package external

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os/exec"
	"strings"

	"git.hypertheory-labs.dev/loom/loom-cli/internal/config"
)

// AddByName adopts a document named the way `list` prints it, against the
// current context.
//
//	loomctl external add loom/cart cart
//
// Nobody should have to type a host's raw-file route to adopt a document. The
// route belongs to the host, so it lives in the context; the published
// directory belongs to the convention, so it lives in the code; and what is
// left — which repository, which document — is the only part a person knows.
func AddByName(root, ownerRepo, name string, out io.Writer) error {
	cfg, err := config.Load()
	if err != nil {
		return err
	}
	ctx, err := cfg.Current()
	if err != nil {
		return err
	}
	if strings.Count(ownerRepo, "/") != 1 {
		return fmt.Errorf("want owner/repo, got %q", ownerRepo)
	}
	if !strings.HasSuffix(name, ".md") {
		name += ".md"
	}

	raw, resolved := ctx.RawURL(ownerRepo, PublishedDir+"/"+name)
	if raw == "" {
		return fmt.Errorf("context %q has flavor %q; known flavors are %s",
			cfg.CurrentContext, ctx.Flavor, config.Flavors())
	}
	if !resolved {
		// The lock must record a resolved URL. A short form that stays short
		// follows whatever the default branch is at the time you ask, so a
		// branch rename would report as a change in the document.
		branch, err := defaultBranch(ctx.CloneURL(ownerRepo))
		if err != nil {
			return fmt.Errorf("resolving the default branch of %s: %w", ownerRepo, err)
		}
		raw = fmt.Sprintf(raw, branch)
	}
	err = Add(root, raw, "", out)

	// A 404 here has a reading the convention does not list, because it can only
	// happen at adoption: the name is wrong. We know the repository, so rather
	// than reporting an ambiguity we can resolve, look.
	var nf *NotFoundError
	if errors.As(err, &nf) {
		var names strings.Builder
		if lerr := List(ctx.CloneURL(ownerRepo), &names); lerr == nil {
			return fmt.Errorf("%s publishes no %q. It publishes:\n%s",
				ownerRepo, name, indent(names.String()))
		}
		// Listing failed too, so the repository itself is unreachable and the
		// original ambiguity stands.
	}
	return err
}

func indent(s string) string {
	var b strings.Builder
	for _, line := range strings.Split(strings.TrimRight(s, "\n"), "\n") {
		fmt.Fprintf(&b, "  %s\n", line)
	}
	return strings.TrimRight(b.String(), "\n")
}

// ListByName enumerates a repository named against the current context.
func ListByName(ownerRepo string, out io.Writer) error {
	cfg, err := config.Load()
	if err != nil {
		return err
	}
	ctx, err := cfg.Current()
	if err != nil {
		return err
	}
	return List(ctx.CloneURL(ownerRepo), out)
}

// defaultBranch asks the remote which branch HEAD points at, without cloning.
//
// Only hosts whose raw URLs do not redirect need this. Gitea resolves its own
// short form, which is why adopting from gitea needs no git at all.
func defaultBranch(cloneURL string) (string, error) {
	cmd := exec.Command("git", "ls-remote", "--symref", cloneURL, "HEAD")
	var stdout, stderr bytes.Buffer
	cmd.Stdout, cmd.Stderr = &stdout, &stderr
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("%w: %s", err, strings.TrimSpace(stderr.String()))
	}
	for _, line := range strings.Split(stdout.String(), "\n") {
		if after, ok := strings.CutPrefix(line, "ref: refs/heads/"); ok {
			return strings.TrimSpace(strings.SplitN(after, "\t", 2)[0]), nil
		}
	}
	return "", fmt.Errorf("no symref in git ls-remote output")
}