// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package worker

import (
	"context"
	"fmt"
	"net/http"
	"sort"
	"strings"
	"time"

	"go.opencensus.io/trace"
	"golang.org/x/mod/semver"
	"golang.org/x/pkgsite/internal"
	"golang.org/x/pkgsite/internal/config"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/experiment"
	"golang.org/x/pkgsite/internal/fetch"
	"golang.org/x/pkgsite/internal/log"
	"golang.org/x/pkgsite/internal/postgres"
	"golang.org/x/pkgsite/internal/proxy"
	"golang.org/x/pkgsite/internal/source"
	"golang.org/x/pkgsite/internal/xcontext"
)

// fetchTimeout bounds the time allowed for fetching a single module.  It is
// mutable for testing purposes.
var fetchTimeout = 2 * config.StatementTimeout

const (
	// Indicates that although we have a valid module, some packages could not be processed.
	hasIncompletePackagesCode = 290
	hasIncompletePackagesDesc = "incomplete packages"
)

// ProxyRemoved is a set of module@version that have been removed from the proxy,
// even though they are still in the index.
var ProxyRemoved = map[string]bool{}

// fetchTask represents the result of a fetch task that was processed.
type fetchTask struct {
	modulePath           string
	requestedVersion     string
	resolvedVersion      string
	goModPath            string
	status               int
	err                  error
	module               *internal.Module
	packageVersionStates []*internal.PackageVersionState
	timings              map[string]time.Duration
}

// FetchAndUpdateState fetches and processes a module version, and then updates
// the module_version_states table according to the result. It returns an HTTP
// status code representing the result of the fetch operation, and a non-nil
// error if this status code is not 200.
func FetchAndUpdateState(ctx context.Context, modulePath, requestedVersion string, proxyClient *proxy.Client, sourceClient *source.Client, db *postgres.DB) (_ int, err error) {
	defer derrors.Wrap(&err, "FetchAndUpdateState(%q, %q)", modulePath, requestedVersion)

	tctx, span := trace.StartSpan(ctx, "FetchAndUpdateState")
	ctx = experiment.NewContext(tctx, experiment.FromContext(ctx))
	span.AddAttributes(
		trace.StringAttribute("modulePath", modulePath),
		trace.StringAttribute("version", requestedVersion))
	defer span.End()

	ft := fetchAndInsertModule(ctx, modulePath, requestedVersion, proxyClient, sourceClient, db)
	span.AddAttributes(trace.Int64Attribute("numPackages", int64(len(ft.packageVersionStates))))
	dbErr := updateVersionMapAndDeleteModulesWithErrors(ctx, db, ft)
	if dbErr != nil {
		log.Error(ctx, dbErr)
		ft.err = err
		ft.status = http.StatusInternalServerError
	}
	if !semver.IsValid(ft.resolvedVersion) {
		return ft.status, ft.err
	}

	// Update the module_version_states table with the new status of
	// module@version. This must happen last, because if it succeeds with a
	// code < 500 but a later action fails, we will never retry the later
	// action.
	// TODO(b/139178863): Split UpsertModuleVersionState into
	// InsertModuleVersionState and UpdateModuleVersionState.
	start := time.Now()
	err = db.UpsertModuleVersionState(ctx, ft.modulePath, ft.resolvedVersion, config.AppVersionLabel(),
		time.Time{}, ft.status, ft.goModPath, ft.err, ft.packageVersionStates)
	ft.timings["db.UpsertModuleVersionState"] = time.Since(start)
	if err != nil {
		log.Error(ctx, err)
		if ft.err != nil {
			ft.status = http.StatusInternalServerError
			ft.err = fmt.Errorf("db.UpsertModuleVersionState: %v, original error: %v", err, ft.err)
		}
		logTaskResult(ctx, ft, "Failed to update module version state")
		return http.StatusInternalServerError, ft.err
	}
	logTaskResult(ctx, ft, "Updated module version state")
	return ft.status, ft.err
}

// fetchAndInsertModule fetches the given module version from the module proxy
// or (in the case of the standard library) from the Go repo and writes the
// resulting data to the database.
//
// The given parentCtx is used for tracing, but fetches actually execute in a
// detached context with fixed timeout, so that fetches are allowed to complete
// even for short-lived requests.
func fetchAndInsertModule(parentCtx context.Context, modulePath, requestedVersion string, proxyClient *proxy.Client, sourceClient *source.Client, db *postgres.DB) *fetchTask {

	ft := &fetchTask{
		modulePath:       modulePath,
		requestedVersion: requestedVersion,
		timings:          map[string]time.Duration{},
	}
	defer func() {
		derrors.Wrap(&ft.err, "fetchAndInsertModule(%q, %q)", modulePath, requestedVersion)
		if ft.err != nil {
			ft.status = derrors.ToHTTPStatus(ft.err)
			ft.resolvedVersion = requestedVersion
		}
	}()

	if ProxyRemoved[modulePath+"@"+requestedVersion] {
		log.Infof(parentCtx, "not fetching %s@%s because it is on the ProxyRemoved list", modulePath, requestedVersion)
		ft.err = derrors.Excluded
		return ft
	}

	exc, err := db.IsExcluded(parentCtx, modulePath)
	if err != nil {
		ft.err = err
		return ft
	}
	if exc {
		ft.err = derrors.Excluded
		return ft
	}

