// Copyright 2026 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package app

import (
	"context"
	"errors"
	"fmt"
	"slices"
	"strings"

	"gitea.dev/tea/internal/clierr"
	"gitea.dev/tea/internal/git"
	"gitea.dev/tea/internal/services"
	"gitea.dev/tea/internal/settings"
	"github.com/spf13/cobra"
)

func (t target) hosts() map[string]settings.Host {
	return map[string]settings.Host{t.Host: t.host}
}

// ownsRemote reports whether the Git remote URL raw names the target's instance and repository.
func (t target) ownsRemote(raw string) bool {
	host, repo, err := settings.RepositoryURL(raw, t.hosts())
	return err == nil && host == t.Host && strings.EqualFold(repo, t.Repo)
}

// remoteCredentials returns Git transport arguments for the URL of the named remote.
func (a *application) remoteCredentials(ctx context.Context, t target, remote string) ([]string, error) {
	raw, err := a.git(ctx, "remote", "get-url", remote)
	if err != nil {
		return nil, err
	}
	return a.gitTransportArguments(t, settings.RemoteIsSSH(raw))
}

func (a *application) checkoutRemote(ctx context.Context, target target, snapshot settings.Snapshot) (string, error) {
	explicit := a.options.remote
	if explicit == "" {
		explicit = snapshot.Preferences.Remote
	}
	if explicit != "" {
		raw, err := a.gitProbe().Output(ctx, a.options.cwd, false, "remote", "get-url", explicit)
		if err == nil && target.ownsRemote(raw) {
			return explicit, nil
		}
		return "", errors.New("selected remote does not match the resolved instance and repository")
	}
	matches, err := a.remotesForRepositoryURLs(ctx, target.hosts(), "", "", target.Repo)
	if err != nil {
		return "", err
	}
	preferredRemotes := []string{"upstream", "origin"}
	if _, tracking := git.CurrentUpstreamRemote(ctx, a.gitProbe(), a.options.cwd); tracking != "" {
		preferredRemotes = append([]string{tracking}, preferredRemotes...)
	}
	for _, preferred := range preferredRemotes {
		if slices.Contains(matches, preferred) {
			return preferred, nil
		}
	}
	if len(matches) == 1 {
		return matches[0], nil
	}
	if len(matches) == 0 {
		return "", errNoMatchingRemote
	}
	return "", errors.New("multiple Git remotes match the selected repository; select --remote")
}

var errNoMatchingRemote = errors.New("no Git remote matches the selected repository; add its base remote before checkout")

func (a *application) pullCheckoutCommand() *cobra.Command {
	var branch string
	var detached, update bool
	cmd := &cobra.Command{Use: "checkout {<number> | <url> | <branch>}", Aliases: []string{"co"}, Short: "Check out a pull request", Long: `Check out the head of a pull request in a local branch.

The branch takes the name of the pull request's head branch when that name is free or
already points at the head; otherwise it is OWNER/BRANCH for a fork, or pr/NUMBER. tea
records the pull request in the branch's Git configuration, so that pr commands without an
argument select it, and the branch tracks the head branch, so that git push updates it.`, Annotations: pullArgumentsAnnotation(nil), Args: argsExact(1), RunE: func(cmd *cobra.Command, args []string) error {
		if detached && (cmd.Flags().Changed("branch") || update) {
			return clierr.Wrap(clierr.Usage, errors.New("--detach and --branch/--update are mutually exclusive"))
		}
		if cmd.Flags().Changed("branch") && strings.TrimSpace(branch) == "" {
			return clierr.Wrap(clierr.Usage, errors.New("--branch cannot be empty"))
		}
		target, n, err := a.pullSelector(cmd, args)
		if err != nil {
			return err
		}
		snapshot, err := a.deps.Settings.Load()
		if err != nil {
			return err
		}
		remote, err := a.checkoutRemote(cmd.Context(), target, snapshot)
		if err != nil {
			return clierr.Wrap(clierr.Usage, err)
		}
		pull, err := (services.Pulls{Client: target.client, Repository: target.Repo}).View(cmd.Context(), n)
		if err != nil {
			return err
		}
		if pull.HeadSHA == "" {
			return errors.New("Gitea did not return the PR head commit")
		}
		if branch == "" && !detached {
			branch = a.checkoutBranchName(cmd.Context(), target, pull)
		}
		rawRemote, err := a.git(cmd.Context(), "remote", "get-url", remote)
		if err != nil {
			return err
		}
		if !target.ownsRemote(rawRemote) {
			return clierr.Wrap(clierr.Usage, errors.New("selected Git remote changed; resolve the repository again before checkout"))
		}
		credentialRemote := rawRemote
		options := git.CheckoutOptions{
			Detached: detached, Update: update, Directory: a.options.cwd, Remote: remote, Number: n, Branch: branch,
			Prompt: a.policy(snapshot).CanPrompt(a.deps.Streams), ExpectedCommit: pull.HeadSHA,
		}
		undoRemote := func() {}
		if !pull.HeadRemoteDeleted && pull.Head != "" && !detached {
			headRemote, headURL, undo, ensureErr := a.ensureHeadRemote(cmd.Context(), target, pull)
			if ensureErr != nil {
				return ensureErr
			}
			if headRemote != "" {
				options.HeadRemote, options.HeadBranch = headRemote, pull.Head
				credentialRemote, undoRemote = headURL, undo
			}
		}
		credentialArgs, err := a.gitTransportArguments(target, settings.RemoteIsSSH(credentialRemote))
		if err != nil {
			undoRemote()
			return err
		}
		options.CredentialArgs = credentialArgs
		result, err := git.CheckoutPull(cmd.Context(), a.deps.Git, options)
		if err != nil {
			undoRemote()
			return err
		}
		if a.options.json != "" {
			return a.writeJSON(cmd, result)
		}
		if result.Detached {
			a.done(cmd, "Checked out #%d at %s (detached HEAD)", n, shortSHA(result.Commit))
		} else {
			a.done(cmd, "Checked out #%d into %s", n, result.Branch)
		}
		return nil
	}}
	cmd.Flags().BoolVar(&update, "update", false, "Fast-forward an existing branch to the PR head; reject divergence")
	cmd.Flags().BoolVar(&detached, "detach", false, "Check out the PR commit without creating or changing a branch")
	cmd.Flags().StringVarP(&branch, "branch", "b", "", "Local branch name (default: the head branch name when free, else OWNER/BRANCH or pr/NUMBER)")
	cmd.ValidArgsFunction = a.completePulls("open")
	cmd.Example = `$ tea pr checkout 13
$ tea pr co feature/login
$ tea pr checkout 13 --branch review-13
$ tea pr checkout 13 --update`
	return cmd
}

