{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}

module PGExtras.Queries.IndexUsage (indexUsageSQL, displayIndexUsage) where

import PGExtras.Helpers (maybeText, maybeInt)
import Database.PostgreSQL.Simple
import Text.RawString.QQ
import qualified Data.Text as Text
import Control.Monad (forM_)
import Data.List (intercalate)

indexUsageSQL :: Query
indexUsageSQL :: Query
indexUsageSQL = [r|SELECT relname,
   CASE idx_scan
     WHEN 0 THEN 'Insufficient data'
     ELSE (100 * idx_scan / (seq_scan + idx_scan))::text
   END percent_of_times_index_used,
   n_live_tup rows_in_table
 FROM
   pg_stat_user_tables
 ORDER BY
   n_live_tup DESC;|]

displayIndexUsage :: [(Maybe Text.Text, Maybe Text.Text, Maybe Int)] -> IO ()
displayIndexUsage :: [(Maybe Text, Maybe Text, Maybe Int)] -> IO ()
displayIndexUsage rows :: [(Maybe Text, Maybe Text, Maybe Int)]
rows = do
  String -> IO ()
putStrLn (String -> IO ()) -> String -> IO ()
forall a b. (a -> b) -> a -> b
$ String
description
  String -> IO ()
putStrLn (String -> IO ()) -> String -> IO ()
forall a b. (a -> b) -> a -> b
$ String -> [String] -> String
forall a. [a] -> [[a]] -> [a]
intercalate " | " [String]
tableHeaders
  [(Maybe Text, Maybe Text, Maybe Int)]
-> ((Maybe Text, Maybe Text, Maybe Int) -> IO ()) -> IO ()
forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
t a -> (a -> m b) -> m ()
forM_ [(Maybe Text, Maybe Text, Maybe Int)]
rows (((Maybe Text, Maybe Text, Maybe Int) -> IO ()) -> IO ())
-> ((Maybe Text, Maybe Text, Maybe Int) -> IO ()) -> IO ()
forall a b. (a -> b) -> a -> b
$ \(arg1 :: Maybe Text
arg1, arg2 :: Maybe Text
arg2, arg3 :: Maybe Int
arg3) ->
    String -> IO ()
putStrLn (String -> IO ()) -> String -> IO ()
forall a b. (a -> b) -> a -> b
$ Maybe Text -> String
maybeText(Maybe Text
arg1) String -> String -> String
forall a. [a] -> [a] -> [a]
++ " | " String -> String -> String
forall a. [a] -> [a] -> [a]
++ Maybe Text -> String
maybeText(Maybe Text
arg2)String -> String -> String
forall a. [a] -> [a] -> [a]
++ " | " String -> String -> String
forall a. [a] -> [a] -> [a]
++ Maybe Int -> String
maybeInt(Maybe Int
arg3)

description :: [Char]
description :: String
description = "Index hit rate (effective databases are at 99% and up)"

tableHeaders :: [[Char]]
tableHeaders :: [String]
tableHeaders = ["relname", "percent_of_times_index_used", "rows_in_table"]