ui_actions.cpp

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/*
Copyright (C) 2002-2020 UFO: Alien Invasion.

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

*/

#include "ui_main.h"
#include "ui_internal.h"
#include "ui_parse.h"
#include "ui_input.h"
#include "ui_node.h"
#include "ui_actions.h"
#include "ui_lua.h"
#include "node/ui_node_abstractnode.h"

#include "../cl_language.h"

typedef struct ui_typedActionToken_s {
    const char* token;
    int type;
    int group;
} ui_typedActionToken_t;

static const ui_typedActionToken_t actionTokens[] = {

    /* 0x2x */
    {"!", EA_OPERATOR_NOT, EA_UNARYOPERATOR},
    {"!=", EA_OPERATOR_NE, EA_BINARYOPERATOR},
    {"%", EA_OPERATOR_MOD, EA_BINARYOPERATOR},
    {"&&", EA_OPERATOR_AND, EA_BINARYOPERATOR},
    {"*", EA_OPERATOR_MUL, EA_BINARYOPERATOR},
    {"+", EA_OPERATOR_ADD, EA_BINARYOPERATOR},
    {"-", EA_OPERATOR_SUB, EA_BINARYOPERATOR},
    {"/", EA_OPERATOR_DIV, EA_BINARYOPERATOR},

    /* 0x3x */
    {"<", EA_OPERATOR_LT, EA_BINARYOPERATOR},
    {"<=", EA_OPERATOR_LE, EA_BINARYOPERATOR},
    {"==", EA_OPERATOR_EQ, EA_BINARYOPERATOR},
    {">", EA_OPERATOR_GT, EA_BINARYOPERATOR},
    {">=", EA_OPERATOR_GE, EA_BINARYOPERATOR},

    /* 0x5x */
    {"^", EA_OPERATOR_XOR, EA_BINARYOPERATOR},

    /* 'a'..'z' */
    {"and", EA_OPERATOR_AND, EA_BINARYOPERATOR},
    {"break", EA_BREAK, EA_ACTION},
    {"call", EA_CALL, EA_ACTION},
    {"cmd", EA_CMD, EA_ACTION},
    {"delete", EA_DELETE, EA_ACTION},
    {"elif", EA_ELIF, EA_ACTION},
    {"else", EA_ELSE, EA_ACTION},
    {"eq", EA_OPERATOR_STR_EQ, EA_BINARYOPERATOR},
    {"exists", EA_OPERATOR_EXISTS, EA_UNARYOPERATOR},
    {"forchildin", EA_FORCHILDIN, EA_ACTION},
    {"if", EA_IF, EA_ACTION},
    {"ne", EA_OPERATOR_STR_NE, EA_BINARYOPERATOR},
    {"not", EA_OPERATOR_NOT, EA_UNARYOPERATOR},
    {"or", EA_OPERATOR_OR, EA_BINARYOPERATOR},
    {"while", EA_WHILE, EA_ACTION},

    /* 0x7x */
    {"||", EA_OPERATOR_OR, EA_BINARYOPERATOR},
};

static void UI_ExecuteActions(const uiAction_t* firstAction, uiCallContext_t* context);

static void UI_CheckActionTokenTypeSanity (void)
{
    for (int i = 0; i < lengthof(actionTokens) - 1; i++) {
        const char* a = actionTokens[i].token;
        const char* b = actionTokens[i + 1].token;
        if (strcmp(a, b) >= 0) {
            Sys_Error("UI_CheckActionTokenTypeSanity: '%s' is before '%s'. actionList must be sorted by alphabet", a, b);
        }
    }
}

int UI_GetActionTokenType (const char* token, int group)
{
    unsigned char min = 0;
    unsigned char max = lengthof(actionTokens);

    while (min != max) {
        const int mid = (min + max) >> 1;
        const int diff = strcmp(actionTokens[mid].token, token);
        assert(mid < max);
        assert(mid >= min);

