package config

import (
	"fmt"
	"net/url"
	"strings"
	"time"
)

// ValidateConfig validates a loaded Config and returns a list of human-readable
// error messages. An empty slice means the config is valid.
// Called at startup — the server must exit 1 if any errors are returned.
func ValidateConfig(cfg *Config) []string {
	var errs []string

	// Issuer must be a valid URL with an http(s) scheme.
	if cfg.Issuer == "" {
		errs = append(errs, "issuer: must not be empty")
	} else {
		u, err := url.Parse(cfg.Issuer)
		if err != nil || u.Scheme == "" || u.Host == "" {
			errs = append(errs, fmt.Sprintf("issuer: %q is not a valid URL (must include scheme and host)", cfg.Issuer))
		} else if u.Scheme != "http" && u.Scheme != "https" {
			errs = append(errs, fmt.Sprintf("issuer: scheme must be http or https, got %q", u.Scheme))
		}
	}

	// Port must be in the valid TCP range.
	if cfg.Port < 1 || cfg.Port > 65535 {
		errs = append(errs, fmt.Sprintf("port: must be between 1 and 65535, got %d", cfg.Port))
	}

	// At least one client must be registered.
	if len(cfg.Clients) == 0 {
		errs = append(errs, "clients: at least one client must be defined")
	}

	// Each client must have at least one redirect URI and a non-empty clientId.
	for i, c := range cfg.Clients {
		prefix := fmt.Sprintf("clients[%d] (%s)", i, c.ClientID)
		if c.ClientID == "" {
			prefix = fmt.Sprintf("clients[%d]", i)
			errs = append(errs, prefix+": clientId must not be empty")
		}
		hasAuthorizationCode := contains(c.GrantTypes, "authorization_code")
		hasClientCredentials := contains(c.GrantTypes, "client_credentials")
		if (hasAuthorizationCode || !hasClientCredentials) && len(c.RedirectURIs) == 0 {
			errs = append(errs, prefix+": redirect_uri: at least one redirectUri must be registered")
		}
		if hasClientCredentials {
			if c.ClientType != "confidential" {
				errs = append(errs, prefix+": client_credentials requires clientType confidential")
			}
			if !strings.HasPrefix(c.SecretRef, "env:") {
				errs = append(errs, prefix+": client_credentials requires an env: secretRef")
			}
			if c.ServiceSubject == "" || c.Tenant == "" {
				errs = append(errs, prefix+": client_credentials requires serviceSubject and tenant")
			}
			if c.TokenLifetime != "" {
				lifetime, err := time.ParseDuration(c.TokenLifetime)
				if err != nil {
					errs = append(errs, prefix+": tokenLifetime must be a valid duration")
				} else if lifetime < time.Minute || lifetime > time.Hour {
					errs = append(errs, prefix+": tokenLifetime must be between 1m and 1h")
				}
			}
		} else if c.TokenLifetime != "" {
			errs = append(errs, prefix+": tokenLifetime is only supported for client_credentials clients")
		}
		// Warn about wildcard redirect URIs (they are blocked at runtime anyway).
		for _, uri := range c.RedirectURIs {
			if strings.ContainsAny(uri, "*?") {
				errs = append(errs, prefix+fmt.Sprintf(": redirect_uri %q must not contain wildcards", uri))
			}
		}
		if c.RegistrationURL != "" {
			if err := validateHandoffURL(c.RegistrationURL); err != nil {
				errs = append(errs, prefix+": registrationUrl: "+err.Error())
			}
		}
		if c.EnrollmentURL != "" {
			if err := validateHandoffURL(c.EnrollmentURL); err != nil {
				errs = append(errs, prefix+": enrollmentUrl: "+err.Error())
			}
		}
	}

	// Private key PEM path must be provided (existence is checked at startup).
	if cfg.PrivateKeyPEM == "" {
		errs = append(errs, "privateKeyPem: path must not be empty")
	}

	return errs
}

func contains(values []string, wanted string) bool {
	for _, value := range values {
		if value == wanted {
			return true
		}
	}
	return false
}

func validateHandoffURL(raw string) error {
	u, err := url.Parse(raw)
	if err != nil || u.Scheme == "" || u.Host == "" {
		return fmt.Errorf("%q is not an absolute URL", raw)
	}
	if u.Scheme != "http" && u.Scheme != "https" {
		return fmt.Errorf("%q scheme must be http or https", raw)
	}
	if u.User != nil {
		return fmt.Errorf("%q must not contain userinfo", raw)
	}
	if strings.ContainsAny(u.Host, "*?") || strings.ContainsAny(u.Path, "*") {
		return fmt.Errorf("%q must not contain wildcards", raw)
	}
	return nil
}