// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// Low-level file I/O functions using Go's os/syscall packages.
// FOPEN, FCLOSE, FREAD, FWRITE, FSEEK, FCREATE, FERASE, FRENAME,
// CURDIR, DIRCHANGE, DIRECTORY, DISKSPACE

package hbrtl

import (
	"five/hbrt"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"sync"
)

// File handle table — maps Harbour handle (int) to Go *os.File
// Protected by mutex for goroutine safety.
var (
	fileHandles   = map[int]*os.File{}
	nextHandle    = 10 // start from 10, avoid 0-2 (stdin/out/err)
	fileHandlesMu sync.Mutex
)

// File handle helpers (thread-safe)
func allocHandle(f *os.File) int {
	fileHandlesMu.Lock()
	defer fileHandlesMu.Unlock()
	h := nextHandle
	nextHandle++
	fileHandles[h] = f
	return h
}

func getHandle(h int) (*os.File, bool) {
	fileHandlesMu.Lock()
	defer fileHandlesMu.Unlock()
	f, ok := fileHandles[h]
	return f, ok
}

func removeHandle(h int) {
	fileHandlesMu.Lock()
	defer fileHandlesMu.Unlock()
	delete(fileHandles, h)
}

// FOPEN(cFileName [, nMode]) → nHandle | -1
// nMode: 0=read, 1=write, 2=readwrite
func FOpen(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	fname := t.Local(1).AsString()
	mode := 0
	if nParams >= 2 && !t.Local(2).IsNil() {
		mode = t.Local(2).AsInt()
	}

	var flag int
	switch mode & 0x03 {
	case 0:
		flag = os.O_RDONLY
	case 1:
		flag = os.O_WRONLY
	case 2:
		flag = os.O_RDWR
	default:
		flag = os.O_RDONLY
	}

	f, err := os.OpenFile(fname, flag, 0644)
	if err != nil {
		SetFError(2) // file not found
		t.RetInt(-1)
		return
	}

	h := allocHandle(f)
	SetFError(0)
	t.RetInt(int64(h))
}

// FCREATE(cFileName [, nAttr]) → nHandle | -1
func FCreate(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	fname := t.Local(1).AsString()
	f, err := os.Create(fname)
	if err != nil {
		SetFError(3)
		t.RetInt(-1)
		return
	}

	h := allocHandle(f)
	SetFError(0)
	t.RetInt(int64(h))
}

// FCLOSE(nHandle) → lSuccess
func FClose(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()

	h := t.Local(1).AsInt()
	f, ok := getHandle(h)
	if !ok {
		SetFError(6) // invalid handle
		t.RetBool(false)
		return
	}
	err := f.Close()
	removeHandle(h)
	SetFError(0)
	t.RetBool(err == nil)
}

// FREAD(nHandle, @cBuffer, nBytes) → nBytesRead
func FRead(t *hbrt.Thread) {
	t.Frame(3, 0)
	defer t.EndProc()

	h := t.Local(1).AsInt()
	nBytes := t.Local(3).AsInt()

	f, ok := getHandle(h)
	if !ok {
		SetFError(6)
		t.RetInt(0)
		return
	}

	buf := make([]byte, nBytes)
	n, err := f.Read(buf)
	if err != nil && n == 0 {
		SetFError(5)
		t.RetInt(0)
		return
	}

	// In Harbour, the 2nd param is passed by reference and filled.
	// In Five, we return the read data as the return value string.
	// The caller should use: nRead := FRead(h, @cBuf, nLen)
	// For simplicity, we set local 2 if it's a byref.
	SetFError(0)
	t.RetString(string(buf[:n]))
}

// FWRITE(nHandle, cBuffer [, nBytes]) → nBytesWritten
func FWrite(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	h := t.Local(1).AsInt()
	data := t.Local(2).AsString()

	f, ok := getHandle(h)
	if !ok {
		SetFError(6)
		t.RetInt(0)
		return
	}

	buf := []byte(data)
	if nParams >= 3 && !t.Local(3).IsNil() {
		nBytes := t.Local(3).AsInt()
		if nBytes < len(buf) {
			buf = buf[:nBytes]
		}
	}

	n, err := f.Write(buf)
	if err != nil {
		SetFError(5)
	} else {
		SetFError(0)
	}
	t.RetInt(int64(n))
}

