refactor: massive refactor to have only one binary to call

README.md

@@ -16,26 +16,61 @@ Also, it's a fresh start from 2025. I do some exercises from other years along t
 ## Repository Structure
 
 ```
-yyyy/
-├── dayXX/
-│   ├── main.go      # The main code to run to print solutions.
-│   ├── main_test.go # The test file that validates the logic.
-│   └── input.txt    # The day's puzzle input.
-└── ...
+├── cmd/
+│   └── aoc/
+│       └── main.go                # CLI entry point that runs solutions
+└── internal/
+    ├── 2020/
+    │   ├── DayOne/
+    │   │   ├── code.go            # Go solution for Day 1 (2020)
+    │   │   └── code_test.go       # Unit tests for Day 1
+    │   └── ...
+    ├── 2021/
+    │   └── ...                    # Additional years and days
+    ├── registry/
+    │   └── registry.go            # Central registry for day runners
+    └── data/
+        ├── 2020/
+        │   ├── DayOne/
+        │   │   └── input.txt      # Puzzle input for Day 1 (2020)
+        │   └── ...
+        └── ...
 ```
 
-Each day's code can be run with:
+Each day's solution is organized into its own folder, named according to the day number (e.g., `DayOne`, `DayTwo`). Inside each folder, you'll find a `code.go` file with the Go implementation of the solution and a `code_test.go` file containing corresponding tests. The input data for each puzzle is located in the `internal/data` directory, mirroring the code structure for easy access.
+
+To connect each solution to the CLI, the repository uses a central registry located in `internal/registry/registry.go`. This registry is essentially a map linking a day key (combining year and day number) to assign a "day runner" which is a struct that specifies the `ParseInput`, `PartOne` and `PartTwo` functions of the day's problem.
+
+When running a solution, the CLI (`cmd/aoc/main.go`) looks up the appropriate runner from the registry based on your command-line input, uses the parsing function to load the input data, and then runs the desired part (or both parts) using the registered solution functions.
+
+## Usage
+
+Build the CLI tool:
 
 ```bash
-cd yyyy/dayXX
-go run main.go
+make
 ```
 
-Expected output:
+Run a day's solution:
 
 ```bash
-Part 1: <answer>
-Part 2: <answer>
+bin/aoc 2020D1      # Run both parts
+bin/aoc 2020D1P1    # Run only part one
+bin/aoc 2020D1P2    # Run only part two
+```
+
+Example output:
+
+```bash
+$ bin/aoc 2020D1
+197451
+138233720
+
+$ bin/aoc 2020D1P1
+197451
+
+$ bin/aoc 2020D1P2
+138233720
 ```
 
 ## Tests
@@ -55,13 +90,18 @@ In this example, the calibration values of these four lines are 12, 38, 15, and
 Adding these together produces 142.
 ```
 
-I'm using these examples to validate my logic.
+I'm using these examples each day to validate my logic.
 
-If you want to run those, you can use:
+Run all tests:
 
 ```bash
-cd dayXX
-go test
+make test
+```
+
+Or run tests for a specific day:
+
+```bash
+go test ./internal/2020/DayOne/...
 ```
 
 ## Notes