/*
 * Copyright (c) 2013, 2014, 2021 Jonas 'Sortie' Termansen.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * time/strftime.c
 * Format time and date into a string.
 */

#ifndef STRFTIME
#define STRFTIME strftime
#define STRFTIME_CHAR char
#define STRFTIME_L(x) x
#endif

#include <sys/cdefs.h>

#include <stdbool.h>
#include <stdint.h>
#include <time.h>
#include <wchar.h>

static const STRFTIME_CHAR* GetWeekdayAbbreviated(const struct tm* tm)
{
	switch ( tm->tm_wday % 7 )
	{
	case 0: return STRFTIME_L("Sun");
	case 1: return STRFTIME_L("Mon");
	case 2: return STRFTIME_L("Tue");
	case 3: return STRFTIME_L("Wed");
	case 4: return STRFTIME_L("Thu");
	case 5: return STRFTIME_L("Fri");
	case 6: return STRFTIME_L("Sat");
	default: __builtin_unreachable();
	}
}

static const STRFTIME_CHAR* GetWeekday(const struct tm* tm)
{
	switch ( tm->tm_wday % 7 )
	{
	case 0: return STRFTIME_L("Sunday");
	case 1: return STRFTIME_L("Monday");
	case 2: return STRFTIME_L("Tuesday");
	case 3: return STRFTIME_L("Wednesday");
	case 4: return STRFTIME_L("Thursday");
	case 5: return STRFTIME_L("Friday");
	case 6: return STRFTIME_L("Saturday");
	default: __builtin_unreachable();
	}
}

static const STRFTIME_CHAR* GetMonthAbbreviated(const struct tm* tm)
{
	switch ( tm->tm_mon % 12 )
	{
	case 0: return STRFTIME_L("Jan");
	case 1: return STRFTIME_L("Feb");
	case 2: return STRFTIME_L("Mar");
	case 3: return STRFTIME_L("Apr");
	case 4: return STRFTIME_L("May");
	case 5: return STRFTIME_L("Jun");
	case 6: return STRFTIME_L("Jul");
	case 7: return STRFTIME_L("Aug");
	case 8: return STRFTIME_L("Sep");
	case 9: return STRFTIME_L("Oct");
	case 10: return STRFTIME_L("Nov");
	case 11: return STRFTIME_L("Dec");
	default: __builtin_unreachable();
	}
}

static const STRFTIME_CHAR* GetMonth(const struct tm* tm)
{
	switch ( tm->tm_mon % 12 )
	{
	case 0: return STRFTIME_L("January");
	case 1: return STRFTIME_L("February");
	case 2: return STRFTIME_L("March");
	case 3: return STRFTIME_L("April");
	case 4: return STRFTIME_L("May");
	case 5: return STRFTIME_L("June");
	case 6: return STRFTIME_L("July");
	case 7: return STRFTIME_L("August");
	case 8: return STRFTIME_L("Sepember");
	case 9: return STRFTIME_L("October");
	case 10: return STRFTIME_L("November");
	case 11: return STRFTIME_L("December");
	default: __builtin_unreachable();
	}
}

static
size_t strftime_convert_uintmax(STRFTIME_CHAR* destination, uintmax_t value)
{
	size_t result = 1;
	uintmax_t copy = value;
	while ( 10 <= copy )
		copy /= 10, result++;
	for ( size_t i = result; i != 0; i-- )
		destination[i-1] = STRFTIME_L('0') + value % 10,
		value /= 10;
	destination[result] = STRFTIME_L('\0');
	return result;
}

static
size_t strftime_convert_int(STRFTIME_CHAR* destination, int value)
{
	if ( value < 0 )
	{
		*destination++ = STRFTIME_L('-');
		return 1 + strftime_convert_uintmax(destination, - (uintmax_t) (intmax_t) value);
	}
	return strftime_convert_uintmax(destination, (uintmax_t) value);
}

size_t STRFTIME(STRFTIME_CHAR* s,
                size_t max,
                const STRFTIME_CHAR* format,
                const struct tm* tm)
{
	size_t ret = 0;

#define OUTPUT_CHAR(expr) \
	do { \
		if ( ret == max ) \
			return 0; \
		s[ret++] = (expr); \
	} while ( 0 )

#define OUTPUT_STRING(expr) \
	do { \
		const STRFTIME_CHAR* out_str = (expr); \
		while ( *out_str ) \
			OUTPUT_CHAR(*out_str++); \
	} while ( 0 )

