/* regex.c
 * Copyright 2023 Anon Anonson, Ognjen 'xolatile' Milan Robovic, Emil Williams
 * SPDX Identifier: GPL-3.0-only / NO WARRANTY / NO GUARANTEE */

#include "regex.h"

#include <assert.h>
#include <string.h>
#include <limits.h>

// ------------------
// ### Char tests ###
// ------------------
static bool is_quantifier(const char c) {
	for (const char * s = "+*?="; *s != '\00'; s++) {
		if (*s == c) {
			return true;
		}
	}
	return false;
}

bool is_magic(const char c) {
	if (is_quantifier(c)) {
		return true;
	}
	for (const char * s = "\\[]."; *s != '\00'; s++) {
		if (*s == c) {
			return true;
		}
	}
	return false;
}



// ----------------------
// ### Internal Types ###
// ----------------------
typedef struct {
	int in;
	char input;
	int to;
	int width;
} delta_t;

typedef struct {
	int in;
	int to;
} offshoot_t;

typedef struct {
	bool    * do_catch;
	bool    * is_negative;
	int     * state;
	int     * width;
	char    * whitelist;
	char    * blacklist;
	regex_t * regex;
} compiler_state;



// ----------------------------------
// ### Regex creation/destruction ###
// ----------------------------------
static int escape_1_to_1(const char c, compiler_state * cs) {
	char * target_list = (*cs->is_negative) ? cs->blacklist : cs->whitelist;
	switch (c) {
		case 't': {
			strcat(target_list, "\t");
		} return 1;
		case 'n': {
			strcat(target_list, "\n");
		} return 1;
		case 'r': {
			strcat(target_list, "\r");
		} return 1;
		case 'b': {
			strcat(target_list, "\b");
		} return 1;
		case '[': {
			strcat(target_list, "[");
		} return 1;
		case ']': {
			strcat(target_list, "]");
		} return 1;
		case '.': {
			strcat(target_list, ".");
		} return 1;
		case '=': {
			strcat(target_list, "=");
		} return 1;
		case '?': {
			strcat(target_list, "?");
		} return 1;
		case '+': {
			strcat(target_list, "+");
		} return 1;
		case '*': {
			strcat(target_list, "*");
		} return 1;
		case '\\': {
			strcat(target_list, "\\");
		} return 1;
	}

