package nncl

import "fmt"
import "os"
import "io"
import "strings"

const MAX_VAR_LENGTH=256

type Ncl struct {

}

func (ncl *Ncl) eval(s string) {
}

/* Token type and control flow constants */
const (
	TCMD = iota
	TWORD
	TPART
	TERROR
)

const (
	FERROR = iota
	FNORMAL
	FRETURN
	FBREAK
	FAGAIN
)

func isSpecial(c rune, quote bool) bool {
  return (c == '$' || (!quote && (c == '{' || c == '}' || c == ';' || c == '\r' ||
                              c == '\n')) ||
          c == '[' || c == ']' || c == '"')
}

func isSpace(c rune) bool {
	return (c == ' ' || c == '\t')
}

func isEnd(c rune) bool {
  return (c == '\n' || c == '\r' || c == ';');
}


func scan(in RuneScanner, line, col *int) (rune, error) {
	r, _, err := in.ReadRune()
	if r == '\n' {
		*col = 0
		*rows = *rows + 1
	}
	*col = *col + 1
	return r, err
}


func next(in RuneScanner, token * string.Builder, quote *bool, line, col *int) (int, error) {
 	var err error
 	var c rune
  	depth := 0
  	var open rune
  	var end  rune

  	for c, err = scan(in, line, col); err != nil ;  c, err = scan(in, line, col) {
		if !*quote {
			 /* Skip leading spaces if not quoted */
			 for ; isSpace(c); c,err = scan(in, line, col) {
			 	if err != nil {
			 		return TERROR, err
			 	}
			 }

			/* Terminate command if not quoted */
			if isEnd(c) {
				token.WriteRune(c)
				return TCMD, nil
			}
		}

  	if (c == '$') { /* Variable token, must not start with a space or quote */
		c2, err := scan(in, line, col)
		if err != nil {
			return TERROR, err
		}
    	if is_space(c2) {
    		return TERROR, fmt.Errorf("Space not allowed after $.")
    	}
    	token.WriteRune(c)
    	mode := *quote
    	*quote = false
    	r, err := next(in, token, quote);
    	*quote = mode
    	if r == TWORD && quote && err == nil {
    		return TPART, nil
    	}
    	return r, err
  	}

  	if (c == '[' || (!*quote && c == '{')) {
    /* Interleaving pairs are not welcome, but it simplifies the code */
    open = c
    end = '}'
    if open == '[' {
    	end = ']'
    }
    for c,_,err, depth = in.ReadRune(), 1 ; depth != 0; c,_,err = in.ReadRune() {
    	if err != nil {
    		return TERROR, error
    	}
      	if c == open {
        	depth++
      	} else if c == end {
        	depth--
      	}
      	token.WriteRune(c)
    }
  } else if c == '"' {
    *quote = !*quote;
    if (*quote) {
      return TPART;
    }
    if (n < 2 || (!ncl_is_space(s[1]) && !ncl_is_end(s[1]))) {
      return TERROR;
    }
    *from = *to = s + 1;
    return TWORD;
  } else if (*s == ']' || *s == '}') {
    /* Unbalanced bracket or brace */
    return TERROR;
  } else {
    while (i < n && (*q || !ncl_is_space(s[i])) && !ncl_is_special(s[i], *q)) {
      i++;
    }
  }
  *to = s + i;
  if (i == n) {
    return TERROR;
  }
  if (*q) {
    return TPART;
  }
  return (ncl_is_space(s[i]) || ncl_is_end(s[i])) ? TWORD : TPART;
}

/* A helper parser struct and macro (requires C99) */
struct ncl_parser {
  const char *from;
  const char *to;
  const char *start;
  const char *end;
  int q;
  int token;
};
#define ncl_each(s, len, skiperr)                                              \
  for (struct ncl_parser p = {NULL, NULL, (s), (s) + (len), 0, TERROR};        \
       p.start < p.end &&                                                      \
       (((p.token = ncl_next(p.start, p.end - p.start, &p.from, &p.to,         \
                             &p.q)) != TERROR) ||                              \
        (skiperr));                                                            \
       p.start = p.to)