#define OUTPUT_INT_PADDED(valexpr, widthexpr, padexpr) \
	do { \
		int val = (valexpr); \
		size_t width = (widthexpr); \
		STRFTIME_CHAR pad = (padexpr); \
		STRFTIME_CHAR str[sizeof(int) * 3]; \
		str[0] = STRFTIME_L('\0'); \
		size_t got = strftime_convert_int(str, val); \
		while ( pad && got < width-- ) \
			OUTPUT_CHAR(pad); \
		OUTPUT_STRING(str); \
	} while ( 0 )

#define OUTPUT_INT(valexpr) OUTPUT_INT_PADDED(valexpr, 0, STRFTIME_L('\0'))

	STRFTIME_CHAR c;
	while ( (c = *format++) )
	{
		if ( c != STRFTIME_L('%') )
		{
			OUTPUT_CHAR(c);
			continue;
		}
		const STRFTIME_CHAR* specifiers_begun_at = format;
		c = *format++;

		// Process any optional flags.
		STRFTIME_CHAR padding_char = STRFTIME_L(' ');
		bool plus_padding = false;
		while ( true )
		{
			switch ( c )
			{
			case STRFTIME_L('0'): padding_char = STRFTIME_L('0'); break;
			case STRFTIME_L('+'): padding_char = STRFTIME_L('0'); plus_padding = true; break;
			default: goto end_of_flags;
			}
			c = *format++;
		}
	end_of_flags:

		// TODO: Support the '+' flag!
		if ( plus_padding )
		{
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		}

		// Process the optional minimum field width.
		size_t field_width = 0;
		while ( STRFTIME_L('0') <= c && c <= STRFTIME_L('9') )
			field_width = field_width * 10 + c - STRFTIME_L('0'),
			c = *format++;

		// Process an optional E or O modifier.
		bool e_modifier = false;
		bool o_modifier = false;
		if ( c == STRFTIME_L('E') )
			e_modifier = true,
			c = *format++;
		else if ( c == STRFTIME_L('O') )
			o_modifier = true,
			c = *format++;

		// TODO: Support the E and O modifiers where marked with the E and O
		//       comments in the below switch.
		if ( e_modifier || o_modifier ) { }

