---@class SSE
---@field active boolean if the stream is not active, you should stop the loop.
---@field private _queue table
local sse = {}

---Construct a new SSE object
---@return SSE
function sse:new()
  ngx.header.content_type = "text/event-stream"
  ngx.header.cache_control = "no-cache"
  ngx.header.connection = "keep-alive"
  ngx.status = ngx.HTTP_OK
  ngx.flush(true)

  local obj = {
    active = true,
    _queue = {},
  }

  ngx.on_abort(function()
    obj.active = false
  end)

  return setmetatable(obj, {__index = sse})
end

---add data to the stream, writing on the next dispatch.
---if `event` is given, it will be the key.
---@param data string
---@param event? string
---@return boolean status
function sse:enqueue(data, event)
  if not self.active then return false end
  table.insert(self._queue, {
    data = data,
    event = event,
  })
  return true
end

---send all events since the last dispatch and flush the queue.
---call this every iteration of the loop.
function sse:dispatch()
  while #self._queue > 0 do
    local msg = table.remove(self._queue, 1)
    if msg.event then
      ngx.print("event: " .. msg.event .. "\n")
    end
    ngx.print("data: " .. msg.data .. "\n\n")
  end
  ngx.flush(true)
end

---close the stream.
function sse:close()
  self.active = false
end

return sse