package config

import (
	"crypto/tls"
	"fmt"
	"log/slog"
	"os"
	"strings"

	mcdslconfig "git.wntrmute.dev/mc/mcdsl/config"
)

// Duration is an alias for the mcdsl config.Duration type, which wraps
// time.Duration with TOML string unmarshalling support. Exported so
// existing code that references config.Duration continues to work.
type Duration = mcdslconfig.Duration

// Config is the top-level mc-proxy configuration.
type Config struct {
	Listeners []Listener `toml:"listeners"`
	Database  Database   `toml:"database"`
	GRPC      GRPC       `toml:"grpc"`
	Firewall  Firewall   `toml:"firewall"`
	Proxy     Proxy      `toml:"proxy"`
	Metrics   Metrics    `toml:"metrics"`
	Log       Log        `toml:"log"`
}

// Metrics holds the Prometheus metrics endpoint configuration.
type Metrics struct {
	Addr string `toml:"addr"` // e.g. "127.0.0.1:9090"
	Path string `toml:"path"` // e.g. "/metrics" (default)
}

// Database holds the database configuration.
type Database struct {
	Path string `toml:"path"`
}

// GRPC holds the gRPC admin API configuration.
type GRPC struct {
	Addr string `toml:"addr"` // Unix socket path (e.g., "/srv/mc-proxy/mc-proxy.sock")
}

// Listener is a proxy listener with its routes.
type Listener struct {
	Addr           string  `toml:"addr"`
	ProxyProtocol  bool    `toml:"proxy_protocol"`
	MaxConnections int64   `toml:"max_connections"` // 0 = unlimited
	Routes         []Route `toml:"routes"`
}

// Route is a proxy route within a listener.
type Route struct {
	Hostname          string     `toml:"hostname"`
	Backend           string     `toml:"backend"`
	Mode              string     `toml:"mode"`                // "l4" (default) or "l7"
	TLSCert           string     `toml:"tls_cert"`            // PEM certificate path (L7 only)
	TLSKey            string     `toml:"tls_key"`             // PEM private key path (L7 only)
	BackendTLS        bool       `toml:"backend_tls"`         // re-encrypt to backend (L7 only)
	SendProxyProtocol bool       `toml:"send_proxy_protocol"` // send PROXY v2 header to backend
	L7Policies        []L7Policy `toml:"l7_policies"`         // HTTP-level policies (L7 only)
}

// L7Policy is an HTTP-level blocking policy for L7 routes.
type L7Policy struct {
	Type  string `toml:"type"`  // "block_user_agent" or "require_header"
	Value string `toml:"value"` // UA substring or header name
}

// Firewall holds the global firewall configuration.
type Firewall struct {
	GeoIPDB          string   `toml:"geoip_db"`
	BlockedIPs       []string `toml:"blocked_ips"`
	BlockedCIDRs     []string `toml:"blocked_cidrs"`
	BlockedCountries []string `toml:"blocked_countries"`
	RateLimit        int64    `toml:"rate_limit"`
	RateWindow       Duration `toml:"rate_window"`
}

// Proxy holds proxy behavior timeouts.
type Proxy struct {
	ConnectTimeout  Duration `toml:"connect_timeout"`
	IdleTimeout     Duration `toml:"idle_timeout"`
	ShutdownTimeout Duration `toml:"shutdown_timeout"`
}

// Log holds logging configuration.
type Log struct {
	Level string `toml:"level"`
}

// SocketPath returns the filesystem path for the Unix socket,
// stripping any "unix:" prefix.
func (g GRPC) SocketPath() string {
	return strings.TrimPrefix(g.Addr, "unix:")
}

// Load reads and validates the mc-proxy configuration from a TOML file.
// Environment variables with the MCPROXY_ prefix override config values.
func Load(path string) (*Config, error) {
	cfg, err := mcdslconfig.Load[Config](path, "MCPROXY")
	if err != nil {
		return nil, err
	}
	return cfg, nil
}

// Validate implements the mcdsl config.Validator interface. It applies
// manual env overrides for fields that the generic reflection-based
// system cannot handle (int64, error-returning duration parsing), then
// validates all config fields.
func (c *Config) Validate() error {
	if err := c.applyManualEnvOverrides(); err != nil {
		return err
	}
	return c.validate()
}

// applyManualEnvOverrides handles env overrides that need error reporting
// or non-standard types (int64 rate limits, duration fields that
// reflection already handles but we want error semantics for).
func (c *Config) applyManualEnvOverrides() error {
	if v := os.Getenv("MCPROXY_FIREWALL_RATE_LIMIT"); v != "" {
		var n int64
		if _, err := fmt.Sscanf(v, "%d", &n); err != nil {
			return fmt.Errorf("MCPROXY_FIREWALL_RATE_LIMIT: %w", err)
		}
		c.Firewall.RateLimit = n
	}
	return nil
}

func (c *Config) validate() error {
	if c.Database.Path == "" {
		return fmt.Errorf("database.path is required")
	}

