package authelia

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"log/slog"
	"os"
	"strings"

	"gopkg.in/yaml.v3"
)

// ConfigOpts holds parameters for generating Authelia's configuration.yml
type ConfigOpts struct {
	Domain         string       // auth portal domain (e.g. auth.payne.io)
	JWTSecret      string       // identity validation JWT secret
	SessionSecret  string       // session cookie secret
	StorageEncKey  string       // storage encryption key (>=20 chars)
	OIDCHMACSecret string       // OIDC HMAC secret
	DefaultPolicy  string       // "one_factor" or "two_factor"
	SessionDomain  string       // cookie domain for SSO (e.g. payne.io) — forward-auth only works for subdomains of this
	DataDir        string       // authelia data directory path
	ListenAddr     string       // listen address (default: 127.0.0.1:9091)
	OIDCClients    []OIDCClient // registered OIDC clients
	SMTPHost       string       // SMTP server host (empty = use filesystem notifier)
	SMTPPort       int          // SMTP server port (default: 587)
	SMTPUsername   string       // SMTP login username (defaults to sender if empty)
	SMTPSender     string       // From address
	SMTPPassword   string       // SMTP password (from secrets)
}

// ValidateConfigOpts checks that required fields are present and valid.
func ValidateConfigOpts(opts ConfigOpts) error {
	if opts.Domain == "" {
		return fmt.Errorf("auth portal domain is required")
	}
	if opts.JWTSecret == "" {
		return fmt.Errorf("JWT secret is required")
	}
	if opts.SessionSecret == "" {
		return fmt.Errorf("session secret is required")
	}
	if len(opts.StorageEncKey) < 20 {
		return fmt.Errorf("storage encryption key must be at least 20 characters, got %d", len(opts.StorageEncKey))
	}
	return nil
}

// GenerateConfig validates options, builds Authelia's configuration.yml, and writes it atomically.
func (m *Manager) GenerateConfig(opts ConfigOpts) error {
	if err := ValidateConfigOpts(opts); err != nil {
		return fmt.Errorf("config validation: %w", err)
	}
	if err := m.EnsureDataDir(); err != nil {
		return err
	}

	if opts.ListenAddr == "" {
		opts.ListenAddr = "127.0.0.1:9091"
	}
	if opts.DefaultPolicy == "" {
		opts.DefaultPolicy = "one_factor"
	}
	if opts.DataDir == "" {
		opts.DataDir = m.dataDir
	}

	cfg := m.buildConfig(opts)

	data, err := yaml.Marshal(cfg)
	if err != nil {
		return fmt.Errorf("marshaling authelia config: %w", err)
	}

	header := "# Authelia Configuration\n# Managed by Wild Central — do not edit manually\n---\n"
	content := header + string(data)

	tmpPath := m.configPath() + ".tmp"
	if err := os.WriteFile(tmpPath, []byte(content), 0600); err != nil {
		return fmt.Errorf("writing temp config: %w", err)
	}

	if err := os.Rename(tmpPath, m.configPath()); err != nil {
		os.Remove(tmpPath)
		return fmt.Errorf("installing config: %w", err)
	}

	slog.Info("authelia config written", "component", "authelia", "path", m.configPath())
	return nil
}

// EnsureJWKS generates an RSA key pair for OIDC token signing if one doesn't exist.
func (m *Manager) EnsureJWKS() error {
	if _, err := os.Stat(m.jwksPath()); err == nil {
		return nil // already exists
	}

	key, err := rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		return fmt.Errorf("generating RSA key: %w", err)
	}

	keyBytes := x509.MarshalPKCS1PrivateKey(key)
	pemBlock := &pem.Block{Type: "RSA PRIVATE KEY", Bytes: keyBytes}
	pemData := pem.EncodeToMemory(pemBlock)

	if err := os.WriteFile(m.jwksPath(), pemData, 0600); err != nil {
		return fmt.Errorf("writing JWKS key: %w", err)
	}

	slog.Info("authelia JWKS key pair generated", "component", "authelia", "path", m.jwksPath())
	return nil
}

// buildConfig constructs the Authelia config as a nested map for YAML marshaling.
func (m *Manager) buildConfig(opts ConfigOpts) map[string]any {
	cfg := map[string]any{
		"theme": "auto",

