#include <GL/gl.h>
#include <GLFW/glfw3.h>
#include <fontconfig/fontconfig.h>
#include <ft2build.h>
#include FT_FREETYPE_H

#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <stdbool.h>

enum align {
	CENTER,
	LEFT,
	RIGHT
};

struct point {
	double x, y;
};

struct line {
	struct point *points;
	size_t count, cap;
};

struct note {
	double x, y;
	char *text;
	enum align align;
	size_t len, cap;
};

enum event {
	EVENT_START,
	EVENT_START_LINE,
	EVENT_START_RECT,
	EVENT_END_SHAPE,
	EVENT_START_NOTE,
	EVENT_MOUSE_MOVE,
	EVENT_MOUSE_DRAG,
};

static struct line *lines = NULL;
static size_t line_count = 0;
static size_t line_cap = 0;

static struct note *notes = NULL;
static size_t note_count = 0;
static size_t note_cap = 0;

static enum event *events = NULL;
static size_t event_count = 0;
static size_t event_cap = 0;

static double canvas_x = 0;
static double canvas_y = 0;

static double cursor_x = 0;
static double cursor_y = 0;

static double drag_canvas_x = 0;
static double drag_canvas_y = 0;
static double drag_cursor_x = 0;
static double drag_cursor_y = 0;

static int window_width = 0;
static int window_height = 0;

static GLuint glyphs[128];
static FT_Vector glyph_advance[128];
static FT_Vector glyph_offset[128];
static FT_Vector glyph_size[128];

static void
die(const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	fputs("xnote: ", stderr);
	vfprintf(stderr, fmt, ap);
	if (*fmt && fmt[strlen(fmt)] == ':')
		perror(NULL);
	else
		putc('\n', stderr);
	va_end(ap);

	exit(1);
}

static void *
append(void *_array, size_t *count, size_t *cap, size_t size)
{
	uint8_t **array = _array;
	if (*count == *cap) {
		if (*cap == 0) *cap = 1;
		*cap *= 2;
		*array = realloc(*array, *cap * size);
		if (!*array) die("realloc:");
	}
	return (void *) (*array + (*count)++ * size);
}

static void
shrink(void *_array, size_t count, size_t *cap, size_t size)
{
	uint8_t **array = _array;
	if (count == 0) {
		*array = NULL;
		*cap = 0;
	} else {
		*cap = count;
		*array = realloc(*array, *cap * size);
		if (!*array) die("realloc:");
	}
}

static void
glfw_error(int rc, const char *error)
{
	die("glfw error (%i): %s", rc, error);
}

static void
push_event(enum event event)
{
	enum event *slot = append(&events,
		&event_count, &event_cap, sizeof(enum event));
	*slot = event;
}

static enum event
pop_event(void)
{
	event_count -= 1;
	enum event event = events[event_count];
	switch (event) {
	case EVENT_START_LINE:
	case EVENT_START_RECT:
		line_count -= 1;
		free(lines[line_count].points);
		break;
	case EVENT_START_NOTE:
		note_count -= 1;
		free(notes[note_count].text);
		break;
	case EVENT_START:
		event_count += 1;
		break;
	default:
		break;
	}
	return event;
}

static void
undo(void)
{
	while (1) {
		switch (pop_event()) {
		case EVENT_START_LINE:
		case EVENT_START_NOTE:
		case EVENT_START_RECT:
		case EVENT_START:
			break;
		default:
			continue;
		}
		break;
	}
	shrink(&events, event_count, &event_cap, sizeof(enum event));
}

static enum event
last_event(void)
{
	return events[event_count - 1];
}

static void
window_resize_cb(GLFWwindow *window, int width, int height)
{
	window_width = width;
	window_height = height;
	glViewport(0, 0, width, height);
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();
	glOrtho(0, width, height, 0, -1, 1);
}

