package merge

import (
	"errors"
	"fmt"
	"net/http"

	"github.com/AlecAivazis/survey/v2"
	"github.com/MakeNowJust/heredoc"
	"github.com/cli/cli/api"
	"github.com/cli/cli/git"
	"github.com/cli/cli/internal/config"
	"github.com/cli/cli/pkg/cmd/pr/shared"
	"github.com/cli/cli/pkg/cmdutil"
	"github.com/cli/cli/pkg/iostreams"
	"github.com/cli/cli/pkg/prompt"
	"github.com/cli/cli/pkg/surveyext"
	"github.com/spf13/cobra"
)

type editor interface {
	Edit(string, string) (string, error)
}

type MergeOptions struct {
	HttpClient func() (*http.Client, error)
	IO         *iostreams.IOStreams
	Branch     func() (string, error)

	Finder shared.PRFinder

	SelectorArg  string
	DeleteBranch bool
	MergeMethod  PullRequestMergeMethod

	AutoMergeEnable  bool
	AutoMergeDisable bool

	Body    string
	BodySet bool
	Editor  editor

	IsDeleteBranchIndicated bool
	CanDeleteLocalBranch    bool
	InteractiveMode         bool
}

func NewCmdMerge(f *cmdutil.Factory, runF func(*MergeOptions) error) *cobra.Command {
	opts := &MergeOptions{
		IO:         f.IOStreams,
		HttpClient: f.HttpClient,
		Branch:     f.Branch,
	}

	var (
		flagMerge  bool
		flagSquash bool
		flagRebase bool
	)

	var bodyFile string

	cmd := &cobra.Command{
		Use:   "merge [<number> | <url> | <branch>]",
		Short: "Merge a pull request",
		Long: heredoc.Doc(`
			Merge a pull request on GitHub.

			Without an argument, the pull request that belongs to the current branch
			is selected.			
    	`),
		Args: cobra.MaximumNArgs(1),
		RunE: func(cmd *cobra.Command, args []string) error {
			opts.Finder = shared.NewFinder(f)

			if repoOverride, _ := cmd.Flags().GetString("repo"); repoOverride != "" && len(args) == 0 {
				return &cmdutil.FlagError{Err: errors.New("argument required when using the --repo flag")}
			}

			if len(args) > 0 {
				opts.SelectorArg = args[0]
			}

			methodFlags := 0
			if flagMerge {
				opts.MergeMethod = PullRequestMergeMethodMerge
				methodFlags++
			}
			if flagRebase {
				opts.MergeMethod = PullRequestMergeMethodRebase
				methodFlags++
			}
			if flagSquash {
				opts.MergeMethod = PullRequestMergeMethodSquash
				methodFlags++
			}
			if methodFlags == 0 {
				if !opts.IO.CanPrompt() {
					return &cmdutil.FlagError{Err: errors.New("--merge, --rebase, or --squash required when not running interactively")}
				}
				opts.InteractiveMode = true
			} else if methodFlags > 1 {
				return &cmdutil.FlagError{Err: errors.New("only one of --merge, --rebase, or --squash can be enabled")}
			}

			opts.IsDeleteBranchIndicated = cmd.Flags().Changed("delete-branch")
			opts.CanDeleteLocalBranch = !cmd.Flags().Changed("repo")

			bodyProvided := cmd.Flags().Changed("body")
			bodyFileProvided := bodyFile != ""

			if err := cmdutil.MutuallyExclusive(
				"specify only one of `--body` or `--body-file`",
				bodyProvided,
				bodyFileProvided,
			); err != nil {
				return err
			}
			if bodyProvided || bodyFileProvided {
				opts.BodySet = true
				if bodyFileProvided {
					b, err := cmdutil.ReadFile(bodyFile, opts.IO.In)
					if err != nil {
						return err
					}
					opts.Body = string(b)
				}

