package ghfs

import (
	"context"
	"fmt"
	"io"
	"io/fs"

	"github.com/google/go-github/v47/github"
)

// fetcher defines the operations we need to take against GitHub so that we can
// easily provide alternative implementations
type fetcher interface {
	getContents(name string) (*github.RepositoryContent, []*github.RepositoryContent, error)
	downloadContents(c *github.RepositoryContent) (io.ReadCloser, error)
}

// ghFetcher talks to GitHub and is used by default
type ghFetcher struct {
	gh               *github.Client
	ctx              context.Context
	owner, repo, ref string
}

func (f *ghFetcher) getContents(name string) (
	*github.RepositoryContent, []*github.RepositoryContent, error,
) {
	file, dir, res, err := f.gh.Repositories.GetContents(
		f.ctx,
		f.owner,
		f.repo,
		name,
		&github.RepositoryContentGetOptions{Ref: f.ref},
	)

	if err := f.responseToErr(name, res, err); err != nil {
		return nil, nil, err
	}

	return file, dir, nil
}

func (f *ghFetcher) downloadContents(file *github.RepositoryContent) (io.ReadCloser, error) {
	if file.GetDownloadURL() == "" {
		return nil, fmt.Errorf("unexpected state: file has no download URL")
	}
	dlRes, err := f.gh.Client().Get(file.GetDownloadURL())
	if err := f.responseToErr(file.GetPath(), &github.Response{Response: dlRes}, err); err != nil {
		return nil, err
	}
	return dlRes.Body, nil
}

// responseToErr checks the response and error from a GitHub operation and
// consolidates it into a single error to check
func (f *ghFetcher) responseToErr(name string, res *github.Response, err error) error {
	// Failure response codes, explicitly check because the request can fail with
	// a nil err.
	switch {
	case res.StatusCode == 404:
		return fmt.Errorf("%w: %s not found in %s/%s@%s",
			fs.ErrNotExist, name, f.owner, f.repo, f.ref)
	case res.StatusCode == 403:
		return fmt.Errorf("%w: failed to retrieve %s from %s/%s@%s",
			fs.ErrPermission, name, f.owner, f.repo, f.ref)
	case err != nil:
		return fmt.Errorf("failed to retrieve %s from %s/%s@%s: %w",
			name, f.owner, f.repo, f.ref, err)
	default:
		return nil
	}
}