history.c

#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>

struct history_record {
	uint8_t line;
	uint8_t column;
	char * characters;
};

struct text {
	uint8_t history_buffer_length;
	uint8_t history_buffer_write_index;
	uint8_t history_buffer_read_index;
	uint8_t body_lines;
	// Would need some more things to track this growable string, but this
	// isn't the focus of the exercise.
	char ** body;
	struct history_record history_buffer [];
};

int
text_body_insert(struct text *text, uint8_t line, uint8_t column, char *characters)
{
	// It should not be possible to go out of bounds.
	if (text->body_lines < line) {
		return -1;
	}

	// Implement insertion along with grow logic.

	return 0;
}

int
text_insert(struct text *text, uint8_t line, uint8_t column, char * characters)
{
	if (text_body_insert(text, line, column, characters)) {
		text->history_buffer_write_index++;
		if(text->history_buffer_write_index >= text->history_buffer_length) {
			// Since this is a circular buffer, once we hit the array boundary we
			// just restart the index. This means that we'll write on top of history.
			// The size of the array determines how much history we can hold on to.
			text->history_buffer_write_index = 0;
		}
		struct history_record record = text->history_buffer[text->history_buffer_write_index];
		if (record.characters != NULL) {
			free(record.characters);
		}
		record.characters = characters;
		record.line = line;
		record.column = column;
		return 0;
	}
	return -1;
}

void
text_delete(struct text *text, uint8_t line, uint8_t column, uint8_t characters)
{
}

void
text_undo(struct text *text)
{
}

void
text_redo(struct text *text)
{
}

int
main()
{
	char body[0][0];
	struct history_record history_buffer[4];

	struct text text = {
		.history_buffer_length = 4,
		.body = body,
		.history_buffer_read_index = 0,
		.history_buffer_write_index = 0,
		.history_buffer = history_buffer
	};

	text_insert(&text, 0, 0, "h");
	text_insert(&text, 0, 1, "e");
	text_insert(&text, 0, 2, "l");
	text_insert(&text, 0, 3, "l");
	text_insert(&text, 0, 4, "0");

	text_undo(&text);
	text_undo(&text);
	text_redo(&text);
	text_redo(&text);

	return 0;
}