package command

import (
	"errors"
	"fmt"
	"net/url"
	"strings"
	"time"

	"github.com/cli/cli/api"
	"github.com/cli/cli/context"
	"github.com/cli/cli/git"
	"github.com/cli/cli/internal/ghrepo"
	"github.com/cli/cli/pkg/githubtemplate"
	"github.com/cli/cli/utils"
	"github.com/spf13/cobra"
)

type defaults struct {
	Title string
	Body  string
}

func computeDefaults(baseRef, headRef string) (defaults, error) {
	commits, err := git.Commits(baseRef, headRef)
	if err != nil {
		return defaults{}, err
	}

	out := defaults{}

	if len(commits) == 1 {
		out.Title = commits[0].Title
		body, err := git.CommitBody(commits[0].Sha)
		if err != nil {
			return defaults{}, err
		}
		out.Body = body
	} else {
		out.Title = utils.Humanize(headRef)

		body := ""
		for _, c := range commits {
			body += fmt.Sprintf("- %s\n", c.Title)
		}
		out.Body = body
	}

	return out, nil
}

func prCreate(cmd *cobra.Command, _ []string) error {
	ctx := contextForCommand(cmd)
	remotes, err := ctx.Remotes()
	if err != nil {
		return err
	}

	client, err := apiClientForContext(ctx)
	if err != nil {
		return fmt.Errorf("could not initialize API client: %w", err)
	}

	baseRepoOverride, _ := cmd.Flags().GetString("repo")
	repoContext, err := context.ResolveRemotesToRepos(remotes, client, baseRepoOverride)
	if err != nil {
		return err
	}

	baseRepo, err := repoContext.BaseRepo()
	if err != nil {
		return fmt.Errorf("could not determine base repository: %w", err)
	}

	headBranch, err := ctx.Branch()
	if err != nil {
		return fmt.Errorf("could not determine the current branch: %w", err)
	}

	var headRepo ghrepo.Interface
	var headRemote *context.Remote

	// determine whether the head branch is already pushed to a remote
	headBranchPushedTo := determineTrackingBranch(remotes, headBranch)
	if headBranchPushedTo != nil {
		for _, r := range remotes {
			if r.Name != headBranchPushedTo.RemoteName {
				continue
			}
			headRepo = r
			headRemote = r
			break
		}
	}

	// otherwise, determine the head repository with info obtained from the API
	if headRepo == nil {
		if r, err := repoContext.HeadRepo(); err == nil {
			headRepo = r
		}
	}

	baseBranch, err := cmd.Flags().GetString("base")
	if err != nil {
		return err
	}
	if baseBranch == "" {
		baseBranch = baseRepo.DefaultBranchRef.Name
	}
	if headBranch == baseBranch && headRepo != nil && ghrepo.IsSame(baseRepo, headRepo) {
		return fmt.Errorf("must be on a branch named differently than %q", baseBranch)
	}

	if ucc, err := git.UncommittedChangeCount(); err == nil && ucc > 0 {
		fmt.Fprintf(cmd.ErrOrStderr(), "Warning: %s\n", utils.Pluralize(ucc, "uncommitted change"))
	}

	title, err := cmd.Flags().GetString("title")
	if err != nil {
		return fmt.Errorf("could not parse title: %w", err)
	}
	body, err := cmd.Flags().GetString("body")
	if err != nil {
		return fmt.Errorf("could not parse body: %w", err)
	}

	baseTrackingBranch := baseBranch
	if baseRemote, err := remotes.FindByRepo(baseRepo.RepoOwner(), baseRepo.RepoName()); err == nil {
		baseTrackingBranch = fmt.Sprintf("%s/%s", baseRemote.Name, baseBranch)
	}
	defs, defaultsErr := computeDefaults(baseTrackingBranch, headBranch)

	isWeb, err := cmd.Flags().GetBool("web")
	if err != nil {
		return fmt.Errorf("could not parse web: %q", err)
	}

	autofill, err := cmd.Flags().GetBool("fill")
	if err != nil {
		return fmt.Errorf("could not parse fill: %q", err)
	}

