#ifndef SLC_H
#define SLC_H

#include<stdint.h> // uint8_t, uint32_t..
#include<string.h> // memcpy, strlen..
#include<stddef.h> // NULL
#include<ctype.h> // isspace

/* Define this if you want to debug the engine doing its thing */
/* #define SLC_DEBUG */

/* Session offset type - defaults to 64 bit because of union types enable storage for it often, but you can override */
#ifndef SLOFFS_T
#define SLOFFS_T uint64_t
#endif

/* Maximum length of words - defaults but you can override; Adds +1 to this for null terminator */
#ifndef SL_MAX_WORD_NAME
#define SL_MAX_WORD_NAME 255
#endif

union word_body {
	SLOFFS_T offset;
	void *ptr;

};
typedef union word_body word_body;

/** Possible word types */
enum SLC_WORDTYP {
	/** Still in plain text */
	SLC_WORDTYP_TEXT = 0,
	/** Native code, use get_word_storage_offset to get what to run (relative pointer or array of pointers) */
	SLC_WORDTYP_NATIVE = 1,
	/** "Threaded code" (utf16-like word offsets) and encoded parentheses IN-PLACE inlined where text was before */
	SLC_WORDTYP_THREADED_INLINE = 2,
	/** "Threaded code" that did not fit in-place and is thus stored in session storage, word offset tells where */
	SLC_WORDTYP_THREADED_SESSION = 3
};
typedef enum SLC_WORDTYP SLC_WORDTYP;

/** Gets padding bytes for a memory address to be padded to alignment */
static inline int get_padding(uint8_t *ptr, int alignment) {
	// return (alignment - (ptr % alignment)) % alignment;
	return (ptrdiff_t)(ptr + alignment - 1) / alignment * alignment;
}

/** Tells if c ends a line (that is either \n or \r) */
static inline char endsline(char c) {
	return (c == '\n') || (c == '\r');
}

/**
 * A word definition starts right after this. After processing it, we inline overwrite random parts of it in memory...
 *
 * Examples:
 *
 * 	#: just_code
 * 	  #dup
 * 	  #inc
 * 	  #swap
 * 	#
 *
 * 	: with_vars @a; @b; @c;
 * 		@a
 * 		inc
 * 		@a(.)
 * 	;
 *
 * 	#builtin: to_prefix
 * 		#swap
 * 		#dup
 *
 *  ^^This built-in generates threaded code / text while processing in a way so that the
 *    to_prefix becomes prefixed with the "right" prefix and '#' exchanged with the current!
 *
 * 	^^The above always needs starting '#builtin' at the definition and inside. That is exchanged to real prefix...
 *    This is used for implementation implementing built-ins with FORTH-like code instead of native (saves native interpret. space)
 *
 * 	#: structural (
 * 		#parse_num
 * 		#dup
 * 		#inc
 * 		#swap
 * 		#print
 * 		#print
 * 	) [ #parse_num #print ] { #parse_num #print }
 * 	#
 */
struct word {
	/** Defines how to understand this word */
	uint8_t flags;
	uint8_t reserved; // Padding to ensure alignment of vars (4byte) */
	uint16_t var_count; // can be zero
	/* XXX: name is stored in symbol table only, not stored here */
	uint32_t first_var;	/* uint32_t ..vars[]; // The local variables memories for the word. Like "@a @b @c". Can be empty! */

	/* Possibly overlapping with first_var (var_count == 0) possibly using that as padding... */

	/* EITHER: */
	/* word_body processed_body; // Where to find the body data (ptr or offset) if its not "inline_data[]" */

	/* OR: */
	/* uint8_t inline_data[]; // The "body" - either text src (contains "ender") or inline threaded code (zero term) */
};
typedef struct word word;

/** Gets the wordtyp from a flags field - see word */
static inline SLC_WORDTYP word_type(uint8_t flags) {
	return (SLC_WORDTYP) (flags >> 6);
}

/** Gets the variable array of the given word */
static inline uint32_t *word_vars(word *w) {
	return &(w->first_var);
}

/** Gets the (inline or processed - same addr) "data" of the word. */
static inline uint8_t *word_inline_data(word *w) {
	uint32_t *vars = (uint32_t *)word_vars(w);
	uint16_t vcnt = w->var_count;

