#include <BAN/Assert.h>
#include <BAN/Limits.h>
#include <ctype.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>

#include <icxxabi.h>

extern "C" char** environ;

extern "C" void _fini();

static void (*at_exit_funcs[64])();
static uint32_t at_exit_funcs_count = 0;

void abort(void)
{
	fflush(nullptr);
	fprintf(stderr, "abort()\n");
	exit(1);
}

void exit(int status)
{
	for (uint32_t i = at_exit_funcs_count; i > 0; i--)
		at_exit_funcs[i - 1]();
	fflush(nullptr);
	__cxa_finalize(nullptr);
	_fini();
	_exit(status);
	ASSERT_NOT_REACHED();
}

int abs(int val)
{
	return val < 0 ? -val : val;
}

int atexit(void (*func)(void))
{
	if (at_exit_funcs_count > sizeof(at_exit_funcs) / sizeof(*at_exit_funcs))
	{
		errno = ENOBUFS;
		return -1;
	}
	at_exit_funcs[at_exit_funcs_count++] = func;
	return 0;
}

template<BAN::integral T>
static T strtoT(const char* str, char** endp, int base)
{
	// validate base
	if (base != 0 && (base < 2 || base > 36))
	{
		errno = EINVAL;
		return 0;
	}

	// parse character to its value in base
	// if digit is not of base, return -1
	auto get_base_digit = [](char c, int base) -> int
	{
		int digit = -1;
		if (isdigit(c))
			digit = c - '0';
		else if (isalpha(c))
			digit = 10 + tolower(c) - 'a';
		if (digit < base)
			return digit;
		return -1;
	};

	// skip whitespace
	while (isspace(*str))
		str++;

	// get sign and skip in
	bool negative = (*str == '-');
	if (*str == '-' || *str == '+')
		str++;

	// determine base from prefix
	if (base == 0)
	{
		if (strncasecmp(str, "0x", 2) == 0)
			base = 16;
		else if (*str == '0')
			base = 8;
		else if (isdigit(*str))
			base = 10;
	}

	// check for invalid conversion
	if (get_base_digit(*str, base) == -1)
	{
		if (endp)
			*endp = const_cast<char*>(str);
		errno = EINVAL;
		return 0;
	}

	// remove "0x" prefix from hexadecimal
	if (base == 16)
	{
		if (strncasecmp(str, "0x", 2) == 0)
			str += 2;
	}

	// limits of type T
	constexpr T max_val = BAN::numeric_limits<T>::max();
	constexpr T min_val = -max_val - 1;

	bool overflow = false;

	T result = 0;
	while (!overflow)
	{
		int digit = get_base_digit(*str, base);
		if (digit == -1)
			break;

		// check for overflow
		if (negative)
		{
			if (result < min_val / base)
				overflow = true;
			else if (result * base < min_val + digit)
				overflow = true;
		}
		else
		{
			if (result > max_val / base)
				overflow = true;
			else if (result * base > max_val - digit)
				overflow = true;
		}

		// calculate result's next step and move to next character
		if (!overflow)
		{
			result = result * base + (negative ? -digit : digit);
			str++;
		}
	}

	// save endp if asked
	if (endp)
	{
		while (get_base_digit(*str, base) != -1)
			str++;
		*endp = const_cast<char*>(str);
	}

	// return error on overflow
	if (overflow)
	{
		errno = ERANGE;
		return negative ? min_val : max_val;
	}

	return negative ? -result : result;
}

int atoi(const char* str)
{
	return strtol(str, nullptr, 10);
}

long atol(const char* str)
{
	return strtol(str, nullptr, 10);
}

long long atoll(const char* str)
{
	return strtoll(str, nullptr, 10);
}

long strtol(const char* __restrict str, char** __restrict endp, int base)
{
	return strtoT<long>(str, endp, base);
}

long long strtoll(const char* __restrict str, char** __restrict endp, int base)
{
	return strtoT<long long>(str, endp, base);
}

