"use client";

import {
  Background,
  BackgroundVariant,
  Controls,
  MarkerType,
  ReactFlow,
  useEdgesState,
  useNodesState,
  type Edge,
  type EdgeChange,
  type EdgeTypes,
  type Node,
  type NodeChange,
  type NodeTypes,
  ReactFlowProvider,
} from "@xyflow/react";
import "@xyflow/react/dist/style.css";
import {
  LayoutGridIcon,
  Loader2Icon,
  MagnetIcon,
  PlusIcon,
  SaveIcon,
  TriangleAlertIcon,
} from "lucide-react";
import { useRouter } from "next/navigation";
import React from "react";

import { Button } from "@/components/ui/button";

import { CategoryBand, type CategoryBandData, type CategoryBandNode } from "./CategoryBand";
import {
  loadEdgeRoutes,
  routeKey,
  saveEdgeRoutes,
  type EdgeRouteMap,
  type RouteWaypoint,
} from "./edgeRoutes";
import { type RouteRect } from "./edgeRouting";
import { edgeVisuals, type EdgeRef } from "./edgeVisuals";
import { applyPins, pinsToFreeze, type CanvasPosition } from "./freeze";
import { computeLayout } from "./layout";
import { mapCategoryDoc, mapTechDoc } from "./mappers";
import { addPrerequisite, buildPrereqRows, removePrerequisite, withPrereqs } from "./prereqEdits";
import { QuickCreateDialog, type QuickCreateResult } from "./QuickCreateDialog";
import { RoutedEdge } from "./RoutedEdge";
import { TechNodeCard, type TechNodeData, type TechNodeModel } from "./TechNode";
import { TechPreviewPanel } from "./TechPreviewPanel";
import {
  COLUMN_STEP,
  NODE_HEIGHT,
  NODE_WIDTH,
  type TreeCategory,
  type TreeTech,
} from "./types";

type ResourceEntry = { id: number; name: string };

export interface TechTreeData {
  techs: TreeTech[];
  categories: TreeCategory[];
  resources: ResourceEntry[];
  canCreate: boolean;
  canCreateCategories: boolean;
  canUpdate: boolean;
  canSetFinalApproval: boolean;
}

/** Tactical chrome for the canvas toolbar controls. */
const TACTICAL_BUTTON =
  "rounded-none border border-white/20 bg-black/50 font-mono text-[10px] tracking-widest uppercase text-white/80 hover:border-white/45 hover:bg-white/10 hover:text-white";

/**
 * Snap-to-grid size (px). Divides COLUMN_STEP (368) and ROW_STEP (184), so a
 * snapped card lines up with the automatic layout instead of drifting off it.
 */
const SNAP_GRID = 46;
const SNAP_STORAGE_KEY = "ptf:tech-tree:snap-to-grid";

const nodeTypes: NodeTypes = {
  techCard: TechNodeCard,
  techBand: CategoryBand,
};

const edgeTypes: EdgeTypes = {
  routed: RoutedEdge,
};

function refLabel(id: number): string {
  return `REF ${id.toString().padStart(3, "0")}`;
}

function buildFlowNodes(
  techs: TreeTech[],
  categories: TreeCategory[],
  layout: ReturnType<typeof computeLayout>,
  connectable: boolean,
): Node[] {
  const warningsByTech = new Map<number, number>();
  for (const warning of layout.warnings) {
    warningsByTech.set(warning.techId, (warningsByTech.get(warning.techId) ?? 0) + 1);
  }
  const categoryById = new Map(categories.map((c) => [c.id, c]));

  const bandNodes: CategoryBandNode[] = layout.bands.map((band) => {
    const memberIds =
      band.key === "uncategorized"
        ? techs
            .filter((t) => t.categoryId === null || !categoryById.has(t.categoryId))
            .map((t) => t.id)
        : techs
            .filter((t) => t.categoryId === Number(band.key.replace("cat-", "")))
            .map((t) => t.id);
    return {
      id: band.key,
      type: "techBand",
      position: { x: band.x, y: band.y },
      // Draggable only from its header (dragHandle), so the band body stays a
      // click-through backdrop while the header moves the whole category.
      draggable: true,
      dragHandle: ".tech-band-drag-handle",
      selectable: false,
      deletable: false,
      zIndex: 0,
      // The band body must never swallow pointer events, otherwise edges under a
      // band cannot be selected and pane clicks die. The header re-enables them.
      style: { width: band.width, height: band.height, pointerEvents: "none" },
      data: { band, techCount: memberIds.length, memberIds },
    };
  });

