import { createHash } from 'node:crypto';
import { readFile } from 'node:fs/promises';
import { resolve } from 'node:path';
import JSZip from 'jszip';
import { extractKnowledgePack, extractQuizPack } from '@/lib/bundle/extract';
import type { FrozenBundleDocument, KnowledgePack, QuizPack } from '@/lib/bundle/types';
import type { ClassroomManifest } from '@/lib/export/classroom-zip-types';
import {
  readFrozenLearningPackageRecord,
  readUniqueMakeloreCoursePackage,
  type FrozenLearningPackageRecord,
} from '@/lib/makelore-course/package';
import type { CoursewareKnowledge } from '@/lib/qa/knowledge';
import type { Scene, Stage } from '@/lib/types/stage';

const SAFE_ID = /^[A-Za-z0-9_-]{1,96}$/;
const SAFE_COURSE_ID = /^[A-Za-z0-9_-]{1,64}$/;
const SHA256 = /^[0-9a-f]{64}$/;
const MAX_JSON_CHARS = 64 * 1024 * 1024;

export interface RuntimeCourseModuleDescriptor {
  moduleId: string;
  index: number;
  title: string;
  summary: string;
  contentHash: string;
  sceneCount: number;
  root: string;
}

export interface MakeloreCourseRecord {
  schemaVersion: 1 | 2;
  courseId: string;
  contentHash: string;
  title: string;
  language?: string;
  mode: 'single' | 'large';
  sceneCount: number;
  moduleCount: number;
  modules: RuntimeCourseModuleDescriptor[];
  /** Only retained for pre-frozen compatibility records. */
  classroom?: { stage: Stage; scenes: Scene[] };
  frozenRecord?: FrozenLearningPackageRecord;
  archive?: JSZip;
}

export interface RuntimeCourseModule {
  course: MakeloreCourseRecord;
  descriptor: RuntimeCourseModuleDescriptor;
  manifest?: ClassroomManifest;
  knowledge: KnowledgePack;
  quiz: QuizPack;
  bundle?: FrozenBundleDocument;
  /** Compatibility path for legacy classroom.json packages. */
  classroom?: { stage: Stage; scenes: Scene[] };
}

function courseStoreRoot(): string {
  const dataRoot = process.env.LEARNING_DATA_DIR || resolve(process.cwd(), 'data');
  return resolve(
    process.env.LEARNING_COURSE_STORE_DIR ||
      process.env.MAKELORE_COURSE_STORE_DIR ||
      resolve(dataRoot, 'makelore-courses'),
  );
}

function sha256(bytes: Uint8Array): string {
  return createHash('sha256').update(bytes).digest('hex');
}

function record(value: unknown): Record<string, unknown> | null {
  return value && typeof value === 'object' && !Array.isArray(value)
    ? (value as Record<string, unknown>)
    : null;
}

function positiveInteger(value: unknown): number | null {
  return typeof value === 'number' && Number.isSafeInteger(value) && value > 0 ? value : null;
}

function safeRoot(value: unknown, moduleId: string): string | null {
  if (typeof value !== 'string') return null;
  const normalized = value.replace(/\\/g, '/').replace(/^\/+|\/+$/g, '');
  if (!normalized || normalized.split('/').some((part) => part === '.' || part === '..')) return null;
  const expected = `modules/${moduleId}`;
  return normalized === expected ? `${expected}/` : null;
}

async function zipJson<T>(zip: JSZip, path: string): Promise<T> {
  const entry = zip.file(path);
  if (!entry) throw new Error(`Frozen course is missing ${path}`);
  const text = await entry.async('string');
  if (text.length > MAX_JSON_CHARS) throw new Error(`Frozen course document is too large: ${path}`);
  return JSON.parse(text) as T;
}

function singleDescriptor(
  courseId: string,
  contentHash: string,
  title: string,
  sceneCount: number,
  moduleId = courseId,
): RuntimeCourseModuleDescriptor {
  return { moduleId, index: 1, title, summary: '', contentHash, sceneCount, root: '' };
}

async function loadFrozenCourse(
  courseId: string,
  contentHash: string,
): Promise<MakeloreCourseRecord | null> {
  const frozen = await readFrozenLearningPackageRecord(courseId);
  if (!frozen || frozen.contentHash !== contentHash) return null;
  const bytes = await readUniqueMakeloreCoursePackage(courseId);
  if (
    !bytes ||
    bytes.byteLength !== frozen.archiveBytes ||
    sha256(bytes) !== frozen.archiveSha256
  ) {
    return null;
  }
  let archive: JSZip;
  try {
    archive = await JSZip.loadAsync(bytes, { checkCRC32: true });
  } catch {
    return null;
  }