        if (diff == 0) {
            if (actionTokens[mid].group == group)
                return actionTokens[mid].type;
            else
                return EA_NULL;
        }

        if (diff > 0)
            max = mid;
        else
            min = mid + 1;
    }
    return EA_NULL;
}

static inline const char* UI_GenCommandReadProperty (const char* input, char* output, int outputSize)
{
    assert(input[0] == '<');
    outputSize--;
    input++;

    while (outputSize && *input != '\0' && *input != ' ' && *input != '>') {
        *output++ = *input++;
        outputSize--;
    }

    if (input[0] != '>')
        return nullptr;

    output[0] = '\0';
    return ++input;
}

int UI_GetParamNumber (const uiCallContext_t* context)
{
    if (context->useCmdParam)
        return Cmd_Argc() - 1;
    return context->paramNumber;
}

const char* UI_GetParam (const uiCallContext_t* context, int paramID)
{
    linkedList_t* current;
    assert(paramID >= 1);

    if (context->useCmdParam)
        return Cmd_Argv(paramID);

    if (paramID > context->paramNumber) {
        Com_Printf("UI_GetParam: %i out of range\n", paramID);
        return "";
    }

    current = context->params;
    while (paramID > 1) {
        current = current->next;
        paramID--;
    }

    return (const char*) current->data;
}

const char* UI_GenInjectedString (const char* input, bool addNewLine, const uiCallContext_t* context)
{
    static char cmd[256];
    int length = sizeof(cmd) - (addNewLine ? 2 : 1);
    static char propertyName[256];
    const char* cin = input;
    char* cout = cmd;

    while (length && cin[0] != '\0') {
        if (cin[0] == '<') {
            /* read propertyName between '<' and '>' */
            const char* next = UI_GenCommandReadProperty(cin, propertyName, sizeof(propertyName));
            if (next) {
                /* cvar injection */
                if (char const* const rest = Q_strstart(propertyName, "cvar:")) {
                    cvar_t const* const cvar = Cvar_Get(rest);
                    const int l = snprintf(cout, length, "%s", cvar->string);
                    cout += l;
                    cin = next;
                    length -= l;
                    continue;
                } else if (char const* const path = Q_strstart(propertyName, "node:")) {
                    uiNode_t* node;
                    const value_t* property;
                    const char* string;
                    int l;
                    UI_ReadNodePath(path, context->source, nullptr, &node, &property);
                    if (!node) {
                        Com_Printf("UI_GenInjectedString: Node '%s' wasn't found; '' returned\n", path);
#ifdef DEBUG
                        Com_Printf("UI_GenInjectedString: Path relative to '%s'\n", UI_GetPath(context->source));
#endif
                        string = "";
                    } else if (!property) {
                        Com_Printf("UI_GenInjectedString: Property '%s' wasn't found; '' returned\n", path);
                        string = "";
                    } else {
                        string = UI_GetStringFromNodeProperty(node, property);
                        if (string == nullptr) {
                            Com_Printf("UI_GenInjectedString: String getter for '%s' property do not exists; '' injected\n", path);
                            string = "";
                        }
                    }

                    l = snprintf(cout, length, "%s", string);
                    cout += l;
                    cin = next;
                    length -= l;
                    continue;
                /* source path injection */
                } else if (char const* const command = Q_strstart(propertyName, "path:")) {
                    if (context->source) {
                        const uiNode_t* node = nullptr;
                        if (Q_streq(command, "root"))
                            node = context->source->root;
                        else if (Q_streq(command, "this"))
                            node = context->source;
                        else if (Q_streq(command, "parent"))
                            node = context->source->parent;
                        else
                            Com_Printf("UI_GenCommand: Command '%s' for path injection unknown\n", command);

                        if (node) {
                            const int l = snprintf(cout, length, "%s", UI_GetPath(node));
                            cout += l;
                            cin = next;
                            length -= l;
                            continue;
                        }
                    }

