package config

import (
	"crypto/rand"
	"encoding/hex"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
)

type Config struct {
	Port              string
	DataDir           string
	DatabasePath      string
	JWTSecret         string
	BaseURL           string
	// BaseURLSet: BASE_URL was configured explicitly. Links in mails (password reset) are only built
	// from it, never from the request's Host header.
	BaseURLSet bool
	AllowRegistration bool
	LogLevel          string
	Debug             bool
	DemoMode          bool

	// Optional SMTP environment variables (can also be overridden/configured in DB system_settings)
	SMTPHost string
	SMTPPort string
	SMTPUser string
	SMTPPass string
	SMTPFrom string
	SMTPTLS  bool
	// SMTPSkipVerify accepts self-signed or mismatching certificates (internal mail servers)
	SMTPSkipVerify bool

	// Legal notices (Impressum, Datenschutz): an external URL and/or Markdown text, shown even before login
	Legal LegalTexts
}

type LegalTexts struct {
	ImprintURL, ImprintContent string
	PrivacyURL, PrivacyContent string
}

// Publicly known JWT secrets (old code default and the placeholders from .env.example, compose and
// README). Signing with one of them would let anyone forge login tokens.
var insecureJWTSecrets = map[string]bool{
	"mindsift-default-selfhosted-jwt-secret-key-2026": true,
	"change_this_to_a_secure_random_key_min_32_chars": true,
	"hier-ein-langer-zufaelliger-wert":                true,
	"changeme":                                        true,
	"secret":                                          true,
}

const jwtSecretFile = "jwt.secret"

// resolveJWTSecret uses JWT_SECRET when it is set to a real value. Otherwise it generates a random
// secret once and keeps it in the data directory, so logins survive restarts without anybody being
// able to forge tokens with a known default.
func resolveJWTSecret(fromEnv, dataDir string) string {
	if v := strings.TrimSpace(fromEnv); v != "" && !insecureJWTSecrets[v] {
		if len(v) < 32 {
			slog.Warn("JWT_SECRET ist kürzer als 32 Zeichen – bitte einen längeren Zufallswert verwenden")
		}
		return v
	} else if v != "" {
		slog.Warn("JWT_SECRET ist ein öffentlich bekannter Platzhalter und wird ignoriert")
	}
	path := filepath.Join(dataDir, jwtSecretFile)
	if data, err := os.ReadFile(path); err == nil {
		if s := strings.TrimSpace(string(data)); len(s) >= 32 {
			return s
		}
	}
	buf := make([]byte, 32)
	if _, err := rand.Read(buf); err != nil {
		panic("crypto/rand: " + err.Error())
	}
	secret := hex.EncodeToString(buf)
	_ = os.MkdirAll(dataDir, 0o755)
	if err := os.WriteFile(path, []byte(secret+"\n"), 0o600); err != nil {
		slog.Error("Erzeugtes JWT-Secret konnte nicht gespeichert werden – Anmeldungen gelten nur bis zum Neustart", "pfad", path, "error", err)
	} else {
		slog.Warn("Kein JWT_SECRET gesetzt: zufälliges Secret erzeugt und im Datenverzeichnis gespeichert. Für Produktion besser JWT_SECRET setzen.", "pfad", path)
	}
	return secret
}

// legalContent reads Markdown from NAME or, for longer texts, from the file named in NAME_FILE.
func legalContent(name string) string {
	if v := strings.TrimSpace(os.Getenv(name)); v != "" {
		return v
	}
	if path := strings.TrimSpace(os.Getenv(name + "_FILE")); path != "" {
		data, err := os.ReadFile(path)
		if err != nil {
			slog.Warn("Rechtstext konnte nicht gelesen werden", "variable", name+"_FILE", "error", err)
			return ""
		}
		return strings.TrimSpace(string(data))
	}
	return ""
}

