// get ready for some MLG...

// The undo system currently works in two layers: a lower-level structless
// stack that records "actions" and a higher-level array of "entries" that
// bundle actions together. An action can either record a single change to a
// specific memory address or a shift of pointers. Entries are what the user
// sees and can contain multiple actions (i.e. adding a source changes the
// value of the string and the increment of how many sources there are).
// Entries are allowed to call functions in case there's something that can't
// be incorporated into this memory model (i.e. deallocating libav contexts
// when a layer's creation is undone), though they should be used only
// when necessary.

// These get four things pushed together: what type the data is, address, the
// original data, and the type again. The type is encoded twice so we always
// know how big the data is whether we're undoing or redoing.
// We need to encode data that's able to go from A -> B as well as B -> A. Thus
// for the ints I encode the difference instead of just whatever the last value
// was. Strings currently just stores both.
void History_Action_Change(memory *Memory, void *DataAddress, void *OriginalData, void *NewData, action_type ActionChange)
{
    Memory->Action.Entry[Memory->Action.Index].NumberOfActions++;
    void *Data = Memory_Advance(Memory, sizeof(action_type), P_UndoBuffer);
    *(action_type *)Data = ActionChange;
    void *UndoEntry = Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
    *(ptrsize *)UndoEntry = (ptrsize)DataAddress;
    switch (ActionChange)
    {
        case action_type_change_u16:
        {
            uint16 OriginalValue = *(uint16 *)OriginalData;
            uint16 NewValue = *(uint16 *)NewData;
            uint16 Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(uint16), P_UndoBuffer);
            *(uint16 *)Data = Difference;
            *(uint16 *)DataAddress = *(uint16 *)NewData;
        } break;
        case action_type_change_i16:
        {
            int16 OriginalValue = *(int16 *)OriginalData;
            int16 NewValue = *(int16 *)NewData;
            int16 Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(int16), P_UndoBuffer);
            *(int16 *)Data = Difference;
            *(int16 *)DataAddress = *(int16 *)NewData;
        } break;
        case action_type_change_u32:
        {
            uint32 OriginalValue = *(uint32 *)OriginalData;
            uint32 NewValue = *(uint32 *)NewData;
            uint32 Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(uint32), P_UndoBuffer);
            *(uint32 *)Data = Difference;
            *(uint32 *)DataAddress = *(uint32 *)NewData;
        } break;
        case action_type_change_i32:
        {
            int32 OriginalValue = *(int32 *)OriginalData;
            int32 NewValue = *(int32 *)NewData;
            int32 Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(int32), P_UndoBuffer);
            *(int32 *)Data = Difference;
            *(int32 *)DataAddress = *(int32 *)NewData;
        } break;
        case action_type_change_r32:
        {
            real32 OriginalValue = *(real32 *)OriginalData;
            real32 NewValue = *(real32 *)NewData;
            real32 Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(real32), P_UndoBuffer);
            *(real32 *)Data = Difference;
            *(real32 *)DataAddress = *(real32 *)NewData;
        } break;
        case action_type_change_u64:
        {
            uint64 OriginalValue = *(uint64 *)OriginalData;
            uint64 NewValue = *(uint64 *)NewData;
            uint64 Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(uint64), P_UndoBuffer);
            *(uint64 *)Data = Difference;
            *(uint64 *)DataAddress = *(uint64 *)NewData;
        } break;
        case action_type_change_ptr:
        {
            ptrsize OriginalValue = *(ptrsize *)OriginalData;
            ptrsize NewValue = *(ptrsize *)NewData;
            ptrsize Difference = NewValue - OriginalValue;
            void *Data = Memory_Advance(Memory, sizeof(ptrsize), P_UndoBuffer);
            *(ptrsize *)Data = Difference;
            *(ptrsize *)DataAddress = *(ptrsize *)NewData;
        } break;
        case action_type_change_string:
        {
            void *Data = Memory_Advance(Memory, STRING_SIZE, P_UndoBuffer);
            CopyStrings(Data, OriginalData);
            Data = Memory_Advance(Memory, STRING_SIZE, P_UndoBuffer);
            CopyStrings(Data, NewData);
            CopyStrings(DataAddress, NewData);
        } break;
        default:
        {
            Assert(0);
        }

    }
    Data = Memory_Advance(Memory, sizeof(action_type), P_UndoBuffer);
    *(action_type *)Data = ActionChange;
}