  const techById = new Map(techs.map((t) => [t.id, t]));
  const techNodes: TechNodeModel[] = layout.nodes.map((node) => {
    const tech = techById.get(node.techId)!;
    return {
      id: String(tech.id),
      type: "techCard",
      position: { x: node.x, y: node.y },
      zIndex: 1,
      style: { width: NODE_WIDTH, height: NODE_HEIGHT },
      data: {
        tech,
        categoryName: tech.categoryId ? categoryById.get(tech.categoryId)?.name ?? null : null,
        refLabel: refLabel(tech.id),
        hasWarning: warningsByTech.has(tech.id),
        connectable,
      },
    };
  });

  return [...bandNodes, ...techNodes];
}

function withAlpha(hex: string, alpha: number): string {
  const value = hex.replace("#", "");
  const r = parseInt(value.slice(0, 2), 16);
  const g = parseInt(value.slice(2, 4), 16);
  const b = parseInt(value.slice(4, 6), 16);
  return `rgba(${r},${g},${b},${alpha})`;
}

/**
 * Prerequisite edges. Each edge takes its progression path's color and its own
 * lane (see edgeVisuals). With a technology selected, edges that do not touch
 * it fade back so its connections stand out.
 */
function buildFlowEdges(
  techs: TreeTech[],
  layout: ReturnType<typeof computeLayout>,
  selectedId: string | null,
  edgeRoutes: EdgeRouteMap,
  editable: boolean,
  onRouteChange: (routeId: string, waypoints: RouteWaypoint[]) => void,
): Edge[] {
  const known = new Set(techs.map((t) => t.id));
  const refs: EdgeRef[] = [];
  const isOr = new Set<string>();
  for (const tech of techs) {
    for (const prereqId of tech.prereqAnd) {
      if (prereqId === tech.id || !known.has(prereqId)) continue;
      refs.push({ id: `and-${prereqId}-${tech.id}`, source: prereqId, target: tech.id });
    }
    for (const prereqId of tech.prereqOr) {
      if (prereqId === tech.id || !known.has(prereqId)) continue;
      const id = `or-${prereqId}-${tech.id}`;
      if (refs.some((r) => r.id === id)) continue;
      refs.push({ id, source: prereqId, target: tech.id });
      isOr.add(id);
    }
  }

  const positions = new Map(layout.nodes.map((n) => [n.techId, { x: n.x, y: n.y }]));
  const visuals = edgeVisuals(techs, refs, positions, COLUMN_STEP);
  const focus = selectedId ? Number(selectedId) : null;

  // Node rectangles for obstacle avoidance; each edge excludes its own ends.
  const obstacles: RouteRect[] = layout.nodes.map((n) => ({
    id: n.techId,
    x: n.x,
    y: n.y,
    width: NODE_WIDTH,
    height: NODE_HEIGHT,
  }));

  return refs.map((ref) => {
    const visual = visuals.get(ref.id)!;
    const or = isOr.has(ref.id);
    const related = focus === null || ref.source === focus || ref.target === focus;
    const alpha = focus === null ? 0.8 : related ? 1 : 0.12;
    const stroke = withAlpha(visual.color, alpha);
    const routeId = routeKey(ref.source, ref.target);
    return {
      id: ref.id,
      source: String(ref.source),
      target: String(ref.target),
      type: "routed",
      animated: or,
      zIndex: focus !== null && related ? 2 : 0,
      style: {
        stroke,
        strokeWidth: focus !== null && related ? 2.25 : 1.5,
        ...(or ? { strokeDasharray: "6 4" } : {}),
      },
      markerEnd: { type: MarkerType.ArrowClosed, color: stroke },
      ...(or
        ? {
            label: "OR",
            labelStyle: { fill: stroke, fontSize: 9, fontFamily: "monospace" },
            labelBgStyle: { fill: "rgba(0,0,0,0.85)", fillOpacity: 0.9 },
          }
        : {}),
      data: {
        pathRoot: visual.pathRoot,
        waypoints: edgeRoutes[routeId] ?? [],
        routeId,
        sourceId: ref.source,
        targetId: ref.target,
        obstacles,
        stepPosition: visual.stepPosition,
        editable,
        onRouteChange,
      },
    } as Edge;
  });
}

