package binary

import (
	"archive/tar"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"github.com/klauspost/compress/zstd"

	"git.spectoria.dev/huntedbytheirs/zeta-reconstruct/internal/depmap"
	"git.spectoria.dev/huntedbytheirs/zeta-reconstruct/internal/registry"
	"git.spectoria.dev/huntedbytheirs/zeta-reconstruct/internal/tarball"
	"git.spectoria.dev/huntedbytheirs/zeta-reconstruct/internal/zeta"
)

// rootMetadata is the set of Arch metadata members that live at the ROOT of
// a .pkg.tar.zst and are never part of the installed payload. Only these
// names at the root are skipped; a dot-file with the same name deeper in the
// tree is real content.
var rootMetadata = map[string]bool{
	".PKGINFO":   true,
	".BUILDINFO": true,
	".MTREE":     true,
	".INSTALL":   true,
	".Changelog": true,
}

// Convert converts an Arch binary package (.pkg.tar.zst) into a Zeta binary
// package:
//
//  1. Open input with a zstd reader and walk the tar members.
//  2. Read and parse the .PKGINFO member (member name ".PKGINFO" or
//     "./.PKGINFO"). Its pkgver is the Zeta version, verbatim (epoch+pkgrel
//     form, e.g. "1.0-1").
//  3. Extract every other member (root dot-metadata skipped) into a temp dir,
//     preserving paths, modes and symlinks.
//  4. Repack the payload with tarball.Write into
//     <out>/packages/<name>/<name>-<version>.tar.gz.
//  5. Emit an archive-mode package.lua next to the tarball, with depends
//     mapped through depmap.MapDep.
//
// An epoch (":" in pkgver) is warned about and never folded: Zeta versioning
// cannot represent it.
func Convert(input string, opts registry.Options) error {
	f, err := os.Open(input)
	if err != nil {
		return fmt.Errorf("convert: open %s: %w", input, err)
	}
	zr, err := zstd.NewReader(f)
	if err != nil {
		_ = f.Close()
		return fmt.Errorf("convert: zstd %s: %w", input, err)
	}
	defer func() {
		zr.Close()
		_ = f.Close()
	}()
	tr := tar.NewReader(zr)

	warn := func(msg string) { fmt.Fprintf(os.Stderr, "warning: %s\n", msg) }

	extracted, err := os.MkdirTemp("", "zr-arch-binary-*")
	if err != nil {
		return fmt.Errorf("convert: temp dir: %w", err)
	}
	defer os.RemoveAll(extracted)

	var info *PKGInfo
	for {
		hdr, err := tr.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return fmt.Errorf("convert: read %s: %w", input, err)
		}

		name := cleanMemberName(hdr.Name)

		// Root dot-metadata: never extracted. .PKGINFO is read from the
		// stream here; the other four are skipped without reading.
		if isRootMetadata(name) {
			if name == ".PKGINFO" {
				content, err := io.ReadAll(tr)
				if err != nil {
					return fmt.Errorf("convert: read .PKGINFO: %w", err)
				}
				info, err = Parse(string(content), warn)
				if err != nil {
					return fmt.Errorf("convert: parse .PKGINFO: %w", err)
				}
			}
			continue
		}

		if err := extractMember(extracted, name, hdr, tr); err != nil {
			return err
		}
	}

	if info == nil {
		return errors.New("convert: archive has no .PKGINFO member")
	}
	if info.Name == "" {
		return errors.New("convert: .PKGINFO has no pkgname")
	}

	if strings.Contains(info.Version, ":") {
		warn(fmt.Sprintf("package %s has epoch in version; epoch is not representable in Zeta versioning", info.Name))
	}