	// Might be overlapping "first_var" in case we had no vars
	uint8_t *after_wars = (uint8_t *)(vars + vcnt);

	int padding = get_padding(after_wars, 8);
	after_wars += padding;
	return after_wars; // no more wars
}

/** Gets the processed body of the word. */
static word_body word_processed_body(word *w) {
	word_body *body = (word_body *)word_inline_data(w);
	return *body;
}

enum SLC_SYM_OP { SLC_SYM_SET, SLC_SYM_GET, SLC_SYM_ERASE };
typedef enum SLC_SYM_OP SLC_SYM_OP;
enum SLC_STACK_OP { SLC_STACK_PUSH, SLC_STACK_POP, SLC_STACK_AT, SLC_STACK_COUNT, SLC_STACK_ERASE };
typedef enum SLC_STACK_OP SLC_STACK_OP;
enum SLC_SESSION_OP {
	SLC_SESSION_ALLOC,
	SLC_SESSION_ERASE,
	SLC_SESSION_PUSH,
	SLC_SESSION_GET,
	SLC_SESSION_SET,
	SLC_SESSION_GET32,
	SLC_SESSION_SET32,
	SLC_SESSION_PROCESS
};
typedef enum SLC_SESSION_OP SLC_SESSION_OP;
enum SLC_IO_OP {
	SLC_IO_OPEN,
	SLC_IO_OPEN_TMP,
	SLC_IO_REMOVE_TMPS,
	SLC_IO_CLOSE,
	SLC_IO_READ,
	SLC_IO_WRITE,
	SLC_IO_LOCK,
	SLC_IO_UNLOCK,
	SLC_IO_CMD,
};
typedef enum SLC_IO_OP SLC_IO_OP;

union symptr {
	uint32_t *varp;
	word *worp;
};
typedef union symptr symptr;

struct do_not_save_charptr {
	char *ptr;
};
typedef struct do_not_save_charptr do_not_save_charptr;

/**
 * Function-abstraction for a "symbol-table".
 *
 * Operations:
 *
 * 		SLC_SYM_SET Saves a mapping from key->word in symbol table. word==NULL removes mapping. Returns ptr back or NULL on errors.
 * 		SLC_SYM_GET Gets the symbol at key (the word parameter is unused). Returns NULL if there is no word for the key.
 * 		SLC_SYM_ERASE Erases the symbol table so it becomes empty again. Can never fail, returns NULL.
 *
 * Rem.: On GET we return a word* in case the key is to a word and a regular uint32_t* if its a variable name!
 *
 * @param op Defines which operation the caller wants.
 * @param key The key (both for SET and GET). This pointer can get easily invalidated so you might need a copy or you do Trie, etc.
 * @param ptr When adding a found word/variable to the symbol table, the key will point to this word* or uint32_t*
 * @returns The word/var definition stored for the key, or NULL when it is not stored yet or op is SET and there was an error.
 */
typedef symptr (*sym)(SLC_SYM_OP op, do_not_save_charptr key, symptr ptr);

/**
 * Function-abstraction for an integer "stack".
 *
 * Operations:
 * 
 * 		SLC_STACK_PUSH pushes the "elem" to the stack. Returns 1 if succeeded, otherwise 0.
 * 		SLC_STACK_POP pops the stack - does not return meaningful value, beware of underflowing!
 * 		SLC_STACK_AT returns the "param"th element down from the top of the stack
 * 		SLC_STACK_COUNT returns the number of elements in the stack
 * 		SLC_STACK_ERASE Makes the stack empty. Basically as if you would POP the COUNT times.
 *
 * @param op Defines which operation the caller wants.
 * @param param On SLC_STACK_PUSH, this is the element to push onto the stack, in case of SLC_STACK_AT, its the index.
 * @return The element at the given stack location in case of SLC_STACK_AT or the count in case of SLC_STACK_COUNT. Can show error!
 */
typedef uint32_t (*stack)(SLC_STACK_OP op, uint32_t param);

