Game example

This example illustrates how to use the Unitag Engine API to create a tiny game (try it here).

Goal

The player is invited to guess a secret number, which is initially chosen randomly and then stored in a cookie until the end of the game. Upon each attempt, the server indicates whether the secret number is higher or lower than the user’s guess.

Implementation

The raw JSON document can be found here.

{

Define the URL that will be used to access this operation. The resulting URL has the following form: http://e.unitag.io/r/{YOUR PATH HERE}.

    "url": "{YOUR PATH HERE}",

Mark this operation as published. This is needed to make it publicly available.

    "state": "PUBLISHED",

Define the global input values:

1. Load the continue value. The result is a boolean which indicates whether a cookie named secret has been sent by the user agent.

2. Once continue is loaded, use its value to compute the secret value. The result is the secret number: either the previous one which is restored from the secret cookie, or a new one which is chosen randomly.

Both continue and secret are implicit data connectors. Their values are computed using an expression langage delimited by a markup syntax: <((...))>. The expression language by itself is largely inspired by JavaScript expressions.

Here are the encountered specificities:

• params.cookie exposes the cookies sent by the user agent
• io allows to access the already computed input values
• $randomInt returns a random integer between the given bounds

    "input": {
        "continue": "<(('secret' in params.cookie))>",
        "$then": {
            "secret": "<((io.continue ? params.cookie.secret : $randomInt(0, 1000)))>"
        }
    },

Define the default entry point of this operation.

    "index": {

Define a local input value, guess, which is computed using some more specificities of the expression language:

• params.url exposes the query string parameters.
• The | operator allows to chain functions by prepending the result of its left operand to the arguments of its right operand. For instance, this expression is equivalent to $parse($get(params.url, 'guess')).
• A function always starts by $, and can be called without parentheses if no argument is needed.
• $get allows to extract an attribute without checking its existence: if params.url.guess does not exists, we obtain null.
• $parse allows to parse any JSON string. Here, it is used to cast a string into a number.

        "input": {
            "guess": "<((params.url | $get('guess') | $parse))>"
        },

Check if the guess parameter is set.

        "if": "<((io.guess != null))>",

If the guess parameter is set, check if the secret number has been found.

        "then": {
            "if": "<((io.guess == io.secret))>",

If the secret number has been found, remove the secret cookie and send a congratulation message.

            "then": {
                "trigger": {
                    "cookie": {"key": "secret", "age": 0}
                },
                "response": "Congratulations! The secret number was <((io.secret))>."
            },

If the secret number has not been found, set the secret cookie and send a JSON response containing an hint.

            "else": {
                "trigger": {
                    "cookie": {"key": "secret", "value": "<((io.secret))>", "age": 300000}
                },
                "response": {
                    "body": {
                        "newGame": "<((!io.continue))>",
                        "hint": "<(((io.guess > io.secret) ? 'LESS' : 'MORE'))>"
                    }
                }
            }
        },

If the guess parameter is not set, send a usage message.

        "else": {
            "response": "Try to guess the secret number with ?guess={YOUR ATTEMPT}"
        }
    }
}

Go further

If you wish to experiment by yourself, you may consider adding the following features:

1. Add another entry point which displays directly the secret number.
2. Protect this entry point by an hardcoded password.
3. Check the credentials against a CSV file (whitelist) instead the hardcoded password.
4. Display a nicer GUI using U.me rendering.