import React, { useEffect, useRef, useState } from "react";

import { FetchGraph } from "../Api.js";

// The graph view, like Obsidian's: every directory and file under a
// directory as a dot (directories in the heading colours by depth, files
// White), joined to its parent directory, and to every file that references
// it (Backend/Graph.py). With directories turned off (Settings > Graph) only
// the files and the references between them are left.
// The layout is a small force simulation: dots push each other apart and
// links pull them together until it settles. One mouse button pans (Settings
// > Graph), the other opens the dot it clicks or moves it when dragged.
// Scroll zooms.

const ChildLength = 50;
const ReferenceLength = 80;
const Repulsion = 900;
const CellSize = 160; // dots further apart than this don't push each other
const LabelZoom = 0.7; // below this, only hovered labels are drawn
const ClickSlop = 4; // pixels a click may wander and still count as a click
// Directories by depth, like the headings: h1 Purple, h2 Blue, ...
const DepthRoles = ["Purple", "Blue", "Green", "Yellow", "Orange", "Red"];
// With ShrinkByDepth, directory dots shrink in even steps from their usual
// size to a file dot's size (a file with one link) at this depth (the red
// ones), and stay that size below it.
const ShrinkDepth = 5;
const FileDotRadius = 3.8;

function ReadRole(Name) {
  return getComputedStyle(document.documentElement).getPropertyValue(`--${Name}`).trim();
}

// Starts each dot near its parent, spread around it, so the simulation
// begins close to a tree and settles quickly. Seeded, so the same directory
// always lays out the same way.
function InitialLayout(Nodes, Links) {
  let Seed = 12345;
  const Random = () => {
    Seed = (Seed * 16807) % 2147483647;
    return Seed / 2147483647;
  };
  const ById = new Map(Nodes.map((Node) => [Node.Id, Node]));
  const ChildrenOf = new Map();
  for (const Link of Links) {
    if (Link.Kind !== "Child") continue;
    if (!ChildrenOf.has(Link.Source)) ChildrenOf.set(Link.Source, []);
    ChildrenOf.get(Link.Source).push(Link.Target);
  }
  const Root = Nodes[0];
  Root.x = 0;
  Root.y = 0;
  const Queue = [Root];
  while (Queue.length) {
    const Parent = Queue.shift();
    const Children = ChildrenOf.get(Parent.Id) || [];
    const Start = Random() * Math.PI * 2;
    Children.forEach((ChildId, Index) => {
      const Child = ById.get(ChildId);
      const Angle = Start + (Index / Children.length) * Math.PI * 2;
      const Distance = ChildLength * (1 + Random() * 0.5);
      Child.x = Parent.x + Math.cos(Angle) * Distance;
      Child.y = Parent.y + Math.sin(Angle) * Distance;
      Queue.push(Child);
    });
  }
  for (const Node of Nodes) {
    Node.vx = 0;
    Node.vy = 0;
    if (Node.x === undefined) {
      Node.x = (Random() - 0.5) * 200;
      Node.y = (Random() - 0.5) * 200;
    }
  }
}

function Tick(Nodes, Links, Alpha) {
  // Repulsion between dots in the same or neighbouring grid cells.
  const Grid = new Map();
  for (const Node of Nodes) {
    const Key = `${Math.floor(Node.x / CellSize)},${Math.floor(Node.y / CellSize)}`;
    if (!Grid.has(Key)) Grid.set(Key, []);
    Grid.get(Key).push(Node);
  }
  for (const Node of Nodes) {
    const CellX = Math.floor(Node.x / CellSize);
    const CellY = Math.floor(Node.y / CellSize);
    for (let DX = -1; DX <= 1; DX++) {
      for (let DY = -1; DY <= 1; DY++) {
        const Others = Grid.get(`${CellX + DX},${CellY + DY}`);
        if (!Others) continue;
        for (const Other of Others) {
          if (Other === Node) continue;
          let X = Node.x - Other.x;
          let Y = Node.y - Other.y;
          let DistanceSquared = X * X + Y * Y;
          if (DistanceSquared > CellSize * CellSize) continue;
          if (DistanceSquared < 1) {
            X = Math.random() - 0.5;
            Y = Math.random() - 0.5;
            DistanceSquared = 1;
          }
          const Force = (Repulsion * Alpha) / DistanceSquared;
          Node.vx += X * Force;
          Node.vy += Y * Force;
        }
      }
    }
  }
  // Links pull towards their rest length.
  for (const Link of Links) {
    const A = Link.SourceNode;
    const B = Link.TargetNode;
    const X = B.x - A.x;
    const Y = B.y - A.y;
    const Distance = Math.sqrt(X * X + Y * Y) || 1;
    const Rest = Link.Kind === "Child" ? ChildLength : ReferenceLength;
    const Strength = Link.Kind === "Child" ? 0.08 : 0.03;
    const Pull = ((Distance - Rest) / Distance) * Strength * Alpha;
    A.vx += X * Pull;
    A.vy += Y * Pull;
    B.vx -= X * Pull;
    B.vy -= Y * Pull;
  }
  // A gentle pull to the middle keeps separate clusters from drifting off.
  for (const Node of Nodes) {
    Node.vx -= Node.x * 0.002 * Alpha;
    Node.vy -= Node.y * 0.002 * Alpha;
    if (Node.Pinned) {
      Node.vx = 0;
      Node.vy = 0;
      continue;
    }
    Node.vx *= 0.6;
    Node.vy *= 0.6;
    Node.x += Node.vx;
    Node.y += Node.vy;
  }
}

