/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * 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 2
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */

#include "glk/glulxe/glulxe.h"

namespace Glk {
namespace Glulxe {

void Glulxe::enter_function(uint funcaddr, uint argc, uint *argv) {
  uint ix, jx;
  acceleration_func accelFunc;
  int locallen;
  int functype;
  uint modeaddr, opaddr, val;
  int loctype, locnum;
  uint addr = funcaddr;

  accelFunc = accel_get_func(addr);
  if (accelFunc) {
    profile_in(addr, stackptr, TRUE);
    val = (this->*accelFunc)(argc, argv);
    profile_out(stackptr);
    pop_callstub(val);
    return;
  }
    
  profile_in(addr, stackptr, FALSE);

  /* Check the Glulx type identifier byte. */
  functype = Mem1(addr);
  if (functype != 0xC0 && functype != 0xC1) {
    if (functype >= 0xC0 && functype <= 0xDF)
      fatal_error_i("Call to unknown type of function.", addr);
    else
      fatal_error_i("Call to non-function.", addr);
  }
  addr++;

  /* Bump the frameptr to the top. */
  frameptr = stackptr;

  /* Go through the function's locals-format list, copying it to the
     call frame. At the same time, we work out how much space the locals
     will actually take up. (Including padding.) */
  ix = 0;
  locallen = 0;
  while (1) {
    /* Grab two bytes from the locals-format list. These are 
       unsigned (0..255 range). */
    loctype = Mem1(addr);
    addr++;
    locnum = Mem1(addr);
    addr++;

    /* Copy them into the call frame. */
    StkW1(frameptr+8+2*ix, loctype);
    StkW1(frameptr+8+2*ix+1, locnum);
    ix++;

    /* If the type is zero, we're done, except possibly for two more
       zero bytes in the call frame (to ensure 4-byte alignment.) */
    if (loctype == 0) {
      /* Make sure ix is even. */
      if (ix & 1) {
        StkW1(frameptr+8+2*ix, 0);
        StkW1(frameptr+8+2*ix+1, 0);
        ix++;
      }
      break;
    }

    /* Pad to 4-byte or 2-byte alignment if these locals are 4 or 2
       bytes long. */
    if (loctype == 4) {
      while (locallen & 3)
        locallen++;
    }
    else if (loctype == 2) {
      while (locallen & 1)
        locallen++;
    }
    else if (loctype == 1) {
      /* no padding */
    }
    else {
      fatal_error("Illegal local type in locals-format list.");
    }

    /* Add the length of the locals themselves. */
    locallen += (loctype * locnum);
  }

  /* Pad the locals to 4-byte alignment. */
  while (locallen & 3)
    locallen++;

  /* We now know how long the locals-frame and locals segments are. */
  localsbase = frameptr+8+2*ix;
  valstackbase = localsbase+locallen;

  /* Test for stack overflow. */
  /* This really isn't good enough; if the format list overflowed the
     stack, we've already written outside the stack array. */
  if (valstackbase >= stacksize)
    fatal_error("Stack overflow in function call.");

  /* Fill in the beginning of the stack frame. */
  StkW4(frameptr+4, 8+2*ix);
  StkW4(frameptr, 8+2*ix+locallen);

  /* Set the stackptr and PC. */
  stackptr = valstackbase;
  pc = addr;

  /* Zero out all the locals. */
  for (jx=0; jx < (uint)locallen; jx++) 
    StkW1(localsbase+jx, 0);