char* getenv(const char* name)
{
	if (environ == nullptr)
		return nullptr;
	size_t len = strlen(name);
	for (int i = 0; environ[i]; i++)
		if (strncmp(name, environ[i], len) == 0)
			if (environ[i][len] == '=')
				return environ[i] + len + 1;
	return nullptr;
}

int system(const char* command)
{
	// FIXME
	if (command == nullptr)
		return 1;

	int pid = fork();
	if (pid == 0)
	{
		execl("/bin/Shell", "Shell", "-c", command, (char*)0);
		exit(1);
	}

	if (pid == -1)
		return -1;

	int stat_val;
	waitpid(pid, &stat_val, 0);
	return stat_val;
}

int setenv(const char* name, const char* val, int overwrite)
{
	if (name == nullptr || !name[0] || strchr(name, '='))
	{
		errno = EINVAL;
		return -1;
	}

	if (!overwrite && getenv(name))
		return 0;

	size_t namelen = strlen(name);
	size_t vallen = strlen(val);

	char* string = (char*)malloc(namelen + vallen + 2);
	memcpy(string, name, namelen);
	string[namelen] = '=';
	memcpy(string + namelen + 1, val, vallen);
	string[namelen + vallen + 1] = '\0';

	return putenv(string);
}

int unsetenv(const char* name)
{
	if (name == nullptr || !name[0] || strchr(name, '='))
	{
		errno = EINVAL;
		return -1;
	}

	size_t len = strlen(name);

	bool found = false;
	for (int i = 0; environ[i]; i++)
	{
		if (!found && strncmp(environ[i], name, len) == 0 && environ[i][len] == '=')
		{
			free(environ[i]);
			found = true;
		}
		if (found)
			environ[i] = environ[i + 1];
	}

	return 0;
}

int putenv(char* string)
{
	if (string == nullptr || !string[0])
	{
		errno = EINVAL;
		return -1;
	}

	if (!environ)
	{
		environ = (char**)malloc(sizeof(char*) * 2);
		if (!environ)
			return -1;
		environ[0] = string;
		environ[1] = nullptr;
		return 0;
	}

	int cnt = 0;
	for (int i = 0; string[i]; i++)
		if (string[i] == '=')
			cnt++;
	if (cnt != 1)
	{
		errno = EINVAL;
		return -1;
	}

	int namelen = strchr(string, '=') - string;
	for (int i = 0; environ[i]; i++)
	{
		if (strncmp(environ[i], string, namelen + 1) == 0)
		{
			free(environ[i]);
			environ[i] = string;
			return 0;
		}
	}

	int env_count = 0;
	while (environ[env_count])
		env_count++;

	char** new_envp = (char**)malloc(sizeof(char*) * (env_count + 2));
	if (new_envp == nullptr)
		return -1;

	for (int i = 0; i < env_count; i++)
		new_envp[i] = environ[i];
	new_envp[env_count] = string;
	new_envp[env_count + 1] = nullptr;

	free(environ);
	environ = new_envp;

	return 0;
}

// Constants and algorithm from https://en.wikipedia.org/wiki/Permuted_congruential_generator

static uint64_t s_rand_state = 0x4d595df4d0f33173;
static constexpr uint64_t s_rand_multiplier = 6364136223846793005;
static constexpr uint64_t s_rand_increment = 1442695040888963407;

static constexpr uint32_t rotr32(uint32_t x, unsigned r)
{
	return x >> r | x << (-r & 31);
}

int rand(void)
{
	uint64_t x = s_rand_state;
	unsigned count = (unsigned)(x >> 59);

	s_rand_state = x * s_rand_multiplier + s_rand_increment;
	x ^= x >> 18;

	return rotr32(x >> 27, count) % RAND_MAX;
}

void srand(unsigned int seed)
{
	s_rand_state = seed + s_rand_increment;
	(void)rand();
}