#define _XOPEN_SOURCE 500
#define _REENTRANT 1
#define _SVID_SOURCE 1

/* Required for lgamma_r on Solaris */
#define __EXTENSIONS__ 1

#include <inttypes.h>
#include <math.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#include "gc.h"
#include "builtin.h"
#include "interp.h"

/* Ex: _SLOT_VALUE(STRUCTURE, v, NAME) */
#define _SLOT_VALUE(t,v,s) (_get_struct(v)->slots[t ## _SLOT_ ## s])
#define _LAMBDA_SLOT(v,s)  _SLOT_VALUE(LAMBDA, v, s)

/* Shorthand for frequently-used fields */
#define ST1 (state->in1.value)
#define ST2 (state->in2.value)
#define ST3 (state->in3.value)

/* Quick references to main builtins */
static gc_root_t structure_type_root;
static gc_root_t template_type_root;
static gc_root_t lambda_type_root;

/*
 * Local helper routines
 */

static bool struct_is_a(value_t s, value_t type);

static value_t vector_ref(value_t v, fixnum_t idx);
static char byte_string_ref(value_t v, fixnum_t idx);
static value_t struct_ref(value_t v, fixnum_t idx);

static void vector_set(value_t v, fixnum_t idx, value_t newval);
static void byte_string_set(value_t v, fixnum_t idx, char newval);
static void struct_set(value_t v, fixnum_t idx, value_t newval);

static value_t make_lambda(interp_state_t *state, value_t templ);

static void translate_callable(interp_state_t *state);
static void run_byte_code(interp_state_t *state);
static void perform_tail_call(interp_state_t *state);

static value_t eval_expression(interp_state_t *state, uint8_t code, uint8_t in1, uint8_t in2);
static value_t eval_unary_expression(interp_state_t *state, uint8_t subcode, uint8_t in);

static void run_statement(interp_state_t *state, uint8_t code, uint8_t in1, uint8_t in2, uint32_t in3);

static value_t get_input(const interp_state_t *state, fixnum_t var);
static void set_output(const interp_state_t *state, fixnum_t var, value_t val);

static void register_state(interp_state_t *state, value_t lambda, value_t argv);
static void unregister_state(interp_state_t *state);

/**********************************************************/

void interpreter_init(void)
{
  register_gc_root(&structure_type_root, lookup_builtin(BI_STRUCTURE));
  register_gc_root(&template_type_root,  lookup_builtin(BI_TEMPLATE));
  register_gc_root(&lambda_type_root,    lookup_builtin(BI_LAMBDA));
}

value_t run_interpreter(value_t lambda, value_t argv)
{
  static bool run_finalizers = true;
  interp_state_t state;

  register_state(&state, lambda, argv);

  /* Keep going until something attempts to tail-call FALSE_VALUE, the original 'k', indicating completion. */
  while (state.lambda.value != FALSE_VALUE)
  {
    /* 'lambda' may be a callable structure; if so, follow the 'callable' proxies and update argv. */
    translate_callable(&state);

    /*
     * Now 'lambda' really is a lambda structure instance (or builtin).
     */

#if 0
    fflush(stdout);
    fputs("LAMBDA:  ", stderr); fprint_value(stderr, state.lambda.value); fputc('\n', stderr);
    fputs("ARGLIST: ", stderr); fprint_value(stderr, state.argv.value);   fputc('\n', stderr);
    fputs("CONT'N:  ", stderr); fprint_value(stderr, state.k.value);      fputc('\n', stderr);
    fputs("CONTEXT: ", stderr); fprint_value(stderr, state.ctx.value);    fputc('\n', stderr);
    fputc('\n', stderr);
    fflush(stderr);
#endif

    if (is_builtin_fn(state.lambda.value))
    {
      /* Builtin functions replace the byte-code and tail-call
       * steps; they also do not require frame variables. */
      state.nframe = 0;
      _get_builtin_fn(state.lambda.value)(&state);
    }
    else
    {
      state.nframe = get_fixnum(_LAMBDA_SLOT(state.lambda.value, FRAME_VARS));
      release_assert((0 <= state.nframe) && (state.nframe <= 120));

      run_byte_code(&state);
      perform_tail_call(&state);
    }

    /* Clear (used) frame-variable slots so they can be GC'd. */
    for (fixnum_t i = 0; i < state.nframe; ++i)
      _get_vector(state.frame.value)->elements[i] = UNDEFINED;

