#include <dos.h>
#include <stdio.h>
#include <stdlib.h>
#include "video.h"
#include "tiles.h"

/*** T I L E S ***/

// Tiles are 16x16 bitmaps, stored as arrays of words.
// Each tile has 4 or 5 planes (depending on whether it is a tile or sprite)
// which are stored adjacant to each other; ie. a 16-word array of blue,
// followed by a 16-word array of green, etc.
// Tiles in RAM are stored byte-swapped to aid in fast bit-shifting, and must
// be byte-swapped before being written to video memory.

// Because bit-shifting operations happen on little-endian words:
// 01234567 89ABCDEF << 3 => 34567XXX BCDEF012
// which is wrong. So instead we do:
// 89ABCDEF 01234567 << 3 => BCDEFXXX 3456789A byteswap => 3456789A BCDEFXXX

void tile_init() {
  setLogicalWidth(PAGE_STRIDE >> 1);
}

void blitTile(unsigned int offsetFrom, unsigned int offsetTo) {
  int y;
  for (y = 0; y < 16; y ++) {
    VID[offsetTo] = VID[offsetFrom ++];
    VID[offsetTo + 1] = VID[offsetFrom ++];
    offsetTo += PAGE_STRIDE;
  }
}

#define D_NOTHING 0x80
#define D_BGTILE 0x81
#define isBufIndex(d) (!((d) & 0x80))

#define NUM_BUFFERS 32
#define nextBufferIndex(i) ((i + 1) % 32)
#define BUF_WSTRIDE 16
#define BUF_WSIZE (BUF_WSTRIDE * 4)
typedef struct {
  unsigned int w;
  unsigned int h;
  int scrollX;
  int scrollY;
  unsigned int pageOffset[2];
  unsigned char dirty[2][PAGE_TILES_COUNT];
  unsigned int tilesOffset;
  unsigned int *memTiles;
  unsigned char *map;
  unsigned int buffer[NUM_BUFFERS][BUF_WSIZE];
  unsigned int bufferOffset[NUM_BUFFERS];
  unsigned char currentPage;
  unsigned char nextBuffer;
  unsigned char firstBuffer;
} TiledScreen_t;

TiledScreen_t screen = { 0, 0, 0, 0, { 0x0600, 0x2B00 }, 0, 0, NULL, NULL,
  0, 0, 0, 0, 0 };

void loadTiles(unsigned int tilesOffset, unsigned int *memTiles) {
  screen.tilesOffset = tilesOffset;
  screen.memTiles = memTiles;
}

void loadMap(unsigned char *map, unsigned int w, unsigned int h) {
  screen.map = map;
  screen.w = w;
  screen.h = h;
  memset(screen.dirty, D_BGTILE, PAGE_TILES_COUNT * 2);
}

int prepareBuffer(int pageX, int pageY) {
  unsigned char *dirty = &screen.dirty[screen.currentPage][pageX + (pageY * PAGE_TILES_W)];
  if (!isBufIndex(*dirty)) {
    unsigned int startX = screen.scrollX >> 4;
    unsigned int startY = screen.scrollY >> 4;
    unsigned char tile = screen.map[startX + pageX + ((startY + pageY) * screen.w)];
    unsigned char ibuffer = screen.nextBuffer;
    screen.nextBuffer = nextBufferIndex(ibuffer);
    *dirty = ibuffer;
    memcpy(screen.buffer[ibuffer], &screen.memTiles[tile * BUF_WSIZE], BUF_WSIZE << 1);
    screen.bufferOffset[ibuffer] = screen.pageOffset[screen.currentPage]
      + (pageX << 1) + (pageY * PAGE_STRIDE * 16);
  }
  return *dirty;
}

void drawSpriteToBuf(unsigned int *sprite, int pageX, int pageY, int shift, int yStart) {
  unsigned int *buf, *mask;
  unsigned int maskval;
  int y, h, plane;
  if (pageX < 0 || pageY < 0 ||
      pageX >= PAGE_TILES_W || pageY >= PAGE_TILES_H ||
      shift >= 16 || shift <= -16 ||
      yStart <= -16 || yStart >= 16) {
    return;
  }

  buf = screen.buffer[prepareBuffer(pageX, pageY)];
  if (yStart < 0) {
    sprite = &sprite[-yStart];
    h = yStart + 16;
  } else {
    buf = &buf[yStart];
    h = 16 - yStart;
  }
  mask = &sprite[BUF_WSTRIDE * 4];
  if (shift < 0) {
    shift = -shift;
    for (plane = 0; plane < 4; plane ++) {
      for (y = 0; y < h; y ++) {
	maskval = mask[y] << shift;
	buf[y] = (buf[y] & ~maskval) | ((sprite[y] << shift) & maskval);
      }
      sprite += BUF_WSTRIDE;
      buf += BUF_WSTRIDE;
    }
  } else {
    for (plane = 0; plane < 4; plane ++) {
      for (y = 0; y < h; y ++) {
	maskval = mask[y] >> shift;
	buf[y] = (buf[y] & ~maskval) | ((sprite[y] >> shift) & maskval);
      }
      sprite += BUF_WSTRIDE;
      buf += BUF_WSTRIDE;
    }
  }
}