			}

			opts.Editor = &userEditor{
				io:     opts.IO,
				config: f.Config,
			}

			if runF != nil {
				return runF(opts)
			}
			return mergeRun(opts)
		},
	}

	cmd.Flags().BoolVarP(&opts.DeleteBranch, "delete-branch", "d", false, "Delete the local and remote branch after merge")
	cmd.Flags().StringVarP(&opts.Body, "body", "b", "", "Body `text` for the merge commit")
	cmd.Flags().StringVarP(&bodyFile, "body-file", "F", "", "Read body text from `file`")
	cmd.Flags().BoolVarP(&flagMerge, "merge", "m", false, "Merge the commits with the base branch")
	cmd.Flags().BoolVarP(&flagRebase, "rebase", "r", false, "Rebase the commits onto the base branch")
	cmd.Flags().BoolVarP(&flagSquash, "squash", "s", false, "Squash the commits into one commit and merge it into the base branch")
	cmd.Flags().BoolVar(&opts.AutoMergeEnable, "auto", false, "Automatically merge only after necessary requirements are met")
	cmd.Flags().BoolVar(&opts.AutoMergeDisable, "disable-auto", false, "Disable auto-merge for this pull request")
	return cmd
}

func mergeRun(opts *MergeOptions) error {
	cs := opts.IO.ColorScheme()

	findOptions := shared.FindOptions{
		Selector: opts.SelectorArg,
		Fields:   []string{"id", "number", "state", "title", "lastCommit", "mergeStateStatus", "headRepositoryOwner", "headRefName"},
	}
	pr, baseRepo, err := opts.Finder.Find(findOptions)
	if err != nil {
		return err
	}

	isTerminal := opts.IO.IsStdoutTTY()

	httpClient, err := opts.HttpClient()
	if err != nil {
		return err
	}
	apiClient := api.NewClientFromHTTP(httpClient)

	if opts.AutoMergeDisable {
		err := disableAutoMerge(httpClient, baseRepo, pr.ID)
		if err != nil {
			return err
		}
		if isTerminal {
			fmt.Fprintf(opts.IO.ErrOut, "%s Auto-merge disabled for pull request #%d\n", cs.SuccessIconWithColor(cs.Green), pr.Number)
		}
		return nil
	}

	if opts.SelectorArg == "" && len(pr.Commits.Nodes) > 0 {
		if localBranchLastCommit, err := git.LastCommit(); err == nil {
			if localBranchLastCommit.Sha != pr.Commits.Nodes[len(pr.Commits.Nodes)-1].Commit.OID {
				fmt.Fprintf(opts.IO.ErrOut,
					"%s Pull request #%d (%s) has diverged from local branch\n", cs.Yellow("!"), pr.Number, pr.Title)
			}
		}
	}

	isPRAlreadyMerged := pr.State == "MERGED"
	if blocked := blockedReason(pr.MergeStateStatus); !opts.AutoMergeEnable && !isPRAlreadyMerged && blocked != "" {
		fmt.Fprintf(opts.IO.ErrOut, "%s Pull request #%d is not mergeable: %s.\n", cs.FailureIcon(), pr.Number, blocked)
		fmt.Fprintf(opts.IO.ErrOut, "To have the pull request merged after all the requirements have been met, add the `--auto` flag.\n")
		return cmdutil.SilentError
	}

	deleteBranch := opts.DeleteBranch
	crossRepoPR := pr.HeadRepositoryOwner.Login != baseRepo.RepoOwner()
	autoMerge := opts.AutoMergeEnable && !isImmediatelyMergeable(pr.MergeStateStatus)

	if !isPRAlreadyMerged {
		payload := mergePayload{
			repo:          baseRepo,
			pullRequestID: pr.ID,
			method:        opts.MergeMethod,
			auto:          autoMerge,
			commitBody:    opts.Body,
			setCommitBody: opts.BodySet,
		}

		if opts.InteractiveMode {
			r, err := api.GitHubRepo(apiClient, baseRepo)
			if err != nil {
				return err
			}
			payload.method, err = mergeMethodSurvey(r)
			if err != nil {
				return err
			}
			deleteBranch, err = deleteBranchSurvey(opts, crossRepoPR)
			if err != nil {
				return err
			}