    /* Clear temporaries. */
    state.in1.value = UNDEFINED;
    state.in2.value = UNDEFINED;
    state.in3.value = UNDEFINED;

    if (run_finalizers)
    {
      value_t v, f;
      get_next_finalizer(&v, &f);

      if (is_object(v))
      {
        gc_root_t f_root;

        register_gc_root(&f_root, f);
        run_finalizers = false;

        /* Note that recursion is limited to a single level by the static variable. */
        run_interpreter(f_root.value, cons(v, NIL));

        run_finalizers = true;
        unregister_gc_root(&f_root);
      }
    }
  }

  unregister_state(&state);

  /* The arguments passed to continuation are the final return value. */
  return state.argv.value;
}

/* TODO: Permit derivatives of 'structure', and improve detection of cycles. */
static bool struct_is_a(value_t s, value_t type)
{
  /* Detect unbounded loops w/ cyclic 'parent' links. */
  int ttl = 256;

  if (!is_struct(s))
    return false;

  for (value_t t = _get_struct(s)->type; t != type; t = _SLOT_VALUE(STRUCTURE, t, SUPER), --ttl)
  {
    if (t == FALSE_VALUE)
      return false;

    release_assert(get_struct(t)->type == structure_type_root.value);
    release_assert(ttl > 0);
  }

  return true;
}

static value_t vector_ref(value_t v, fixnum_t idx)
{
  vector_t *vec = get_vector(v);
  release_assert((idx >= 0) && (idx < vec->size));
  return vec->elements[idx];
}

static char byte_string_ref(value_t v, fixnum_t idx)
{
  byte_string_t *str = get_byte_string(v);
  release_assert((idx >= 0) && (idx < str->size));
  return str->bytes[idx];
}

static value_t struct_ref(value_t v, fixnum_t idx)
{
  struct_t *s = get_struct(v);
  release_assert((idx >= 0) && (idx < s->nslots));
  return s->slots[idx];
}

static void vector_set(value_t v, fixnum_t idx, value_t newval)
{
  vector_t *vec = get_vector(v);
  release_assert((idx >= 0) && (idx < vec->size));
  vec->elements[idx] = newval;
}

static void byte_string_set(value_t v, fixnum_t idx, char newval)
{
  byte_string_t *str = get_byte_string(v);
  release_assert((idx >= 0) && (idx < str->size));
  str->bytes[idx] = newval;
}

static void struct_set(value_t v, fixnum_t idx, value_t newval)
{
  struct_t *s = get_struct(v);

  release_assert(struct_is_a(s->type, structure_type_root.value));
  release_assert(_get_boolean(_SLOT_VALUE(STRUCTURE, s->type, MUTABLE)));
  release_assert((idx >= 0) && (idx < s->nslots));

  s->slots[idx] = newval;
}

static value_t make_lambda(interp_state_t *state, value_t templ)
{
  gc_root_t templ_root, lambda_root;
  struct_t *ls;
  struct_t *ts;
  vector_t *l_inst;
  byte_string_t *t_inst;
  value_t temp;

  /* If it's not a template object, just return as-is. */
  if (!struct_is_a(templ, template_type_root.value))
    return templ;
  
  register_gc_root(&templ_root, templ);
  register_gc_root(&lambda_root, make_struct(lambda_type_root.value, LAMBDA_SLOTS));
  
  /* Need to do this first, since it can call the garbage collector. */
  temp = make_vector(get_byte_string(get_struct(templ_root.value)
                                       ->slots[TEMPLATE_SLOT_INSTANCE_VARS])->size,
                     UNDEFINED);
  _LAMBDA_SLOT(lambda_root.value, INSTANCE_VARS) = temp;

  ls = _get_struct(lambda_root.value);
  ts = _get_struct(templ_root.value);

