package pkg

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"context"
	"encoding/binary"
	"errors"
	"io"
	"io/fs"
	"net/http"
	"os"
	"sync"

	"hakurei.app/container/check"
)

const (
	// TarUncompressed denotes an uncompressed tarball.
	TarUncompressed = iota
	// TarGzip denotes a tarball compressed via [gzip].
	TarGzip
)

// A tarArtifact is an [Artifact] unpacking a tarball backed by a [File].
type tarArtifact struct {
	// Computed ahead of time from the checksum of the identifier of f appended
	// with parameters of tarArtifact.
	id ID

	// Caller-supplied backing tarball.
	f File
	// Compression on top of the tarball.
	compression uint64

	// Populated when submitting to or loading from [Cache].
	pathname *check.Absolute
	// Checksum of cured directory. Valid if pathname is not nil.
	checksum Checksum

	// Instance of [Cache] to submit the cured artifact to.
	c *Cache
	// Protects the Pathname critical section.
	mu sync.Mutex
}

// NewTar returns a new [Artifact] backed by the supplied [File] and
// compression method.
func (c *Cache) NewTar(f File, compression uint64) Artifact {
	return &tarArtifact{id: KindTar.Ident(
		binary.LittleEndian.AppendUint64(nil, compression), f,
	), f: f, compression: compression, c: c}
}

// NewHTTPGetTar is abbreviation for NewHTTPGet passed to NewTar.
func (c *Cache) NewHTTPGetTar(
	ctx context.Context,
	hc *http.Client,
	url string,
	checksum Checksum,
	compression uint64,
) (Artifact, error) {
	f, err := c.NewHTTPGet(ctx, hc, url, checksum)
	if err != nil {
		return nil, err
	}
	return c.NewTar(f, compression), nil
}

// Kind returns the hardcoded [Kind] constant.
func (a *tarArtifact) Kind() Kind { return KindTar }

// ID returns the identifier prepared ahead of time.
func (a *tarArtifact) ID() ID { return a.id }

// Hash cures the [Artifact] and returns its hash.
func (a *tarArtifact) Hash() (Checksum, error) {
	_, err := a.Pathname()
	return a.checksum, err
}

// A DisallowedTypeflagError describes a disallowed typeflag encountered while
// unpacking a tarball.
type DisallowedTypeflagError byte

func (e DisallowedTypeflagError) Error() string {
	return "disallowed typeflag '" + string(e) + "'"
}

// Pathname cures the [Artifact] and returns its pathname in the [Cache].
func (a *tarArtifact) Pathname() (*check.Absolute, error) {
	a.mu.Lock()
	defer a.mu.Unlock()

	if a.pathname != nil {
		return a.pathname, nil
	}

	pathname, _, err := a.c.Store(a.id, func(work *check.Absolute) (err error) {
		var tr io.ReadCloser

		{
			var data []byte
			data, err = a.f.Data()
			if err != nil {
				return
			}
			tr = io.NopCloser(bytes.NewReader(data))
		}

		defer func() {
			closeErr := tr.Close()
			if err == nil {
				err = closeErr
			}
		}()

		switch a.compression {
		case TarUncompressed:
			break

		case TarGzip:
			if tr, err = gzip.NewReader(tr); err != nil {
				return
			}
			break

		default:
			return os.ErrInvalid
		}

		type dirTargetPerm struct {
			path *check.Absolute
			mode fs.FileMode
		}
		var madeDirectories []dirTargetPerm

		var header *tar.Header
		r := tar.NewReader(tr)
		for header, err = r.Next(); err == nil; header, err = r.Next() {
			typeflag := header.Typeflag
			for {
				switch typeflag {
				case 0:
					if len(header.Name) > 0 && header.Name[len(header.Name)-1] == '/' {
						typeflag = tar.TypeDir
					} else {
						typeflag = tar.TypeReg
					}
					continue

				case tar.TypeReg:
					var f *os.File
					if f, err = os.OpenFile(
						work.Append(header.Name).String(),
						os.O_CREATE|os.O_EXCL|os.O_WRONLY,
						header.FileInfo().Mode()&0400,
					); err != nil {
						return
					}
					if _, err = io.Copy(f, r); err != nil {
						_ = f.Close()
						return
					} else if err = f.Close(); err != nil {
						return
					}
					break

				case tar.TypeLink:
					if err = os.Link(
						header.Linkname,
						work.Append(header.Name).String(),
					); err != nil {
						return
					}
					break

				case tar.TypeSymlink:
					if err = os.Symlink(
						header.Linkname,
						work.Append(header.Name).String(),
					); err != nil {
						return
					}
					break

				case tar.TypeDir:
					pathname := work.Append(header.Name)
					madeDirectories = append(madeDirectories, dirTargetPerm{
						path: pathname,
						mode: header.FileInfo().Mode(),
					})
					if err = os.MkdirAll(
						pathname.String(),
						0700,
					); err != nil {
						return
					}
					break

				default:
					return DisallowedTypeflagError(typeflag)
				}

				break
			}
		}
		if errors.Is(err, io.EOF) {
			err = nil
		}

		if err == nil {
			for _, e := range madeDirectories {
				if err = os.Chmod(e.path.String(), e.mode&0500); err != nil {
					return
				}
			}
			err = os.Chmod(work.String(), 0500)
		}
		return
	}, &a.checksum, false)
	if err != nil {
		return nil, err
	}

	a.pathname = pathname
	return pathname, nil
}