/*
    3dsspec - Nintendo 3DS Spectrum emulator

    Copyright (C) 2021  Ian Cowburn <ianc@noddybox.co.uk>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, see <http://www.gnu.org/licenses/>

    -------------------------------------------------------------------------

    Provides the emulation for the Spectrum

*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <3ds.h>

#include "spec.h"
#include "gui.h"
#include "framebuffer.h"

#include "stream.h"

#include "config.h"

#include "spec48_bin.h"

#ifndef TRUE
#define TRUE 1
#endif

#ifndef FALSE
#define FALSE 0
#endif

/* ---------------------------------------- STATICS
*/
#define ROMLEN		0x4000
#define ROM_SAVE	0x2fc
#define ROM_LOAD	0x347

#define ED_SAVE		0xf0
#define ED_LOAD		0xf1

#define SLOW_TSTATES	16000
#define FAST_TSTATES	64000

#define E_LINE		16404
#define LASTK1		16421
#define LASTK2		16422
#define MARGIN		16424
#define FRAMES		16436
#define CDFLAG		16443

#define NMI_PERIOD      208

/* The SPEC screen and memory
*/
static int              fast_mode=FALSE;
static int              nmigen=FALSE;
static int              hsync=FALSE;
static int              drawing_screen=FALSE;
static int              ula_line_counter;

static u16              black;
static u16              white;

#define	SCR_W		256
#define	SCR_H		192
#define	TXT_W		32
#define	TXT_H		24

static Z80Byte		mem[0x10000];

static u16              screen[SCR_W*SCR_H];
static int              ula_ptr;

static Z80Word		RAMBOT=0;
static Z80Word		RAMTOP=0;

#define DFILE		0x400c

#define WORD(a)		(mem[a] | (Z80Word)mem[a+1]<<8)

/* Tape
*/
static int		enable_filesystem;
static int		allow_save;
static const Z80Byte	*tape_image;
static int		tape_len;

static char		last_dir[FILENAME_MAX] = "/";

/* The keyboard
*/
static Z80Byte		matrix[8];

static struct
{
    int row;
    int bit;
} key_matrix[]=
    {
    	{3,0x01}, {3,0x02}, {3,0x04}, {3,0x08}, {3,0x10}, 	/* 1 - 5 */
    	{4,0x10}, {4,0x08}, {4,0x04}, {4,0x02}, {4,0x01}, 	/* 6 - 0 */
    	{2,0x01}, {2,0x02}, {2,0x04}, {2,0x08}, {2,0x10}, 	/* Q - T */
    	{5,0x10}, {5,0x08}, {5,0x04}, {5,0x02}, {5,0x01}, 	/* Y - P */
    	{1,0x01}, {1,0x02}, {1,0x04}, {1,0x08}, {1,0x10}, 	/* A - G */
    	{6,0x10}, {6,0x08}, {6,0x04}, {6,0x02}, {6,0x01}, 	/* H - NL */
    	{0,0x01}, {0,0x02}, {0,0x04}, {0,0x08}, {0,0x10}, 	/* CAPS - V */
    	{7,0x10}, {7,0x08}, {7,0x04}, {7,0x02}, {7,0x01} 	/* B - SPACE */
    };


/* ---------------------------------------- PRIVATE FUNCTIONS
*/
#define PEEKW(addr)		(mem[addr] | (Z80Word)mem[addr+1]<<8)

#define POKEW(addr,val)         do					\
                                {					\
                                    Z80Word wa=addr;			\
                                    Z80Word wv=val;			\
                                    mem[wa]=wv;				\
                                    mem[wa+1]=wv>>8;			\
                                } while(0)

static void RomPatch(void)
{
    static const Z80Byte save[]=
    {
    	0xed, ED_SAVE,		/* (SAVE)		*/
	0xc3, 0x07, 0x02,	/* JP $0207		*/
	0xff			/* End of patch		*/
    };

    static const Z80Byte load[]=
    {
    	0xed, ED_LOAD,		/* (LOAD)		*/
	0xc3, 0x07, 0x02,	/* JP $0207		*/
	0xff			/* End of patch		*/
    };

