Index match fifo stock valuation

Hello guys.
I want to match costs and revenues as they occurred in their specific dates. The workbook attached may help you understand what I want but below is a summary.

How the workbook works.

• Prices sheet extracts unique items from purchases sheet and shows the latest buying price and selling price along with current stock.
• Sales sheet picks Items from Prices sheet and has Data Validation for the items
• Purchases sheet records all new items as they are bought and registers the buying and selling price as of that particular stock and date.
• Counted Stock is free stock that was given to the business before any purchases were made so if free stock is empty, it means 0 stock was given freely for that specific item
• The Items in Purchases sheet are always sorted by date with the items randomly distributed as the purchases occurred.

What I need.

1. Counted stock value should be matched to the first purchase cost of that specific item.
2. Current stock column in the Prices sheet should pick counted stock plus purchases, less sold stock.
3. Value of Current Stock should match the cost of stock when bought at their various dates.
4. Sales sheet should match revenues with costs as they occurred at their various dates using First In First Out system.