import PDFDocument from 'pdfkit';
import { LabelFontFamily, LabelTextElement } from './label-element.types';

export const MM_TO_PT = 72 / 25.4;

/** Glyph metrics in AFM units (1/1000 of the font size). */
export interface FontMetrics {
  xHeight: number;
  capHeight: number;
}

export interface TextMeasurer {
  /** Height in pt the element's text needs at the element's width and font. */
  heightOfStringPt(text: string, element: LabelTextElement): number;
}

/** The pdfkit standard font a family/style combination prints with. */
export function pdfFontName(
  family: LabelFontFamily,
  bold: boolean,
  italic: boolean,
): string {
  const base =
    family === 'serif' ? 'Times' : family === 'mono' ? 'Courier' : 'Helvetica';
  if (base === 'Times') {
    if (bold && italic) return 'Times-BoldItalic';
    if (bold) return 'Times-Bold';
    if (italic) return 'Times-Italic';
    return 'Times-Roman';
  }
  const suffix =
    bold && italic ? '-BoldOblique' : bold ? '-Bold' : italic ? '-Oblique' : '';
  return `${base}${suffix}`;
}

/** Height in mm of a glyph class: size in pt x metric / 1000 x 25.4 / 72. */
export function heightMm(fontSizePt: number, metricPer1000: number): number {
  return ((fontSizePt * metricPer1000) / 1000) * (25.4 / 72);
}

// pdfkit keeps the loaded font in the private field `_font`; this is the one
// place that reads it. font-metrics.spec.ts pins the values, so a pdfkit
// update that moves or renames the field fails there and nowhere else.
interface PdfDocumentInternals {
  _font?: { xHeight?: unknown; capHeight?: unknown };
}

const metricsCache = new Map<string, FontMetrics>();

/** AFM x-height and cap height of a built-in PDF font. */
export function fontMetricsOf(
  family: LabelFontFamily,
  bold: boolean,
  italic: boolean,
): FontMetrics {
  const name = pdfFontName(family, bold, italic);
  const cached = metricsCache.get(name);
  if (cached) {
    return cached;
  }
  const doc = new PDFDocument({ size: 'A4', margin: 0 });
  doc.font(name);
  const font = (doc as unknown as PdfDocumentInternals)._font;
  const { xHeight, capHeight } = font ?? {};
  if (
    typeof xHeight !== 'number' ||
    typeof capHeight !== 'number' ||
    !(xHeight > 0) ||
    !(capHeight > 0)
  ) {
    throw new Error(`No AFM metrics for font ${name}`);
  }
  const metrics = { xHeight, capHeight };
  metricsCache.set(name, metrics);
  return metrics;
}

/** Measures text with a throw-away PDF document; nothing is written out. */
export function pdfTextMeasurer(): TextMeasurer {
  const doc = new PDFDocument({ size: 'A4', margin: 0 });
  return {
    heightOfStringPt(text, element) {
      if (text === '') {
        return 0;
      }
      return doc
        .font(pdfFontName(element.fontFamily, element.bold, element.italic))
        .fontSize(element.fontSize)
        .heightOfString(text, { width: element.width * MM_TO_PT });
    },
  };
}