import { BufferGeometry, Float32BufferAttribute, Vector3, type Group, type Mesh } from "three";
import type {
  DungeonNavigationComponentPolicy,
  DungeonNavigationLink,
  DungeonNavigationTopologySummary,
  DungeonTraversalRamp,
} from "./dungeonTypes";
import { bridgeDungeonStairNavigation, dungeonRampNavigationBridges, smoothDungeonStairGeometry } from "./dungeonTraversalRamps";
import {
  buildPartyNavigationGraph,
  buildPartyNavigationGraphFromDetourTopology,
  type PartyNavigationGraph,
  type PartyNavigationDetourTopology,
} from "./partyNavigation";
import { MAX_SYNCHRONOUS_PARTY_NAVIGATION_TRIANGLES } from "./partyNavigationPolicy";

const MAX_CACHED_NAVIGATION_GRAPHS = 8;
const graphCache = new Map<string, PartyNavigationGraph>();

export function cachedPartyNavigationGraph(
  url: string,
  links: readonly DungeonNavigationLink[],
  ramps: readonly DungeonTraversalRamp[] = [],
  retainSurfaceTriangles = false,
  detourTopologySummary?: DungeonNavigationTopologySummary,
  navigationComponentPolicy?: DungeonNavigationComponentPolicy,
  navigationAssetChecksum?: string,
): PartyNavigationGraph | null {
  return graphCache.get(graphCacheKey(url, links, ramps)
    + (retainSurfaceTriangles ? ":floor-validation" : "")
    + detourTopologyCacheKey(detourTopologySummary)
    + navigationIdentityCacheKey(navigationComponentPolicy, navigationAssetChecksum)) ?? null;
}

function navigationIdentityCacheKey(
  policy: DungeonNavigationComponentPolicy | undefined,
  checksum: string | undefined,
): string {
  if (!policy && !checksum) return "";
  return `:navigation-${policy ?? "default"}-${encodeURIComponent(checksum ?? "unversioned")}`;
}

function detourTopologyCacheKey(summary: DungeonNavigationTopologySummary | undefined): string {
  return summary
    ? `:detour-${summary.schemaVersion}-${summary.polygonCount}-${summary.directedLinkCount}-${summary.detailTriangleCount}`
      + (summary.assetChecksum ? `-${encodeURIComponent(summary.assetChecksum)}` : "")
    : "";
}

function validateDetourTopologyManifestCounts(
  rawTopology: PartyNavigationDetourTopology | undefined,
  summary: DungeonNavigationTopologySummary | undefined,
): void {
  if (!rawTopology && !summary) return;
  if (!rawTopology || !summary) {
    throw new Error("Source-pinned Detour navigation requires both GLB topology extras and a manifest summary.");
  }
  if (
    rawTopology.schemaVersion !== summary.schemaVersion
    || rawTopology.polygonCount !== summary.polygonCount
    || rawTopology.directedLinkCount !== summary.directedLinkCount
    || rawTopology.detailTriangleCount !== summary.detailTriangleCount
    || rawTopology.geometryTriangleCount !== summary.detailTriangleCount
    || rawTopology.unrepresentedLinkCount !== 0
    || rawTopology.polygons.length !== summary.polygonCount
    || rawTopology.links.length !== summary.directedLinkCount
  ) {
    throw new Error("Source-pinned Detour GLB topology counts do not match its reviewed manifest summary.");
  }
}

function graphCacheKey(
  url: string,
  offMeshLinks: readonly DungeonNavigationLink[],
  ramps: readonly DungeonTraversalRamp[],
): string {
  const links = offMeshLinks.map((link) => [
    link.id,
    link.start,
    link.end,
    link.bidirectional,
  ]);
  return `${url}:${JSON.stringify([links, ramps])}`;
}

function navigationGeometry(
  scene: Group,
  componentPolicy: DungeonNavigationComponentPolicy | undefined,
  maxSourceTriangles: number,
): BufferGeometry {
  scene.updateMatrixWorld(true);
  if (componentPolicy === "all-components") {
    const sourceMeshes: Mesh[] = [];
    let sourceTriangleCount = 0;
    scene.traverse((node) => {
      const mesh = node as Mesh;
      if (!mesh.isMesh) return;
      const position = mesh.geometry.getAttribute("position");
      if (!position || position.count < 3) return;
      const indexCount = mesh.geometry.getIndex()?.count ?? position.count;
      if (indexCount < 3 || indexCount % 3 !== 0) {
        throw new Error("An all-components party navigation mesh must contain complete triangles.");
      }
      sourceMeshes.push(mesh);
      sourceTriangleCount += indexCount / 3;
    });
    if (!sourceMeshes.length) throw new Error("The party navigation GLB has no triangle geometry.");
    if (sourceTriangleCount > maxSourceTriangles) {
      throw new Error(
        `Party navigation geometry has ${sourceTriangleCount} triangles; maximum is ${maxSourceTriangles}.`,
      );
    }

