/*
 * Copyright (c) Camden Dixie O'Brien
 * SPDX-License-Identifier: AGPL-3.0-only
 */

#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <assert.h>
#include <ctype.h>
#include <libxml/parser.h>
#include <math.h>
#include <stdbool.h>
#include <string.h>

#define SCALE 4

#define TILESIZE 32
#define VIEWWIDTH (8 * TILESIZE)
#define VIEWHEIGHT (6 * TILESIZE)

#define MAX_PATH_LEN 128

#define MAP_ASSET "/map.tmx"
#define MAPWIDTH 112
#define MAPHEIGHT 112
#define MAPSHIFTX 48
#define MAPSHIFTY 48

#define TSASSET "/tileset.png"
#define TSCOLS 56

#define PIASSET "/player/idle/down.png"
#define PIWIDTH 48
#define PIHEIGHT 64
#define PIANIMLEN 8

#define WALKSPEED 72 // pixels per second

#define BASEANIMPERIOD 200

typedef struct {
	bool left, right, up, down;
} input_state_t;

typedef struct {
	double x, y;
} dvec_t;

static SDL_Window *window;
static SDL_Renderer *renderer;
static unsigned map[MAPWIDTH][MAPHEIGHT];
static SDL_Texture *tstex, *pitex;
static input_state_t input;

static inline double mag(dvec_t v)
{
	return sqrt(v.x * v.x + v.y * v.y);
}

int main(int argc, char *argv[])
{
	char path[MAX_PATH_LEN];

	if (2 != argc) {
		fprintf(stderr, "Usage: %s ASSETS-DIR\n", argv[0]);
		return 1;
	}

	// Set up SDL window
	int err = SDL_Init(SDL_INIT_VIDEO);
	assert(0 == err);
	window = SDL_CreateWindow(
	    "2D Game", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
	    SCALE * VIEWWIDTH, SCALE * VIEWHEIGHT, 0);
	assert(NULL != window);
	renderer = SDL_CreateRenderer(window, -1, 0);
	assert(NULL != renderer);

	// Find chunk nodes in map XML
	xmlDocPtr doc;
	xmlNodePtr node;
	assert(strlen(argv[1]) + strlen(MAP_ASSET) < MAX_PATH_LEN);
	strcpy(path, argv[1]);
	strcat(path, MAP_ASSET);
	doc = xmlParseFile(path);
	assert(NULL != doc);
	node = xmlDocGetRootElement(doc);
	assert(0 == xmlStrcmp(node->name, (const xmlChar *)"map"));
	node = node->xmlChildrenNode;
	while (NULL != node
	       && xmlStrcmp(node->name, (const xmlChar *)"layer") != 0)
		node = node->next;
	assert(NULL != node);
	node = node->xmlChildrenNode;
	while (NULL != node
	       && xmlStrcmp(node->name, (const xmlChar *)"data") != 0)
		node = node->next;
	assert(NULL != node);

	// Iterate through chunks and populate map array.
	xmlNodePtr chunk_contents;
	for (node = node->xmlChildrenNode; NULL != node; node = node->next) {
		if (0 != xmlStrcmp(node->name, (const xmlChar *)"chunk"))
			continue;

		xmlChar *x_attr, *y_attr;
		x_attr = xmlGetProp(node, (const xmlChar *)"x");
		y_attr = xmlGetProp(node, (const xmlChar *)"y");
		const int chunk_x = atoi((const char *)x_attr);
		const int chunk_y = atoi((const char *)y_attr);

		chunk_contents = node->xmlChildrenNode;
		assert(
		    0 == xmlStrcmp(chunk_contents->name, (const xmlChar *)"text"));
		int x = chunk_x + MAPSHIFTX, y = chunk_y + MAPSHIFTY;
		xmlChar buf[10];
		const xmlChar *p, *q;
		q = chunk_contents->content;
		while (isspace((const char)*q))
			++q;
		p = q;
		while ('\0' != *q) {
			switch (*q) {
			case (xmlChar)',':
				memset(buf, 0, sizeof(buf));
				memcpy(buf, p, sizeof(xmlChar) * (q - p));
				assert(x < MAPWIDTH && y < MAPHEIGHT);
				map[x][y] = (unsigned)atoi((const char *)buf);
				++x;
				p = ++q;
				break;
			case (xmlChar)'\n':
				if (x < MAPWIDTH) {
					memset(buf, 0, sizeof(buf));
					memcpy(buf, p, sizeof(xmlChar) * (q - p));
					assert(y < MAPHEIGHT);
					map[x][y] = (unsigned)atoi((const char *)buf);
				}
				x = chunk_x + MAPSHIFTX;
				++y;
				p = ++q;
				break;
			default:
				++q;
				break;
			}
		}
	}