			allowEditMsg := payload.method != PullRequestMergeMethodRebase

			action, err := confirmSurvey(allowEditMsg)
			if err != nil {
				return fmt.Errorf("unable to confirm: %w", err)
			}

			if action == shared.EditCommitMessageAction {
				if !payload.setCommitBody {
					payload.commitBody, err = getMergeText(httpClient, baseRepo, pr.ID, payload.method)
					if err != nil {
						return err
					}
				}

				payload.commitBody, err = opts.Editor.Edit("*.md", payload.commitBody)
				if err != nil {
					return err
				}
				payload.setCommitBody = true

				action, err = confirmSurvey(false)
				if err != nil {
					return fmt.Errorf("unable to confirm: %w", err)
				}
			}
			if action == shared.CancelAction {
				fmt.Fprintln(opts.IO.ErrOut, "Cancelled.")
				return cmdutil.CancelError
			}
		}

		err = mergePullRequest(httpClient, payload)
		if err != nil {
			return err
		}

		if isTerminal {
			if payload.auto {
				method := ""
				switch payload.method {
				case PullRequestMergeMethodRebase:
					method = " via rebase"
				case PullRequestMergeMethodSquash:
					method = " via squash"
				}
				fmt.Fprintf(opts.IO.ErrOut, "%s Pull request #%d will be automatically merged%s when all requirements are met\n", cs.SuccessIconWithColor(cs.Green), pr.Number, method)
			} else {
				action := "Merged"
				switch payload.method {
				case PullRequestMergeMethodRebase:
					action = "Rebased and merged"
				case PullRequestMergeMethodSquash:
					action = "Squashed and merged"
				}
				fmt.Fprintf(opts.IO.ErrOut, "%s %s pull request #%d (%s)\n", cs.SuccessIconWithColor(cs.Magenta), action, pr.Number, pr.Title)
			}
		}
	} else if !opts.IsDeleteBranchIndicated && opts.InteractiveMode && !crossRepoPR && !opts.AutoMergeEnable {
		err := prompt.SurveyAskOne(&survey.Confirm{
			Message: fmt.Sprintf("Pull request #%d was already merged. Delete the branch locally?", pr.Number),
			Default: false,
		}, &deleteBranch)
		if err != nil {
			return fmt.Errorf("could not prompt: %w", err)
		}
	} else if crossRepoPR {
		fmt.Fprintf(opts.IO.ErrOut, "%s Pull request #%d was already merged\n", cs.WarningIcon(), pr.Number)
	}

	if !deleteBranch || crossRepoPR || autoMerge {
		return nil
	}

	branchSwitchString := ""

	if opts.CanDeleteLocalBranch {
		currentBranch, err := opts.Branch()
		if err != nil {
			return err
		}

		var branchToSwitchTo string
		if currentBranch == pr.HeadRefName {
			branchToSwitchTo, err = api.RepoDefaultBranch(apiClient, baseRepo)
			if err != nil {
				return err
			}
			err = git.CheckoutBranch(branchToSwitchTo)
			if err != nil {
				return err
			}
		}

		localBranchExists := git.HasLocalBranch(pr.HeadRefName)
		if localBranchExists {
			err = git.DeleteLocalBranch(pr.HeadRefName)
			if err != nil {
				err = fmt.Errorf("failed to delete local branch %s: %w", cs.Cyan(pr.HeadRefName), err)
				return err
			}
		}

		if branchToSwitchTo != "" {
			branchSwitchString = fmt.Sprintf(" and switched to branch %s", cs.Cyan(branchToSwitchTo))
		}
	}

	if !isPRAlreadyMerged {
		err = api.BranchDeleteRemote(apiClient, baseRepo, pr.HeadRefName)
		var httpErr api.HTTPError
		// The ref might have already been deleted by GitHub
		if err != nil && (!errors.As(err, &httpErr) || httpErr.StatusCode != 422) {
			err = fmt.Errorf("failed to delete remote branch %s: %w", cs.Cyan(pr.HeadRefName), err)
			return err
		}
	}