	// Deps: map each declared dependency through the Arch→Zeta name map.
	// Dropped deps are skipped (MapDep already warned).
	var deps []string
	for _, d := range info.Depends {
		if mapped, ok := depmap.MapDep(d, warn); ok {
			deps = append(deps, mapped)
		}
	}

	pkgDir := filepath.Join(opts.Output, "packages", info.Name)
	if err := os.MkdirAll(pkgDir, 0o755); err != nil {
		return fmt.Errorf("convert: mkdir %s: %w", pkgDir, err)
	}

	tarballPath := filepath.Join(pkgDir, info.Name+"-"+info.Version+".tar.gz")
	sum, err := tarball.Write(extracted, tarballPath)
	if err != nil {
		return fmt.Errorf("convert: repack payload: %w", err)
	}

	m := &zeta.Manifest{
		Name:    info.Name,
		Version: info.Version,
		Summary: info.Desc,
		URL:     opts.Repo + "/packages/" + info.Name + "/" + info.Name + "-" + info.Version + ".tar.gz",
		SHA256:  sum,
		Deps:    deps,
		Archive: &zeta.Archive{Strip: 1},
	}

	src, err := m.Emit()
	if err != nil {
		return fmt.Errorf("convert: emit manifest: %w", err)
	}
	manifestPath := filepath.Join(pkgDir, "package.lua")
	if err := os.WriteFile(manifestPath, []byte(src), 0o644); err != nil {
		return fmt.Errorf("convert: write %s: %w", manifestPath, err)
	}
	return nil
}

// cleanMemberName strips the "./" prefix (and any leading slashes) GNU tar
// prepends, yielding the canonical root-relative member name.
func cleanMemberName(name string) string {
	for strings.HasPrefix(name, "./") {
		name = name[2:]
	}
	return name
}

// isRootMetadata reports whether name is one of the Arch metadata members at
// the ROOT of the archive (no directory component).
func isRootMetadata(name string) bool {
	if name == "" || name == "." {
		return false
	}
	if strings.Contains(name, "/") {
		return false
	}
	return rootMetadata[name]
}

// extractMember extracts a single tar member under root, preserving paths,
// modes and symlinks. Directories are created; hard links, FIFOs and device
// nodes are skipped, matching tarball.Write's policy.
func extractMember(root, name string, hdr *tar.Header, r io.Reader) error {
	if name == "" || name == "." {
		return nil // the archive root entry itself
	}
	if strings.HasPrefix(name, "/") || !relativeInside(name) {
		return fmt.Errorf("convert: member %q escapes the extraction root", name)
	}

	target := filepath.Join(root, filepath.FromSlash(name))
	switch hdr.Typeflag {
	case tar.TypeDir:
		mode := os.FileMode(hdr.Mode).Perm()
		if mode == 0 {
			mode = 0o755
		}
		return os.MkdirAll(target, mode)

	case tar.TypeReg, tar.TypeRegA:
		if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
			return err
		}
		mode := os.FileMode(hdr.Mode).Perm()
		if mode == 0 {
			mode = 0o644
		}
		_ = os.Remove(target) // never write through a pre-existing symlink
		f, err := os.OpenFile(target, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
		if err != nil {
			return fmt.Errorf("convert: extract %s: %w", name, err)
		}
		if _, err := io.Copy(f, r); err != nil {
			_ = f.Close()
			return fmt.Errorf("convert: extract %s: %w", name, err)
		}
		return f.Close()

	case tar.TypeSymlink:
		if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
			return err
		}
		_ = os.Remove(target)
		if err := os.Symlink(hdr.Linkname, target); err != nil {
			return fmt.Errorf("convert: extract symlink %s: %w", name, err)
		}
		return nil

	default:
		// Hard links, FIFOs, devices, sparse files: skipped like the
		// repack step.
		return nil
	}
}

// relativeInside reports whether the slash-separated relative path p never
// climbs above its root. Port of ZETA/lib/path.lua relative_inside.
func relativeInside(p string) bool {
	depth := 0
	for _, seg := range strings.Split(p, "/") {
		switch seg {
		case "..":
			depth--
			if depth < 0 {
				return false
			}
		case "", ".":
		default:
			depth++
		}
	}
	return true
}