1 files changed, 67 insertions, 0 deletions
diff --git a/src/undo.h b/src/undo.h
new file mode 100644
index 0000000..42022c5
--- /dev/null
+++ b/src/undo.h
@@ -0,0 +1,67 @@
+#include <stdbool.h>
+#include <stdint.h>
+
+enum undo_record_type {
+  Undo_Boundary = 1,
+  Undo_Add = 2,
+  Undo_Delete = 3,
+};
+
+struct position {
+  uint32_t row;
+  uint32_t col;
+};
+
+struct undo_boundary {
+  bool save_point;
+};
+
+struct undo_add {
+  struct position begin;
+  struct position end;
+};
+
+struct undo_delete {
+  struct position pos;
+  uint8_t *data;
+  uint32_t nbytes;
+};
+
+struct undo_record {
+  enum undo_record_type type;
+
+  union {
+    struct undo_boundary boundary;
+    struct undo_add add;
+    struct undo_delete delete;
+  };
+};
+
+#define INVALID_TOP -1
+
+struct undo_stack {
+  struct undo_record *records;
+  uint32_t nrecords;
+  uint32_t top;
+  uint32_t capacity;
+  bool undo_in_progress;
+};
+
+void undo_init(struct undo_stack *undo, uint32_t initial_capacity);
+void undo_clear(struct undo_stack *undo);
+void undo_destroy(struct undo_stack *undo);
+
+uint32_t undo_push_boundary(struct undo_stack *undo,
+                            struct undo_boundary boundary);
+
+uint32_t undo_push_add(struct undo_stack *undo, struct undo_add add);
+uint32_t undo_push_delete(struct undo_stack *undo, struct undo_delete delete);
+
+void undo_begin(struct undo_stack *undo);
+void undo_next(struct undo_stack *undo, struct undo_record **records_out,
+               uint32_t *nrecords_out);
+void undo_end(struct undo_stack *undo);
+
+uint32_t undo_size(struct undo_stack *undo);
+uint32_t undo_current_position(struct undo_stack *undo);
+const char *undo_dump(struct undo_stack *undo);