Initial implementation for the tax calculation.

.github/workflows/build-and-tests.yaml

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+name: Build & Test
+run-name: ""
+on:
+  push:
+  pull_request:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  Build-and-Test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: Build the workspace
+        run: cargo build --verbose
+      - name: Test the workspace
+        run: cargo test --verbose

.gitignore

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+/target

Cargo.toml

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+[workspace]
+resolver = "2"
+members = [
+    "net_income_germany",
+    "net_income_germany_cmd",
+]

README.md

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+# Net Income (Germany)
+[![Build & Test](https://github.com/awinterstein/net-income-germany/actions/workflows/build-and-tests.yaml/badge.svg)](https://github.com/awinterstein/net-income-germany/actions/workflows/build-and-tests.yaml)
+
+See documentation for the net income module in the sudirectory [net_income_germany](net_income_germany/).

net_income_germany/Cargo.toml

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+[package]
+name = "net-income-germany"
+description = "Net income calculation for a given gross income based on the German social security and income tax rules."
+publish = ["cerritus"]
+license = "MPL-2.0"
+version = "0.1.0"
+edition = "2021"
+authors = ["Adrian Winterstein <adrian@winterstein.biz>"]
+repository = "https://deposito.cerritus.eu/freelancing/net-income-germany"

net_income_germany/README.md

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+# net-income-germany
+
+Calculates the net income from a given yearly gross income.
+
+## Example
+```rust
+// set the necessary input data values
+let tax_data = net_income_germany::TaxData {
+    gross_income: 80000, // the gross income of one year
+    expenses: 5300, // the tax-deductible expenses of one year
+    fixed_retirement: Some(800), // an optional fixed monthly retirement rate (otherwise percentage applies)
+    self_employed: false, // whether social security taxes should be calculated for a self-employed person
+    married: false, // whether tax splitting due to marriage should apply
+};
+
+// create the default configuration for a specific year
+let config = net_income_germany::config::create(2025)?;
+
+// do the tax calculation based on the input data values
+let tax_result = net_income_germany::calculate(&config, &tax_data)?;
+
+// access the results (in this example just the resulting net income)
+println!("Net income: {}", tax_result.net_income);
+
+```
+
+License: MPL-2.0