package vfs

import (
    "errors"
    "io/fs"
    "sync"
)

// MultiReader passes {Lstat, ReadDir, OpenFile(flag=O_RDONLY)} down the stack
// and all others are invalid
//
// MultiReader is modeled after [io.MultiReader].
func MultiReader(fsyss ...FS) FS {
    var mu sync.Mutex
    return Filesystem{
        LstatFunc: func(name string) (fs.FileInfo, error) {
            if len(fsyss) == 0 {
                return nil, fs.ErrNotExist
            }

            mu.Lock()
            defer mu.Unlock()

            for _, fsys := range fsyss {
                info, err := fsys.Lstat(name)
                if !errors.Is(err, fs.ErrNotExist) {
                    return info, err
                }
            }

            return nil, fs.ErrNotExist
        },

        ReadDirFunc: func(name string) ([]fs.DirEntry, error) {
            if len(fsyss) == 0 {
                return nil, fs.ErrNotExist
            }

            mu.Lock()
            defer mu.Unlock()

            for _, fsys := range fsyss {
                entries, err := fsys.ReadDir(name)
                if !errors.Is(err, fs.ErrNotExist) {
                    return entries, err
                }
            }

            return nil, fs.ErrNotExist
        },

        OpenFileFunc: func(name string, flag int, perm fs.FileMode) (ReadWriteSyncCloser, error) {
            if len(fsyss) == 0 {
                return nil, fs.ErrNotExist
            } else if flag != O_RDONLY {
                return nil, fs.ErrInvalid
            }

            mu.Lock()
            defer mu.Unlock()

            for _, fsys := range fsyss {
                f, err := fsys.OpenFile(name, flag, perm)
                if !errors.Is(err, fs.ErrNotExist) {
                    return f, err
                }
            }

            return nil, fs.ErrNotExist
        },
    }
}

// WithDevStdin overlays dev/stdin.
//
// BUG(jfrech): 2024-05-21: Not implemented.
func WithDevStdin(fsys FS) FS {
    return fsys

/*
    // TODO(jfrech): 2024-05-21: Implement or expunge.
    return Filesystem{
        LstatFunc: func(name string) (fs.FileInfo, error) {
            if name == "dev/stdin" {
                panic("nyi")
            }

            return fsys.Lstat(name)
        }

        ChmodFunc: func(name string, perm fs.FileMode) error
        MkdirAllFunc: func(name string, perm fs.FileMode) error
        RemoveFunc: func(name string) error
        ReadDirFunc: func(name string) ([]fs.DirEntry, error)
        RenameFunc: func(oldname, newname string) error
        OpenFileFunc: func(name string, flag int, perm fs.FileMode) (ReadWriteSyncCloser, error)

        LstatFunc: func(name string) (fs.FileInfo, error) {
            return nil, fs.ErrNotExist
        },
        OpenFileFunc: func(name string, flag int, perm fs.FileMode) (ReadWriteSyncCloser, error) {
    },
*/
}