# Laya PHP SDK

PHP client for [Laya](https://github.com/NandhaKishorM/laya), the open-source System 1 decision engine. You give Laya some state (free text or a structured document) and a set of questions. It answers each question with a choice, a score or a yes/no probability, plus a confidence value.

The SDK is a thin layer over Laya's HTTP API. It builds the JSON request, sends it over any PSR-18 HTTP client, and wraps the response in small value objects.

## Requirements

- PHP 8.1+ (uses `readonly` properties and `never`-style `throw` expressions)
- A running Laya server (the default URL is `http://127.0.0.1:8000`)
- An HTTP client: Guzzle is installed with the package. If your app already uses another PSR-18 client (Symfony HttpClient, etc.), the SDK discovers and prefers it through `php-http/discovery`.

## Installation

```bash
composer require liquidsky/laya_php_sdk
```

## Quick start

```php
use Laya\Laya;
use Laya\Question\ChoiceQuestion;
use Laya\Question\QuestionSet;
use Laya\Question\ScoreQuestion;
use Laya\Question\YesNoQuestion;

$client = Laya::client('http://127.0.0.1:8000');

$questions = QuestionSet::make()
    ->add(
        (new ChoiceQuestion('category', 'What is this ticket about?'))
            ->option('billing', 'Payments, invoices, refunds')
            ->option('bug', 'Something is broken')
            ->option('other', 'Anything else')
    )
    ->add(new ScoreQuestion('urgency', 'How urgent is this?', ['not urgent', 'soon', 'critical']))
    ->add(new YesNoQuestion('angry', 'Is the customer upset?'));

$decisions = $client->decide('My card was charged twice and nobody replies!!', $questions);

$decisions->get('category')->choice();       // "billing"
$decisions->get('urgency')->score();         // e.g. 2.0
$decisions->get('angry')->probability();     // e.g. 0.93  (P(yes))
$decisions->get('angry')->confidence();      // e.g. 0.88
$decisions->routedModel;                     // model Laya routed to, if reported
```

## How it works

```a
 state + QuestionSet ──► LayaClient::decide() ──► POST /predict ──► Laya server
                                                                        │
 DecisionSet / Decision ◄── DecisionSet::fromResponse() ◄── JSON ◄──────┘
```

1. **Build questions.** Each question is an object implementing `Question` (`name()` and `toArray()`). A `QuestionSet` collects them, keyed by name.
2. **Call `decide()`.** `LayaClient::decide()` sends this body to `POST /predict`:

   ```json
   {
     "state": { "body": "My card was charged twice..." },
     "questions": {
       "category": { "type": "choice", "instructions": "...", "criteria": { "billing": "..." } },
       "urgency":  { "type": "score",  "instructions": "...", "criteria": ["not urgent", "soon", "critical"] },
       "angry":    { "type": "noul",   "instructions": "..." }
     },
     "model": "optional-model-name"
   }
   ```

   A string `$state` is wrapped as `{"body": "<string>"}`. An array is sent as-is. `model` is only included if you pass it.
3. **Read the answers.** The response's `answers.<name>` entries become `Decision` objects inside a `DecisionSet`. `routing.model` is exposed as `$decisions->routedModel`.

## Question types

| Class | Wire `type` | Constructor / builder | Read with |
|---|---|---|---|
| `ChoiceQuestion` | `choice` | `new ChoiceQuestion($name, $instructions)` then `->option($label, $description)` | `choice()` |
| `ScoreQuestion` | `score` | `new ScoreQuestion($name, $instructions, list<string> $scale)` | `score()` |
| `YesNoQuestion` | `noul` | `new YesNoQuestion($name, $instructions)` | `probability()` |

`noul` is the name Laya's API uses for a yes/no question. The value is the probability of "yes".

To add your own type, implement `Laya\Question\Question`.

## Reading results

`$decisions->get($name)` returns a `Decision`, or throws `OutOfBoundsException` if the server returned no answer for that name.

| Member | Returns |
|---|---|
| `$decision->name`, `$decision->type` | Question name and the type reported by the server |
| `choice()` | Chosen label (`choice` questions), else `null` |
| `score()` | Score as float (`score` questions), else `null` |
| `probability()` | P(yes) as float (`noul` questions), else `null` |
| `confidence()` | Confidence as float, or `null` |
| `distribution()` | Full probability distribution from the response |

## Other endpoints

```php
$client->models();   // GET /models, returns the decoded JSON as an array
```

## Errors

- HTTP status 400 or above throws `Laya\Exception\UnexpectedResponseException`. Its message includes the server's `detail` field when present, and `statusCode()` returns the HTTP status.
- Invalid JSON in a response or request throws `JsonException`.
- Network failures surface as whatever your PSR-18 client throws (`Psr\Http\Client\ClientExceptionInterface`).
- `Laya::client()` throws if no PSR-18 client or PSR-17 factory can be discovered.

## Using your own HTTP client

`Laya::client()` auto-discovers dependencies. To control them (timeouts, auth headers, middleware), construct the client yourself:

```php
use Laya\LayaClient;

$client = new LayaClient(
    $psr18Client,          // Psr\Http\Client\ClientInterface
    $psr17RequestFactory,  // Psr\Http\Message\RequestFactoryInterface
    $psr17StreamFactory,   // Psr\Http\Message\StreamFactoryInterface
    'https://laya.example.com',
);
```

Configure timeouts and authentication on the PSR-18 client you pass in. The SDK adds only `Content-Type` and `Accept` headers.

## Project layout

```
src/
├── Laya.php                  Factory: Laya::client() with auto-discovery
├── LayaClient.php            decide(), models(); builds and sends requests
├── Exception/
│   └── UnexpectedResponseException.php
├── Question/
│   ├── Question.php          Interface
│   ├── QuestionSet.php       Named collection, serialises to the "questions" object
│   ├── ChoiceQuestion.php
│   ├── ScoreQuestion.php
│   └── YesNoQuestion.php
└── Result/
    ├── DecisionSet.php       Parsed response, lookup by question name
    └── Decision.php          One answer
```

## License

MIT