package storage

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"encoding/base32"
	"errors"
	"fmt"
	"io"
	"strings"
	"time"

	jose "gopkg.in/square/go-jose.v2"
)

var (
	// ErrNotFound is the error returned by storages if a resource cannot be found.
	ErrNotFound = errors.New("not found")

	// ErrAlreadyExists is the error returned by storages if a resource ID is taken during a create.
	ErrAlreadyExists = errors.New("ID already exists")
)

// Kubernetes only allows lower case letters for names.
//
// TODO(ericchiang): refactor ID creation onto the storage.
var encoding = base32.NewEncoding("abcdefghijklmnopqrstuvwxyz234567")

// NewID returns a random string which can be used as an ID for objects.
func NewID() string {
	buff := make([]byte, 16) // 128 bit random ID.
	if _, err := io.ReadFull(rand.Reader, buff); err != nil {
		panic(err)
	}
	// Trim padding
	return strings.TrimRight(encoding.EncodeToString(buff), "=")
}

// GCResult returns the number of objects deleted by garbage collection.
type GCResult struct {
	AuthRequests int64
	AuthCodes    int64
}

// Storage is the storage interface used by the server. Implementations, at minimum
// require compare-and-swap atomic actions.
//
// Implementations are expected to perform their own garbage collection of
// expired objects (expect keys, which are handled by the server).
type Storage interface {
	Close() error

	// TODO(ericchiang): Let the storages set the IDs of these objects.
	CreateAuthRequest(a AuthRequest) error
	CreateClient(c Client) error
	CreateAuthCode(c AuthCode) error
	CreateRefresh(r RefreshToken) error
	CreatePassword(p Password) error

	// TODO(ericchiang): return (T, bool, error) so we can indicate not found
	// requests that way instead of using ErrNotFound.
	GetAuthRequest(id string) (AuthRequest, error)
	GetAuthCode(id string) (AuthCode, error)
	GetClient(id string) (Client, error)
	GetKeys() (Keys, error)
	GetRefresh(id string) (RefreshToken, error)
	GetPassword(email string) (Password, error)

	ListClients() ([]Client, error)
	ListRefreshTokens() ([]RefreshToken, error)

	// Delete methods MUST be atomic.
	DeleteAuthRequest(id string) error
	DeleteAuthCode(code string) error
	DeleteClient(id string) error
	DeleteRefresh(id string) error
	DeletePassword(email string) error

	// Update functions are assumed to be a performed within a single object transaction.
	//
	// updaters may be called multiple times.
	UpdateClient(id string, updater func(old Client) (Client, error)) error
	UpdateKeys(updater func(old Keys) (Keys, error)) error
	UpdateAuthRequest(id string, updater func(a AuthRequest) (AuthRequest, error)) error
	UpdatePassword(email string, updater func(p Password) (Password, error)) error

	// GarbageCollect deletes all expired AuthCodes and AuthRequests.
	GarbageCollect(now time.Time) (GCResult, error)
}

// Client represents an OAuth2 client.
//
// For further reading see:
//   * Trusted peers: https://developers.google.com/identity/protocols/CrossClientAuth
//   * Public clients: https://developers.google.com/api-client-library/python/auth/installed-app
type Client struct {
	// Client ID and secret used to identify the client.
	ID     string `json:"id" yaml:"id"`
	Secret string `json:"secret" yaml:"secret"`

	// A registered set of redirect URIs. When redirecting from dex to the client, the URI
	// requested to redirect to MUST match one of these values, unless the client is "public".
	RedirectURIs []string `json:"redirectURIs" yaml:"redirectURIs"`

	// TrustedPeers are a list of peers which can issue tokens on this client's behalf using
	// the dynamic "oauth2:server:client_id:(client_id)" scope. If a peer makes such a request,
	// this client's ID will appear as the ID Token's audience.
	//
	// Clients inherently trust themselves.
	TrustedPeers []string `json:"trustedPeers" yaml:"trustedPeers"`

	// Public clients must use either use a redirectURL 127.0.0.1:X or "urn:ietf:wg:oauth:2.0:oob"
	Public bool `json:"public" yaml:"public"`

	// Name and LogoURL used when displaying this client to the end user.
	Name    string `json:"name" yaml:"name"`
	LogoURL string `json:"logoURL" yaml:"logoURL"`
}

// Claims represents the ID Token claims supported by the server.
type Claims struct {
	UserID        string
	Username      string
	Email         string
	EmailVerified bool

	Groups []string
}

// AuthRequest represents a OAuth2 client authorization request. It holds the state
// of a single auth flow up to the point that the user authorizes the client.
type AuthRequest struct {
	// ID used to identify the authorization request.
	ID string

	// ID of the client requesting authorization from a user.
	ClientID string

	// Values parsed from the initial request. These describe the resources the client is
	// requesting as well as values describing the form of the response.
	ResponseTypes []string
	Scopes        []string
	RedirectURI   string
	Nonce         string
	State         string

