/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ 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; version 2 of the License.                      │
│                                                                              │
│ 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 "libc/bits/weaken.h"
#include "libc/fmt/conv.h"
#include "libc/fmt/fmt.h"
#include "libc/mem/mem.h"
#include "libc/runtime/runtime.h"
#include "libc/str/oldutf16.internal.h"
#include "libc/str/str.h"
#include "libc/str/tpdecodecb.internal.h"
#include "libc/sysv/errfuns.h"

/**
 * String / file / stream decoder.
 *
 * This scanf implementation is able to tokenize strings containing
 * 8-bit through 128-bit integers (with validation), floating point
 * numbers, etc. It can also be used to convert UTF-8 to UTF-16/32.
 *
 *   - `%d`  parses integer
 *   - `%ms` parses string allocating buffer assigning pointer
 *
 * @param callback supplies UTF-8 characters using -1 sentinel
 * @param fmt is a computer program embedded inside a c string, written
 *     in a domain-specific programming language that, by design, lacks
 *     Turing-completeness
 * @param va points to the variadic argument state
 * @see libc/fmt/pflink.h (dynamic memory is not a requirement)
 */
int vcscanf(int callback(void *), int unget(int, void *), void *arg,
            const char *fmt, va_list va) {
  struct FreeMe {
    struct FreeMe *next;
    void *ptr;
  } *freeme = NULL;
  const unsigned char *p = (const unsigned char *)fmt;
  unsigned i = 0;
  int items = 0;
  int c = callback(arg);
  while (c != -1) {
    switch (p[i++]) {
      case '\0':
        if (c != -1 && unget) {
          unget(c, arg);
        }
        goto Done;
      case ' ':
      case '\t':
      case '\n':
      case '\r':
      case '\v':
        while (isspace(c)) {
          c = callback(arg);
        }
        break;
      case '%': {
        uintmax_t number;
        void *buf;
        size_t bufsize;
        unsigned width = 0;
        unsigned char bits = 32;
        unsigned char charbytes = sizeof(char);
        unsigned char diglet;
        unsigned char base;
        unsigned char prefix;
        bool rawmode = false;
        bool issigned = false;
        bool ismalloc = false;
        bool isneg = false;
        bool thousands = false;
        bool discard = false;
        for (;;) {
          switch (p[i++]) {
            case '%': /* %% → % */
              goto NonDirectiveCharacter;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
              width *= 10;
              width += p[i - 1] - '0';
              break;
            case '*':
              discard = true;
              break;
            case 'm':
              ismalloc = true;
              break;
            case 'c':
              rawmode = true;
              if (!width) width = 1;
              /* εpsilon transition */
            case 's':
              goto DecodeString;
            case '\'':
              thousands = true;
              break;
            case 'j': /* 128-bit */
              bits = sizeof(intmax_t) * 8;
              break;
            case 'l': /* long */
            case 'L': /* loooong */
              charbytes = sizeof(wchar_t);
              /* fallthrough */
            case 't': /* ptrdiff_t */
            case 'Z': /* size_t */
            case 'z': /* size_t */
              bits = 64;
              break;
            case 'h': /* short and char */
              charbytes = sizeof(char16_t);
              bits >>= 1;
              break;
            case 'b': /* binary */
              base = 2;
              prefix = 'b';
              goto ConsumeBasePrefix;
            case 'p': /* pointer (NexGen32e) */
              bits = 48;
              /* fallthrough */
            case 'x':
            case 'X': /* hexadecimal */
              base = 16;
              prefix = 'x';
              goto ConsumeBasePrefix;
            case 'o': /* octal */
              base = 8;
              goto DecodeNumber;
            case 'd': /* decimal */
            case 'n': /* TODO(jart): flexidecimal */
              issigned = true;
              if (c == '+' || (isneg = c == '-')) {
                c = callback(arg);
              }
              /* εpsilon transition */
            case 'u':
