Skill: swagger-kotlin-conventions

Skill: swagger-kotlin-conventions

Rules for generating Android Kotlin models from Swagger/OpenAPI data. This skill is used by the swagger-model-generator agent.

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1. Naming Conventions

1.1 Class Names

Layer	Rule	Example
Data model	Ktor prefix + Swagger name	KtorProduct, KtorCreateProductRequest
Domain model	Swagger name, no changes	Product
Data enum	Ktor prefix + Swagger name	KtorProductStatus
Domain enum	Swagger name, no changes	ProductStatus

1.2 File Names

File type	Name	Location
Data response model	KtorProduct.kt	feature/{name}/data/model/
Data request model	KtorCreateProductRequest.kt	feature/{name}/data/model/
Data enum	KtorProductStatus.kt	feature/{name}/data/model/
Domain model	Product.kt	feature/{name}/domain/model/
Domain enum	ProductStatus.kt	feature/{name}/domain/model/
Mapper	KtorProductMapper.kt	feature/{name}/data/model/
Enum mapper	KtorProductStatusMapper.kt	feature/{name}/data/model/

1.3 Package Structure

{base_package}.feature.{feature_name}.data.model
{base_package}.feature.{feature_name}.domain.model

Example: com.company.app.feature.catalog.data.model

---

2. Data Model (Response)

package com.company.app.feature.catalog.data.model

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

/**
 * Product entity from the catalog
 */
@Serializable
data class KtorProduct(
    /** Unique product identifier */
    @SerialName("id") val id: Int,
    /** Display name of the product */
    @SerialName("product_name") val productName: String,
    /** Optional product description */
    @SerialName("description") val description: String? = null,
    @SerialName("price") val price: Double,
    /** Product category */
    @SerialName("category") val category: KtorCategory,
    /** Search tags */
    @SerialName("tags") val tags: List<String> = emptyList(),
    @SerialName("images") val images: List<KtorProductImage> = emptyList(),
    /** Creation timestamp in ISO 8601 */
    @SerialName("created_at") val createdAt: String,
    /** Current product status */
    @SerialName("status") val status: KtorProductStatus
)

Rules:

• @Serializable on the class
• @SerialName("jsonKey") on EVERY field — even when jsonKey == kotlinName
• Field name: camelCase (from snake_case or kebab-case JSON key)
• nullable=true → Type? = null
• nullable=false + List type → List<Type> = emptyList()
• nullable=false + non-list → Type (no default)
• description != null → /** description */ comment before field
• description == null → no comment
• Model description != null → /** description */ KDoc before class

---

3. Data Model (Request)

package com.company.app.feature.catalog.data.model

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
data class KtorCreateProductRequest(
    @SerialName("name") val name: String,
    @SerialName("price") val price: Double,
    @SerialName("category_id") val categoryId: Int
)

Rules (differences from response):

• Same annotation rules as response
• NO Domain model generated
• NO Mapper generated

---

4. Domain Model (Response only)

package com.company.app.feature.catalog.domain.model

/**
 * Product entity from the catalog
 */
data class Product(
    /** Unique product identifier */
    val id: Int,
    /** Display name of the product */
    val productName: String,
    /** Optional product description */
    val description: String?,
    val price: Double,
    /** Product category */
    val category: Category,
    /** Search tags */
    val tags: List<String>,
    val images: List<ProductImage>,
    /** Creation timestamp in ISO 8601 */
    val createdAt: String,
    /** Current product status */
    val status: ProductStatus
)

Rules:

• No @Serializable, no @SerialName — pure domain class
• All type references use plain names (no Ktor prefix)
• nullable=true → Type? (no = null default)
• Lists → List<Type> (no = emptyList() default)
• KDoc comments transferred 1:1 from the Data model

---

5. Enum (Data)

package com.company.app.feature.catalog.data.model

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

/**
 * Possible product statuses
 */
@Serializable
enum class KtorProductStatus {
    @SerialName("active") ACTIVE,
    @SerialName("archived") ARCHIVED,
    @SerialName("draft") DRAFT,
    UNKNOWN
}

Rules:

