plot_daily_gas_usage.jl

function plot_daily_gas_usage(df_all_gas::DataFrame,
                              month::String,
                              year::Int64)

    df_gas = process_gas_df(df_all_gas)

    df_gas = filter(row -> occursin(month, Dates.monthname(row.Date)) &&
	                            Dates.year(row.Date) == year,
		                    df_gas)

    total_gas = sum(df_gas.CentralHeating) + sum(df_gas.HotWater)
    total_gas = round(total_gas, digits = 2)

    sdf_gas = stack(df_gas, 
	            [:CentralHeating, :HotWater], 
	            variable_name = :UsageType,
	            value_name = :UsageUnits)	

    figure = sdf_gas |>
	     @vlplot(:bar,
	     x = {:Date, 
	          "axis" = {"title" = "Time",
		   "labelFontSize" = 10, 
		   "titleFontSize" = 12,
		  }},
	     y = {:UsageUnits, 
		   "axis" = {"title" = "Gas usage [m^3]",
		   "labelFontSize" = 10, 
		   "titleFontSize" = 12 }},
	     width = 500, 
	     height = 300,
	    "title" = {"text" = "Daily gas usage from $month - $year, total = $total_gas m^3", 
		       "fontSize" = 14},
	     color = :UsageType)

    return figure
	
end