//
// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
        "bytes"
        "context"
        "crypto"
        "crypto/x509"
        "fmt"
        "os"
        "path/filepath"

        "github.com/pkg/errors"
        "github.com/spf13/viper"

        "github.com/sigstore/sigstore/pkg/cryptoutils"
        "github.com/sigstore/timestamp-authority/pkg/log"
        "github.com/sigstore/timestamp-authority/pkg/signer"
        tsx509 "github.com/sigstore/timestamp-authority/pkg/x509"
)

type API struct {
        tsaSigner     crypto.Signer       // the signer to use for timestamping
        tsaSignerHash crypto.Hash         // hash algorithm used to hash pre-signed timestamps
        certChain     []*x509.Certificate // timestamping cert chain
        certChainPem  string              // PEM encoded timestamping cert chain
        includeChain  bool                // Whether to include the full issuing chain or just the leaf certificate
}

func NewAPI() (*API, error) {
        ctx := context.Background()

        tsaSignerHash, err := signer.HashToAlg(viper.GetString("timestamp-signer-hash"))
        if err != nil {
                return nil, errors.Wrap(err, "error getting hash")
        }
        tsaSigner, err := signer.NewCryptoSigner(ctx, tsaSignerHash,
                viper.GetString("timestamp-signer"),
                viper.GetString("kms-key-resource"),
                viper.GetString("tink-key-resource"), viper.GetString("tink-keyset-path"),
                viper.GetString("tink-hcvault-token"),
                viper.GetString("file-signer-key-path"), viper.GetString("file-signer-passwd"))
        if err != nil {
                return nil, errors.Wrap(err, "getting new tsa signer")
        }

        var certChain []*x509.Certificate

        // KMS, Tink and File signers require a provided certificate chain
        if viper.GetString("timestamp-signer") != signer.MemoryScheme {
                certChainPath := viper.GetString("certificate-chain-path")
                data, err := os.ReadFile(filepath.Clean(certChainPath))
                if err != nil {
                        return nil, err
                }
                certChain, err = cryptoutils.LoadCertificatesFromPEM(bytes.NewReader(data))
                if err != nil {
                        return nil, err
                }
                if err := tsx509.VerifyCertChain(certChain, tsaSigner); err != nil {
                        return nil, err
                }
        } else {
                // Generate an in-memory TSA certificate chain
                certChain, err = signer.NewTimestampingCertWithChain(tsaSigner)
                if err != nil {
                        return nil, errors.Wrap(err, "generating timestamping cert chain")
                }
        }

        certChainPEM, err := cryptoutils.MarshalCertificatesToPEM(certChain)
        if err != nil {
                return nil, fmt.Errorf("marshal certificates to PEM: %w", err)
        }

        return &API{
                tsaSigner:     tsaSigner,
                tsaSignerHash: tsaSignerHash,
                certChain:     certChain,
                certChainPem:  string(certChainPEM),
                includeChain:  viper.GetBool("include-chain-in-response"),
        }, nil
}

var (
        api *API
)

func ConfigureAPI() {
        var err error

        api, err = NewAPI()
        if err != nil {
                log.Logger.Panic(err)
        }
}

// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
        "fmt"
        "net/http"
        "regexp"

        "github.com/go-openapi/runtime/middleware"
        "github.com/mitchellh/mapstructure"

        "github.com/sigstore/timestamp-authority/pkg/generated/models"
        "github.com/sigstore/timestamp-authority/pkg/generated/restapi/operations/timestamp"
        "github.com/sigstore/timestamp-authority/pkg/log"
)

const (
        failedToGenerateTimestampResponse        = "Error generating timestamp response"
        WeakHashAlgorithmTimestampRequest        = "Weak hash algorithm in timestamp request"
        InconsistentDigestLengthTimestampRequest = "Message digest has incorrect length for specified algorithm"
)

func errorMsg(message string, code int) *models.Error {
        return &models.Error{
                Code:    int64(code),
                Message: message,
        }
}

func handleTimestampAPIError(params interface{}, code int, err error, message string, fields ...interface{}) middleware.Responder {
        if message == "" {
                message = http.StatusText(code)
        }

