package backend

import (
	"context"
	"os"
)

// Env resolves refs through process-environment indirection: ref.Source
// is the variable name. This is the crush exposure-minimization pattern —
// configs carry env var NAMES, never literals. The value is read on
// demand and kept in memory only.
type Env struct{}

// NewEnv returns the env backend.
func NewEnv() *Env { return &Env{} }

// Name implements Backend.
func (e *Env) Name() string { return "env" }

// Resolve implements Backend.
func (e *Env) Resolve(ctx context.Context, ref Ref) (string, error) {
	v, ok := os.LookupEnv(ref.Source)
	if !ok {
		return "", Err(ref, e.Name(), ReasonMissingKey)
	}
	if v == "" {
		return "", Err(ref, e.Name(), ReasonEmptyValue)
	}
	return v, nil
}