#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "jv.h"
#include "jv_dtoa.h"
#include "jv_parse.h"
#include "jv_unicode.h"

typedef const char* presult;

#define TRY(x) do {presult msg__ = (x); if (msg__) return msg__; } while(0)
#ifdef __GNUC__
#define pfunc __attribute__((warn_unused_result)) presult
#else
#define pfunc presult
#endif

void jv_parser_init(struct jv_parser* p) {
  p->stack = 0;
  p->stacklen = p->stackpos = 0;
  p->hasnext = 0;
  p->next = jv_invalid(); //FIXME: jv_invalid
  p->tokenbuf = 0;
  p->tokenlen = p->tokenpos = 0;
  p->st = JV_PARSER_NORMAL;
  jvp_dtoa_context_init(&p->dtoa);
}

void jv_parser_free(struct jv_parser* p) {
  if (p->hasnext) jv_free(p->next);
  free(p->stack);
  free(p->tokenbuf);
  jvp_dtoa_context_free(&p->dtoa);
}

static pfunc value(struct jv_parser* p, jv val) {
  if (p->hasnext) return "Expected separator between values";
  p->hasnext = 1;
  p->next = val;
  return 0;
}

static void push(struct jv_parser* p, jv v) {
  assert(p->stackpos <= p->stacklen);
  if (p->stackpos == p->stacklen) {
    p->stacklen = p->stacklen * 2 + 10;
    p->stack = realloc(p->stack, p->stacklen * sizeof(jv));
  }
  assert(p->stackpos < p->stacklen);
  p->stack[p->stackpos++] = v;
}

static pfunc token(struct jv_parser* p, char ch) {
  switch (ch) {
  case '[':
    if (p->hasnext) return "Expected separator between values";
    push(p, jv_array());
    break;

  case '{':
    if (p->hasnext) return "Expected separator between values";
    push(p, jv_object());
    break;

  case ':':
    if (!p->hasnext) 
      return "Expected string key before ':'";
    if (p->stackpos == 0 || jv_get_kind(p->stack[p->stackpos-1]) != JV_KIND_OBJECT)
      return "':' not as part of an object";
    if (jv_get_kind(p->next) != JV_KIND_STRING)
      return "Object keys must be strings";
    push(p, p->next);
    p->hasnext = 0;
    break;

  case ',':
    if (!p->hasnext)
      return "Expected value before ','";
    if (p->stackpos == 0)
      return "',' not as part of an object or array";
    if (jv_get_kind(p->stack[p->stackpos-1]) == JV_KIND_ARRAY) {
      p->stack[p->stackpos-1] = jv_array_append(p->stack[p->stackpos-1], p->next);
      p->hasnext = 0;
    } else if (jv_get_kind(p->stack[p->stackpos-1]) == JV_KIND_STRING) {
      assert(p->stackpos > 1 && jv_get_kind(p->stack[p->stackpos-2]) == JV_KIND_OBJECT);
      p->stack[p->stackpos-2] = jv_object_set(p->stack[p->stackpos-2], 
                                              p->stack[p->stackpos-1], p->next);
      p->stackpos--;
      p->hasnext = 0;
    } else {
      // this case hits on input like {"a", "b"}
      return "Objects must consist of key:value pairs";
    }
    break;

  case ']':
    if (p->stackpos == 0 || jv_get_kind(p->stack[p->stackpos-1]) != JV_KIND_ARRAY)
      return "Unmatched ']'";
    if (p->hasnext) {
      p->stack[p->stackpos-1] = jv_array_append(p->stack[p->stackpos-1], p->next);
      p->hasnext = 0;
    } else {
      if (jv_array_length(jv_copy(p->stack[p->stackpos-1])) != 0) {
        // this case hits on input like [1,2,3,]
        return "Expected another array element";
      }
    }
    p->hasnext = 1;
    p->next = p->stack[--p->stackpos];
    break;

  case '}':
    if (p->stackpos == 0)
      return "Unmatched '}'";
    if (p->hasnext) {
      if (jv_get_kind(p->stack[p->stackpos-1]) != JV_KIND_STRING)
        return "Objects must consist of key:value pairs";
      assert(p->stackpos > 1 && jv_get_kind(p->stack[p->stackpos-2]) == JV_KIND_OBJECT);
      p->stack[p->stackpos-2] = jv_object_set(p->stack[p->stackpos-2], 
                                              p->stack[p->stackpos-1], p->next);
      p->stackpos--;
      p->hasnext = 0;
    } else {
      if (jv_get_kind(p->stack[p->stackpos-1]) != JV_KIND_OBJECT)
        return "Unmatched '}'";
      if (jv_object_length(jv_copy(p->stack[p->stackpos-1])) != 0)
        return "Expected another key-value pair";
    }
    p->hasnext = 1;
    p->next = p->stack[--p->stackpos];
    break;
  }
  return 0;
}


static void tokenadd(struct jv_parser* p, char c) {
  assert(p->tokenpos <= p->tokenlen);
  if (p->tokenpos == p->tokenlen) {
    p->tokenlen = p->tokenlen*2 + 256;
    p->tokenbuf = realloc(p->tokenbuf, p->tokenlen);
  }
  assert(p->tokenpos < p->tokenlen);
  p->tokenbuf[p->tokenpos++] = c;
}

static int unhex4(char* hex) {
  int r = 0;
  for (int i=0; i<4; i++) {
    char c = *hex++;
    int n;
    if ('0' <= c && c <= '9') n = c - '0';
    else if ('a' <= c && c <= 'f') n = c - 'a' + 10;
    else if ('A' <= c && c <= 'F') n = c - 'A' + 10;
    r <<= 4;
    r |= n;
  }
  return r;
}