static void
mouse_move_cb(GLFWwindow *window, double x, double y)
{
	cursor_x = x;
	cursor_y = y;
	if (last_event() == EVENT_START_LINE) {
		struct line *line = &lines[line_count-1];
		if (line->count > 0) {
			struct point *last_point = &line->points[line->count-1];
			if (cursor_x == last_point->x && cursor_y == last_point->y)
				return;
		}
		struct point *point = append(&line->points,
			&line->count, &line->cap, sizeof(struct point));
		point->x = canvas_x + cursor_x;
		point->y = canvas_y + cursor_y;
	} else if (last_event() == EVENT_START_RECT) {
		struct line *line = &lines[line_count-1];
		line->points[1].x = canvas_x + cursor_x;
		line->points[2].x = canvas_x + cursor_x;
		line->points[2].y = canvas_y + cursor_y;
		line->points[3].y = canvas_y + cursor_y;
	} else if (last_event() == EVENT_MOUSE_DRAG) {
		canvas_x = drag_canvas_x - (cursor_x - drag_cursor_x);
		canvas_y = drag_canvas_y - (cursor_y - drag_cursor_y);
	} else if (last_event() != EVENT_MOUSE_MOVE) {
		push_event(EVENT_MOUSE_MOVE);
	}
}

static void
mouse_press_cb(GLFWwindow *window, int button, int action, int mods)
{
	if (button == GLFW_MOUSE_BUTTON_LEFT) {
		if (action == GLFW_PRESS) {
			struct line *line = append(&lines,
				&line_count, &line_cap, sizeof(struct line));
			line->count = line->cap = 0;
			line->points = NULL;
			struct point *point = append(&line->points,
				&line->count, &line->cap, sizeof(struct point));
			point->x = canvas_x + cursor_x;
			point->y = canvas_y + cursor_y;
			push_event(EVENT_START_LINE);
		} else if (action == GLFW_RELEASE) {
			if (last_event() == EVENT_START_LINE
					|| last_event() == EVENT_START_RECT) {
				struct line *line = &lines[line_count-1];
				shrink(&line->points, line->count,
					&line->cap, sizeof(struct point));
				push_event(EVENT_END_SHAPE);
			}
		}
	} else if (button == GLFW_MOUSE_BUTTON_RIGHT
			|| button == GLFW_MOUSE_BUTTON_MIDDLE) {
		if (action == GLFW_PRESS) {
			drag_canvas_x = canvas_x;
			drag_canvas_y = canvas_y;
			drag_cursor_x = cursor_x;
			drag_cursor_y = cursor_y;
			push_event(EVENT_MOUSE_DRAG);
		} else if (action == GLFW_RELEASE && last_event() == EVENT_MOUSE_DRAG) {
			pop_event();
		}
	}
}

static void
key_char_cb(GLFWwindow *window, unsigned int codepoint)
{
	if (codepoint < 10 || codepoint >= 128)
		return;

	if (last_event() != EVENT_START_NOTE) {
		struct note *note = append(&notes, &note_count, &note_cap, sizeof(struct note));
		note->text = NULL;
		note->align = CENTER;
		note->len = note->cap = 0;
		note->x = canvas_x + cursor_x;
		note->y = canvas_y + cursor_y;
		push_event(EVENT_START_NOTE);
	}

	struct note *note = &notes[note_count - 1];
	*(char *)append(&note->text, &note->len, &note->cap, 1) = codepoint;
}

