package bnp

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

	abiv1 "git.dev.alexdunmow.com/block/core/abi/v1"
	"github.com/klauspost/compress/zstd"
	"google.golang.org/protobuf/proto"
)

// These constants and the validation flow below are a DELIBERATE duplication
// of the CMS reader (cms backend/plugin/bnp/reader.go, WO-WZ-008). core cannot
// import the CMS module, so `ninja plugin verify` re-implements the same gate a
// publisher's artifact will meet at load time. WO-WZ-010's integration suite
// keeps the two copies in lockstep; change both together.
const (
	// supportedABIMajor is the ABI major version a host understands.
	supportedABIMajor uint32 = 1
	// maxArtifactBytes caps total decompressed size (matches the registry
	// publish cap, 1 GiB) to bound a decompression bomb.
	maxArtifactBytes int64 = 1 << 30
	// maxEntryBytes caps a single extracted file.
	maxEntryBytes int64 = 512 * 1024 * 1024
)

// VerifyResult reports what a valid artifact contains.
type VerifyResult struct {
	Name          string
	Version       string
	ABIVersion    uint32
	DataDir       bool
	BlockCount    int
	HasMigrations bool
	HasSchemas    bool
	HasAssets     bool
	HasWeb        bool
}

// Verify extracts bnpPath into a temp dir and applies the reader's checks:
// path-safety + size caps on extraction, required members present, manifest
// decodes, abi major supported, non-empty name, and manifest name == plugin.mod
// name. The temp dir is always cleaned up. A named error is returned for each
// malformed class.
func Verify(bnpPath string) (*VerifyResult, error) {
	destDir, err := os.MkdirTemp("", "ninja-verify-*")
	if err != nil {
		return nil, fmt.Errorf("bnp: temp dir: %w", err)
	}
	defer func() { _ = os.RemoveAll(destDir) }()

	f, err := os.Open(bnpPath)
	if err != nil {
		return nil, fmt.Errorf("bnp: open %s: %w", bnpPath, err)
	}
	defer func() { _ = f.Close() }()

	if err := extractTarZst(f, destDir); err != nil {
		return nil, err
	}

	for _, req := range []string{fileWasm, fileMod, fileManifest} {
		if !fileRegular(filepath.Join(destDir, req)) {
			return nil, fmt.Errorf("bnp: artifact missing required %s", req)
		}
	}

	manifestBytes, err := os.ReadFile(filepath.Join(destDir, fileManifest))
	if err != nil {
		return nil, fmt.Errorf("bnp: read manifest.pb: %w", err)
	}
	manifest := &abiv1.PluginManifest{}
	if err := proto.Unmarshal(manifestBytes, manifest); err != nil {
		return nil, fmt.Errorf("bnp: decode manifest.pb: %w", err)
	}
	if v := manifest.GetAbiVersion(); v != supportedABIMajor {
		return nil, fmt.Errorf("bnp: unsupported abi_version %d (host supports %d)", v, supportedABIMajor)
	}
	name := manifest.GetName()
	if name == "" {
		return nil, errors.New("bnp: manifest has empty name")
	}

	modBytes, err := os.ReadFile(filepath.Join(destDir, fileMod))
	if err != nil {
		return nil, fmt.Errorf("bnp: read plugin.mod: %w", err)
	}
	modName := parseModName(modBytes)
	if modName == "" {
		return nil, errors.New("bnp: plugin.mod has no name")
	}
	if modName != name {
		return nil, fmt.Errorf("bnp: manifest name %q != plugin.mod name %q", name, modName)
	}

	return &VerifyResult{
		Name:          name,
		Version:       manifest.GetVersion(),
		ABIVersion:    manifest.GetAbiVersion(),
		DataDir:       manifest.GetDataDir(),
		BlockCount:    len(manifest.GetBlocks()),
		HasMigrations: dirExists(filepath.Join(destDir, "migrations")),
		HasSchemas:    dirExists(filepath.Join(destDir, "schemas")),
		HasAssets:     dirExists(filepath.Join(destDir, "assets")),
		HasWeb:        dirExists(filepath.Join(destDir, "web")),
	}, nil
}

// ReadManifest extracts a .bnp into a temp dir (with the same path-safety and
// size caps as Verify) and returns its decoded manifest.pb. It does not enforce
// the name-match / abi checks — use Verify for the full gate.
func ReadManifest(bnpPath string) (*abiv1.PluginManifest, error) {
	destDir, err := os.MkdirTemp("", "ninja-manifest-*")
	if err != nil {
		return nil, fmt.Errorf("bnp: temp dir: %w", err)
	}
	defer func() { _ = os.RemoveAll(destDir) }()

	f, err := os.Open(bnpPath)
	if err != nil {
		return nil, fmt.Errorf("bnp: open %s: %w", bnpPath, err)
	}
	defer func() { _ = f.Close() }()
	if err := extractTarZst(f, destDir); err != nil {
		return nil, err
	}
	b, err := os.ReadFile(filepath.Join(destDir, fileManifest))
	if err != nil {
		return nil, fmt.Errorf("bnp: read manifest.pb: %w", err)
	}
	m := &abiv1.PluginManifest{}
	if err := proto.Unmarshal(b, m); err != nil {
		return nil, fmt.Errorf("bnp: decode manifest.pb: %w", err)
	}
	return m, nil
}