// Helper functions for common types of data changes.
void History_Action_Change_SwapBool(memory *Memory, bool32 *Bool)
{
    bool32 OppositeBool = *Bool ^ 1;
    History_Action_Change(Memory, Bool, Bool, &OppositeBool, action_type_change_i32);
}

void History_Action_Change_Increment(memory *Memory, void *Data, action_type ActionChange)
{
    switch (ActionChange)
    {
        case action_type_change_u16:
        {
            uint16 DataPlusOne = (*(uint16 *)Data) + 1;
            History_Action_Change(Memory, Data, Data, &DataPlusOne, ActionChange);
        } break;
        case action_type_change_i16:
        {
            int16 DataPlusOne = (*(int16 *)Data) + 1;
            History_Action_Change(Memory, Data, Data, &DataPlusOne, ActionChange);
        } break;
        case action_type_change_u32:
        {
            uint32 DataPlusOne = (*(uint32 *)Data) + 1;
            History_Action_Change(Memory, Data, Data, &DataPlusOne, ActionChange);
        } break;
        case action_type_change_i32:
        {
            int32 DataPlusOne = (*(int32 *)Data) + 1;
            History_Action_Change(Memory, Data, Data, &DataPlusOne, ActionChange);
        } break;
        case action_type_change_r32:
        {
            real32 DataPlusOne = (*(real32 *)Data) + 1;
            History_Action_Change(Memory, Data, Data, &DataPlusOne, ActionChange);
        } break;
        case action_type_change_u64:
        {
            uint64 DataPlusOne = (*(uint64 *)Data) + 1;
            History_Action_Change(Memory, Data, Data, &DataPlusOne, ActionChange);
        } break;
        default:
        {
            Assert(0);
        }
    }
}

void History_Action_Shift(memory *Memory, action_type ActionChange, void *DataAddress, int16 Direction, int16 Index)
{
    Memory->Action.Entry[Memory->Action.Index].NumberOfActions++;
    void *Data = Memory_Advance(Memory, sizeof(action_type), P_UndoBuffer);
    *(action_type *)Data = ActionChange;
    switch (ActionChange)
    {
        case action_type_shift_keyframe:
        {
            void *DataPropertyAddress = Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            *(ptrsize *)DataPropertyAddress = (ptrsize)DataAddress;
            void *DataDirection = Memory_Advance(Memory, sizeof(int16), P_UndoBuffer);
            *(ptrsize *)DataDirection = (ptrsize)Direction;
            void *DataIndex = Memory_Advance(Memory, sizeof(int16), P_UndoBuffer);
            *(ptrsize *)DataIndex = (ptrsize)Index;
        } break;
        default:
        {
            Assert(0);
        } break;
    }
    Data = Memory_Advance(Memory, sizeof(action_type), P_UndoBuffer);
    *(action_type *)Data = ActionChange;
}

// This is only called when we're certain the action is going to be taken.
void History_Entry_Commit(memory *Memory, action_entry_type Type, char *Name)
{
    // We need to at least clear NumberOfActions in case this index is being reused.
    Memory->Action.Entry[Memory->Action.Index] = {};
    Memory->Action.Entry[Memory->Action.Index].Name = Name;
    Memory->Action.Entry[Memory->Action.Index].Type = Type;
    // Effectively deletes entries in front if we're beginning out of an undo.
    // It wouldn't be all that much more difficult to support branched undoing
    // now that I think about it... (would anyone use it though?)
    if (Memory->Action.Index != Memory->Action.NumberOfEntries) {
        Memory->Action.NumberOfEntries = Memory->Action.Index;
    }
}

void History_Entry_SetPointer(memory *Memory, void *Data)
{
    Memory->Action.Entry[Memory->Action.Index].ExtraPointer = Data;
}

void History_Entry_End(memory *Memory)
{
    Memory->Action.Index++;
    Memory->Action.NumberOfEntries++;
}

// The pointer is unwinded.
void History_Action_Undo(memory *Memory) {
    void *LastPos = Memory_Rewind(Memory, sizeof(action_type), P_UndoBuffer);
    action_type *ActionType = (action_type *)LastPos;

