//go:generate ../tools/cmd/genjwt.sh
//go:generate stringer -type=TokenOption -output=token_options_gen.go

// Package jwt implements JSON Web Tokens as described in https://tools.ietf.org/html/rfc7519
package jwt

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"sync/atomic"

	"github.com/lestrrat-go/jwx/v2"
	"github.com/lestrrat-go/jwx/v2/internal/json"
	"github.com/lestrrat-go/jwx/v2/jws"
	"github.com/lestrrat-go/jwx/v2/jwt/internal/types"
)

var errInvalidJWT = errors.New(`invalid JWT`)

// ErrInvalidJWT returns the opaque error value that is returned when
// `jwt.Parse` fails due to not being able to deduce the format of
// the incoming buffer
func ErrInvalidJWT() error {
	return errInvalidJWT
}

// Settings controls global settings that are specific to JWTs.
func Settings(options ...GlobalOption) {
	var flattenAudienceBool bool
	var parsePedantic bool
	var parsePrecision = types.MaxPrecision + 1  // illegal value, so we can detect nothing was set
	var formatPrecision = types.MaxPrecision + 1 // illegal value, so we can detect nothing was set

	//nolint:forcetypeassert
	for _, option := range options {
		switch option.Ident() {
		case identFlattenAudience{}:
			flattenAudienceBool = option.Value().(bool)
		case identNumericDateParsePedantic{}:
			parsePedantic = option.Value().(bool)
		case identNumericDateParsePrecision{}:
			v := option.Value().(int)
			// only accept this value if it's in our desired range
			if v >= 0 && v <= int(types.MaxPrecision) {
				parsePrecision = uint32(v)
			}
		case identNumericDateFormatPrecision{}:
			v := option.Value().(int)
			// only accept this value if it's in our desired range
			if v >= 0 && v <= int(types.MaxPrecision) {
				formatPrecision = uint32(v)
			}
		}
	}

	if parsePrecision <= types.MaxPrecision { // remember we set default to max + 1
		v := atomic.LoadUint32(&types.ParsePrecision)
		if v != parsePrecision {
			atomic.CompareAndSwapUint32(&types.ParsePrecision, v, parsePrecision)
		}
	}

	if formatPrecision <= types.MaxPrecision { // remember we set default to max + 1
		v := atomic.LoadUint32(&types.FormatPrecision)
		if v != formatPrecision {
			atomic.CompareAndSwapUint32(&types.FormatPrecision, v, formatPrecision)
		}
	}

	{
		v := atomic.LoadUint32(&types.Pedantic)
		if (v == 1) != parsePedantic {
			var newVal uint32
			if parsePedantic {
				newVal = 1
			}
			atomic.CompareAndSwapUint32(&types.Pedantic, v, newVal)
		}
	}

	{
		defaultOptionsMu.Lock()
		if flattenAudienceBool {
			defaultOptions.Enable(FlattenAudience)
		} else {
			defaultOptions.Disable(FlattenAudience)
		}
		defaultOptionsMu.Unlock()
	}
}

var registry = json.NewRegistry()

// ParseString calls Parse against a string
func ParseString(s string, options ...ParseOption) (Token, error) {
	return parseBytes([]byte(s), options...)
}

// Parse parses the JWT token payload and creates a new `jwt.Token` object.
// The token must be encoded in either JSON format or compact format.
//
// This function can only work with either raw JWT (JSON) and JWS (Compact or JSON).
// If you need JWE support on top of it, you will need to rollout your
// own workaround.
//
// If the token is signed and you want to verify the payload matches the signature,
// you must pass the jwt.WithKey(alg, key) or jwt.WithKeySet(jwk.Set) option.
// If you do not specify these parameters, no verification will be performed.
//
// During verification, if the JWS headers specify a key ID (`kid`), the
// key used for verification must match the specified ID. If you are somehow
// using a key without a `kid` (which is highly unlikely if you are working
// with a JWT from a well know provider), you can workaround this by modifying
// the `jwk.Key` and setting the `kid` header.
//
// If you also want to assert the validity of the JWT itself (i.e. expiration
// and such), use the `Validate()` function on the returned token, or pass the
// `WithValidate(true)` option. Validate options can also be passed to
// `Parse`
//
// This function takes both ParseOption and ValidateOption types:
// ParseOptions control the parsing behavior, and ValidateOptions are
// passed to `Validate()` when `jwt.WithValidate` is specified.
func Parse(s []byte, options ...ParseOption) (Token, error) {
	return parseBytes(s, options...)
}

// ParseInsecure is exactly the same as Parse(), but it disables
// signature verification and token validation.
//
// You cannot override `jwt.WithVerify()` or `jwt.WithValidate()`
// using this function. Providing these options would result in
// an error
func ParseInsecure(s []byte, options ...ParseOption) (Token, error) {
	for _, option := range options {
		switch option.Ident() {
		case identVerify{}, identValidate{}:
			return nil, fmt.Errorf(`jwt.ParseInsecure: jwt.WithVerify() and jwt.WithValidate() may not be specified`)
		}
	}

	options = append(options, WithVerify(false), WithValidate(false))
	return Parse(s, options...)
}

