import { Injectable } from '@nestjs/common';
import ExcelJS from 'exceljs';

import { PdfRenderService } from '../billing/documents/pdf-render.service';
import { buildTabularFallbackPdf } from '../billing/documents/styled-pdf.util';

// ponytail: in-memory Workbook, cap below. Switch to ExcelJS's streaming
// WorkbookWriter if an export ever needs to outgrow XLSX_ROW_CAP.
export const XLSX_ROW_CAP = 50_000;
// ponytail: CSV is buffered through the same Workbook as xlsx, so it shares the
// cap. Switch to qb.stream() + res.write() if a dataset needs more than this.
export const CSV_ROW_CAP = 50_000;
// ponytail: HTML→PDF render cost grows with row count; larger exports must
// use XLSX or CSV instead.
export const PDF_ROW_CAP = 5_000;

/**
 * Value types a tabular export understands. A superset of `ReportColumn['type']`
 * so a report's own columns are assignable here unchanged.
 */
export type ExportFieldType =
  | 'string'
  | 'number'
  | 'money'
  | 'tons'
  | 'percent'
  | 'date'
  | 'datetime'
  | 'boolean';

/** The minimum a column must describe to be written to a sheet. */
export interface ExportColumnLike {
  key: string;
  label: string;
  type: ExportFieldType;
}

/** Headline figures printed above the table. xlsx/pdf only — never in CSV. */
export interface ExportKpiLike {
  label: string;
  value: number;
  unit?: string;
}

/**
 * One tabular document, independent of where the rows came from. A report and a
 * dataset export both reduce to this, which is what lets them share one writer.
 */
export interface TabularDoc {
  /** Sheet name (truncated to Excel's 31-char limit) and the PDF's <h1>. */
  title: string;
  description?: string;
  /** Log label handed to PdfRenderService, e.g. "report:bookings-list". */
  label: string;
  columns: ExportColumnLike[];
  rows: Record<string, unknown>[];
  kpis?: ExportKpiLike[];
}

const NUMBER_FORMAT: Partial<Record<ExportFieldType, string>> = {
  money: '#,##0.00',
  tons: '#,##0.0',
  percent: '0"%"',
  number: '#,##0',
};

function formatCell(value: unknown, type: ExportFieldType): string {
  if (value === null || value === undefined) return '';
  if (type === 'money' || type === 'number') {
    return Number(value).toLocaleString('en-US', { maximumFractionDigits: 2 });
  }
  if (type === 'tons') return `${Number(value).toLocaleString('en-US')} t`;
  if (type === 'percent') return `${value}%`;
  if (type === 'boolean') return value ? 'Yes' : 'No';
  return String(value);
}

@Injectable()
export class TabularExportService {
  constructor(private readonly pdfRender: PdfRenderService) {}

  async toXlsx(doc: TabularDoc): Promise<Buffer> {
    const workbook = this.buildWorkbook(doc, { includeKpis: true });
    const buffer = await workbook.xlsx.writeBuffer();
    return Buffer.from(buffer);
  }

  /**
   * CSV via ExcelJS's own writer, off the same Workbook xlsx builds — it already
   * handles quoting, embedded commas and embedded newlines. Hand-rolling
   * `row.join(',')` breaks on the first customer name containing a comma.
   *
   * KPIs are deliberately omitted: a preamble row plus a blank row before the
   * header stops the file parsing as a plain table, and CSV's whole point here
   * is being machine-readable.
   */
  async toCsv(doc: TabularDoc): Promise<Buffer> {
    const workbook = this.buildWorkbook(doc, { includeKpis: false });
    const buffer = await workbook.csv.writeBuffer();
    return Buffer.from(buffer);
  }

  async toPdf(doc: TabularDoc): Promise<Buffer> {
    const html = this.buildHtml(doc);
    return this.pdfRender.htmlToPdfBuffer(html, {
      label: doc.label,
      landscape: true,
      // Without this, a box with no Chromium silently degrades to
      // genericFallbackPdf — a ~900-character text dump instead of a table.
      // buildTabularFallbackPdf parses exactly the markup buildHtml emits.
      fallback: buildTabularFallbackPdf,
    });
  }

  private buildWorkbook(doc: TabularDoc, opts: { includeKpis: boolean }): ExcelJS.Workbook {
    const workbook = new ExcelJS.Workbook();
    const sheet = workbook.addWorksheet(doc.title.slice(0, 31));
    const { columns, rows, kpis } = doc;

    if (opts.includeKpis && kpis?.length) {
      sheet.addRow(
        kpis.map((k) => `${k.label}: ${k.value.toLocaleString()}${k.unit ? ` ${k.unit}` : ''}`),
      );
      sheet.addRow([]);
    }

    const headerRow = sheet.addRow(columns.map((c) => c.label));
    headerRow.font = { bold: true };

    for (const row of rows) {
      sheet.addRow(columns.map((c) => row[c.key] ?? null));
    }

    columns.forEach((col, i) => {
      const format = NUMBER_FORMAT[col.type];
      const excelCol = sheet.getColumn(i + 1);
      excelCol.width = Math.max(col.label.length + 2, 12);
      if (format) excelCol.numFmt = format;
    });

    return workbook;
  }

  private buildHtml(doc: TabularDoc): string {
    const { title, description, columns, rows, kpis } = doc;
    const esc = (v: unknown) =>
      String(v ?? '').replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');

    const kpiHtml = kpis?.length
      ? `<div style="display:flex;gap:24px;margin-bottom:16px">${kpis
          .map(
            (k) =>
              `<div class="tile"><div style="font-size:11px;color:#666">${esc(k.label)}</div><div style="font-size:16px;font-weight:600">${k.value.toLocaleString()}${k.unit ? ` ${esc(k.unit)}` : ''}</div></div>`,
          )
          .join('')}</div>`
      : '';

    const head = columns.map((c) => `<th>${esc(c.label)}</th>`).join('');
    const body = rows
      .map(
        (row) =>
          `<tr>${columns.map((c) => `<td>${esc(formatCell(row[c.key], c.type))}</td>`).join('')}</tr>`,
      )
      .join('');

    return `<!doctype html><html><head><meta charset="utf-8"><style>
      body { font-family: Arial, sans-serif; font-size: 10px; color: #111; }
      h1 { font-size: 16px; margin-bottom: 4px; }
      p.subtitle { color: #666; margin: 0 0 12px; }
      table { width: 100%; border-collapse: collapse; }
      th, td { border: 1px solid #ddd; padding: 4px 6px; text-align: left; }
      th { background: #f3f3f3; }
    </style></head><body>
      <h1>${esc(title)}</h1>
      <p class="subtitle">${esc(description ?? '')}</p>
      ${kpiHtml}
      <table><thead><tr>${head}</tr></thead><tbody>${body}</tbody></table>
    </body></html>`;
  }
}