/* ------------------------------------------------------- */
/* ------------------------------------------------------- */
/* ------------------------------------------------------- */
/* ------------------------------------------------------- */
/* ------------------------------------------------------- */
typedef char ncl_value_t;

const char *ncl_string(ncl_value_t *v) { return v; }
int ncl_int(ncl_value_t *v) { return atoi(v); }
int ncl_length(ncl_value_t *v) { return v == NULL ? 0 : strlen(v); }

void ncl_free(ncl_value_t *v) { free(v); }

ncl_value_t *ncl_append_string(ncl_value_t *v, s string) {
  size_t n = ncl_length(v);
  v = realloc(v, n + len + 1);
  memset((char *)ncl_string(v) + n, 0, len + 1);
  strncpy((char *)ncl_string(v) + n, s, len);
  return v;
}

ncl_value_t *ncl_append(ncl_value_t *v, ncl_value_t *tail) {
  v = ncl_append_string(v, ncl_string(tail), ncl_length(tail));
  ncl_free(tail);
  return v;
}

ncl_value_t *ncl_alloc(s string) {
  return ncl_append_string(NULL, s, len);
}

ncl_value_t *ncl_dup(ncl_value_t *v) {
  return ncl_alloc(ncl_string(v), ncl_length(v));
}

ncl_value_t *ncl_list_alloc() { return ncl_alloc("", 0); }

int ncl_list_length(ncl_value_t *v) {
  int count = 0;
  ncl_each(ncl_string(v), ncl_length(v) + 1, 0) {
    if (p.token == TWORD) {
      count++;
    }
  }
  return count;
}

void ncl_list_free(ncl_value_t *v) { free(v); }

ncl_value_t *ncl_list_at(ncl_value_t *v, int index) {
  int i = 0;
  ncl_each(ncl_string(v), ncl_length(v) + 1, 0) {
    if (p.token == TWORD) {
      if (i == index) {
        if (p.from[0] == '{') {
          return ncl_alloc(p.from + 1, p.to - p.from - 2);
        }
        return ncl_alloc(p.from, p.to - p.from);
      }
      i++;
    }
  }
  return NULL;
}

ncl_value_t *ncl_list_append(ncl_value_t *v, ncl_value_t *tail) {
  if (ncl_length(v) > 0) {
    v = ncl_append(v, ncl_alloc(" ", 2));
  }
  if (ncl_length(tail) > 0) {
    int q = 0;
    const char *p;
    for (p = ncl_string(tail); *p; p++) {
      if (ncl_is_space(*p) || ncl_is_special(*p, 0)) {
        q = 1;
        break;
      }
    }
    if (q) {
      v = ncl_append(v, ncl_alloc("{", 1));
    }
    v = ncl_append(v, ncl_dup(tail));
    if (q) {
      v = ncl_append(v, ncl_alloc("}", 1));
    }
  } else {
    v = ncl_append(v, ncl_alloc("{}", 2));
  }
  return v;
}

/* ----------------------------- */
/* ----------------------------- */
/* ----------------------------- */
/* ----------------------------- */

typedef int (*ncl_cmd_fn_t)(struct ncl *, ncl_value_t *, void *);

struct ncl_cmd {
  ncl_value_t *name;
  int arity;
  ncl_cmd_fn_t fn;
  void *arg;
  struct ncl_cmd *next;
};

struct ncl_var {
  ncl_value_t *name;
  ncl_value_t *value;
  struct ncl_var *next;
};

struct ncl_env {
  struct ncl_var *vars;
  struct ncl_env *parent;
};

static struct ncl_env *ncl_env_alloc(struct ncl_env *parent) {
  struct ncl_env *env = malloc(sizeof(*env));
  env->vars = NULL;
  env->parent = parent;
  return env;
}

static struct ncl_var *ncl_env_var(struct ncl_env *env, ncl_value_t *name) {
  struct ncl_var *var = malloc(sizeof(struct ncl_var));
  var->name = ncl_dup(name);
  var->next = env->vars;
  var->value = ncl_alloc("", 0);
  env->vars = var;
  return var;
}

static struct ncl_env *ncl_env_free(struct ncl_env *env) {
  struct ncl_env *parent = env->parent;
  while (env->vars) {
    struct ncl_var *var = env->vars;
    env->vars = env->vars->next;
    ncl_free(var->name);
    ncl_free(var->value);
    free(var);
  }
  free(env);
  return parent;
}

struct ncl {
  struct ncl_env *env;
  struct ncl_cmd *cmds;
  ncl_value_t *result;
};

ncl_value_t *ncl_var(struct ncl *ncl, ncl_value_t *name, ncl_value_t *v) {
  DBG("var(%s := %.*s)\n", ncl_string(name), ncl_length(v), ncl_string(v));
  struct ncl_var *var;
  for (var = ncl->env->vars; var != NULL; var = var->next) {
    if (strcmp(var->name, ncl_string(name)) == 0) {
      break;
    }
  }
  if (var == NULL) {
    var = ncl_env_var(ncl->env, name);
  }
  if (v != NULL) {
    ncl_free(var->value);
    var->value = ncl_dup(v);
    ncl_free(v);
  }
  return var->value;
}

