package git

import (
	"context"
	"fmt"
	"strings"
)

// PrepareTaggedCheckout fetches one explicit tag ref, checks its peeled commit
// against expectedCommit, and checks out that commit detached.
func PrepareTaggedCheckout(ctx context.Context, repositoryDir, version, remote, expectedCommit string) error {
	if !validVersionRef(version) || !validObjectID(expectedCommit) {
		return fmt.Errorf("invalid tagged checkout identity %q at %q", expectedCommit, version)
	}
	ref := "refs/tags/" + version
	if _, err := run(ctx, repositoryDir, nil, "fetch", "--no-tags", remote, ref+":"+ref); err != nil {
		return fmt.Errorf("fetch tag %s from remote %s: %w", version, remote, err)
	}
	source, err := InspectTaggedSource(ctx, repositoryDir, version)
	if err != nil {
		return err
	}
	if !strings.EqualFold(source.TagCommit, expectedCommit) {
		return fmt.Errorf("tag %s resolves to commit %s, expected %s", version, source.TagCommit, expectedCommit)
	}
	if _, err := run(ctx, repositoryDir, nil, "checkout", "--detach", source.TagCommit); err != nil {
		return fmt.Errorf("check out tag %s at %s: %w", version, source.TagCommit, err)
	}
	head, err := run(ctx, repositoryDir, nil, "rev-parse", "--verify", "HEAD^{commit}")
	if err != nil {
		return fmt.Errorf("verify prepared checkout HEAD: %w", err)
	}
	if !strings.EqualFold(strings.TrimSpace(head), expectedCommit) {
		return fmt.Errorf("prepared checkout HEAD is %s, expected %s", strings.TrimSpace(head), expectedCommit)
	}
	return nil
}