/**
 * Persist canvas positions in ONE request (one SQL statement server-side).
 * Never PATCH per node: dozens of concurrent document updates exhausted the
 * database pool and could take the server down. Null x/y clears a pin.
 */
async function saveTreePositions(
  updates: { id: number; x: number | null; y: number | null }[],
): Promise<void> {
  if (updates.length === 0) return;
  const res = await fetch("/api/tech-tree/positions", {
    method: "POST",
    credentials: "same-origin",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ positions: updates }),
  });
  if (!res.ok) {
    const body = await res.json().catch(() => null);
    throw new Error(body?.error || `Could not save positions (HTTP ${res.status}).`);
  }
}

async function fetchCollection<T>(slug: string): Promise<T[]> {
  const res = await fetch(`/api/${slug}?limit=0&depth=0&sort=name`, {
    credentials: "same-origin",
  });
  if (!res.ok) return [];
  const body = await res.json();
  return body?.docs ?? [];
}

function CanvasInner({ data }: { data: TechTreeData }) {
  const router = useRouter();
  const [techs, setTechs] = React.useState(data.techs);
  const [categories, setCategories] = React.useState(data.categories);
  const [resources, setResources] = React.useState(data.resources);
  const [selectedId, setSelectedId] = React.useState<string | null>(null);
  const [createOpen, setCreateOpen] = React.useState(false);
  // Label of the layout write in flight ("Arranging...", "Saving positions...");
  // null when idle. Drives the toolbar status chip and locks layout controls.
  const [layoutBusy, setLayoutBusy] = React.useState<string | null>(null);

  // Manual edge routing, loaded from this browser's storage on mount. Empty =
  // the edge draws its automatic path.
  const [edgeRoutes, setEdgeRoutes] = React.useState<EdgeRouteMap>({});
  React.useEffect(() => {
    setEdgeRoutes(loadEdgeRoutes());
  }, []);
  const handleRouteChange = React.useCallback(
    (routeId: string, waypoints: RouteWaypoint[]) => {
      setEdgeRoutes((prev) => {
        const next = { ...prev };
        if (waypoints.length === 0) delete next[routeId];
        else next[routeId] = waypoints;
        saveEdgeRoutes(next);
        return next;
      });
    },
    [],
  );

  const layout = React.useMemo(() => computeLayout(techs, categories), [techs, categories]);
  const flowNodes = React.useMemo(
    () => buildFlowNodes(techs, categories, layout, data.canUpdate),
    [techs, categories, layout, data.canUpdate],
  );
  const flowEdges = React.useMemo(
    () =>
      buildFlowEdges(techs, layout, selectedId, edgeRoutes, data.canUpdate, handleRouteChange),
    [techs, layout, selectedId, edgeRoutes, data.canUpdate, handleRouteChange],
  );

  // Controlled nodes/edges: React Flow needs the change handlers to apply
  // drag and selection updates in controlled mode.
  const [nodes, setNodes, onNodesChange] = useNodesState<Node>([]);
  React.useEffect(() => {
    setNodes(flowNodes);
  }, [flowNodes, setNodes]);

  const [edges, setEdges, onEdgesChange] = useEdgesState<Edge>([]);
  React.useEffect(() => {
    setEdges(flowEdges);
  }, [flowEdges, setEdges]);

  // Latest rendered card positions, read by the freeze diff below.
  const nodesRef = React.useRef<Node[]>([]);
  nodesRef.current = nodes;
  const currentPositions = React.useCallback((): Map<number, CanvasPosition> => {
    const map = new Map<number, CanvasPosition>();
    for (const node of nodesRef.current) {
      if (node.type !== "techCard") continue;
      map.set(Number(node.id), { x: node.position.x, y: node.position.y });
    }
    return map;
  }, []);

  /** Persist freeze pins (skipping ids whose own PATCH already carries one). */
  const persistPins = React.useCallback(
    async (pins: Map<number, CanvasPosition>, skip: Set<number> = new Set()) => {
      await saveTreePositions(
        [...pins].filter(([id]) => !skip.has(id)).map(([id, pin]) => ({ id, x: pin.x, y: pin.y })),
      );
    },
    [],
  );

