import { renderToBuffer } from "@react-pdf/renderer";
import { getDocument } from "pdfjs-dist/legacy/build/pdf.mjs";
import type { ReactElement } from "react";

export interface TextBox {
  str: string;
  x0: number;
  x1: number;
  /** Distance from the top edge of the page, in points. */
  top: number;
  bottom: number;
}

export interface PageText {
  width: number;
  height: number;
  items: TextBox[];
}

export interface RenderedPdf {
  pages: PageText[];
  /** Raw PDF bytes as a latin1 string, for grepping object dictionaries. */
  raw: string;
  bytes: Uint8Array;
}

/** Renders a react-pdf element under Node and returns the text boxes pdf.js finds on each page. */
export async function renderPdfText(element: ReactElement): Promise<RenderedPdf> {
  // The renderToBuffer type wants a <Document> element; any element that renders one works.
  const buf = await renderToBuffer(element as Parameters<typeof renderToBuffer>[0]);
  const raw = buf.toString("latin1");
  const bytes = new Uint8Array(buf);

  const task = getDocument({
    data: new Uint8Array(buf),
    useSystemFonts: false,
    disableFontFace: true,
  });
  const doc = await task.promise;

  const pages: PageText[] = [];
  for (let n = 1; n <= doc.numPages; n++) {
    const page = await doc.getPage(n);
    const [, , width, height] = page.view;
    const content = await page.getTextContent();
    const items: TextBox[] = [];
    for (const item of content.items) {
      if (!("str" in item) || item.str.trim() === "") continue;
      const x = item.transform[4];
      const f = item.transform[5];
      items.push({
        str: item.str,
        x0: x,
        x1: x + item.width,
        top: height - f - item.height,
        bottom: height - f,
      });
    }
    pages.push({ width, height, items });
  }
  await task.destroy();
  return { pages, raw, bytes };
}

/** Pairs of items on one page whose boxes overlap (horizontal tolerance 0.5pt, vertical overlap must exceed 2pt). */
export function findOverlaps(page: PageText): Array<[TextBox, TextBox]> {
  const out: Array<[TextBox, TextBox]> = [];
  const its = page.items;
  for (let i = 0; i < its.length; i++) {
    for (let j = i + 1; j < its.length; j++) {
      const a = its[i];
      const b = its[j];
      const h = Math.min(a.x1, b.x1) - Math.max(a.x0, b.x0);
      const v = Math.min(a.bottom, b.bottom) - Math.max(a.top, b.top);
      if (h > 0.5 && v > 2) out.push([a, b]);
    }
  }
  return out;
}

export const describeBox = (t: TextBox) =>
  `"${t.str}" [x ${t.x0.toFixed(1)}..${t.x1.toFixed(1)}, y ${t.top.toFixed(1)}..${t.bottom.toFixed(1)}]`;