import sharp from 'sharp'

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

const OG_WIDTH = 1200
const OG_HEIGHT = 630
const MAX_TITLE_LINES = 3
const MAX_CHARS_PER_LINE = 38

// ---------------------------------------------------------------------------
// Helpers (exported for testing)
// ---------------------------------------------------------------------------

/**
 * Escape special XML characters to prevent SVG injection.
 */
export function escapeXml(text: string): string {
  return text
    .replace(/&/g, '&')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;')
    .replace(/'/g, '&apos;')
}

/**
 * Word-wrap text into lines of at most `maxCharsPerLine` characters,
 * limited to `maxLines` total. If truncated, the last line ends with
 * an ellipsis character.
 */
export function wrapText(text: string, maxCharsPerLine: number, maxLines: number): string[] {
  const words = text.split(/\s+/).filter((w) => w.length > 0)
  if (words.length === 0) {
    return []
  }

  const lines: string[] = []
  let currentLine = ''

  for (const word of words) {
    if (lines.length >= maxLines) {
      break
    }

    const testLine = currentLine ? `${currentLine} ${word}` : word
    if (testLine.length > maxCharsPerLine && currentLine) {
      lines.push(currentLine)
      currentLine = word
    } else {
      currentLine = testLine
    }
  }

  if (currentLine && lines.length < maxLines) {
    lines.push(currentLine)
  }

  // Check if text was truncated
  const joinedLength = lines.join(' ').length
  const fullLength = words.join(' ').length
  if (fullLength > joinedLength && lines.length > 0) {
    const lastIdx = lines.length - 1
    const lastLine = lines[lastIdx] ?? ''
    if (lastLine.length > maxCharsPerLine - 1) {
      lines[lastIdx] = lastLine.slice(0, maxCharsPerLine - 1) + '\u2026'
    } else {
      lines[lastIdx] = lastLine + '\u2026'
    }
  }

  return lines
}

// ---------------------------------------------------------------------------
// SVG generation
// ---------------------------------------------------------------------------

export interface OgImageParams {
  title: string
  category: string
  communityName: string
}

/**
 * Generate an SVG string for a cross-post OG image.
 *
 * Layout (1200x630):
 * - Dark background (#1c1b22)
 * - Category badge (cyan pill)
 * - Community name (grey subheading)
 * - Topic title (white, word-wrapped, max 3 lines)
 * - Barazo branding footer
 */
export function generateOgSvg(params: OgImageParams): string {
  const titleLines = wrapText(params.title, MAX_CHARS_PER_LINE, MAX_TITLE_LINES)
  const categoryText = escapeXml(params.category.toUpperCase())
  const communityText = escapeXml(params.communityName)

  // Estimate category badge width (~11px per char + 32px padding)
  const categoryWidth = String(Math.max(categoryText.length * 11 + 32, 60))
  const categoryTextX = String(60 + 16)
  const categoryTextY = String(60 + 24)
  const footerY = String(OG_HEIGHT - 40)
  const brandingX = String(OG_WIDTH - 60)
  const width = String(OG_WIDTH)
  const height = String(OG_HEIGHT)

  const titleSvg = titleLines
    .map(
      (line, i) =>
        `<text x="60" y="${String(280 + i * 60)}" font-family="sans-serif" font-size="48" font-weight="bold" fill="white">${escapeXml(line)}</text>`
    )
    .join('\n    ')

  return `<svg width="${width}" height="${height}" xmlns="http://www.w3.org/2000/svg">
  <rect width="${width}" height="${height}" fill="#1c1b22"/>

  <!-- Category badge -->
  <rect x="60" y="60" width="${categoryWidth}" height="36" rx="8" fill="#0ea5e9"/>
  <text x="${categoryTextX}" y="${categoryTextY}" font-family="sans-serif" font-size="16" font-weight="600" fill="white" dominant-baseline="central">${categoryText}</text>

  <!-- Community name -->
  <text x="60" y="150" font-family="sans-serif" font-size="24" fill="#9ca3af">${communityText}</text>

  <!-- Topic title -->
  ${titleSvg}

  <!-- Barazo branding -->
  <text x="60" y="${footerY}" font-family="sans-serif" font-size="18" fill="#6b7280">Powered by Barazo</text>
  <text x="${brandingX}" y="${footerY}" font-family="sans-serif" font-size="18" fill="#6b7280" text-anchor="end">barazo.forum</text>
</svg>`
}

// ---------------------------------------------------------------------------
// PNG generation
// ---------------------------------------------------------------------------

/**
 * Generate a branded OG image as a PNG buffer.
 *
 * Produces a 1200x630 PNG suitable for use as the `thumb` in
 * Bluesky's `app.bsky.embed.external` records.
 */
export async function generateOgImage(params: OgImageParams): Promise<Buffer> {
  const svg = generateOgSvg(params)
  return sharp(Buffer.from(svg)).png().toBuffer()
}