/** @file numericx.c
 * Source code of the number translator command-line interface.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <errno.h>

#define PROG_NAME "numericx"


/* ||COMPILATION FLAGS|| */

/**
 * @name Compilation Flags
 *
 * These are the valid compilation flags for the definition of numerical systems.
 * Use them to make the program show more output, or
 * to set the proprieties of the FROM and the TO numerical system.
 *
 * @{
 */

/**
 * @param bool
 *
 * Configuration of the resulting numeral system
 * to have the units place on the end of the writing direction (on the right).
 */
#ifndef TO_UNITS_ON_THE_END
#define TO_UNITS_ON_THE_END false
#endif

/**
 * @param bool
 *
 * Configuration of the numeral system of the number input
 * to have the units place on the end of the writing direction (on the right).
 */
#ifndef FROM_UNITS_ON_THE_END
#define FROM_UNITS_ON_THE_END false
#endif

/**
 * @param bool
 *
 * Configuration of the resulting numeral system
 * to start counting on the second number, being the
 * first number void.
 */
#ifndef TO_FIRST_NUMBER_VOID
#define TO_FIRST_NUMBER_VOID false
#endif

/**
 * @param bool
 *
 * Configuration of the numeral system of the number input
 * to start counting on the second number, being the
 * first number void.
 */
#ifndef FROM_FIRST_NUMBER_VOID
#define FROM_FIRST_NUMBER_VOID false
#endif

/**
 * @param bool
 *
 * Configuration of the resulting numeral system
 * to have the first number as an infinite number,
 * for example, if the first number is 'A', then
 * A == AA == AAA == AAAA ...
 */
#ifndef TO_INFINITE_BASE
#define TO_INFINITE_BASE false
#endif

/**
 * @param bool
 *
 * Configuration of the numeral system of the number input
 * to have the first number as an infinite number,
 * for example, if the first number is 'A', then
 * A == AA == AAA == AAAA ...
 */
#ifndef FROM_INFINITE_BASE
#define FROM_INFINITE_BASE false
#endif

/** @} */

/* ||DATA STRUCTURE|| */

/**
 * @brief Numeral structure
 *
 * This struct is in use to apply our operations on the number.
 * The number are converted to this struct, the operations are applied,
 * and on the end, the resulting number is converted from this struct.
 */
typedef struct NumeralPtr
{
	char const* symbol; /**< a pointer to the glyph/numeral/symbol of this digit. */
	struct NumeralPtr *next; /**< a pointer to the next digit */
	struct NumeralPtr *previous; /**< a pointer to the previous digit */
} numeral_ptr;


/* ||FUNCTIONS|| */

/**
 * @brief Create new digit for numeral_ptr.
 *
 * It needs the last_numeral ('last_numeral') into which will
 * add the new numeral, and also need to know the symbol of the
 * new numeral ('to_first').
 *
 * @param last_numeral - last numeral_ptr* into which new numeral_ptr will be added.
 * @param to_first - symbol of the new digit.
 *
 * @return pointer to new numeral_ptr in case of success.
 * @return NULL in case of no memory.
 */
numeral_ptr*
new_digit(numeral_ptr* last_numeral, char const* to_first)
{
	numeral_ptr* new_numeral = malloc(sizeof(numeral_ptr));
	if(new_numeral == NULL)
	{
		fprintf(stderr, "error: %s: %s!", PROG_NAME, strerror(ENOMEM));
		return NULL;
	}

	new_numeral->symbol = to_first;
	new_numeral->previous = last_numeral;
	new_numeral->next = NULL;

	return new_numeral;
}

/**
 * @brief Initializer of numeral_ptr
 *
 * Creates a number of the form numeral_ptr that
 * begins with 'case' number of cases, and all cases
 * are set to 'to_first' char.
 *
 * @param to_first - the symbol of the cases for the new number.
 * @param cases - number of cases of the new number.
 *
 * @return pointer to numeral_ptr in case of success.
 * @return NULL in case of no memory ( because depends
 * on new_digit() ).
 */
numeral_ptr*
numeral_infinity(char const* to_first, size_t cases)
{
	numeral_ptr* starting_case = new_digit(NULL, to_first);
	numeral_ptr* other_case = starting_case;