int ncl_result(struct ncl *ncl, int flow, ncl_value_t *result) {
  DBG("ncl_result %.*s, flow=%d\n", ncl_length(result), ncl_string(result),
      flow);
  ncl_free(ncl->result);
  ncl->result = result;
  return flow;
}

int ncl_subst(struct ncl *ncl, s string) {
  DBG("subst(%.*s)\n", (int)len, s);
  if (len == 0) {
    return ncl_result(ncl, FNORMAL, ncl_alloc("", 0));
  }
  switch (s[0]) {
  case '{':
    if (len <= 1) {
      return ncl_result(ncl, FERROR, ncl_alloc("", 0));
    }
    return ncl_result(ncl, FNORMAL, ncl_alloc(s + 1, len - 2));
  case '$': {
    if (len >= MAX_VAR_LENGTH) {
      return ncl_result(ncl, FERROR, ncl_alloc("", 0));
    }
    char buf[5 + MAX_VAR_LENGTH] = "set ";
    strncat(buf, s + 1, len - 1);
    return ncl_eval(ncl, buf, strlen(buf) + 1);
  }
  case '[': {
    ncl_value_t *expr = ncl_alloc(s + 1, len - 2);
    int r = ncl_eval(ncl, ncl_string(expr), ncl_length(expr) + 1);
    ncl_free(expr);
    return r;
  }
  default:
    return ncl_result(ncl, FNORMAL, ncl_alloc(s, len));
  }
}

int ncl_eval(struct ncl *ncl, s string) {
  DBG("eval(%.*s)->\n", (int)len, s);
  ncl_value_t *list = ncl_list_alloc();
  ncl_value_t *cur = NULL;
  ncl_each(s, len, 1) {
    DBG("ncl_next %d %.*s\n", p.token, (int)(p.to - p.from), p.from);
    switch (p.token) {
    case TERROR:
      DBG("eval: FERROR, lexer error\n");
      return ncl_result(ncl, FERROR, ncl_alloc("", 0));
    case TWORD:
      DBG("token %.*s, length=%d, cur=%p (3.1.1)\n", (int)(p.to - p.from),
          p.from, (int)(p.to - p.from), cur);
      if (cur != NULL) {
        ncl_subst(ncl, p.from, p.to - p.from);
        ncl_value_t *part = ncl_dup(ncl->result);
        cur = ncl_append(cur, part);
      } else {
        ncl_subst(ncl, p.from, p.to - p.from);
        cur = ncl_dup(ncl->result);
      }
      list = ncl_list_append(list, cur);
      ncl_free(cur);
      cur = NULL;
      break;
    case TPART:
      ncl_subst(ncl, p.from, p.to - p.from);
      ncl_value_t *part = ncl_dup(ncl->result);
      cur = ncl_append(cur, part);
      break;
    case TCMD:
      if (ncl_list_length(list) == 0) {
        ncl_result(ncl, FNORMAL, ncl_alloc("", 0));
      } else {
        ncl_value_t *cmdname = ncl_list_at(list, 0);
        struct ncl_cmd *cmd = NULL;
        int r = FERROR;
        for (cmd = ncl->cmds; cmd != NULL; cmd = cmd->next) {
          if (strcmp(ncl_string(cmdname), ncl_string(cmd->name)) == 0) {
            if (cmd->arity == 0 || cmd->arity == ncl_list_length(list)) {
              r = cmd->fn(ncl, list, cmd->arg);
              break;
            }
          }
        }
        ncl_free(cmdname);
        if (cmd == NULL || r != FNORMAL) {
          ncl_list_free(list);
          return r;
        }
      }
      ncl_list_free(list);
      list = ncl_list_alloc();
      break;
    }
  }
  ncl_list_free(list);
  return FNORMAL;
}