                /* no prefix */
                } else {
                    /* source property injection */
                    if (context->source) {
                        /* find property definition */
                        const value_t* property = UI_GetPropertyFromBehaviour(context->source->behaviour, propertyName);
                        if (property) {
                            const char* value;
                            int l;
                            /* inject the property value */
                            value = UI_GetStringFromNodeProperty(context->source, property);
                            if (value == nullptr)
                                value = "";
                            l = snprintf(cout, length, "%s", value);
                            cout += l;
                            cin = next;
                            length -= l;
                            continue;
                        }
                    }

                    /* param injection */
                    if (UI_GetParamNumber(context) != 0) {
                        int arg;
                        const int checked = sscanf(propertyName, "%d", &arg);
                        if (checked == 1 && arg >= 1 && arg <= UI_GetParamNumber(context)) {
                            const int l = snprintf(cout, length, "%s", UI_GetParam(context, arg));
                            cout += l;
                            cin = next;
                            length -= l;
                            continue;
                        }
                    }
                }
            }
        }
        *cout++ = *cin++;
        length--;
    }

    /* is buffer too small? */
    assert(cin[0] == '\0');

    if (addNewLine)
        *cout++ = '\n';

    *cout++ = '\0';

    /* copy the result into a free va slot */
    return va("%s", cmd);
}

static void UI_NodeSetPropertyFromActionValue (uiNode_t* node, const value_t* property, const uiCallContext_t* context, uiAction_t* value)
{
    /* @todo we can use a new EA_VALUE type to flag already parsed values, we dont need to do it again and again */
    /* pre compute value if possible */
    if (value->type == EA_VALUE_STRING) {
        const char* string = value->d.terminal.d1.constString;
        if ((property->type & V_UI_MASK) == V_UI_CVAR && Q_strstart(string, "*cvar:")) {
            Com_GetValue<void*>(node, property) = value->d.terminal.d1.data;
        } else {
            UI_InitRawActionValue(value, node, property, string);
        }
    }

    /* decode RAW value */
    if (value->type == EA_VALUE_RAW) {
        const void* rawValue = value->d.terminal.d1.constData;
        const int rawType = value->d.terminal.d2.integer;
        UI_NodeSetPropertyFromRAW(node, property, rawValue, rawType);
    }
    /* else it is an expression */
    else {
        const char* string = UI_GetStringFromExpression(value, context);
        UI_NodeSetProperty(node, property, string);
    }
}

static inline void UI_ExecuteSetAction (const uiAction_t* action, const uiCallContext_t* context)
{
    const char* path;
    uiNode_t* node;
    const value_t* property;
    const uiAction_t* left;
    uiAction_t* right;

    left = action->d.nonTerminal.left;
    if (left == nullptr) {
        Com_Printf("UI_ExecuteSetAction: Action without left operand skipped.\n");
        return;
    }

    right = action->d.nonTerminal.right;
    if (right == nullptr) {
        Com_Printf("UI_ExecuteSetAction: Action without right operand skipped.\n");
        return;
    }

    if (left->type == EA_VALUE_CVARNAME || left->type == EA_VALUE_CVARNAME_WITHINJECTION) {
        const char* cvarName;

        if (left->type == EA_VALUE_CVARNAME)
            cvarName = left->d.terminal.d1.constString;
        else
            cvarName = UI_GenInjectedString(left->d.terminal.d1.constString, false, context);

        const char* textValue = CL_Translate(UI_GetStringFromExpression(right, context));
        Cvar_ForceSet(cvarName, textValue);
        return;
    }

    /* search the node */
    if (left->type == EA_VALUE_PATHPROPERTY)
        path = left->d.terminal.d1.constString;
    else if (left->type == EA_VALUE_PATHPROPERTY_WITHINJECTION)
        path = UI_GenInjectedString(left->d.terminal.d1.constString, false, context);
    else
        Com_Error(ERR_FATAL, "UI_ExecuteSetAction: Property setter with wrong type '%d'", left->type);