// checkoutBranchName names the local branch for a pull request (D13): its head branch name when
// that is free or already at the head, else OWNER/BRANCH for a fork, else pr/NUMBER. A branch that
// an earlier checkout of the same pull request created is reused, so that --update can advance it.
func (a *application) checkoutBranchName(ctx context.Context, t target, pull services.Pull) string {
	fallback := fmt.Sprintf("pr/%d", pull.Number)
	if pull.HeadRemoteDeleted || pull.Head == "" {
		return fallback
	}
	candidates := []string{pull.Head}
	if owner, _, _ := strings.Cut(pull.HeadRepo, "/"); owner != "" && !strings.EqualFold(pull.HeadRepo, t.Repo) {
		candidates = append(candidates, owner+"/"+pull.Head)
	}
	for _, name := range candidates {
		tip, err := a.gitProbe().Output(ctx, a.options.cwd, false, "rev-parse", "--verify", "refs/heads/"+name+"^{commit}")
		if err != nil || tip == pull.HeadSHA || git.ReadBranchConfig(ctx, a.gitProbe(), a.options.cwd, name).PullNumber == pull.Number {
			return name
		}
	}
	return fallback
}

// ensureHeadRemote returns the remote holding the PR head, adding one when none matches.
// An empty name means the head repository has no usable clone URL and the base remote's PR ref should be used.
func (a *application) ensureHeadRemote(ctx context.Context, target target, pull services.Pull) (name, remoteURL string, undo func(), err error) {
	matches, err := a.remotesForRepositoryURLs(ctx, target.hosts(), pull.HeadCloneURL, pull.HeadSSHURL, pull.HeadRepo)
	if err != nil {
		return "", "", nil, err
	}
	existing := ""
	switch {
	case a.options.remote != "" && slices.Contains(matches, a.options.remote):
		existing = a.options.remote
	case len(matches) == 1:
		existing = matches[0]
	case len(matches) > 1:
		for _, preferred := range []string{"origin", "upstream"} {
			if slices.Contains(matches, preferred) {
				existing = preferred
				break
			}
		}
		if existing == "" {
			return "", "", nil, clierr.Wrap(clierr.Usage, errors.New("multiple Git remotes match the pull request head repository; select --remote"))
		}
	}
	if existing != "" {
		raw, err := a.git(ctx, "remote", "get-url", existing)
		return existing, raw, func() {}, err
	}
	remoteURL, _, urlErr := cloneURLForProtocol(pull.HeadCloneURL, pull.HeadSSHURL, target.gitProtocol)
	if urlErr != nil {
		return "", "", nil, nil
	}
	name = "pulls/" + pull.HeadRepo
	if pull.HeadRepo == "" {
		name = "pulls/head"
	}
	if _, err := a.git(ctx, "remote", "add", "--", name, remoteURL); err != nil {
		return "", "", nil, fmt.Errorf("could not add head remote %s: %w", name, err)
	}
	// Detached from the command context so an interrupt (Ctrl-C) still removes the half-used remote.
	cleanup := context.WithoutCancel(ctx)
	return name, remoteURL, func() { _, _ = a.git(cleanup, "remote", "remove", "--", name) }, nil
}