• @Serializable on the class
• @SerialName("originalJsonValue") on every value EXCEPT UNKNOWN
• Enum values: SCREAMING_SNAKE_CASE
• UNKNOWN is always the last value — no @SerialName
• KDoc on class if description != null

---

6. Enum (Domain)

package com.company.app.feature.catalog.domain.model

enum class ProductStatus {
    ACTIVE,
    ARCHIVED,
    DRAFT,
    UNKNOWN
}

Rules:

• No annotations
• Same values as Data enum
• UNKNOWN always present

---

7. Mapper (Response model)

package com.company.app.feature.catalog.data.model

fun KtorProduct.toDomain(): Product = Product(
    id = id,
    productName = productName,
    description = description,
    price = price,
    category = category.toDomain(),
    tags = tags,
    images = images.map { it.toDomain() },
    createdAt = createdAt,
    status = status.toDomain()
)

Rules:

• Extension function: fun KtorModel.toDomain(): Model = Model(
• Function name is ALWAYS .toDomain() — no variations
• No reverse mapper (domain → data)
• Primitives and strings: field = field
• ref: types → field = field.toDomain()
• List<ref:> → field = field.map { it.toDomain() }
• enum: → field = field.toDomain()
• Nullable ref: → field = field?.toDomain()
• Nullable List<ref:> → field = field?.map { it.toDomain() }
• One mapper file per model: KtorProductMapper.kt
• File location: same data/model/ folder as the data model

---

8. Enum Mapper

package com.company.app.feature.catalog.data.model

fun KtorProductStatus.toDomain(): ProductStatus = when (this) {
    KtorProductStatus.ACTIVE -> ProductStatus.ACTIVE
    KtorProductStatus.ARCHIVED -> ProductStatus.ARCHIVED
    KtorProductStatus.DRAFT -> ProductStatus.DRAFT
    KtorProductStatus.UNKNOWN -> ProductStatus.UNKNOWN
}

Rules:

• when expression with exhaustive mapping
• Every value explicitly mapped (including UNKNOWN)
• One file per enum: KtorProductStatusMapper.kt

---

9. kotlinType Reference (from script output)

The script outputs kotlinType values with these formats. Apply prefix rules when generating code:

Script kotlinType	Data layer	Domain layer
"Int"	Int	Int
"Long"	Long	Long
"Double"	Double	Double
"Float"	Float	Float
"Boolean"	Boolean	Boolean
"String"	String	String
"ref:Product"	KtorProduct	Product
"enum:ProductStatus"	KtorProductStatus	ProductStatus
"List<String>"	List<String>	List<String>
"List<ref:Product>"	List<KtorProduct>	List<Product>
"List<enum:Status>"	List<KtorStatus>	List<Status>
"Map<String, JsonElement>"	Map<String, JsonElement>	Map<String, Any?>
"Map<String, String>"	Map<String, String>	Map<String, String>
"JsonElement"	JsonElement	Any?
"sealed:Name"	sealed class KtorName	sealed class Name
"Any"	Any	Any

---

10. Complex Cases

See references/edge-cases.md for detailed guidance on:

• Response wrappers (ApiResponse<T>)
• Inline nested objects
• allOf composition
• oneOf/anyOf polymorphism
• Circular references
• Kotlin reserved words as field names
• additionalProperties

---

11. File Generation Checklist

For each model, verify before writing:

Data model:

• @Serializable annotation on class
• @SerialName on every single field (no exceptions)
• Ktor prefix on all reference types
• Correct imports: kotlinx.serialization.SerialName, kotlinx.serialization.Serializable
• Nullable fields have = null default
• List fields have = emptyList() default
• KDoc only on fields/classes with non-null description

Domain model:

• No serialization imports or annotations
• No Ktor prefix on any type
• Nullable fields are Type? without default value
• Lists are List<Type> without default value

Mapper:

• Function name is exactly .toDomain()
• All fields mapped
• Nested objects call .toDomain()
• Lists use .map { it.toDomain() }
• No reverse mapper exists

Enum:

• UNKNOWN value present in both Data and Domain
• @SerialName on all enum values except UNKNOWN
• Enum mapper covers all values exhaustively