  /* All but the instance variables are just shallow-copied. */
  ls->slots[LAMBDA_SLOT_GLOBAL_VARS]  = ts->slots[TEMPLATE_SLOT_GLOBAL_VARS];
  ls->slots[LAMBDA_SLOT_FRAME_VARS]   = ts->slots[TEMPLATE_SLOT_FRAME_VARS];
  ls->slots[LAMBDA_SLOT_BYTE_CODE]    = ts->slots[TEMPLATE_SLOT_BYTE_CODE];
  ls->slots[LAMBDA_SLOT_TAIL_CALL]    = ts->slots[TEMPLATE_SLOT_TAIL_CALL];
  ls->slots[LAMBDA_SLOT_ARG_LIST]     = ts->slots[TEMPLATE_SLOT_ARG_LIST];
  ls->slots[LAMBDA_SLOT_CONTINUATION] = ts->slots[TEMPLATE_SLOT_CONTINUATION];
  ls->slots[LAMBDA_SLOT_CONTEXT]      = ts->slots[TEMPLATE_SLOT_CONTEXT];

  l_inst = _get_vector(ls->slots[LAMBDA_SLOT_INSTANCE_VARS]);
  t_inst = get_byte_string(ts->slots[TEMPLATE_SLOT_INSTANCE_VARS]);

  for (size_t i = 0; i < t_inst->size; ++i)
  {
    l_inst->elements[i] = get_input(state, t_inst->bytes[i]);
  }

  unregister_gc_root(&templ_root);
  unregister_gc_root(&lambda_root);

  return lambda_root.value;
}

static void translate_callable(interp_state_t *state)
{
  while (!is_builtin_fn(state->lambda.value) &&
         !struct_is_a(state->lambda.value, lambda_type_root.value))
  {
    /* If it's not a lambda, built-in function, or typed structure, then
     * it's not callable and I have no idea what to do with it. */
    release_assert(struct_is_a(get_struct(state->lambda.value)->type, structure_type_root.value));

    /* Prepend structure instance to argument list, per proxy protocol. */
    state->argv.value = cons(state->lambda.value, state->argv.value);

    /* Follow link to next callable. */
    state->lambda.value = _SLOT_VALUE(STRUCTURE, _get_struct(state->lambda.value)->type, CALLABLE);
  }
}

static void run_byte_code(interp_state_t *state)
{
  gc_root_t bc_root;

  register_gc_root(&bc_root, _LAMBDA_SLOT(state->lambda.value, BYTE_CODE));

  for (size_t offset = 0; (offset+3) < _get_byte_string(bc_root.value)->size; offset += 4)
  {
    uint8_t bytes[4];
    
    memcpy(bytes, _get_byte_string(bc_root.value)->bytes + offset, 4);

    switch (bytes[0])
    {
    case 0x00 ... 0x3f: /* expression */
      set_output(state, bytes[1], eval_expression(state, bytes[0], bytes[2], bytes[3]));
      break;
    case 0x40 ... 0x7f: /* statement */
      run_statement(state, bytes[0], bytes[1], bytes[2], bytes[3]);
      break;
    case 0x80 ... 0xff: /* conditional */
      set_output(state, bytes[0],
          get_input(state, _get_boolean(get_input(state, bytes[1]))
                             ? bytes[2] : bytes[3]));
      break;
    }
  }

  unregister_gc_root(&bc_root);
}

static void perform_tail_call(interp_state_t *state)
{
  value_t new_lambda, new_argv, new_ctx, new_k;

  new_lambda = get_input(state, get_fixnum(_LAMBDA_SLOT(state->lambda.value, TAIL_CALL)));
  new_argv   = get_input(state, get_fixnum(_LAMBDA_SLOT(state->lambda.value, ARG_LIST)));
  new_k      = get_input(state, get_fixnum(_LAMBDA_SLOT(state->lambda.value, CONTINUATION)));
  new_ctx    = get_input(state, get_fixnum(_LAMBDA_SLOT(state->lambda.value, CONTEXT)));

