// Copyright 2017 clair 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 debian implements a vulnerability source updater using the Debian
// Security Tracker.
package debian

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"strings"

	log "github.com/sirupsen/logrus"

	"github.com/coreos/clair/database"
	"github.com/coreos/clair/ext/versionfmt"
	"github.com/coreos/clair/ext/versionfmt/dpkg"
	"github.com/coreos/clair/ext/vulnsrc"
	"github.com/coreos/clair/pkg/commonerr"
	"github.com/coreos/clair/pkg/httputil"
)

const (
	url          = "https://security-tracker.debian.org/tracker/data/json"
	cveURLPrefix = "https://security-tracker.debian.org/tracker"
	updaterFlag  = "debianUpdater"
)

type jsonData map[string]map[string]jsonVuln

type jsonVuln struct {
	Description string             `json:"description"`
	Releases    map[string]jsonRel `json:"releases"`
}

type jsonRel struct {
	FixedVersion string `json:"fixed_version"`
	Status       string `json:"status"`
	Urgency      string `json:"urgency"`
}

type updater struct{}

func init() {
	vulnsrc.RegisterUpdater("debian", &updater{})
}

func (u *updater) Update(datastore database.Datastore) (resp vulnsrc.UpdateResponse, err error) {
	log.WithField("package", "Debian").Info("Start fetching vulnerabilities")

	tx, err := datastore.Begin()
	if err != nil {
		return resp, err
	}

	// Get the hash of the latest update's JSON data
	latestHash, ok, err := tx.FindKeyValue(updaterFlag)
	if err != nil {
		return resp, err
	}

	// NOTE(sida): The transaction won't mutate the database and I want the
	// transaction to be short.
	if err := tx.Rollback(); err != nil {
		return resp, err
	}

	if !ok {
		latestHash = ""
	}

	// Download JSON.
	r, err := httputil.GetWithUserAgent(url)
	if err != nil {
		log.WithError(err).Error("could not download Debian's update")
		return resp, commonerr.ErrCouldNotDownload
	}

	defer r.Body.Close()

	if !httputil.Status2xx(r) {
		log.WithField("StatusCode", r.StatusCode).Error("Failed to update Debian")
		return resp, commonerr.ErrCouldNotDownload
	}

	// Parse the JSON.
	resp, err = buildResponse(r.Body, latestHash)
	if err != nil {
		return resp, err
	}

	return resp, nil
}

func (u *updater) Clean() {}

func buildResponse(jsonReader io.Reader, latestKnownHash string) (resp vulnsrc.UpdateResponse, err error) {
	hash := latestKnownHash

	// Defer the addition of flag information to the response.
	defer func() {
		if err == nil {
			resp.FlagName = updaterFlag
			resp.FlagValue = hash
		}
	}()

	// Create a TeeReader so that we can unmarshal into JSON and write to a hash
	// digest at the same time.
	jsonSHA := sha256.New()
	teedJSONReader := io.TeeReader(jsonReader, jsonSHA)

	// Unmarshal JSON.
	var data jsonData
	err = json.NewDecoder(teedJSONReader).Decode(&data)
	if err != nil {
		log.WithError(err).Error("could not unmarshal Debian's JSON")
		return resp, commonerr.ErrCouldNotParse
	}

	// Calculate the hash and skip updating if the hash has been seen before.
	hash = hex.EncodeToString(jsonSHA.Sum(nil))
	if latestKnownHash == hash {
		log.WithField("package", "Debian").Debug("no update")
		return resp, nil
	}

	// Extract vulnerability data from Debian's JSON schema.
	var unknownReleases map[string]struct{}
	resp.Vulnerabilities, unknownReleases = parseDebianJSON(&data)

