package config

import (
	"crypto/tls"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"net/url"
	"os"
	"time"

	"github.com/cespare/xxhash/v2"
	"github.com/mitchellh/hashstructure"

	"github.com/pomerium/pomerium/internal/cryptutil"
	"github.com/pomerium/pomerium/internal/urlutil"
)

// Policy contains route specific configuration and access settings.
type Policy struct {
	From string `mapstructure:"from" yaml:"from"`
	To   string `mapstructure:"to" yaml:"to"`
	// Identity related policy
	AllowedUsers   []string `mapstructure:"allowed_users" yaml:"allowed_users,omitempty" json:"allowed_users,omitempty"`
	AllowedGroups  []string `mapstructure:"allowed_groups" yaml:"allowed_groups,omitempty" json:"allowed_groups,omitempty"`
	AllowedDomains []string `mapstructure:"allowed_domains" yaml:"allowed_domains,omitempty" json:"allowed_domains,omitempty"`

	Source      *StringURL `yaml:",omitempty" json:"source,omitempty" hash:"ignore"`
	Destination *url.URL   `yaml:",omitempty" json:"destination,omitempty" hash:"ignore"`

	// Additional route matching options
	Prefix string `mapstructure:"prefix" yaml:"prefix,omitempty" json:"prefix,omitempty"`
	Path   string `mapstructure:"path" yaml:"path,omitempty" json:"path,omitempty"`
	Regex  string `mapstructure:"regex" yaml:"regex,omitempty" json:"regex,omitempty"`

	// Allow unauthenticated HTTP OPTIONS requests as per the CORS spec
	// https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#Preflighted_requests
	CORSAllowPreflight bool `mapstructure:"cors_allow_preflight" yaml:"cors_allow_preflight,omitempty"`

	// Allow any public request to access this route. **Bypasses authentication**
	AllowPublicUnauthenticatedAccess bool `mapstructure:"allow_public_unauthenticated_access" yaml:"allow_public_unauthenticated_access,omitempty"`

	// UpstreamTimeout is the route specific timeout. Must be less than the global
	// timeout. If unset,  route will fallback to the proxy's DefaultUpstreamTimeout.
	UpstreamTimeout time.Duration `mapstructure:"timeout" yaml:"timeout,omitempty"`

	// Enable proxying of websocket connections by removing the default timeout handler.
	// Caution: Enabling this feature could result in abuse via DOS attacks.
	AllowWebsockets bool `mapstructure:"allow_websockets"  yaml:"allow_websockets,omitempty"`

	// TLSSkipVerify controls whether a client verifies the server's certificate
	// chain and host name.
	// If TLSSkipVerify is true, TLS accepts any certificate presented by the
	// server and any host name in that certificate.
	// In this mode, TLS is susceptible to man-in-the-middle attacks.
	// This should be used only for testing.
	TLSSkipVerify bool `mapstructure:"tls_skip_verify" yaml:"tls_skip_verify,omitempty"`

	// TLSServerName overrides the hostname in the `to` field. This is useful
	// if your backend is an HTTPS server with a valid certificate, but you
	// want to communicate to the backend with an internal hostname (e.g.
	// Docker container name).
	TLSServerName string `mapstructure:"tls_server_name" yaml:"tls_server_name,omitempty"`

	// TLSCustomCA defines the  root certificate to use with a given
	// route when verifying server certificates.
	TLSCustomCA     string `mapstructure:"tls_custom_ca" yaml:"tls_custom_ca,omitempty"`
	TLSCustomCAFile string `mapstructure:"tls_custom_ca_file" yaml:"tls_custom_ca_file,omitempty"`

	// Contains the x.509 client certificate to present to the downstream
	// host.
	TLSClientCert     string           `mapstructure:"tls_client_cert" yaml:"tls_client_cert,omitempty"`
	TLSClientKey      string           `mapstructure:"tls_client_key" yaml:"tls_client_key,omitempty"`
	TLSClientCertFile string           `mapstructure:"tls_client_cert_file" yaml:"tls_client_cert_file,omitempty"`
	TLSClientKeyFile  string           `mapstructure:"tls_client_key_file" yaml:"tls_client_key_file,omitempty"`
	ClientCertificate *tls.Certificate `yaml:",omitempty" hash:"ignore"`

	// SetRequestHeaders adds a collection of headers to the downstream request
	// in the form of key value pairs. Note bene, this will overwrite the
	// value of any existing value of a given header key.
	SetRequestHeaders map[string]string `mapstructure:"set_request_headers" yaml:"set_request_headers,omitempty"`