  // Nodes are data-driven: block React Flow's own remove changes so Backspace
  // can never blank a node out of the canvas (positions/selection still flow).
  const handleNodesChange = React.useCallback(
    (changes: NodeChange<Node>[]) => {
      const allowed = changes.filter((change) => change.type !== "remove");
      if (allowed.length > 0) onNodesChange(allowed);
    },
    [onNodesChange],
  );

  // Edge removal is a data change (it drops a prerequisite), handled in
  // onEdgesDelete; selection changes still flow so edges can be picked.
  const handleEdgesChange = React.useCallback(
    (changes: EdgeChange[]) => {
      const allowed = changes.filter((change) => change.type !== "remove");
      if (allowed.length > 0) onEdgesChange(allowed);
    },
    [onEdgesChange],
  );

  const [connectError, setConnectError] = React.useState<string | null>(null);
  React.useEffect(() => {
    if (!connectError) return;
    const timer = window.setTimeout(() => setConnectError(null), 6000);
    return () => window.clearTimeout(timer);
  }, [connectError]);

  const hasManualPositions = techs.some((t) => t.treePosition !== null);

  const [saveStatus, setSaveStatus] = React.useState<string | null>(null);
  React.useEffect(() => {
    if (!saveStatus) return;
    const timer = window.setTimeout(() => setSaveStatus(null), 3000);
    return () => window.clearTimeout(timer);
  }, [saveStatus]);

  // Snap-to-grid setting (default on). Persisted per browser so it survives a
  // reload; read in an effect to avoid an SSR/client hydration mismatch.
  const [snapToGrid, setSnapToGrid] = React.useState(true);
  React.useEffect(() => {
    try {
      const stored = window.localStorage.getItem(SNAP_STORAGE_KEY);
      if (stored !== null) setSnapToGrid(stored === "true");
    } catch {
      // Storage can be unavailable (private mode); keep the default.
    }
  }, []);
  const toggleSnapToGrid = React.useCallback(() => {
    setSnapToGrid((prev) => {
      const next = !prev;
      try {
        window.localStorage.setItem(SNAP_STORAGE_KEY, String(next));
      } catch {
        // ignore
      }
      return next;
    });
  }, []);
  const snapValue = React.useCallback(
    (v: number) => (snapToGrid ? Math.round(v / SNAP_GRID) * SNAP_GRID : Math.round(v)),
    [snapToGrid],
  );

  const patchPrereqs = React.useCallback(
    async (
      targetId: number,
      lists: { and: number[]; or: number[] },
      pin?: { x: number; y: number },
    ) => {
      const res = await fetch(`/api/technologies/${targetId}`, {
        method: "PATCH",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({
          requirements: { prerequisiteTechnologies: buildPrereqRows(lists) },
          ...(pin ? { treePosition: pin } : {}),
        }),
      });
      if (!res.ok) {
        const body = await res.json().catch(() => null);
        throw new Error(body?.errors?.[0]?.message || `Save failed (HTTP ${res.status}).`);
      }
    },
    [],
  );

  const handleConnect = React.useCallback(
    async (connection: { source: string | null; target: string | null }) => {
      if (!connection.source || !connection.target) return;
      const sourceId = Number(connection.source);
      const targetId = Number(connection.target);
      const result = addPrerequisite(techs, targetId, sourceId, "and");
      if (!result.ok) {
        setConnectError(result.error);
        return;
      }
      setConnectError(null);

      // Stability: nothing on screen moves because of a connection. Every card
      // the ordered layout would relocate (the target, its dependents, column
      // neighbours) is pinned where it sits; "Auto-arrange" re-orders them.
      const updated = techs.map((t) =>
        t.id === targetId ? withPrereqs(t, result.lists) : t,
      );
      const pins = pinsToFreeze(currentPositions(), updated, categories);
      setTechs(applyPins(updated, pins));
      try {
        await patchPrereqs(targetId, result.lists, pins.get(targetId));
        await persistPins(pins, new Set([targetId]));
      } catch (e) {
        setConnectError(e instanceof Error ? e.message : "Could not save the connection.");
        await refresh();
      }
    },
    // eslint-disable-next-line react-hooks/exhaustive-deps
    [techs, categories, patchPrereqs, currentPositions, persistPins],
  );

