// Text buffers - These store the contents of a file.
// To make inserting characters faster, the file contents are split up into
// blocks of a few thousand bytes. Block boundaries are not necessarily
// on character boundaries, so one block might have part of a UTF-8 character
// with the next block having the rest.
#include "unicode.h"
#include "util.c"
#include "text.h"

#define TEXT_BLOCK_MAX_SIZE 400
// Once two adjacent blocks are at most this big, combine them into
// one bigger text block.
#define TEXT_BLOCK_COMBINE_SIZE (3*(TEXT_BLOCK_MAX_SIZE / 4))
// A good size for text blocks to be. When a file is loaded, there
// shouldn't be just full blocks, because they will all immediately split.
// Instead, we use blocks of this size.
#define TEXT_BLOCK_DEFAULT_SIZE (3*(TEXT_BLOCK_MAX_SIZE / 4))
typedef struct {
	u16 len;
	char *contents;
} TextBlock;

typedef struct {
	u32 nblocks; // number of text blocks
	double scroll_x, scroll_y; // number of characters scrolled in the x/y direction
	TextBlock *blocks;
} TextBuffer;

// Returns a new block added at index `where`,
// or NULL if there's not enough memory.
static TextBlock *text_buffer_add_block(TextBuffer *buffer, u32 where) {
	// make sure we can actually allocate enough memory for the contents of the block
	// before doing anything
	char *block_contents = calloc(1, TEXT_BLOCK_MAX_SIZE);
	if (!block_contents) {
		return NULL;
	}

	u32 nblocks_before = buffer->nblocks;
	u32 nblocks_after = buffer->nblocks + 1;
	if (util_is_power_of_2(nblocks_after)) {
		// whenever the number of blocks is a power of 2, we need to grow the blocks array.
		buffer->blocks = realloc(buffer->blocks, 2 * nblocks_after * sizeof *buffer->blocks);
		if (!buffer->blocks) {
			// out of memory
			free(block_contents);
			return NULL;
		}
	}
	if (where != nblocks_before) { // if we aren't just inserting the block at the end,
		// make space for the new block
		memmove(buffer->blocks + (where + 1), buffer->blocks + where, nblocks_before - where);
	}
	
	TextBlock *block = buffer->blocks + where;
	util_zero_memory(block, sizeof *buffer->blocks); // zero everything
	block->contents = block_contents;

	
	buffer->nblocks = nblocks_after;
	return block;
}

Status text_buffer_load_file(TextBuffer *buffer, FILE *fp) {
	char block_contents[TEXT_BLOCK_DEFAULT_SIZE];
	size_t bytes_read;

	util_zero_memory(buffer, sizeof *buffer);
	
	// read file one block at a time
	do {
		bytes_read = fread(block_contents, 1, sizeof block_contents, fp);
		if (bytes_read > 0) {
			TextBlock *block = text_buffer_add_block(buffer, buffer->nblocks);
			if (!block) {
				return false;
			}
			memcpy(block->contents, block_contents, bytes_read);
			block->len = (u16)bytes_read;
		}
	} while (bytes_read == sizeof block_contents);
	if (ferror(fp))	
		return false;
	return true;
}

static void text_buffer_print_internal(TextBuffer *buffer, bool debug) {
	printf("\033[2J\033[;H");
	TextBlock *blocks = buffer->blocks;
	u32 nblocks = buffer->nblocks;
	
	for (u32 i = 0; i < nblocks; ++i) {
		TextBlock *block = &blocks[i];
		fwrite(block->contents, 1, block->len, stdout);
		if (debug)
			printf("\n\n------\n\n"); // NOTE: could be bad with UTF-8
	}
	fflush(stdout);
}

// print the contents of a buffer to stdout
void text_buffer_print(TextBuffer *buffer) {
	text_buffer_print_internal(buffer, false);
}

// print the contents of a buffer to stdout, along with debugging information
void text_buffer_print_debug(TextBuffer *buffer) {
	text_buffer_print_internal(buffer, true);
}

// Does not free the pointer `buffer` (buffer might not have even been allocated with malloc)
void text_buffer_free(TextBuffer *buffer) {
	TextBlock *blocks = buffer->blocks;
	u32 nblocks = buffer->nblocks;
	for (u32 i = 0; i < nblocks; ++i) {
		free(blocks[i].contents);
	}
	free(blocks);
}

void text_buffer_scroll(TextBuffer *buffer, double dx, double dy) {
	buffer->scroll_x += dx;
	buffer->scroll_y += dy;
}

// Render the text buffer in the given rectangle
void text_buffer_render(TextBuffer *buffer, Font *font, float x1, float y1, float x2, float y2) {
	mbstate_t mbstate = {0};
	uint nblocks = buffer->nblocks;
	TextBlock *blocks = buffer->blocks;
	float char_height = text_font_char_height(font);
	glColor3f(0.5f,0.5f,0.5f);
	glBegin(GL_LINE_STRIP);
	glVertex2f(x1,y1);
	glVertex2f(x1,y2);
	glVertex2f(x2,y2);
	glVertex2f(x2,y1);
	glVertex2f(x1-1,y1);
	glEnd();

	glColor3f(1,1,1);
	text_chars_begin(font);
	TextRenderState text_state = {
		.x = x1, .y = y1 + text_font_char_height(font),
		.min_x = x1, .min_y = y1,
		.max_x = x2, .max_y = y2
	};

	// @TODO: make this better (we should figure out where to start rendering, etc.)
	text_state.x -= (float)buffer->scroll_x * char_height;
	text_state.y -= (float)buffer->scroll_y * char_height;

	for (uint block_idx = 0; block_idx < nblocks; ++block_idx) {
		TextBlock *block = &blocks[block_idx];
		char *p = block->contents, *end = p + block->len;
		while (p != end) {
			char32_t c;
			size_t n = mbrtoc32(&c, p, (size_t)(end - p), &mbstate);
			if (n == 0) {
				// null character
				c = UNICODE_BOX_CHARACTER;
				++p;
			} else if (n == (size_t)(-3)) {
				// no bytes consumed, but a character was produced
			} else if (n == (size_t)(-2)) {
				// incomplete character at end of block.
				c = 0;
				p = end;
			} else if (n == (size_t)(-1)) {
				// invalid UTF-8
				c = UNICODE_BOX_CHARACTER;
				++p;
			} else {
				p += n;
			}
			switch (c) {
			case L'\n':
				text_state.x = x1;
				text_state.y += text_font_char_height(font);
				break;
			case L'\r': break; // for CRLF line endings
			case L'\t':
				for (int i = 0; i < 4; ++i)
					text_render_char(font, L' ', &text_state);
				break;
			default:
				text_render_char(font, c, &text_state);
				break;
			}
		}
	}
	text_chars_end(font);
}