static void
key_press_cb(GLFWwindow *window, int key, int scancode, int action, int mods)
{
	if (action == GLFW_PRESS || action == GLFW_REPEAT) {
		const char *keysym = glfwGetKeyName(key, scancode);
		if (key == GLFW_KEY_ENTER) {
			key_char_cb(window, '\n');
			return;
		}
		if ((mods & GLFW_MOD_CONTROL) && keysym && !strcmp(keysym, "z")) {
			if (event_count) undo();
		} else if ((mods & GLFW_MOD_CONTROL)
				&& keysym && !strcmp(keysym, "l")
				&& last_event() == EVENT_START_NOTE) {
			notes[note_count-1].align = LEFT;
		} else if ((mods & GLFW_MOD_CONTROL)
				&& keysym && !strcmp(keysym, "r")
				&& last_event() == EVENT_START_NOTE) {
			notes[note_count-1].align = RIGHT;
		} else if ((mods & GLFW_MOD_CONTROL)
				&& keysym && !strcmp(keysym, "c")
				&& last_event() == EVENT_START_NOTE) {
			notes[note_count-1].align = CENTER;
		} else if (action == GLFW_PRESS && (mods & GLFW_MOD_CONTROL)
				&& keysym && !strcmp(keysym, "r")) {
			struct line *line = append(&lines,
				&line_count, &line_cap, sizeof(struct line));
			line->count = line->cap = 5;
			line->points = malloc(line->count * sizeof(struct point));
			for (size_t i = 0; i < line->count; i++) {
				line->points[i].x = canvas_x + cursor_x;
				line->points[i].y = canvas_y + cursor_y;
			}
			push_event(EVENT_START_RECT);
		} else if ((mods & GLFW_MOD_CONTROL) && keysym && !strcmp(keysym, "c")) {
			for (size_t i = 0; i < line_count; i++)
				free(lines[i].points);
			line_count = 0;
			for (size_t i = 0; i < note_count; i++)
				free(notes[i].text);
			note_count = 0;
			event_count = 0;
		} else if ((mods & GLFW_MOD_CONTROL) && keysym && !strcmp(keysym, "q")) {
			exit(0);
		} else if (key == GLFW_KEY_BACKSPACE && last_event() == EVENT_START_NOTE) {
			if (note_count) {
				struct note *note = &notes[note_count - 1];
				if (note->len > 1) {
					note->len -= 1;
					shrink(&note->text, note->len, &note->cap, 1);
				} else if (note->len == 1) {
					pop_event();
				}
			}
		}
	}
}

static void
draw_texture(int texture, double x, double y)
{
	glBindTexture(GL_TEXTURE_2D, texture);
	glBegin(GL_QUADS);
}

static void
draw_text(const char *text, enum align align, size_t len, GLint x, GLint y)
{
	if (len == 0) return;

	GLint sx = x;
	size_t i = 0;
	while (i < len) {
		size_t k = i;

		double width = glyph_offset[text[0]].x;
		for (; k < len; k++) {
			if (text[k] == '\n') break;
			width += glyph_advance[text[k]].x;
		}

		if (k > i) {
			width -= glyph_advance[text[k-1]].x;
			width += glyph_size[text[k-1]].x;

			x = sx;
			if (align == CENTER) {
				x -= width / 2;
			} else if (align == RIGHT) {
				x -= width;
			}

			glEnable(GL_TEXTURE_2D);
			for (k = i; k < len; k++) {
				if (text[k] == '\n') break;
				GLint gx = x + glyph_offset[text[k]].x;
				GLint gy = y - glyph_offset[text[k]].y;
				GLint sx = glyph_size[text[k]].x;
				GLint sy = glyph_size[text[k]].y;
				glBindTexture(GL_TEXTURE_2D, glyphs[text[k]]);
				glBegin(GL_QUADS);
				glTexCoord2d(0, 1); glVertex2i(gx, gy + sy);
				glTexCoord2d(1, 1); glVertex2i(gx + sx, gy + sy);
				glTexCoord2d(1, 0); glVertex2i(gx + sx, gy);
				glTexCoord2d(0, 0); glVertex2i(gx, gy);
				glEnd();
				x += glyph_advance[text[k]].x;
			}
			glDisable(GL_TEXTURE_2D);
		}

		y += glyph_size['0'].y * 1.4;
		i = k + 1;
	}
}

int
main(void)
{
	glfwSetErrorCallback(glfw_error);

	if (!glfwInit()) die("glfwInit");