    int f;

    for(f=0;save[f]!=0xff;f++)
    {
	mem[ROM_SAVE+f]=save[f];
    }

    for(f=0;load[f]!=0xff;f++)
    {
	mem[ROM_LOAD+f]=load[f];
    }
}

/* Open a tape file the passed address
*/
static FILE *OpenTapeFile(Z80Word addr, int *cancelled, const char *mode)
{
    static const char zx_chars[] = "\"#$:?()><=+-*/;,."
				   "0123456789"
				   "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    FILE *fp;
    char full_fn[FILENAME_MAX] = DEFAULT_SNAPDIR;
    char fn[FILENAME_MAX];
    int f;
    int done;

    fp = NULL;
    f = 0;
    done = FALSE;
    *cancelled = FALSE;

    while(f<(FILENAME_MAX-3) && !done)
    {
    	int ch;

	ch = mem[addr++];

	if (ch&0x80)
	{
	    done = TRUE;
	    ch &= 0x7f;
	}

	if (ch>=11 && ch<=63)
	{
	    fn[f++] = zx_chars[ch-11];
	}
    }

    if (fn[0] == '*')
    {
    	if (GUI_FileSelect(last_dir,fn,".P"))
	{
	    fp = fopen(fn, mode);
	}
	else
	{
	    *cancelled = TRUE;
	}

	SK_DisplayKeyboard();
    }
    else
    {
	fn[f++] = '.';
	fn[f++] = 'P';
	fn[f] = 0;

	strcat(full_fn,fn);

	if (!(fp = fopen(full_fn, mode)))
	{
	    fp = fopen(fn, mode);
	}
    }

    return fp;
}


static void LoadInternalTape(Z80 *z80)
{
    memcpy(mem+0x4009,tape_image,tape_len);
}


static void LoadExternalTape(FILE *tape, Z80 *z80)
{
    int c;
    Z80Byte *a;

    a=mem+0x4009;

    while((c=getc(tape))!=EOF)
    {
    	*a++=c;
    }
}


static void SaveExternalTape(FILE *tape, Z80 *z80)
{
    int f;
    int end;

    f = 0x4009;
    end = WORD(E_LINE);

    while(f <= end)
    {
    	fputc(mem[f++], tape);
    }
}


static int CheckTimers(Z80 *z80, Z80Val val)
{
    static Z80Word last_PC;
    static Z80Byte last_R;
    int ret = TRUE;

    /* See if we're started or stopping executing the display file
    */
    if (z80->PC > 0x7fff)
    {
        if (last_PC < 0x8000)
        {
            drawing_screen = TRUE;
            ula_ptr = 0;
        }
    }

    if (z80->PC < 0x8000)
    {
        if (last_PC > 0x7fff && ula_ptr == SCR_W * SCR_H)
        {
            drawing_screen = FALSE;
            ula_ptr = 0;
            Z80ResetCycles(z80, val - SLOW_TSTATES);
            ret = FALSE;
        }
    }

    last_PC = z80->PC;

    /* Check HSYNC generation
    */
    if (hsync && !nmigen)
    {
        if (last_R & 0x40 && !(z80->R & 0x40))
        {
            Z80Interrupt(z80, 0xff);
            ula_line_counter = (ula_line_counter + 1) % 8;
        }
    }

    last_R = z80->R;

    /* Check NMI generator
    */
    if (nmigen && val > NMI_PERIOD)
    {
        Z80NMI(z80);
        Z80ResetCycles(z80, val - NMI_PERIOD);
    }