        re := regexp.MustCompile("^(.*)Params$")
        typeStr := fmt.Sprintf("%T", params)
        handler := re.FindStringSubmatch(typeStr)[1]

        logMsg := func(r *http.Request) {
                log.RequestIDLogger(r).Errorw("exiting with error", append([]interface{}{"handler", handler, "statusCode", code, "clientMessage", message, "error", err}, fields...)...)
                paramsFields := map[string]interface{}{}
                if err := mapstructure.Decode(params, &paramsFields); err == nil {
                        log.RequestIDLogger(r).Debug(paramsFields)
                }
        }

        switch params := params.(type) {
        case timestamp.GetTimestampResponseParams:
                logMsg(params.HTTPRequest)
                switch code {
                case http.StatusBadRequest:
                        return timestamp.NewGetTimestampResponseBadRequest().WithPayload(errorMsg(message, code))
                case http.StatusNotImplemented:
                        return timestamp.NewGetTimestampResponseNotImplemented()
                default:
                        return timestamp.NewGetTimestampResponseDefault(code).WithPayload(errorMsg(message, code))
                }
        case timestamp.GetTimestampCertChainParams:
                logMsg(params.HTTPRequest)
                switch code {
                case http.StatusNotFound:
                        return timestamp.NewGetTimestampCertChainNotFound()
                default:
                        return timestamp.NewGetTimestampCertChainDefault(code).WithPayload(errorMsg(message, code))
                }
        default:
                log.Logger.Errorf("unable to find method for type %T; error: %v", params, err)
                return middleware.Error(http.StatusInternalServerError, http.StatusText(http.StatusInternalServerError))
        }
}

//
// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
        "math"
        "time"

        "github.com/prometheus/client_golang/prometheus"
        "github.com/prometheus/client_golang/prometheus/promauto"
        "sigs.k8s.io/release-utils/version"
)

var (
        MetricLatency = promauto.NewHistogramVec(prometheus.HistogramOpts{
                Name: "timestamp_authority_api_latency",
                Help: "API Latency on calls",
        }, []string{"path", "code"})

        MetricLatencySummary = promauto.NewSummaryVec(prometheus.SummaryOpts{
                Name: "timestamp_authority_api_latency_summary",
                Help: "API Latency on calls",
        }, []string{"path", "code"})

        MetricRequestLatency = promauto.NewHistogramVec(prometheus.HistogramOpts{
                Name: "timestamp_authority_latency_by_api",
                Help: "API Latency (in ns) by path and method",
                Buckets: prometheus.ExponentialBucketsRange(
                        float64(time.Millisecond),
                        float64(4*time.Second),
                        10),
        }, []string{"path", "method"})

        MetricRequestCount = promauto.NewCounterVec(prometheus.CounterOpts{
                Name: "timestamp_authority_http_requests_total",
                Help: "Total number of HTTP requests by status code, path, and method.",
        }, []string{"code", "path", "method"})

        MetricNTPLatency = promauto.NewHistogramVec(prometheus.HistogramOpts{
                Name: "timestamp_authority_ntp_latency",
                Help: "NTP request latency",
        }, []string{"host"})

        MetricNTPSyncCount = promauto.NewCounterVec(prometheus.CounterOpts{
                Name: "timestamp_authority_ntp_sync_total",
                Help: "Total number of NTP requests against a remote server",
        }, []string{"host", "failed"})

        MetricNTPErrorCount = promauto.NewCounterVec(prometheus.CounterOpts{
                Name: "timestamp_authority_ntp_errors_total",
                Help: "Total number of NTP related errors",
        }, []string{"reason"})

        _ = promauto.NewGaugeFunc(
                prometheus.GaugeOpts{
                        Name: "timestamp_authority_certificate_valid_days_remaining",
                        Help: "Number of days remaining in validity period of signing certificate",
                },
                func() float64 {
                        // if api hasn't been initialized yet, then we can't know the validity period;
                        // so we return MaxFloat64 to not cause an alarm if someone fetches the metric
                        // before the initialization has completed
                        if api == nil {
                                return math.MaxFloat64
                        }
                        // compute minimum validity inclusive of leaf, any intermediates (if present), and root
                        minValidity := api.certChain[0].NotAfter
                        for _, cert := range api.certChain[1:] {
                                if cert.NotAfter.Before(minValidity) {
                                        minValidity = cert.NotAfter
                                }
                        }
                        return time.Until(minValidity).Hours() / 24
                })

