package execenv

import (
	"archive/zip"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
)

// UnpackWheel 把 wheel 解进 site-packages。wheel 是 zip；这里不执行任何入口脚本。
func UnpackWheel(wheelPath, sitePackages string) error {
	zr, err := zip.OpenReader(wheelPath)
	if err != nil {
		return fmt.Errorf("execenv: open wheel: %w", err)
	}
	defer zr.Close()
	if err := os.MkdirAll(sitePackages, 0o755); err != nil {
		return err
	}
	root := filepath.Clean(sitePackages)
	for _, f := range zr.File {
		name := filepath.Clean(f.Name)
		if name == "." || strings.HasPrefix(name, "..") || filepath.IsAbs(name) {
			return fmt.Errorf("execenv: wheel path escapes: %s", f.Name)
		}
		// 安装器脚本不落地，避免把「解包」变成「执行」。
		if strings.Contains(name, ".data/scripts/") {
			continue
		}
		dest := filepath.Join(root, name)
		if !strings.HasPrefix(dest, root+string(os.PathSeparator)) && dest != root {
			return fmt.Errorf("execenv: wheel path escapes: %s", f.Name)
		}
		if f.FileInfo().IsDir() {
			if err := os.MkdirAll(dest, 0o755); err != nil {
				return err
			}
			continue
		}
		if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
			return err
		}
		rc, err := f.Open()
		if err != nil {
			return err
		}
		out, err := os.OpenFile(dest, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o644)
		if err != nil {
			rc.Close()
			return err
		}
		_, cerr := io.Copy(out, rc)
		out.Close()
		rc.Close()
		if cerr != nil {
			return cerr
		}
	}
	return nil
}

// BuildLayer 把已经在 wheelhouse 里的 wheel 解进新层。目录已存在则直接复用。
func (r *Root) BuildLayer(l Lock) (string, error) {
	id, err := r.WriteLock(l)
	if err != nil {
		return "", err
	}
	dest := r.LayerDir(id)
	if st, err := os.Stat(dest); err == nil && st.IsDir() {
		return id, nil
	}
	for _, pkg := range l.Packages {
		wheel := filepath.Join(r.Wheelhouse(), pkg.SHA256+".whl")
		if _, err := os.Stat(wheel); err != nil {
			alt := filepath.Join(r.Wheelhouse(), pkg.Filename)
			if _, err2 := os.Stat(alt); err2 != nil {
				return "", fmt.Errorf("execenv: wheel missing for %s", pkg.Name)
			}
			wheel = alt
		}
		sum, err := fileSHA256(wheel)
		if err != nil {
			return "", err
		}
		if pkg.SHA256 != "" && !strings.EqualFold(sum, pkg.SHA256) {
			return "", fmt.Errorf("execenv: hash mismatch for %s: got %s want %s", pkg.Name, sum, pkg.SHA256)
		}
		if err := UnpackWheel(wheel, dest); err != nil {
			_ = os.RemoveAll(filepath.Dir(dest))
			return "", err
		}
	}
	if err := os.MkdirAll(dest, 0o755); err != nil {
		return "", err
	}
	return id, nil
}

func fileSHA256(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()
	h := sha256New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	return h.Sum(), nil
}