# JSPG: JSON Schema Postgres

**JSPG** is a high-performance PostgreSQL extension for in-memory JSON Schema validation, specifically targeting **Draft 2020-12**.

It is designed to serve as the validation engine for the "Punc" architecture, where the database is the single source of truth for all data models and API contracts.

## 🎯 Goals

1.  **Draft 2020-12 Compliance**: Attempt to adhere to the official JSON Schema Draft 2020-12 specification.
2.  **Ultra-Fast Validation**: Compile schemas into an optimized in-memory representation for near-instant validation during high-throughput workloads.
3.  **Connection-Bound Caching**: Leverage the PostgreSQL session lifecycle to maintain a per-connection schema cache, eliminating the need for repetitive parsing.
4.  **Structural Inheritance**: Support object-oriented schema design via Implicit Keyword Shadowing and virtual `$family` references.
5.  **Punc Integration**: validation is aware of the "Punc" context (request/response) and can validate `cue` objects efficiently.

## 🔌 API Reference

The extension exposes the following functions to PostgreSQL:

### `cache_json_schemas(enums jsonb, types jsonb, puncs jsonb) -> jsonb`

Loads and compiles the entire schema registry into the session's memory, atomically replacing the previous validator.

*   **Inputs**:
    *   `enums`: Array of enum definitions.
    *   `types`: Array of type definitions (core entities).
    *   `puncs`: Array of punc (function) definitions with request/response schemas.
*   **Behavior**:
    *   Parses all inputs into an internal schema graph.
    *   Resolves all internal references (`$ref`).
    *   Generates virtual union schemas for type hierarchies referenced via `$family`.
    *   Compiles schemas into validators.
*   **Returns**: `{"response": "success"}` or an error object.

### `mask_json_schema(schema_id text, instance jsonb) -> jsonb`

Validates a JSON instance and returns a new JSON object with unknown properties removed (pruned) based on the schema.

*   **Inputs**:
    *   `schema_id`: The `$id` of the schema to mask against.
    *   `instance`: The JSON data to mask.
*   **Returns**:
    *   On success: A `Drop` containing the **masked data**.
    *   On failure: A `Drop` containing validation errors.

### `validate_json_schema(schema_id text, instance jsonb) -> jsonb`

Validates a JSON instance against a pre-compiled schema.

*   **Inputs**:
    *   `schema_id`: The `$id` of the schema to validate against (e.g., `person`, `save_person.request`).
    *   `instance`: The JSON data to validate.
*   **Returns**:
    *   On success: `{"response": "success"}`
    *   On failure: A JSON object containing structured errors (e.g., `{"errors": [...]}`).

### `json_schema_cached(schema_id text) -> bool`

Checks if a specific schema ID is currently present in the cache.

### `clear_json_schemas() -> jsonb`

Clears the current session's schema cache, freeing memory.

### `show_json_schemas() -> jsonb`

Returns a debug dump of the currently cached schemas (for development/debugging).

## ✨ Custom Features & Deviations

JSPG implements specific extensions to the Draft 2020-12 standard to support the Punc architecture's object-oriented needs.

### 1. Implicit Keyword Shadowing
Standard JSON Schema composition (`allOf`) is additive (Intersection), meaning constraints can only be tightened, not replaced. However, JSPG treats `$ref` differently when it appears alongside other properties to support object-oriented inheritance.

*   **Inheritance (`$ref` + `properties`)**: When a schema uses `$ref` *and* defines its own properties, JSPG implements **Smart Merge** (or Shadowing). If a property is defined in the current schema, its constraints take precedence over the inherited constraints for that specific keyword.
    *   *Example*: If `Entity` defines `type: { const: "entity" }` and `Person` (which refs Entity) defines `type: { const: "person" }`, validation passes for "person". The local `const` shadows the inherited `const`.
    *   *Granularity*: Shadowing is per-keyword. If `Entity` defined `type: { const: "entity", minLength: 5 }`, `Person` would shadow `const` but still inherit `minLength: 5`.

*   **Composition (`allOf`)**: When using `allOf`, standard intersection rules apply. No shadowing occurs; all constraints from all branches must pass. This is used for mixins or interfaces.

### 2. Virtual Family References (`$family`)
To support polymorphic fields (e.g., a field that accepts any "User" type), JSPG generates virtual schemas representing type hierarchies.

