# indie:lang_version = 5
from indie import indicator, param, source, plot, color
from indie.algorithms import Ema, Sma


@indicator('Env', overlay_main_pane=True)  # Envelope
@param.int('length', default=20, min=1)
@param.float('percent', default=10.0)
@param.source('src', default=source.CLOSE, title='Source')
@param.bool('exponential', default=False)
@plot.line('lower', color=color.BLUE, title='Lower')
@plot.line('basis', color=color.RED, title='Basis')
@plot.line('upper', color=color.BLUE, title='Upper')
@plot.fill('lower', 'upper', color=color.AQUA(0.05), title='Background')
def Main(self, length, percent, src, exponential):
    basis = 0.0
    if exponential:
        basis = Ema.new(src, length)[0]
    else:
        basis = Sma.new(src, length)[0]
    k = percent / 100.0
    upper = basis * (1 + k)
    lower = basis * (1 - k)
    return lower, basis, upper, plot.Fill()