	if isTerminal {
		fmt.Fprintf(opts.IO.ErrOut, "%s Deleted branch %s%s\n", cs.SuccessIconWithColor(cs.Red), cs.Cyan(pr.HeadRefName), branchSwitchString)
	}

	return nil
}

func mergeMethodSurvey(baseRepo *api.Repository) (PullRequestMergeMethod, error) {
	type mergeOption struct {
		title  string
		method PullRequestMergeMethod
	}

	var mergeOpts []mergeOption
	if baseRepo.MergeCommitAllowed {
		opt := mergeOption{title: "Create a merge commit", method: PullRequestMergeMethodMerge}
		mergeOpts = append(mergeOpts, opt)
	}
	if baseRepo.RebaseMergeAllowed {
		opt := mergeOption{title: "Rebase and merge", method: PullRequestMergeMethodRebase}
		mergeOpts = append(mergeOpts, opt)
	}
	if baseRepo.SquashMergeAllowed {
		opt := mergeOption{title: "Squash and merge", method: PullRequestMergeMethodSquash}
		mergeOpts = append(mergeOpts, opt)
	}

	var surveyOpts []string
	for _, v := range mergeOpts {
		surveyOpts = append(surveyOpts, v.title)
	}

	mergeQuestion := &survey.Select{
		Message: "What merge method would you like to use?",
		Options: surveyOpts,
	}

	var result int
	err := prompt.SurveyAskOne(mergeQuestion, &result)
	return mergeOpts[result].method, err
}

func deleteBranchSurvey(opts *MergeOptions, crossRepoPR bool) (bool, error) {
	if !crossRepoPR && !opts.IsDeleteBranchIndicated {
		var message string
		if opts.CanDeleteLocalBranch {
			message = "Delete the branch locally and on GitHub?"
		} else {
			message = "Delete the branch on GitHub?"
		}

		var result bool
		submit := &survey.Confirm{
			Message: message,
			Default: false,
		}
		err := prompt.SurveyAskOne(submit, &result)
		return result, err
	}

	return opts.DeleteBranch, nil
}

func confirmSurvey(allowEditMsg bool) (shared.Action, error) {
	const (
		submitLabel        = "Submit"
		editCommitMsgLabel = "Edit commit message"
		cancelLabel        = "Cancel"
	)

	options := []string{submitLabel}
	if allowEditMsg {
		options = append(options, editCommitMsgLabel)
	}
	options = append(options, cancelLabel)

	var result string
	submit := &survey.Select{
		Message: "What's next?",
		Options: options,
	}
	err := prompt.SurveyAskOne(submit, &result)
	if err != nil {
		return shared.CancelAction, fmt.Errorf("could not prompt: %w", err)
	}

	switch result {
	case submitLabel:
		return shared.SubmitAction, nil
	case editCommitMsgLabel:
		return shared.EditCommitMessageAction, nil
	default:
		return shared.CancelAction, nil
	}
}

type userEditor struct {
	io     *iostreams.IOStreams
	config func() (config.Config, error)
}

func (e *userEditor) Edit(filename, startingText string) (string, error) {
	editorCommand, err := cmdutil.DetermineEditor(e.config)
	if err != nil {
		return "", err
	}

	return surveyext.Edit(editorCommand, filename, startingText, e.io.In, e.io.Out, e.io.ErrOut, nil)
}

// blockedReason translates various MergeStateStatus GraphQL values into human-readable reason
func blockedReason(status string) string {
	switch status {
	case "BLOCKED":
		return "the base branch policy prohibits the merge"
	case "BEHIND":
		return "the head branch is not up to date with the base branch"
	case "DIRTY":
		return "the merge commit cannot be cleanly created"
	default:
		return ""
	}
}

func isImmediatelyMergeable(status string) bool {
	switch status {
	case "CLEAN", "HAS_HOOKS", "UNSTABLE":
		return true
	default:
		return false
	}
}