config/config.go

package config

import (
	"bytes"
	"errors"
	"os"
	"path/filepath"
	"strings"
	"time"

	"apigo.cc/go/cast"
	"apigo.cc/go/convert"
	"apigo.cc/go/file"
)

type Duration time.Duration

func (d *Duration) UnmarshalJSON(value []byte) error {
	result, err := time.ParseDuration(string(bytes.Trim(value, "\"")))
	if err == nil {
		*d = Duration(result)
	}
	return err
}

func (d *Duration) UnmarshalYAML(value interface{}) error {
	result, err := time.ParseDuration(cast.String(value))
	if err == nil {
		*d = Duration(result)
	}
	return err
}

func (d Duration) MarshalJSON() ([]byte, error) {
	return []byte("\"" + time.Duration(d).String() + "\""), nil
}

func (d Duration) MarshalYAML() (interface{}, error) {
	return time.Duration(d).String(), nil
}

func (d Duration) TimeDuration() time.Duration {
	return time.Duration(d)
}

// LoadConfig loads configuration from a file, then applies env.json/yaml if exists,
// and finally overrides with environment variables.
func LoadConfig(name string, conf interface{}) error {
	var errs []error

	// 1. Load base file
	filename := resolveConfigFilePath(name)
	if filename != "" {
		if err := file.UnmarshalFile(filename, conf); err != nil {
			errs = append(errs, err)
		}
	}

	// 2. Load env.json/yaml if present
	envFile := resolveConfigFilePath("env")
	if envFile != "" {
		envConf := map[string]interface{}{}
		if err := file.UnmarshalFile(envFile, &envConf); err == nil {
			convert.To(envConf, conf)
		} else {
			errs = append(errs, err)
		}
	}

	// 3. Apply Environment Variable overrides
	applyEnvOverrides(conf)

	return errors.Join(errs...)
}

func resolveConfigPath(name string) string {
	// If it already has an extension, check directly
	if strings.HasSuffix(name, ".json") || strings.HasSuffix(name, ".yml") || strings.HasSuffix(name, ".yaml") {
		if file.Exists(name) {
			return name
		}
		return ""
	}

	// Otherwise, check for .yml then .json
	if file.Exists(name + ".yml") {
		return name + ".yml"
	}
	if file.Exists(name + ".json") {
		return name + ".json"
	}
	return ""
}

func resolveConfigFilePath(name string) string {
	// Search in: current dir, executable dir, user home dir
	dirs := []string{"."}
	if execPath, err := os.Executable(); err == nil {
		dirs = append(dirs, filepath.Dir(execPath))
	}
	if home, err := os.UserHomeDir(); err == nil {
		dirs = append(dirs, home)
	}

	for _, d := range dirs {
		p := filepath.Join(d, name)
		if f := resolveConfigPath(p); f != "" {
			return f
		}
	}
	return ""
}

func applyEnvOverrides(conf interface{}) {
	envMap := make(map[string]interface{})
	for _, e := range os.Environ() {
		pair := strings.SplitN(e, "=", 2)
		if len(pair) != 2 {
			continue
		}
		
		// Convert DB_HOST to {"db": {"host": value}}
		parts := strings.Split(strings.ToLower(pair[0]), "_")
		curr := envMap
		for i := 0; i < len(parts)-1; i++ {
			if _, ok := curr[parts[i]]; !ok {
				curr[parts[i]] = make(map[string]interface{})
			}
			if next, ok := curr[parts[i]].(map[string]interface{}); ok {
				curr = next
			} else {
				break
			}
		}
		curr[parts[len(parts)-1]] = pair[1]
	}

	convert.To(envMap, conf)
}