template.lua

local template = {}

function template.escape(data)
  return tostring(data == nil and "" or data):gsub("[\">/<'&]", {
    ["&"] = "&amp;",
    ["<"] = "&lt;",
    [">"] = "&gt;",
    ['"'] = "&quot;",
    ["'"] = "&#39;",
    ["/"] = "&#47;"
  })
end

-- If it's lua 5.2+, _ENV will appears
local wrapper_fn do
  if _ENV then 
    local wrapper, err = load(
      [[return function(_ENV,exec,...) local f=...; f(exec, _ENV); end]],
      "wrapper", "t"
    )
    if not wrapper then error(err) end
    wrapper_fn = wrapper()
  end
end

function template.print(data, args, callback)
  local callback = callback or print
  
  local env = args or {}
  setmetatable(env, { __index = _G })

  local function exec(ins)
    if type(ins) ~= "function" then
      return callback(tostring(ins == nil and "" or ins))
    end
    -- if type(data) == "function"

    -- Lua 5.2+ , use call delegate
    if wrapper_fn then
      return wrapper_fn(env, exec, ins)
    end

    -- Lua 5.1
    setfenv(ins, env)
    ins(exec)
  end

  exec(data)
end


local template_entry do
  local s = "function(_"
  if not _ENV
  then s = s .. ') '
  else s = s .. ",_ENV) "
  end
  template_entry = s
end

function template.parse(data, minify)
  local str =
    "return " .. template_entry .. 
      "function __(...)" ..
        "_(require('template').escape(...))" ..
      "end " ..
      "_[=[" ..
      data:
        gsub("[][]=[][]", ']=]_"%1"_[=['):
        gsub("<%%=", "]=]_("):
        gsub("<%%", "]=]__("):
        gsub("%%>", ")_[=["):
        gsub("<%?", "]=] "):
        gsub("%?>", " _[=[") ..
      "]=] " ..
    "end"

  if minify then
    str = str:
      gsub("^[ %s]*", ""):
      gsub("[ %s]*$", ""):
      gsub("%s+", " ")
  end
  return str
end

--[[
  `loadstring` was deprecated since 5.2, use `load` instead
  (see: https://www.lua.org/manual/5.2/manual.html#8.2)
]]--
local loadstring = loadstring or function(str, chkn)
  return load(str, chkn or str, 't') -- We will pass _ENV manually
end

function template.compile(...)
  local f, err = loadstring(template.parse(...))
  if err then error(err); end
  return f()
end

function template.render(data, args)
  local parts = {}
  local i = 0

  template.print(data, args, function(p)
    i = i + 1
    parts[i] = p
  end)

  return table.concat(parts)
end

return template