*   **Mechanism**: When caching types, if a type defines a `hierarchy` (e.g., `["entity", "organization", "person"]`), JSPG generates a virtual `oneOf` family containing refs to all valid descendants. These can be pointed to exclusively by using `{"$family": "organization"}`. Because `$family` is a macro-pointer that swaps in the virtual union, it **must** be used exclusively in its schema object; you cannot define other properties alongside it.

### 3. Strict by Default & Extensibility
JSPG enforces a "Secure by Default" philosophy. All schemas are treated as if `unevaluatedProperties: false` (and `unevaluatedItems: false`) is set, unless explicitly overridden.

*   **Strictness**: By default, any property or array item in the instance data that is not explicitly defined in the schema causes a validation error. This prevents clients from sending undeclared fields or extra array elements.
*   **Extensibility (`extensible: true`)**: To allow a free-for-all of additional, undefined properties or extra array items, you must add `"extensible": true` to the schema. This globally disables the strictness check for that object or array, useful for types designed to be completely open.
*   **Structured Additional Properties (`additionalProperties: {...}`)**: Instead of a boolean free-for-all, you can define `additionalProperties` as a schema object (e.g., `{"type": "string"}`). This maintains strictness (no arbitrary keys) but allows any extra keys as long as their values match the defined structure.
*   **Ref Boundaries**: Strictness is reset when crossing `$ref` boundaries. The referenced schema's strictness is determined by its own definition (strict by default unless `extensible: true`), ignoring the caller's state.
*   **Inheritance**: Strictness is inherited. A schema extending a strict parent will also be strict unless it declares itself `extensible: true`. Conversely, a schema extending a loose parent will also be loose unless it declares itself `extensible: false`.

### 4. Format Leniency for Empty Strings
To simplify frontend form logic, the format validators for `uuid`, `date-time`, and `email` explicitly allow empty strings (`""`). This treats an empty string as "present but unset" rather than "invalid format".

### 5. Masking (Constructive Validation)
JSPG supports a "Constructive Validation" mode via `mask_json_schema`. This is designed for high-performance API responses where the schema dictates the exact shape of the returned data.

*   **Mechanism**: The validator traverses the instance against the schema.
*   **Valid Fields**: Kept in the output.
*   **Unknown/Extra Fields**: Silently removed (pruned) if `extensible: false` (default).
*   **Invalid Fields**: Still trigger standard validation errors.

This allows the database to return "raw" joined rows (e.g. `SELECT * FROM person JOIN organization ...`) and have JSPG automatically shape the result into the expected API response, removing any internal or unrelated columns not defined in the schema.

## 🏗️ Architecture

The extension is written in Rust using `pgrx` and structures its schema parser to mirror the Punc Generator's design:

*   **Single `Schema` Struct**: A unified struct representing the exact layout of a JSON Schema object, including standard keywords and custom vocabularies (`form`, `display`, etc.).
*   **Compiler Phase**: schema JSONs are parsed into this struct, linked (references resolved), and then compiled into an efficient validation tree.
*   **Validation Phase**: The compiled validators traverse the JSON instance using `serde_json::Value`.

### Concurrency & Threading ("Atomic Swap")

To support high-throughput validation while allowing for runtime schema updates (e.g., during development or hot-reloading), JSPG uses an **Atomic Swap** pattern.

1.  **Immutable Validator**: The `Validator` struct immutably owns the `Registry`. Once created, a validator instance (and its registry) never changes.
2.  **Global Pointer**: A global `RwLock<Option<Arc<Validator>>>` holds the current active validator.
3.  **Lock-Free Reads**: Validation requests acquire a read lock just long enough to clone the `Arc` (incrementing a reference count), then release the lock immediately. Validation proceeds on the snapshot, ensuring no blocking during schema updates.
4.  **Atomic Updates**: When schemas are reloaded (`cache_json_schemas`), a new `Registry` and `Validator` are built entirely on the stack. The global pointer is then atomically swapped to the new instance under a write lock.

## 🧪 Testing

Testing is driven by standard Rust unit tests that load JSON fixtures.

*   **Isolation**: Each test file runs with its own isolated `Registry` and `Validator` instance, created on the stack. This eliminates global state interference and allows tests to run in parallel.
*   **Fixtures**: The tests are located in `tests/fixtures/*.json` and are executed via `cargo test`.