// A blank "Session list" Word document for the Import page: a three-column table
// (session number, title, passage) in exactly the shape the importer reads, with a few example
// rows to overwrite. Built in the browser on demand, so the `docx` library only downloads when
// someone actually asks for the template.
import {
  Document, Packer, Paragraph, ShadingType, Table, TableCell, TableRow, TextRun, WidthType, HeadingLevel,
} from 'docx';

export const TEMPLATE_FILENAME = 'session-list-template.docx';

// Example rows show each kind of passage the importer understands.
export const TEMPLATE_ROWS = [
  ['1', 'Paul’s greeting', '1:1–4'],
  ['2', 'Appointing elders', '1:5–9'],
  ['3', 'Rebuking false teachers', '1:10–16'],
  ['4', 'A recap of chapter 1', '—'], // no passage: becomes a divider or intro with no verses
  ['5', 'Teaching sound doctrine', '2:1–10'],
  ['6', 'A passage that crosses a chapter', '2:11–3:2'],
];

const cell = (text, { bold = false, shade = false, width } = {}) => new TableCell({
  width: { size: width, type: WidthType.PERCENTAGE },
  shading: shade ? { type: ShadingType.CLEAR, fill: 'EDE7D9', color: 'auto' } : undefined,
  margins: { top: 80, bottom: 80, left: 120, right: 120 },
  children: [new Paragraph({ children: [new TextRun({ text, bold })] })],
});

const row = (cells, header = false) => new TableRow({
  tableHeader: header,
  children: cells.map((text, i) => cell(text, { bold: header, shade: header, width: [15, 55, 30][i] })),
});

const note = (text) => new Paragraph({ spacing: { after: 100 }, children: [new TextRun({ text })] });

export function buildImportTemplateDocument() {
  return new Document({
    sections: [{
      children: [
        new Paragraph({ heading: HeadingLevel.HEADING_1, children: [new TextRun({ text: 'Session list' })] }),
        note('Replace the example rows below with your own, one row per session, then upload this file on the Import page.'),
        note('Passage: chapter:verse, like 1:1–4. To cross a chapter, write both chapters, like 2:11–3:2. For a session with no passage (an intro or a recap), write — (a dash).'),
        note('You choose the book on the Import page, so leave it out of the Passage column. Keep the three columns, and delete any example rows you don’t need.'),
        new Table({
          width: { size: 100, type: WidthType.PERCENTAGE },
          rows: [row(['Session #', 'Title', 'Passage'], true), ...TEMPLATE_ROWS.map((r) => row(r))],
        }),
      ],
    }],
  });
}

// Builds the template and hands it to the browser as a download.
export async function downloadImportTemplate() {
  const blob = await Packer.toBlob(buildImportTemplateDocument());
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = TEMPLATE_FILENAME;
  document.body.appendChild(a);
  a.click();
  a.remove();
  URL.revokeObjectURL(url);
}