	action := SubmitAction
	if isWeb {
		action = PreviewAction
		if (title == "" || body == "") && defaultsErr != nil {
			return fmt.Errorf("could not compute title or body defaults: %w", defaultsErr)
		}
	} else if autofill {
		if defaultsErr != nil {
			return fmt.Errorf("could not compute title or body defaults: %w", defaultsErr)
		}
		title = defs.Title
		body = defs.Body
	}

	if !isWeb {
		headBranchLabel := headBranch
		if headRepo != nil && !ghrepo.IsSame(baseRepo, headRepo) {
			headBranchLabel = fmt.Sprintf("%s:%s", headRepo.RepoOwner(), headBranch)
		}
		existingPR, err := api.PullRequestForBranch(client, baseRepo, baseBranch, headBranchLabel)
		var notFound *api.NotFoundError
		if err != nil && !errors.As(err, &notFound) {
			return fmt.Errorf("error checking for existing pull request: %w", err)
		}
		if err == nil {
			return fmt.Errorf("a pull request for branch %q into branch %q already exists:\n%s", headBranchLabel, baseBranch, existingPR.URL)
		}
	}

	if !isWeb && !autofill {
		fmt.Fprintf(colorableErr(cmd), "\nCreating pull request for %s into %s in %s\n\n",
			utils.Cyan(headBranch),
			utils.Cyan(baseBranch),
			ghrepo.FullName(baseRepo))
		if (title == "" || body == "") && defaultsErr != nil {
			fmt.Fprintf(colorableErr(cmd), "%s warning: could not compute title or body defaults: %s\n", utils.Yellow("!"), defaultsErr)
		}
	}

	// TODO: only drop into interactive mode if stdin & stdout are a tty
	if !isWeb && !autofill && (title == "" || body == "") {
		var templateFiles []string
		if rootDir, err := git.ToplevelDir(); err == nil {
			// TODO: figure out how to stub this in tests
			templateFiles = githubtemplate.Find(rootDir, "PULL_REQUEST_TEMPLATE")
		}

		tb, err := titleBodySurvey(cmd, title, body, defs, templateFiles)
		if err != nil {
			return fmt.Errorf("could not collect title and/or body: %w", err)
		}

		action = tb.Action

		if action == CancelAction {
			fmt.Fprintln(cmd.ErrOrStderr(), "Discarding.")
			return nil
		}

		if title == "" {
			title = tb.Title
		}
		if body == "" {
			body = tb.Body
		}
	}

	if action == SubmitAction && title == "" {
		return errors.New("pull request title must not be blank")
	}

	isDraft, err := cmd.Flags().GetBool("draft")
	if err != nil {
		return fmt.Errorf("could not parse draft: %w", err)
	}
	if isDraft && isWeb {
		return errors.New("the --draft flag is not supported with --web")
	}

	didForkRepo := false
	// if a head repository could not be determined so far, automatically create
	// one by forking the base repository
	if headRepo == nil {
		if baseRepo.IsPrivate {
			return fmt.Errorf("cannot fork private repository '%s'", ghrepo.FullName(baseRepo))
		}
		headRepo, err = api.ForkRepo(client, baseRepo)
		if err != nil {
			return fmt.Errorf("error forking repo: %w", err)
		}
		didForkRepo = true
	}

	headBranchLabel := headBranch
	if !ghrepo.IsSame(baseRepo, headRepo) {
		headBranchLabel = fmt.Sprintf("%s:%s", headRepo.RepoOwner(), headBranch)
	}

	if headRemote == nil {
		headRemote, _ = repoContext.RemoteForRepo(headRepo)
	}

	// There are two cases when an existing remote for the head repo will be
	// missing:
	// 1. the head repo was just created by auto-forking;
	// 2. an existing fork was discovered by quering the API.
	//
	// In either case, we want to add the head repo as a new git remote so we
	// can push to it.
	if headRemote == nil {
		// TODO: support non-HTTPS git remote URLs
		headRepoURL := fmt.Sprintf("https://github.com/%s.git", ghrepo.FullName(headRepo))
		// TODO: prevent clashes with another remote of a same name
		gitRemote, err := git.AddRemote("fork", headRepoURL)
		if err != nil {
			return fmt.Errorf("error adding remote: %w", err)
		}
		headRemote = &context.Remote{
			Remote: gitRemote,
			Owner:  headRepo.RepoOwner(),
			Repo:   headRepo.RepoName(),
		}
	}

