#!python
# -*- coding: utf-8 -*-
u"""
Display tilemap BG.

cursor key or WASD : scroll

Windows10 x64 21H1 + Python 3.9.7 64bit + pygame 2.0.1
"""

import json
import pygame
import sys

SCRW, SCRH = 800, 600

pygame.init()
screen = pygame.display.set_mode((SCRW, SCRH), pygame.DOUBLEBUF)

# load Tiled json file
bglayout = "road_layout.json"
with open(bglayout, 'r') as f:
    data = json.load(f)

map_w = int(data["width"])
map_h = int(data["height"])
tile_w = int(data["tilewidth"])
tile_h = int(data["tileheight"])

# get tilemap, convert start ID 1 to 0.
bgtilemap = list(map(lambda x: x-1, data["layers"][0]["data"]))

# load bg chip image
imgname = "road_chip.png"
img = pygame.image.load(imgname).convert_alpha()

# split bg chip image
bgchips = []
w, h = tile_w, tile_h
xc = img.get_width() // w
yc = img.get_height() // h
for yi in range(yc):
    for xi in range(xc):
        x, y = xi * w, yi * h
        bgchips.append(img.subsurface(pygame.Rect(x, y, w, h)))

xofs, yofs = 0, 0
xofs_max = max(0, map_w - (SCRW // tile_w))
yofs_max = max(0, map_h - (SCRH // tile_h))

running = True

clock = pygame.time.Clock()

# Main loop
while running:

    # update
    
    # check event
    for ev in pygame.event.get():
        if ev.type == pygame.QUIT:
            running = False
        if ev.type == pygame.KEYDOWN:
            if ev.key == pygame.K_ESCAPE or ev.key == pygame.K_q:
                # Push ESC or Q key
                running = False

    # scroll BG
    pygame.event.pump()
    pressed = pygame.key.get_pressed()
    if pressed[pygame.K_LEFT] or pressed[pygame.K_a]:
        xofs -= 1
        if xofs < 0:
            xofs = 0
    if pressed[pygame.K_RIGHT] or pressed[pygame.K_d]:
        xofs += 1
        if xofs > xofs_max:
            xofs = xofs_max
    if pressed[pygame.K_UP] or pressed[pygame.K_w]:
        yofs -= 1
        if yofs < 0:
            yofs = 0
    if pressed[pygame.K_DOWN] or pressed[pygame.K_s]:
        yofs += 1
        if yofs > yofs_max:
            yofs = yofs_max

    # draw start
    screen.fill((40, 60, 200))   # clear screen

    # draw tilemap BG
    xc = SCRW // tile_w
    yc = SCRH // tile_h
    for yi in range(yc):
        for xi in range(xc):
            xii = xi + xofs
            yii = yi + yofs
            if xii >= map_w or yii >= map_h:
                continue
            i = bgtilemap[yii * map_w + xii]
            x = xi * tile_w
            y = yi * tile_h
            screen.blit(bgchips[i], (x, y))

    pygame.display.flip()
    clock.tick_busy_loop(60)
    
    cap = "Tilemap BG - %5.2f FPS" % (clock.get_fps())
    pygame.display.set_caption(cap)

pygame.quit()
sys.exit()