void drawSprite(unsigned int *sprite, int x, int y) {
  int pageX = (int)(x - (screen.scrollX & 0xfff0)) >> 4;
  int pageY = (int)(y - (screen.scrollY & 0xfff0)) >> 4;
  int pageOffsetX = x & 0x0f;
  int pageOffsetY = y & 0x0f;

  drawSpriteToBuf(sprite, pageX, pageY, pageOffsetX, pageOffsetY);
  drawSpriteToBuf(sprite, pageX + 1, pageY, pageOffsetX - 16, pageOffsetY);
  drawSpriteToBuf(sprite, pageX, pageY + 1, pageOffsetX, pageOffsetY - 16);
  drawSpriteToBuf(sprite, pageX + 1, pageY + 1, pageOffsetX - 16, pageOffsetY - 16);
}

void scroll(int newX, int newY) {
  newX = min(max(newX, 0), (screen.w << 4) - 320);
  newY = min(max(newY, 0), (screen.h << 4) - 200);
  if ((screen.scrollX & 0xfff0) != (newX & 0xfff0) ||
      (screen.scrollY & 0xfff0) != (newY & 0xfff0)) {
    int mapX, mapY;
    unsigned char page;
    for (page = 0; page < 2; page ++) {
      int mapOffsetOld = (screen.scrollX >> 4) + ((screen.scrollY >> 4) * screen.w);
      int mapOffsetNew = (newX >> 4) + ((newY >> 4) * screen.w);
      unsigned char *dirty = screen.dirty[page];
      for (mapY = 0; mapY < PAGE_TILES_H; mapY ++) {
	for (mapX = 0; mapX < PAGE_TILES_W; mapX ++) {
	  if (*dirty != D_NOTHING ||
	    screen.map[mapOffsetOld + mapX] != screen.map[mapOffsetNew + mapX]) {
	    *dirty = D_BGTILE;
	  }
	  dirty ++;
	}
	mapOffsetNew += screen.w;
	mapOffsetOld += screen.w;
      }
    }
  }
  screen.scrollX = newX;
  screen.scrollY = newY;
}

void drawScreen() {
  unsigned int startX = screen.scrollX >> 4;
  unsigned int startY = screen.scrollY >> 4;
  unsigned int offsetX = screen.scrollX - (startX << 4);
  unsigned int offsetY = screen.scrollY - (startY << 4);
  unsigned int drawOffset = screen.pageOffset[screen.currentPage];
  unsigned int scrollOffset = drawOffset + (offsetX >> 3) + (offsetY * PAGE_STRIDE);
  unsigned char *dirty = screen.dirty[screen.currentPage];
  unsigned int x, y, di, plane, bmp;

  setAllPlanes();
  setWriteMode(1);

  di = 0;
  for (y = startY; y < startY + PAGE_TILES_H; y ++) {
    for (x = startX; x < startX + PAGE_TILES_W; x ++) {
      if (dirty[di++] == D_BGTILE) {
	blitTile(
	  screen.tilesOffset + (screen.map[x + (y * screen.w)] << 5),
	  drawOffset);
      }
      drawOffset += 2;
    }
    drawOffset += PAGE_STRIDE * 15;
  }
  setWriteMode(0);
  for(plane = 0; plane < 4; plane ++) {
    setPlane(plane);
    for (di = screen.firstBuffer; di != screen.nextBuffer; di = nextBufferIndex(di)) {
      drawOffset = screen.bufferOffset[di] >> 1;
      for (y = 0; y < 16; y ++) {
	bmp = screen.buffer[di][y + (BUF_WSTRIDE * plane)];
	WVID[drawOffset] = (bmp << 8) | (bmp >> 8);
	drawOffset += PAGE_STRIDE >> 1;
      }
    }
  }
  setAllPlanes();
  setDisplayOffset(scrollOffset);
  setHorizontalPan(screen.scrollX & 0x07);

  screen.currentPage ^= 1;
  screen.firstBuffer = screen.nextBuffer;
  for (di = 0; di < PAGE_TILES_COUNT; di ++) {
    dirty[di] = isBufIndex(dirty[di]) ? D_BGTILE : D_NOTHING;
  }
}