// FSEEK(nHandle, nOffset [, nOrigin]) → nNewPos
// nOrigin: 0=begin, 1=current, 2=end
func FSeek(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	h := t.Local(1).AsInt()
	offset := t.Local(2).AsLong()
	origin := 0
	if nParams >= 3 && !t.Local(3).IsNil() {
		origin = t.Local(3).AsInt()
	}

	f, ok := getHandle(h)
	if !ok {
		SetFError(6)
		t.RetInt(0)
		return
	}

	var whence int
	switch origin {
	case 0:
		whence = 0 // io.SeekStart
	case 1:
		whence = 1 // io.SeekCurrent
	case 2:
		whence = 2 // io.SeekEnd
	}

	pos, err := f.Seek(offset, whence)
	if err != nil {
		SetFError(5)
		t.RetInt(0)
		return
	}
	SetFError(0)
	t.RetLong(pos)
}

// FERASE(cFileName) → nResult (0=success, -1=error)
func FErase(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()

	fname := t.Local(1).AsString()
	err := os.Remove(fname)
	if err != nil {
		SetFError(2)
		t.RetInt(-1)
		return
	}
	SetFError(0)
	t.RetInt(0)
}

// FRENAME(cOldFile, cNewFile) → nResult (0=success, -1=error)
func FRename(t *hbrt.Thread) {
	t.Frame(2, 0)
	defer t.EndProc()

	oldName := t.Local(1).AsString()
	newName := t.Local(2).AsString()
	err := os.Rename(oldName, newName)
	if err != nil {
		SetFError(2)
		t.RetInt(-1)
		return
	}
	SetFError(0)
	t.RetInt(0)
}

// CURDIR([cDrive]) → cCurrentDir
func CurDir(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	dir, err := os.Getwd()
	if err != nil {
		t.RetString("")
		return
	}
	// Remove leading separator (Harbour convention)
	if len(dir) > 0 && (dir[0] == '/' || dir[0] == '\\') {
		dir = dir[1:]
	}
	t.RetString(dir)
}

// DIRCHANGE(cNewDir) → nResult (0=success, -1=error)
func DirChange(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()

	dir := t.Local(1).AsString()
	err := os.Chdir(dir)
	if err != nil {
		t.RetInt(-1)
		return
	}
	t.RetInt(0)
}

// DIRECTORY(cDirSpec [, cAttr]) → aFiles
// Returns array of {cName, nSize, cDate, cTime, cAttr}
func Directory(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	spec := t.Local(1).AsString()
	dir := filepath.Dir(spec)
	pattern := filepath.Base(spec)

	if dir == "" {
		dir = "."
	}

	entries, err := os.ReadDir(dir)
	if err != nil {
		t.RetVal(hbrt.MakeArray(0))
		return
	}

	var items []hbrt.Value
	for _, e := range entries {
		name := e.Name()
		matched, _ := filepath.Match(pattern, name)
		if !matched && pattern != "*" && pattern != "*.*" {
			continue
		}

		info, err := e.Info()
		if err != nil {
			continue
		}

		// {cName, nSize, cDate, cTime, cAttr}
		modTime := info.ModTime()
		dateStr := modTime.Format("2006-01-02")
		timeStr := modTime.Format("15:04:05")
		attrStr := fileAttrStr(info.Mode())

		entry := []hbrt.Value{
			hbrt.MakeString(name),
			hbrt.MakeNumInt(info.Size()),
			hbrt.MakeString(dateStr),
			hbrt.MakeString(timeStr),
			hbrt.MakeString(attrStr),
		}
		items = append(items, hbrt.MakeArrayFrom(entry))
	}

	if len(items) == 0 {
		t.RetVal(hbrt.MakeArray(0))
	} else {
		t.RetVal(hbrt.MakeArrayFrom(items))
	}
}

func fileAttrStr(mode fs.FileMode) string {
	var s strings.Builder
	if mode.IsDir() {
		s.WriteByte('D')
	}
	if mode&0200 == 0 {
		s.WriteByte('R') // read-only
	}
	if strings.HasPrefix(filepath.Base(mode.String()), ".") {
		s.WriteByte('H') // hidden (unix convention)
	}
	if s.Len() == 0 {
		return ""
	}
	return s.String()
}