import { PAINT_BUDGET } from "./paint";

export const PAINT_DEPTH_VISIBILITY_SCHEMA_VERSION = 1 as const;
export const PAINT_DEPTH_VISIBILITY_BUDGET = {
  maxVertexSamples: PAINT_BUDGET.maxSamples,
  maxReadbackBytes: PAINT_BUDGET.maxStrokeBytes,
  maxDimension: 4096,
} as const;

export type PaintDepthVisibilityBackend = "MAIN_THREAD_WEBGL2" | "OFFSCREEN_WEBGL2";

export interface PaintDepthVisibilityRequestIR {
  schemaVersion: typeof PAINT_DEPTH_VISIBILITY_SCHEMA_VERSION;
  objectId: string;
  meshId: string;
  revision: number;
  vertexIndices: number[];
}

export interface PaintDepthVisibilityResultIR extends PaintDepthVisibilityRequestIR {
  backend: PaintDepthVisibilityBackend;
  source: "GPU_RGBA_DEPTH_READBACK";
  width: number;
  height: number;
  depthReadbackBytes: number;
  occluderPixelCount: number;
  visibleVertexIndices: number[];
}

export type PaintDepthVisibilityErrorCode =
  | "PAINT_SCHEMA_INVALID"
  | "PAINT_BUDGET_EXCEEDED"
  | "PAINT_DEPTH_UNAVAILABLE"
  | "REVISION_CONFLICT";

export class PaintDepthVisibilityError extends Error {
  constructor(readonly code: PaintDepthVisibilityErrorCode, message: string) {
    super(`${code}: ${message}`);
    this.name = "PaintDepthVisibilityError";
  }
}

const encoder = new TextEncoder();
const REQUEST_FIELDS = new Set(["schemaVersion", "objectId", "meshId", "revision", "vertexIndices"]);
const RESULT_FIELDS = new Set([
  ...REQUEST_FIELDS,
  "backend",
  "source",
  "width",
  "height",
  "depthReadbackBytes",
  "occluderPixelCount",
  "visibleVertexIndices",
]);

function fail(code: PaintDepthVisibilityErrorCode, message: string): never {
  throw new PaintDepthVisibilityError(code, message);
}

function record(value: unknown, label: string): Record<string, unknown> {
  if (typeof value !== "object" || value === null || Array.isArray(value)) fail("PAINT_SCHEMA_INVALID", `${label} must be an object`);
  return value as Record<string, unknown>;
}

function exact(value: Record<string, unknown>, fields: ReadonlySet<string>, label: string): void {
  if (Object.keys(value).some((field) => !fields.has(field))) fail("PAINT_SCHEMA_INVALID", `${label} contains undeclared fields`);
}

function identity(value: unknown, prefix: "object:" | "mesh:", label: string): string {
  if (typeof value !== "string" || !value.startsWith(prefix) || value.length <= prefix.length || encoder.encode(value).byteLength > 256) {
    fail("PAINT_SCHEMA_INVALID", `${label} is not a bounded ${prefix} identity`);
  }
  return value;
}

function nonNegativeInteger(value: unknown, label: string): number {
  if (typeof value !== "number" || !Number.isSafeInteger(value) || value < 0) fail("PAINT_SCHEMA_INVALID", `${label} must be a non-negative safe integer`);
  return value;
}

function vertexIndices(value: unknown, label: string): number[] {
  if (!Array.isArray(value) || value.length === 0) fail("PAINT_SCHEMA_INVALID", `${label} must contain at least one vertex`);
  if (value.length > PAINT_DEPTH_VISIBILITY_BUDGET.maxVertexSamples) fail("PAINT_BUDGET_EXCEEDED", `${label} exceeds the depth sample budget`);
  const parsed = value.map((item, index) => nonNegativeInteger(item, `${label}[${index}]`));
  const unique = new Set(parsed);
  if (unique.size !== parsed.length) fail("PAINT_SCHEMA_INVALID", `${label} contains duplicate vertex identities`);
  return [...unique].sort((left, right) => left - right);
}

function resultVertexIndices(value: unknown): number[] {
  if (!Array.isArray(value)) fail("PAINT_SCHEMA_INVALID", "visibleVertexIndices must be an array");
  if (value.length === 0) return [];
  return vertexIndices(value, "visibleVertexIndices");
}

