// Minimal single-page PDF writer — no dependency (jspdf/pdf-lib) needed.
// Builds a valid PDF byte-for-byte using the base14 Helvetica font, which every
// PDF reader supports without embedding. Good enough for text/table documents
// like a payslip breakdown; not a general-purpose PDF library.

export interface PdfLine {
  text: string
  x: number
  y: number
  size?: number
  bold?: boolean
  color?: [number, number, number] // 0-1 RGB
}

const PAGE_WIDTH = 612 // US Letter, points
const PAGE_HEIGHT = 792

function escapePdfText(s: string): string {
  return s.replace(/\\/g, "\\\\").replace(/\(/g, "\\(").replace(/\)/g, "\\)")
}

/** Builds a one-page PDF from absolutely-positioned text lines (origin bottom-left, like PDF space). */
export function buildSimplePdf(lines: PdfLine[]): Blob {
  const content: string[] = ["q"]
  let currentFont: "F1" | "F2" | null = null
  let currentSize: number | null = null
  let currentColor: string | null = null

  for (const line of lines) {
    const font = line.bold ? "F2" : "F1"
    const size = line.size ?? 11
    const [r, g, b] = line.color ?? [0.07, 0.07, 0.07]
    const colorKey = `${r},${g},${b}`

    if (colorKey !== currentColor) {
      content.push(`${r.toFixed(3)} ${g.toFixed(3)} ${b.toFixed(3)} rg`)
      currentColor = colorKey
    }
    content.push("BT")
    if (font !== currentFont || size !== currentSize) {
      content.push(`/${font} ${size} Tf`)
      currentFont = font
      currentSize = size
    }
    content.push(`${line.x.toFixed(2)} ${line.y.toFixed(2)} Td`)
    content.push(`(${escapePdfText(line.text)}) Tj`)
    content.push("ET")
  }
  content.push("Q")
  const contentStream = content.join("\n")

  const objects: string[] = []
  objects.push("<< /Type /Catalog /Pages 2 0 R >>")
  objects.push("<< /Type /Pages /Kids [3 0 R] /Count 1 >>")
  objects.push(
    `<< /Type /Page /Parent 2 0 R /MediaBox [0 0 ${PAGE_WIDTH} ${PAGE_HEIGHT}] /Resources << /Font << /F1 4 0 R /F2 5 0 R >> >> /Contents 6 0 R >>`
  )
  objects.push("<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica >>")
  objects.push("<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica-Bold >>")
  objects.push(`<< /Length ${contentStream.length} >>\nstream\n${contentStream}\nendstream`)

  let pdf = "%PDF-1.4\n"
  const offsets: number[] = [0]
  objects.forEach((obj, i) => {
    offsets.push(pdf.length)
    pdf += `${i + 1} 0 obj\n${obj}\nendobj\n`
  })

  const xrefStart = pdf.length
  let xref = `xref\n0 ${objects.length + 1}\n0000000000 65535 f \n`
  for (let i = 1; i <= objects.length; i++) {
    xref += `${offsets[i].toString().padStart(10, "0")} 00000 n \n`
  }
  pdf += xref
  pdf += `trailer\n<< /Size ${objects.length + 1} /Root 1 0 R >>\nstartxref\n${xrefStart}\n%%EOF`

  return new Blob([pdf], { type: "application/pdf" })
}

export function downloadPdf(blob: Blob, filename: string) {
  const url = URL.createObjectURL(blob)
  const a = document.createElement("a")
  a.href = url
  a.download = filename
  a.click()
  URL.revokeObjectURL(url)
}