  if (functype == 0xC0) {
    /* Push the function arguments on the stack. The locals have already
       been zeroed. */
    if (stackptr+4*(argc+1) >= stacksize)
      fatal_error("Stack overflow in function arguments."); 
    for (ix=0; ix<argc; ix++) {
      val = argv[(argc-1)-ix];
      StkW4(stackptr, val);
      stackptr += 4;
    }
    StkW4(stackptr, argc);
    stackptr += 4;
  }
  else {
    /* Copy in function arguments. This is a bit gross, since we have to
       follow the locals format. If there are fewer arguments than locals,
       that's fine -- we've already zeroed out this space. If there are
       more arguments than locals, the extras are silently dropped. */
    modeaddr = frameptr+8;
    opaddr = localsbase;
    ix = 0;
    while (ix < argc) {
      loctype = Stk1(modeaddr);
      modeaddr++;
      locnum = Stk1(modeaddr);
      modeaddr++;
      if (loctype == 0)
        break;
      if (loctype == 4) {
        while (opaddr & 3)
          opaddr++;
        while (ix < argc && locnum) {
          val = argv[ix];
          StkW4(opaddr, val);
          opaddr += 4;
          ix++;
          locnum--;
        }
      }
      else if (loctype == 2) {
        while (opaddr & 1)
          opaddr++;
        while (ix < argc && locnum) {
          val = argv[ix] & 0xFFFF;
          StkW2(opaddr, val);
          opaddr += 2;
          ix++;
          locnum--;
        }
      }
      else if (loctype == 1) {
        while (ix < argc && locnum) {
          val = argv[ix] & 0xFF;
          StkW1(opaddr, val);
          opaddr += 1;
          ix++;
          locnum--;
        }
      }
    }
  }

  /* If the debugger is compiled in, check for a breakpoint on this
     function. (Checking the function address, not the starting PC.) */
  debugger_check_func_breakpoint(funcaddr);
}

void Glulxe::leave_function() {
  profile_out(stackptr);
  stackptr = frameptr;
}

void Glulxe::push_callstub(uint desttype, uint destaddr) {
  if (stackptr+16 > stacksize)
    fatal_error("Stack overflow in callstub.");
  StkW4(stackptr+0, desttype);
  StkW4(stackptr+4, destaddr);
  StkW4(stackptr+8, pc);
  StkW4(stackptr+12, frameptr);
  stackptr += 16;
}

void Glulxe::pop_callstub(uint returnvalue) {
  uint desttype, destaddr;
  uint newpc, newframeptr;

  if (stackptr < 16)
    fatal_error("Stack underflow in callstub.");
  stackptr -= 16;

  newframeptr = Stk4(stackptr+12);
  newpc = Stk4(stackptr+8);
  destaddr = Stk4(stackptr+4);
  desttype = Stk4(stackptr+0);

  pc = newpc;
  frameptr = newframeptr;

  /* Recompute valstackbase and localsbase */
  valstackbase = frameptr + Stk4(frameptr);
  localsbase = frameptr + Stk4(frameptr+4);

  switch (desttype) {

  case 0x11:
    fatal_error("String-terminator call stub at end of function call.");
    break;

  case 0x10:
    /* This call stub was pushed during a string-decoding operation!
       We have to restart it. (Note that the return value is discarded.) */
    stream_string(pc, 0xE1, destaddr); 
    break;

  case 0x12:
    /* This call stub was pushed during a number-printing operation.
       Restart that. (Return value discarded.) */
    stream_num(pc, true, destaddr);
    break;

  case 0x13:
    /* This call stub was pushed during a C-string printing operation.
       We have to restart it. (Note that the return value is discarded.) */
    stream_string(pc, 0xE0, destaddr); 
    break;

  case 0x14:
    /* This call stub was pushed during a Unicode printing operation.
       We have to restart it. (Note that the return value is discarded.) */
    stream_string(pc, 0xE2, destaddr); 
    break;

  default:
    /* We're back in the original frame, so we can store the returnvalue. 
       (If we tried to do this before resetting frameptr, a result
       destination on the stack would go astray.) */
    store_operand(desttype, destaddr, returnvalue);
    break;
  }
}

uint Glulxe::pop_callstub_string(int *bitnum) {
  uint desttype, destaddr, newpc;

  if (stackptr < 16)
    fatal_error("Stack underflow in callstub.");
  stackptr -= 16;

  newpc = Stk4(stackptr+8);
  destaddr = Stk4(stackptr+4);
  desttype = Stk4(stackptr+0);

  pc = newpc;

  if (desttype == 0x11) {
    return 0;
  }
  if (desttype == 0x10) {
    *bitnum = destaddr;
    return pc;
  }

  fatal_error("Function-terminator call stub at end of string.");
  return 0;
}

} // End of namespace Glulxe
} // End of namespace Glk