# The algorithm:

To retrieve the most YouTube video ids in order to retrieve the most video captions, we need to retrieve the most YouTube channels.
So to discover the YouTube channels graph with a breadth-first search, we proceed as follows:
1. Provide a starting set of channels.
2. Given a channel, retrieve other channels thanks to its content by using [YouTube Data API v3](https://developers.google.com/youtube/v3) and [YouTube operational API](https://github.com/Benjamin-Loison/YouTube-operational-API) and then repeat 1. for each retrieved channel.

A ready to be used by the end-user website instance of this project is hosted at: https://crawler.yt.lemnoslife.com

See more details on [the Wiki](https://gitea.lemnoslife.com/Benjamin_Loison/YouTube_captions_search_engine/wiki).

# Running the YouTube graph discovery algorithm:

Because of [the current compression mechanism](https://gitea.lemnoslife.com/Benjamin_Loison/YouTube_captions_search_engine/issues/30), Linux is the only known OS able to run this algorithm.

To clone the repository, run:

```sh
git clone https://gitea.lemnoslife.com/Benjamin_Loison/YouTube_captions_search_engine
```

Move to the cloned repository by running:

```sh
cd YouTube_captions_search_engine/
```

To install the dependencies on an `apt` based Linux distribution of this project make sure to have [`pip`](https://pip.pypa.io/en/stable/installation/) and run:

```sh
sudo apt install nlohmann-json3-dev
pip install yt-dlp
```

To compile the YouTube discovery graph algorithm, run:

```sh
make
```

To see the command line arguments of the algorithm, run:

```sh
./youtubeCaptionsSearchEngine -h
```

To run the YouTube discovery graph algorithm, run:

```sh
./youtubeCaptionsSearchEngine
```

Except if you provide the argument `--youtube-operational-api-instance-url https://yt.lemnoslife.com`, you have [to host your own instance of the YouTube operational API](https://github.com/Benjamin-Loison/YouTube-operational-API/#install-your-own-instance-of-the-api).

Except if you provide the argument `--no-keys`, you have to provide at least one [YouTube Data API v3 key](https://developers.google.com/youtube/v3/getting-started) in `keys.txt`.

# Hosting the website enabling users to make requests:

Move to the `website/` folder by running:

```sh
cd website/
```

To install its dependencies make sure to have [`composer`](https://getcomposer.org/doc/00-intro.md) installed and run:

```sh
composer install
pip install webvtt-py
```

Add the following configuration to your Nginx website one:

```nginx
    # Make the default webpage of your website to be `index.php`.
    index index.php;

    # Allow end-users to retrieve the content of a file within a channel zip.
    location /channels {
        rewrite ^(.*).zip$ /channels.php;
        rewrite ^(.*).zip/(.*).json$ /channels.php;
        rewrite ^(.*).zip/(.*).txt$ /channels.php;
        rewrite ^(.*).zip/(.*).vtt$ /channels.php;
        # Allow end-users to list `channels/` content.
        autoindex on;
    }

    # Disable end-users to access to other end-users requests.
    location /users {
        deny all;
    }

    # Configure the websocket endpoint.
    location /websocket {
        # switch off logging
        access_log off;

        # redirect all HTTP traffic to localhost
        proxy_pass http://localhost:4430;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

        # WebSocket support (nginx 1.4)
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";

        # timeout extension, possibly keep this short if using a ping strategy
        proxy_read_timeout 99999s;
    }
```

Start the websocket worker by running:

```sh
php websockets.php
```