package frontend

import (
	"context"
	"errors"
	"fmt"
	"html"
	"net/http"
	"net/url"
	"regexp"
	"strings"
	"time"

	"github.com/google/safehtml/template"
	"github.com/google/safehtml/template/uncheckedconversions"
	"golang.org/x/pkgsite/internal"
	"golang.org/x/pkgsite/internal/cookie"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/log"
	"golang.org/x/pkgsite/internal/postgres"
	"golang.org/x/pkgsite/internal/stdlib"
)

var errUnitNotFoundWithoutFetch = &serverError{
	status: http.StatusNotFound,
	epage: &errorPage{
		messageTemplate: template.MakeTrustedTemplate(`
					    <h3 class="Error-message">{{.StatusText}}</h3>
					    <p class="Error-message">Check that you entered the URL correctly or try fetching it following the
                        <a href="/about#adding-a-package">instructions here</a>.</p>`),
		MessageData: struct{ StatusText string }{http.StatusText(http.StatusNotFound)},
	},
}

func (s *Server) servePathNotFoundPage(w http.ResponseWriter, r *http.Request,
	ds internal.DataSource, fullPath, modulePath, requestedVersion string) (err error) {
	defer derrors.Wrap(&err, "servePathNotFoundPage(w, r, %q, %q)", fullPath, requestedVersion)

	db, ok := ds.(*postgres.DB)
	if !ok {
		return proxydatasourceNotSupportedErr()
	}
	ctx := r.Context()

	if stdlib.Contains(fullPath) {
		var path string
		path, err = stdlibPathForShortcut(ctx, db, fullPath)

			log.Error(ctx, err)
		}
		if path != "" {
			http.Redirect(w, r, fmt.Sprintf("/%s", path), http.StatusFound)
			return
		}
		return &serverError{status: http.StatusNotFound}
	}

	fr, err := previousFetchStatusAndResponse(ctx, db, fullPath, modulePath, requestedVersion)

		if !errors.Is(err, derrors.NotFound) {
			log.Error(ctx, err)
		}
		return pathNotFoundError(fullPath, requestedVersion)
	}

	switch fr.status {
	case http.StatusFound, derrors.ToStatus(derrors.AlternativeModule):

			return errUnitNotFoundWithoutFetch
		}
		vm, err := db.GetVersionMap(ctx, fr.goModPath, internal.LatestVersion)
		if (err != nil && !errors.Is(err, derrors.NotFound)) ||

			return errUnitNotFoundWithoutFetch
		}
		u := constructUnitURL(fr.goModPath, fr.goModPath, internal.LatestVersion)
		cookie.Set(w, cookie.AlternativeModuleFlash, fullPath, u)
		http.Redirect(w, r, u, http.StatusFound)
		return nil
	case http.StatusInternalServerError:
		return pathNotFoundError(fullPath, requestedVersion)
	default:
		if u := githubPathRedirect(fullPath); u != "" {
			http.Redirect(w, r, u, http.StatusFound)
			return
		}

		if fr.status == http.StatusNotFound && time.Since(fr.updatedAt) > s.taskIDChangeInterval {
			return pathNotFoundError(fullPath, requestedVersion)
		}

		nm, err := ds.GetNestedModules(ctx, fullPath)
		if err == nil && len(nm) > 0 {
			http.Redirect(w, r, "/search?q="+url.QueryEscape(fullPath), http.StatusFound)
			return nil
		}
		return &serverError{
			status: fr.status,
			epage: &errorPage{
				messageTemplate: uncheckedconversions.TrustedTemplateFromStringKnownToSatisfyTypeContract(`
					    <h3 class="Error-message">{{.StatusText}}</h3>
					    <p class="Error-message">` + html.UnescapeString(fr.responseText) + `</p>`),
				MessageData: struct{ StatusText string }{http.StatusText(fr.status)},
			},
		}
	}
}

var githubRegexp = regexp.MustCompile(`(blob|tree)(/[^/]+)?`)

func githubPathRedirect(fullPath string) string {
	parts := strings.Split(fullPath, "/")
	if len(parts) <= 3 || parts[0] != "github.com" {
		return ""
	}
	m := strings.Split(fullPath, "/"+githubRegexp.FindString(fullPath))
	if len(m) != 2 {
		return ""
	}
	p := m[0]
	if m[1] != "" {
		p = m[0] + m[1]
	}
	return constructUnitURL(p, p, internal.LatestVersion)
}

func pathNotFoundError(fullPath, requestedVersion string) error {
	if !isSupportedVersion(fullPath, requestedVersion) {
		return invalidVersionError(fullPath, requestedVersion)
	}
	if stdlib.Contains(fullPath) {
		return &serverError{status: http.StatusNotFound}
	}
	path := fullPath
	if requestedVersion != internal.LatestVersion {
		path = fmt.Sprintf("%s@%s", fullPath, requestedVersion)
	}
	return &serverError{
		status: http.StatusNotFound,
		epage: &errorPage{
			templateName: "fetch.tmpl",
			MessageData:  path,
		},
	}
}

func previousFetchStatusAndResponse(ctx context.Context, db *postgres.DB,
	fullPath, modulePath, requestedVersion string) (_ *fetchResult, err error) {
	defer derrors.Wrap(&err, "previousFetchStatusAndResponse(w, r, %q, %q)", fullPath, requestedVersion)

	paths, err := modulePathsToFetch(ctx, db, fullPath, modulePath)
	if err != nil {
		return nil, err

	vm, err := db.GetVersionMap(ctx, paths[0], requestedVersion)
	if err != nil {
		return nil, err

	if vm != nil &&
		(vm.Status >= 500 ||
			vm.Status == derrors.ToStatus(derrors.AlternativeModule) ||
			vm.Status == derrors.ToStatus(derrors.BadModule)) {
		return resultFromFetchRequest([]*fetchResult{
			{
				modulePath: vm.ModulePath,
				goModPath:  vm.GoModPath,
				status:     vm.Status,
				err:        errors.New(vm.Error),
			},
		}, fullPath, requestedVersion)
	}

	majPath, maj, err := db.GetLatestMajorPathForV1Path(ctx, fullPath)
	if err != nil && err != derrors.NotFound {
		return nil, err
	}
	if majPath != fullPath && maj != 1 && majPath != "" {
		return &fetchResult{
			modulePath: majPath,
			goModPath:  majPath,
			status:     http.StatusFound,
		}, nil
	}
	vms, err := db.GetVersionMaps(ctx, paths, requestedVersion)
	if err != nil {
		return nil, err
	}
	var fetchResults []*fetchResult
	for _, vm := range vms {
		fr := fetchResultFromVersionMap(vm)
		fetchResults = append(fetchResults, fr)
		if vm.Status == http.StatusOK || vm.Status == 290 {
			fr.err = errPathDoesNotExistInModule
		}
	}
	if len(fetchResults) == 0 {
		return nil, derrors.NotFound
	}
	return resultFromFetchRequest(fetchResults, fullPath, requestedVersion)
}

func fetchResultFromVersionMap(vm *internal.VersionMap) *fetchResult {
	var err error
	if vm.Error != "" {
		err = errors.New(vm.Error)
	}
	return &fetchResult{
		modulePath: vm.ModulePath,
		goModPath:  vm.GoModPath,
		status:     vm.Status,
		updatedAt:  vm.UpdatedAt,
		err:        err,
	}