ADR-0012: Logger Interface Design

Status

Accepted

Context

We're using zap for logging, but want to abstract it behind an interface for:

Testability (mock logger in tests)
Flexibility (could swap implementations)
Module compatibility (modules use interface, not concrete type)

We need to decide on the interface design.

Decision

Create a simple logger interface that matches zap's API pattern but uses generic types:

type Field interface {
    // Field represents a key-value pair for structured logging
}

type Logger interface {
    Debug(msg string, fields ...Field)
    Info(msg string, fields ...Field)
    Warn(msg string, fields ...Field)
    Error(msg string, fields ...Field)
    With(fields ...Field) Logger
}

Implementation:

Use zap.Field as the Field type (no abstraction needed for now)

Provide helper functions in pkg/logger for creating fields:

func String(key, value string) Field
func Int(key string, value int) Field
func Error(err error) Field

Rationale:

Simple interface that modules can depend on
Matches zap's usage patterns
Easy to test with mock implementations
Allows future swap if needed (though unlikely)

Consequences

Positive

Clean abstraction for modules
Testable with mocks
Simple API for modules to use

Negative

Slight indirection overhead
Need to maintain interface compatibility

Implementation Notes

Define interface in pkg/logger/logger.go
Implement in internal/logger/zap_logger.go
Export helper functions in pkg/logger/fields.go
Modules import pkg/logger, not internal/logger

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