/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
│vi: set et ft=c ts=8 tw=8 fenc=utf-8                                       :vi│
╚──────────────────────────────────────────────────────────────────────────────╝
│                                                                              │
│  smallz4cat                                                                  │
│  Copyright (c) 2016-2019 Stephan Brumme. All rights reserved.                │
│  See https://create.stephan-brumme.com/smallz4/                              │
│                                                                              │
│  Permission is hereby granted, free of charge, to any person obtaining       │
│  a copy of this software and associated documentation files (the             │
│  "Software"), to deal in the Software without restriction, including         │
│  without limitation the rights to use, copy, modify, merge, publish,         │
│  distribute, sublicense, and/or sell copies of the Software, and to          │
│  permit persons to whom the Software is furnished to do so, subject to       │
│  the following conditions:                                                   │
│                                                                              │
│  The above copyright notice and this permission notice shall be              │
│  included in all copies or substantial portions of the Software.             │
│                                                                              │
│  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,             │
│  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF          │
│  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.      │
│  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY        │
│  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,        │
│  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE           │
│  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                      │
│                                                                              │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/mem/mem.h"
#include "libc/mem/gc.internal.h"
#include "libc/runtime/runtime.h"
#include "libc/stdio/stdio.h"
#include "libc/str/str.h"

/**
 * @fileoverview shorter, more readable, albeit slower re-implementation
 *     of lz4cat ( https://github.com/Cyan4973/xxHash )
 *
 * Limitations:
 *
 * - Skippable frames and legacy frames are not implemented (and most
 *   likely never will)
 *
 * - Checksums are not verified (see https://create.stephan-brumme.com/xxhash/
 *   for a simple implementation)
 *
 * Replace getByteFromIn() and sendToOut() by your own code if you need
 * in-memory LZ4 decompression. Corrupted data causes a call to
 * unlz4error().
 */

#define HISTORY_SIZE     65536  // don't change
#define READ_BUFFER_SIZE 1024   // change at will

static void unlz4error(const char* msg) {
  fputs("ERROR: ", stderr);
  fputs(msg, stderr);
  fputc('\n', stderr);
  exit(1);
}

typedef unsigned char (*GET_BYTE)(void*);
typedef void (*SEND_BYTES)(const unsigned char*, unsigned int, void*);

struct UserPtr {
  // file handles
  FILE* in;
  FILE* out;
  unsigned char readBuffer[READ_BUFFER_SIZE];
  unsigned int pos;
  unsigned int available;
};

/// read a single byte (with simple buffering)
static unsigned char getByteFromIn(void* userPtr) {
  struct UserPtr* user = (struct UserPtr*)userPtr;
  if (user->pos == user->available) {
    user->pos = 0;
    user->available = fread(user->readBuffer, 1, READ_BUFFER_SIZE, user->in);
    if (user->available == 0) unlz4error("out of data");
  }
  return user->readBuffer[user->pos++];
}

/// write a block of bytes
static void sendBytesToOut(const unsigned char* data, unsigned int numBytes,
                           void* userPtr) {
  /// cast user-specific data
  struct UserPtr* user = (struct UserPtr*)userPtr;
  if (data != NULL && numBytes > 0) fwrite(data, 1, numBytes, user->out);
}

/// decompress everything in input stream (accessed via getByte) and write to
/// output stream (via sendBytes)
void unlz4_userPtr(GET_BYTE getByte, SEND_BYTES sendBytes,
                   const char* dictionary, void* userPtr) {
  // signature
  unsigned char signature1 = getByte(userPtr);
  unsigned char signature2 = getByte(userPtr);
  unsigned char signature3 = getByte(userPtr);
  unsigned char signature4 = getByte(userPtr);
  unsigned int signature =
      (signature4 << 24) | (signature3 << 16) | (signature2 << 8) | signature1;
  unsigned char isModern = (signature == 0x184D2204);
  unsigned char isLegacy = (signature == 0x184C2102);
  if (!isModern && !isLegacy) unlz4error("invalid signature");

  unsigned char hasBlockChecksum = false;
  unsigned char hasContentSize = false;
  unsigned char hasContentChecksum = false;
  unsigned char hasDictionaryID = false;
  if (isModern) {
    // flags
    unsigned char flags = getByte(userPtr);
    hasBlockChecksum = flags & 16;
    hasContentSize = flags & 8;
    hasContentChecksum = flags & 4;
    hasDictionaryID = flags & 1;