/**
 * Function-abstraction for a "session-storage".
 *
 * Operations:
 * 		SLC_SESSION_ALLOC allocates parameter amount of memory and returns an accessor index.
 * 		SLC_SESSION_ERASE erase the session storage (all of it) - all parameters are unused
 * 		SLC_SESSION_PUSH adds the given byte (value in i) to the end of the session storage (by growing it) - j unused
 * 		SLC_SESSION_GET gets byte at the ith accessor index - j unused
 * 		SLC_SESSION_SET gets byte at the ith accessor index to be of (byte)j
 * 		SLC_SESSION_GET32 gets uint32_t at the ith accessor index - j unused. XXX: Beware, architectures unaligned access crash!
 * 		SLC_SESSION_SET32 gets uint32_t at the ith accessor index to be of j. XXX: Beware, architectures unaligned access crash!
 * 		SLC_SESSION_PROCESS gets the last j bytes and moves them overriding bytes at index i, then "shrinks" the storage by j.
 *
 * @param op Defines which operation the caller wants.
 * @param i Used on SESSION_GET and is the accessor index, in case of SESSIN_ALLOC it is the amount to allocate.
 * @param j Used on SESSION_SET as the byte value and on SESSION_PROCESS as the amount of bytes to "process" / shrink.
 * @returns The accessor index in case of ALLOC (0xFFFFFFFF == -1 means error), on get it returns the store BYTE as uint32_t
 */
typedef uint32_t (*session)(SLC_SESSION_OP op, uint32_t i, uint32_t j);

union iores {
	/** Either the terminal cmd result or the handle pointer. NULL means some kind of error */
	const char *ptr;
	/** The read character */
	char c;
};
typedef union iores iores;

/**
 * Function-abstraction for io connectors.
 *
 * Operations:
 *
 * 		SLC_IO_OPEN Opens a PERSISTENT file with the given name. Returns the handle pointer (or NULL on error).
 * 		SLC_IO_CLOSE Closes a PERSISTENT file with the given handle.
 * 		SLC_IO_OPEN_TMP Opens a TEMPORARY file with the given name. Returns the handle pointer.
 * 		SLC_IO_CLOSE_TMP Removes the TEMPORARY file with the given handle.
 * 		SLC_IO_READ Reads a character from the given file handle. Returns '\0' on EOF and being out of data!
 * 		SLC_IO_WRITE Writes a character to the given file handle. The 'param' points to the character to write (1 byte)
 * 		SLC_IO_LOCK Locks the given file handle for exclusive reads and writes (others need to use lock/unlock too)
 * 		SLC_IO_UNLOCK Locks the given file handle for exclusive reads and writes (others need to use lock/unlock too)
 * 		SLC_IO_CMD Runs the given command on the operating system. The 'param' is the command (+args) and returned is std output.
 *
 * @param op Defines which operation the caller wants.
 * @param param The name or temporary name or command or the handle pointer parameter depending on op.
 * @returns A handle pointer or pointer to character to read / written or closed/unlocked handle (NULL on errors). Also cmd stdout.
 */
typedef iores (*ioconn)(SLC_IO_OP op, const char *param);

/**
 * Function-abstraction for reading the source code char-by-char.
 */
typedef char (*coderead)();

/** States the main state-engine can pick up - use characters for debugging better */
enum slc_state : uint8_t {
	/** Before things */
	SLC_START = 's',
	/** In a comment */
	SLC_COMMENT = 'c',
	/** In multi-line comment */
	SLC_MULTILINE_COMMENT = 'm',
	/** Name part of word-definition (after ':') - whitespace ends it */
	SLC_DEF_NAME = 'd',
	/** Variable-listing part of word-definition - endline, '(', '[' or '{' ends it */
	SLC_DEF_VAR = 'D',
	/** Raw body part of the word definition - these can contain local variable accesses + words, depth counted by vars */
	SLC_DEF_BODY = 'b',
	/** Name part of a word "call" (non-definition). Ends by whitespace, '@' (in case of variable) or various parentheses */
	SLC_WORD_NAME = 'w',
	/** Variable call (MYWORD@MYVAR) - we get to be here from SLC_WORD_NAME or from START */
	SLC_WORD_VAR = 'W',
	/** Syntax error state - recovers by newlines */
	SLC_SYN_ERROR = 'e',
};
typedef enum slc_state slc_state;

static inline slc_state slc_comment_statechange_in(
		slc_state current_state,
		char c,
		const char *singleline_comment,
		const char *multiline_comment_opener,
		int *comment_i,
		int *multiline_i){

	char s = singleline_comment[*comment_i];
	char m = multiline_comment_opener[*multiline_i];