  const handleEdgesDelete = React.useCallback(
    async (deleted: Edge[]) => {
      let next = techs;
      const listsByTarget = new Map<number, { and: number[]; or: number[] }>();
      for (const edge of deleted) {
        const targetId = Number(edge.target);
        const result = removePrerequisite(next, targetId, Number(edge.source));
        if (!result.ok) continue;
        listsByTarget.set(targetId, result.lists);
        next = next.map((t) => (t.id === targetId ? withPrereqs(t, result.lists) : t));
      }
      if (listsByTarget.size === 0) return;
      const pins = pinsToFreeze(currentPositions(), next, categories);
      setTechs(applyPins(next, pins));
      try {
        for (const [targetId, lists] of listsByTarget) {
          await patchPrereqs(targetId, lists, pins.get(targetId));
        }
        await persistPins(pins, new Set(listsByTarget.keys()));
      } catch (e) {
        setConnectError(e instanceof Error ? e.message : "Could not remove the prerequisite.");
        await refresh();
      }
    },
    // eslint-disable-next-line react-hooks/exhaustive-deps
    [techs, categories, patchPrereqs, currentPositions, persistPins],
  );

  /**
   * Persist one or more card positions to `treePosition` (optimistic local
   * update first, then one bulk write). Used by card drags (a multi-selection
   * moves several cards at once) and by category-band drags (every member).
   */
  const persistPositions = React.useCallback(
    async (positions: { id: number; x: number; y: number }[]) => {
      if (positions.length === 0) return;
      const byId = new Map(positions.map((p) => [p.id, p]));
      setTechs((prev) =>
        prev.map((t) => {
          const p = byId.get(t.id);
          return p ? { ...t, treePosition: { x: p.x, y: p.y } } : t;
        }),
      );
      try {
        await saveTreePositions(positions);
      } catch (e) {
        // The optimistic position stays on screen; a reload shows what is stored.
        setConnectError(e instanceof Error ? e.message : "Could not save positions.");
      }
    },
    [],
  );

  // Live session for a category-band drag: the header moves the band and every
  // member card moves with it (positions are committed on drag stop).
  const bandDragRef = React.useRef<{
    bandId: string;
    start: { x: number; y: number };
    members: Map<number, { x: number; y: number }>;
  } | null>(null);

  const handleNodeDragStart = React.useCallback((node: Node) => {
    if (node.type !== "techBand") {
      bandDragRef.current = null;
      return;
    }
    // The drag callbacks only hand us the DRAGGED set (just this band), so read
    // the member cards' start positions from the full rendered node list.
    const memberIds = (node.data as CategoryBandData).memberIds ?? [];
    const members = new Map<number, { x: number; y: number }>();
    for (const id of memberIds) {
      const card = nodesRef.current.find((candidate) => candidate.id === String(id));
      if (card) members.set(id, { x: card.position.x, y: card.position.y });
    }
    bandDragRef.current = {
      bandId: node.id,
      start: { x: node.position.x, y: node.position.y },
      members,
    };
  }, []);

  const handleNodeDrag = React.useCallback(
    (node: Node) => {
      const session = bandDragRef.current;
      if (!session || node.type !== "techBand" || session.bandId !== node.id) return;
      const dx = node.position.x - session.start.x;
      const dy = node.position.y - session.start.y;
      setNodes((prev) =>
        prev.map((n) => {
          if (n.type !== "techCard") return n;
          const start = session.members.get(Number(n.id));
          if (!start) return n;
          return { ...n, position: { x: start.x + dx, y: start.y + dy } };
        }),
      );
    },
    [setNodes],
  );

  const handleNodeDragStop = React.useCallback(
    (node: Node, allNodes: Node[]) => {
      if (node.type === "techBand") {
        const session = bandDragRef.current;
        bandDragRef.current = null;
        if (!session) return;
        const dx = node.position.x - session.start.x;
        const dy = node.position.y - session.start.y;
        void persistPositions(
          [...session.members].map(([id, start]) => ({
            id,
            x: snapValue(start.x + dx),
            y: snapValue(start.y + dy),
          })),
        );
        return;
      }
      // A card drag can move a whole multi-selection: persist every dragged card
      // (React Flow hands us the full set, not just the one under the pointer).
      const cards = allNodes.filter((n) => n.type === "techCard");
      if (cards.length === 0) return;
      void persistPositions(
        cards.map((n) => ({
          id: Number(n.id),
          x: snapValue(n.position.x),
          y: snapValue(n.position.y),
        })),
      );
    },
    [persistPositions, snapValue],
  );

