/* ============================================================
   exportXlsx.js — brand-styled spreadsheet exports.

   One shared exporter so every "Export" button produces the same
   dashboard-flavoured file: TalentFlow green title band, mint meta row,
   ink-teal header, zebra data rows, frozen header + autofilter.

   exceljs is ~1MB, so it is imported dynamically — Vite splits it into
   its own chunk that only ever downloads when an export is clicked.
   ============================================================ */

/** Utopia Brands palette (ARGB, from styles.css brand constants). */
const BRAND = {
  green: 'FF004D43',   // deep green — title band, like the sidebar/action colour
  ink: 'FF1A3134',     // ink teal — header row
  lime: 'FFCEFF71',    // signature lime — title text accent
  mint: 'FFEAFFF4',    // mint white — meta row fill
  zebra: 'FFF1F7F4',   // app background — alternating data rows
  border: 'FFDBE8E2',  // hairline borders
  text: 'FF10231F',
  sub: 'FF4A625C',
  white: 'FFFFFFFF',
}

const thin = { style: 'thin', color: { argb: BRAND.border } }

/**
 * Build and download a styled .xlsx.
 *
 * @param {object} opts
 * @param {string} opts.filename   without extension
 * @param {string} opts.title      big brand-band line, e.g. "Recruitment Inbox"
 * @param {string} opts.subtitle   meta line, e.g. "All Applications · 512 rows · 02/09/2026"
 * @param {Array<{header: string, key: string, width?: number}>} opts.columns
 * @param {Array<object>} opts.rows   keyed by columns[].key; null/undefined print blank
 */
export async function exportStyledXlsx({ filename, title, subtitle, columns, rows }) {
  const ExcelJS = (await import('exceljs')).default
  const wb = new ExcelJS.Workbook()
  wb.creator = 'TalentFlow ATS'
  wb.created = new Date()

  const ws = wb.addWorksheet(title.slice(0, 31) || 'Export', {
    views: [{ state: 'frozen', ySplit: 3 }],
  })

  ws.columns = columns.map((c) => ({ key: c.key, width: c.width ?? 18 }))
  const span = columns.length

  // Row 1 — brand title band
  const titleRow = ws.addRow([title])
  ws.mergeCells(1, 1, 1, span)
  titleRow.height = 30
  const titleCell = ws.getCell(1, 1)
  titleCell.font = { name: 'Calibri', size: 14, bold: true, color: { argb: BRAND.lime } }
  titleCell.fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: BRAND.green } }
  titleCell.alignment = { vertical: 'middle', indent: 1 }

  // Row 2 — meta line
  const metaRow = ws.addRow([subtitle])
  ws.mergeCells(2, 1, 2, span)
  metaRow.height = 20
  const metaCell = ws.getCell(2, 1)
  metaCell.font = { name: 'Calibri', size: 10, color: { argb: BRAND.sub } }
  metaCell.fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: BRAND.mint } }
  metaCell.alignment = { vertical: 'middle', indent: 1 }

  // Row 3 — column headers
  const headRow = ws.addRow(columns.map((c) => c.header))
  headRow.height = 22
  headRow.eachCell((cell) => {
    cell.font = { name: 'Calibri', size: 10, bold: true, color: { argb: BRAND.white } }
    cell.fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: BRAND.ink } }
    cell.alignment = { vertical: 'middle' }
    cell.border = { bottom: { style: 'medium', color: { argb: BRAND.lime } } }
  })

  // Data — zebra rows with hairline borders
  for (const [i, r] of rows.entries()) {
    const row = ws.addRow(columns.map((c) => r[c.key] ?? ''))
    row.eachCell({ includeEmpty: true }, (cell) => {
      cell.font = { name: 'Calibri', size: 10, color: { argb: BRAND.text } }
      if (i % 2 === 1) cell.fill = { type: 'pattern', pattern: 'solid', fgColor: { argb: BRAND.zebra } }
      cell.border = { bottom: thin, right: thin }
      cell.alignment = { vertical: 'middle', wrapText: false }
    })
  }

  ws.autoFilter = { from: { row: 3, column: 1 }, to: { row: 3, column: span } }

  const buf = await wb.xlsx.writeBuffer()
  const blob = new Blob([buf], { type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' })
  const a = document.createElement('a')
  a.href = URL.createObjectURL(blob)
  a.download = `${filename}.xlsx`
  document.body.appendChild(a)
  a.click()
  a.remove()
  URL.revokeObjectURL(a.href)
}