	// The client has indicated that the end user must be shown an approval prompt
	// on all requests. The server cannot cache their initial action for subsequent
	// attempts.
	ForceApprovalPrompt bool

	Expiry time.Time

	// Has the user proved their identity through a backing identity provider?
	//
	// If false, the following fields are invalid.
	LoggedIn bool

	// The identity of the end user. Generally nil until the user authenticates
	// with a backend.
	Claims Claims

	// The connector used to login the user and any data the connector wishes to persists.
	// Set when the user authenticates.
	ConnectorID   string
	ConnectorData []byte
}

// AuthCode represents a code which can be exchanged for an OAuth2 token response.
//
// This value is created once an end user has authorized a client, the server has
// redirect the end user back to the client, but the client hasn't exchanged the
// code for an access_token and id_token.
type AuthCode struct {
	// Actual string returned as the "code" value.
	ID string

	// The client this code value is valid for. When exchanging the code for a
	// token response, the client must use its client_secret to authenticate.
	ClientID string

	// As part of the OAuth2 spec when a client makes a token request it MUST
	// present the same redirect_uri as the initial redirect. This values is saved
	// to make this check.
	//
	// https://tools.ietf.org/html/rfc6749#section-4.1.3
	RedirectURI string

	// If provided by the client in the initial request, the provider MUST create
	// a ID Token with this nonce in the JWT payload.
	Nonce string

	// Scopes authorized by the end user for the client.
	Scopes []string

	// Authentication data provided by an upstream source.
	ConnectorID   string
	ConnectorData []byte
	Claims        Claims

	Expiry time.Time
}

// RefreshToken is an OAuth2 refresh token which allows a client to request new
// tokens on the end user's behalf.
type RefreshToken struct {
	// The actual refresh token.
	RefreshToken string

	// Client this refresh token is valid for.
	ClientID string

	// Authentication data provided by an upstream source.
	ConnectorID   string
	ConnectorData []byte
	Claims        Claims

	// Scopes present in the initial request. Refresh requests may specify a set
	// of scopes different from the initial request when refreshing a token,
	// however those scopes must be encompassed by this set.
	Scopes []string

	// Nonce value supplied during the initial redirect. This is required to be part
	// of the claims of any future id_token generated by the client.
	Nonce string
}

// Password is an email to password mapping managed by the storage.
type Password struct {
	// Email and identifying name of the password. Emails are assumed to be valid and
	// determining that an end-user controls the address is left to an outside application.
	//
	// Emails are case insensitive and should be standardized by the storage.
	//
	// Storages that don't support an extended character set for IDs, such as '.' and '@'
	// (cough cough, kubernetes), must map this value appropriately.
	Email string `yaml:"email"`

	// Bcrypt encoded hash of the password. This package enforces a min cost value of 10
	Hash []byte `yaml:"hash"`

	// Optional username to display. NOT used during login.
	Username string `yaml:"username"`

	// Randomly generated user ID. This is NOT the primary ID of the Password object.
	UserID string `yaml:"userID"`
}

// VerificationKey is a rotated signing key which can still be used to verify
// signatures.
type VerificationKey struct {
	PublicKey *jose.JSONWebKey `json:"publicKey"`
	Expiry    time.Time        `json:"expiry"`
}

// Keys hold encryption and signing keys.
type Keys struct {
	// Key for creating and verifying signatures. These may be nil.
	SigningKey    *jose.JSONWebKey
	SigningKeyPub *jose.JSONWebKey

	// Old signing keys which have been rotated but can still be used to validate
	// existing signatures.
	VerificationKeys []VerificationKey

	// The next time the signing key will rotate.
	//
	// For caching purposes, implementations MUST NOT update keys before this time.
	NextRotation time.Time
}

// Sign creates a JWT using the signing key.
func (k Keys) Sign(payload []byte) (jws string, err error) {
	if k.SigningKey == nil {
		return "", fmt.Errorf("no key to sign payload with")
	}
	signingKey := jose.SigningKey{Key: k.SigningKey}

	switch key := k.SigningKey.Key.(type) {
	case *rsa.PrivateKey:
		// TODO(ericchiang): Allow different cryptographic hashes.
		signingKey.Algorithm = jose.RS256
	case *ecdsa.PrivateKey:
		switch key.Params() {
		case elliptic.P256().Params():
			signingKey.Algorithm = jose.ES256
		case elliptic.P384().Params():
			signingKey.Algorithm = jose.ES384
		case elliptic.P521().Params():
			signingKey.Algorithm = jose.ES512
		default:
			return "", errors.New("unsupported ecdsa curve")
		}
	}

	signer, err := jose.NewSigner(signingKey, &jose.SignerOptions{})
	if err != nil {
		return "", fmt.Errorf("new signier: %v", err)
	}
	signature, err := signer.Sign(payload)
	if err != nil {
		return "", fmt.Errorf("signing payload: %v", err)
	}
	return signature.CompactSerialize()
}