	for(size_t i = 2; i <= cases; ++i)
	{
		other_case->next = new_digit(other_case, to_first);
		other_case = other_case->next;
	}

	return starting_case;
}

/**
 * @brief Increment numeral_ptr 'numeral' one unit up.
 *
 * It needs 'num_first' as the first numeral of the numerical
 * system. Also needs 'num_last' as the last numeral of the
 * numerical system.
 * When incrementing, if the function adds a new digit/numeral, it
 * will use the 'brand_new_digit' as its new numeral/digit.
 *
 * @param numeral - numeral to increment.
 * @param num_first - number's numeral system first numeral.
 * @param num_last - number's numeral system last numeral.
 * @param brand_new_digit - brand new created numeral, if needed by incrementation.
 */
void
increment(numeral_ptr* numeral, char* num_first, char* num_last, char* brand_new_digit)
{
	bool cycled = false;

	if( numeral->symbol == num_last )
	{
		if( numeral->next == NULL )
			numeral->next = new_digit(numeral, brand_new_digit);
		else
			increment(numeral->next, num_first, num_last, brand_new_digit);

		cycled = true;
	}

	if( cycled )
		numeral->symbol = num_first;
	else
		++(numeral->symbol);
}

/**
 * @brief Decrement a string 'number' by one unit.
 *
 * It needs to know the first numeral ('first_numeral') and also the
 * last numeral ('last_numeral'). It also needs the numeral system in
 * form of a string ('numeral_system') to know which is the numeral
 * before the actual numeral that needs decrementation.
 *
 * @param number - the string number to be decremented.
 * @param first_numeral - number's numeral system first numeral.
 * @param last_numeral - number's numeral system last numeral.
 * @param numeral_system - string of the corresponding number's numeral system numeral.
 */
void
decrement_number_string(char* number, char* first_numeral, char* last_numeral, char* numeral_system)
{
	while( *number == *first_numeral )
	{
		*number = *last_numeral;
		++number;
	}

	if( *number == '\0' )
	{
		*(--number) = '\0';
	}
	else
	{
		while( !(*numeral_system == *number) )
			++numeral_system;

		*number = *(--numeral_system);
	}
}

/**
 * @brief Check if numeral_ptr and string are of the same value
 *
 * Compares if a numeral_ptr ('numeral') matches the string ('number_arg').
 *
 * @param numeral - numeral_ptr to check.
 * @param number_arg - string to check.
 *
 * @return true if matches.
 * @return false if doesn't match.
 */
bool
is_the_same(numeral_ptr* numeral, char* number_arg)
{
	while( !(numeral == NULL) )
	{
		if( *(numeral->symbol) == *(number_arg) )
		{
			numeral = numeral->next;
			++(number_arg);
			continue;
		}

		return false;
	}

	return (*number_arg == '\0') ? true : false;
}

/**
 * @brief Print numeral
 *
 * Prints to standard output numeral_ptr ('numeral').
 *
 * @param numeral - numeral_ptr to print.
 */
void
print_numeral(numeral_ptr* numeral)
{
	if( TO_UNITS_ON_THE_END )
	{
		while( !(numeral->next == NULL) )
			numeral = numeral->next;

		while( !(numeral == NULL) )
		{
			printf("%c", *(numeral->symbol));
			numeral = numeral->previous;
		}
	}
	else
	{
		while( !(numeral == NULL) )
		{
			printf("%c", *(numeral->symbol));
			numeral = numeral->next;
		}
	}
}

/**
 * @brief Reverse a string.
 *
 * @param string - string to be reversed.
 */
void
reverse_string(char* string)
{
	char tmp;
	char* string_end = string + strlen(string);

	while ( --string_end > string )
	{
		tmp = *string;
		*string++ = *string_end;
		*string_end = tmp;
	}
}