export default function GraphPane({
  RootName,
  DirectoryPath,
  ShowDirectories,
  PanButton,
  ColourByDepth,
  ShrinkByDepth,
  OnOpenNode,
  OnClose,
}) {
  const [Scope, SetScope] = useState("Root");
  const [Graph, SetGraph] = useState(null);
  const [Error, SetError] = useState(null);
  const CanvasRef = useRef(null);
  const StateRef = useRef(null);

  const ScopePath = Scope === "Root" ? "" : DirectoryPath;

  useEffect(() => {
    SetGraph(null);
    SetError(null);
    FetchGraph(RootName, ScopePath)
      .then(SetGraph)
      .catch((Failure) => SetError(Failure.message));
  }, [RootName, ScopePath]);

  useEffect(() => {
    if (!Graph) return undefined;
    const Canvas = CanvasRef.current;
    const Context = Canvas.getContext("2d");
    const Nodes = Graph.Nodes.filter((Node) => ShowDirectories || !Node.IsDirectory).map((Node) => ({ ...Node, Degree: 0 }));
    const ById = new Map(Nodes.map((Node) => [Node.Id, Node]));
    const Links = Graph.Links.filter(
      (Link) => (ShowDirectories || Link.Kind === "Reference") && ById.has(Link.Source) && ById.has(Link.Target),
    ).map((Link) => ({
      ...Link,
      SourceNode: ById.get(Link.Source),
      TargetNode: ById.get(Link.Target),
    }));
    const Neighbours = new Map(Nodes.map((Node) => [Node, new Set()]));
    for (const Link of Links) {
      Link.SourceNode.Degree += 1;
      Link.TargetNode.Degree += 1;
      Neighbours.get(Link.SourceNode).add(Link.TargetNode);
      Neighbours.get(Link.TargetNode).add(Link.SourceNode);
    }
    for (const Node of Nodes) {
      Node.Radius = Node.IsDirectory ? 5 + Math.sqrt(Node.Degree) * 1.6 : 3 + Math.sqrt(Node.Degree) * 0.8;
    }
    if (!Nodes.length) return undefined;
    InitialLayout(Nodes, Links);

    const Colours = {
      Background: ReadRole("Background"),
      Directory: ReadRole("Purple"),
      File: ReadRole("White"),
      Child: ReadRole("Border"),
      Reference: ReadRole("Blue"),
      Text: ReadRole("Text"),
      Muted: ReadRole("TextMuted"),
    };
    const FontFamily = ReadRole("FontFamily");
    const DepthColours = DepthRoles.map(ReadRole);
    const BaseDepth = Graph.Path ? Graph.Path.split("/").length : 0;
    for (const Node of Nodes) {
      const Depth = (Node.Id ? Node.Id.split("/").length : 0) - BaseDepth;
      if (!Node.IsDirectory) {
        Node.Colour = Colours.File;
        continue;
      }
      Node.Colour = ColourByDepth ? DepthColours[Depth % DepthColours.length] : Colours.Directory;
      if (ShrinkByDepth) {
        const Step = Math.min(Depth, ShrinkDepth) / ShrinkDepth;
        Node.Radius += (FileDotRadius - Node.Radius) * Step;
      }
    }
    // Anything but "Left" (including an old "Middle") pans with Right.
    const PanNumber = PanButton === "Left" ? 0 : 2;
    const OpenNumber = PanNumber === 0 ? 2 : 0;

    const State = {
      Zoom: 1,
      PanX: 0,
      PanY: 0,
      Alpha: 1,
      Hovered: null,
      Dragging: null,
      Panning: null,
      Moved: false,
      Frame: 0,
      Width: 0,
      Height: 0,
    };
    StateRef.current = State;

    function ToScreen(Node) {
      return [Node.x * State.Zoom + State.PanX, Node.y * State.Zoom + State.PanY];
    }