    /* We should only be able to execute FAST_TSTATES if we're not drawing the
       screen.
    */
    if (val >= FAST_TSTATES)
    {
	Z80ResetCycles(z80,val-FAST_TSTATES);

	if (mem[CDFLAG] & 0x80)
	{
	    fast_mode = FALSE;
	}
	else
	{
            fast_mode = TRUE;
	}

	ret = FALSE;
    }

    return ret;
}


static int EDCallback(Z80 *z80, Z80Val data)
{
    switch((Z80Byte)data)
    {
    	case ED_SAVE:
	    if (allow_save && z80->DE.w<0x8000)
	    {
		FILE *fp;
		int cancel;

		if ((fp=OpenTapeFile(z80->HL.w, &cancel, "wb")))
		{
		    SaveExternalTape(fp,z80);
		    fclose(fp);
		}
	    }
	    break;

    	case ED_LOAD:
	    /* Try and load the external file if a name given.  Otherwise, we
	       try the internal one.  Some of this is slightly dodgy -- it was
	       never intended for the emulator to be doing any GUI related
	       nonsense (like the alerts) but simply emulating.
	    */
	    if (enable_filesystem && z80->DE.w<0x8000)
	    {
		FILE *fp;
		int cancel;

		if ((fp=OpenTapeFile(z80->DE.w, &cancel, "rb")))
		{
		    LoadExternalTape(fp,z80);
		    fclose(fp);
		}
		else
		{
		    if (!cancel)
		    {
			GUI_Alert(FALSE,"Couldn't open tape");
			SK_DisplayKeyboard();
		    }
		}
	    }
	    else
	    {
		if (tape_image)
		{
		    LoadInternalTape(z80);
		}
		else
		{
		    GUI_Alert(FALSE,"No tape image selected");
		    SK_DisplayKeyboard();
		}
	    }

	    mem[CDFLAG]=0xc0;
	    break;

	default:
	    break;
    }

    return TRUE;
}


/* ---------------------------------------- EXPORTED INTERFACES
*/
void SPECInit(Z80 *z80)
{
    Z80Word f;

    black = FB_GetColour(COL_BLACK);
    white = FB_GetColour(COL_WHITE);

    /* Load the ROM
    */
    memcpy(mem,spec48_bin,ROMLEN);

    /* Patch the ROM
    */
    RomPatch();
    Z80LodgeCallback(z80,eZ80_EDHook,EDCallback);
    Z80LodgeCallback(z80,eZ80_Instruction,CheckTimers);

    /* Mirror the ROM
    */
    memcpy(mem+ROMLEN,mem,ROMLEN);

    /* Memory size (16K)
    */
    RAMBOT=0x4000;
    RAMTOP=RAMBOT+0x4000;

    for(f = RAMBOT; f <= RAMTOP; f++)
    {
    	mem[f] = 0;
    }

    for(f = 0; f < 8; f++)
    {
    	matrix[f] = 0x1f;
    }
}


void SPECRenderDisplay(Framebuffer *fb, Z80 *z80)
{
    if (fast_mode)
    {
        u16 x;
        u16 y;

        for(x = 0; x < fb->width; x++)
        {
            for(y = 0; y < fb->height; y++)
            {
                FB_ADDR(fb, x, y) = ((x+y) % 2) ? black : white;
            }
        }
    }
    else
    {
        int x;
        int y;

        FB_Clear(fb, COL_WHITE);

        for(y = 0; y < SCR_H; y++)
        {
            for(x = 0; x < SCR_W; x++)
            {
                FB_ADDR(fb, 72 + x, fb->height - 24 - y) =
                                            screen[x + y * SCR_W];
            }
        }
    }
}


void SPECHandleKey(SoftKey key, int is_pressed)
{
    if (key<SK_CONFIG)
    {
	if (is_pressed)
	{
	    matrix[key_matrix[key].row]&=~key_matrix[key].bit;
	}
	else
	{
	    matrix[key_matrix[key].row]|=key_matrix[key].bit;
	}
    }
    else
    {
    	/* TODO: Joysticks?  Were there any common ones for the 81? */
    }
}


Z80Byte SPECReadMem(Z80 *z80, Z80Word addr)
{
    if (addr & 0x8000)
    {
        Z80Byte b;

        b = mem[addr & 0x7fff];