// ParseReader calls Parse against an io.Reader
func ParseReader(src io.Reader, options ...ParseOption) (Token, error) {
	// We're going to need the raw bytes regardless. Read it.
	data, err := io.ReadAll(src)
	if err != nil {
		return nil, fmt.Errorf(`failed to read from token data source: %w`, err)
	}
	return parseBytes(data, options...)
}

type parseCtx struct {
	token            Token
	validateOpts     []ValidateOption
	verifyOpts       []jws.VerifyOption
	localReg         *json.Registry
	pedantic         bool
	skipVerification bool
	validate         bool
}

func parseBytes(data []byte, options ...ParseOption) (Token, error) {
	var ctx parseCtx

	// Validation is turned on by default. You need to specify
	// jwt.WithValidate(false) if you want to disable it
	ctx.validate = true

	// Verification is required (i.e., it is assumed that the incoming
	// data is in JWS format) unless the user explicitly asks for
	// it to be skipped.
	verification := true

	var verifyOpts []Option
	for _, o := range options {
		if v, ok := o.(ValidateOption); ok {
			ctx.validateOpts = append(ctx.validateOpts, v)
			continue
		}

		//nolint:forcetypeassert
		switch o.Ident() {
		case identKey{}, identKeySet{}, identVerifyAuto{}, identKeyProvider{}:
			verifyOpts = append(verifyOpts, o)
		case identToken{}:
			token, ok := o.Value().(Token)
			if !ok {
				return nil, fmt.Errorf(`invalid token passed via WithToken() option (%T)`, o.Value())
			}
			ctx.token = token
		case identPedantic{}:
			ctx.pedantic = o.Value().(bool)
		case identValidate{}:
			ctx.validate = o.Value().(bool)
		case identVerify{}:
			verification = o.Value().(bool)
		case identTypedClaim{}:
			pair := o.Value().(claimPair)
			if ctx.localReg == nil {
				ctx.localReg = json.NewRegistry()
			}
			ctx.localReg.Register(pair.Name, pair.Value)
		}
	}

	if !verification {
		ctx.skipVerification = true
	}

	lvo := len(verifyOpts)
	if lvo == 0 && verification {
		return nil, fmt.Errorf(`jwt.Parse: no keys for verification are provided (use jwt.WithVerify(false) to explicitly skip)`)
	}

	if lvo > 0 {
		converted, err := toVerifyOptions(verifyOpts...)
		if err != nil {
			return nil, fmt.Errorf(`jwt.Parse: failed to convert options into jws.VerifyOption: %w`, err)
		}
		ctx.verifyOpts = converted
	}

	data = bytes.TrimSpace(data)
	return parse(&ctx, data)
}

const (
	_JwsVerifyInvalid = iota
	_JwsVerifyDone
	_JwsVerifyExpectNested
	_JwsVerifySkipped
)

var _ = _JwsVerifyInvalid

func verifyJWS(ctx *parseCtx, payload []byte) ([]byte, int, error) {
	if len(ctx.verifyOpts) == 0 {
		return nil, _JwsVerifySkipped, nil
	}

	verified, err := jws.Verify(payload, ctx.verifyOpts...)
	return verified, _JwsVerifyDone, err
}

// verify parameter exists to make sure that we don't accidentally skip
// over verification just because alg == ""  or key == nil or something.
func parse(ctx *parseCtx, data []byte) (Token, error) {
	payload := data
	const maxDecodeLevels = 2

	// If cty = `JWT`, we expect this to be a nested structure
	var expectNested bool

OUTER:
	for i := 0; i < maxDecodeLevels; i++ {
		switch kind := jwx.GuessFormat(payload); kind {
		case jwx.JWT:
			if ctx.pedantic {
				if expectNested {
					return nil, fmt.Errorf(`expected nested encrypted/signed payload, got raw JWT`)
				}
			}

			if i == 0 {
				// We were NOT enveloped in other formats
				if !ctx.skipVerification {
					if _, _, err := verifyJWS(ctx, payload); err != nil {
						return nil, err
					}
				}
			}

			break OUTER
		case jwx.InvalidFormat:
			return nil, ErrInvalidJWT()
		case jwx.UnknownFormat:
			// "Unknown" may include invalid JWTs, for example, those who lack "aud"
			// claim. We could be pedantic and reject these
			if ctx.pedantic {
				return nil, fmt.Errorf(`unknown JWT format (pedantic)`)
			}

			if i == 0 {
				// We were NOT enveloped in other formats
				if !ctx.skipVerification {
					if _, _, err := verifyJWS(ctx, payload); err != nil {
						return nil, err
					}
				}
			}
			break OUTER
		case jwx.JWS:
			// Food for thought: This is going to break if you have multiple layers of
			// JWS enveloping using different keys. It is highly unlikely use case,
			// but it might happen.