  if (frozen.mode === 'single') {
    let bundle: FrozenBundleDocument;
    try {
      bundle = await zipJson<FrozenBundleDocument>(archive, 'bundle.json');
    } catch {
      return null;
    }
    const moduleId = bundle.meta?.coursewareId;
    if (
      typeof moduleId !== 'string' ||
      !SAFE_ID.test(moduleId) ||
      bundle.meta.contentHash !== contentHash ||
      !archive.file('manifest.json') ||
      !archive.file('knowledge/knowledge.json') ||
      !archive.file('quiz/quiz.json')
    ) {
      return null;
    }
    return {
      schemaVersion: frozen.schemaVersion,
      courseId,
      contentHash,
      title: frozen.title,
      language: frozen.language,
      mode: 'single',
      sceneCount: frozen.sceneCount,
      moduleCount: 1,
      modules: [singleDescriptor(courseId, contentHash, frozen.title, frozen.sceneCount, moduleId)],
      frozenRecord: frozen,
      archive,
    };
  }

  const structure = record(frozen.courseStructure);
  const structureModules = Array.isArray(structure?.modules)
    ? structure.modules.map(record).filter((item): item is Record<string, unknown> => item !== null)
    : [];
  let courseDocument: Record<string, unknown>;
  try {
    courseDocument = record(await zipJson<unknown>(archive, 'course.json')) ?? {};
  } catch {
    return null;
  }
  const courseModules = Array.isArray(courseDocument.modules)
    ? courseDocument.modules.map(record).filter((item): item is Record<string, unknown> => item !== null)
    : [];
  if (
    structure?.kind !== 'learning-course-aggregate' ||
    structure.contentHash !== contentHash ||
    courseDocument.kind !== 'learning-course-aggregate' ||
    courseDocument.courseId !== courseId ||
    courseDocument.contentHash !== contentHash ||
    structureModules.length === 0 ||
    courseModules.length !== structureModules.length
  ) {
    return null;
  }

  const modules: RuntimeCourseModuleDescriptor[] = [];
  for (const [position, source] of structureModules.entries()) {
    const moduleId = source.coursewareId;
    const moduleHash = source.contentHash;
    const index = positiveInteger(source.index);
    const declared = courseModules.find((candidate) => candidate.moduleId === moduleId);
    const root = safeRoot(declared?.path, typeof moduleId === 'string' ? moduleId : '');
    if (
      typeof moduleId !== 'string' ||
      !SAFE_ID.test(moduleId) ||
      typeof moduleHash !== 'string' ||
      !SHA256.test(moduleHash) ||
      index === null ||
      !declared ||
      declared.contentHash !== moduleHash ||
      declared.index !== index ||
      !root ||
      !archive.file(`${root}manifest.json`) ||
      !archive.file(`${root}bundle.json`) ||
      !archive.file(`${root}knowledge/knowledge.json`) ||
      !archive.file(`${root}quiz/quiz.json`)
    ) {
      return null;
    }
    const sceneCount = positiveInteger(source.sceneCount);
    modules.push({
      moduleId,
      index,
      title: typeof source.title === 'string' ? source.title : `Module ${position + 1}`,
      summary: typeof source.description === 'string' ? source.description : '',
      contentHash: moduleHash,
      sceneCount: sceneCount ?? 0,
      root,
    });
  }
  if (
    new Set(modules.map((module) => module.moduleId)).size !== modules.length ||
    modules.some((module, index) => index > 0 && module.index <= modules[index - 1]!.index)
  ) {
    return null;
  }
  return {
    schemaVersion: frozen.schemaVersion,
    courseId,
    contentHash,
    title: frozen.title,
    language: frozen.language,
    mode: 'large',
    sceneCount: frozen.sceneCount,
    moduleCount: modules.length,
    modules,
    frozenRecord: frozen,
    archive,
  };
}