              base = 10;
              goto DecodeNumber;
            default:
              items = einval();
              goto Done;
          }
        }
      ConsumeBasePrefix:
        if (c == '0') {
          c = callback(arg);
          if (c == prefix || c == prefix + ('a' - 'A')) {
            c = callback(arg);
          }
        }
      DecodeNumber:
        if (c != -1) {
          number = 0;
          do {
            diglet = kBase36[(unsigned char)c];
            if (1 <= diglet && diglet <= base) {
              number *= base;
              number += diglet - 1;
            } else if (thousands && diglet == ',') {
              /* ignore */
            } else {
              break;
            }
          } while ((c = callback(arg)) != -1);
          if (!discard) {
            uintmax_t bane = (uintmax_t)1 << (bits - 1);
            if (!(number & ~((bane - 1) | (issigned ? 0 : bane))) ||
                (issigned && number == bane /* two's complement bane */)) {
              ++items;
            } else {
              items = erange();
              goto Done;
            }
            if (issigned && isneg) {
              number = ~number + 1;
            }
            void *out = va_arg(va, void *);
            switch (bits) {
              case sizeof(uintmax_t) * CHAR_BIT:
                *(uintmax_t *)out = number;
                break;
              case 48:
              case 64:
                *(uint64_t *)out = (uint64_t)number;
                break;
              case 32:
                *(uint32_t *)out = (uint32_t)number;
                break;
              case 16:
                *(uint16_t *)out = (uint16_t)number;
                break;
              case 8:
              default:
                *(uint8_t *)out = (uint8_t)number;
                break;
            }
          }
        }
        continue;
      DecodeString:
        bufsize = !width ? 32 : rawmode ? width : width + 1;
        if (discard) {
          buf = NULL;
        } else if (ismalloc) {
          buf = weaken(malloc)(bufsize * charbytes);
          struct FreeMe *entry;
          if (buf && (entry = weaken(calloc)(1, sizeof(struct FreeMe)))) {
            entry->ptr = buf;
            entry->next = freeme;
            freeme = entry;
          }
        } else {
          buf = va_arg(va, void *);
        }
        if (buf) {
          size_t j = 0;
          for (;;) {
            if (ismalloc && !width && j + 2 + 1 >= bufsize &&
                !weaken(__grow)(&buf, &bufsize, charbytes, 0)) {
              width = bufsize - 1;
            }
            if (c != -1 && j + !rawmode < bufsize && (rawmode || !isspace(c))) {
              if (charbytes == 1) {
                ((unsigned char *)buf)[j++] = (unsigned char)c;
                c = callback(arg);
              } else if (tpdecodecb((wint_t *)&c, c, (void *)callback, arg) !=
                         -1) {
                if (charbytes == sizeof(char16_t)) {
                  j += abs(pututf16(&((char16_t *)buf)[j], bufsize - j - 1, c,
                                    false));
                } else {
                  ((wchar_t *)buf)[j++] = (wchar_t)c;
                }
                c = callback(arg);
              }
            } else {
              if (!rawmode && j < bufsize) {
                if (charbytes == sizeof(char)) {
                  ((unsigned char *)buf)[j] = '\0';
                } else if (charbytes == sizeof(char16_t)) {
                  ((char16_t *)buf)[j] = u'\0';
                } else if (charbytes == sizeof(wchar_t)) {
                  ((wchar_t *)buf)[j] = L'\0';
                }
              }
              break;
            }
          }
          ++items;
          if (ismalloc) {
            *va_arg(va, char **) = buf;
          }
        } else {
          do {
            if (isspace(c)) break;
          } while ((c = callback(arg)) != -1);
        }
        break;
      }
      default:
      NonDirectiveCharacter:
        c = (c == p[i - 1]) ? callback(arg) : -1;
        break;
    }
  }
Done:
  while (freeme) {
    struct FreeMe *entry = freeme;
    freeme = entry->next;
    if (items == -1) {
      weaken(free_s)((void **)&entry->ptr);
    }
    weaken(free_s)((void **)&entry);
  }
  return items;
}