  state->lambda.value = new_lambda;
  state->argv.value   = new_argv;
  state->k.value      = new_k;
  state->ctx.value    = new_ctx;
}

static value_t eval_expression(interp_state_t *state, uint8_t code, uint8_t in1, uint8_t in2)
{
  if (code != 0x00)
  {
    ST1 = get_input(state, in1);
    ST2 = get_input(state, in2);
  }

  switch (code)
  {
  case 0x00: return eval_unary_expression(state, in1, in2);
  case 0x01: return boolean_value(ST1 == ST2);
  case 0x02: return cons(ST1, ST2);
  case 0x03: return make_vector(get_fixnum(ST1), ST2);
  case 0x04: return make_byte_string(get_fixnum(ST1), (char)get_fixnum(ST2));
  case 0x05: return vector_ref(ST1, get_fixnum(ST2));
  case 0x06: return fixnum_value(byte_string_ref(ST1, get_fixnum(ST2)));
  case 0x07: return struct_ref(ST1, get_fixnum(ST2));
  case 0x08: return fixnum_value(get_fixnum(ST1) + get_fixnum(ST2));
  case 0x09: return fixnum_value(get_fixnum(ST1) - get_fixnum(ST2));
  case 0x0a: return fixnum_value(get_fixnum(ST1) * get_fixnum(ST2));
  case 0x0b: return fixnum_value(get_fixnum(ST1) / get_fixnum(ST2));
  case 0x0c: return fixnum_value(get_fixnum(ST1) % get_fixnum(ST2));
  case 0x0d: return boolean_value(get_fixnum(ST1) < get_fixnum(ST2));
  case 0x0e: return boolean_value(get_fixnum(ST1) >= get_fixnum(ST2));
  case 0x10: return fixnum_value(get_fixnum(ST1) & get_fixnum(ST2));
  case 0x11: return fixnum_value(get_fixnum(ST1) | get_fixnum(ST2));
  case 0x12: return fixnum_value(get_fixnum(ST1) ^ get_fixnum(ST2));
  case 0x14: return fixnum_value(get_fixnum(ST1) << get_fixnum(ST2));
  case 0x15: return fixnum_value(get_fixnum(ST1) >> get_fixnum(ST2));
  case 0x16: return fixnum_value((unsigned long)get_fixnum(ST1) >> get_fixnum(ST2));
  case 0x18: return make_float(get_float(ST1) + get_float(ST2));
  case 0x19: return make_float(get_float(ST1) - get_float(ST2));
  case 0x1a: return make_float(get_float(ST1) * get_float(ST2));
  case 0x1b: return make_float(get_float(ST1) / get_float(ST2));
  case 0x1c: return boolean_value(get_float(ST1) == get_float(ST2));
  case 0x1d: return boolean_value(get_float(ST1) < get_float(ST2));
  case 0x1e: return boolean_value(get_float(ST1) >= get_float(ST2));
  case 0x20: return make_float(atan2(get_float(ST1), get_float(ST2)));
  case 0x21: return make_float(pow(get_float(ST1), get_float(ST2)));
  case 0x22: return make_float(ldexp(get_float(ST1), get_fixnum(ST2)));
  case 0x23: return make_float(fmod(get_float(ST1), get_float(ST2)));
  case 0x24: return make_float(hypot(get_float(ST1), get_float(ST2)));
  case 0x25: return make_float(jn(get_fixnum(ST1), get_float(ST2)));
  case 0x26: return make_float(yn(get_fixnum(ST1), get_float(ST2)));
  case 0x27: return make_float(nextafter(get_float(ST1), get_float(ST2)));
  case 0x28: return make_float(remainder(get_float(ST1), get_float(ST2)));
  case 0x29: return make_float(scalb(get_float(ST1), get_float(ST2)));
  default: release_assert(NOTREACHED("Invalid byte-code!"));
  }

  return UNDEFINED;
}

static value_t eval_unary_expression(interp_state_t *state, uint8_t subcode, uint8_t in)
{
  release_assert(subcode != 0);
  ST1 = get_input(state, in);