export function validatePaintDepthVisibilityRequest(value: unknown, currentRevision: number): PaintDepthVisibilityRequestIR {
  const request = record(value, "Paint depth visibility request");
  exact(request, REQUEST_FIELDS, "Paint depth visibility request");
  if (request.schemaVersion !== PAINT_DEPTH_VISIBILITY_SCHEMA_VERSION) fail("PAINT_SCHEMA_INVALID", "Paint depth visibility schema is unsupported");
  const revision = nonNegativeInteger(request.revision, "revision");
  if (!Number.isSafeInteger(currentRevision) || currentRevision < 0) fail("PAINT_SCHEMA_INVALID", "current revision is invalid");
  if (revision !== currentRevision) fail("REVISION_CONFLICT", "Paint depth visibility request is stale");
  return {
    schemaVersion: PAINT_DEPTH_VISIBILITY_SCHEMA_VERSION,
    objectId: identity(request.objectId, "object:", "objectId"),
    meshId: identity(request.meshId, "mesh:", "meshId"),
    revision,
    vertexIndices: vertexIndices(request.vertexIndices, "vertexIndices"),
  };
}

export function validatePaintDepthVisibilityResult(
  value: unknown,
  requestValue: PaintDepthVisibilityRequestIR,
): PaintDepthVisibilityResultIR {
  const result = record(value, "Paint depth visibility result");
  exact(result, RESULT_FIELDS, "Paint depth visibility result");
  const request = validatePaintDepthVisibilityRequest({
    schemaVersion: result.schemaVersion,
    objectId: result.objectId,
    meshId: result.meshId,
    revision: result.revision,
    vertexIndices: result.vertexIndices,
  }, requestValue.revision);
  if (request.objectId !== requestValue.objectId || request.meshId !== requestValue.meshId ||
      request.vertexIndices.length !== requestValue.vertexIndices.length ||
      request.vertexIndices.some((index, offset) => index !== requestValue.vertexIndices[offset])) {
    fail("PAINT_SCHEMA_INVALID", "Paint depth visibility result does not match its request");
  }
  const backend = result.backend;
  if (backend !== "MAIN_THREAD_WEBGL2" && backend !== "OFFSCREEN_WEBGL2") fail("PAINT_SCHEMA_INVALID", "Paint depth backend is invalid");
  if (result.source !== "GPU_RGBA_DEPTH_READBACK") fail("PAINT_SCHEMA_INVALID", "Paint depth source is invalid");
  const width = nonNegativeInteger(result.width, "width");
  const height = nonNegativeInteger(result.height, "height");
  if (width < 1 || height < 1 || width > PAINT_DEPTH_VISIBILITY_BUDGET.maxDimension || height > PAINT_DEPTH_VISIBILITY_BUDGET.maxDimension) {
    fail("PAINT_BUDGET_EXCEEDED", "Paint depth dimensions exceed the readback budget");
  }
  const depthReadbackBytes = nonNegativeInteger(result.depthReadbackBytes, "depthReadbackBytes");
  if (depthReadbackBytes !== width * height * 4 || depthReadbackBytes > PAINT_DEPTH_VISIBILITY_BUDGET.maxReadbackBytes) {
    fail("PAINT_BUDGET_EXCEEDED", "Paint depth readback byte length is invalid");
  }
  const occluderPixelCount = nonNegativeInteger(result.occluderPixelCount, "occluderPixelCount");
  if (occluderPixelCount > width * height) fail("PAINT_SCHEMA_INVALID", "Paint depth occluder count exceeds the target");
  const visibleVertexIndices = resultVertexIndices(result.visibleVertexIndices);
  const requested = new Set(request.vertexIndices);
  if (visibleVertexIndices.some((index) => !requested.has(index))) fail("PAINT_SCHEMA_INVALID", "Paint depth result contains an unrequested vertex");
  return {
    ...request,
    backend,
    source: "GPU_RGBA_DEPTH_READBACK",
    width,
    height,
    depthReadbackBytes,
    occluderPixelCount,
    visibleVertexIndices,
  };
}