async function loadLegacyCourse(
  courseId: string,
  contentHash: string,
): Promise<MakeloreCourseRecord | null> {
  let value: unknown;
  try {
    value = JSON.parse(await readFile(resolve(courseStoreRoot(), `${courseId}.json`), 'utf8'));
  } catch {
    return null;
  }
  const legacy = record(value);
  const classroom = record(legacy?.classroom);
  if (
    legacy?.schemaVersion !== 1 ||
    legacy.courseId !== courseId ||
    legacy.contentHash !== contentHash ||
    typeof legacy.title !== 'string' ||
    !classroom ||
    !record(classroom.stage) ||
    !Array.isArray(classroom.scenes)
  ) {
    return null;
  }
  const typedClassroom = classroom as unknown as { stage: Stage; scenes: Scene[] };
  return {
    schemaVersion: 1,
    courseId,
    contentHash,
    title: legacy.title,
    ...(typeof legacy.language === 'string' ? { language: legacy.language } : {}),
    mode: 'single',
    sceneCount: typedClassroom.scenes.length,
    moduleCount: 1,
    modules: [singleDescriptor(courseId, contentHash, legacy.title, typedClassroom.scenes.length)],
    classroom: typedClassroom,
  };
}

export function parseLearningBinding(key: string): { courseId: string; contentHash: string } | null {
  const split = key.lastIndexOf(':');
  if (split <= 0) return null;
  const courseId = key.slice(0, split);
  const contentHash = key.slice(split + 1);
  return SAFE_COURSE_ID.test(courseId) && SHA256.test(contentHash)
    ? { courseId, contentHash }
    : null;
}

/** Resolve only an exact aggregate course ID + content hash. */
export async function loadMakeloreCourse(
  courseId: string,
  contentHash: string,
): Promise<MakeloreCourseRecord | null> {
  if (!SAFE_COURSE_ID.test(courseId) || !SHA256.test(contentHash)) return null;
  return (await loadFrozenCourse(courseId, contentHash)) ?? loadLegacyCourse(courseId, contentHash);
}

export async function resolveMakeloreCourseModule(
  course: MakeloreCourseRecord,
  selection: { moduleId?: string | null; moduleContentHash?: string | null } = {},
): Promise<RuntimeCourseModule | null> {
  let descriptor: RuntimeCourseModuleDescriptor | undefined;
  if (course.mode === 'large') {
    if (!selection.moduleId || !selection.moduleContentHash) return null;
    descriptor = course.modules.find((module) => module.moduleId === selection.moduleId);
    if (!descriptor || descriptor.contentHash !== selection.moduleContentHash) return null;
  } else {
    descriptor = course.modules[0];
    if (!descriptor) return null;
    if (
      selection.moduleId &&
      selection.moduleId !== descriptor.moduleId &&
      selection.moduleId !== course.courseId
    ) {
      return null;
    }
    if (selection.moduleContentHash && selection.moduleContentHash !== course.contentHash) return null;
  }

  if (!course.archive) {
    const classroom = course.classroom;
    if (!classroom) return null;
    return {
      course,
      descriptor,
      classroom,
      knowledge: extractKnowledgePack(descriptor.moduleId, classroom.stage, classroom.scenes),
      quiz: extractQuizPack(classroom.scenes),
    };
  }

  try {
    const [bundle, manifest, knowledge, quiz] = await Promise.all([
      zipJson<FrozenBundleDocument>(course.archive, `${descriptor.root}bundle.json`),
      zipJson<ClassroomManifest>(course.archive, `${descriptor.root}manifest.json`),
      zipJson<KnowledgePack>(course.archive, `${descriptor.root}knowledge/knowledge.json`),
      zipJson<QuizPack>(course.archive, `${descriptor.root}quiz/quiz.json`),
    ]);
    if (
      bundle.meta?.coursewareId !== descriptor.moduleId ||
      bundle.meta.contentHash !== descriptor.contentHash ||
      !Array.isArray(manifest.scenes) ||
      !Array.isArray(knowledge.scenes) ||
      !Array.isArray(quiz.scenes) ||
      manifest.scenes.length !== descriptor.sceneCount
    ) {
      return null;
    }
    return { course, descriptor, manifest, knowledge, quiz, bundle };
  } catch {
    return null;
  }
}

export function courseKnowledge(module: RuntimeCourseModule): CoursewareKnowledge {
  return {
    coursewareId: module.descriptor.moduleId,
    title: module.descriptor.title,
    language: module.bundle?.meta.language ?? module.course.language,
    knowledge: module.knowledge,
    quiz: module.quiz,
  };
}

/** Synthetic scene identity used by Makelore when materializing a frozen manifest. */
export function runtimeSceneId(
  course: MakeloreCourseRecord,
  module: RuntimeCourseModuleDescriptor,
  sceneIndex: number,
): string {
  return `learning_${course.courseId}_${module.moduleId}_s${sceneIndex}`;
}