    /* context->tagNode holds reference to child in iteration loop if applicable */
    UI_ReadNodePath(path, context->source, context->tagNode, &node, &property);
    if (!node) {
        Com_Printf("UI_ExecuteSetAction: node \"%s\" doesn't exist (source: %s)\n", path, UI_GetPath(context->source));
        return;
    }
    if (!property) {
        Com_Printf("UI_ExecuteSetAction: property \"%s\" doesn't exist (source: %s)\n", path, UI_GetPath(context->source));
        return;
    }

    UI_NodeSetPropertyFromActionValue(node, property, context, right);
}

static inline void UI_ExecuteCallAction (const uiAction_t* action, const uiCallContext_t* context)
{
    uiNode_t* callNode = nullptr;
    uiAction_t* param;
    uiAction_t* left = action->d.nonTerminal.left;
    uiCallContext_t newContext;
    const value_t* callProperty = nullptr;
    value_t luaMethod;
    const char* path = left->d.terminal.d1.constString;

    // clear luaMethod structure before using it
    memset(&luaMethod, 0, sizeof(luaMethod));

    if (left->type == EA_VALUE_PATHPROPERTY || left->type == EA_VALUE_PATHNODE)
        path = left->d.terminal.d1.constString;
    else if (left->type == EA_VALUE_PATHPROPERTY_WITHINJECTION || left->type == EA_VALUE_PATHNODE_WITHINJECTION)
        path = UI_GenInjectedString(left->d.terminal.d1.constString, false, context);

    UI_ReadNodePath(path, context->source, context->tagNode, &callNode, &callProperty, &luaMethod);
    if ((callNode == nullptr) && (!luaMethod.type)) {
        Com_Printf("UI_ExecuteCallAction: Node from path \"%s\" not found (relative to \"%s\").\n", path, UI_GetPath(context->source));
        return;
    }
    if (callProperty != nullptr && callProperty->type != V_UI_ACTION && callProperty->type != V_UI_NODEMETHOD && callProperty->type != V_UI_NODEMETHOD_LUA) {
        Com_Printf("UI_ExecuteCallAction: Call operand %d unsupported. (%s)\n", callProperty->type, UI_GetPath(callNode));
        return;
    }

    newContext.source = callNode;
    newContext.params = nullptr;
    newContext.paramNumber = 0;
    newContext.varNumber = 0;
    newContext.varPosition = context->varPosition + context->varNumber;
    newContext.breakLoop = false;

    if (action->type == EA_LISTENER) {
        newContext.useCmdParam = context->useCmdParam;

        if (!newContext.useCmdParam) {
            linkedList_t* p = context->params;
            while (p) {
                const char* value = (char*) p->data;
                LIST_AddString(&newContext.params, value);
                newContext.paramNumber++;
                p = p->next;
            }
        }
    } else {
        newContext.useCmdParam = false;

        param = action->d.nonTerminal.right;
        while (param) {
            const char* value;
            value = UI_GetStringFromExpression(param, context);
            LIST_AddString(&newContext.params, value);
            newContext.paramNumber++;
            param = param->next;
        }
    }

    if (luaMethod.type == V_UI_NODEMETHOD_LUA) {
        UI_ExecuteLuaMethod(callNode, luaMethod.ofs, newContext.params, newContext.paramNumber);
        Mem_Free(const_cast<char*>(luaMethod.string));
    }
    else if (callProperty == nullptr || callProperty->type == V_UI_ACTION) {
        uiAction_t const* const actionsRef = callProperty ? Com_GetValue<uiAction_t*>(callNode, callProperty) : callNode->onClick;
        if (actionsRef)
            UI_ExecuteActions(actionsRef, &newContext);
        if (callNode->lua_onClick != LUA_NOREF) {
            if (newContext.useCmdParam)
                UI_ExecuteLuaConFunc(callNode, callNode->lua_onClick);
            else
                UI_ExecuteLuaMethod(callNode, callNode->lua_onClick, newContext.params, newContext.paramNumber);
        }
    }
    else if (callProperty->type == V_UI_NODEMETHOD) {
        uiNodeMethod_t func = (uiNodeMethod_t) callProperty->ofs;
        func(callNode, &newContext);
    }
    else {
        /* unreachable, already checked few line before */
        assert(false);
    }