  switch (subcode)
  {
  case 0x01: return ST1;
  case 0x02: return get_box(ST1)->value;
  case 0x03: return get_pair(ST1)->car;
  case 0x04: return get_pair(ST1)->cdr;
  case 0x08: return boolean_value(is_boolean(ST1));
  case 0x09: return boolean_value(is_fixnum(ST1));
  case 0x0a: return boolean_value(is_box(ST1));
  case 0x0b: return boolean_value(is_pair(ST1));
  case 0x0c: return boolean_value(is_vector(ST1));
  case 0x0d: return boolean_value(is_byte_string(ST1));
  case 0x0e: return boolean_value(is_struct(ST1));
  case 0x0f: return boolean_value(is_float(ST1));
  case 0x10: return boolean_value(is_builtin_fn(ST1));
  case 0x18: return make_box(ST1);
  case 0x19: {
               vector_t *vec;
               release_assert(struct_is_a(ST1, structure_type_root.value));
               vec = get_vector(_SLOT_VALUE(STRUCTURE, ST1, SLOTS));
               return make_struct(ST1, vec->size);
             }
  case 0x1a: return make_float((native_float_t)get_fixnum(ST1));
  case 0x1b: return make_lambda(state, ST1);
  case 0x20: return boolean_value(!_get_boolean(ST1));
  case 0x21: return fixnum_value(~get_fixnum(ST1));
  case 0x22: return fixnum_value(-get_fixnum(ST1));
  case 0x23: return make_float(-get_float(ST1));
  case 0x28: return fixnum_value(get_vector(ST1)->size);
  case 0x29: return fixnum_value(get_byte_string(ST1)->size);
  case 0x2a: return fixnum_value(get_struct(ST1)->nslots);
  case 0x2b: return get_struct(ST1)->type;
  case 0x30: return make_float(acos(get_float(ST1)));
  case 0x31: return make_float(asin(get_float(ST1)));
  case 0x32: return make_float(atan(get_float(ST1)));
  case 0x33: return make_float(cos(get_float(ST1)));
  case 0x34: return make_float(sin(get_float(ST1)));
  case 0x35: return make_float(tan(get_float(ST1)));
  case 0x36: return make_float(cosh(get_float(ST1)));
  case 0x37: return make_float(sinh(get_float(ST1)));
  case 0x38: return make_float(tanh(get_float(ST1)));
  case 0x39: return make_float(exp(get_float(ST1)));
  case 0x3a: {
               int exp;
               ST2 = make_float(frexp(get_float(ST1), &exp));
               return cons(ST2, fixnum_value(exp));
             }
  case 0x3b: return make_float(log(get_float(ST1)));
  case 0x3c: return make_float(log10(get_float(ST1)));
  case 0x3d: {
               double integral_part;
               ST2 = make_float(modf(get_float(ST1), &integral_part));
               ST3 = make_float(integral_part);
               return cons(ST2, ST3);
             }
  case 0x3e: return make_float(sqrt(get_float(ST1)));
  case 0x3f: return make_float(ceil(get_float(ST1)));
  case 0x40: return make_float(fabs(get_float(ST1)));
  case 0x41: return make_float(floor(get_float(ST1)));
  case 0x50: return make_float(erf(get_float(ST1)));
  case 0x51: return make_float(erfc(get_float(ST1)));
  case 0x52: return make_float(j0(get_float(ST1)));
  case 0x53: return make_float(j1(get_float(ST1)));
  case 0x54: {
               int signgamp;
               ST2 = make_float(lgamma_r(get_float(ST1), &signgamp));
               return cons(ST2, fixnum_value(signgamp));
             }
  case 0x55: return make_float(y0(get_float(ST1)));
  case 0x56: return make_float(y1(get_float(ST1)));
  case 0x57: return make_float(asinh(get_float(ST1)));
  case 0x58: return make_float(acosh(get_float(ST1)));
  case 0x59: return make_float(atanh(get_float(ST1)));
  case 0x5a: return make_float(cbrt(get_float(ST1)));
  case 0x5b: return make_float(logb(get_float(ST1)));
  case 0x5c: return make_float(expm1(get_float(ST1)));
  case 0x5d: return make_float(ilogb(get_float(ST1)));
  case 0x5e: return make_float(log1p(get_float(ST1)));
  case 0x70: return boolean_value(isnormal(get_float(ST1)));
  case 0x71: return boolean_value(isfinite(get_float(ST1)));
  case 0x72: return boolean_value(fpclassify(get_float(ST1)) == FP_SUBNORMAL);
  case 0x73: return boolean_value(isinf(get_float(ST1)));
  case 0x74: return boolean_value(isnan(get_float(ST1)));
  default: release_assert(NOTREACHED("Invalid unary sub-bytecode."));
  }

