const VALID_FORMATS = ["Letter", "Legal", "Tabloid", "Ledger", "A0", "A1", "A2", "A3", "A4", "A5", "A6"];
const FORMAT_MAP = new Map(VALID_FORMATS.map(f => [f.toLowerCase(), f]));
const PAGE_RANGES_RE = /^\d+(-\d*)?(\s*,\s*\d+(-\d*)?)*$/;
const MARGIN_KEYS = new Set(["top", "right", "bottom", "left"]);
const VALID_WAIT_UNTIL = ["load", "domcontentloaded", "networkidle0", "networkidle2"];
const MAX_TEMPLATE_SIZE = 102400; // 100KB in characters

type PdfInput = Record<string, any>;
type ValidResult = { valid: true; sanitized: Record<string, any> };
type InvalidResult = { valid: false; error: string };

export function validatePdfOptions(opts: PdfInput): ValidResult | InvalidResult {
  if (!opts || typeof opts !== "object") return { valid: true, sanitized: {} };

  const sanitized: Record<string, any> = {};

  // scale
  if (opts.scale !== undefined) {
    if (typeof opts.scale !== "number" || opts.scale < 0.1 || opts.scale > 2.0) {
      return { valid: false, error: "scale must be a number between 0.1 and 2.0" };
    }
    sanitized.scale = opts.scale;
  }

  // format
  if (opts.format !== undefined) {
    if (typeof opts.format !== "string") {
      return { valid: false, error: "format must be a string" };
    }
    const canonical = FORMAT_MAP.get(opts.format.toLowerCase());
    if (!canonical) {
      return { valid: false, error: `format must be one of: ${VALID_FORMATS.join(", ")}` };
    }
    sanitized.format = canonical;
  }

  // booleans
  for (const field of ["landscape", "printBackground", "displayHeaderFooter", "preferCSSPageSize"]) {
    if (opts[field] !== undefined) {
      if (typeof opts[field] !== "boolean") {
        return { valid: false, error: `${field} must be a boolean` };
      }
      sanitized[field] = opts[field];
    }
  }

  // width/height
  for (const field of ["width", "height"]) {
    if (opts[field] !== undefined) {
      if (typeof opts[field] !== "string") {
        return { valid: false, error: `${field} must be a string (CSS dimension)` };
      }
      sanitized[field] = opts[field];
    }
  }

  // margin
  if (opts.margin !== undefined) {
    if (typeof opts.margin !== "object" || opts.margin === null || Array.isArray(opts.margin)) {
      return { valid: false, error: "margin must be an object with top/right/bottom/left string fields" };
    }
    for (const key of Object.keys(opts.margin)) {
      if (!MARGIN_KEYS.has(key)) {
        return { valid: false, error: `margin contains unknown key: ${key}` };
      }
      if (typeof opts.margin[key] !== "string") {
        return { valid: false, error: `margin.${key} must be a string` };
      }
    }
    sanitized.margin = { ...opts.margin };
  }

  // pageRanges
  if (opts.pageRanges !== undefined) {
    if (typeof opts.pageRanges !== "string") {
      return { valid: false, error: "pageRanges must be a string" };
    }
    if (!PAGE_RANGES_RE.test(opts.pageRanges.trim())) {
      return { valid: false, error: "pageRanges must match pattern like '1-5', '1,3,5', or '2-'" };
    }
    sanitized.pageRanges = opts.pageRanges;
  }

  // waitUntil
  if (opts.waitUntil !== undefined) {
    if (typeof opts.waitUntil !== "string") {
      return { valid: false, error: "waitUntil must be a string" };
    }
    if (!VALID_WAIT_UNTIL.includes(opts.waitUntil)) {
      return { valid: false, error: `waitUntil must be one of: ${VALID_WAIT_UNTIL.join(", ")}` };
    }
    sanitized.waitUntil = opts.waitUntil;
  }

  // headerTemplate
  if (opts.headerTemplate !== undefined) {
    if (typeof opts.headerTemplate !== "string") {
      return { valid: false, error: "headerTemplate must be a string" };
    }
    if (opts.headerTemplate.length > MAX_TEMPLATE_SIZE) {
      return { valid: false, error: "headerTemplate must not exceed 100KB" };
    }
    sanitized.headerTemplate = opts.headerTemplate;
  }

  // footerTemplate
  if (opts.footerTemplate !== undefined) {
    if (typeof opts.footerTemplate !== "string") {
      return { valid: false, error: "footerTemplate must be a string" };
    }
    if (opts.footerTemplate.length > MAX_TEMPLATE_SIZE) {
      return { valid: false, error: "footerTemplate must not exceed 100KB" };
    }
    sanitized.footerTemplate = opts.footerTemplate;
  }

  return { valid: true, sanitized };
}