source: tags/initial/ARBDB/adlundo.h

enum g_b_undo_entry_type {
                GB_UNDO_ENTRY_TYPE_DELETED,
                GB_UNDO_ENTRY_TYPE_CREATED,
                GB_UNDO_ENTRY_TYPE_MODIFY,
                GB_UNDO_ENTRY_TYPE_MODIFY_ARRAY
        };

struct g_b_undo_gbd_struct {
        GBQUARK                 key;
        struct gb_data_base_type *gbd;
};

struct g_b_undo_struct;
struct g_b_undo_entry_struct {
    struct g_b_undo_struct *father;
    struct g_b_undo_entry_struct *next;
    short type;
    short flag;
    
    struct gb_data_base_type    *source;
    int                         gbm_index;
                        /* The original(changed element) or father */
    long                                sizeof_this;
    union {
        struct gb_transaction_save *ts;
        struct g_b_undo_gbd_struct gs;
    } d;
};      

struct g_b_undo_header_struct;
struct g_b_undo_struct {
        struct g_b_undo_header_struct   *father;
        struct g_b_undo_entry_struct    *entries;
        struct g_b_undo_struct          *next;
        long            time_of_day;    /* the begin of the transaction */
        long            sizeof_this;    /* the size of one undo */
};

struct g_b_undo_header_struct {
        struct g_b_undo_struct *stack;
        long            sizeof_this;    /* the size of all existing undos */
        long            nstack;         /* number of available undos */ 
};

struct g_b_undo_mgr_struct {
        long                    max_size_of_all_undos;
        struct g_b_undo_struct          *valid_u;
        struct g_b_undo_header_struct   *u;     /* undo */
        struct g_b_undo_header_struct   *r;     /* redo */
};