	// Load tileset
	assert(strlen(argv[1]) + strlen(TSASSET) < MAX_PATH_LEN);
	strcpy(path, argv[1]);
	strcat(path, TSASSET);
	tstex = IMG_LoadTexture(renderer, path);
	assert(NULL != tstex);

	// Load player idle spritesheet
	assert(strlen(argv[1]) + strlen(PIASSET) < MAX_PATH_LEN);
	strcpy(path, argv[1]);
	strcat(path, PIASSET);
	pitex = IMG_LoadTexture(renderer, path);
	assert(NULL != pitex);

	// Initialize view and player
	dvec_t vpos = { 512, 0 };
	SDL_Rect psrc = { .y = 0, .w = PIWIDTH, .h = PIHEIGHT };
	SDL_Rect pdest = { .w = SCALE * PIWIDTH, .h = SCALE * PIHEIGHT };
	dvec_t pvel = { 0, 0 }, ppos = { 640, 96 };

	SDL_Event event;
	uint64_t prevt = SDL_GetTicks64();
	while (1) {
		// Calculate dt
		const uint64_t t = SDL_GetTicks64();
		const uint64_t dt = t - prevt;
		prevt = t;

		// Handle events
		SDL_PollEvent(&event);
		switch (event.type) {
		case SDL_QUIT:
			goto quit;

		case SDL_KEYDOWN:
			switch (event.key.keysym.sym) {
			case SDLK_LEFT:
				input.left = true;
				break;
			case SDLK_RIGHT:
				input.right = true;
				break;
			case SDLK_UP:
				input.up = true;
				break;
			case SDLK_DOWN:
				input.down = true;
				break;
			default:
				break;
			}
			break;

		case SDL_KEYUP:
			switch (event.key.keysym.sym) {
			case SDLK_LEFT:
				input.left = false;
				break;
			case SDLK_RIGHT:
				input.right = false;
				break;
			case SDLK_UP:
				input.up = false;
				break;
			case SDLK_DOWN:
				input.down = false;
				break;
			default:
				break;
			}
			break;

		default:
			break;
		}

		// Calculate and apply velocity
		pvel.x = (input.left ? -1 : 0) + (input.right ? 1 : 0);
		pvel.y = (input.up ? -1 : 0) + (input.down ? 1 : 0);
		const double pspeed = mag(pvel);
		if (pspeed != 0) {
			pvel.x *= WALKSPEED / pspeed;
			pvel.y *= WALKSPEED / pspeed;
			ppos.x += (double)dt / 1000.0 * pvel.x;
			ppos.y += (double)dt / 1000.0 * pvel.y;
		}

		// Update view
		const dvec_t pvdisp = {
			.x = ppos.x - (vpos.x + VIEWWIDTH / 2),
			.y = ppos.y - (vpos.y + VIEWHEIGHT / 2),
		};
		if (mag(pvdisp) > 72) {
			vpos.x += (double)dt / 1000.0 * pvel.x;
			vpos.y += (double)dt / 1000.0 * pvel.y;
		}

		SDL_RenderClear(renderer);

		// Draw map
		const int startx = TILESIZE * floor(vpos.x / TILESIZE);
		const int starty = TILESIZE * floor(vpos.y / TILESIZE);
		for (int y = starty; y < vpos.y + VIEWHEIGHT; y += TILESIZE) {
			for (int x = startx; x < vpos.x + VIEWWIDTH; x += TILESIZE) {
				const unsigned row = x / TILESIZE + MAPSHIFTX;
				const unsigned col = y / TILESIZE + MAPSHIFTY;
				if (row >= MAPWIDTH || col >= MAPHEIGHT)
					continue;
				const unsigned tileid = map[row][col];
				if (0 == tileid)
					continue;
				const SDL_Rect src = {
					.x = TILESIZE * ((tileid - 1) % TSCOLS),
					.y = TILESIZE * ((tileid - 1) / TSCOLS),
					.w = TILESIZE,
					.h = TILESIZE,
				};
				const SDL_Rect dest = {
					.x = SCALE * (x - vpos.x),
					.y = SCALE * (y - vpos.y),
					.w = SCALE * TILESIZE,
					.h = SCALE * TILESIZE,
				};
				SDL_RenderCopy(renderer, tstex, &src, &dest);
			}
		}

		// Draw player
		const unsigned piframe = (t / BASEANIMPERIOD) % PANIMLEN;
		psrc.x = PWIDTH * piframe;
		pdest.x = SCALE * (int)(ppos.x - vpos.x - PWIDTH / 2);
		pdest.y = SCALE * (int)(ppos.y - vpos.y - PHEIGHT / 2);
		SDL_RenderCopy(renderer, pidle, &psrc, &pdest);

		SDL_RenderPresent(renderer);
	}

quit:
	SDL_DestroyRenderer(renderer);
	SDL_DestroyWindow(window);
	SDL_Quit();

	return 0;
}