    LIST_Delete(&newContext.params);
}

uiValue_t* UI_GetVariable (const uiCallContext_t* context, int relativeVarId)
{
    const int varId = context->varPosition + relativeVarId;
    assert(relativeVarId >= 0);
    assert(relativeVarId < context->varNumber);
    return &(ui_global.variableStack[varId]);
}

static void UI_ReleaseVariable (uiValue_t* variable)
{
    switch (variable->type) {
    case EA_VALUE_STRING:
        UI_FreeStringProperty(variable->value.string);
        break;
    case EA_VALUE_FLOAT:
    case EA_VALUE_NODE:
    case EA_VALUE_CVAR:
        /* nothing */
        break;
    default:
        Com_Error(ERR_FATAL, "UI_ReleaseVariable: Variable type \"%d\" unsupported", variable->type);
    }

    /* bug safe, but useless */
    OBJZERO(*variable);
}

static void UI_ExecuteAction (const uiAction_t* action, uiCallContext_t* context)
{
    switch (action->type) {
    case EA_NULL:
        /* do nothing */
        break;

    case EA_CMD:
        /* execute a command */
        if (action->d.terminal.d1.constString)
            Cbuf_AddText("%s\n", UI_GenInjectedString(action->d.terminal.d1.constString, true, context));
        break;

    case EA_CALL:
    case EA_LISTENER:
        UI_ExecuteCallAction(action, context);
        break;

    case EA_POPVARS:
        {
            const int number = action->d.terminal.d1.integer;
            assert(number <= context->varNumber);
            for (int i = 0; i < number; i++) {
                const int varId = context->varPosition + context->varNumber - i - 1;
                UI_ReleaseVariable(&(ui_global.variableStack[varId]));
            }
            context->varNumber -= number;
        }
        break;

    case EA_PUSHVARS:
#ifdef DEBUG
        /* check sanity */
#endif
        context->varNumber += action->d.terminal.d1.integer;
        if (context->varNumber >= UI_MAX_VARIABLESTACK)
            Com_Error(ERR_FATAL, "UI_ExecuteAction: Variable stack full. UI_MAX_VARIABLESTACK hit.");
        break;

    case EA_ASSIGN:
        UI_ExecuteSetAction(action, context);
        break;

    case EA_DELETE:
        {
            const char* cvarname = action->d.nonTerminal.left->d.terminal.d1.constString;
            Cvar_Delete(cvarname);
            break;
        }

    case EA_WHILE:
        {
            int loop = 0;
            while (UI_GetBooleanFromExpression(action->d.nonTerminal.left, context)) {
                UI_ExecuteActions(action->d.nonTerminal.right, context);
                if (context->breakLoop) {
                    context->breakLoop = false;
                    break;
                }
                if (loop > 1000) {
                    Com_Printf("UI_ExecuteAction: Infinite loop. Force breaking 'while'\n");
                    break;
                }
                loop++;
            }
            break;
        }

    /*
        expected usage in .ufo scripts:

        forchildin ( *node:someNode ) {
            ...
            *node:child  <-- reference the child being iterated
            ...
        }
    */
    case EA_FORCHILDIN:
        {
            uiNode_t* root;
            root = UI_GetNodeFromExpression(action->d.nonTerminal.left, context, nullptr);
            if (!root) {
                break;
            }

