108 lines
2.7 KiB
Go
108 lines
2.7 KiB
Go
package app
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import (
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"context"
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"errors"
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"flag"
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"fmt"
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"os"
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"reflect"
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"gopkg.in/yaml.v3"
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"gitea.libretechconsulting.com/rmcguire/go-app/pkg/config"
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)
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// Used to unmarshal config and environment into a custom type
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// that overloads *config.AppConfig. Will perform normal env
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// substitutions for AppConfig, but env overrides for custom type
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// are up to the caller.
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func MustLoadConfigInto[T any](ctx context.Context, into T) (context.Context, T) {
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// Step 1: Check our custom type for required *config.AppConfig
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if err := hasAppConfig(into); err != nil {
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panic(err)
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}
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// Step 2: Do the normal thing
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ctx = MustSetupConfigAndLogging(ctx)
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// Step 3: Extract the config
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cfg := config.MustFromCtx(ctx)
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// Step 4: Unmarshal custom config
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configPath := flag.Lookup("config")
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if configPath != nil && configPath.Value.String() != "" {
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file, err := os.Open(configPath.Value.String())
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if err != nil {
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panic(fmt.Errorf("could not open config file: %w", err))
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}
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defer file.Close()
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decoder := yaml.NewDecoder(file)
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if err := decoder.Decode(into); err != nil {
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panic(fmt.Errorf("could not decode config file: %w", err))
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}
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}
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// Step 5: Re-apply AppConfig to custom type
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if err := setAppConfig(into, cfg); err != nil {
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panic(err)
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}
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// Step 6: Update context, return custom type
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return ctx, into
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}
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func setAppConfig[T any](target T, appConfig *config.AppConfig) error {
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// Ensure target is a pointer to a struct
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v := reflect.ValueOf(target)
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if v.Kind() != reflect.Ptr || v.IsNil() {
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return errors.New("target must be a non-nil pointer to a struct")
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}
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v = v.Elem() // Dereference the pointer
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if v.Kind() != reflect.Struct {
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return errors.New("target must be a pointer to a struct")
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}
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// Replace *config.AppConfig
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for i := 0; i < v.NumField(); i++ {
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field := v.Field(i)
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if field.Type() == reflect.TypeOf((*config.AppConfig)(nil)) {
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if !field.CanSet() {
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return fmt.Errorf("field %q cannot be set", v.Type().Field(i).Name)
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}
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field.Set(reflect.ValueOf(appConfig))
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return nil
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}
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}
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return errors.New("no *config.AppConfig field found in target struct")
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}
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func hasAppConfig[T any](target T) error {
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v := reflect.ValueOf(target)
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if v.Kind() != reflect.Ptr || v.IsNil() {
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return errors.New("target must be a non-nil pointer to a struct")
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}
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v = v.Elem()
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if v.Kind() != reflect.Struct {
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return errors.New("target must be a pointer to a struct")
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}
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hasAppConfig := false
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for i := 0; i < v.NumField(); i++ {
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field := v.Type().Field(i)
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if field.Type == reflect.TypeOf((*config.AppConfig)(nil)) {
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hasAppConfig = true
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break
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}
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}
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if !hasAppConfig {
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return errors.New("struct does not contain a *config.AppConfig field")
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}
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return nil
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}
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