		switch ( c )
		{
		case STRFTIME_L('a'): OUTPUT_STRING(GetWeekdayAbbreviated(tm)); break;
		case STRFTIME_L('A'): OUTPUT_STRING(GetWeekday(tm)); break;
		case STRFTIME_L('b'): OUTPUT_STRING(GetMonthAbbreviated(tm)); break;
		case STRFTIME_L('B'): OUTPUT_STRING(GetMonth(tm)); break;
		case STRFTIME_L('c'): /*E*/
			OUTPUT_STRING(GetWeekday(tm));
			OUTPUT_STRING(STRFTIME_L(" "));
			OUTPUT_STRING(GetMonthAbbreviated(tm));
			OUTPUT_STRING(STRFTIME_L(" "));
			OUTPUT_INT_PADDED(tm->tm_mday, 2, STRFTIME_L('0'));
			OUTPUT_STRING(STRFTIME_L(" "));
			OUTPUT_INT_PADDED(tm->tm_hour, 2, STRFTIME_L('0'));
			OUTPUT_STRING(STRFTIME_L(":"));
			OUTPUT_INT_PADDED(tm->tm_min, 2, STRFTIME_L('0'));
			OUTPUT_STRING(STRFTIME_L(":"));
			OUTPUT_INT_PADDED(tm->tm_sec, 2, STRFTIME_L('0'));
			break;
		case STRFTIME_L('C'): /*E*/
			if ( !field_width )
				field_width = 2;
			OUTPUT_INT_PADDED((tm->tm_year + 1900) / 100, field_width, padding_char);
			break;
		case STRFTIME_L('d'): OUTPUT_INT_PADDED(tm->tm_mday, 2, STRFTIME_L('0')); break; /*O*/
		case STRFTIME_L('D'):
			OUTPUT_INT_PADDED(tm->tm_mon + 1, 2, STRFTIME_L('0'));
			OUTPUT_CHAR('/');
			OUTPUT_INT_PADDED(tm->tm_mday, 2, STRFTIME_L('0'));
			OUTPUT_CHAR('/');
			OUTPUT_INT_PADDED((tm->tm_year + 1900) % 100, 2, STRFTIME_L('0'));
			break;
		case STRFTIME_L('e'): OUTPUT_INT_PADDED(tm->tm_mday, 2, STRFTIME_L(' ')); break; /*O*/
		case STRFTIME_L('F'):
			// TODO: Behavior if padding is requested.
			OUTPUT_INT_PADDED(tm->tm_year + 1900, 4, STRFTIME_L('0'));
			OUTPUT_CHAR('-');
			OUTPUT_INT_PADDED(tm->tm_mon + 1, 2, STRFTIME_L('0'));
			OUTPUT_CHAR('-');
			OUTPUT_INT_PADDED(tm->tm_mday, 2, STRFTIME_L('0'));
			break;
		case STRFTIME_L('g'):
			// TODO: These require a bit of intelligence.
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		case STRFTIME_L('G'):
			// TODO: These require a bit of intelligence.
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		case STRFTIME_L('h'): OUTPUT_STRING(GetMonthAbbreviated(tm)); break;
		case STRFTIME_L('H'): OUTPUT_INT_PADDED(tm->tm_hour, 2, STRFTIME_L('0')); break; /*O*/
		case STRFTIME_L('I'): OUTPUT_INT_PADDED((tm->tm_hour + 11) % 12 + 1, 2, STRFTIME_L('0')); break; /*O*/
		case STRFTIME_L('j'): OUTPUT_INT_PADDED(tm->tm_yday + 1, 3, STRFTIME_L('0')); break;
		case STRFTIME_L('m'): OUTPUT_INT_PADDED(tm->tm_mon + 1, 2, STRFTIME_L('0')); break; /*O*/
		case STRFTIME_L('M'): OUTPUT_INT_PADDED(tm->tm_min, 2, STRFTIME_L('0')); break; /*O*/
		case STRFTIME_L('n'): OUTPUT_CHAR(STRFTIME_L('\n')); break;
		case STRFTIME_L('p'): OUTPUT_STRING(tm->tm_hour < 12 ? STRFTIME_L("AM") : STRFTIME_L("PM")); break;
		case STRFTIME_L('r'):
			OUTPUT_INT_PADDED(tm->tm_hour % 12 + 1, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_min, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_sec, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(' ');
			OUTPUT_STRING(tm->tm_hour < 12 ? STRFTIME_L("AM") : STRFTIME_L("PM"));
			break;
		case STRFTIME_L('R'):
			OUTPUT_INT_PADDED(tm->tm_hour, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_min, 2, STRFTIME_L('0'));
			break;
		case STRFTIME_L('S'): OUTPUT_INT_PADDED(tm->tm_sec, 2, STRFTIME_L('0')); break; /*O*/
		case STRFTIME_L('t'): OUTPUT_CHAR(STRFTIME_L('\t')); break;
		case STRFTIME_L('T'):
			OUTPUT_INT_PADDED(tm->tm_hour, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_min, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_sec, 2, STRFTIME_L('0'));
			break;
		case STRFTIME_L('u'): OUTPUT_INT(tm->tm_yday); break; /*O*/
		case STRFTIME_L('U'): /*O*/
			// TODO: These require a bit of intelligence.
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		case STRFTIME_L('V'): /*O*/
			// TODO: These require a bit of intelligence.
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		case STRFTIME_L('w'): OUTPUT_INT(tm->tm_wday); break; /*O*/
		case STRFTIME_L('W'): /*O*/
			// TODO: These require a bit of intelligence.
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		case STRFTIME_L('x'):
			OUTPUT_INT_PADDED(tm->tm_mon + 1, 2, STRFTIME_L('0'));
			OUTPUT_CHAR('/');
			OUTPUT_INT_PADDED(tm->tm_mday, 2, STRFTIME_L('0'));
			OUTPUT_CHAR('/');
			OUTPUT_INT_PADDED((tm->tm_year + 1900) % 100, 2, STRFTIME_L('0'));
			break; /*E*/
		case STRFTIME_L('X'):
			OUTPUT_INT_PADDED(tm->tm_hour, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_min, 2, STRFTIME_L('0'));
			OUTPUT_CHAR(':');
			OUTPUT_INT_PADDED(tm->tm_sec, 2, STRFTIME_L('0'));
			break; /*E*/
		case STRFTIME_L('y'): OUTPUT_INT_PADDED((tm->tm_year + 1900) % 100, 2, STRFTIME_L('0')); break; /*EO*/
		case STRFTIME_L('Y'): OUTPUT_INT(tm->tm_year + 1900); break; /*E*/
		case STRFTIME_L('z'):
			// TODO: struct tm doesn't have all this information available!
			OUTPUT_STRING(STRFTIME_L("+0000"));
			break;
		case STRFTIME_L('Z'):
			// TODO: struct tm doesn't have all this information available!
			OUTPUT_STRING(STRFTIME_L("UTC"));
			break;
		case STRFTIME_L('%'): OUTPUT_CHAR(STRFTIME_L('%')); break;
		default:
			OUTPUT_CHAR('%');
			format = specifiers_begun_at;
			continue;
		}
	}
	if ( ret == max )
		return 0;
	s[ret] = STRFTIME_L('\0');
	return ret;
}