	return 0;
}

static int escape_1_to_N(const char c, compiler_state * cs) {
	char * target_list = (*cs->is_negative) ? cs->blacklist : cs->whitelist;
	switch(c) {
		case 'i': {
			const char identifier_chars[] = "@0123456789_"
			                                "\300\301\302\303\304"
			                                "\305\306\307\310\311"
			                                "\312\313\314\315\316"
			                                "\317\320\321\322\323"
			                                "\324\325\326\327\330"
			                                "\331\332\333\334\335"
			                                "\336\337";
			strcpy(target_list, identifier_chars);
			return sizeof(identifier_chars)-1;
		};
		case 'I': {
			const char identifier_chars[] = "@_"
			                                "\300\301\302\303\304"
			                                "\305\306\307\310\311"
			                                "\312\313\314\315\316"
			                                "\317\320\321\322\323"
			                                "\324\325\326\327\330"
			                                "\331\332\333\334\335"
			                                "\336\337";
			strcpy(target_list, identifier_chars);
			return sizeof(identifier_chars)-1;
		};
		case 'k': {
			const char keyword_chars[] = "@0123456789_"
			                             "\300\301\302\303\304"
			                             "\305\306\307\310\311"
			                             "\312\313\314\315\316"
			                             "\317\320\321\322\323"
			                             "\324\325\326\327\330"
			                             "\331\332\333\334\335"
			                             "\336\337";
			strcpy(target_list, keyword_chars);
			return sizeof(keyword_chars)-1;
		};
		case 'K': {
			const char keyword_chars[] = "@_"
			                             "\300\301\302\303\304"
			                             "\305\306\307\310\311"
			                             "\312\313\314\315\316"
			                             "\317\320\321\322\323"
			                             "\324\325\326\327\330"
			                             "\331\332\333\334\335"
			                             "\336\337";
			strcpy(target_list, keyword_chars);
			return sizeof(keyword_chars)-1;
		};
		case 'f': {
			const char filename_chars[] = "@0123456789/.-_+,#$%~=";
			strcpy(target_list, filename_chars);
			return sizeof(filename_chars)-1;
		};
		case 'F': {
			const char filename_chars[] = "@/.-_+,#$%~=";
			strcpy(target_list, filename_chars);
			return sizeof(filename_chars)-1;
		};
		case 'p': {
			const char printable_chars[] = "@"
			                               "\241\242\243\244\245"
			                               "\246\247\250\251\252"
			                               "\253\254\255\256\257"
			                               "\260\261\262\263\264"
			                               "\265\266\267\270\271"
			                               "\272\273\274\275\276"
			                               "\277"
			                               "\300\301\302\303\304"
			                               "\305\306\307\310\311"
			                               "\312\313\314\315\316"
			                               "\317\320\321\322\323"
			                               "\324\325\326\327\330"
			                               "\331\332\333\334\335"
			                               "\336\337";
			strcpy(target_list, printable_chars);
			return sizeof(printable_chars)-1;
		};
		case 'P': {
			const char printable_chars[] = "@"
			                               "\241\242\243\244\245"
			                               "\246\247\250\251\252"
			                               "\253\254\255\256\257"
			                               "\260\261\262\263\264"
			                               "\265\266\267\270\271"
			                               "\272\273\274\275\276"
			                               "\277"
			                               "\300\301\302\303\304"
			                               "\305\306\307\310\311"
			                               "\312\313\314\315\316"
			                               "\317\320\321\322\323"
			                               "\324\325\326\327\330"
			                               "\331\332\333\334\335"
			                               "\336\337";
			strcpy(target_list, printable_chars);
			return sizeof(printable_chars)-1;
		};
		case 's': {
			const char whitespace_chars[] = " \t\v\n";
			strcpy(target_list, whitespace_chars);
			return sizeof(whitespace_chars)-1;
		};
		case 'd': {
			const char digit_chars[] = "0123456789";
			strcpy(target_list, digit_chars);
			return sizeof(digit_chars)-1;
		};
		case 'x': {
			const char hex_chars[] = "0123456789"
			                         "abcdef"
			                         "ABCDEF";
			strcpy(target_list, hex_chars);
			return sizeof(hex_chars)-1;
		};
		case 'o': {
			const char oct_chars[] = "01234567";
			strcpy(target_list, oct_chars);
			return sizeof(oct_chars)-1;
		};
		case 'w': {
			const char word_chars[] = "0123456789"
			                          "abcdefghijklmnopqrstuwxyz"
			                          "ABCDEFGHIJKLMNOPQRSTUWXYZ"
			                          "_";
			strcpy(target_list, word_chars);
			return sizeof(word_chars)-1;
		};
		case 'h': {
			const char very_word_chars[] = "abcdefghijklmnopqrstuwxyz"
			                               "ABCDEFGHIJKLMNOPQRSTUWXYZ"
			                               "_";
			strcpy(target_list, very_word_chars);
			return sizeof(very_word_chars)-1;
		};
		case 'a': {
			const char alpha_chars[] = "abcdefghijklmnopqrstuwxyz"
			                           "ABCDEFGHIJKLMNOPQRSTUWXYZ";
			strcpy(target_list, alpha_chars);
			return sizeof(alpha_chars)-1;
		};
		case 'l': {
			const char lower_alpha_chars[] = "abcdefghijklmnopqrstuwxyz";
			strcpy(target_list, lower_alpha_chars);
			return sizeof(lower_alpha_chars)-1;
		};
		case 'u': {
			const char upper_alpha_chars[] = "ABCDEFGHIJKLMNOPQRSTUWXYZ";
			strcpy(target_list, upper_alpha_chars);
			return sizeof(upper_alpha_chars)-1;
		};
	}

