    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.Chart.Plot.Candle
    -- Copyright   :  (c) Tim Docker 2006, 2014
    -- License     :  BSD-style (see chart/COPYRIGHT)
    --
    -- Candlestick charts for financial plotting
    --
    {-# LANGUAGE TemplateHaskell #-}

    module Graphics.Rendering.Chart.Plot.Candle(
        PlotCandle(..),
        Candle(..),

        plot_candle_title,
        plot_candle_line_style,
        plot_candle_tick_length,
        plot_candle_width,
        plot_candle_centre,
        plot_candle_fill,
        plot_candle_rise_fill_style,
        plot_candle_fall_fill_style,
        plot_candle_values,
    ) where

    import Control.Lens hiding (op)
    import Data.Monoid

    import Graphics.Rendering.Chart.Geometry hiding (close)
    import Graphics.Rendering.Chart.Drawing
    import Graphics.Rendering.Chart.Plot.Types
    import Control.Monad
    import Data.Colour (opaque)
    import Data.Colour.Names (white, blue)
    import Data.Default.Class

    -- | Value defining a financial interval: opening and closing prices, with
    --   maxima and minima; and a style in which to render them.
    --   By convention, there are different fill styles depending on whether
    --   the price rises (open < close) or falls (close < open).
    --   (This plot type can also be re-purposed for statistical intervals, e.g.
    --    minimum, first quartile, median, third quartile, maximum.)
    data PlotCandle x y = PlotCandle {
        _plot_candle_title           :: String,
        _plot_candle_line_style      :: LineStyle,
        _plot_candle_fill            :: Bool,
        _plot_candle_rise_fill_style :: FillStyle,
        _plot_candle_fall_fill_style :: FillStyle,
        _plot_candle_tick_length     :: Double,
        _plot_candle_width           :: Double,
        _plot_candle_centre          :: Double,
        _plot_candle_values          :: [Candle x y]
    }

    -- | A Value holding price intervals for a given x-coord.
    --   An alternative view is that these are statistical intervals: the
    --   0th, 25th, 50th, 75th, and 100th percentiles.
    data Candle x y = Candle { candle_x     :: x
                             , candle_low   :: y
                             , candle_open  :: y
                             , candle_mid   :: y
                             , candle_close :: y
                             , candle_high  :: y
                             } deriving (Show)

    instance ToPlot PlotCandle where
        toPlot p = Plot {
            _plot_render     = renderPlotCandle p,
            _plot_legend     = [(_plot_candle_title p, renderPlotLegendCandle p)],
            _plot_all_points = ( map candle_x pts
                               , concat [ [candle_low c, candle_high c]
                                        | c <- pts ] )
        }
          where
            pts = _plot_candle_values p

    renderPlotCandle :: PlotCandle x y -> PointMapFn x y -> BackendProgram ()
    renderPlotCandle p pmap =
        mapM_ (drawCandle p . candlemap) (_plot_candle_values p)
      where
        candlemap (Candle x lo op mid cl hi) =
            Candle x' lo' op' mid' cl' hi'
            where (Point x' mid')  = pmap' (x,mid)
                  (Point _  lo')   = pmap' (x,lo)
                  (Point _  op')   = pmap' (x,op)
                  (Point _  cl')   = pmap' (x,cl)
                  (Point _  hi')   = pmap' (x,hi)
        pmap' = mapXY pmap

    drawCandle :: PlotCandle x y -> Candle Double Double -> BackendProgram ()
    drawCandle ps (Candle x lo open mid close hi) = do
            let tl = _plot_candle_tick_length ps
            let wd = _plot_candle_width ps
            let ct = _plot_candle_centre ps
            let f  = _plot_candle_fill ps
            -- the pixel coordinate system is inverted wrt the value coords.
            when f $ withFillStyle (if open >= close
                                       then _plot_candle_rise_fill_style ps
                                       else _plot_candle_fall_fill_style ps) $
                        fillPath $ moveTo' (x-wd) open
                                <> lineTo' (x-wd) close
                                <> lineTo' (x+wd) close
                                <> lineTo' (x+wd) open
                                <> lineTo' (x-wd) open

            withLineStyle (_plot_candle_line_style ps) $ do
              strokePath $ moveTo' (x-wd) open
                        <> lineTo' (x-wd) close
                        <> lineTo' (x+wd) close
                        <> lineTo' (x+wd) open
                        <> lineTo' (x-wd) open

              strokePath $ moveTo' x (min lo hi)
                        <> lineTo' x (min open close)
                        <> moveTo' x (max open close)
                        <> lineTo' x (max hi lo)

              when (tl > 0) $ strokePath $ moveTo' (x-tl) lo
                                        <> lineTo' (x+tl) lo
                                        <> moveTo' (x-tl) hi
                                        <> lineTo' (x+tl) hi

              when (ct > 0) $ strokePath $ moveTo' (x-ct) mid
                                        <> lineTo' (x+ct) mid

    renderPlotLegendCandle :: PlotCandle x y -> Rect -> BackendProgram ()
    renderPlotLegendCandle pc (Rect p1 p2) = do
        drawCandle pc2 (Candle (xwid*1/4) lo open mid close hi)
        drawCandle pc2 (Candle (xwid*2/3) lo close mid open hi)
      where
        pc2   = pc { _plot_candle_width = 2 }
        xwid  = p_x p1 + p_x p2
        lo    = max (p_y p1) (p_y p2)
        mid   = (p_y p1 + p_y p2)/2
        hi    = min (p_y p1) (p_y p2)
        open  = (lo + mid) / 2
        close = (mid + hi) / 2

    instance Default (PlotCandle x y) where
      def = PlotCandle
        { _plot_candle_title       = ""
        , _plot_candle_line_style  = solidLine 1 $ opaque blue
        , _plot_candle_fill        = False
        , _plot_candle_rise_fill_style  = solidFillStyle $ opaque white
        , _plot_candle_fall_fill_style  = solidFillStyle $ opaque blue
        , _plot_candle_tick_length = 2
        , _plot_candle_width       = 5
        , _plot_candle_centre      = 0
        , _plot_candle_values      = []
        }

    $( makeLenses ''PlotCandle )