  const handleSavePositions = React.useCallback(async () => {
    // Commit the current on-screen position of every node to treePosition, so
    // the exact arrangement survives a reload. Unlike a drag (one node) or a
    // connection (only what would move), this pins the whole tree to whatever
    // React Flow actually rendered.
    const pins = new Map<number, CanvasPosition>();
    const current = currentPositions();
    for (const tech of techs) {
      const pos = current.get(tech.id);
      if (pos) {
        pins.set(tech.id, { x: Math.round(pos.x), y: Math.round(pos.y) });
      }
    }
    if (pins.size === 0) {
      setSaveStatus("Nothing to save.");
      return;
    }
    if (layoutBusy) return;
    setTechs((prev) =>
      prev.map((t) => {
        const pin = pins.get(t.id);
        return pin ? { ...t, treePosition: pin } : t;
      }),
    );
    setLayoutBusy("Saving positions...");
    setConnectError(null);
    try {
      await persistPins(pins);
      setSaveStatus(`Positions saved. ${pins.size} node(s).`);
    } catch (e) {
      setConnectError(e instanceof Error ? e.message : "Could not save positions.");
    } finally {
      setLayoutBusy(null);
    }
  }, [techs, currentPositions, persistPins, layoutBusy]);

  const handleAutoArrange = React.useCallback(async () => {
    const pinned = techs.filter((t) => t.treePosition !== null);
    if (pinned.length === 0 || layoutBusy) return;
    const previous = new Map(pinned.map((t) => [t.id, t.treePosition]));

    // Optimistic: re-lay the canvas out at once so the click visibly does
    // something, then persist every cleared pin in a single request.
    setLayoutBusy("Arranging...");
    setConnectError(null);
    setTechs((prev) => prev.map((t) => (t.treePosition ? { ...t, treePosition: null } : t)));
    try {
      await saveTreePositions(pinned.map((t) => ({ id: t.id, x: null, y: null })));
      setSaveStatus(`Layout reset. ${pinned.length} node(s) re-arranged.`);
    } catch (e) {
      // Put the pins back so the canvas matches what is actually stored.
      setTechs((prev) =>
        prev.map((t) => (previous.has(t.id) ? { ...t, treePosition: previous.get(t.id) ?? null } : t)),
      );
      setConnectError(e instanceof Error ? e.message : "Could not reset the layout.");
    } finally {
      setLayoutBusy(null);
    }
  }, [techs, layoutBusy]);

  const techById = React.useMemo(
    () => new Map(techs.map((t) => [String(t.id), t])),
    [techs],
  );
  const selectedTech = selectedId ? techById.get(selectedId) ?? null : null;

  /**
   * Re-read the tree. With `freeze`, cards the fresh data would relocate are
   * pinned at their current spot first (panel saves, quick-create), so the
   * canvas stays still. Error recovery calls it without freeze to show truth.
   */
  const refresh = React.useCallback(
    async (options: { freeze?: boolean } = {}) => {
      const [techDocs, categoryDocs, resourceDocs] = await Promise.all([
        fetchCollection<Record<string, unknown>>("technologies"),
        fetchCollection<Record<string, unknown>>("tech-categories"),
        fetchCollection<Record<string, unknown>>("resources"),
      ]);
      let nextTechs = techDocs.map(mapTechDoc);
      const nextCategories = categoryDocs.map(mapCategoryDoc);
      if (options.freeze) {
        const pins = pinsToFreeze(currentPositions(), nextTechs, nextCategories);
        nextTechs = applyPins(nextTechs, pins);
        persistPins(pins).catch((e: unknown) =>
          setConnectError(e instanceof Error ? e.message : "Could not save positions."),
        );
      }
      setTechs(nextTechs);
      setCategories(nextCategories);
      setResources(resourceDocs.map((d) => ({ id: d.id as number, name: String(d.name ?? "") })));
    },
    [currentPositions, persistPins],
  );

  const handleCreated = React.useCallback(
    async (result: QuickCreateResult) => {
      await refresh({ freeze: true });
      setSelectedId(String(result.techId));
      router.push(`/admin/collections/technologies/${result.techId}`);
    },
    [refresh, router],
  );

  const selectedWarnings = React.useMemo(
    () =>
      selectedTech
        ? layout.warnings.filter((w) => w.techId === selectedTech.id).map((w) => w.message)
        : [],
    [selectedTech, layout],
  );