	return 0;
}

static int escape_to_negative(const char              c,
	                                compiler_state * cs) {
	switch (c) {
		case 'D': {
			const char digit_chars[] = "0123456789";
			strcpy(cs->blacklist, digit_chars);
			*cs->is_negative = true;
			return sizeof(digit_chars)-1;
		};
	}

	return 0;
}

//static int compile_hologram(char * hologram, char * whitelist) {
//	if (hologram[0] == '\\') {
//		switch (hologram[1]) {
//			case '<': {
//				const char very_word_chars[] = "abcdefghijklmnopqrstuwxyz"
//											   "ABCDEFGHIJKLMNOPQRSTUWXYZ"
//											   "_";
//				strcat(whitelist, very_word_chars);
//				is_negative = true;
//				HOOK_ALL(0, whitelist, 0)
//			} break;
//		}
//	}
//}

static int compile_dot(compiler_state * cs) {
	*cs->do_catch = true;
	return true;
}

static int compile_escape(const char                    c,
                                compiler_state *       cs) {

	return escape_1_to_1(c, cs)
		|| escape_1_to_N(c, cs)
		|| escape_to_negative(c, cs)
		//|| compile_hologram(*s, whitelist)
		;
}

static int compile_range(const char           * const range,
                               compiler_state *          cs) {
	assert((range[0] == '[') && "Not a range.");

	char * target_list = (*cs->is_negative) ? cs->blacklist : cs->whitelist;

	const char * s;
	if (range[1] == '^') {
		*cs->is_negative = true;
		s = range + 2;
	} else {
		s = range + 1;
	}
	for (; *s != ']'; s++) {
		assert((*s != '\0') && "Unclosed range.");
		char c = *s;
		if (c == '\\') {
			s += 1;
			assert(compile_escape(*s, cs) && "Unknown escape.");
		} else if (*(s+1) == '-') {
			char end = *(s+2);
			assert((c < end) && "Endless range.");
			for (char cc = c; cc < end+1; cc++) {
				strncat(target_list,  &cc, 1);
				strncat(target_list, "\0", 1);
			}
			s += 2;
		} else {
			strncat(target_list,   &c, 1);
		}
	}

	return ((s - range) + 1);
}

void filter_blacklist(const char * const whitelist,
                      const char * const blacklist,
                            char * const  filtered) {
	for (char * black_pointer = blacklist; *black_pointer != '\0'; black_pointer++) {
		for(char * white_pointer = blacklist; *white_pointer != '\0'; white_pointer++) {
			if (*black_pointer == *white_pointer) {
				goto long_continue;
			}
		}
		strncat(filtered, black_pointer, 1);
		long_continue:
	}
}

#define HALT_AND_CATCH_FIRE INT_MIN

void HOOK_ALL(      int              from,
              const char * const      str,
                    int                to,
                    compiler_state *   cs) {

	int hook_to = (to == HALT_AND_CATCH_FIRE) ? -1 : ((*cs->state) + to);


	for (const char * s = str; *s != '\0'; s++) {
		delta_t * delta = malloc(sizeof(delta_t));
		delta->in    = *cs->state + from;
		delta->input = *s;
		delta->to    = hook_to;
		delta->width = *cs->width;
		vector_push(&cs->regex->delta_table,
		            &delta);
	}
}

void OFFSHOOT(int             from,
              int               to,
              compiler_state *  cs) {
	offshoot_t * offshoot = malloc(sizeof(offshoot_t));
	offshoot->in = *cs->state + from; 
	offshoot->to = *cs->state + to;
	vector_push(&cs->regex->catch_table,
	            &offshoot);
}

regex_t * regex_compile(const char * const pattern) {
	regex_t * regex = (regex_t *)malloc(sizeof(regex_t));
	regex->str = strdup(pattern);
	vector_init(&regex->delta_table, sizeof(delta_t*), 0UL);
	vector_init(&regex->catch_table, sizeof(offshoot_t*), 0UL);

	int state = 0;

	bool do_catch;
	bool is_negative;
	int width;
	char whitelist[64];
	char blacklist[64];

	compiler_state cs = {
		.do_catch    = &do_catch,
		.is_negative = &is_negative,
		.state       = &state,
		.width       = &width,
		.whitelist   = whitelist,
		.blacklist   = blacklist,
		.regex       = regex,
	};

	for (const char * s = pattern; *s != '\00';) {
		// Reset the compiler
		assert(!is_quantifier(*pattern) && "Pattern starts with quantifier.");
		whitelist[0] = '\00';
		blacklist[0] = '\00';
		do_catch     = false;
		is_negative  = false;
		width        = 1;