            int loop = 0;
            for (uiNode_t* node = root->firstChild; node; node = node->next, loop++) {
                /* associate the child node with the call context so it can be referenced inside the
                   script block */
                context->tagNode = node;
                /* execute the script block inside the forchildin loop */
                UI_ExecuteActions(action->d.nonTerminal.right, context);
                /* clean the tag node */
                context->tagNode = nullptr;
                if (context->breakLoop) {
                    context->breakLoop = false;
                    break;
                }
                if (loop > 1000) {
                    Com_Printf("UI_ExecuteAction: Infinite loop. Force breaking 'forchildin'\n");
                    break;
                }
            }
            break;
        }

    case EA_BREAK:
        {
            /* flag to break, the caller must check this flag before processing the next action in the list */
            Com_Printf("BREAK: break statement found\n");
            context->breakLoop = true;
            break;
        }

    case EA_IF:
        if (UI_GetBooleanFromExpression(action->d.nonTerminal.left, context)) {
            UI_ExecuteActions(action->d.nonTerminal.right, context);
            return;
        }
        action = action->next;
        while (action && action->type == EA_ELIF) {
            if (UI_GetBooleanFromExpression(action->d.nonTerminal.left, context)) {
                UI_ExecuteActions(action->d.nonTerminal.right, context);
                return;
            }
            action = action->next;
        }
        if (action && action->type == EA_ELSE) {
            UI_ExecuteActions(action->d.nonTerminal.right, context);
        }
        break;

    case EA_ELSE:
    case EA_ELIF:
        /* previous EA_IF execute this action */
        break;

    default:
        Com_Error(ERR_FATAL, "UI_ExecuteAction: Unknown action type %i", action->type);
    }
}

static void UI_ExecuteActions (const uiAction_t* firstAction, uiCallContext_t* context)
{
    static int callnumber = 0;
    if (callnumber++ > 20) {
        Com_Printf("UI_ExecuteActions: Break possible infinite recursion, source [%s]\n", UI_GetPath(context->source));
        return;
    }
    for (const uiAction_t* action = firstAction; action && !context->breakLoop; action = action->next) {
        UI_ExecuteAction(action, context);
    }
    callnumber--;
}

void UI_ExecuteConFuncActions (uiNode_t* source, const uiAction_t* firstAction)
{
    uiCallContext_t context;
    OBJZERO(context);
    context.source = source;
    context.useCmdParam = true;
    UI_ExecuteActions(firstAction, &context);
}

void UI_ExecuteEventActions (uiNode_t* source, const uiAction_t* firstAction)
{
    uiCallContext_t context;
    OBJZERO(context);
    context.source = source;
    context.useCmdParam = false;
    UI_ExecuteActions(firstAction, &context);
}

void UI_ExecuteEventActionsEx (uiNode_t* source, const uiAction_t* firstAction, linkedList_t* params)
{
    uiCallContext_t context;
    OBJZERO(context);
    context.source = source;
    context.useCmdParam = false;
    context.params = params;
    context.paramNumber = LIST_Count(params);
    UI_ExecuteActions(firstAction, &context);
}

bool UI_IsInjectedString (const char* string)
{
    const char* c = string;
    assert(string);
    while (*c != '\0') {
        if (*c == '<') {
            const char* d = c + 1;
            if (*d != '>') {
                while (*d) {
                    if (*d == '>')
                        return true;
                    if (*d == ' ' || *d == '\t' || *d == '\n' || *d == '\r')
                        break;
                    d++;
                }
            }
        }
        c++;
    }
    return false;
}

void UI_FreeStringProperty (void* pointer)
{
    /* skip const string */
    if ((uintptr_t)ui_global.adata <= (uintptr_t)pointer && (uintptr_t)pointer < (uintptr_t)ui_global.adata + (uintptr_t)ui_global.adataize)
        return;

    /* skip pointer out of ui_dynStringPool */
    if (!_Mem_AllocatedInPool(ui_dynStringPool, pointer))
        return;