  return (
    <div
      className="relative tech-tree-canvas"
      style={{
        height: "calc(100dvh - 56px)",
        backgroundColor: "#05070a",
      }}
      data-testid="tech-tree-canvas"
    >
      <ReactFlow
        nodes={nodes}
        edges={edges}
        onNodesChange={handleNodesChange}
        onEdgesChange={handleEdgesChange}
        nodeTypes={nodeTypes}
        edgeTypes={edgeTypes}
        fitView
        fitViewOptions={{ padding: 0.15, maxZoom: 0.85 }}
        minZoom={0.08}
        // Freeze dragging while a layout write is in flight so a drag cannot
        // race (and be overwritten by) the bulk save.
        nodesDraggable={layoutBusy === null}
        snapToGrid={snapToGrid}
        snapGrid={[SNAP_GRID, SNAP_GRID]}
        nodesConnectable={data.canUpdate}
        onConnect={(connection) => {
          void handleConnect(connection);
        }}
        onConnectEnd={(event, connectionState) => {
          // React Flow only resolves drops onto a handle. If the pointer was
          // released over a node card instead, resolve that card ourselves so
          // "drag onto the technology" works the way people expect. Validation
          // (duplicates, cycles) lives in handleConnect, which reports errors.
          if (!data.canUpdate) return;
          if (!("fromNode" in connectionState)) return;
          if (connectionState.toHandle) return; // dropped on a handle: onConnect leads
          const sourceId = connectionState.fromNode?.id;
          if (!sourceId) return;
          const point = event as MouseEvent;
          const element = document.elementFromPoint(point.clientX ?? 0, point.clientY ?? 0);
          const nodeElement = element?.closest?.(".react-flow__node") as HTMLElement | null;
          const targetId = nodeElement?.getAttribute("data-id");
          if (!targetId || targetId === sourceId) return;
          void handleConnect({ source: sourceId, target: targetId });
        }}
        onEdgesDelete={(deleted) => {
          void handleEdgesDelete(deleted);
        }}
        onNodeClick={(event, node) => {
          // Ctrl/Cmd-click is a multi-select gesture, not an edit gesture: do not
          // pop the side panel, which would cover the canvas mid-selection.
          if (event.ctrlKey || event.metaKey) return;
          if (node.type === "techCard") setSelectedId(node.id);
        }}
        onNodeDragStart={(_, node) => handleNodeDragStart(node)}
        onNodeDrag={(_, node) => handleNodeDrag(node)}
        onNodeDragStop={(_, node, draggedNodes) => handleNodeDragStop(node, draggedNodes)}
        onPaneClick={() => setSelectedId(null)}
        proOptions={{ hideAttribution: false }}
      >
        <Background
          variant={BackgroundVariant.Lines}
          gap={SNAP_GRID}
          size={1}
          color="rgba(255,255,255,0.055)"
        />
        <Controls showInteractive={false} />
      </ReactFlow>