		// Translate char
		switch (*s) {
			case '.': {
				compile_dot(&cs);
			} break;
			case '\\': {
				s += 1;
				assert(compile_escape(*s, &cs) && "Unknown escape.");
			} break;
			case '[': {
				s += compile_range(s, &cs) - 1;
			} break;
			default: {
				whitelist[0] = *s;
				whitelist[1] = '\00';
			} break;
		}

		s += 1;

		// Compile with quantifier
		switch (*s) {
			case '=':
			case '?': {
				HOOK_ALL(0, whitelist, +1, &cs);
				if (do_catch || is_negative) {
					OFFSHOOT(0, +1, &cs);
				}
				s += 1;
			} break;
			case '*': {
				HOOK_ALL(0, whitelist,  0, &cs);
				if (do_catch) {
					OFFSHOOT(0, +1, &cs);
				} else if (is_negative) {
					OFFSHOOT(0,  0, &cs);
				}
				s += 1;
			} break;
			case '+': {
				HOOK_ALL(0, whitelist, +1, &cs);
				if (do_catch || is_negative) {
					OFFSHOOT(0, +1, &cs);
				}
				state += 1;
				HOOK_ALL(0, whitelist,  0, &cs);
				if (do_catch || is_negative) {
					OFFSHOOT(0, 0, &cs);
				}
				s += 1;
			} break;
			default: { // Literal
				HOOK_ALL(0, whitelist, +1, &cs);
				if (do_catch || is_negative) {
					OFFSHOOT(0, +1, &cs);
				}
				state += 1;
			} break;
		}

		// Compile blacklist
		if (*blacklist) {
			char filtered_blacklist[64];
			filtered_blacklist[0] = '\0'; 
			filter_blacklist(whitelist, blacklist, filtered_blacklist);
			HOOK_ALL(0, filtered_blacklist, HALT_AND_CATCH_FIRE, &cs);
		}
	}

	regex->accepting_state = state;

	return regex;
}

int regex_free(regex_t * const regex) {
	free(regex->str);
	vector_free(&regex->delta_table);
	vector_free(&regex->catch_table);
	free(regex);
	return 0;
}



// -----------------
// ### Searching ###
// -----------------
static bool catch_(const regex_t * const regex,
                         int     * const state) {
	for (size_t i = 0; i < regex->catch_table.element_count; i++){
		const offshoot_t * const offshoot = *(offshoot_t**)vector_get(&regex->catch_table, i);
		if (offshoot->in == *state) {
			*state = offshoot->to;
			return true;
		}
	}
	return false;
}

static int regex_assert(const regex_t * const  regex,
                         const char    * const string,
                               int              state,
                               int              width) {
	for (const char * s = string; *s != '\00'; s++) {
		// delta
		for (size_t i = 0; i < regex->delta_table.element_count; i++) {
			const delta_t * const delta = *(delta_t**)vector_get(&regex->delta_table, i);
			if ((delta->in == state) 
			&&  (delta->input == *s)) {
				int r = regex_assert(regex, s + delta->width, delta->to, width + 1);
				if(r){
					return r;
				}
			}
		}

		if (catch_(regex, &state)) {
			width += 1;
			continue;
		}

		return (state == regex->accepting_state) ? width : false;
	}

	return false;
}

int regex_match(      regex_t *        regex,
                const char    * const string) {
	if (regex == NULL) {
		return false;
	}
	if (string == NULL) {
		return true;
	}

	return regex_assert(regex, string, 0, 0);
}

bool regex_search(      regex_t *        regex,
                  const char    * const string) {

	return (bool)regex_match(regex, string);
}