        _ = promauto.NewGaugeFunc(
                prometheus.GaugeOpts{
                        Namespace: "timestamp_authority",
                        Name:      "build_info",
                        Help:      "A metric with a constant '1' value labeled by version, revision, branch, and goversion from which timestamp-authority was built.",
                        ConstLabels: prometheus.Labels{
                                "version":    version.GetVersionInfo().GitVersion,
                                "revision":   version.GetVersionInfo().GitCommit,
                                "build_date": version.GetVersionInfo().BuildDate,
                                "goversion":  version.GetVersionInfo().GoVersion,
                        },
                },
                func() float64 { return 1 },
        )
)

// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
        "bytes"
        "crypto"
        "encoding/asn1"
        "encoding/base64"
        "encoding/json"
        "fmt"
        "io"
        "math/big"
        "net/http"
        "strconv"
        "strings"
        "time"

        "github.com/digitorus/timestamp"
        "github.com/go-openapi/runtime/middleware"
        "github.com/pkg/errors"
        ts "github.com/sigstore/timestamp-authority/pkg/generated/restapi/operations/timestamp"
        "github.com/sigstore/timestamp-authority/pkg/verification"
)

type JSONRequest struct {
        ArtifactHash  string   `json:"artifactHash"`
        Certificates  bool     `json:"certificates"`
        HashAlgorithm string   `json:"hashAlgorithm"`
        Nonce         *big.Int `json:"nonce"`
        TSAPolicyOID  string   `json:"tsaPolicyOID"`
}

func getHashAlg(alg string) (crypto.Hash, string, error) {
        lowercaseAlg := strings.ToLower(alg)
        switch lowercaseAlg {
        case "sha256":
                return crypto.SHA256, "", nil
        case "sha384":
                return crypto.SHA384, "", nil
        case "sha512":
                return crypto.SHA512, "", nil
        case "sha1":
                return 0, WeakHashAlgorithmTimestampRequest, verification.ErrWeakHashAlg
        default:
                return 0, failedToGenerateTimestampResponse, fmt.Errorf("unsupported hash algorithm: %s", alg)
        }
}

// ParseJSONRequest parses a JSON request into a timestamp.Request struct
func ParseJSONRequest(reqBytes []byte) (*timestamp.Request, string, error) {
        // unmarshal the request bytes into a JSONRequest struct
        var req JSONRequest
        if err := json.Unmarshal(reqBytes, &req); err != nil {
                return nil, failedToGenerateTimestampResponse, fmt.Errorf("failed to parse JSON into request: %v", err)
        }

        // after unmarshalling, parse the JSONRequest.Artifact into a Reader and parse the remaining
        // fields into a a timestamp.RequestOptions struct
        hashAlgo, errMsg, err := getHashAlg(req.HashAlgorithm)
        if err != nil {
                return nil, errMsg, fmt.Errorf("failed to parse hash algorithm: %v", err)
        }

        var oidInts []int
        if req.TSAPolicyOID == "" {
                oidInts = nil
        } else {
                for _, v := range strings.Split(req.TSAPolicyOID, ".") {
                        i, _ := strconv.Atoi(v)
                        oidInts = append(oidInts, i)
                }
        }

        // decode the base64 encoded artifact hash
        decoded, err := base64.StdEncoding.DecodeString(req.ArtifactHash)
        if err != nil {
                return nil, failedToGenerateTimestampResponse, fmt.Errorf("failed to decode base64 encoded artifact hash: %v", err)
        }