      {/* Toolbar */}
      <div className="absolute top-4 left-4 z-20 flex items-center gap-3 rounded-none border border-white/15 bg-black/60 px-3 py-2 backdrop-blur-sm">
        <span className="font-mono text-[10px] tracking-widest text-white/60 uppercase">
          TECH TREE // COMMAND
        </span>
        {layout.warnings.length > 0 ? (
          <span
            className="flex items-center gap-1 font-mono text-[10px] tracking-widest text-amber-400 uppercase"
            title={layout.warnings.map((w) => w.message).join("\n")}
            data-testid="tech-tree-warnings"
          >
            <TriangleAlertIcon className="size-3" />
            {layout.warnings.length} TIMELINE WARNING{layout.warnings.length === 1 ? "" : "S"}
          </span>
        ) : null}
        {connectError ? (
          <span
            className="font-mono text-[10px] tracking-widest text-red-400 uppercase"
            data-testid="tech-tree-connect-error"
          >
            {connectError}
          </span>
        ) : null}
        {layoutBusy ? (
          <span
            role="status"
            aria-live="polite"
            className="flex items-center gap-1.5 font-mono text-[10px] tracking-widest text-[#67e8f9] uppercase"
            data-testid="tech-tree-layout-busy"
          >
            <Loader2Icon className="size-3 animate-spin" />
            {layoutBusy}
          </span>
        ) : saveStatus ? (
          <span
            className="font-mono text-[10px] tracking-widest text-emerald-400 uppercase"
            data-testid="tech-tree-save-status"
          >
            {saveStatus}
          </span>
        ) : null}
        {data.canUpdate ? (
          <Button
            size="sm"
            variant="ghost"
            onClick={toggleSnapToGrid}
            aria-pressed={snapToGrid}
            title="Snap dragged cards to the grid so they line up with the layout"
            data-testid="tech-tree-snap-toggle"
            className={
              snapToGrid
                ? `${TACTICAL_BUTTON} border-[#22d3ee]/60 bg-[#22d3ee]/15 text-[#a5f3fc] hover:border-[#22d3ee]/80 hover:bg-[#22d3ee]/20 hover:text-[#cffafe]`
                : TACTICAL_BUTTON
            }
          >
            <MagnetIcon className="size-3.5" />
            Snap: {snapToGrid ? "On" : "Off"}
          </Button>
        ) : null}
        {data.canUpdate ? (
          <Button
            size="sm"
            variant="ghost"
            onClick={handleSavePositions}
            disabled={layoutBusy !== null}
            title="Save the current positions of every node so the layout stays the same on your next visit"
            data-testid="tech-tree-save-positions"
            className={TACTICAL_BUTTON}
          >
            <SaveIcon className="size-3.5" />
            Save positions
          </Button>
        ) : null}
        {data.canUpdate && hasManualPositions ? (
          <Button
            size="sm"
            variant="ghost"
            onClick={handleAutoArrange}
            disabled={layoutBusy !== null}
            title="Clear manual node positions and restore the automatic layout"
            data-testid="tech-tree-auto-arrange"
            className={TACTICAL_BUTTON}
          >
            <LayoutGridIcon className="size-3.5" />
            Auto-arrange
          </Button>
        ) : null}
        {data.canCreate ? (
          <Button
            size="sm"
            variant="ghost"
            onClick={() => setCreateOpen(true)}
            data-testid="tech-tree-create"
            className={`${TACTICAL_BUTTON} border-[#22d3ee]/40 text-[#67e8f9] hover:border-[#22d3ee]/70 hover:bg-[#22d3ee]/10 hover:text-[#a5f3fc]`}
          >
            <PlusIcon className="size-3.5" />
            New Technology
          </Button>
        ) : null}
        {data.canUpdate ? (
          <span className="hidden font-mono text-[9px] tracking-widest text-white/35 uppercase lg:inline">
            DRAG NODE EDGE TO LINK A PREREQUISITE · SELECT AN EDGE + BACKSPACE TO REMOVE
          </span>
        ) : null}
      </div>

      {/* Empty state */}
      {techs.length === 0 ? (
        <div className="pointer-events-none absolute inset-0 z-10 flex items-center justify-center">
          <div className="pointer-events-auto rounded-none border border-white/15 bg-black/70 px-6 py-5 text-center backdrop-blur-sm">
            <p className="font-mono text-[10px] tracking-widest text-white/50 uppercase">
              NO TECHNOLOGIES ON RECORD
            </p>
            <p className="mt-1 text-sm text-white/70">
              Create the first technology to start the tree.
            </p>
            {data.canCreate ? (
              <Button
                className={`${TACTICAL_BUTTON} mt-3`}
                size="sm"
                variant="ghost"
                onClick={() => setCreateOpen(true)}
              >
                <PlusIcon className="size-3.5" />
                New Technology
              </Button>
            ) : null}
          </div>
        </div>
      ) : null}

      {/* Preview / edit panel */}
      {selectedTech ? (
        <TechPreviewPanel
          tech={selectedTech}
          categories={categories}
          resources={resources}
          allTechs={techs}
          canUpdate={data.canUpdate}
          canCreateCategories={data.canCreateCategories}
          canSetFinalApproval={data.canSetFinalApproval}
          warnings={selectedWarnings}
          onClose={() => setSelectedId(null)}
          onEdit={() => router.push(`/admin/collections/technologies/${selectedTech.id}`)}
          onSaved={() => {
            void refresh({ freeze: true });
          }}
        />
      ) : null}

      <QuickCreateDialog
        open={createOpen}
        onOpenChange={setCreateOpen}
        categories={categories}
        canCreateCategories={data.canCreateCategories}
        onCreated={handleCreated}
      />
    </div>
  );
}

export function TechTreeCanvas({ data }: { data: TechTreeData }) {
  return (
    <ReactFlowProvider>
      <CanvasInner data={data} />
    </ReactFlowProvider>
  );
}