diff -r 84a541c6e093 -r e70e855cea89 ui/motif/text.c
--- a/ui/motif/text.c	Wed Mar 26 15:53:43 2014 +0100
+++ b/ui/motif/text.c	Wed Mar 26 22:02:57 2014 +0100
@@ -52,6 +52,16 @@
         value->set = ui_textarea_set;
         value->value = NULL;
         value->obj = text_area;
+        
+        if(!value->undomgr) {
+            value->undomgr = ui_create_undomgr();
+        }
+        
+        XtAddCallback(
+                text_area,
+                XmNmodifyVerifyCallback,
+                (XtCallbackProc)ui_text_modify_callback,
+                value);
     }
     
     return text_area;
@@ -74,3 +84,160 @@
     text->value = NULL;
     XmTextSetString(text->obj, str);
 }
+
+UiUndoMgr* ui_create_undomgr() {
+    UiUndoMgr *mgr = malloc(sizeof(UiUndoMgr));
+    mgr->begin = NULL;
+    mgr->cur = NULL;
+    mgr->length = 0;
+    mgr->event = 1;
+    return mgr;
+}
+
+void ui_text_modify_callback(Widget widget, UiText *value, XtPointer data) {
+    XmTextVerifyCallbackStruct *txv = (XmTextVerifyCallbackStruct*)data;
+    int type = txv->text->length > 0 ? UI_TEXTBUF_INSERT : UI_TEXTBUF_DELETE;
+    UiUndoMgr *mgr = value->undomgr;
+    if(!mgr->event) {
+        return;
+    }
+    
+    char *text = txv->text->ptr;
+    int length = txv->text->length;
+    
+    if(mgr->cur) {
+        UcxList *elm = mgr->cur->next;
+        if(elm) {
+            mgr->cur->next = NULL;
+            while(elm) {
+                elm->prev = NULL;   
+                UcxList *next = elm->next;
+                ui_free_textbuf_op(elm->data);
+                free(elm);
+                elm = next;
+            }
+        }
+        
+        if(type == UI_TEXTBUF_INSERT) {
+            UiTextBufOp *last_op = mgr->cur->data;
+            if(
+                last_op->type == UI_TEXTBUF_INSERT &&
+                ui_check_insertstr(last_op->text, last_op->len, text, length) == 0)
+            {
+                // append text to last op
+                int ln = last_op->len;
+                char *newtext = malloc(ln + length + 1);
+                memcpy(newtext, last_op->text, ln);
+                memcpy(newtext+ln, text, length);
+                newtext[ln+length] = '\0';
+                
+                last_op->text = newtext;
+                last_op->len = ln + length;
+                last_op->end += length;
+
+                return;
+            }
+        }
+    }
+    
+    char *str;
+    if(type == UI_TEXTBUF_INSERT) {
+        str = malloc(length + 1);
+        memcpy(str, text, length);
+        str[length] = 0;
+    } else {
+        length = txv->endPos - txv->startPos;
+        str = malloc(length + 1);
+        XmTextGetSubstring(value->obj, txv->startPos, length, length+1, str);
+    }
+    
+    UiTextBufOp *op = malloc(sizeof(UiTextBufOp));
+    op->type = type;
+    op->start = txv->startPos;
+    op->end = txv->endPos + 1;
+    op->len = length;
+    op->text = str;
+    
+    UcxList *elm = ucx_list_append(NULL, op);
+    mgr->cur = elm;
+    mgr->begin = ucx_list_concat(mgr->begin, elm);
+}
+
+int ui_check_insertstr(char *oldstr, int oldlen, char *newstr, int newlen) {
+    // return 1 if oldstr + newstr are one word
+    
+    int has_space = 0;
+    for(int i=0;i<oldlen;i++) {
+        if(oldstr[i] < 33) {
+            has_space = 1;
+            break;
+        }
+    }
+    
+    for(int i=0;i<newlen;i++) {
+        if(has_space && newstr[i] > 32) {
+            return 1;
+        }
+    }
+    
+    return 0;
+}
+
+void ui_free_textbuf_op(UiTextBufOp *op) {
+    if(op->text) {
+        free(op->text);
+    }
+    free(op);
+}
+
+
+void ui_text_undo(UiText *value) {
+    UiUndoMgr *mgr = value->undomgr;
+    
+    if(mgr->cur) {
+        UiTextBufOp *op = mgr->cur->data;
+        mgr->event = 0;
+        switch(op->type) {
+            case UI_TEXTBUF_INSERT: {
+                XmTextReplace(value->obj, op->start, op->end, "");
+                break;
+            }
+            case UI_TEXTBUF_DELETE: {
+                XmTextInsert(value->obj, op->start, op->text);
+                break;
+            }
+        }
+        mgr->event = 1;
+        mgr->cur = mgr->cur->prev;
+    }
+}
+
+void ui_text_redo(UiText *value) {
+    UiUndoMgr *mgr = value->undomgr;
+    
+    UcxList *elm = NULL;
+    if(mgr->cur) {
+        if(mgr->cur->next) {
+            elm = mgr->cur->next;
+        }
+    } else if(mgr->begin) {
+        elm = mgr->begin;
+    }
+    
+    if(elm) {
+        UiTextBufOp *op = elm->data;
+        mgr->event = 0;
+        switch(op->type) {
+            case UI_TEXTBUF_INSERT: {
+                XmTextInsert(value->obj, op->start, op->text);
+                break;
+            }
+            case UI_TEXTBUF_DELETE: {
+                XmTextReplace(value->obj, op->start, op->end, "");
+                break;
+            }
+        }
+        mgr->event = 1;
+        mgr->cur = elm;
+    }
+}