// Package config loads application configuration from a YAML file + env vars.
// Priority (highest → lowest): env vars → config file → defaults.
//
// Usage:
//
//	cfg, err := config.Load("config/dev.yaml")
//	fmt.Println(cfg.App.Port)
package config

import (
	"fmt"

	"github.com/spf13/viper"
)

// Config is the root configuration object. Add sub-structs as the app grows.
type Config struct {
	App    AppConfig    `mapstructure:"app"`
	Logger LoggerConfig `mapstructure:"logger"`
}

// AppConfig holds generic application settings.
type AppConfig struct {
	Name string `mapstructure:"name"`
	Port int    `mapstructure:"port"`
	Env  string `mapstructure:"env"` // dev | staging | prod
}

// LoggerConfig controls logging behavior.
type LoggerConfig struct {
	Level string `mapstructure:"level"` // debug | info | warn | error
}

// Load reads the YAML file at path and overlays any matching environment
// variables (e.g. APP_PORT overrides app.port).
func Load(path string) (*Config, error) {
	v := viper.New()

	v.SetConfigFile(path)

	// Allow every config key to be overridden by an env var.
	// e.g. APP_PORT=9090 overrides app.port
	v.AutomaticEnv()

	// Sensible defaults so the binary works without a config file.
	v.SetDefault("app.name", "go-template")
	v.SetDefault("app.port", 8080)
	v.SetDefault("app.env", "dev")
	v.SetDefault("logger.level", "info")

	if err := v.ReadInConfig(); err != nil {
		return nil, fmt.Errorf("config: reading %q: %w", path, err)
	}

	var cfg Config
	if err := v.Unmarshal(&cfg); err != nil {
		return nil, fmt.Errorf("config: unmarshalling: %w", err)
	}

	return &cfg, nil
}