        /* If bit 6 of the byte is set it is sent to the CPU, otherwise it is
           used to generate the video signal and zero sent to the CPU
        */
        if (b & 0x40)
        {
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
            screen[ula_ptr++] = white;
        }
        else
        {
            Z80Word base;
            int inv;
            int f;

            inv=b & 0x80;
            b &= 0x3f;

            base = ((Z80Word)z80->I<<8)|(b<<3)|ula_line_counter;

            b = mem[base];

            for(f = 0; f < 8; f++)
            {
                if (b & 0x80)
                {
                    screen[ula_ptr++] = rand(); // inv ? white : black;
                }
                else
                {
                    screen[ula_ptr++] = rand(); // inv ? black : white;
                }

                b = b << 1;
            }

            b = 0;
        }

        return b;
    }
    else
    {
        return mem[addr];
    }
}


void SPECWriteMem(Z80 *z80, Z80Word addr, Z80Byte val)
{
    if (addr>=RAMBOT && addr<=RAMTOP)
    {
	mem[addr]=val;
    }
}


Z80Byte SPECReadPort(Z80 *z80, Z80Word port)
{
    Z80Byte b=0;

    switch(port&0xff)
    {
    	case 0xfe:	/* ULA */
	    /* Key matrix
	    */
	    switch(port&0xff00)
	    {
	    	case 0xfe00:
		    b=matrix[0];
		    break;
	    	case 0xfd00:
		    b=matrix[1];
		    break;
	    	case 0xfb00:
		    b=matrix[2];
		    break;
	    	case 0xf700:
		    b=matrix[3];
		    break;
	    	case 0xef00:
		    b=matrix[4];
		    break;
	    	case 0xdf00:
		    b=matrix[5];
		    break;
	    	case 0xbf00:
		    b=matrix[6];
		    break;
	    	case 0x7f00:
		    b=matrix[7];
		    break;
	    }

	    /* Some code expects some of the top bits set...  Of course, whether
	       or not this may be worse as other code doesn't expect the bits,
	       we shall find out!
	    */
	    b |= 0x60;

            /* Reset ULA line counter
            */
            ula_line_counter = 0;

	    break;

	default:
	    b = 0xff;	/* Idle bus */
	    break;
    }

    return b;
}


void SPECWritePort(Z80 *z80, Z80Word port, Z80Byte val)
{
    switch(port&0xff)
    {
    	case 0xfd:              /* NMI generator OFF */
            nmigen = FALSE;
	    break;

	case 0xfe:              /* NMI generator ON */
            nmigen = TRUE;
            Z80ResetCycles(z80, 0);
	    break;

        case 0xff:              /* HSYNC generator ON */
            hsync = TRUE;
            break;
    }
}


void SPECReset(Z80 *z80)
{
    int f;

    for(f=0;f<8;f++)
    	matrix[f]=0x1f;

    Z80Reset(z80);
    Z80ResetCycles(z80,0);

    nmigen = FALSE;
    hsync = FALSE;
}


void SPECEnableFileSystem(int enable)
{
    enable_filesystem=enable;
}


void SPECSetTape(const Z80Byte *image, int len)
{
    tape_image=image;
    tape_len=len;
}


void SPECReconfigure(void)
{
    allow_save = enable_filesystem && DSSPEC_Config[DSSPEC_ALLOW_TAPE_SAVE];
}


void SPECSaveSnapshot(FILE *fp)
{
    int f;

    for(f=0; f<sizeof mem; f++)
    {
	PUT_Byte(fp, mem[f]);
    }

    for(f=0; f<sizeof matrix; f++)
    {
	PUT_Byte(fp, matrix[f]);
    }

    PUT_ULong(fp, RAMBOT);
    PUT_ULong(fp, RAMTOP);
}


void SPECLoadSnapshot(FILE *fp)
{
    int f;

    for(f=0; f<sizeof mem; f++)
    {
	mem[f] = GET_Byte(fp);
    }

    for(f=0; f<sizeof matrix; f++)
    {
	matrix[f] = GET_Byte(fp);
    }

    RAMBOT = GET_ULong(fp);
    RAMTOP = GET_ULong(fp);
}


/* END OF FILE */