application-layer

Application Layer Rules

Overview

Rules for working with the Application layer (internal/application/). This layer orchestrates use cases and defines port interfaces.

Structure

internal/application/
├── dto/           # Data Transfer Objects
│   ├── btc/       # Bitcoin DTOs
│   └── ripple/    # XRP DTOs
├── ports/         # Interface definitions (abstractions)
│   ├── api/       # External API interfaces (btc, eth, xrp)
│   ├── file/      # File storage interfaces
│   ├── repository/# Repository interfaces (cold, watch)
│   └── wallet/    # Wallet key generator interfaces
└── usecase/       # Use case implementations
    ├── keygen/    # Key generation (btc, bch, eth, xrp, shared)
    ├── sign/      # Signing (btc, bch, eth, xrp, shared)
    ├── watch/     # Watch wallet (btc, bch, eth, xrp, shared)
    └── shared/    # Shared helpers

Port Interfaces (application/ports/)

CRITICAL: Interfaces are defined where they are USED, not where they are implemented.

Rules

• Define interfaces in application/ports/ for infrastructure abstractions
• Use application-layer DTOs in method signatures (NOT infrastructure types)
• Infrastructure packages implement these interfaces

Example

// application/ports/api/btc/interface.go
package btc

import btcdto "internal/application/dto/btc"

type Bitcoiner interface {
    GetBalance() (btcutil.Amount, error)
    GetAddressInfo(addr string) (*btcdto.AddressInfo, error)  // Uses DTO
}

DTOs (application/dto/)

Rules

• DTOs define data structures for port interface method signatures
• Keep DTOs simple - no business logic
• Map infrastructure types to DTOs in infrastructure layer

Example

// application/dto/btc/dto.go
package btc

type AddressInfo struct {
    Address      string
    ScriptPubKey string
    IsWitness    bool
    Labels       []string
}

Use Cases (application/usecase/)

Rules

• Each use case represents a single business operation
• Depend on port interfaces, not concrete implementations
• Delegate business logic to domain layer
• Wrap errors with context
• Should be kept as simple as possible, and specific functionality should be delegated to shared package layers such as the domain layer or /pkg.