#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

#define NUM_COMPRESSORS              4
#define COMPRESSION_METHODS         96 /* sum of all values for the methods field in compressors */
#define MAX_FILE_SIZE            32768
#define SHORT_COMMAND_COUNT         32
#define MAX_COMMAND_COUNT         1024
#define LOOKBACK_LIMIT             128 /* highest negative valid count for a copy command */
#define LOOKAHEAD_LIMIT           3072 /* maximum lookahead distance for the first pass of multi-pass compression */
#define MULTIPASS_SKIP_THRESHOLD    64

#if __STDC_VERSION__ >= 201112L
	// <noreturn.h> forces "noreturn void", which is silly and redundant; this is simpler
	#define noreturn _Noreturn void
#else
	#define noreturn void /* fallback */
#endif

struct command {
  unsigned command: 3; // commands 0-6 as per compression spec; command 7 is used as a dummy placeholder
  unsigned count:  12; // always equals the uncompressed data length
  signed value:    17; // offset for commands 0 (into source) and 4-6 (into decompressed output); repeated bytes for commands 1-2
};

struct compressor {
  unsigned methods;
  const char * name;
  struct command * (* function) (const unsigned char *, const unsigned char *, unsigned short *, unsigned);
};

struct options {
  const char * input;
  const char * output;
  unsigned method; // method to use, or >= COMPRESSION_METHODS to try them all
  unsigned char mode; // 0: compress, 1: compress to text, 2: uncompress, 3: dump commands as text
  unsigned char alignment; // 1 << value
};

// global.c
extern const struct compressor compressors[];
extern const unsigned char bit_flipping_table[];
extern char option_name_buffer[];

// main.c
int main(int, char **);
struct command * compress(const unsigned char *, unsigned short *, unsigned);

// merging.c
struct command * select_optimal_sequence(struct command **, const unsigned short *, unsigned short *);
struct command * select_command_sequence(struct command **, const unsigned short *, int, unsigned short *);
struct command * merge_command_sequences(const struct command *, unsigned short, const struct command *, unsigned short, unsigned short *);

// mpcomp.c
struct command * try_compress_multi_pass(const unsigned char *, const unsigned char *, unsigned short *, unsigned);
struct command pick_command_for_pass(const unsigned char *, const unsigned char *, const unsigned char *, const short *, unsigned short,
                                     unsigned short, unsigned);
struct command pick_repetition_for_pass(const unsigned char *, unsigned short, unsigned short, unsigned);
struct command pick_copy_for_pass(const unsigned char *, const unsigned char *, const short *, unsigned char, unsigned short, unsigned short, unsigned);

// nullcomp.c
struct command * store_uncompressed(const unsigned char *, const unsigned char *, unsigned short *, unsigned);

// options.c
struct options get_options(int, char **);
unsigned parse_numeric_option_argument(char ***, unsigned);
int parse_compressor_option_argument(char ***);
const char * get_argument_for_option(char ***, const char **);
noreturn usage(const char *);
noreturn list_compressors(void);

// output.c
void write_commands_to_textfile(const char *, const struct command *, unsigned, const unsigned char *, unsigned char);
void write_commands_and_padding_to_textfile(const char *, const struct command *, unsigned, const unsigned char *, unsigned, unsigned);
void write_command_to_textfile(FILE *, struct command, const unsigned char *);
void write_commands_to_file(const char *, const struct command *, unsigned, const unsigned char *, unsigned char);
void write_command_to_file(FILE *, struct command, const unsigned char *);
void write_raw_data_to_file(const char *, const void *, unsigned);

// packing.c
void optimize(struct command *, unsigned short);
void repack(struct command **, unsigned short *);

// repcomp.c
struct command * try_compress_repetitions(const unsigned char *, const unsigned char *, unsigned short *, unsigned);
struct command find_repetition_at_position(const unsigned char *, unsigned short, unsigned short);

// spcomp.c
struct command * try_compress_single_pass(const unsigned char *, const unsigned char *, unsigned short *, unsigned);
struct command find_best_copy(const unsigned char *, unsigned short, unsigned short, const unsigned char *, unsigned);
unsigned short scan_forwards(const unsigned char *, unsigned short, const unsigned char *, unsigned short, short *);
unsigned short scan_backwards(const unsigned char *, unsigned short, unsigned short, short *);
struct command find_best_repetition(const unsigned char *, unsigned short, unsigned short);

// uncomp.c
struct command * get_commands_from_file(const unsigned char *, unsigned short * restrict, unsigned short * restrict);
unsigned char * get_uncompressed_data(const struct command *, const unsigned char *, unsigned short *);

// util.c
noreturn error_exit(int, const char *, ...);
unsigned char * read_file_into_buffer(const char *, unsigned short *);
struct command pick_best_command(unsigned, struct command, ...);
int is_better(struct command, struct command);
short command_size(struct command);
unsigned short compressed_length(const struct command *, unsigned short);