require "cjson"

-- Generic decoder for Canary JSON data. This will extract all JSON
-- keys and add them to the `Fields` variable of the created
-- Heka message.
--
-- Example use:
--
-- [CanaryDecoder]
-- type = "SandboxDecoder"
-- script_type = "lua"
-- filename = "/usr/share/heka/lua_decoders/canary.lua"
-- module_directory = "/usr/share/lua"
--
-- [HttpInput]
-- url = "https://api.canary.io/checks/https-github.com/measurements?range=10"
-- ticker_interval = 1
-- decoder = "CanaryDecoder"
--
-- [fileoutput]
-- type = "FileOutput"
-- message_matcher = "Fields[location] == 'do-ny2'"
-- path = "/var/log/heka/canary-output.log"
-- prefix_ts = true
-- perm = "666"

function process_message()
   local raw_message = read_message("Payload")

   local json = cjson.decode(raw_message)
   if not json then
     -- When plain text is found, ship it in it's raw form.
     inject_message(raw_message)
     return 0
   end

   for element = 1, #json do
     local cj2 = cjson.new()

     local fields = json[element]
     if fields.check then
       fields.check_id = fields.check.id
       fields.check_url = fields.check.url
       fields.check = nil
     end

     local message = {
       Type = "Canary",
       Payload = cj2.encode(json[element]),
       Fields = fields
     }

     inject_message(message)
   end
   return 0
end