    // only version 1 file format
    unsigned char version = flags >> 6;
    if (version != 1) unlz4error("only LZ4 file format version 1 supported");

    // ignore blocksize
    char numIgnore = 1;

    // ignore, skip 8 bytes
    if (hasContentSize) numIgnore += 8;
    // ignore, skip 4 bytes
    if (hasDictionaryID) numIgnore += 4;

    // ignore header checksum (xxhash32 of everything up this point & 0xFF)
    numIgnore++;

    // skip all those ignored bytes
    while (numIgnore--) getByte(userPtr);
  }

  // contains the latest decoded data
  unsigned char* history = gc(malloc(HISTORY_SIZE));
  // next free position in history[]
  unsigned int pos = 0;

  // dictionary compression is a recently introduced feature, just move its
  // contents to the buffer
  if (dictionary != NULL) {
    // open dictionary
    FILE* dict = fopen(dictionary, "rb");
    if (!dict) unlz4error("cannot open dictionary");

    // get dictionary's filesize
    fseek(dict, 0, SEEK_END);
    long dictSize = ftell(dict);
    // only the last 64k are relevant
    long relevant = dictSize < 65536 ? 0 : dictSize - 65536;
    fseek(dict, relevant, SEEK_SET);
    if (dictSize > 65536) dictSize = 65536;
    // read it and store it at the end of the buffer
    fread(history + HISTORY_SIZE - dictSize, 1, dictSize, dict);
    fclose(dict);
  }

  // parse all blocks until blockSize == 0
  while (1) {
    // block size
    unsigned int blockSize = getByte(userPtr);
    blockSize |= (unsigned int)getByte(userPtr) << 8;
    blockSize |= (unsigned int)getByte(userPtr) << 16;
    blockSize |= (unsigned int)getByte(userPtr) << 24;

    // highest bit set ?
    unsigned char isCompressed = isLegacy || (blockSize & 0x80000000) == 0;
    if (isModern) blockSize &= 0x7FFFFFFF;

    // stop after last block
    if (blockSize == 0) break;

    if (isCompressed) {
      // decompress block
      unsigned int blockOffset = 0;
      unsigned int numWritten = 0;
      while (blockOffset < blockSize) {
        // get a token
        unsigned char token = getByte(userPtr);
        blockOffset++;

        // determine number of literals
        unsigned int numLiterals = token >> 4;
        if (numLiterals == 15) {
          // number of literals length encoded in more than 1 byte
          unsigned char current;
          do {
            current = getByte(userPtr);
            numLiterals += current;
            blockOffset++;
          } while (current == 255);
        }

        blockOffset += numLiterals;

        // copy all those literals
        if (pos + numLiterals < HISTORY_SIZE) {
          // fast loop
          while (numLiterals-- > 0) history[pos++] = getByte(userPtr);
        } else {
          // slow loop
          while (numLiterals-- > 0) {
            history[pos++] = getByte(userPtr);

            // flush output buffer
            if (pos == HISTORY_SIZE) {
              sendBytes(history, HISTORY_SIZE, userPtr);
              numWritten += HISTORY_SIZE;
              pos = 0;
            }
          }
        }

        // last token has only literals
        if (blockOffset == blockSize) break;

        // match distance is encoded in two bytes (little endian)
        unsigned int delta = getByte(userPtr);
        delta |= (unsigned int)getByte(userPtr) << 8;
        // zero isn't allowed
        if (delta == 0) unlz4error("invalid offset");
        blockOffset += 2;

