#include "aplwc_internal.h"

struct scan_state {
	struct string *text;
	size_t offset;
	int skip_number_and_identifier;
};

static void
init_scan_state(struct scan_state *state, struct string *text)
{
	state->text = text;
	state->offset = 0;
	state->skip_number_and_identifier = 0;
}

static int
is_space(uint32_t c)
{
	return c == ' ';
}

static int
is_letter(uint32_t c)
{
	return ((c >= 'a') && (c <= 'z')) || ((c >= 'A') && (c <= 'Z'));
}

static int
is_digit(uint32_t c)
{
	return (c >= '0') && (c <= '9');
}

static uint32_t
peek(struct scan_state *state)
{
	return string_char(state->text, state->offset);
}

static uint32_t 
advance(struct scan_state *state)
{
	state->offset += char_length(state->text, state->offset);
	state->skip_number_and_identifier = 0;
	return peek(state);
}

static void
skip_space(struct scan_state *state)
{
	while(is_space(peek(state)))
		advance(state);
}

static int
single_sym(struct scan_state *state, struct token *token)
{
	uint32_t c;

	c = peek(state);

	switch(c){
	case 0x2190: token->tag = TOKEN_TAG_LEFT_ARROW; break;
	case 0x22C4: token->tag = TOKEN_TAG_DIAMOND; break;
	case 0x2207: token->tag = TOKEN_TAG_DEL; break;
	case 0x2336: token->tag = TOKEN_TAG_IBEAM; break;
	case 0x2395: token->tag = TOKEN_TAG_QUAD; break;
	case '\n':   token->tag = TOKEN_TAG_NEWLINE; break;
	case '(':    token->tag = TOKEN_TAG_LEFT_PAREN; break;
	case ')':    token->tag = TOKEN_TAG_RIGHT_PAREN; break;
	default:     token->tag = TOKEN_TAG_UNKNOWN_SYM; break;
	}

	advance(state);
	return 1;
}

static int 
identifier(struct scan_state *state, struct token *token)
{
	uint32_t c;
	if(state->skip_number_and_identifier || (!is_letter(peek(state))))
		return 0;

	do
		c = advance(state);
	while(is_letter(c) || is_digit(c) || (c == '_'));

	token->tag = TOKEN_TAG_IDENTIFIER;
	state->skip_number_and_identifier = 1;
	return 1;
}

static int
keyword(struct scan_state *state, struct token *token)
{
	uint32_t c;
	if(peek(state) != ':')
		return 0;

	do
		c = advance(state);
	while(is_letter(c));

	token->tag = TOKEN_TAG_KEYWORD;
	return 1;
}

static int 
number(struct scan_state *state, struct token *token)
{
	uint32_t c;
	int has_digits;

	c = peek(state);

	if(state->skip_number_and_identifier)
		return 0;

	has_digits = 0;

	if(c == 0xAF) /* High minus */
		c = advance(state);
	
	if(is_digit(c)){ /* integer part */
		has_digits = 1;	
		do
			c = advance(state);
		while(is_digit(c));
	}

	if(c == '.'){
		c = advance(state);

		if(is_digit(c)){ /* fractional part */
			has_digits = 1;
			do
				c = advance(state);
			while(is_digit(c));
		}
	}

	if(has_digits == 0)
		return 0;

	token->tag = TOKEN_TAG_NUMBER;
	state->skip_number_and_identifier = 1;
	return 1;
}

static int
text(struct scan_state *state, struct token *token)
{
	uint32_t c;

	c = peek(state);
	if(c != '\'')
		return 0;

	do
		c = advance(state);
	while((c != '\n') && (c != 0) && (c != '\''));

	if(c == '\'')
		advance(state);
	else
		return 0;

	token->tag = TOKEN_TAG_TEXT;
	return 1;
}

static enum aplwc_rc
next_token(struct scan_state *state, struct token *token)
{
	size_t i;
	int (*scans[])(struct scan_state *, struct token *token) = {
		identifier,
		keyword,
		number,
		text,
		single_sym /* Must be last */
	};

	skip_space(state);
	token->start = state->offset;
	for(i = 0; i < NELEM(scans); i++){
		if(scans[i](state, token))
			break;
		state->offset = token->start;
	}
	token->end = state->offset;
	skip_space(state);
	if(token->start == token->end)
		return APLWC_INVALID_SYNTAX;
	else
		return APLWC_OK;
}

static enum aplwc_rc 
check(struct string *text, size_t *n)
{
	struct scan_state state;
	struct token token;
	enum aplwc_rc ret;
	size_t count;

	init_scan_state(&state, text);

	for(count = 0; peek(&state); count++){
		ret = next_token(&state, &token);
		if(ret != APLWC_OK)
			return ret;
	}

	*n = count;
	return APLWC_OK;
}

static void
scan(struct string *text, struct token_list *tokens)
{
	struct scan_state state;
	enum aplwc_rc ret;
	size_t count;

	init_scan_state(&state, text);

	for(count = 0; peek(&state); count++){
		ret = next_token(&state, &tokens->tokens[count]);
		assert(ret == APLWC_OK);
	}
}

struct token_list *
scan_string(struct aplwc *aplwc, struct string *text, int oneline)
{
	enum aplwc_rc rc;
	struct token_list *tokens;
	size_t n, i;

	rc = check(text, &n);
	if(rc != APLWC_OK){
		aplwc->last_error = rc;
		return NULL;
	}

	tokens = memory_alloc_token_list(aplwc, n);
	if(tokens == NULL)
		return NULL;
	tokens->text = text;
	tokens->length = n;
	scan(text, tokens);

	for(i = 0; oneline && (i < n); i++){
		if(tokens->tokens[i].tag != TOKEN_TAG_NEWLINE)
			continue;

		for(i++; i < n; i++){
			if(tokens->tokens[i].tag != TOKEN_TAG_NEWLINE)
				return NULL;
		}
	}

	return tokens;
}

enum aplwc_rc
check_tokens(struct token_list *tokens)
{
	size_t i;
	enum aplwc_rc rc;

	for(i = 0, rc = APLWC_OK; (rc == APLWC_OK) && (i < tokens->length); i++){
		switch(tokens->tokens[i].tag){
		case TOKEN_TAG_UNKNOWN_SYM:
			rc = APLWC_INVALID_SYNTAX;
			break;
		default:
			break;
		}
	}

	return rc;
}