			// skipVerification should only be set to true by us. It's used
			// when we just want to parse the JWT out of a payload
			if !ctx.skipVerification {
				// nested return value means:
				// false (next envelope _may_ need to be processed)
				// true (next envelope MUST be processed)
				v, state, err := verifyJWS(ctx, payload)
				if err != nil {
					return nil, err
				}

				if state != _JwsVerifySkipped {
					payload = v

					// We only check for cty and typ if the pedantic flag is enabled
					if !ctx.pedantic {
						continue
					}

					if state == _JwsVerifyExpectNested {
						expectNested = true
						continue OUTER
					}

					// if we're not nested, we found our target. bail out of this loop
					break OUTER
				}
			}

			// No verification.
			m, err := jws.Parse(data)
			if err != nil {
				return nil, fmt.Errorf(`invalid jws message: %w`, err)
			}
			payload = m.Payload()
		default:
			return nil, fmt.Errorf(`unsupported format (layer: #%d)`, i+1)
		}
		expectNested = false
	}

	if ctx.token == nil {
		ctx.token = New()
	}

	if ctx.localReg != nil {
		dcToken, ok := ctx.token.(TokenWithDecodeCtx)
		if !ok {
			return nil, fmt.Errorf(`typed claim was requested, but the token (%T) does not support DecodeCtx`, ctx.token)
		}
		dc := json.NewDecodeCtx(ctx.localReg)
		dcToken.SetDecodeCtx(dc)
		defer func() { dcToken.SetDecodeCtx(nil) }()
	}

	if err := json.Unmarshal(payload, ctx.token); err != nil {
		return nil, fmt.Errorf(`failed to parse token: %w`, err)
	}

	if ctx.validate {
		if err := Validate(ctx.token, ctx.validateOpts...); err != nil {
			return nil, err
		}
	}
	return ctx.token, nil
}

// Sign is a convenience function to create a signed JWT token serialized in
// compact form.
//
// It accepts either a raw key (e.g. rsa.PrivateKey, ecdsa.PrivateKey, etc)
// or a jwk.Key, and the name of the algorithm that should be used to sign
// the token.
//
// If the key is a jwk.Key and the key contains a key ID (`kid` field),
// then it is added to the protected header generated by the signature
//
// The algorithm specified in the `alg` parameter must be able to support
// the type of key you provided, otherwise an error is returned.
// For convenience `alg` is of type jwa.KeyAlgorithm so you can pass
// the return value of `(jwk.Key).Algorithm()` directly, but in practice
// it must be an instance of jwa.SignatureAlgorithm, otherwise an error
// is returned.
//
// The protected header will also automatically have the `typ` field set
// to the literal value `JWT`, unless you provide a custom value for it
// by jwt.WithHeaders option.
func Sign(t Token, options ...SignOption) ([]byte, error) {
	var soptions []jws.SignOption
	if l := len(options); l > 0 {
		// we need to from SignOption to Option because ... reasons
		// (todo: when go1.18 prevails, use type parameters
		rawoptions := make([]Option, l)
		for i, option := range options {
			rawoptions[i] = option
		}

		converted, err := toSignOptions(rawoptions...)
		if err != nil {
			return nil, fmt.Errorf(`jwt.Sign: failed to convert options into jws.SignOption: %w`, err)
		}
		soptions = converted
	}
	return NewSerializer().sign(soptions...).Serialize(t)
}

// Equal compares two JWT tokens. Do not use `reflect.Equal` or the like
// to compare tokens as they will also compare extra detail such as
// sync.Mutex objects used to control concurrent access.
//
// The comparison for values is currently done using a simple equality ("=="),
// except for time.Time, which uses time.Equal after dropping the monotonic
// clock and truncating the values to 1 second accuracy.
//
// if both t1 and t2 are nil, returns true
func Equal(t1, t2 Token) bool {
	if t1 == nil && t2 == nil {
		return true
	}

	// we already checked for t1 == t2 == nil, so safe to do this
	if t1 == nil || t2 == nil {
		return false
	}

	j1, err := json.Marshal(t1)
	if err != nil {
		return false
	}

	j2, err := json.Marshal(t2)
	if err != nil {
		return false
	}

	return bytes.Equal(j1, j2)
}

func (t *stdToken) Clone() (Token, error) {
	dst := New()

	dst.Options().Set(*(t.Options()))
	for _, pair := range t.makePairs() {
		//nolint:forcetypeassert
		key := pair.Key.(string)
		if err := dst.Set(key, pair.Value); err != nil {
			return nil, fmt.Errorf(`failed to set %s: %w`, key, err)
		}
	}
	return dst, nil
}

// RegisterCustomField allows users to specify that a private field
// be decoded as an instance of the specified type. This option has
// a global effect.
//
// For example, suppose you have a custom field `x-birthday`, which
// you want to represent as a string formatted in RFC3339 in JSON,
// but want it back as `time.Time`.
//
// In that case you would register a custom field as follows
//
//	jwt.RegisterCustomField(`x-birthday`, timeT)
//
// Then `token.Get("x-birthday")` will still return an `interface{}`,
// but you can convert its type to `time.Time`
//
//	bdayif, _ := token.Get(`x-birthday`)
//	bday := bdayif.(time.Time)
func RegisterCustomField(name string, object interface{}) {
	registry.Register(name, object)
}