module Database.RRDtool
    ( DataSource(..)
    , Expr(..)
    , createRRD
    )
    where

import Data.Time.Clock
import Data.Time.Clock.POSIX


-- |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
    | 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 :: !Expr
      }
    deriving (Eq, Ord, Show)

data Expr
    = UNK
    deriving (Show, Eq, Ord)

-- |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"