package config

import (
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

const defaultEnvPrefix = "GO_OMNI_"

// LoadFromEnv loads application settings from GO_OMNI_* variables. The
// database settings remain owned by database.ConfigFromEnv.
func LoadFromEnv(prefix string) (Config, error) {
	return applyEnv(Default(), prefix)
}

// ApplyEnv overlays nonempty environment values on a caller's defaults or file
// settings, then validates the result. Caller-owned slices are not retained.
func ApplyEnv(defaults Config, prefix string) (Config, error) {
	defaults.Errors = defaults.Errors.Clone()
	defaults.TrustedProxies = append([]string(nil), defaults.TrustedProxies...)
	defaults.Log.RedactKeys = append([]string(nil), defaults.Log.RedactKeys...)
	return applyEnv(defaults, prefix)
}

func applyEnv(cfg Config, prefix string) (Config, error) {
	prefix = strings.TrimSpace(prefix)
	if prefix == "" {
		prefix = defaultEnvPrefix
	}
	cfg.Address = envString(prefix+"HTTP_ADDR", cfg.Address)
	cfg.Transport = envString(prefix+"TRANSPORT", cfg.Transport)
	cfg.TLS.CertFile = envString(prefix+"TLS_CERT_FILE", cfg.TLS.CertFile)
	cfg.TLS.KeyFile = envString(prefix+"TLS_KEY_FILE", cfg.TLS.KeyFile)
	cfg.RequestIDHeader = envString(prefix+"REQUEST_ID_HEADER", cfg.RequestIDHeader)
	if value := strings.TrimSpace(os.Getenv(prefix + "TRUSTED_PROXIES")); value != "" {
		cfg.TrustedProxies = strings.Split(value, ",")
		for i := range cfg.TrustedProxies {
			cfg.TrustedProxies[i] = strings.TrimSpace(cfg.TrustedProxies[i])
		}
	}
	cfg.Log.Level = envString(prefix+"LOG_LEVEL", cfg.Log.Level)
	cfg.Log.Format = envString(prefix+"LOG_FORMAT", cfg.Log.Format)
	cfg.Log.Output = envString(prefix+"LOG_OUTPUT", cfg.Log.Output)
	cfg.Log.File = envString(prefix+"LOG_FILE", cfg.Log.File)
	cfg.Log.Service = envString(prefix+"SERVICE", cfg.Log.Service)
	cfg.Log.Environment = envString(prefix+"ENVIRONMENT", cfg.Log.Environment)

	var err error
	for _, field := range []struct {
		name  string
		value *time.Duration
	}{
		{"HTTP_READ_HEADER_TIMEOUT", &cfg.HTTP.ReadHeaderTimeout},
		{"HTTP_READ_TIMEOUT", &cfg.HTTP.ReadTimeout},
		{"HTTP_WRITE_TIMEOUT", &cfg.HTTP.WriteTimeout},
		{"HTTP_IDLE_TIMEOUT", &cfg.HTTP.IdleTimeout},
	} {
		if value := strings.TrimSpace(os.Getenv(prefix + field.name)); value != "" {
			*field.value, err = time.ParseDuration(value)
			if err != nil {
				return Config{}, fmt.Errorf("%s%s must be a duration: %w", prefix, field.name, err)
			}
		}
	}
	if value := strings.TrimSpace(os.Getenv(prefix + "HTTP_MAX_HEADER_BYTES")); value != "" {
		cfg.HTTP.MaxHeaderBytes, err = strconv.Atoi(value)
		if err != nil {
			return Config{}, fmt.Errorf("%sHTTP_MAX_HEADER_BYTES must be an integer: %w", prefix, err)
		}
	}
	if cfg.EnableLogger, err = envBool(prefix+"ENABLE_LOGGER", cfg.EnableLogger); err != nil {
		return Config{}, err
	}
	if cfg.Log.AddSource, err = envBool(prefix+"LOG_ADD_SOURCE", cfg.Log.AddSource); err != nil {
		return Config{}, err
	}
	if value := strings.TrimSpace(os.Getenv(prefix + "SLOW_REQUEST_THRESHOLD")); value != "" {
		cfg.SlowRequestThreshold, err = time.ParseDuration(value)
		if err != nil {
			return Config{}, fmt.Errorf("%sSLOW_REQUEST_THRESHOLD must be a duration: %w", prefix, err)
		}
	}
	if value := strings.TrimSpace(os.Getenv(prefix + "SHUTDOWN_TIMEOUT")); value != "" {
		cfg.ShutdownTimeout, err = time.ParseDuration(value)
		if err != nil {
			return Config{}, fmt.Errorf("%sSHUTDOWN_TIMEOUT must be a duration: %w", prefix, err)
		}
	}
	if err := cfg.Validate(); err != nil {
		return Config{}, err
	}
	return cfg, nil
}

func envString(key, fallback string) string {
	if value := strings.TrimSpace(os.Getenv(key)); value != "" {
		return value
	}
	return fallback
}

func envBool(key string, fallback bool) (bool, error) {
	value := strings.TrimSpace(os.Getenv(key))
	if value == "" {
		return fallback, nil
	}
	parsed, err := strconv.ParseBool(value)
	if err != nil {
		return false, fmt.Errorf("%s must be a boolean: %w", key, err)
	}
	return parsed, nil
}