package app

import (
	"errors"
	"fmt"
	"os"
	"strings"

	"gopkg.in/yaml.v3"
)

const defaultConfigPath = "configs/config.example.yaml"

// Config contains the settings required to start the application.
type Config struct {
	Environment string         `yaml:"environment"`
	HTTP        HTTPConfig     `yaml:"http"`
	Database    DatabaseConfig `yaml:"database"`
}

type HTTPConfig struct {
	Address string `yaml:"address"`
}

type DatabaseConfig struct {
	URL string `yaml:"url"`
}

// LoadConfig reads configuration from YAML, applies environment overrides,
// and validates the result. An empty path uses CONFIG_FILE when set.
func LoadConfig(path string) (Config, error) {
	if path == "" {
		path = os.Getenv("CONFIG_FILE")
	}
	if path == "" {
		path = defaultConfigPath
	}

	contents, err := os.ReadFile(path)
	if err != nil {
		return Config{}, fmt.Errorf("read config %q: %w", path, err)
	}

	var config Config
	if err := yaml.Unmarshal(contents, &config); err != nil {
		return Config{}, fmt.Errorf("parse config %q: %w", path, err)
	}

	applyEnvironment(&config)
	if err := config.Validate(); err != nil {
		return Config{}, fmt.Errorf("validate config: %w", err)
	}

	return config, nil
}

func (config Config) Validate() error {
	var missing []string
	if strings.TrimSpace(config.Environment) == "" {
		missing = append(missing, "environment")
	}
	if strings.TrimSpace(config.HTTP.Address) == "" {
		missing = append(missing, "http.address")
	}
	if strings.TrimSpace(config.Database.URL) == "" {
		missing = append(missing, "database.url")
	}
	if len(missing) > 0 {
		return errors.New("missing required values: " + strings.Join(missing, ", "))
	}
	return nil
}

func applyEnvironment(config *Config) {
	if value := os.Getenv("APP_ENVIRONMENT"); value != "" {
		config.Environment = value
	}
	if value := os.Getenv("APP_HTTP_ADDRESS"); value != "" {
		config.HTTP.Address = value
	}
	if value := os.Getenv("APP_DATABASE_URL"); value != "" {
		config.Database.URL = value
	}
}