	// Log unknown releases
	for k := range unknownReleases {
		note := fmt.Sprintf("Debian %s is not mapped to any version number (eg. Jessie->8). Please update me.", k)
		resp.Notes = append(resp.Notes, note)
		log.Warning(note)
	}

	return resp, nil
}

func parseDebianJSON(data *jsonData) (vulnerabilities []database.VulnerabilityWithAffected, unknownReleases map[string]struct{}) {
	mvulnerabilities := make(map[string]*database.VulnerabilityWithAffected)
	unknownReleases = make(map[string]struct{})

	for pkgName, pkgNode := range *data {
		for vulnName, vulnNode := range pkgNode {
			for releaseName, releaseNode := range vulnNode.Releases {
				// Attempt to detect the release number.
				if _, isReleaseKnown := database.DebianReleasesMapping[releaseName]; !isReleaseKnown {
					unknownReleases[releaseName] = struct{}{}
					continue
				}

				// Skip if the status is not determined or the vulnerability is a temporary one.
				// TODO: maybe add "undetermined" as Unknown severity.
				if !strings.HasPrefix(vulnName, "CVE-") || releaseNode.Status == "undetermined" {
					continue
				}

				// Get or create the vulnerability.
				vulnerability, vulnerabilityAlreadyExists := mvulnerabilities[vulnName]
				if !vulnerabilityAlreadyExists {
					vulnerability = &database.VulnerabilityWithAffected{
						Vulnerability: database.Vulnerability{
							Name:        vulnName,
							Link:        strings.Join([]string{cveURLPrefix, "/", vulnName}, ""),
							Severity:    database.UnknownSeverity,
							Description: vulnNode.Description,
						},
					}
				}

				// Set the priority of the vulnerability.
				// In the JSON, a vulnerability has one urgency per package it affects.
				severity := SeverityFromUrgency(releaseNode.Urgency)
				if severity.Compare(vulnerability.Severity) > 0 {
					// The highest urgency should be the one set.
					vulnerability.Severity = severity
				}

				// Determine the version of the package the vulnerability affects.
				var version string
				var err error
				if releaseNode.Status == "open" {
					// Open means that the package is currently vulnerable in the latest
					// version of this Debian release.
					version = versionfmt.MaxVersion
				} else if releaseNode.Status == "resolved" {
					// Resolved means that the vulnerability has been fixed in
					// "fixed_version" (if affected).
					err = versionfmt.Valid(dpkg.ParserName, releaseNode.FixedVersion)
					if err != nil {
						log.WithError(err).WithField("version", version).Warning("could not parse package version. skipping")
						continue
					}

					// FixedVersion = "0" means that the vulnerability affecting
					// current feature is not that important
					if releaseNode.FixedVersion != "0" {
						version = releaseNode.FixedVersion
					}
				}

				if version == "" {
					continue
				}

				var fixedInVersion string
				if version != versionfmt.MaxVersion {
					fixedInVersion = version
				}

				// Create and add the feature version.
				pkg := database.AffectedFeature{
					FeatureName:     pkgName,
					AffectedVersion: version,
					FixedInVersion:  fixedInVersion,
					Namespace: database.Namespace{
						Name:          "debian:" + database.DebianReleasesMapping[releaseName],
						VersionFormat: dpkg.ParserName,
					},
				}
				vulnerability.Affected = append(vulnerability.Affected, pkg)

				// Store the vulnerability.
				mvulnerabilities[vulnName] = vulnerability
			}
		}
	}

	// Convert the vulnerabilities map to a slice
	for _, v := range mvulnerabilities {
		vulnerabilities = append(vulnerabilities, *v)
	}

	return
}

// SeverityFromUrgency converts the urgency scale used by the Debian Security
// Bug Tracker into a database.Severity.
func SeverityFromUrgency(urgency string) database.Severity {
	switch urgency {
	case "not yet assigned":
		return database.UnknownSeverity

	case "end-of-life", "unimportant":
		return database.NegligibleSeverity

	case "low", "low*", "low**":
		return database.LowSeverity

	case "medium", "medium*", "medium**":
		return database.MediumSeverity

	case "high", "high*", "high**":
		return database.HighSeverity

	default:
		log.WithField("urgency", urgency).Warning("could not determine vulnerability severity from urgency")
		return database.UnknownSeverity
	}
}