// extractTarZst streams a zstd-compressed tar into destDir, rejecting
// non-regular entries, absolute/traversal paths, and enforcing size caps.
func extractTarZst(r io.Reader, destDir string) error {
	zr, err := zstd.NewReader(r)
	if err != nil {
		return fmt.Errorf("bnp: open zstd stream: %w", err)
	}
	defer zr.Close()

	tr := tar.NewReader(zr)
	var total int64
	root, err := filepath.Abs(destDir)
	if err != nil {
		return fmt.Errorf("bnp: resolve dest: %w", err)
	}

	for {
		hdr, err := tr.Next()
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			return fmt.Errorf("bnp: read tar: %w", err)
		}

		switch hdr.Typeflag {
		case tar.TypeReg, tar.TypeDir:
		default:
			return fmt.Errorf("bnp: rejected non-regular entry %q (type %d)", hdr.Name, hdr.Typeflag)
		}

		target, err := safeJoin(root, hdr.Name)
		if err != nil {
			return err
		}

		if hdr.Typeflag == tar.TypeDir {
			if err := os.MkdirAll(target, 0o755); err != nil {
				return fmt.Errorf("bnp: mkdir %q: %w", hdr.Name, err)
			}
			continue
		}

		if hdr.Size > maxEntryBytes {
			return fmt.Errorf("bnp: entry %q exceeds per-file cap (%d > %d)", hdr.Name, hdr.Size, maxEntryBytes)
		}
		if total+hdr.Size > maxArtifactBytes {
			return fmt.Errorf("bnp: artifact exceeds total size cap (%d)", maxArtifactBytes)
		}
		if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
			return fmt.Errorf("bnp: mkdir for %q: %w", hdr.Name, err)
		}
		n, err := writeExtractedFile(target, io.LimitReader(tr, maxArtifactBytes-total))
		if err != nil {
			return fmt.Errorf("bnp: extract %q: %w", hdr.Name, err)
		}
		total += n
		if total > maxArtifactBytes {
			return fmt.Errorf("bnp: artifact exceeds total size cap (%d)", maxArtifactBytes)
		}
	}
	return nil
}

// safeJoin joins a relative tar entry onto root, rejecting absolute paths and
// traversal segments.
func safeJoin(root, name string) (string, error) {
	norm := strings.ReplaceAll(name, `\`, "/")
	if norm == "" || norm == "." {
		return "", fmt.Errorf("bnp: empty entry name %q", name)
	}
	if filepath.IsAbs(name) || strings.HasPrefix(norm, "/") {
		return "", fmt.Errorf("bnp: absolute entry path %q rejected", name)
	}
	for _, seg := range strings.Split(norm, "/") {
		if seg == ".." {
			return "", fmt.Errorf("bnp: entry %q contains a traversal segment", name)
		}
	}
	target := filepath.Join(root, filepath.Clean(norm))
	rel, err := filepath.Rel(root, target)
	if err != nil || rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
		return "", fmt.Errorf("bnp: entry %q escapes artifact root", name)
	}
	return target, nil
}

func writeExtractedFile(path string, r io.Reader) (int64, error) {
	out, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
	if err != nil {
		return 0, err
	}
	n, err := io.Copy(out, r)
	closeErr := out.Close()
	if err != nil {
		return n, err
	}
	return n, closeErr
}

func fileRegular(p string) bool {
	fi, err := os.Stat(p)
	return err == nil && fi.Mode().IsRegular()
}

func dirExists(p string) bool {
	fi, err := os.Stat(p)
	return err == nil && fi.IsDir()
}

// parseModName extracts the `name = "..."` value from a plugin.mod body,
// mirroring the reader's tolerant line scan (works whether or not the key sits
// under a [plugin] table).
func parseModName(data []byte) string {
	sc := bufio.NewScanner(bytes.NewReader(data))
	for sc.Scan() {
		after, ok := strings.CutPrefix(strings.TrimSpace(sc.Text()), "name")
		if !ok {
			continue
		}
		val, ok := strings.CutPrefix(strings.TrimSpace(after), "=")
		if !ok {
			continue
		}
		val = strings.Trim(strings.TrimSpace(val), `"`)
		if val != "" {
			return val
		}
	}
	return ""
}