Added Graphql

pkg/readers/graphql/README.md

@@ -0,0 +1,203 @@
+# GraphQL Schema Reader
+
+The GraphQL reader parses GraphQL Schema Definition Language (SDL) files and converts them into RelSpec's internal database model.
+
+## Features
+
+- **Standard GraphQL SDL** support (generic, non-framework-specific)
+- **Type to Table mapping**: GraphQL types become database tables
+- **Field to Column mapping**: GraphQL fields become table columns
+- **Enum support**: GraphQL enums are preserved
+- **Custom scalars**: DateTime, JSON, Date automatically mapped to appropriate SQL types
+- **Implicit relationships**: Detects relationships from field types
+- **Many-to-many support**: Creates junction tables for bidirectional array relationships
+- **Configurable ID mapping**: Choose between bigint (default) or UUID for ID fields
+
+## Supported GraphQL Features
+
+### Built-in Scalars
+- `ID` → bigint (default) or uuid (configurable)
+- `String` → text
+- `Int` → integer
+- `Float` → double precision
+- `Boolean` → boolean
+
+### Custom Scalars
+- `DateTime` → timestamp
+- `JSON` → jsonb
+- `Date` → date
+- `Time` → time
+- `Decimal` → numeric
+
+Additional custom scalars can be mapped via metadata.
+
+### Relationships
+
+Relationships are inferred from field types:
+
+```graphql
+type Post {
+  id: ID!
+  title: String!
+  author: User!        # Many-to-one (creates authorId FK column, NOT NULL)
+  reviewer: User       # Many-to-one nullable (creates reviewerId FK column, NULL)
+  tags: [Tag!]!        # One-to-many or many-to-many (depending on reverse)
+}
+
+type User {
+  id: ID!
+  posts: [Post!]!      # Reverse of Post.author (no FK created)
+}
+
+type Tag {
+  id: ID!
+  posts: [Post!]!      # Many-to-many with Post (creates PostTag junction table)
+}
+```
+
+**Relationship Detection Rules:**
+- Single type reference (`user: User`) → Creates FK column (e.g., `userId`)
+- Array type reference (`posts: [Post!]!`) → One-to-many reverse (no FK on this table)
+- Bidirectional arrays → Many-to-many (creates junction table)
+
+### Enums
+
+```graphql
+enum Role {
+  ADMIN
+  USER
+  GUEST
+}
+
+type User {
+  role: Role!
+}
+```
+
+Enums are preserved in the schema and can be used as column types.
+
+## Usage
+
+### Basic Usage
+
+```go
+import (
+    "git.warky.dev/wdevs/relspecgo/pkg/readers"
+    "git.warky.dev/wdevs/relspecgo/pkg/readers/graphql"
+)
+
+opts := &readers.ReaderOptions{
+    FilePath: "schema.graphql",
+}
+
+reader := graphql.NewReader(opts)
+db, err := reader.ReadDatabase()
+```
+
+### With UUID ID Type
+
+```go
+opts := &readers.ReaderOptions{
+    FilePath: "schema.graphql",
+    Metadata: map[string]interface{}{
+        "idType": "uuid",  // Map ID scalar to uuid instead of bigint
+    },
+}
+
+reader := graphql.NewReader(opts)
+db, err := reader.ReadDatabase()
+```
+
+### With Per-Type ID Mapping
+
+```go
+opts := &readers.ReaderOptions{
+    FilePath: "schema.graphql",
+    Metadata: map[string]interface{}{
+        "typeIdMappings": map[string]string{
+            "User": "uuid",    // User.id → uuid
+            "Post": "bigint",  // Post.id → bigint
+        },
+    },
+}
+```
+
+### With Custom Scalar Mappings
+
+```go
+opts := &readers.ReaderOptions{
+    FilePath: "schema.graphql",
+    Metadata: map[string]interface{}{
+        "customScalarMappings": map[string]string{
+            "Upload":  "bytea",
+            "Decimal": "numeric(10,2)",
+        },
+    },
+}
+```
+
+## CLI Usage
+
+```bash
+# Convert GraphQL to JSON
+relspec convert --from graphql --from-path schema.graphql \
+                --to json --to-path schema.json
+
+# Convert GraphQL to GORM models
+relspec convert --from graphql --from-path schema.graphql \
+                --to gorm --to-path models/ --package models
+
+# Convert GraphQL to PostgreSQL SQL
+relspec convert --from graphql --from-path schema.graphql \
+                --to pgsql --to-path schema.sql
+```
+
+## Metadata Options
+
+| Option | Type | Description | Default |
+|--------|------|-------------|---------|
+| `idType` | string | Global ID type mapping ("bigint" or "uuid") | "bigint" |
+| `typeIdMappings` | map[string]string | Per-type ID mappings | {} |
+| `customScalarMappings` | map[string]string | Custom scalar to SQL type mappings | {} |
+| `schemaName` | string | Schema name for all tables | "public" |
+
+## Limitations
+
+- Only supports GraphQL SDL (Schema Definition Language), not queries or mutations
+- Directives are ignored (except for future extensibility)
+- Interfaces and Unions are not supported
+- GraphQL's concept of "schema" is different from database schemas; all types go into a single database schema (default: "public")
+
+## Example
+
+**Input** (`schema.graphql`):
+```graphql
+scalar DateTime
+
+enum Role {
+  ADMIN
+  USER
+}
+
+type User {
+  id: ID!
+  email: String!
+  role: Role!
+  createdAt: DateTime!
+  posts: [Post!]!
+}
+
+type Post {
+  id: ID!
+  title: String!
+  content: String
+  published: Boolean!
+  author: User!
+}
+```
+
+**Result**: Database with:
+- 2 tables: `User` and `Post`
+- `Post` table has `authorId` foreign key to `User.id`
+- `Role` enum with values: ADMIN, USER
+- Custom scalar `DateTime` mapped to `timestamp`