// legalURL accepts only http(s) links, so a misconfiguration cannot inject javascript: URLs.
func legalURL(name string) string {
	v := strings.TrimSpace(os.Getenv(name))
	if v == "" {
		return ""
	}
	if !strings.HasPrefix(v, "https://") && !strings.HasPrefix(v, "http://") {
		slog.Warn("Rechtstext-URL ignoriert: nur http(s) erlaubt", "variable", name)
		return ""
	}
	return v
}

func Load() *Config {
	port := getEnv("PORT", "8080")
	dataDir := getEnv("DATA_DIR", "./data")
	dbURL := getEnv("DATABASE_URL", "")

	dbPath := filepath.Join(dataDir, "mindsift.db")
	if strings.HasPrefix(dbURL, "sqlite://") {
		dbPath = strings.TrimPrefix(dbURL, "sqlite://")
	} else if dbURL != "" && !strings.HasPrefix(dbURL, "postgres") {
		dbPath = dbURL
	}

	jwtSecret := resolveJWTSecret(os.Getenv("JWT_SECRET"), filepath.Dir(dbPath))
	baseURL := getEnv("BASE_URL", "http://localhost:"+port)
	allowReg := strings.ToLower(getEnv("ALLOW_REGISTRATION", "false")) == "true"

	debugVal := strings.ToLower(getEnv("DEBUG", "false"))
	debug := debugVal == "true" || debugVal == "1" || debugVal == "yes" || debugVal == "on"

	logLevel := strings.ToLower(getEnv("LOG_LEVEL", "info"))
	if debug {
		logLevel = "debug"
	}

	demoVal := strings.ToLower(getEnv("MINDA_DEMO", getEnv("MINDSIFT_DEMO", getEnv("DEMO_MODE", "false"))))
	demoMode := demoVal == "true" || demoVal == "1" || demoVal == "yes" || demoVal == "on"

	smtpHost := getEnv("SMTP_HOST", "")
	smtpPort := getEnv("SMTP_PORT", "587")
	smtpUser := getEnv("SMTP_USER", "")
	smtpPass := getEnv("SMTP_PASS", "")
	smtpFrom := getEnv("SMTP_FROM", "")
	smtpTLS := strings.ToLower(getEnv("SMTP_TLS", "true")) != "false"
	smtpSkipVerify := strings.ToLower(getEnv("SMTP_SKIP_VERIFY", "false")) == "true"

	return &Config{
		Port:              port,
		DataDir:           dataDir,
		DatabasePath:      dbPath,
		JWTSecret:         jwtSecret,
		BaseURL:           baseURL,
		BaseURLSet:        strings.TrimSpace(os.Getenv("BASE_URL")) != "",
		AllowRegistration: allowReg,
		LogLevel:          logLevel,
		Debug:             debug,
		DemoMode:          demoMode,
		SMTPHost:          smtpHost,
		SMTPPort:          smtpPort,
		SMTPUser:          smtpUser,
		SMTPPass:          smtpPass,
		SMTPFrom:          smtpFrom,
		SMTPTLS:           smtpTLS,
		SMTPSkipVerify:    smtpSkipVerify,
		Legal: LegalTexts{
			ImprintURL:     legalURL("LEGAL_IMPRINT_URL"),
			ImprintContent: legalContent("LEGAL_IMPRINT_CONTENT"),
			PrivacyURL:     legalURL("LEGAL_PRIVACY_URL"),
			PrivacyContent: legalContent("LEGAL_PRIVACY_CONTENT"),
		},
	}
}

// SlogLevel parses Config.LogLevel into a standard slog.Level.
func (c *Config) SlogLevel() slog.Level {
	switch strings.ToLower(strings.TrimSpace(c.LogLevel)) {
	case "debug":
		return slog.LevelDebug
	case "warn", "warning":
		return slog.LevelWarn
	case "error":
		return slog.LevelError
	default:
		return slog.LevelInfo
	}
}

func getEnv(key, fallback string) string {
	if val, ok := os.LookupEnv(key); ok && strings.TrimSpace(val) != "" {
		return strings.TrimSpace(val)
	}
	return fallback
}