	/* Check if we have finished processing */
	if(s == 0) { *comment_i = 0; return SLC_COMMENT; }
	if(m == 0) { *multiline_i = 0; return SLC_MULTILINE_COMMENT; }

	/* Single-line comment progress */
	if(c == s) {
		++(*comment_i);
	} else {
		*comment_i = 0;
	}

	/* Multi-line comment progress */
	if(c == m) {
		++(*multiline_i);
	} else {
		*multiline_i = 0;
	}

	return current_state;
}

static inline slc_state slc_multiline_comment_statechange_out(
		slc_state current_state,
		char c,
		const char *multiline_comment_closer,
		int *multiline_i){

	char m = multiline_comment_closer[*multiline_i];

	/* Check if we have finished processing */
	if(m == 0) { *multiline_i = 0; return SLC_START; }

	/* Multi-line comment progress */
	if(c == m) {
		++(*multiline_i);
	} else {
		*multiline_i = 0;
	}

	return current_state;
}

/** Handles state change into word definitions */
static inline slc_state slc_def_name_statechange(
		slc_state current_state,
		char prevc,
		char c,
		const char *prefix,
		int *prefix_i) {

	/* If not a whitespace currently, check the prefix, otherwise check ending ':' */
	if(!isspace(c)) {
		/* Early exit for not-a-definition sub-state */
		if(*prefix_i < 0) {
			return current_state;
		}

		/* Read prefix */
		if(prefix[*prefix_i] != 0) {
			if(prefix[*prefix_i] == c) {
				++(*prefix_i);
			} else {
				*prefix_i = -1;
			}
		} else {
			if(c == ':') {
				*prefix_i = 0; /* XXX: restarts scan */
				return SLC_WORD_NAME;
			} else {
				*prefix_i = -1;
			}
		}

		return current_state;
	} else {
		/* Not Found: Probably a word occurence */
		*prefix_i = 0; /* XXX: restarts scan */
		return current_state;
	}
}

/** Handles state change into word occurences - shared wordname with def_name_statechange! */
static inline slc_state slc_word_statechange(
		slc_state current_state,
		char c,
		int *wordname_i,
		const char *wordname) {
	// FIXME: Implement
	return current_state;
}

#define SET_SLC_START \
	comment_i = 0; \
	multiline_i = 0; \
	prefix_i = 0; \
	wordname_i = 0; \
	wordname[0] = 0; \
	state = SLC_START;

