges) {
            if (e.toId == node.id)
                incoming.Add(e);
        }
        return incoming;
    }
    List<DagEdge> GetOutgoingEdges(DagNode node) {
        List<DagEdge> outgoing = new();
        foreach (DagEdge e in edges) {
            if (e.fromId == node.id)
                outgoing.Add(e);
        }
        return outgoing;
    }

    void DrawNucleus(DagNode n) {
        Vector3 position = n.position;

        Handles.color = Color.white * 0.9f;
        Handles.DrawSolidDisc(n.position, Vector3.forward, n.radius);

        if (GetIncomingEdges(n).Count == 0)
            DrawArrowHead(n.position - new Vector2(n.radius + 10, 0), n.position - new Vector2(n.radius + 5, 0), 10f / zoom, 12f / zoom, Color.white);
        if (GetOutgoingEdges(n).Count == 0)
            DrawArrowHead(n.position + new Vector2(n.radius + 10, 0), n.position + new Vector2(n.radius + 15, 0), 10f / zoom, 12f / zoom, Color.white);

        Handles.color = Color.white;
        GUIStyle style = new(EditorStyles.label) {
            alignment = TextAnchor.UpperCenter,
            normal = { textColor = Color.white },
            fontStyle = FontStyle.Bold,
        };
        Vector3 labelPos = position - Vector3.down * (n.radius + 10f); // below disc along up axis
        Handles.Label(labelPos, n.title, style);
    }

    void DrawEdgeCircleNodes(DagNode from, DagNode to) {
        Vector2 a = from.position;
        Vector2 b = to.position;
        if (a == b) return;

        Handles.color = Color.white * 0.9f;
        Handles.DrawLine(from.position, to.position);

        // Vector2 dir = (b - a).normalized;
        // Vector2 start = a + dir * from.radius;
        // Vector2 end = b - dir * to.radius;

        //DrawArrowHead(end - dir * 2f, end, 10f / zoom, 12f / zoom, Color.white);

    }

    void DrawArrowHead(Vector2 from, Vector2 to, float headWidth, float headLength, Color color) {
        Vector2 dir = (to - from).normalized;
        if (dir == Vector2.zero) return;
        Vector2 right = new Vector2(-dir.y, dir.x);

        Vector3 p1 = to;
        Vector3 p2 = to - dir * headLength + right * headWidth * 0.5f;
        Vector3 p3 = to - dir * headLength - right * headWidth * 0.5f;

        Handles.color = color;
        Handles.DrawAAConvexPolygon(p1, p2, p3);
    }

    // Left-to-right layered layout (sources on the left, sinks on the right)
    void ComputeLeftToRightLayout() {
        // build adjacency and indegree
        var adj = nodes.ToDictionary(n => n.id, n => new List<int>());
        var indeg = nodes.ToDictionary(n => n.id, n => 0);
        foreach (var e in edges) {
            if (!adj.ContainsKey(e.fromId) || !adj.ContainsKey(e.toId)) continue;
            adj[e.fromId].Add(e.toId);
            indeg[e.toId]++;
        }

        // Kahn's algorithm to compute topological layers (horizontal layers)
        Dictionary<int, int> layer = new();
        Queue<int> q = new(indeg.Where(kv => kv.Value == 0).Select(kv => kv.Key));
        foreach (var id in q) layer[id] = 0;

        while (q.Count > 0) {
            int u = q.Dequeue();
            int l = layer[u];
            foreach (var v in adj[u]) {
                // prefer placing v at least one layer after u
                if (!layer.ContainsKey(v) || layer[v] < l + 1) layer[v] = l + 1;
                indeg[v]--;
                if (indeg[v] == 0) q.Enqueue(v);
            }
        }

        // Any unreachable nodes -> assign next layers
        int maxLayer = layer.Count > 0 ? layer.Values.Max() : 0;
        foreach (var n in nodes) {
            if (!layer.ContainsKey(n.id)) {
                maxLayer++;
                layer[n.id] = maxLayer;
            }
        }