		"server": map[string]any{
			"address": "tcp://" + opts.ListenAddr + "/",
		},

		"log": map[string]any{
			"level": "info",
		},

		"totp": map[string]any{
			"issuer": "Wild Cloud",
		},

		"authentication_backend": map[string]any{
			"file": map[string]any{
				"path": m.usersDBPath(),
				"password": map[string]any{
					"algorithm":   "argon2id",
					"iterations":  3,
					"memory":      65536,
					"parallelism": 2,
					"key_length":  32,
					"salt_length": 16,
				},
			},
		},

		"access_control": map[string]any{
			"default_policy": opts.DefaultPolicy,
		},

		"session": map[string]any{
			"name":   "wild_central_session",
			"secret": opts.SessionSecret,
			"cookies": []map[string]any{
				{
					"domain":       opts.SessionDomain,
					"authelia_url": "https://" + opts.Domain,
				},
			},
		},

		"storage": map[string]any{
			"encryption_key": opts.StorageEncKey,
			"local": map[string]any{
				"path": m.sqlitePath(),
			},
		},

		"notifier": buildNotifier(opts, m.notificationPath()),

		"identity_validation": map[string]any{
			"reset_password": map[string]any{
				"jwt_secret": opts.JWTSecret,
			},
		},
	}

	// OIDC provider configuration — only emitted when clients exist.
	// Authelia requires at least one client when the OIDC section is present.
	if opts.OIDCHMACSecret != "" && len(opts.OIDCClients) > 0 {
		oidcCfg := map[string]any{
			"hmac_secret": opts.OIDCHMACSecret,
		}

		// Inline the JWKS private key directly (avoids needing template filters)
		if jwksData, err := os.ReadFile(m.jwksPath()); err == nil {
			oidcCfg["jwks"] = []map[string]any{
				{
					"key_id":    "wild-central",
					"algorithm": "RS256",
					"use":       "sig",
					"key":       string(jwksData),
				},
			}
		}

		{
			var clients []map[string]any
			for _, c := range opts.OIDCClients {
				client := map[string]any{
					"client_id":            c.ID,
					"client_name":          c.Name,
					"client_secret":        c.Secret, // already hashed
					"redirect_uris":        c.RedirectURIs,
					"scopes":               c.Scopes,
					"authorization_policy": c.Policy,
				}
				if c.ConsentMode != "" {
					client["consent_mode"] = c.ConsentMode
				}
				clients = append(clients, client)
			}
			oidcCfg["clients"] = clients
		}

		cfg["identity_providers"] = map[string]any{
			"oidc": oidcCfg,
		}
	}

	return cfg
}

// buildNotifier returns the notifier config — SMTP if configured, filesystem otherwise.
func buildNotifier(opts ConfigOpts, filesystemPath string) map[string]any {
	if opts.SMTPHost != "" && opts.SMTPSender != "" {
		username := opts.SMTPUsername
		if username == "" {
			username = opts.SMTPSender
		}
		port := opts.SMTPPort
		if port == 0 {
			port = 587
		}
		// Use the modern address format: submission:// for STARTTLS on 587, smtps:// for implicit TLS on 465
		scheme := "submission"
		if port == 465 {
			scheme = "smtps"
		}
		smtp := map[string]any{
			"address":  fmt.Sprintf("%s://%s:%d", scheme, opts.SMTPHost, port),
			"sender":   opts.SMTPSender,
			"username": username,
			"password": opts.SMTPPassword,
			"tls": map[string]any{
				"server_name": opts.SMTPHost,
			},
		}
		return map[string]any{"smtp": smtp}
	}
	return map[string]any{
		"filesystem": map[string]any{
			"filename": filesystemPath,
		},
	}
}

// GenerateSecret creates a cryptographically random hex string of the given byte length.
func GenerateSecret(byteLen int) (string, error) {
	b := make([]byte, byteLen)
	if _, err := rand.Read(b); err != nil {
		return "", fmt.Errorf("generating random bytes: %w", err)
	}
	return fmt.Sprintf("%x", b), nil
}

// SessionDomainFromAuthDomain extracts the parent domain for session cookie scoping.
// "auth.payne.io" -> "payne.io", "auth.sub.example.com" -> "sub.example.com"
func SessionDomainFromAuthDomain(authDomain string) string {
	parts := strings.SplitN(authDomain, ".", 2)
	if len(parts) == 2 {
		return parts[1]
	}
	return authDomain
}