package agent

import (
	"errors"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"syscall"

	"github.com/x-grk/longpolling-remote-access/internal/proto"
)

// fsCopy copies or moves Src to Dst, following Conflict when Dst exists.
func fsCopy(a proto.FSCopyArgs) (any, error) {
	src, dst := filepath.Clean(a.Src), filepath.Clean(a.Dst)
	if a.Src == "" || a.Dst == "" {
		return nil, errors.New("не указан путь")
	}
	if src == dst {
		return nil, errors.New("откуда и куда - одно и то же")
	}
	if strings.HasPrefix(dst, src+string(filepath.Separator)) {
		return nil, errors.New("нельзя положить папку внутрь неё самой")
	}
	if _, err := os.Lstat(src); err != nil {
		return nil, err
	}
	if _, err := os.Stat(filepath.Dir(dst)); err != nil {
		return nil, fmt.Errorf("нет папки %s", filepath.Dir(dst))
	}
	c := &copier{move: a.Move, conflict: a.Conflict}
	if err := c.place(src, dst); err != nil {
		return map[string]int{"done": c.done, "skipped": c.skipped}, err
	}
	return map[string]int{"done": c.done, "skipped": c.skipped}, nil
}

type copier struct {
	move          bool
	conflict      string
	done, skipped int
}

// place puts src at dst. Two folders merge when the rule allows it; anything
// else that is in the way stops, is replaced or is kept, by the rule.
func (c *copier) place(src, dst string) error {
	si, err := os.Lstat(src)
	if err != nil {
		return err
	}
	di, err := os.Lstat(dst)
	if err == nil {
		if c.conflict != "replace" && c.conflict != "skip" {
			return fmt.Errorf("%s уже существует", dst)
		}
		if si.IsDir() && di.IsDir() {
			entries, err := os.ReadDir(src)
			if err != nil {
				return err
			}
			for _, e := range entries {
				if err := c.place(filepath.Join(src, e.Name()), filepath.Join(dst, e.Name())); err != nil {
					return err
				}
			}
			if c.move {
				// Whatever was skipped stays where it was.
				_ = os.Remove(src)
			}
			return nil
		}
		if c.conflict == "skip" {
			c.skipped++
			return nil
		}
		if err := os.RemoveAll(dst); err != nil {
			return err
		}
	} else if !errors.Is(err, fs.ErrNotExist) {
		return err
	}
	if c.move {
		err := os.Rename(src, dst)
		if err == nil {
			c.done++
			return nil
		}
		// Another file system: copy, then take the original away.
		if !errors.Is(err, syscall.EXDEV) {
			return err
		}
		if err := c.copyTree(src, dst); err != nil {
			return err
		}
		return os.RemoveAll(src)
	}
	return c.copyTree(src, dst)
}

// copyTree copies a file, a symlink or a whole folder, keeping modes and
// times.
func (c *copier) copyTree(src, dst string) error {
	return filepath.WalkDir(src, func(p string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		rel, _ := filepath.Rel(src, p)
		to := filepath.Join(dst, rel)
		info, err := os.Lstat(p)
		if err != nil {
			return err
		}
		switch {
		case info.Mode()&fs.ModeSymlink != 0:
			link, err := os.Readlink(p)
			if err != nil {
				return err
			}
			if err := os.Symlink(link, to); err != nil {
				return err
			}
		case info.IsDir():
			if err := os.Mkdir(to, info.Mode().Perm()); err != nil && !errors.Is(err, fs.ErrExist) {
				return err
			}
		case info.Mode().IsRegular():
			if err := copyFile(p, to, info); err != nil {
				return err
			}
		default:
			return nil // sockets, devices: not copied
		}
		c.done++
		if st, ok := info.Sys().(*syscall.Stat_t); ok {
			_ = os.Lchown(to, int(st.Uid), int(st.Gid))
		}
		if info.Mode()&fs.ModeSymlink == 0 {
			_ = os.Chtimes(to, info.ModTime(), info.ModTime())
		}
		return nil
	})
}

func copyFile(src, dst string, info fs.FileInfo) error {
	in, err := os.Open(src)
	if err != nil {
		return err
	}
	defer in.Close()
	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, info.Mode().Perm())
	if err != nil {
		return err
	}
	if _, err := io.Copy(out, in); err != nil {
		out.Close()
		os.Remove(dst)
		return err
	}
	if err := out.Close(); err != nil {
		return err
	}
	return os.Chmod(dst, info.Mode()&(fs.ModePerm|fs.ModeSetuid|fs.ModeSetgid|fs.ModeSticky))
}