        // Group nodes by layer (left to right)
        var layers = layer.GroupBy(kv => kv.Value).OrderBy(g => g.Key).Select(g => g.Select(x => x.Key).ToList()).ToList();

        // Layout parameters (horizontal spacing drives left->right)
        float hSpacing = 150f;
        float vSpacing = 100f;

        // Place nodes: x increases with layer index, y spaced within layer
        for (int li = 0; li < layers.Count; li++) {
            var lst = layers[li];
            float totalHeight = (lst.Count - 1) * vSpacing;
            for (int i = 0; i < lst.Count; i++) {
                int id = lst[i];
                var n = GetNodeById(id);
                if (n == null) continue;
                float x = hSpacing + li * hSpacing;
                float y = 400 - totalHeight / 2f + i * vSpacing;
                // Debug.Log($"({li}, {i}) -> {x}, {y}");
                n.position = new Vector2(x, y);
            }
        }

        Repaint();
    }

    void FitToView() {
        if (nodes.Count == 0) return;
        // compute bounds including radii
        Rect bounds = new Rect(nodes[0].position - Vector2.one * nodes[0].radius, Vector2.one * nodes[0].radius * 2f);
        foreach (var n in nodes)
            bounds = RectUnion(bounds, new Rect(n.position - Vector2.one * n.radius, Vector2.one * n.radius * 2f));

        // center graph at origin (0,0) then set pan so it appears centered in window
        Vector2 graphCenter = bounds.center;
        // move nodes so center is at origin
        for (int i = 0; i < nodes.Count; i++)
            nodes[i].position -= graphCenter;

        // reset pan/zoom so centered
        pan = Vector2.zero;
        zoom = 1.0f;
        Repaint();
    }


    static Rect RectUnion(Rect a, Rect b) {
        float xMin = Mathf.Min(a.xMin, b.xMin);
        float xMax = Mathf.Max(a.xMax, b.xMax);
        float yMin = Mathf.Min(a.yMin, b.yMin);
        float yMax = Mathf.Max(a.yMax, b.yMax);
        return Rect.MinMaxRect(xMin, yMin, xMax, yMax);
    }

    Vector2 ScreenToGraph_old(Vector2 screenPos) {
        Vector2 origin = new Vector2(position.width / 2, position.height / 2);
        // invert the GUI.matrix transform (approx for current simple transforms)
        return (screenPos - (origin + pan)) / zoom + origin * (1 - 1 / zoom);
    }
    Vector2 ScreenToGraph(Vector2 screenPos) {
        Vector2 windowCenter = new Vector2(position.width / 2f, position.height / 2f);
        Rect bounds = GetGraphBounds();
        Vector2 graphCenter = bounds.center;
        Vector2 autoPan = -graphCenter;
        // inverse of: screen -> translate by -(windowCenter+autoPan+pan), scale by 1/zoom, translate by windowCenter
        return (screenPos - (windowCenter + autoPan + pan)) / zoom + windowCenter;
    }


    Rect GetGraphBounds() {
        if (nodes == null || nodes.Count == 0) return new Rect(Vector2.zero, Vector2.one);
        Rect bounds = new(
            nodes[0].position - Vector2.one * nodes[0].radius,
            2f * nodes[0].radius * Vector2.one);
        foreach (var n in nodes)
            bounds = RectUnion(bounds,
                new Rect(n.position - Vector2.one * n.radius, 2f * n.radius * Vector2.one));
        return bounds;
    }



    int HitTestNode(Vector2 graphPos) {
        // returns node id under point or -1
        for (int i = nodes.Count - 1; i >= 0; i--) {
            var n = nodes[i];
            if ((graphPos - n.position).sqrMagnitude <= n.radius * n.radius) return n.id;
        }
        return -1;
    }

}