    function ToWorld(X, Y) {
      return [(X - State.PanX) / State.Zoom, (Y - State.PanY) / State.Zoom];
    }

    function Resize() {
      const Rect = Canvas.getBoundingClientRect();
      const Ratio = window.devicePixelRatio || 1;
      const First = State.Width === 0;
      State.Width = Rect.width;
      State.Height = Rect.height;
      Canvas.width = Math.round(Rect.width * Ratio);
      Canvas.height = Math.round(Rect.height * Ratio);
      Context.setTransform(Ratio, 0, 0, Ratio, 0, 0);
      if (First) {
        State.PanX = Rect.width / 2;
        State.PanY = Rect.height / 2;
      }
    }

    function Draw() {
      const Focus = State.Dragging || State.Hovered;
      const Lit = Focus ? Neighbours.get(Focus) : null;
      Context.fillStyle = Colours.Background;
      Context.fillRect(0, 0, State.Width, State.Height);

      for (const Link of Links) {
        const Touching = Focus && (Link.SourceNode === Focus || Link.TargetNode === Focus);
        Context.globalAlpha = Focus && !Touching ? 0.15 : Link.Kind === "Child" ? 0.8 : 0.9;
        Context.strokeStyle = Touching ? Colours.Directory : Link.Kind === "Child" ? Colours.Child : Colours.Reference;
        Context.lineWidth = Touching ? 1.5 : 1;
        const [X1, Y1] = ToScreen(Link.SourceNode);
        const [X2, Y2] = ToScreen(Link.TargetNode);
        Context.beginPath();
        Context.moveTo(X1, Y1);
        Context.lineTo(X2, Y2);
        Context.stroke();
      }

      Context.font = `12px ${FontFamily}`;
      Context.textAlign = "center";
      Context.textBaseline = "top";
      for (const Node of Nodes) {
        const IsLit = !Focus || Node === Focus || Lit.has(Node);
        const [X, Y] = ToScreen(Node);
        if (X < -50 || Y < -50 || X > State.Width + 50 || Y > State.Height + 50) continue;
        const Radius = Math.max(2, Node.Radius * Math.sqrt(State.Zoom));
        Context.globalAlpha = IsLit ? 1 : 0.2;
        Context.fillStyle = Node.Colour;
        Context.beginPath();
        Context.arc(X, Y, Radius, 0, Math.PI * 2);
        Context.fill();
        if (Node === Focus) {
          Context.strokeStyle = Colours.Directory;
          Context.lineWidth = 2;
          Context.beginPath();
          Context.arc(X, Y, Radius + 3, 0, Math.PI * 2);
          Context.stroke();
        }
        const ShowLabel = Focus ? IsLit : State.Zoom >= LabelZoom || Node.IsDirectory;
        if (ShowLabel) {
          Context.fillStyle = Node === Focus ? Colours.Text : Colours.Muted;
          Context.fillText(Node.Name, X, Y + Radius + 3);
        }
      }
      Context.globalAlpha = 1;
    }

    function Loop() {
      if (State.Alpha > 0.005 || State.Dragging) {
        Tick(Nodes, Links, Math.max(State.Alpha, State.Dragging ? 0.1 : 0));
        State.Alpha *= 0.985;
      }
      Draw();
      State.Frame = requestAnimationFrame(Loop);
    }

    function NodeAt(X, Y) {
      let Best = null;
      let BestDistance = Infinity;
      for (const Node of Nodes) {
        const [NX, NY] = ToScreen(Node);
        const Distance = Math.hypot(NX - X, NY - Y);
        const Reach = Math.max(6, Node.Radius * Math.sqrt(State.Zoom) + 4);
        if (Distance < Reach && Distance < BestDistance) {
          Best = Node;
          BestDistance = Distance;
        }
      }
      return Best;
    }

    function LocalPoint(Event) {
      const Rect = Canvas.getBoundingClientRect();
      return [Event.clientX - Rect.left, Event.clientY - Rect.top];
    }

    function OnMouseDown(Event) {
      const [X, Y] = LocalPoint(Event);
      const Node = NodeAt(X, Y);
      State.Moved = false;
      State.DownAt = [X, Y];
      Event.preventDefault();
      if (Event.button === OpenNumber && Node) {
        // The open button on a dot: a click opens it, a drag moves it.
        State.Dragging = Node;
        Node.Pinned = true;
      } else if (Event.button === PanNumber) {
        State.Panning = [X, Y, State.PanX, State.PanY];
      }
    }

