local babycode = {}

---renders babycode to html
---@param s string input babycode
---@param escape_html fun(s: string): string function that escapes html
function babycode.to_html(s, escape_html)
  if not s or s == "" then return "" end
  -- extract code blocks first and store them as placeholders
  -- don't want to process bbcode embedded into a code block
  local code_blocks = {}
  local inline_codes = {}
  s = escape_html(s)
  local text = s:gsub("%[code%](.-)%[/code%]", function(code)
    local is_inline = code:match("\n") == nil
    if is_inline then
      table.insert(inline_codes, code)
      return "\1ICODE:"..#inline_codes.."\1"
    else
      -- strip leading and trailing newlines, preserve others
      local m, _ = code:gsub("^%s*(.-)%s*$", "%1")
      table.insert(code_blocks, m)
      return "\1CODE:"..#code_blocks.."\1"
    end
  end)

  local url_tags = {}
  -- replace `[url=https://example.com]Example[/url] tags
  text = text:gsub("%[url=([^%]]+)%](.-)%[/url%]", function(url, label)
    table.insert(url_tags, {url = url, label = label})
    return "\1URL:"..#url_tags.."\1"
  end)
  
  -- replace `[url]https://example.com[/url] tags
  -- text = text:gsub("%[url%]([^%]]+)%[/url%]", function(url)
  --   return '<a href="'..url..'">'..url..'</a>'
  -- end)

  -- bold, italics, strikethrough
  text = text:gsub("%[b%](.-)%[/b%]", "<strong>%1</strong>")
  text = text:gsub("%[i%](.-)%[/i%]", "<em>%1</em>")
  text = text:gsub("%[s%](.-)%[/s%]", "<del>%1</del>")
  
  text = text:gsub("%[quote%](.-)%[/quote%]", "<blockquote>%1</blockquote>")

  -- replace loose links
  text = text:gsub("(https?://[%w-_%.%?%.:/%+=&~%@#%%]+[%w-/])", function(url)
    if not text:find('<a[^>]*>'..url..'</a>') then
      return '<a href="'..url..'">'..url..'</a>'
    end
    return url
  end)

  text = text:gsub("\1URL:(%d+)\1", function(n)
    local url = url_tags[tonumber(n)]
    return ("<a href=%s>%s</a>"):format(url.url, url.label)
  end)

  -- rule
  text = text:gsub("\n+%-%-%-", "<hr>")
  
  -- normalize newlines, replace them with <br>
  text = text:gsub("\r?\n\r?\n+", "<br>")--:gsub("\r?\n", "<br>")

  -- replace code block placeholders back with their original contents
  text = text:gsub("\1CODE:(%d+)\1", function(n)
    local code = code_blocks[tonumber(n)]
    local button = ("<button type=button class=\"copy-code\" value=\"%s\">Copy</button>"):format(code)
    return "<pre><span class=\"copy-code-container\">" .. button .. "</span><code>"..code.."</code></pre>"
  end)
  
  text = text:gsub("\1ICODE:(%d+)\1", function (n)
    local code = inline_codes[tonumber(n)]
    return "<code class=\"inline-code\">" .. code .. "</code>"
  end)

  return text
end

return babycode