# 🐣 Understanding What It Means to "Implement a Method"

Many users new to CCP expect to upload a notebook and run it. However, defining a **method** in CCP means turning your algorithm into a structured, executable process.

This guide explains the key concepts you need to know.

---

## 1. The Algorithm is NOT the Data

When building a method:

- Your **algorithm** (code) must be independent from your **data**.
- CCP will allow users to pass **different data** to your method at runtime.
- This means your code must accept parameters and file paths.

❌ Example of what not to do:  
A Jupyter notebook with hardcoded datasets loaded from your desktop.

✅ What to do instead:  
Write a Python script or function that takes arguments (e.g., input file, output path, parameters).

---

## 2. The Algorithm Must Be Executable from Shell

Your algorithm must be runnable via a **command line** like:

```bash
python my_tool.py --input /ccp_data/input.csv --output /ccp_data/output.txt
```

This allows CCP to call your method automatically.

---

## 3. Expose Parameters Explicitly

Your script must:

- Accept **mandatory** and **optional** parameters
- Fail gracefully if required parameters are missing
- Print useful output to `stdout` or files

Example using [argparse](https://docs.python.org/3/library/argparse.html) in Python:

```python
import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--input', required=True)
parser.add_argument('--output', required=True)
parser.add_argument('--threshold', type=float, default=0.5)
args = parser.parse_args()
```

---

## 4. Docker Image and Code Access

Your method will run inside a **Docker container**. You must:

- Choose an image (e.g., `python:3.9`, or one with `gdal`, `scikit-learn`, etc.)
- Make sure your code is **publicly accessible** via Git or file URL

Later, you'll be able to bundle everything in a custom Docker image — this is part of the 🐳 **[Consolidation](/04_methods_development/08_consolidation.md)** phase.

---

## 5. Prepare a Public Repository with Your Code

To execute your method, CCP must **clone your code at runtime**. You need to:

- Prepare a **public Git repository** (e.g., GitHub, Gitea, GitLab)
- Place all your source files in it: scripts, modules, data loading functions
- Include a file to declare **dependencies**

### Examples

- For **Python**: `requirements.txt`
- For **R**: a script like `install.R` with `install.packages(...)`
- For **Java**: a built JAR with dependencies or a `pom.xml` for Maven
- For **Shell**: just ensure all referenced commands exist in the container

Then, in your **deploy script**, you must:

```bash
# Clone the source code (mandatory!)
git clone https://github.com/your-user/myproject.git /src/myproject

# Install dependencies (Python example)
pip install -r /src/myproject/requirements.txt
```

---

## 6. Deploy and Execute Scripts

CCP separates two steps:

### ✅ Deploy script

Used to **prepare the environment**, typically:

- Clone your repo
- Install dependencies
- Download input data (if needed)

### ✅ Execute script

Used to **run the algorithm**, using:

- Inputs passed by the user
- Paths like `/ccp_data/input.csv` and `/ccp_data/output.txt`

These scripts are defined in your `method.json` under `additionalParameters`.

---

## 7. Where to Put Inputs and Outputs

- Use `/ccp_data/` as the shared working directory
- All files passed as input will be placed here
- You should write all output files here too

This ensures they can be returned to the user or archived properly.

---

## Summary

| Concept         | What You Need to Do                                  |
| --------------- | ---------------------------------------------------- |
| Algorithm logic | Make it independent from specific data               |
| Execution       | Run via shell command with arguments                 |
| Parameters      | Clearly define required and optional                 |
| Docker          | Choose a suitable base image                         |
| Code access     | Use a **public Git repo**, clone it at deploy phase  |
| Dependencies    | Use `requirements.txt`, `install.R`, `pom.xml`, etc. |
| Deploy phase    | Clone repo, install dependencies, download inputs    |
| Execute phase   | Run your script using inputs placeholders            |
| Output files    | Save them in `/ccp_data/`                            |