	parentSpan := trace.FromContext(parentCtx)
	// A fixed timeout for FetchAndInsertModule to allow module processing to
	// succeed even for extremely short lived requests.
	ctx, cancel := context.WithTimeout(xcontext.Detach(parentCtx), fetchTimeout)
	defer cancel()

	ctx, span := trace.StartSpanWithRemoteParent(ctx, "worker.fetchAndInsertModule", parentSpan.SpanContext())
	defer span.End()

	start := time.Now()
	res, err := fetch.FetchModule(ctx, modulePath, requestedVersion, proxyClient, sourceClient)
	ft.timings["fetch.FetchModule"] = time.Since(start)
	if err != nil {
		ft.err = err
		ft.status = derrors.ToHTTPStatus(ft.err)
		logf := log.Errorf
		if ft.status < 500 {
			logf = log.Infof
		}
		logf(ctx, "Error executing fetch: %v (code %d)", ft.err, ft.status)
		if res != nil {
			ft.goModPath = res.GoModPath
			ft.packageVersionStates = res.PackageVersionStates
		}
		return ft
	}
	log.Infof(ctx, "fetch.FetchVersion succeeded for %s@%s", res.Module.ModulePath, res.Module.Version)

	ft.resolvedVersion = res.Module.Version
	ft.goModPath = res.GoModPath
	ft.module = res.Module
	ft.packageVersionStates = res.PackageVersionStates
	ft.status = http.StatusOK
	if res.HasIncompletePackages {
		ft.status = hasIncompletePackagesCode
	}
	start = time.Now()
	err = db.InsertModule(ctx, res.Module)
	ft.timings["db.InsertModule"] = time.Since(start)
	if err != nil {
		log.Error(ctx, err)

		ft.status = derrors.ToHTTPStatus(err)
		ft.err = err
		return ft
	}
	log.Infof(ctx, "db.InsertModule succeeded for %s@%s", res.Module.ModulePath, res.Module.Version)
	return ft
}

func updateVersionMapAndDeleteModulesWithErrors(ctx context.Context, db *postgres.DB, ft *fetchTask) (err error) {
	defer derrors.Wrap(&err, "updateVersionMapAndDeleteModulesWithErrors(%q, %q, %q, %d, %v)",
		ft.modulePath, ft.requestedVersion, ft.resolvedVersion, ft.status, ft.err)

	ctx, span := trace.StartSpan(ctx, "worker.updateFetchResult")
	defer span.End()

	var errMsg string
	if ft.err != nil {
		errMsg = ft.err.Error()
	}
	vm := &internal.VersionMap{
		ModulePath:       ft.modulePath,
		RequestedVersion: ft.requestedVersion,
		ResolvedVersion:  ft.resolvedVersion,
		Status:           ft.status,
		Error:            errMsg,
	}
	start := time.Now()
	err = db.UpsertVersionMap(ctx, vm)
	ft.timings["db.UpsertVersionMap"] = time.Since(start)
	if err != nil {
		return err
	}
	if !semver.IsValid(vm.ResolvedVersion) {
		// If the requestedVersion was not successfully resolved, at
		// this point it will be the same as the resolvedVersion.
		// No additional tables need to be updated.
		return nil
	}

	// If there were any errors processing the module then we didn't insert it.
	// Delete it in case we are reprocessing an existing module.
	if vm.Status > 400 {
		log.Infof(ctx, "%s@%s: code=%d, deleting", vm.ModulePath, vm.ResolvedVersion, vm.Status)
		start = time.Now()
		err = db.DeleteModule(ctx, vm.ModulePath, vm.ResolvedVersion)
		ft.timings["db.DeleteModule"] = time.Since(start)
		if err != nil {
			return err
		}
	}

	// If this was an alternative path (ft.status == 491) and there is an older
	// version in search_documents, delete it. This is the case where a module's
	// canonical path was changed by the addition of a go.mod file. For example,
	// versions of logrus before it acquired a go.mod file could have the path
	// github.com/Sirupsen/logrus, but once the go.mod file specifies that the
	// path is all lower-case, the old versions should not show up in search. We
	// still leave their pages in the database so users of those old versions
	// can still view documentation.
	if vm.Status == derrors.ToHTTPStatus(derrors.AlternativeModule) {
		log.Infof(ctx, "%s@%s: code=491, deleting older version from search", vm.ModulePath, vm.ResolvedVersion)
		start = time.Now()
		err = db.DeleteOlderVersionFromSearchDocuments(ctx, vm.ModulePath, vm.ResolvedVersion)
		ft.timings["db.DeleteOlderVersionFromSearchDocuments"] = time.Since(start)
		if err != nil {
			return err
		}
	}
	return nil
}

func logTaskResult(ctx context.Context, ft *fetchTask, prefix string) {
	var times []string
	for k, v := range ft.timings {
		times = append(times, fmt.Sprintf("%s=%.3fs", k, v.Seconds()))
	}
	sort.Strings(times)
	msg := strings.Join(times, ", ")
	logf := log.Infof
	if ft.status == http.StatusInternalServerError {
		logf = log.Errorf
	}
	logf(ctx, "%s for %s@%s: code=%d, num_packages=%d, err=%v; timings: %s",
		prefix, ft.modulePath, ft.resolvedVersion, ft.status, len(ft.packageVersionStates), ft.err, msg)
}