    Mem_Free(pointer);
}

uiAction_t* UI_AllocStaticCommandAction (const char* command)
{
    uiAction_t* action = UI_AllocStaticAction();
    action->type = EA_CMD;
    action->d.terminal.d1.constString = command;
    return action;
}

void UI_PoolAllocAction (uiAction_t** action, int type, const void* data)
{
    if (*action)
        Com_Error(ERR_FATAL, "There is already an action assigned");
    *action = Mem_PoolAllocType(uiAction_t, ui_sysPool);
    (*action)->type = type;
    switch (type) {
    case EA_CMD:
        (*action)->d.terminal.d1.constString = Mem_PoolStrDup((const char*)data, ui_sysPool, 0);
        break;
    default:
        Com_Error(ERR_FATAL, "Action type %i is not yet implemented", type);
    }
}

void UI_AddListener (uiNode_t* node, const value_t* property, const uiNode_t* functionNode)
{
    /* all nodes are now created in a dynamic way, so this check is removed */
    /*
    if (node->dynamic) {
        Com_Printf("UI_AddListener: '%s' is a dynamic node. We can't listen it.\n", UI_GetPath(node));
        return;
    }
    if (functionNode->dynamic) {
        Com_Printf("UI_AddListener: '%s' is a dynamic node. It can't be a listener callback.\n", UI_GetPath(functionNode));
        return;
    }
    */

    /* create the call action */
    uiAction_t* const action = Mem_PoolAllocType(uiAction_t, ui_sysPool);
    uiAction_t* const value  = Mem_PoolAllocType(uiAction_t, ui_sysPool);
    value->d.terminal.d1.constString = Mem_PoolStrDup(UI_GetPath(functionNode), ui_sysPool, 0);
    value->next = nullptr;
    action->type = EA_LISTENER;
    action->d.nonTerminal.left = value;
    action->d.terminal.d2.constData = &functionNode->onClick;
    action->next = nullptr;

    /* insert the action */
    uiAction_t** anchor = &Com_GetValue<uiAction_t*>(node, property);
    while (*anchor)
        anchor = &(*anchor)->next;
    *anchor = action;
}

static void UI_AddListener_f (void)
{
    uiNode_t* node;
    uiNode_t* function;
    const value_t* property;

    if (Cmd_Argc() != 3) {
        Com_Printf("Usage: %s <pathnode@event> <pathnode>\n", Cmd_Argv(0));
        return;
    }

    UI_ReadNodePath(Cmd_Argv(1), nullptr, nullptr, &node, &property);
    if (node == nullptr) {
        Com_Printf("UI_AddListener_f: '%s' node not found.\n", Cmd_Argv(1));
        return;
    }
    if (property == nullptr || property->type != V_UI_ACTION) {
        Com_Printf("UI_AddListener_f: '%s' property not found, or is not an event.\n", Cmd_Argv(1));
        return;
    }

    function = UI_GetNodeByPath(Cmd_Argv(2));
    if (function == nullptr) {
        Com_Printf("UI_AddListener_f: '%s' node not found.\n", Cmd_Argv(2));
        return;
    }

    UI_AddListener(node, property, function);
}

void UI_RemoveListener (uiNode_t* node, const value_t* property, uiNode_t* functionNode)
{
    void* data;

    /* data we must remove */
    data = (void*) &functionNode->onClick;

    /* remove the action */
    uiAction_t*& action = Com_GetValue<uiAction_t*>(node, property);
    if (uiAction_t* lastAction = action) {
        uiAction_t* tmp = nullptr;
        if (lastAction->type == EA_LISTENER && lastAction->d.terminal.d2.constData == data) {
            tmp = lastAction;
            action = lastAction->next;
        } else {
            while (lastAction->next) {
                if (lastAction->next->type == EA_LISTENER && lastAction->next->d.terminal.d2.constData == data)
                    break;
                lastAction = lastAction->next;
            }
            if (lastAction->next) {
                tmp = lastAction->next;
                lastAction->next = lastAction->next->next;
            }
        }
        if (tmp) {
            uiAction_t* value = tmp->d.nonTerminal.left;
            Mem_Free(value->d.terminal.d1.data);
            Mem_Free(value);
            Mem_Free(tmp);
        }
        else
            Com_Printf("UI_RemoveListener_f: '%s' into '%s' not found.\n", Cmd_Argv(2), Cmd_Argv(1));
    }
}

static void UI_RemoveListener_f (void)
{
    uiNode_t* node;
    uiNode_t* function;
    const value_t* property;

    if (Cmd_Argc() != 3) {
        Com_Printf("Usage: %s <pathnode@event> <pathnode>\n", Cmd_Argv(0));
        return;
    }