/**
 * This function runs the main slc engine over a snippet of code.
 *
 * The code_src is the entry of what we start interpreting, but you can do (un)buffered reads in it
 * because we will use session_storage to store the source code data into memory while processing...
 * Rem.: This also helps with the "include" directives using io_connector and do some kind of recursion maybe.
 * Rem.: This architecture also let us try to immediately "threaded_code" optimize the newly added word definition,
 *       which is possible if it relies on no forward references - this is the most happy case in my opinion!
 *
 * The session_storage is where we process the words data (possibly introducing threaded code as early as possible).
 * This should also let the code "allocate" some random memory too and get an offset for it (there will be no other way).
 *
 * The symbol_table not only store "words", but direct access offsets for:
 *
 * - words themselves (direct offset)
 * - variables of the words (direct offset)
 *
 * The code stack is what the interpreter uses for return addresses, the data stack however is FORTH-style usual stack.
 * The "insert_stack" collects things that we will read instead of reading the code_src AFTER a return from current word.
 * A \0 value should be there at the end of it until we RETURN from the word - from when we start processing.
 *
 * The io_connector is needed so that the engine have connection for temporary and real files and things simulating those.
 *
 * The prefix, ender and varprefix strings really just help when you use SLC to define a compiler and you need these.
 *
 * @param code_src The input source code to interpret / run. Code ends either with \0 or EOF.
 * @param session_storage Can allocate and use arbitrary memory with this.
 * @param symbol_table The symbol table to use while processing.
 * @param code_stack The code stack (return addresses) to use.
 * @param nesting_stack The stack used for the state-machine of the nested words.
 * @param data_stack The data stack (forth-like stack) to use.
 * @param insert_stack Used for temporarily expanding the input stream (one word level above current) with further words.
 * @param io_connector The engine uses this to open/close pipes/files and write/read them.
 * @param singleline_comment Like "//" - the character string that makes the rest of the line being comment. Can be "" (no NULL).
 * @param multiline_comment_opener The character string that starts a multiline comment. Like / and * for C. Can be "" (no NULL).
 * @param multiline_comment_closer The character string that ends a multiline comment. Like * and / for C. Can be "" (no NULL).
 * @param prefix The prefix added to the lookup of built-ins. Useful when you write a compiler with SLC. Defaults to "" (empty).
 * @param ender The character string that ends a word definition. Defaults to ";".
 * @param varprefix The character string that prefixes variable declarations. Defaults to "@".
 */
static inline void slc(
		coderead code_src,
		session session_storage,
		sym symbol_table,
		stack code_stack,
		stack nesting_stack,
		stack data_stack,
		stack insert_stack,
		ioconn io_connector,
		const char *singleline_comment,
		const char *multiline_comment_opener,
		const char *multiline_comment_closer,
		const char *prefix,
		const char *ender,
		const char *varprefix) {

	char last_is_endl = 0;
	int line = 0;
	int col = -1;
	char is_indenting = 1;
	int indent = 0;

	slc_state state;
	int comment_i;
	int multiline_i;
	int prefix_i;
	int wordname_i;
	char wordname[SL_MAX_WORD_NAME + 1];

	SET_SLC_START

	char prevc = 0;
	char c = 0;
	while(((c = code_src()) != 0)) {
		/* Handle lines and columns, parts of indenting */
		if(endsline(c)) {
			/* Handles \n, \r, \r\n and \n\r this way and counts empty lines properly */
			/* De-Morgan (!a || b) == (a => b) so (last_is_endl => (prevc == c)) */
			if(!last_is_endl || (prevc == c)) {
				++line;
				col = 0;
				/* Indent part */
				is_indenting = 1;
				indent = 0;
			}
			last_is_endl = 1;
		} else { last_is_endl = 0; ++col; }

		/* Handle indenting */
		if((c == '	') || (c == ' ')) {
			indent += is_indenting;
		} else {
			/* Defends against state-changer endline */
			is_indenting = endsline(c);
		}
	process_char:
#ifdef SLC_DEBUG
		fprintf(stderr, "%c state:%c @ line:%d col:%d indent:%d\n", c, state, line, col, indent);
#endif
		switch(state) {
			case SLC_START:
				/* state -> comment | multiline_comment */
				state = slc_comment_statechange_in(
						state,
						c,
						singleline_comment,
						multiline_comment_opener, 
						&comment_i,
						&multiline_i);

				/* state -> def_name */
				if(state == SLC_START) {
					state = slc_def_name_statechange(
							state,
							prevc,
							c,
							prefix,
							&prefix_i);
				}

				/* state -> word_name | word_var */
				if(state == SLC_START) {
					state = slc_word_statechange(
							state,
							c,
							&wordname_i,
							wordname);
				}

				break;
			case SLC_COMMENT:
				if(endsline(c)) { SET_SLC_START }
				break;
			case SLC_MULTILINE_COMMENT:
				state = slc_multiline_comment_statechange_out(
						state,
						c,
						multiline_comment_closer,
						&multiline_i);
				if(state == SLC_START) { SET_SLC_START }
				break;
			case SLC_DEF_NAME:
				// TODO
				break;
			case SLC_DEF_VAR:
				break;
			case SLC_DEF_BODY:
				break;
			case SLC_WORD_NAME:
				break;
			case SLC_WORD_VAR:
				break;
			case SLC_SYN_ERROR:
				/* Recover from slc syntax errors at endlines for now */
				if(endsline(c)) { SET_SLC_START }
				break;
		}

		prevc = c;
	}
}

#endif /* SLC_H */