    const mergedPositions = new Float32Array(sourceTriangleCount * 9);
    const point = new Vector3();
    let outputOffset = 0;
    for (const mesh of sourceMeshes) {
      const geometry = mesh.geometry;
      const position = geometry.getAttribute("position");
      const index = geometry.getIndex();
      const indexCount = index?.count ?? position.count;
      for (let sourceIndex = 0; sourceIndex < indexCount; sourceIndex += 1) {
        const vertexIndex = index ? index.getX(sourceIndex) : sourceIndex;
        if (!Number.isInteger(vertexIndex) || vertexIndex < 0 || vertexIndex >= position.count) {
          throw new Error(`Party navigation index ${sourceIndex} references an invalid vertex.`);
        }
        point.fromBufferAttribute(position, vertexIndex).applyMatrix4(mesh.matrixWorld);
        mergedPositions[outputOffset++] = point.x;
        mergedPositions[outputOffset++] = point.y;
        mergedPositions[outputOffset++] = point.z;
      }
    }
    const merged = new BufferGeometry();
    merged.setAttribute("position", new Float32BufferAttribute(mergedPositions, 3));
    return merged;
  }

  let sourceMesh: Mesh | null = null;
  let largestVertexCount = 0;
  scene.traverse((node) => {
    const mesh = node as Mesh;
    const count = mesh.isMesh ? mesh.geometry.getAttribute("position")?.count ?? 0 : 0;
    if (count > largestVertexCount) {
      sourceMesh = mesh;
      largestVertexCount = count;
    }
  });
  if (!sourceMesh) throw new Error("The party navigation GLB has no triangle geometry.");
  const geometry = (sourceMesh as Mesh).geometry.clone();
  const position = geometry.getAttribute("position");
  // BufferAttribute.applyMatrix4 writes back through the source component
  // type. Quantized normalized integers therefore clamp world coordinates to
  // [-1, 1] while baking their node transform. Expand them to floats first.
  if (position.normalized) {
    const expanded = new Float32Array(position.count * 3);
    for (let index = 0; index < position.count; index += 1) {
      expanded[index * 3] = position.getX(index);
      expanded[index * 3 + 1] = position.getY(index);
      expanded[index * 3 + 2] = position.getZ(index);
    }
    geometry.setAttribute("position", new Float32BufferAttribute(expanded, 3));
  }
  geometry.applyMatrix4((sourceMesh as Mesh).matrixWorld);
  return geometry;
}

export function preparePartyNavigationGraph(
  url: string,
  scene: Group,
  offMeshLinks: readonly DungeonNavigationLink[],
  ramps: readonly DungeonTraversalRamp[] = [],
  maxSourceTriangles = MAX_SYNCHRONOUS_PARTY_NAVIGATION_TRIANGLES,
  retainSurfaceTriangles = false,
  detourTopology?: PartyNavigationDetourTopology,
  detourTopologySummary?: DungeonNavigationTopologySummary,
  navigationComponentPolicy?: DungeonNavigationComponentPolicy,
  navigationAssetChecksum?: string,
): PartyNavigationGraph {
  validateDetourTopologyManifestCounts(detourTopology, detourTopologySummary);
  if (detourTopology && navigationComponentPolicy) {
    throw new Error("Source-pinned Detour topology cannot be combined with inferred all-components navigation.");
  }
  const cacheKey = graphCacheKey(url, offMeshLinks, ramps)
    + (retainSurfaceTriangles ? ":floor-validation" : "")
    + detourTopologyCacheKey(detourTopologySummary)
    + navigationIdentityCacheKey(navigationComponentPolicy, navigationAssetChecksum);
  const cached = graphCache.get(cacheKey);
  if (cached) {
    graphCache.delete(cacheKey);
    graphCache.set(cacheKey, cached);
    return cached;
  }

  const geometry = navigationGeometry(scene, navigationComponentPolicy, maxSourceTriangles);
  let graph: PartyNavigationGraph;
  try {
    if (detourTopology) {
      if (ramps.length || offMeshLinks.length) {
        throw new Error("Source-pinned Detour topology cannot be combined with inferred ramp or off-mesh links.");
      }
      graph = buildPartyNavigationGraphFromDetourTopology(geometry, detourTopology);
    } else {
      if (ramps.length) {
        // Recast normally lifts its walkable surface slightly above collision.
        smoothDungeonStairGeometry(geometry, ramps, 0.05);
        bridgeDungeonStairNavigation(geometry, ramps, 0.05);
      }
      const bridgedLinks = new Set(ramps.flatMap((ramp) => dungeonRampNavigationBridges(ramp).map((bridge) => bridge.linkId)));
      graph = buildPartyNavigationGraph(geometry, {
        maxSourceTriangles,
        retainSurfaceTriangles,
        retainAllComponents: navigationComponentPolicy === "all-components",
        offMeshLinks: offMeshLinks.filter((link) => !bridgedLinks.has(link.id)),
      });
    }
  } finally {
    geometry.dispose();
  }
  graphCache.set(cacheKey, graph);
  if (graphCache.size > MAX_CACHED_NAVIGATION_GRAPHS) {
    const oldest = graphCache.keys().next().value as string | undefined;
    if (oldest) graphCache.delete(oldest);
  }
  return graph;
}