/**
 * @brief Does string belongs to numeral system?
 *
 * Check if string 'number' belongs to the numerical
 * system ('numeral_system'), which is also a string.
 * Belonging mean all the symbols of 'number' are included
 * in 'numeral_system'.
 *
 * @param numeral_system - numeral system string to check against.
 * @param number - number to see if belongs.
 *
 * @return true if it belongs.
 * @return false if it doesn't belong.
 */
bool
is_valid_number(char* numeral_system, char *number)
{
	/*
	if( *number == '-' || *number == '+' )
		++number;
	*/
	while( !(*number == '\0') )
	{
		if( strchr(numeral_system, *number) == NULL )
			return false;
		++number;
	}

	return true;
}

/**
 * @brief Free numeral memory.
 *
 * Free up numeral_ptr ('numeral') linked chain.
 *
 * @param numeral - numeral_ptr to free.
 */
void
free_numeral(numeral_ptr* numeral)
{
	numeral_ptr* tmp = NULL;

	while( !(numeral == NULL) )
	{
		tmp = numeral->next;
		free(numeral);
		numeral = tmp;
	}
}

/**
 * @brief Free numericx result.
 *
 * Function frees up the result of numericx_translate(),
 * after we are done with it.
 *
 * @param string - char pointer to be free.
 */
void
numericx_free(char* string)
{
	free(string);
}

/**
 * @brief Convert numeral_ptr to string.
 *
 * Allocates space for string and converts numeral_ptr* to char*.
 *
 * @param numeral - numeral_ptr to be converted to string.
 * @param result_with_units_on_the_end - define if result has units on the end.
 *
 * @return char pointer to converted string in case of success.
 * @return NULL in case of no memory.
 */
char*
numeral_to_string(numeral_ptr* numeral, bool result_with_units_on_the_end)
{
	size_t length = 1;
	numeral_ptr* numeral_last = numeral;

	while( !(numeral_last->next == NULL) )
	{
		++length;
		numeral_last = numeral_last->next;
	}

	char* result = malloc((length + 1) * sizeof(char));
	char* tmp = result;

	if( !result_with_units_on_the_end )
	{
		for( numeral_ptr* digit = numeral;
				!(digit == NULL); digit = digit->next)
		{
			*tmp = *(digit->symbol);
			++tmp;
		}
	}
	else
	{
		for( numeral_ptr* digit = numeral_last;
				!(digit == NULL); digit = digit->previous)
		{
			*tmp = *(digit->symbol);
			++tmp;
		}
	}

	*(tmp) = '\0';

	return result;
}

/**
 * @brief Translate string to a different numerical system.
 *
 * After definition of the 'from' numerical system proprieties and the
 * 'to' numerical system proprieties, will be translate 'number' from the
 * 'from' to the 'to' numerical system, resulting in a string.
 *
 * @param from - string with all the numerals of the number's numerical system.
 * @param to - string with all the numerals of the resulting number's numerical system.
 * @param from_units_on_the_end - does the translate from numerical system have units on the end (on the right)?
 * @param to_units_on_the_end - does the translate to numerical system have units on the end (on the right)?
 * @param from_first_number_void - does the translate from numerical system start counting on the second number?
 * @param to_first_number_void - does the translate to numerical system start counting on the second number?
 * @param from_infinite_base - is the translate from numerical system first numeral infinite? For example, if first numeral is 'A', then does 'A' == 'AA' == 'AAA' == 'AAAA' ... ?
 * @param to_infinite_base - is the translate to numerical system first numeral infinite? For example, if first numeral is 'A', then does 'A' == 'AA' == 'AAA' == 'AAAA' ... ?
 * @param number - number of the from numerical system, to be translated into the to numerical system
 *
 * @return NULL in case of failure
 * @return string of translated number, in case of success
 */
char*
numericx_translate(char* from, bool from_units_on_the_end, bool from_first_number_void, bool from_infinite_base, char* to, bool to_units_on_the_end, bool to_first_number_void, bool to_infinite_base, char* number)
{

