package virtfs

import (
	"context"
	"os"
	"time"
)

// Standard permission constants for EDSL-built trees.
const (
	PermChildDir     os.FileMode = 0555
	PermIdx          os.FileMode = 0444
	PermMkdir        os.FileMode = 0755
	PermMkdirPrivate os.FileMode = 0700
)

// File is an open handle to a single named blob.
type File interface {
	Stat() (os.FileInfo, error)
	Read() ([]byte, error)
	Write(data []byte) error
	Close() error // called when fid is clunked/closed
	BlockingRead(ctx context.Context, base string) (content []byte, nextBase string, err error)

	// Read-side contracts (mutually exclusive — at most one true):
	//   BlockingReadMode — blocks up to 500ms for next value, returns it or empty, EOF on 2nd read
	//   StreamMode       — blocks indefinitely, streams data incrementally, FD lives until EOF
	//   RdwrMode         — write blocks until result produced, read returns result once
	BlockingReadMode() bool
	StreamMode() bool
	RdwrMode() bool
}

// fileConfig implements File via function pointers.
type fileConfig struct {
	StatFn         func() (os.FileInfo, error)
	ReadFn         func() ([]byte, error)
	WriteFn        func([]byte) error
	CloseFn        func() error
	BlockingReadFn func(context.Context, string) ([]byte, string, error)
	BlockingRead_  bool // one-shot waiter: block 500ms, return once, EOF on 2nd read
	StreamMode_    bool // indefinite stream: block forever, keep FD open
	Rdwr_          bool // rdwr: write blocks on write, read returns result once
}

func (e *fileConfig) Stat() (os.FileInfo, error) { return e.StatFn() }
func (e *fileConfig) Read() ([]byte, error)      { return e.ReadFn() }
func (e *fileConfig) Write(data []byte) error    { return e.WriteFn(data) }
func (e *fileConfig) Close() error {
	if e.CloseFn != nil {
		return e.CloseFn()
	}
	return nil
}
func (e *fileConfig) BlockingRead(ctx context.Context, base string) ([]byte, string, error) {
	return e.BlockingReadFn(ctx, base)
}
func (e *fileConfig) BlockingReadMode() bool { return e.BlockingRead_ }
func (e *fileConfig) StreamMode() bool       { return e.StreamMode_ }
func (e *fileConfig) RdwrMode() bool         { return e.Rdwr_ }

// SyntheticFileInfo implements os.FileInfo for entries with no backing file.
type SyntheticFileInfo struct {
	Name_  string
	Mode_  os.FileMode
	Size_  int64
	IsDir_ bool
	UID_   string
	GID_   string
	Vers_  uint32
}

func (f *SyntheticFileInfo) Name() string       { return f.Name_ }
func (f *SyntheticFileInfo) Size() int64        { return f.Size_ }
func (f *SyntheticFileInfo) Mode() os.FileMode  { return f.Mode_ }
func (f *SyntheticFileInfo) ModTime() time.Time { return time.Time{} }
func (f *SyntheticFileInfo) IsDir() bool        { return f.IsDir_ }
func (f *SyntheticFileInfo) Sys() any           { return nil }

// syntheticEntry implements os.DirEntry for entries with no backing file.
type syntheticEntry struct {
	name  string
	mode  os.FileMode
	isDir bool
}

func (e *syntheticEntry) Name() string { return e.name }
func (e *syntheticEntry) IsDir() bool  { return e.isDir }
func (e *syntheticEntry) Type() os.FileMode {
	if e.isDir {
		return os.ModeDir
	}
	return 0
}
func (e *syntheticEntry) Info() (os.FileInfo, error) {
	return &SyntheticFileInfo{Name_: e.name, Mode_: e.mode, IsDir_: e.isDir}, nil
}

// fileEntry returns a synthetic file DirEntry.
func fileEntry(name string, mode os.FileMode) os.DirEntry {
	return &syntheticEntry{name: name, mode: mode}
}

// dirEntry returns a synthetic directory DirEntry.
func dirEntry(name string, mode os.FileMode) os.DirEntry {
	return &syntheticEntry{name: name, mode: mode, isDir: true}
}