    function OnMouseMove(Event) {
      const [X, Y] = LocalPoint(Event);
      if (State.Dragging) {
        State.Moved = State.Moved || Math.hypot(X - State.DownAt[0], Y - State.DownAt[1]) > ClickSlop;
        if (State.Moved) {
          const [WX, WY] = ToWorld(X, Y);
          State.Dragging.x = WX;
          State.Dragging.y = WY;
          State.Alpha = Math.max(State.Alpha, 0.3);
        }
        return;
      }
      if (State.Panning) {
        const [StartX, StartY, PanX, PanY] = State.Panning;
        State.PanX = PanX + X - StartX;
        State.PanY = PanY + Y - StartY;
        return;
      }
      State.Hovered = NodeAt(X, Y);
      Canvas.style.cursor = State.Hovered ? "pointer" : "grab";
    }

    function OnMouseUp() {
      const Clicked = State.Dragging && !State.Moved ? State.Dragging : null;
      if (State.Dragging) State.Dragging.Pinned = false;
      State.Dragging = null;
      State.Panning = null;
      if (Clicked) OnOpenNode(Clicked);
    }

    function OnWheel(Event) {
      Event.preventDefault();
      const [X, Y] = LocalPoint(Event);
      const [WX, WY] = ToWorld(X, Y);
      State.Zoom = Math.min(5, Math.max(0.1, State.Zoom * Math.exp(-Event.deltaY * 0.0015)));
      State.PanX = X - WX * State.Zoom;
      State.PanY = Y - WY * State.Zoom;
    }

    function OnContextMenu(Event) {
      Event.preventDefault(); // right-click pans or opens here, never the browser menu
    }

    function OnLeave() {
      State.Hovered = null;
      OnMouseUp();
    }

    Resize();
    const Observer = new ResizeObserver(Resize);
    Observer.observe(Canvas);
    Canvas.addEventListener("mousedown", OnMouseDown);
    Canvas.addEventListener("mousemove", OnMouseMove);
    window.addEventListener("mouseup", OnMouseUp);
    Canvas.addEventListener("mouseleave", OnLeave);
    Canvas.addEventListener("contextmenu", OnContextMenu);
    Canvas.addEventListener("wheel", OnWheel, { passive: false });
    State.Frame = requestAnimationFrame(Loop);

    return () => {
      cancelAnimationFrame(State.Frame);
      Observer.disconnect();
      Canvas.removeEventListener("mousedown", OnMouseDown);
      Canvas.removeEventListener("mousemove", OnMouseMove);
      window.removeEventListener("mouseup", OnMouseUp);
      Canvas.removeEventListener("mouseleave", OnLeave);
      Canvas.removeEventListener("contextmenu", OnContextMenu);
      Canvas.removeEventListener("wheel", OnWheel);
    };
  }, [Graph, ShowDirectories, PanButton, ColourByDepth, ShrinkByDepth]);

  const FileCount = Graph ? Graph.Nodes.filter((Node) => !Node.IsDirectory).length : 0;
  const DirectoryCount = Graph ? Graph.Nodes.length - FileCount : 0;

  return (
    <div className="GraphPane">
      <div className="PreviewToolbar">
        <button onClick={OnClose}>Close</button>
        <select value={Scope} onChange={(Event) => SetScope(Event.target.value)}>
          <option value="Root">Whole root</option>
          <option value="Directory" disabled={!DirectoryPath}>
            This directory{DirectoryPath ? ` (${DirectoryPath})` : ""}
          </option>
        </select>
        <span className="GraphLegend">
          {ShowDirectories && !ColourByDepth && (
            <>
              <span className="GraphLegendDirectory">●</span> Directory
            </>
          )}
          {ShowDirectories && ColourByDepth && (
            <>
              <span className="GraphLegendDirectory">●</span>
              <span className="GraphLegendDepth1">●</span>
              <span className="GraphLegendDepth2">●</span> Directories by depth
            </>
          )}
          <span className="GraphLegendFile">●</span> File
          <span className="GraphLegendReference">─</span> Reference
        </span>
        {Graph && (
          <span className="GraphCount">
            {ShowDirectories ? `${DirectoryCount} directories, ` : ""}
            {FileCount} files
            {Graph.Truncated ? " (cut short: too many to show)" : ""}
          </span>
        )}
      </div>
      {Error && <div className="PreviewEmpty">{Error}</div>}
      {!Graph && !Error && <div className="PreviewEmpty">Building the graph…</div>}
      {Graph && <canvas ref={CanvasRef} className="GraphCanvas" />}
      <div className="GraphHint">
        {PanButton === "Left"
          ? "Drag to pan, right-click a dot to open it (right-drag moves it), scroll to zoom."
          : "Right-drag to pan, click a dot to open it (drag moves it), scroll to zoom."}
      </div>
    </div>
  );
}