        // match length (always >= 4, therefore length is stored minus 4)
        unsigned int matchLength = 4 + (token & 0x0F);
        if (matchLength == 4 + 0x0F) {
          unsigned char current;
          do  // match length encoded in more than 1 byte
          {
            current = getByte(userPtr);
            matchLength += current;
            blockOffset++;
          } while (current == 255);
        }

        // copy match
        unsigned int referencePos =
            (pos >= delta) ? (pos - delta) : (HISTORY_SIZE + pos - delta);
        // start and end within the current 64k block ?
        if (pos + matchLength < HISTORY_SIZE &&
            referencePos + matchLength < HISTORY_SIZE) {
          // read/write continuous block (no wrap-around at the end of
          // history[]) fast copy
          if (pos >= referencePos + matchLength ||
              referencePos >= pos + matchLength) {
            // non-overlapping
            memcpy(history + pos, history + referencePos, matchLength);
            pos += matchLength;
          } else {
            // overlapping, slower byte-wise copy
            while (matchLength-- > 0) history[pos++] = history[referencePos++];
          }
        } else {
          // either read or write wraps around at the end of history[]
          while (matchLength-- > 0) {
            // copy single byte
            history[pos++] = history[referencePos++];

            // cannot write anymore ? => wrap around
            if (pos == HISTORY_SIZE) {
              // flush output buffer
              sendBytes(history, HISTORY_SIZE, userPtr);
              numWritten += HISTORY_SIZE;
              pos = 0;
            }
            // wrap-around of read location
            referencePos %= HISTORY_SIZE;
          }
        }
      }

      // all legacy blocks must be completely filled - except for the last one
      if (isLegacy && numWritten + pos < 8 * 1024 * 1024) break;
    } else {
      // copy uncompressed data and add to history, too (if next block is
      // compressed and some matches refer to this block)
      while (blockSize-- > 0) {
        // copy a byte ...
        history[pos++] = getByte(userPtr);
        // ... until buffer is full => send to output
        if (pos == HISTORY_SIZE) {
          sendBytes(history, HISTORY_SIZE, userPtr);
          pos = 0;
        }
      }
    }

    if (hasBlockChecksum) {
      // ignore checksum, skip 4 bytes
      getByte(userPtr);
      getByte(userPtr);
      getByte(userPtr);
      getByte(userPtr);
    }
  }

  if (hasContentChecksum) {
    // ignore checksum, skip 4 bytes
    getByte(userPtr);
    getByte(userPtr);
    getByte(userPtr);
    getByte(userPtr);
  }

  // flush output buffer
  sendBytes(history, pos, userPtr);
}

/// old interface where getByte and sendBytes use global file handles
void unlz4(GET_BYTE getByte, SEND_BYTES sendBytes, const char* dictionary) {
  unlz4_userPtr(getByte, sendBytes, dictionary, NULL);
}

/// parse command-line
int main(int argc, const char* argv[]) {
  // default input/output streams
  struct UserPtr user = {.in = stdin,
                         .out = stdout,
                         .pos = 0,  // initial input buffer is empty
                         .available = 0};

  const char* dictionary = NULL;

  // first command-line parameter is our input filename / but ignore "-" which
  // stands for STDIN
  int parameter;
  for (parameter = 1; parameter < argc; parameter++) {
    const char* current = argv[parameter];
    // dictionary
    if (current[0] == '-' && current[1] == 'D') {
      if (parameter + 1 >= argc) unlz4error("no dictionary filename found");
      dictionary = argv[++parameter];
      continue;
    }

    // filename
    // read from STDIN, default behavior
    if (current[0] != '-' && current[1] != '\0') {
      // already have a filename - at most one filename is allowed (except for
      // dictionary) ?
      if (user.in != stdin)
        unlz4error("can only decompress one file at a time");
      // get handle
      user.in = fopen(argv[1], "rb");
      if (!user.in) unlz4error("file not found");
    }
  }

  // and go !
  unlz4_userPtr(getByteFromIn, sendBytesToOut, dictionary, &user);
  return 0;
}