/* --------------------------------- */
/* --------------------------------- */
/* --------------------------------- */
/* --------------------------------- */
/* --------------------------------- */
void ncl_register(struct ncl *ncl, const char *name, ncl_cmd_fn_t fn, int arity,
                  void *arg) {
  struct ncl_cmd *cmd = malloc(sizeof(struct ncl_cmd));
  cmd->name = ncl_alloc(name, strlen(name));
  cmd->fn = fn;
  cmd->arg = arg;
  cmd->arity = arity;
  cmd->next = ncl->cmds;
  ncl->cmds = cmd;
}

static int ncl_cmd_set(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  ncl_value_t *var = ncl_list_at(args, 1);
  ncl_value_t *val = ncl_list_at(args, 2);
  int r = ncl_result(ncl, FNORMAL, ncl_dup(ncl_var(ncl, var, val)));
  ncl_free(var);
  return r;
}

static int ncl_cmd_subst(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  ncl_value_t *s = ncl_list_at(args, 1);
  int r = ncl_subst(ncl, ncl_string(s), ncl_length(s));
  ncl_free(s);
  return r;
}

#ifndef TCL_DISABLE_PUTS
static int ncl_cmd_puts(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  ncl_value_t *text = ncl_list_at(args, 1);
  puts(ncl_string(text));
  putchar('\n');
  return ncl_result(ncl, FNORMAL, text);
}
#endif

static int ncl_user_proc(struct ncl *ncl, ncl_value_t *args, void *arg) {
  ncl_value_t *code = (ncl_value_t *)arg;
  ncl_value_t *params = ncl_list_at(code, 2);
  ncl_value_t *body = ncl_list_at(code, 3);
  ncl->env = ncl_env_alloc(ncl->env);
  for (int i = 0; i < ncl_list_length(params); i++) {
    ncl_value_t *param = ncl_list_at(params, i);
    ncl_value_t *v = ncl_list_at(args, i + 1);
    ncl_var(ncl, param, v);
    ncl_free(param);
  }
  ncl_eval(ncl, ncl_string(body), ncl_length(body) + 1);
  ncl->env = ncl_env_free(ncl->env);
  ncl_free(params);
  ncl_free(body);
  return FNORMAL;
}

static int ncl_cmd_proc(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  ncl_value_t *name = ncl_list_at(args, 1);
  ncl_register(ncl, ncl_string(name), ncl_user_proc, 0, ncl_dup(args));
  ncl_free(name);
  return ncl_result(ncl, FNORMAL, ncl_alloc("", 0));
}

static int ncl_cmd_if(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  int i = 1;
  int n = ncl_list_length(args);
  int r = FNORMAL;
  while (i < n) {
    ncl_value_t *cond = ncl_list_at(args, i);
    ncl_value_t *branch = NULL;
    if (i + 1 < n) {
      branch = ncl_list_at(args, i + 1);
    }
    r = ncl_eval(ncl, ncl_string(cond), ncl_length(cond) + 1);
    ncl_free(cond);
    if (r != FNORMAL) {
      ncl_free(branch);
      break;
    }
    if (ncl_int(ncl->result)) {
      r = ncl_eval(ncl, ncl_string(branch), ncl_length(branch) + 1);
      ncl_free(branch);
      break;
    }
    i = i + 2;
    ncl_free(branch);
  }
  return r;
}

static int ncl_cmd_flow(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  int r = FERROR;
  ncl_value_t *flowval = ncl_list_at(args, 0);
  const char *flow = ncl_string(flowval);
  if (strcmp(flow, "break") == 0) {
    r = FBREAK;
  } else if (strcmp(flow, "continue") == 0) {
    r = FAGAIN;
  } else if (strcmp(flow, "return") == 0) {
    r = ncl_result(ncl, FRETURN, ncl_list_at(args, 1));
  }
  ncl_free(flowval);
  return r;
}

static int ncl_cmd_while(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  ncl_value_t *cond = ncl_list_at(args, 1);
  ncl_value_t *loop = ncl_list_at(args, 2);
  int r;
  for (;;) {
    r = ncl_eval(ncl, ncl_string(cond), ncl_length(cond) + 1);
    if (r != FNORMAL) {
      ncl_free(cond);
      ncl_free(loop);
      return r;
    }
    if (!ncl_int(ncl->result)) {
      ncl_free(cond);
      ncl_free(loop);
      return FNORMAL;
    }
    int r = ncl_eval(ncl, ncl_string(loop), ncl_length(loop) + 1);
    switch (r) {
    case FBREAK:
      ncl_free(cond);
      ncl_free(loop);
      return FNORMAL;
    case FRETURN:
      ncl_free(cond);
      ncl_free(loop);
      return FRETURN;
    case FAGAIN:
      continue;
    case FERROR:
      ncl_free(cond);
      ncl_free(loop);
      return FERROR;
    }
  }
}