  return UNDEFINED;
}

static void run_statement(interp_state_t *state, uint8_t code, uint8_t in1, uint8_t in2, uint32_t in3)
{
  ST1 = get_input(state, in1);
  ST2 = get_input(state, in2);

  if (code >= 0x60)
  {
    ST3 = get_input(state, in3);
  }

  switch (code)
  {
  case 0x40: get_box(ST1)->value = ST2; break;
  case 0x41: get_pair(ST1)->car = ST2; break;
  case 0x42: get_pair(ST1)->cdr = ST2; break;
  case 0x60: vector_set(ST1, get_fixnum(ST2), ST3); break;
  case 0x61: byte_string_set(ST1, get_fixnum(ST2), (char)get_fixnum(ST3)); break;
  case 0x62: struct_set(ST1, get_fixnum(ST2), ST3); break;
  }
}

static value_t get_input(const interp_state_t *state, fixnum_t var)
{
  release_assert((var >= 0) && (var <= 255));

  switch (var)
  {
  case 0:
    return NIL;
  case 1 ... 63:
    {
      vector_t *vec = get_vector(_LAMBDA_SLOT(state->lambda.value, GLOBAL_VARS));
      var -= 1;

      release_assert(var < vec->size);
      return vec->elements[var];
    }
  case 64 ... 127:
    {
      vector_t *vec = get_vector(_LAMBDA_SLOT(state->lambda.value, INSTANCE_VARS));
      var -= 64;

      release_assert(var < vec->size);
      return vec->elements[var];
    }
  case 128 ... 247:
    {
      /* Frame is allocated by interpreter, so we know it's a vector already. */
      vector_t *vec = _get_vector(state->frame.value);
      var -= 128;

      release_assert(var < state->nframe);
      return vec->elements[var];
    }
  /* 248 ... 251 are reserved */
  case 252:
    return state->lambda.value;
  case 253:
    return state->argv.value;
  case 254:
    return state->k.value;
  case 255:
    return state->ctx.value;
  default:
    return UNDEFINED;
  }
}

static void set_output(const interp_state_t *state, fixnum_t var, value_t val)
{
  vector_t *vec = _get_vector(state->frame.value);

  /* Only frame variables can be output targets for bytecode instructions. */
  release_assert((var >= 128) && (var <= 255));

  var -= 128;
  release_assert(var < state->nframe);
  vec->elements[var] = val;
}

static void register_state(interp_state_t *state, value_t lambda, value_t argv)
{
  register_gc_root(&state->lambda, lambda);
  register_gc_root(&state->argv,   argv);
  register_gc_root(&state->frame,  make_vector(120, UNDEFINED));
  register_gc_root(&state->k,      FALSE_VALUE);
  register_gc_root(&state->ctx,    FALSE_VALUE);
  register_gc_root(&state->in1,    FALSE_VALUE);
  register_gc_root(&state->in2,    FALSE_VALUE);
  register_gc_root(&state->in3,    FALSE_VALUE);
}

static void unregister_state(interp_state_t *state)
{
  unregister_gc_root(&state->lambda);
  unregister_gc_root(&state->argv);
  unregister_gc_root(&state->frame);
  unregister_gc_root(&state->k);
  unregister_gc_root(&state->ctx);
  unregister_gc_root(&state->in1);
  unregister_gc_root(&state->in2);
  unregister_gc_root(&state->in3);
}

/* vim:set sw=2 expandtab: */