        // create a timestamp request from the request's JSON body
        tsReq := timestamp.Request{
                HashAlgorithm: hashAlgo,
                HashedMessage: decoded,
                Certificates:  req.Certificates,
                Nonce:         req.Nonce,
                TSAPolicyOID:  oidInts,
        }

        return verifyTimestampRequest(&tsReq)
}

func parseDERRequest(reqBytes []byte) (*timestamp.Request, string, error) {
        parsed, err := timestamp.ParseRequest(reqBytes)
        if err != nil {
                return nil, failedToGenerateTimestampResponse, err
        }

        return verifyTimestampRequest(parsed)
}

func getContentType(r *http.Request) (string, error) {
        contentTypeHeader := r.Header.Get("Content-Type")
        splitHeader := strings.Split(contentTypeHeader, "application/")
        if len(splitHeader) != 2 {
                return "", errors.New("expected header value to be split into two pieces")
        }
        return splitHeader[1], nil
}

func requestBodyToTimestampReq(reqBytes []byte, contentType string) (*timestamp.Request, string, error) {
        switch contentType {
        case "json":
                return ParseJSONRequest(reqBytes)
        case "timestamp-query":
                return parseDERRequest(reqBytes)
        default:
                return nil, failedToGenerateTimestampResponse, fmt.Errorf("unsupported content type")
        }
}

func TimestampResponseHandler(params ts.GetTimestampResponseParams) middleware.Responder {
        requestBytes, err := io.ReadAll(params.Request)
        if err != nil {
                return handleTimestampAPIError(params, http.StatusBadRequest, err, failedToGenerateTimestampResponse)
        }

        contentType, err := getContentType(params.HTTPRequest)
        if err != nil {
                return handleTimestampAPIError(params, http.StatusUnsupportedMediaType, err, failedToGenerateTimestampResponse)
        }

        req, errMsg, err := requestBodyToTimestampReq(requestBytes, contentType)
        if err != nil {
                return handleTimestampAPIError(params, http.StatusBadRequest, err, errMsg)
        }

        policyID := req.TSAPolicyOID
        if policyID.String() == "" {
                policyID = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 2}
        }

        duration, _ := time.ParseDuration("1s")

        tsStruct := timestamp.Timestamp{
                HashAlgorithm: req.HashAlgorithm,
                HashedMessage: req.HashedMessage,
                // The field here is going to be serialized as a GeneralizedTime, and RFC5280
                // states that the GeneralizedTime values MUST be expressed in Greenwich Mean Time.
                // However, go asn1/marshal will happily accept other formats. So we force it directly here.
                // https://datatracker.ietf.org/doc/html/rfc5280#section-4.1.2.5.2
                Time:     time.Now().UTC(),
                Nonce:    req.Nonce,
                Policy:   policyID,
                Ordering: false,
                Accuracy: duration,
                // Not qualified for the european directive
                Qualified:         false,
                AddTSACertificate: req.Certificates,
                ExtraExtensions:   req.Extensions,
        }
        if api.includeChain {
                tsStruct.Certificates = api.certChain[1:] // Issuing CA certificate down to root
        }

        resp, err := tsStruct.CreateResponseWithOpts(api.certChain[0], api.tsaSigner, api.tsaSignerHash)
        if err != nil {
                return handleTimestampAPIError(params, http.StatusInternalServerError, err, failedToGenerateTimestampResponse)
        }

        return ts.NewGetTimestampResponseCreated().WithPayload(io.NopCloser(bytes.NewReader(resp)))
}

func GetTimestampCertChainHandler(_ ts.GetTimestampCertChainParams) middleware.Responder {
        return ts.NewGetTimestampCertChainOK().WithPayload(api.certChainPem)
}

func verifyTimestampRequest(tsReq *timestamp.Request) (*timestamp.Request, string, error) {
        if err := verification.VerifyRequest(tsReq); err != nil {
                // verify that the request's hash algorithm is not weak
                if errors.Is(err, verification.ErrWeakHashAlg) {
                        return nil, WeakHashAlgorithmTimestampRequest, err
                }
                // verify that the request's hash algorithm is supported
                if errors.Is(err, verification.ErrUnsupportedHashAlg) {
                        return nil, failedToGenerateTimestampResponse, err
                }
                // verify that the request's digest length is consistent with the request's hash algorithm
                if errors.Is(err, verification.ErrInconsistentDigestLength) {
                        return nil, InconsistentDigestLengthTimestampRequest, err
                }
                return nil, failedToGenerateTimestampResponse, err
        }

        return tsReq, "", nil
}