feat(config): adding a configuration loader

config/loader.go

@@ -0,0 +1,154 @@
+package config
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+// Loader reads configuration values from environment variables,
+// optionally resolving GCP secrets. Errors are accumulated and
+// surfaced via Err().
+type Loader struct {
+	ctx context.Context
+	err error
+}
+
+// NewLoader returns a new Loader bound to the given context.
+func NewLoader(ctx context.Context) *Loader {
+	return &Loader{ctx: ctx}
+}
+
+// Err returns the first error encountered during loading, if any.
+func (l *Loader) Err() error {
+	return l.err
+}
+
+// MustErr panics if any error was encountered during loading.
+// Useful for fail-fast initialisation in main().
+func (l *Loader) MustErr() {
+	if l.err != nil {
+		panic(l.err)
+	}
+}
+
+// Str returns the string value of key, or fallback if unset.
+func (l *Loader) Str(key, fallback string) string {
+	return load(l, key, fallback, castString)
+}
+
+// Int returns the int value of key, or fallback if unset.
+func (l *Loader) Int(key string, fallback int) int {
+	return load(l, key, fallback, castInt)
+}
+
+// Int64 returns the int64 value of key, or fallback if unset.
+func (l *Loader) Int64(key string, fallback int64) int64 {
+	return load(l, key, fallback, castInt64)
+}
+
+// Float64 returns the float64 value of key, or fallback if unset.
+func (l *Loader) Float64(key string, fallback float64) float64 {
+	return load(l, key, fallback, castFloat64)
+}
+
+// Bool returns the boolean value of key, or fallback if unset.
+// Accepted truthy values: "1", "t", "true" (case-insensitive).
+func (l *Loader) Bool(key string, fallback bool) bool {
+	return load(l, key, fallback, castBool)
+}
+
+// Duration returns the time.Duration value of key, or fallback if unset.
+// Values must be valid Go duration strings, e.g. "5s", "1m30s".
+func (l *Loader) Duration(key string, fallback time.Duration) time.Duration {
+	return load(l, key, fallback, castDuration)
+}
+
+// Required returns the string value of key. If the key is unset, it
+// records an error and returns an empty string. Use when there is no
+// sensible fallback.
+func (l *Loader) Required(key string) string {
+	if l.err != nil {
+		return ""
+	}
+	raw := os.Getenv(key)
+	if raw == "" {
+		l.err = fmt.Errorf("config: required key %q is not set", key)
+		return ""
+	}
+	resolved, err := ResolveSecretFromGCP(l.ctx, raw)
+	if err != nil {
+		l.err = fmt.Errorf("config: resolve %q: %w", key, err)
+		return ""
+	}
+	return resolved
+}
+
+// load is the generic backbone used by all typed accessors.
+// It resolves the env var through GCP if needed, then casts it.
+func load[T any](l *Loader, key string, fallback T, cast func(string) (T, error)) T {
+	if l.err != nil {
+		return fallback
+	}
+	raw := os.Getenv(key)
+	if raw == "" {
+		return fallback
+	}
+	resolved, err := ResolveSecretFromGCP(l.ctx, raw)
+	if err != nil {
+		l.err = fmt.Errorf("config: resolve %q: %w", key, err)
+		return fallback
+	}
+	val, err := cast(resolved)
+	if err != nil {
+		l.err = fmt.Errorf("config: cast %q=%q: %w", key, resolved, err)
+		return fallback
+	}
+	return val
+}
+
+func castString(s string) (string, error) {
+	return s, nil
+}
+
+func castInt(s string) (int, error) {
+	v, err := strconv.Atoi(s)
+	if err != nil {
+		return 0, fmt.Errorf("expected int, got %q", s)
+	}
+	return v, nil
+}
+
+func castInt64(s string) (int64, error) {
+	v, err := strconv.ParseInt(s, 10, 64)
+	if err != nil {
+		return 0, fmt.Errorf("expected int64, got %q", s)
+	}
+	return v, nil
+}
+
+func castFloat64(s string) (float64, error) {
+	v, err := strconv.ParseFloat(s, 64)
+	if err != nil {
+		return 0, fmt.Errorf("expected float64, got %q", s)
+	}
+	return v, nil
+}
+
+func castBool(s string) (bool, error) {
+	v, err := strconv.ParseBool(s)
+	if err != nil {
+		return false, fmt.Errorf("expected bool, got %q", s)
+	}
+	return v, nil
+}
+
+func castDuration(s string) (time.Duration, error) {
+	v, err := time.ParseDuration(s)
+	if err != nil {
+		return 0, fmt.Errorf("expected duration (e.g. \"5s\"), got %q", s)
+	}
+	return v, nil
+}

go.mod

@@ -2,6 +2,8 @@ module github.com/thetreep/toolbox
 
 go 1.23
 
+toolchain go1.23.12
+
 require (
 	braces.dev/errtrace v0.3.0
 	cloud.google.com/go/secretmanager v1.13.3
@@ -10,8 +12,10 @@ require (
 	github.com/cockroachdb/errors v1.11.1
 	github.com/jussi-kalliokoski/slogdriver v1.0.1
 	github.com/kr/pretty v0.3.1
+	github.com/lmittmann/tint v1.0.7
 	github.com/nicksnyder/go-i18n/v2 v2.4.1
 	github.com/nyaruka/phonenumbers v1.3.6
+	github.com/sqlc-dev/pqtype v0.3.0
 	github.com/stretchr/testify v1.9.0
 	github.com/urfave/cli v1.22.14
 	go.opencensus.io v0.24.0
@@ -44,12 +48,10 @@ require (
 	github.com/googleapis/gax-go/v2 v2.12.5 // indirect
 	github.com/jussi-kalliokoski/goldjson v1.0.0 // indirect
 	github.com/kr/text v0.2.0 // indirect
-	github.com/lmittmann/tint v1.0.7 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rogpeppe/go-internal v1.12.0 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
-	github.com/sqlc-dev/pqtype v0.3.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.49.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.49.0 // indirect
 	go.opentelemetry.io/otel/metric v1.24.0 // indirect