Forex cycle (calculate the average rate 'M' automatice)

Dears,

My customer is implementing Forex and Commodities:

1- what should be the Day,month, year end closing for such a components in TRM?

Note:i have read posts on SCN but there were transactions related to other component and i didn't know whats related to the above!

2- In foreign currency exchange company, how to calculate the average cost for a currency based on the purchase rate?! for example:

The company local currency is SAR, bought 1000 USD with exchange rate 1 USD = 3.75 SAR (purchase rate)

then bought another 100 USD with exchange rate 1 USD = 3.77 SAR (Purchase rate)

so the total cost for 1100 USD should be 3.76 which equals 4136 SAR

if i sell 500 USD with rate 1 USD = 3.79 SAR (sales price ) which equal 1895 SAR as a revenue but the profit will be as below

500 * average rate calculated (3.76) = 1880 SAR so the profit is 15 SAR

how can such a cycle be implemented on Forex ?

Thanks in advance

Regards,

Ahmed Samir