	// Validate listeners if provided (used for seeding on first run).
	for i := range c.Listeners {
		l := &c.Listeners[i]
		if l.Addr == "" {
			return fmt.Errorf("listener %d: addr is required", i)
		}
		if l.MaxConnections < 0 {
			return fmt.Errorf("listener %d (%s): max_connections must not be negative", i, l.Addr)
		}
		seen := make(map[string]bool)
		for j := range l.Routes {
			r := &l.Routes[j]
			if r.Hostname == "" {
				return fmt.Errorf("listener %d (%s), route %d: hostname is required", i, l.Addr, j)
			}
			if r.Backend == "" {
				return fmt.Errorf("listener %d (%s), route %d: backend is required", i, l.Addr, j)
			}
			if seen[r.Hostname] {
				return fmt.Errorf("listener %d (%s), route %d: duplicate hostname %q", i, l.Addr, j, r.Hostname)
			}
			seen[r.Hostname] = true

			if r.Mode == "" {
				r.Mode = "l4"
			}
			if r.Mode != "l4" && r.Mode != "l7" {
				return fmt.Errorf("listener %d (%s), route %d (%s): mode must be \"l4\" or \"l7\", got %q",
					i, l.Addr, j, r.Hostname, r.Mode)
			}

			if r.Mode == "l4" && (r.TLSCert != "" || r.TLSKey != "") {
				slog.Warn("L4 route has tls_cert/tls_key set (ignored)",
					"listener", l.Addr, "hostname", r.Hostname)
			}

			if r.Mode == "l7" {
				if r.TLSCert == "" || r.TLSKey == "" {
					return fmt.Errorf("listener %d (%s), route %d (%s): L7 routes require tls_cert and tls_key",
						i, l.Addr, j, r.Hostname)
				}
				if _, err := tls.LoadX509KeyPair(r.TLSCert, r.TLSKey); err != nil {
					return fmt.Errorf("listener %d (%s), route %d (%s): loading TLS cert/key: %w",
						i, l.Addr, j, r.Hostname, err)
				}
			}

			// Validate L7 policies.
			if r.Mode == "l4" && len(r.L7Policies) > 0 {
				slog.Warn("L4 route has l7_policies set (ignored)",
					"listener", l.Addr, "hostname", r.Hostname)
			}
			for k, p := range r.L7Policies {
				if p.Type != "block_user_agent" && p.Type != "require_header" {
					return fmt.Errorf("listener %d (%s), route %d (%s), policy %d: type must be \"block_user_agent\" or \"require_header\", got %q",
						i, l.Addr, j, r.Hostname, k, p.Type)
				}
				if p.Value == "" {
					return fmt.Errorf("listener %d (%s), route %d (%s), policy %d: value is required",
						i, l.Addr, j, r.Hostname, k)
				}
			}
		}
	}

	if len(c.Firewall.BlockedCountries) > 0 && c.Firewall.GeoIPDB == "" {
		return fmt.Errorf("firewall: geoip_db is required when blocked_countries is set")
	}

	if c.Firewall.RateLimit < 0 {
		return fmt.Errorf("firewall.rate_limit must not be negative")
	}
	if c.Firewall.RateWindow.Duration < 0 {
		return fmt.Errorf("firewall.rate_window must not be negative")
	}
	if c.Firewall.RateLimit > 0 && c.Firewall.RateWindow.Duration == 0 {
		return fmt.Errorf("firewall.rate_window is required when rate_limit is set")
	}

	if c.GRPC.Addr != "" {
		socketPath := c.GRPC.SocketPath()
		if !strings.Contains(socketPath, "/") {
			return fmt.Errorf("grpc.addr must be a Unix socket path (e.g., /srv/mc-proxy/mc-proxy.sock)")
		}
	}

	if c.Metrics.Addr != "" && c.Metrics.Path != "" && !strings.HasPrefix(c.Metrics.Path, "/") {
		return fmt.Errorf("metrics.path must start with \"/\"")
	}

	if c.Proxy.ConnectTimeout.Duration < 0 {
		return fmt.Errorf("proxy.connect_timeout must not be negative")
	}
	if c.Proxy.IdleTimeout.Duration < 0 {
		return fmt.Errorf("proxy.idle_timeout must not be negative")
	}
	if c.Proxy.ShutdownTimeout.Duration < 0 {
		return fmt.Errorf("proxy.shutdown_timeout must not be negative")
	}

	return nil
}