	/* Check if number belongs to it's numerical system */
	if( !is_valid_number(from, number) )
	{
		fprintf(stderr, "error: %s: %s.\nValid numerals are: \"%s\"\n",
				PROG_NAME, strerror(EDOM), from);
		return NULL;
	}

	/* _first and _last variables */
	char* from_first = from;
	char* from_last = from + (strlen(from) - 1);

	char* to_first = to;
	char* to_last = to + (strlen(to) - 1);

	if( from_units_on_the_end )
	{
		reverse_string(number);
	}

	/* initializing counting and result */
	numeral_ptr* counting = NULL;
	numeral_ptr* result = NULL;

	if( from_infinite_base )
		counting = numeral_infinity(from_first, strlen(number));
	else
		counting = numeral_infinity(from_first, 1);

	result = numeral_infinity(to_first, 1);

	/* first number void */
	if( !(from_first_number_void && to_first_number_void) )
	{
		if( from_first_number_void )
		{
			if( strlen(number) == 1 && *number == *from_first )
			{
				free_numeral(counting);
				free_numeral(result);
				fprintf(stderr, "error: %s: unrepresentable void number\n", PROG_NAME);
				return NULL;
			}
			decrement_number_string(number, from_first, from_last, from_first);
		}

		if( to_first_number_void )
			increment(result, to_first, to_last, to_first);
	}

	/* minor optimization for the cycle below */
	char* to_second = NULL;

	if( to_infinite_base )
		to_second = to_first + 1;

	/* increments until it finishes */
	while( !is_the_same(counting, number) )
	{
		if( to_infinite_base )
			increment(result, to_first, to_last, to_second);
		else
			increment(result, to_first, to_last, to_first);

		increment(counting, from_first, from_last, from_first);
	}

	/* result to string (result_string) */
	char* result_string = numeral_to_string(result, to_units_on_the_end);

	/* free memory */
	free_numeral(counting);
	free_numeral(result);

	return result_string;
}

/* ||MAIN FUNCTION|| */

/**
 * @brief Translate number.
 *
 * Main function that does the translation of the number.
 */
int
main(int argc, char* argv[])
{
	/* argument processing */
	if( !(argc == 2) )
	{
		fprintf(stderr, "usage: %s <number>\n", PROG_NAME);
		exit(EXIT_FAILURE);
	}

	/* Number variables to be converted */
	char* number = argv[1];

	/* Arguments for translation */
	char* from = malloc( (strlen(FROM_NUMERICALS) + 1) * sizeof(char) );
	char* to = malloc( (strlen(TO_NUMERICALS) + 1) * sizeof(char) );

	strcpy(from, FROM_NUMERICALS);
	strcpy(to, TO_NUMERICALS);

	bool to_units_on_the_end = TO_UNITS_ON_THE_END;
	bool from_units_on_the_end = FROM_UNITS_ON_THE_END;
	bool to_first_number_void = TO_FIRST_NUMBER_VOID;
	bool from_first_number_void = FROM_FIRST_NUMBER_VOID;
	bool to_infinite_base = TO_INFINITE_BASE;
	bool from_infinite_base = FROM_INFINITE_BASE;

	/* Check if number belongs to it's numerical system */
	if( !is_valid_number(from, number) )
	{
		fprintf(stderr, "error: %s: %s.\nValid numerals are: \"%s\"\n",
				PROG_NAME, strerror(EDOM), from);
		free(from);
		free(to);
		exit(EDOM);
	}

	/* Translation */
	char* result = numericx_translate(
			from, from_units_on_the_end, from_first_number_void, from_infinite_base,
			to, to_units_on_the_end, to_first_number_void, to_infinite_base,
			number);

	/* Test for translation failure */
	if( result == NULL )
	{
		fprintf(stderr, "error: %s: Invalid translation\n", PROG_NAME);
		free(from);
		free(to);
		return EXIT_FAILURE;
	}

	/* Print */
	printf("%s\n", result);

	/* Free */
	free(from);
	free(to);
	numericx_free(result);

	return EXIT_SUCCESS;
}