A little CLI to calculate income tax.

To use the CLI you need to build it from source. To do so you need a Rust toolchain. The easiest way to get one is to use rustup.

Once rust is installed you can run the CLI with Cargo:

$ cargo run
   ...
tax-calculator 0.1.0
Chris Connelly <[email protected]>

USAGE:
    tax-calculator <year> <gross_income>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

ARGS:
    <year>
    <gross_income>

The CLI requires two positional arguments:

1. A tax year, specified as the starting year (e.g. 2018 would represent the 2018-2019 tax year). Tax schedules are defined for years 2018, 2017, 2016, and 2015.
2. A gross income.

Positional arguments can be given to cargo run after a --, for example:

$ cargo run -- 2018 £43,500
    ...
Tax Year: 2018-2019
Gross Salary: £43,500.00

Personal Allowance: £11,850.00

Taxable Income: £31,650.00

Starter rate: £2,000.00 @ 0.19 = £380.00
Basic rate: £10,149.00 @ 0.2 = £2,029.80
Intermediate rate: £19,429.00 @ 0.21 = £4,080.09
Higher rate: £72.00 @ 0.4 = £28.80

Total Tax Due: £6,518.69

The CLI entrypoint is implemented in src/main.rs along with most of the argument handling and output formatting.

src/lib.rs defines the public API of the crate and sets up the tax schedules for the years given in the task.

src/gbp.rs contains a minimal implementation of a data type for GBP amounts with impls for idiomatic usage in formatting, parsing, and arithmetic (though only the operators required for the task have been implemented).

src/tax.rs defines structs and methods for working with tax, in particular a tax::Schedule struct representing the income tax schedule for a particular year including the tax free allowance and income tax bands.

You can view the project's documentation with:

$ cargo doc --no-deps --open

The project has no tests as such, however several of the documentation examples contain assertions to demonstrate return values etc. These assertions are then executed when cargo tests the documentation. These can be run using:

$ cargo test