    switch (*ActionType)
    {
        case action_type_change_u16:
        {
            uint16 *Difference = (uint16 *)Memory_Rewind(Memory, sizeof(uint16), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(uint16 *)*Address -= *Difference;
        } break;
        case action_type_change_i16:
        {
            int16 *Difference = (int16 *)Memory_Rewind(Memory, sizeof(int16), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(int16 *)*Address -= *Difference;
        } break;
        case action_type_change_u32:
        {
            uint32 *Difference = (uint32 *)Memory_Rewind(Memory, sizeof(uint32), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(uint32 *)*Address -= *Difference;
        } break;
        case action_type_change_i32:
        {
            int32 *Difference = (int32 *)Memory_Rewind(Memory, sizeof(int32), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(int32 *)*Address -= *Difference;
        } break;
        case action_type_change_r32:
        {
            real32 *Difference = (real32 *)Memory_Rewind(Memory, sizeof(real32), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(real32 *)*Address -= *Difference;
        } break;
        case action_type_change_u64:
        {
            uint64 *Difference = (uint64 *)Memory_Rewind(Memory, sizeof(uint64), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(uint64 *)*Address -= *Difference;
        } break;
        case action_type_change_ptr:
        {
            ptrsize *Difference = (ptrsize *)Memory_Rewind(Memory, sizeof(ptrsize), P_UndoBuffer);
            void **Address = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            *(ptrsize *)*Address -= *Difference;
        } break;
        case action_type_change_string:
        {
            Assert(0);
        } break;
        case action_type_shift_keyframe:
        {
            void *DataIndex = Memory_Rewind(Memory, sizeof(int16), P_UndoBuffer);
            void *DataDirection = Memory_Rewind(Memory, sizeof(int16), P_UndoBuffer);
            void **DataPropertyAddress = (void **)Memory_Rewind(Memory, sizeof(void *), P_UndoBuffer);
            ShiftKeyframes((property_channel *)*DataPropertyAddress, *(int16 *)DataDirection * -1, *(int16 *)DataIndex);
        } break;
        default:
        {
            Assert(0);
        } break;
    }
    void *EndPos = Memory_Rewind(Memory, sizeof(action_type), P_UndoBuffer);
}

// The pointer is rewinded.
void History_Action_Redo(memory *Memory) {
    void *LastPos = Memory_Advance(Memory, sizeof(action_type), P_UndoBuffer);
    action_type *ActionType = (action_type *)LastPos;

    switch (*ActionType)
    {
        case action_type_change_u16:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            uint16 *Difference = (uint16 *)Memory_Advance(Memory, sizeof(uint16), P_UndoBuffer);
            *(uint16 *)*Address += *Difference;
        } break;
        case action_type_change_i16:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            int16 *Difference = (int16 *)Memory_Advance(Memory, sizeof(int16), P_UndoBuffer);
            *(int16 *)*Address += *Difference;
        } break;
        case action_type_change_u32:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            uint32 *Difference = (uint32 *)Memory_Advance(Memory, sizeof(uint32), P_UndoBuffer);
            *(uint32 *)*Address += *Difference;
        } break;
        case action_type_change_i32:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            int32 *Difference = (int32 *)Memory_Advance(Memory, sizeof(int32), P_UndoBuffer);
            *(int32 *)*Address += *Difference;
        } break;
        case action_type_change_r32:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            real32 *Difference = (real32 *)Memory_Advance(Memory, sizeof(real32), P_UndoBuffer);
            *(real32 *)*Address += *Difference;
        } break;
        case action_type_change_u64:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            uint64 *Difference = (uint64 *)Memory_Advance(Memory, sizeof(uint64), P_UndoBuffer);
            *(uint64 *)*Address += *Difference;
        } break;
        case action_type_change_ptr:
        {
            void **Address = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            ptrsize *Difference = (ptrsize *)Memory_Advance(Memory, sizeof(ptrsize), P_UndoBuffer);
            *(ptrsize *)*Address += *Difference;
        } break;
        case action_type_change_string:
        {
            Assert(0);
        } break;
        case action_type_shift_keyframe:
        {
            void **DataPropertyAddress = (void **)Memory_Advance(Memory, sizeof(void *), P_UndoBuffer);
            void *DataDirection = Memory_Advance(Memory, sizeof(int16), P_UndoBuffer);
            void *DataIndex = Memory_Advance(Memory, sizeof(int16), P_UndoBuffer);
            ShiftKeyframes((property_channel *)*DataPropertyAddress, *(int16 *)DataDirection, *(int16 *)DataIndex);
        } break;
        default:
        {
            Assert(0);
        } break;
    }
    void *EndPos = Memory_Advance(Memory, sizeof(action_type), P_UndoBuffer);
}

void History_Undo(memory *Memory) {
    if (Memory->Action.Index != 0) {
        Memory->Action.Index--;
        action_entry Entry = Memory->Action.Entry[Memory->Action.Index];
        switch (Entry.Type)
        {
            case action_entry_layerinit:
            {
                AV_Dealloc((av_info *)*(ptrsize *)Entry.ExtraPointer);
                *(ptrsize *)Entry.ExtraPointer = 0x0;   // what actually dereferences the pointer
            } break;
            case action_entry_default:
            {
            } break;
        }
        for (int i = 0; i < Entry.NumberOfActions; i++)
            History_Action_Undo(Memory);
    }
}

void History_Redo(memory *Memory) {
    if (Memory->Action.Index != Memory->Action.NumberOfEntries) {
        action_entry Entry = Memory->Action.Entry[Memory->Action.Index];
        switch (Entry.Type)
        {
            case action_entry_layerinit:
            {
            } break;
            case action_entry_default:
            {
            } break;
        }
        for (int i = 0; i < Entry.NumberOfActions; i++)
            History_Action_Redo(Memory);
        Memory->Action.Index++;
    }
}