module Database.RRDtool.Create
    ( DataSource
    , ExternalDSType(..)
    , ExternalDataSource(..)
    , ComputedDataSource(..)
    , createRRD

    -- Data.HList
    , (.*.)    
    , HNil(..)

    -- Database.RRDtool.Expression
    , Constant(..)
    , IsVarName
    , Variable(..)
    , CommonUnaryOp(..)
    , CommonBinaryOp(..)
    , CommonTrinaryOp(..)
    , CommonSetOp(..)
    , TrendOp(..)
    , VariableShiftPredictOp(..)
    , FixedShiftPredictOp(..)
    , CommonValue(..)
    )
    where

import Data.HList
import Data.Time.Clock
import Data.Time.Clock.POSIX
import Database.RRDtool.Expression


-- |A single RRD can accept input from several data sources (DS), for
-- example incoming and outgoing traffic on a specific communication
-- line. With the DS configuration option you must define some basic
-- properties of each data source you want to store in the RRD.
--
-- /NOTE on COUNTER vs DERIVE/
--
-- by Don Baarda <don.baarda@baesystems.com>
--
-- If you cannot tolerate ever mistaking the occasional counter reset
-- for a legitimate counter wrap, and would prefer \"Unknowns\" for
-- all legitimate counter wraps and resets, always use DERIVE with
-- @'dsMin' = 0@. Otherwise, using COUNTER with a suitable max will
-- return correct values for all legitimate counter wraps, mark some
-- counter resets as \"Unknown\", but can mistake some counter resets
-- for a legitimate counter wrap.
--
-- For a 5 minute step and 32-bit counter, the probability of
-- mistaking a counter reset for a legitimate wrap is arguably about
-- 0.8% per 1Mbps of maximum bandwidth. Note that this equates to 80%
-- for 100Mbps interfaces, so for high bandwidth interfaces and a
-- 32bit counter, DERIVE with @'dsMin' = 0@ is probably preferable. If
-- you are using a 64bit counter, just about any max setting will
-- eliminate the possibility of mistaking a reset for a counter wrap.
class DataSource ds

data ExternalDSType
    = GAUGE    -- ^GAUGE is for things like temperatures or number of
               -- people in a room or the value of a RedHat share.
    | COUNTER  -- ^COUNTER is for continuous incrementing counters
               -- like the ifInOctets counter in a router. The COUNTER
               -- data source assumes that the counter never
               -- decreases, except when a counter overflows. The
               -- update function takes the overflow into account. The
               -- counter is stored as a per-second rate. When the
               -- counter overflows, RRDtool checks if the overflow
               -- happened at the 32bit or 64bit border and acts
               -- accordingly by adding an appropriate value to the
               -- result.
    | DERIVE   -- ^DERIVE will store the derivative of the line going
               -- from the last to the current value of the data
               -- source. This can be useful for gauges, for example,
               -- to measure the rate of people entering or leaving a
               -- room. Internally, derive works exactly like COUNTER
               -- but without overflow checks. So if your counter does
               -- not reset at 32 or 64 bit you might want to use
               -- DERIVE and combine it with a 'dsMin' value of 0.
    | ABSOLUTE -- ^ABSOLUTE is for counters which get reset upon
               -- reading. This is used for fast counters which tend
               -- to overflow. So instead of reading them normally you
               -- reset them after every read to make sure you have a
               -- maximum time available before the next
               -- overflow. Another usage is for things you count like
               -- number of messages since the last update.
    deriving (Show, Eq, Ord)

instance DataSource ExternalDSType

data ExternalDataSource
    = ExternalDataSource {
        -- |The name you will use to reference this particular data
        -- source from an RRD. A ds name must be 1 to 19 characters
        -- long in the characters @[a-zA-Z0-9_]@.
        edsName :: !String
        -- |The type of this data source.
      , edsType :: !ExternalDSType
        -- |Defines the maximum number of seconds that may pass
        -- between two updates of this data source before the value of
        -- the data source is assumed to be @*UNKNOWN*@.
      , edsHeartbeat :: !NominalDiffTime
        -- |'edsMin' and 'edsMax' Define the expected range values for
        -- data supplied by a data source. If 'edsMin' and\/or 'edsMax'
        -- any value outside the defined range will be regarded as
        -- @*UNKNOWN*@. If you do not know or care about 'edsMin' and
        -- 'edsMax', set them to 'Nothing' for unknown. Note that
        -- 'edsMin' and 'edsMax' always refer to the processed values of
        -- the DS. For a traffic-'COUNTER' type DS this would be the
        -- maximum and minimum data-rate expected from the device.
        --
        -- If information on minimal\/maximal expected values is
        -- available, always set the min and\/or max properties. This
        -- will help RRDtool in doing a simple sanity check on the
        -- data supplied when running update.
      , edsMin :: !(Maybe Double)
        -- |See 'edsMin'.
      , edsMax :: !(Maybe Double)
      }
    deriving (Show, Eq, Ord)


-- |ComputedDataSource is for storing the result of a formula applied
-- to other data sources in the RRD. This data source is not supplied
-- a value on update, but rather its Primary Data Points (PDPs) are
-- computed from the PDPs of the data sources according to the
-- rpn-expression that defines the formula. Consolidation functions
-- are then applied normally to the PDPs of the COMPUTE data source
-- (that is the rpn-expression is only applied to generate PDPs). In
-- database software, such data sets are referred to as \"virtual\" or
-- \"computed\" columns.
--
-- FIXME: doc links
data ComputedDataSource e
    = ComputedDataSource {
        -- |See 'edsName'
        cdsName :: !String
        -- |rpn-expression defines the formula used to compute the
        -- PDPs of a COMPUTE data source from other data sources in
        -- the same \<RRD\>. It is similar to defining a CDEF argument
        -- for the graph command.  For COMPUTE data sources, the
        -- following RPN operations are not supported: COUNT, PREV,
        -- TIME, and LTIME. In addition, in defining the RPN
        -- expression, the COMPUTE data source may only refer to the
        -- names of data source listed previously in the create
        -- command. This is similar to the restriction that CDEFs must
        -- refer only to DEFs and CDEFs previously defined in the same
        -- graph command.
        -- 
        -- FIXME: doc links
      , cdsExpr :: !e
    }
    deriving (Show, Eq, Ord)

instance IsCommonExpr e => DataSource (ComputedDataSource e)


dsTest = ComputedDataSource {
           cdsName = "foo"
--       , dsExpr = Previous :<: Const 100
--       , dsExpr = Var "foo" :<: Const 100
         , cdsExpr = AverageOf (Const 100 .*. Const 200 .*. HNil)
         }

-- |The 'createRRD' function lets you set up new Round Robin Database
-- (RRD) files. The file is created at its final, full size and filled
-- with @*UNKNOWN*@ data.
createRRD
    :: FilePath -- ^The name of the RRD you want to create. RRD files
                -- should end with the extension @.rrd@. However,
                -- RRDtool will accept any filename.
    -> Bool -- ^Do not clobber an existing file of the same name.
    -> Maybe POSIXTime -- ^Specifies the time in seconds since
                       -- @1970-01-01 UTC@ when the first value should
                       -- be added to the RRD. RRDtool will not accept
                       -- any data timed before or at the time
                       -- specified. (default: @now - 10s@)
    -> Maybe NominalDiffTime -- ^Specifies the base interval in
                             -- seconds with which data will be fed
                             -- into the RRD. (default: 300 sec)
--    -> [DataSource] -- ^Data sources to accept input from.
    -> IO ()
createRRD = error "FIXME"