// Package config loads the Control Service configuration from the process
// environment. Every secret comes from the environment (environment.d); nothing
// is compiled into the binary and nothing is read from a committed file.
package config

import (
	"errors"
	"fmt"
	"log/slog"
	"os"
	"strconv"
	"strings"
	"time"
)

// Config is the fully resolved runtime configuration.
type Config struct {
	// Addr is the listen address, for example ":8791".
	Addr string
	// DBPath is the SQLite database file, for example "/data/control.db".
	DBPath string
	// SessionSecret signs the session cookie. Required, >= 16 bytes.
	SessionSecret []byte
	// AdminUsername is the single dashboard login name (Sam).
	AdminUsername string
	// AdminPassword is the plaintext password. Optional if AdminPasswordHash is set.
	AdminPassword string
	// AdminPasswordHash is a bcrypt hash. Optional if AdminPassword is set.
	AdminPasswordHash string
	// CookieSecure sets the Secure attribute on cookies. Keep true behind HTTPS.
	CookieSecure bool
	// SessionTTL is how long a session cookie stays valid.
	SessionTTL time.Duration
	// LogLevel is the slog level.
	LogLevel slog.Level
	// AppEnv is a label such as "production" or "development".
	AppEnv string
	// Version is injected at build time.
	Version string
}

// Load reads and validates the configuration.
func Load() (*Config, error) {
	cfg := &Config{
		Addr:              env("CONTROL_ADDR", ":8791"),
		DBPath:            env("CONTROL_DB_PATH", "/data/control.db"),
		AdminUsername:     env("CONTROL_ADMIN_USERNAME", "sam"),
		AdminPassword:     os.Getenv("CONTROL_ADMIN_PASSWORD"),
		AdminPasswordHash: os.Getenv("CONTROL_ADMIN_PASSWORD_HASH"),
		CookieSecure:      envBool("CONTROL_COOKIE_SECURE", true),
		AppEnv:            env("CONTROL_APP_ENV", "production"),
	}

	secret := os.Getenv("CONTROL_SESSION_SECRET")
	if len(secret) < 16 {
		return nil, errors.New("CONTROL_SESSION_SECRET must be set and at least 16 characters")
	}
	cfg.SessionSecret = []byte(secret)

	if cfg.AdminPassword == "" && cfg.AdminPasswordHash == "" {
		return nil, errors.New("set CONTROL_ADMIN_PASSWORD or CONTROL_ADMIN_PASSWORD_HASH")
	}
	if cfg.AdminUsername == "" {
		return nil, errors.New("CONTROL_ADMIN_USERNAME must not be empty")
	}

	ttl, err := time.ParseDuration(env("CONTROL_SESSION_TTL", "12h"))
	if err != nil {
		return nil, fmt.Errorf("CONTROL_SESSION_TTL: %w", err)
	}
	cfg.SessionTTL = ttl

	lvl, err := parseLevel(env("CONTROL_LOG_LEVEL", "info"))
	if err != nil {
		return nil, err
	}
	cfg.LogLevel = lvl

	return cfg, nil
}

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

func envBool(key string, fallback bool) bool {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	b, err := strconv.ParseBool(v)
	if err != nil {
		return fallback
	}
	return b
}

func parseLevel(s string) (slog.Level, error) {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case "debug":
		return slog.LevelDebug, nil
	case "info", "":
		return slog.LevelInfo, nil
	case "warn", "warning":
		return slog.LevelWarn, nil
	case "error":
		return slog.LevelError, nil
	default:
		return 0, fmt.Errorf("CONTROL_LOG_LEVEL: unknown level %q", s)
	}
}