static pfunc found_string(struct jv_parser* p) {
  char* in = p->tokenbuf;
  char* out = p->tokenbuf;
  char* end = p->tokenbuf + p->tokenpos;
  
  while (in < end) {
    char c = *in++;
    if (c == '\\') {
      if (in >= end)
        return "Expected escape character at end of string";
      c = *in++;
      switch (c) {
      case '\\':
      case '"':
      case '/': *out++ = c;    break;
      case 'b': *out++ = '\b'; break;
      case 'f': *out++ = '\f'; break;
      case 't': *out++ = '\t'; break;
      case 'n': *out++ = '\n'; break;
      case 'r': *out++ = '\r'; break;

      case 'u':
        /* ahh, the complicated case */
        if (in + 4 > end)
          return "Invalid \\uXXXX escape";
        unsigned long codepoint = unhex4(in);
        in += 4;
        if (0xD800 <= codepoint && codepoint <= 0xDBFF) {
          /* who thought UTF-16 surrogate pairs were a good idea? */
          if (in + 6 > end || in[0] != '\\' || in[1] != 'u')
            return "Invalid \\uXXXX\\uXXXX surrogate pair escape";
          unsigned long surrogate = unhex4(in+2);
          if (!(0xDC00 <= surrogate && surrogate <= 0xDFFF))
            return "Invalid \\uXXXX\\uXXXX surrogate pair escape";
          in += 6;
          codepoint = 0x10000 + (((codepoint - 0xD800) << 10)
                                 |(surrogate - 0xDC00));
        }
        // FIXME assert valid codepoint
        out += jvp_utf8_encode(codepoint, out);
        break;

      default:
        return "Invalid escape";
      }
    } else {
      *out++ = c;
    }
  }
  TRY(value(p, jv_string_sized(p->tokenbuf, out - p->tokenbuf)));
  p->tokenpos = 0;
  return 0;
}

static pfunc check_literal(struct jv_parser* p) {
  if (p->tokenpos == 0) return 0;

  const char* pattern = 0;
  int plen;
  jv v;
  switch (p->tokenbuf[0]) {
  case 't': pattern = "true"; plen = 4; v = jv_true(); break;
  case 'f': pattern = "false"; plen = 5; v = jv_false(); break;
  case 'n': pattern = "null"; plen = 4; v = jv_null(); break;
  }
  if (pattern) {
    if (p->tokenpos != plen) return "Invalid literal";
    for (int i=0; i<plen; i++) 
      if (p->tokenbuf[i] != pattern[i])
        return "Invalid literal";
    TRY(value(p, v));
  } else {
    // FIXME: better parser
    p->tokenbuf[p->tokenpos] = 0; // FIXME: invalid
    char* end = 0;
    double d = jvp_strtod(&p->dtoa, p->tokenbuf, &end);
    if (end == 0 || *end != 0)
      return "Invalid numeric literal";
    TRY(value(p, jv_number(d)));
  }
  p->tokenpos = 0;
  return 0;
}

typedef enum {
  LITERAL,
  WHITESPACE,
  STRUCTURE,
  QUOTE,
  INVALID
} chclass;

static chclass classify(char c) {
  switch (c) {
  case ' ':
  case '\t':
  case '\r':
  case '\n':
    return WHITESPACE;
  case '"':
    return QUOTE;
  case '[':
  case ',':
  case ']':
  case '{':
  case ':':
  case '}':
    return STRUCTURE;
  default:
    return LITERAL;
  }
}




static pfunc scan(struct jv_parser* p, char ch) {
  if (p->st == JV_PARSER_NORMAL) {
    chclass cls = classify(ch);
    if (cls != LITERAL) {
      TRY(check_literal(p));
    }
    switch (cls) {
    case LITERAL:
      tokenadd(p, ch);
      break;
    case WHITESPACE:
      break;
    case QUOTE:
      p->st = JV_PARSER_STRING;
      break;
    case STRUCTURE:
      TRY(token(p, ch));
      break;
    case INVALID:
      return "Invalid character";
    }
  } else {
    if (ch == '"' && p->st == JV_PARSER_STRING) {
      TRY(found_string(p));
      p->st = JV_PARSER_NORMAL;
    } else {
      tokenadd(p, ch);
      if (ch == '\\' && p->st == JV_PARSER_STRING) {
        p->st = JV_PARSER_STRING_ESCAPE;
      } else {
        p->st = JV_PARSER_STRING;
      }
    }
  }
  return 0;
}

static pfunc finish(struct jv_parser* p) {
  if (p->st != JV_PARSER_NORMAL)
    return "Unfinished string";
  TRY(check_literal(p));

  if (p->stackpos != 0)
    return "Unfinished JSON term";
  
  // this will happen on the empty string
  if (!p->hasnext)
    return "Expected JSON value";
  
  return 0;
}

jv jv_parse_sized(const char* string, int length) {
  struct jv_parser parser;
  jv_parser_init(&parser);

  const char* p = string;
  char ch;
  while (p < string + length) {
    ch = *p++;
    presult msg = scan(&parser, ch);
    if (msg){
      printf("ERROR: %s (parsing '%s')\n", msg, string);
      return jv_invalid();
    }
  }
  presult msg = finish(&parser);
  if (msg) {
    printf("ERROR: %s (parsing '%s')\n", msg, string);
    return jv_invalid();
  }
  jv value = jv_copy(parser.next);
  jv_parser_free(&parser);
  return value;
}

jv jv_parse(const char* string) {
  return jv_parse_sized(string, strlen(string));
}