Devi is a double-entry accounting system. It allows projects to leverage a mature ledger and standard statements and reporting.

This is currently intended as a simple proof of concept for a library that could be of value to projects such as retail platforms - however we may eventually mature this in to a package which could be available through hex for your projects.

Most retail platforms leave accouning practices as an afterthought. This works fine so long as financial transactions remain simple - but eventually a point is reached where features such as reporting, refunds, or payment splitting cause extremely complex logic.

A common riddle to illustrate.

Three people split a $30 hotel room evently three ways. The hotel asks an employee to deliver a refund of $5. The guests tip the employee $2 and then each receive a dollar. This means that their original payment of $10 each is now $9. $9 * 3 is $27... plus the $2 tip is $29... so where did the other dollar go?

The riddle illustrates the dangers of mixing accounting logic. The $2 value only exists on one side of an equation:

25 + 3 + 2 == (9 + 1) + (9 + 1) + (9 + 1)

... so trying to assess it on the incorrect side causes hard-to-understand bugs. We've seen those kinds of bugs in production on dozens of retail libraries -- with massive amounts of code used to prevent them.

This library looks to remove those kinds of errors using standard accouning practices.

Lint the project with mix credo --strict

Run tests with mix test

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/devi.