module Database.RRDtool.Create
    ( DataSource(..)
    , 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.
data DataSource
    = -- |GAUGE is for things like temperatures or number of people in
      -- a room or the value of a RedHat share.
    GAUGE {
        -- |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_]@.
        dsName :: !String
        -- |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*@.
      , dsHeartbeat :: !NominalDiffTime
        -- |'dsMin' and 'dsMax' Define the expected range values for
        -- data supplied by a data source. If 'dsMin' and\/or 'dsMax'
        -- any value outside the defined range will be regarded as
        -- @*UNKNOWN*@. If you do not know or care about 'dsMin' and
        -- 'dsMax', set them to 'Nothing' for unknown. Note that
        -- 'dsMin' and 'dsMax' 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.
      , dsMin :: !(Maybe Double)
        -- |See 'dsMin'.
      , dsMax :: !(Maybe Double)
    }
    -- |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.
    | COUNTER {
        dsName      :: !String
      , dsHeartbeat :: !NominalDiffTime
      , dsMin       :: !(Maybe Double)
      , dsMax       :: !(Maybe Double)
    }
    -- |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.
    | DERIVE {
        dsName      :: !String
      , dsHeartbeat :: !NominalDiffTime
      , dsMin       :: !(Maybe Double)
      , dsMax       :: !(Maybe Double)
    }
    -- |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.
    | ABSOLUTE {
        dsName      :: !String
      , dsHeartbeat :: !NominalDiffTime
      , dsMin       :: !(Maybe Double)
      , dsMax       :: !(Maybe Double)
    }
    -- |COMPUTE 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
    | forall a. IsCommonExpr a => COMPUTE {
        dsName :: !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
      , dsExpr :: !a
    }

dsTest :: DataSource
dsTest = COMPUTE {
           dsName = "foo"
--         , dsExpr = Previous :<: Const 100
--         , dsExpr = Var "foo" :<: Const 100
           , dsExpr = 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"