    UI_ReadNodePath(Cmd_Argv(1), nullptr, nullptr, &node, &property);
    if (node == nullptr) {
        Com_Printf("UI_RemoveListener_f: '%s' node not found.\n", Cmd_Argv(1));
        return;
    }
    if (property == nullptr || property->type != V_UI_ACTION) {
        Com_Printf("UI_RemoveListener_f: '%s' property not found, or is not an event.\n", Cmd_Argv(1));
        return;
    }

    function = UI_GetNodeByPath(Cmd_Argv(2));
    if (function == nullptr) {
        Com_Printf("UI_RemoveListener_f: '%s' node not found.\n", Cmd_Argv(2));
        return;
    }

    UI_RemoveListener(node, property, function);
}

static void UI_CvarChangeListener (const char* cvarName, const char* oldValue, const char* newValue, void* data)
{
    linkedList_t* list = static_cast<linkedList_t*>(data);
    LIST_Foreach(list, char const, confunc) {
        UI_ExecuteConfunc("%s %s %s", confunc, oldValue, newValue);
    }
}

static void UI_AddCvarListener_f (void)
{
    const char* cvarName;
    const char* confuncName;
    cvarChangeListener_t* l;

    if (Cmd_Argc() != 3) {
        Com_Printf("Usage: %s <cvar> <confunc>\n", Cmd_Argv(0));
        return;
    }

    cvarName = Cmd_Argv(1);
    confuncName = Cmd_Argv(2);
    l = Cvar_RegisterChangeListener(cvarName, UI_CvarChangeListener);
    if (LIST_ContainsString(static_cast<linkedList_t*>(l->data), confuncName) == nullptr)
        LIST_AddString(reinterpret_cast<linkedList_t**>(&l->data), confuncName);
}

static void UI_RemoveCvarListener_f (void)
{
    const char* cvarName;
    const char* confuncName;
    cvar_t* var;

    if (Cmd_Argc() != 3) {
        Com_Printf("Usage: %s <cvar> <confunc>\n", Cmd_Argv(0));
        return;
    }

    cvarName = Cmd_Argv(1);
    confuncName = Cmd_Argv(2);

    var = Cvar_FindVar(cvarName);
    if (var == nullptr)
        return;

    cvarChangeListener_t* l = var->changeListener;
    while (l) {
        if (l->exec == UI_CvarChangeListener) {
            linkedList_t* entry = const_cast<linkedList_t*>(LIST_ContainsString(static_cast<linkedList_t*>(l->data), confuncName));
            if (entry != nullptr)
                LIST_RemoveEntry(reinterpret_cast<linkedList_t**>(&l->data), entry);
            if (LIST_IsEmpty(static_cast<linkedList_t*>(l->data))) {
                Cvar_UnRegisterChangeListener(cvarName, UI_CvarChangeListener);
            }
            return;
        }
        l = l->next;
    }
}

void UI_InitActions (void)
{
    UI_CheckActionTokenTypeSanity();
    Cmd_AddCommand("ui_addcvarlistener", UI_AddCvarListener_f, "Add a confunc to a cvar change event");
    Cmd_AddCommand("ui_removecvarlistener", UI_RemoveCvarListener_f, "Remove a confunc from a cvar change event");
    Cmd_AddCommand("ui_addlistener", UI_AddListener_f, "Add a function into a node event");
    Cmd_AddCommand("ui_removelistener", UI_RemoveListener_f, "Remove a function from a node event");
}