local babycode = {}

local string_trim = require("lapis.util").trim
local emoji = require("lib.babycode-emoji")

local function s_split(s, delimiter, max_matches, trim, allow_empty)
  local result = {}
  if s == "" then
    return result
  end
  trim = trim == nil and true or trim
  local tr = function(subj)
    if trim then return string_trim(subj) else return subj end
  end
  max_matches = max_matches or -1
  allow_empty = allow_empty == nil and true or allow_empty
  
  if delimiter == "" then
    for i=1, #s do
      local c = s:sub(i, 1)
      if allow_empty or c ~= "" then
        table.insert(result, c)
        if max_matches > 0 and #result == max_matches then
          break
        end
      end
    end
    return result
  end
  
  local current_pos = 1
  local delim_len = #delimiter
  
  while true do
    if max_matches > 0 and #result >= max_matches then
      break
    end
---@diagnostic disable-next-line: param-type-mismatch
    local start_pos, end_pos = s:find(delimiter, current_pos, true)
    if not start_pos then
      break
    end
    local substr = s:sub(current_pos, start_pos - 1)
    if allow_empty or substr ~= "" then
      table.insert(result, tr(substr))
    end
    current_pos = end_pos + 1
  end
  
  local substr = s:sub(current_pos)
  if allow_empty or substr ~= "" then
    table.insert(result, tr(substr))
  end
  
  return result
end

local function get_list_items(list_body, escape_html)
  list_body = list_body:gsub("  +%s*\r?\n", "<br>")
  list_body = list_body:gsub("(%S)(\r?\n\r?\n)\r?\n*", "%1\1")
  local list_items = s_split(list_body, "\1")
  local lis = ""
  for _, li in ipairs(list_items) do
    local rendered = babycode.to_html(li, escape_html)
    lis = lis .. "<li>" .. rendered .. "</li>"
  end
  return lis
end

---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
  local text = escape_html(s)
  -- extract code blocks and store them as placeholders
  -- don't want to process bbcode embedded into a code block
  local code_blocks = {}
  local inline_codes = {}
  text = text: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)
  
  text = text:gsub("%[ul%](.-)%[/ul%]", function(list_body)
    return "<ul>" .. get_list_items(list_body, escape_html) .. "</ul>"
  end)
  text = text:gsub("%[ol%](.-)%[/ol%]", function(list_body)
    return "<ol>" .. get_list_items(list_body, escape_html) .. "</ol>"
  end)
  
  -- images
  local images = {}
  text = text:gsub("%[img=(.-)%](.-)%[/img%]", function (img, alt)
    table.insert(images, {img = img, alt = alt})
    return "\1IMG:"..#images.."\1"
  end)
  
  -- normalize newlines, attempt #4
  text = text:gsub("  +%s*\r?\n", "<br>")
  text = text:gsub("(%S)(\r?\n\r?\n)\r?\n*", "%1<br><br>")

  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)

  -- 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>")
  
  -- these can be nested, so replace open and closed separately
  text = text:gsub("%[(/?)quote%]", "<%1blockquote>")
  
  text = text:gsub(":(.-):", function(code)
    if emoji[code] then
      return emoji[code]
    else
      return code
    end
  end)

  -- 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>")

  -- <div class=\"post-img-container\"><img src=%1 alt=%2></div>
  text = text:gsub("\1IMG:(%d+)\1", function (n)
    local img = images[tonumber(n)]
    return ("<div class=\"block-img-container\"><img class=\"block-img\" src=\"%s\" alt=\"%s\"></div>"):format(img.img, img.alt)
  end)
  -- 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