{-# LANGUAGE NoImplicitPrelude, PackageImports, UnicodeSyntax #-}

module System.ProgressBar
    ( -- * Progress bars
      progressBar
    , mkProgressBar
      -- * Labels
    , Label
    , noLabel
    , msg
    , percentage
    , exact
    ) where

import "base" Data.Bool     ( otherwise )
import "base" Data.Function ( ($) )
import "base" Data.List     ( null, length, genericLength, genericReplicate )
import "base" Data.Ord      ( min, max )
import "base" Data.Ratio    ( (%) )
import "base" Data.String   ( String )
import "base" Prelude       ( (+), (-), round, floor )
import "base" System.IO     ( IO, putStr, putChar )
import "base" Text.Printf   ( printf )
import "base" Text.Show     ( show )
import "base-unicode-symbols" Data.Bool.Unicode ( (∧) )
import "base-unicode-symbols" Data.Eq.Unicode   ( (≢) )
import "base-unicode-symbols" Prelude.Unicode   ( ℤ, ℚ, (⋅) )


-- | Print a progress bar
--
-- Erases the current line! (by outputting '\r') Does not print a
-- newline '\n'. Subsequent invocations will overwrite the previous
-- output.
--
-- Remember to set the correct buffering mode for stdout:
--
-- > import System.IO ( hSetBuffering, BufferMode(NoBuffering), stdout )
-- > hSetBuffering stdout NoBuffering
progressBar ∷ Label -- ^ Prefixed label.
            → Label -- ^ Postfixed label.
            → ℤ     -- ^ Total progress bar width in characters.
            → ℤ     -- ^ Amount of work completed.
            → ℤ     -- ^ Total amount of work.
            → IO ()
progressBar mkPreLabel mkPostLabel width todo done = do
    putChar '\r'
    putStr $ mkProgressBar mkPreLabel mkPostLabel width todo done

-- | Renders a progress bar
--
-- >>> mkProgressBar (msg "Working") percentage 40 30 100
-- "Working [=======>.................]  30%"
mkProgressBar ∷ Label -- ^ Prefixed label.
              → Label -- ^ Postfixed label.
              → ℤ     -- ^ Total progress bar width in characters.
              → ℤ     -- ^ Amount of work completed.
              → ℤ     -- ^ Total amount of work.
              → String
mkProgressBar mkPreLabel mkPostLabel width todo done =
    printf "%s%s[%s%s%s]%s%s"
           preLabel
           prePad
           (genericReplicate completed '=')
           (if remaining ≢ 0 ∧ completed ≢ 0 then ">" else "")
           (genericReplicate (remaining - if completed ≢ 0 then 1 else 0)
                             '.'
           )
           postPad
           postLabel
  where
    -- Amount of work completed.
    fraction ∷ ℚ
    fraction | done ≢ 0  = todo % done
             | otherwise = 0 % 1

    -- Amount of characters available to visualize the progress.
    effectiveWidth = max 0 $ width - usedSpace
    usedSpace = 2 + genericLength preLabel
                  + genericLength postLabel
                  + genericLength prePad
                  + genericLength postPad

    -- Number of characters needed to represent the amount of work
    -- that is completed. Note that this can not always be represented
    -- by an integer.
    numCompletedChars ∷ ℚ
    numCompletedChars = fraction ⋅ (effectiveWidth % 1)

    completed, remaining ∷ ℤ
    completed = min effectiveWidth $ floor numCompletedChars
    remaining = effectiveWidth - completed

    preLabel, postLabel ∷ String
    preLabel  = mkPreLabel  todo done
    postLabel = mkPostLabel todo done

    prePad, postPad ∷ String
    prePad  = pad preLabel
    postPad = pad postLabel

    pad ∷ String → String
    pad s | null s    = ""
          | otherwise = " "


-- | A label that can be pre- or postfixed to a progress bar.
type Label = ℤ → ℤ → String

-- | The empty label.
--
-- >>> noLabel 30 100
-- ""
noLabel ∷ Label
noLabel = msg ""

-- | A label consisting of a static string.
--
-- >>> msg "foo" 30 100
-- "foo"
msg ∷ String → Label
msg s _ _ = s

-- | A label which displays the progress as a percentage.
--
-- Constant width property:
-- ∀ d t : ℕ. d ≤ t → length (percentage d t) ≡ 4
--
-- >>> percentage 30 100
-- " 30%"

-- ∀ d t : ℕ. d ≤ t → length (percentage d t) ≡ 3
percentage ∷ Label
percentage done todo = printf "%3i%%" (round (done % todo ⋅ 100) ∷ ℤ)

-- | A label which displays the progress as a fraction of the total
-- amount of work.
--
-- Equal width property:
-- ∀ d₁ d₂ t : ℕ. d₁ ≤ d₂ ≤ t → length (exact d₁ t) ≡ length (exact d₂ t)
--
-- >>> exact 30 100
-- " 30/100"

-- ∀ d₁ d₂ t : ℕ. d₁ ≤ d₂ ≤ t → length (exact d₁ t) ≡ length (exact d₂ t)
exact ∷ Label
exact done total = printf "%*i/%s" (length totalStr) done totalStr
  where
    totalStr = show total