app: add code for macOS and Windows apps under 'app' (#12933)

* app: add code for macOS and Windows apps under 'app'

* app: add readme

* app: windows and linux only for now

* ci: fix ui CI validation

---------

Co-authored-by: jmorganca <jmorganca@gmail.com>

app/dialog/cocoa/dlg_darwin.go

@@ -0,0 +1,183 @@
+package cocoa
+
+// #cgo darwin LDFLAGS: -framework Cocoa
+// #include <stdlib.h>
+// #include <sys/syslimits.h>
+// #include "dlg.h"
+import "C"
+
+import (
+	"bytes"
+	"errors"
+	"unsafe"
+)
+
+type AlertParams struct {
+	p C.AlertDlgParams
+}
+
+func mkAlertParams(msg, title string, style C.AlertStyle) *AlertParams {
+	a := AlertParams{C.AlertDlgParams{msg: C.CString(msg), style: style}}
+	if title != "" {
+		a.p.title = C.CString(title)
+	}
+	return &a
+}
+
+func (a *AlertParams) run() C.DlgResult {
+	return C.alertDlg(&a.p)
+}
+
+func (a *AlertParams) free() {
+	C.free(unsafe.Pointer(a.p.msg))
+	if a.p.title != nil {
+		C.free(unsafe.Pointer(a.p.title))
+	}
+}
+
+func nsStr(s string) unsafe.Pointer {
+	return C.NSStr(unsafe.Pointer(&[]byte(s)[0]), C.int(len(s)))
+}
+
+func YesNoDlg(msg, title string) bool {
+	a := mkAlertParams(msg, title, C.MSG_YESNO)
+	defer a.free()
+	return a.run() == C.DLG_OK
+}
+
+func InfoDlg(msg, title string) {
+	a := mkAlertParams(msg, title, C.MSG_INFO)
+	defer a.free()
+	a.run()
+}
+
+func ErrorDlg(msg, title string) {
+	a := mkAlertParams(msg, title, C.MSG_ERROR)
+	defer a.free()
+	a.run()
+}
+
+const (
+	BUFSIZE             = C.PATH_MAX
+	MULTI_FILE_BUF_SIZE = 32768
+)
+
+// MultiFileDlg opens a file dialog that allows multiple file selection
+func MultiFileDlg(title string, exts []string, relaxExt bool, startDir string, showHidden bool) ([]string, error) {
+	return fileDlgWithOptions(C.LOADDLG, title, exts, relaxExt, startDir, "", showHidden, true)
+}
+
+// FileDlg opens a file dialog for single file selection (kept for compatibility)
+func FileDlg(save bool, title string, exts []string, relaxExt bool, startDir string, filename string, showHidden bool) (string, error) {
+	mode := C.LOADDLG
+	if save {
+		mode = C.SAVEDLG
+	}
+	files, err := fileDlgWithOptions(mode, title, exts, relaxExt, startDir, filename, showHidden, false)
+	if err != nil {
+		return "", err
+	}
+	if len(files) == 0 {
+		return "", nil
+	}
+	return files[0], nil
+}
+
+func DirDlg(title string, startDir string, showHidden bool) (string, error) {
+	files, err := fileDlgWithOptions(C.DIRDLG, title, nil, false, startDir, "", showHidden, false)
+	if err != nil {
+		return "", err
+	}
+	if len(files) == 0 {
+		return "", nil
+	}
+	return files[0], nil
+}
+
+// fileDlgWithOptions is the unified file dialog function that handles both single and multiple selection
+func fileDlgWithOptions(mode int, title string, exts []string, relaxExt bool, startDir, filename string, showHidden, allowMultiple bool) ([]string, error) {
+	// Use larger buffer for multiple files, smaller for single
+	bufSize := BUFSIZE
+	if allowMultiple {
+		bufSize = MULTI_FILE_BUF_SIZE
+	}
+
+	p := C.FileDlgParams{
+		mode: C.int(mode),
+		nbuf: C.int(bufSize),
+	}
+
+	if allowMultiple {
+		p.allowMultiple = C.int(1) // Enable multiple selection //nolint:structcheck
+	}
+	if showHidden {
+		p.showHidden = 1
+	}
+
+	p.buf = (*C.char)(C.malloc(C.size_t(bufSize)))
+	defer C.free(unsafe.Pointer(p.buf))
+	buf := (*(*[MULTI_FILE_BUF_SIZE]byte)(unsafe.Pointer(p.buf)))[:bufSize]
+
+	if title != "" {
+		p.title = C.CString(title)
+		defer C.free(unsafe.Pointer(p.title))
+	}
+	if startDir != "" {
+		p.startDir = C.CString(startDir)
+		defer C.free(unsafe.Pointer(p.startDir))
+	}
+	if filename != "" {
+		p.filename = C.CString(filename)
+		defer C.free(unsafe.Pointer(p.filename))
+	}
+
+	if len(exts) > 0 {
+		if len(exts) > 999 {
+			panic("more than 999 extensions not supported")
+		}
+		ptrSize := int(unsafe.Sizeof(&title))
+		p.exts = (*unsafe.Pointer)(C.malloc(C.size_t(ptrSize * len(exts))))
+		defer C.free(unsafe.Pointer(p.exts))
+		cext := (*(*[999]unsafe.Pointer)(unsafe.Pointer(p.exts)))[:]
+		for i, ext := range exts {
+			cext[i] = nsStr(ext)
+			defer C.NSRelease(cext[i])
+		}
+		p.numext = C.int(len(exts))
+		if relaxExt {
+			p.relaxext = 1
+		}
+	}
+
+	// Execute dialog and parse results
+	switch C.fileDlg(&p) {
+	case C.DLG_OK:
+		if allowMultiple {
+			// Parse multiple null-terminated strings from buffer
+			var files []string
+			start := 0
+			for i := range len(buf) - 1 {
+				if buf[i] == 0 {
+					if i > start {
+						files = append(files, string(buf[start:i]))
+					}
+					start = i + 1
+					// Check for double null (end of list)
+					if i+1 < len(buf) && buf[i+1] == 0 {
+						break
+					}
+				}
+			}
+			return files, nil
+		} else {
+			// Single file - return as array for consistency
+			filename := string(buf[:bytes.Index(buf, []byte{0})])
+			return []string{filename}, nil
+		}
+	case C.DLG_CANCEL:
+		return nil, nil
+	case C.DLG_URLFAIL:
+		return nil, errors.New("failed to get file-system representation for selected URL")
+	}
+	panic("unhandled case")
+}