/** Render plain-text-only messages with clickable links and readable line breaks. */

const URL_RE = /https?:\/\/[^\s<>"')\]]+/gi

function escapeHtml(text: string): string {
  return text
    .replace(/&/g, "&amp;")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;")
}

function linkifyEscapedText(text: string): string {
  let out = ""
  let last = 0
  for (const match of text.matchAll(URL_RE)) {
    const index = match.index ?? 0
    out += text.slice(last, index)
    const url = match[0]
    out += `<a href="${url}" target="_blank" rel="noopener noreferrer">${url}</a>`
    last = index + url.length
  }
  out += text.slice(last)
  return out
}

/** Insert breaks before common transactional-mail markers when the body is one long line. */
function softenPlainTextWall(text: string): string {
  if (text.includes("\n")) return text
  return text
    .replace(/,\s*(Cher(?:e)?\s)/gi, ",\n\n$1")
    .replace(/,\s*(Le \d{2}\/\d{2}\/\d{4})/g, ",\n\n$1")
    .replace(/\.\s+(Nous restons)/g, ".\n\n$1")
    .replace(/\.\s+(L['’]équipe)/g, ".\n\n$1")
    .replace(/\.\s+(Pour obtenir)/g, ".\n\n$1")
    .replace(/\.\s+(Vous pouvez)/g, ".\n\n$1")
}

export function plainTextToDisplayHtml(text: string): string {
  const normalized = softenPlainTextWall(text.trim())
  const escaped = escapeHtml(normalized)
  const linked = linkifyEscapedText(escaped)
  return `<pre style="white-space:pre-wrap;font-family:inherit;margin:0;line-height:1.5;">${linked}</pre>`
}