	// automatically push the branch if it hasn't been pushed anywhere yet
	if headBranchPushedTo == nil {
		pushTries := 0
		maxPushTries := 3
		for {
			if err := git.Push(headRemote.Name, fmt.Sprintf("HEAD:%s", headBranch)); err != nil {
				if didForkRepo && pushTries < maxPushTries {
					pushTries++
					// first wait 2 seconds after forking, then 4s, then 6s
					waitSeconds := 2 * pushTries
					fmt.Fprintf(cmd.ErrOrStderr(), "waiting %s before retrying...\n", utils.Pluralize(waitSeconds, "second"))
					time.Sleep(time.Duration(waitSeconds) * time.Second)
					continue
				}
				return err
			}
			break
		}
	}

	if action == SubmitAction {
		params := map[string]interface{}{
			"title":       title,
			"body":        body,
			"draft":       isDraft,
			"baseRefName": baseBranch,
			"headRefName": headBranchLabel,
		}

		pr, err := api.CreatePullRequest(client, baseRepo, params)
		if err != nil {
			return fmt.Errorf("failed to create pull request: %w", err)
		}

		fmt.Fprintln(cmd.OutOrStdout(), pr.URL)
	} else if action == PreviewAction {
		openURL := generateCompareURL(baseRepo, baseBranch, headBranchLabel, title, body)
		// TODO could exceed max url length for explorer
		fmt.Fprintf(cmd.ErrOrStderr(), "Opening %s in your browser.\n", displayURL(openURL))
		return utils.OpenInBrowser(openURL)
	} else {
		panic("Unreachable state")
	}

	return nil
}

func determineTrackingBranch(remotes context.Remotes, headBranch string) *git.TrackingRef {
	refsForLookup := []string{"HEAD"}
	var trackingRefs []git.TrackingRef

	headBranchConfig := git.ReadBranchConfig(headBranch)
	if headBranchConfig.RemoteName != "" {
		tr := git.TrackingRef{
			RemoteName: headBranchConfig.RemoteName,
			BranchName: strings.TrimPrefix(headBranchConfig.MergeRef, "refs/heads/"),
		}
		trackingRefs = append(trackingRefs, tr)
		refsForLookup = append(refsForLookup, tr.String())
	}

	for _, remote := range remotes {
		tr := git.TrackingRef{
			RemoteName: remote.Name,
			BranchName: headBranch,
		}
		trackingRefs = append(trackingRefs, tr)
		refsForLookup = append(refsForLookup, tr.String())
	}

	resolvedRefs, _ := git.ShowRefs(refsForLookup...)
	if len(resolvedRefs) > 1 {
		for _, r := range resolvedRefs[1:] {
			if r.Hash != resolvedRefs[0].Hash {
				continue
			}
			for _, tr := range trackingRefs {
				if tr.String() != r.Name {
					continue
				}
				return &tr
			}
		}
	}

	return nil
}

func generateCompareURL(r ghrepo.Interface, base, head, title, body string) string {
	u := fmt.Sprintf(
		"https://github.com/%s/compare/%s...%s?expand=1",
		ghrepo.FullName(r),
		base,
		head,
	)
	if title != "" {
		u += "&title=" + url.QueryEscape(title)
	}
	if body != "" {
		u += "&body=" + url.QueryEscape(body)
	}
	return u
}

var prCreateCmd = &cobra.Command{
	Use:   "create",
	Short: "Create a pull request",
	RunE:  prCreate,
}

func init() {
	prCreateCmd.Flags().BoolP("draft", "d", false,
		"Mark pull request as a draft")
	prCreateCmd.Flags().StringP("title", "t", "",
		"Supply a title. Will prompt for one otherwise.")
	prCreateCmd.Flags().StringP("body", "b", "",
		"Supply a body. Will prompt for one otherwise.")
	prCreateCmd.Flags().StringP("base", "B", "",
		"The branch into which you want your code merged")
	prCreateCmd.Flags().BoolP("web", "w", false, "Open the web browser to create a pull request")
	prCreateCmd.Flags().BoolP("fill", "f", false, "Do not prompt for title/body and just use commit info")
}