	GLFWwindow *window = glfwCreateWindow(640, 480, "xnote", NULL, NULL);
	if (!window) die("glfwCreateWindow");

	glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_HIDDEN);
	glfwSetWindowSizeCallback(window, window_resize_cb);
	glfwSetCursorPosCallback(window, mouse_move_cb);
	glfwSetMouseButtonCallback(window, mouse_press_cb);
	glfwSetKeyCallback(window, key_press_cb);
	glfwSetCharCallback(window, key_char_cb);
	glfwMakeContextCurrent(window);

	glClearColor(0, 0, 0, 0);
	glColor3f(1, 1, 1);
	glLineWidth(2);
	glPointSize(2);

	glfwGetCursorPos(window, &cursor_x, &cursor_y);
	glfwGetWindowSize(window, &window_width, &window_height);

	window_resize_cb(window, window_width, window_height);

	push_event(EVENT_START);

	const char *fontname = getenv("XNOTE_FONT") ?: "Arial";
	FcConfig *config = FcInitLoadConfigAndFonts();
	FcPattern *pattern = FcNameParse((const FcChar8 *)fontname);
	FcConfigSubstitute(config, pattern, FcMatchPattern);
	FcDefaultSubstitute(pattern);
	FcResult result;
	FcPattern *font = FcFontMatch(config, pattern, &result);
	if (!font) die("Failed to load font: %s", fontname);
	FcChar8 *filepath = NULL;
	assert(FcPatternGetString(font, FC_FILE, 0, &filepath) == FcResultMatch);
	int fontsize = 0;
	assert(FcPatternGetInteger(font, FC_SIZE, 0, &fontsize) == FcResultMatch);

	FT_Library freetype;
	FT_Face face;
	assert(!FT_Init_FreeType(&freetype));
	assert(!FT_New_Face(freetype, (const char *)filepath, 0, &face));
	assert(!FT_Set_Char_Size(face, 0, fontsize * 64, 300, 300));

	FcPatternDestroy(pattern);
	FcConfigDestroy(config);

	glGenTextures(128, glyphs);
	for (size_t c = 0; c < 128; c++) {
		FT_UInt glyph_index = FT_Get_Char_Index(face, (FT_UInt32)c);
		assert(!FT_Load_Glyph(face, glyph_index, FT_LOAD_RENDER));
		glyph_advance[c].x = face->glyph->advance.x >> 6;
		glyph_advance[c].y = face->glyph->advance.y >> 6;
		glyph_offset[c].x = face->glyph->bitmap_left;
		glyph_offset[c].y = face->glyph->bitmap_top;
		glyph_size[c].x = face->glyph->bitmap.width;
		glyph_size[c].y = face->glyph->bitmap.rows;
		glBindTexture(GL_TEXTURE_2D, glyphs[c]);
		glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB,
			face->glyph->bitmap.width, face->glyph->bitmap.rows,
			0, GL_LUMINANCE, GL_UNSIGNED_BYTE,
			face->glyph->bitmap.buffer);
	}

	while (!glfwWindowShouldClose(window)) {
		glClear(GL_COLOR_BUFFER_BIT);

		for (size_t i = 0; i < note_count; i++) {
			struct note *note = &notes[i];
			draw_text(note->text, note->align, note->len,
				note->x - canvas_x, note->y - canvas_y);
		}

		for (size_t i = 0; i < line_count; i++) {
			struct line *line = &lines[i];
			glBegin(GL_LINE_STRIP);
			for (size_t k = 0; k < line->count; k++)
				glVertex2f(line->points[k].x - canvas_x,
					line->points[k].y - canvas_y);
			glEnd();
		}

		glBegin(GL_POINTS);
		glVertex2f(cursor_x, cursor_y);
		glEnd();

		glfwSwapBuffers(window);

		glfwPollEvents();
	}

	glfwTerminate();
	FT_Done_Face(face);
	FT_Done_FreeType(freetype);
}