import type { GenerateClassroomInput } from '@/lib/server/classroom-generation';
import {
  CourseMaterialError,
  extractManagedCourseMaterials,
} from '@/lib/server/managed-course-materials';

export const LEARNING_GENERATION_CONTRACT_VERSION = 2 as const;
export type LearningGenerationMode = 'single' | 'large';

export interface LearningGenerationRequest {
  contractVersion: typeof LEARNING_GENERATION_CONTRACT_VERSION;
  ownerUserId: string;
  mode: LearningGenerationMode;
  input: GenerateClassroomInput;
  materialCount: number;
}

export class LearningGenerationRequestError extends Error {
  constructor(
    readonly code: string,
    readonly status: number,
    message: string,
  ) {
    super(message);
    this.name = 'LearningGenerationRequestError';
  }
}

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

function compatibilityBoolean(
  value: unknown,
  snakeCaseValue: unknown,
  fallback = false,
): boolean {
  const selected = value ?? snakeCaseValue;
  if (selected === undefined) return fallback;
  if (typeof selected !== 'boolean') {
    throw new LearningGenerationRequestError(
      'invalid_request',
      400,
      'Generation option values must be booleans',
    );
  }
  return selected;
}

async function requestPayload(
  request: Request,
): Promise<{ body: Record<string, unknown>; files: File[] }> {
  const contentType = request.headers.get('content-type')?.toLowerCase() ?? '';
  if (contentType.includes('multipart/form-data')) {
    const contentLength = Number(request.headers.get('content-length') ?? '');
    if (Number.isFinite(contentLength) && contentLength > 155 * 1024 * 1024) {
      throw new LearningGenerationRequestError(
        'materials_too_large',
        413,
        'Multipart request exceeds the course-material upload limit',
      );
    }
    const form = await request.formData().catch(() => null);
    if (!form) {
      throw new LearningGenerationRequestError('invalid_request', 400, 'Malformed multipart body');
    }
    const rawOptions = form.get('options');
    if (typeof rawOptions !== 'string') {
      throw new LearningGenerationRequestError(
        'invalid_request',
        400,
        'Multipart generation requires an options JSON field',
      );
    }
    const body = asRecord(JSON.parse(rawOptions) as unknown);
    if (!body) {
      throw new LearningGenerationRequestError('invalid_request', 400, 'Invalid options JSON');
    }
    const files = form
      .getAll('materials')
      .filter((part): part is File => part instanceof File);
    if (files.length !== form.getAll('materials').length) {
      throw new LearningGenerationRequestError(
        'invalid_request',
        400,
        'Every materials field must be a file',
      );
    }
    return { body, files };
  }

  if (!contentType.includes('application/json')) {
    throw new LearningGenerationRequestError(
      'unsupported_media_type',
      415,
      'Expected application/json or multipart/form-data',
    );
  }
  const body = asRecord(await request.json().catch(() => null));
  if (!body) throw new LearningGenerationRequestError('invalid_request', 400, 'Invalid JSON body');
  return { body, files: [] };
}

export async function parseLearningGenerationRequest(
  request: Request,
): Promise<LearningGenerationRequest> {
  const { body, files } = await requestPayload(request);
  const version = body.contractVersion ?? body.contract_version;
  if (version !== undefined && version !== LEARNING_GENERATION_CONTRACT_VERSION) {
    throw new LearningGenerationRequestError(
      'unsupported_contract_version',
      400,
      `Only generation contract version ${LEARNING_GENERATION_CONTRACT_VERSION} is supported`,
    );
  }
  const owner = body.owner_user_id;
  if (
    typeof owner !== 'string' ||
    !owner.trim() ||
    owner.trim().length > 256 ||
    /[\u0000-\u001f\u007f]/.test(owner)
  ) {
    throw new LearningGenerationRequestError('invalid_owner', 400, 'Invalid owner_user_id');
  }
  if (body.mode !== 'single' && body.mode !== 'large') {
    throw new LearningGenerationRequestError(
      'invalid_mode',
      400,
      'mode must be "single" or "large"',
    );
  }
  if (
    typeof body.requirement !== 'string' ||
    !body.requirement.trim() ||
    body.requirement.trim().length > 20_000
  ) {
    throw new LearningGenerationRequestError(
      'invalid_requirement',
      400,
      'requirement must contain 1-20000 characters',
    );
  }
  const forbidden = [
    'providerId',
    'apiKey',
    'baseUrl',
    'storageKey',
    'webSearchApiKey',
    'webSearchProviderId',
  ].find((field) => body[field] !== undefined);
  if (forbidden) {
    throw new LearningGenerationRequestError(
      'caller_provider_configuration_forbidden',
      400,
      `${forbidden} is server-managed and cannot be supplied by the caller`,
    );
  }

  let pdfContent: { text: string; images: string[] } | undefined;
  try {
    if (files.length > 0) pdfContent = await extractManagedCourseMaterials(files);
  } catch (error) {
    if (error instanceof CourseMaterialError) {
      throw new LearningGenerationRequestError(error.code, error.status, error.message);
    }
    throw error;
  }

  return {
    contractVersion: LEARNING_GENERATION_CONTRACT_VERSION,
    ownerUserId: owner.trim(),
    mode: body.mode,
    materialCount: files.length,
    input: {
      requirement: body.requirement.trim(),
      enableWebSearch: compatibilityBoolean(body.enableWebSearch, body.enable_web_search),
      enableImageGeneration: compatibilityBoolean(
        body.enableImageGeneration,
        body.enable_image_generation,
      ),
      enableVideoGeneration: compatibilityBoolean(
        body.enableVideoGeneration,
        body.enable_video_generation,
      ),
      enableTTS: compatibilityBoolean(body.enableTTS, body.enable_tts),
      interactiveMode: compatibilityBoolean(body.interactiveMode, body.interactive_mode),
      taskEngineMode: compatibilityBoolean(body.taskEngineMode, body.task_engine_mode),
      ...(pdfContent ? { pdfContent } : {}),
    },
  };
}