	// RemoveRequestHeaders removes a collection of headers from a downstream request.
	// Note that this has lower priority than `SetRequestHeaders`, if you specify `X-Custom-Header` in both
	// `SetRequestHeaders` and `RemoveRequestHeaders`, then the header won't be removed.
	RemoveRequestHeaders []string `mapstructure:"remove_request_headers" yaml:"remove_request_headers,omitempty"`

	// PreserveHostHeader disables host header rewriting.
	//
	// https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_set_header
	PreserveHostHeader bool `mapstructure:"preserve_host_header" yaml:"preserve_host_header,omitempty"`

	// PassIdentityHeaders controls whether to add a user's identity headers to the downstream request.
	// These includes:
	//
	//  - X-Pomerium-Jwt-Assertion
	//  - X-Pomerium-Claim-*
	//
	PassIdentityHeaders bool `mapstructure:"pass_identity_headers" yaml:"pass_identity_headers,omitempty"`
}

// Validate checks the validity of a policy.
func (p *Policy) Validate() error {
	var err error
	source, err := urlutil.ParseAndValidateURL(p.From)
	if err != nil {
		return fmt.Errorf("config: policy bad source url %w", err)
	}

	// Make sure there's no path set on the from url
	if !(source.Path == "" || source.Path == "/") {
		return fmt.Errorf("config: policy source url (%s) contains a path, but it should be set using the path field instead",
			source.String())
	}

	p.Source = &StringURL{source}

	p.Destination, err = urlutil.ParseAndValidateURL(p.To)
	if err != nil {
		return fmt.Errorf("config: policy bad destination url %w", err)
	}

	// Only allow public access if no other whitelists are in place
	if p.AllowPublicUnauthenticatedAccess && (p.AllowedDomains != nil || p.AllowedGroups != nil || p.AllowedUsers != nil) {
		return fmt.Errorf("config: policy route marked as public but contains whitelists")
	}

	if (p.TLSClientCert == "" && p.TLSClientKey != "") || (p.TLSClientCert != "" && p.TLSClientKey == "") ||
		(p.TLSClientCertFile == "" && p.TLSClientKeyFile != "") || (p.TLSClientCertFile != "" && p.TLSClientKeyFile == "") {
		return fmt.Errorf("config: client certificate key and cert both must be non-empty")
	}

	if p.TLSClientCert != "" && p.TLSClientKey != "" {
		p.ClientCertificate, err = cryptutil.CertificateFromBase64(p.TLSClientCert, p.TLSClientKey)
		if err != nil {
			return fmt.Errorf("config: couldn't decode client cert %w", err)
		}
	} else if p.TLSClientCertFile != "" && p.TLSClientKeyFile != "" {
		p.ClientCertificate, err = cryptutil.CertificateFromFile(p.TLSClientCertFile, p.TLSClientKeyFile)
		if err != nil {
			return fmt.Errorf("config: couldn't load client cert file %w", err)
		}
	}

	if p.TLSCustomCA != "" {
		_, err := base64.StdEncoding.DecodeString(p.TLSCustomCA)
		if err != nil {
			return fmt.Errorf("config: couldn't decode custom ca: %w", err)
		}
	} else if p.TLSCustomCAFile != "" {
		_, err := os.Stat(p.TLSCustomCAFile)
		if err != nil {
			return fmt.Errorf("config: couldn't load client ca file: %w", err)
		}
	}

	return nil
}

// Checksum returns the xxhash hash for the policy.
func (p *Policy) Checksum() uint64 {
	cs, _ := hashstructure.Hash(p, &hashstructure.HashOptions{
		Hasher: xxhash.New(),
	})
	return cs
}

// RouteID returns a unique identifier for a route
func (p *Policy) RouteID() uint64 {
	id := routeID{
		Source:      p.Source,
		Destination: p.Destination,
		Prefix:      p.Prefix,
		Path:        p.Path,
		Regex:       p.Regex,
	}

	cs, _ := hashstructure.Hash(id, &hashstructure.HashOptions{
		Hasher: xxhash.New(),
	})
	return cs
}

func (p *Policy) String() string {
	if p.Source == nil || p.Destination == nil {
		return fmt.Sprintf("%s → %s", p.From, p.To)
	}
	return fmt.Sprintf("%s → %s", p.Source.String(), p.Destination.String())
}

// StringURL stores a URL as a string in json.
type StringURL struct {
	*url.URL
}

// MarshalJSON returns the URLs host as json.
func (u *StringURL) MarshalJSON() ([]byte, error) {
	return json.Marshal(u.String())
}

type routeID struct {
	Source      *StringURL
	Destination *url.URL
	Prefix      string
	Path        string
	Regex       string
}