#ifndef TCL_DISABLE_MATH
static int ncl_cmd_math(struct ncl *ncl, ncl_value_t *args, void *arg) {
  (void)arg;
  char buf[64];
  ncl_value_t *opval = ncl_list_at(args, 0);
  ncl_value_t *aval = ncl_list_at(args, 1);
  ncl_value_t *bval = ncl_list_at(args, 2);
  const char *op = ncl_string(opval);
  int a = ncl_int(aval);
  int b = ncl_int(bval);
  int c = 0;
  if (op[0] == '+') {
    c = a + b;
  } else if (op[0] == '-') {
    c = a - b;
  } else if (op[0] == '*') {
    c = a * b;
  } else if (op[0] == '/') {
    c = a / b;
  } else if (op[0] == '>' && op[1] == '\0') {
    c = a > b;
  } else if (op[0] == '>' && op[1] == '=') {
    c = a >= b;
  } else if (op[0] == '<' && op[1] == '\0') {
    c = a < b;
  } else if (op[0] == '<' && op[1] == '=') {
    c = a <= b;
  } else if (op[0] == '=' && op[1] == '=') {
    c = a == b;
  } else if (op[0] == '!' && op[1] == '=') {
    c = a != b;
  }

  char *p = buf + sizeof(buf) - 1;
  char neg = (c < 0);
  *p-- = 0;
  if (neg) {
    c = -c;
  }
  do {
    *p-- = '0' + (c % 10);
    c = c / 10;
  } while (c > 0);
  if (neg) {
    *p-- = '-';
  }
  p++;

  ncl_free(opval);
  ncl_free(aval);
  ncl_free(bval);
  return ncl_result(ncl, FNORMAL, ncl_alloc(p, strlen(p)));
}
#endif

void ncl_init(struct ncl *ncl) {
  ncl->env = ncl_env_alloc(NULL);
  ncl->result = ncl_alloc("", 0);
  ncl->cmds = NULL;
  ncl_register(ncl, "set", ncl_cmd_set, 0, NULL);
  ncl_register(ncl, "subst", ncl_cmd_subst, 2, NULL);
#ifndef TCL_DISABLE_PUTS
  ncl_register(ncl, "puts", ncl_cmd_puts, 2, NULL);
#endif
  ncl_register(ncl, "proc", ncl_cmd_proc, 4, NULL);
  ncl_register(ncl, "if", ncl_cmd_if, 0, NULL);
  ncl_register(ncl, "while", ncl_cmd_while, 3, NULL);
  ncl_register(ncl, "return", ncl_cmd_flow, 0, NULL);
  ncl_register(ncl, "break", ncl_cmd_flow, 1, NULL);
  ncl_register(ncl, "continue", ncl_cmd_flow, 1, NULL);
#ifndef TCL_DISABLE_MATH
  char *math[] = {"+", "-", "*", "/", ">", ">=", "<", "<=", "==", "!="};
  for (unsigned int i = 0; i < (sizeof(math) / sizeof(math[0])); i++) {
    ncl_register(ncl, math[i], ncl_cmd_math, 3, NULL);
  }
#endif
}

void ncl_destroy(struct ncl *ncl) {
  while (ncl->env) {
    ncl->env = ncl_env_free(ncl->env);
  }
  while (ncl->cmds) {
    struct ncl_cmd *cmd = ncl->cmds;
    ncl->cmds = ncl->cmds->next;
    ncl_free(cmd->name);
    free(cmd->arg);
    free(cmd);
  }
  ncl_free(ncl->result);
}

#ifndef TEST
#define CHUNK 1024

int main() {
  struct ncl ncl;
  int buflen = CHUNK;
  char *buf = malloc(buflen);
  int i = 0;

  ncl_init(&ncl);
  while (1) {
    int inp = fgetc(stdin);

    if (i > buflen - 1) {
      buf = realloc(buf, buflen += CHUNK);
    }

    if (inp == 0 || inp == EOF) {
      break;
    }

    buf[i++] = inp;

    ncl_each(buf, i, 1) {
      if (p.token == TERROR && (p.to - buf) != i) {
        memset(buf, 0, buflen);
        i = 0;
        break;
      } else if (p.token == TCMD && *(p.from) != '\0') {
        int r = ncl_eval(&ncl, buf, strlen(buf));
        if (r != FERROR) {
          printf("result> %.*s\n", ncl_length(ncl.result),
                 ncl_string(ncl.result));
        } else {
          printf("?!\n");
        }

        memset(buf, 0, buflen);
        i = 0;
        break;
      }
    }
  }

  free(buf);

  if (i) {
    printf("incomplete input\n");
    return -1;
  }

  return 0;
}
#endif