#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>

#include "parser.h"
#include "util.h"

typedef struct Cursor{
	const char *s;
	int l;
} Cursor;

typedef enum Tokentype{
	TT_EOF, //str=NULL, len=-1
	TT_SYMBOL,
	TT_WORD,
	TT_QUOTEDWORD,
	TT_NUMBER,
	TT_STRING,

	TT_ERR=-1 //str is an error description, len=-1
} Tokentype;

typedef struct Token{
	Tokentype type;
	const char *str; //pointer into source
	int len;
} Token;

#define SYMBOLCHARS "'()[]"


static Token tt_make(Tokentype type,const char *str,int len){
	Token tok={type,str,len};
	return tok;
}

static Token tt_eof(void){
	return tt_make(TT_EOF,NULL,-1);
}

static Token tt_err(const char *errstr){
	return tt_make(TT_ERR,errstr,-1);
}


static void advance(Cursor *cursor,int n){
	assert(cursor->l>=n);
	cursor->s+=n;
	cursor->l-=n;
}

static bool iswordchar(char c){
	return strchr(SYMBOLCHARS,c)==NULL&&c>=33&&c<=126;
}

static Token nexttoken(Cursor *cursor){
	while(cursor->l>=1&&isspace(*cursor->s))advance(cursor,1);
	if(cursor->l==0)return tt_eof();

	bool acted;
	do {
		acted=false;
		if(*cursor->s==';'){
			acted=true;
			int i;
			for(i=1;i<cursor->l;i++){
				if(cursor->s[i]=='\n')break;
			}
			if(i>=cursor->l-1){
				advance(cursor,cursor->l);
				return tt_eof();
			}
			advance(cursor,i+1);
		}

		if(cursor->l>=4&&cursor->s[0]=='#'&&cursor->s[1]=='|'){
			acted=true;
			int i;
			for(i=3;i<cursor->l;i++){
				if(cursor->s[i-1]=='|'&&cursor->s[i]=='#')break;
			}
			if(i>=cursor->l-1){
				advance(cursor,cursor->l);
				return tt_eof();
			}
			advance(cursor,i+1);
		}
	} while(acted);

	while(cursor->l>=1&&isspace(*cursor->s))advance(cursor,1);
	if(cursor->l==0)return tt_eof();

	if(strchr(SYMBOLCHARS,*cursor->s)!=NULL){
		advance(cursor,1);
		return tt_make(TT_SYMBOL,cursor->s-1,1);
	}

	if(isdigit(*cursor->s)||(cursor->l>=2&&cursor->s[0]=='-'&&isdigit(cursor->s[1]))){
		char *endp;
		strtod(cursor->s,&endp);
		assert(endp>cursor->s);
		int len=endp-cursor->s;
		advance(cursor,len);
		return tt_make(TT_NUMBER,cursor->s-len,len);
	}

	if(*cursor->s=='"'){
		int i;
		for(i=1;i<cursor->l;i++){
			if(cursor->s[i]=='"')break;
			if(cursor->s[i]=='\\')i++;
		}
		if(i==cursor->l){
			return tt_err("Unclosed string in source");
		}
		i++;
		advance(cursor,i);
		return tt_make(TT_STRING,cursor->s-i,i);
	}

	bool isquoted=false;
	if(*cursor->s=='\''){
		isquoted=true;
		advance(cursor,1);
		if(cursor->l==0||!iswordchar(*cursor->s)){
			return tt_err("Lone single quote in source");
		}
	}

	int i;
	for(i=0;i<cursor->l;i++){
		if(!iswordchar(cursor->s[i]))break;
	}
	if(i==0){
		return tt_err("Unrecognised character while looking for next token");
	}
	advance(cursor,i);
	return tt_make(isquoted?TT_QUOTEDWORD:TT_WORD,cursor->s-i,i);
}


static bool ishexdigit(char c){
	return (c>='0'&&c<='9')||(c>='a'&&c<='f')||(c>='A'&&c<='F');
}

static int hexnum(char c){
	return c<='9'?c-'0':(c&~32)-'A';
}


static ParseRet pr_ast(AST *ast){
	ParseRet pr={ast,NULL};
	return pr;
}

static ParseRet pr_err(char *errstr){
	ParseRet pr={NULL,errstr};
	return pr;
}

static ParseRet pr_err_c(const char *errstr){
	return pr_err(copystring(errstr));
}

static ParseRet parse_(Cursor *cursor){
	Token tok=nexttoken(cursor);
	switch(tok.type){
		case TT_EOF:
			return pr_err_c("Unexpected end-of-file");

		case TT_SYMBOL:{
			char closing;
			if(tok.len!=1)assert(false);
			if(tok.str[0]=='\''){
				ParseRet pr=parse_(cursor);
				if(pr.errstr)return pr;
				if(pr.ast->type==AST_WORD){
					char *word=pr.ast->wo.word;
					pr.ast->type=AST_SYMBOL;
					pr.ast->sy.name=word;
					pr.ast->sy.symid=-1;
					return pr;
				}
				return pr_ast(ast_quoted(pr.ast));
			}

			if(tok.str[0]=='(')closing=')';
			else if(tok.str[0]=='[')closing=']';
			else if(tok.str[0]==')'||tok.str[0]==']'){
				return pr_err_c("Unexpected closing paren in source");
			} else assert(false);

			int sz=2,len=0;
			AST **nodes=malloc(sz,AST*);
			while(true){
				Cursor cur2v=*cursor,*cur2=&cur2v;
				Token t=nexttoken(cur2);
				if(t.type==TT_SYMBOL&&t.len==1&&t.str[0]==closing){
					*cursor=cur2v;
					break;
				}
				if(t.type==TT_EOF){
					for(int i=0;i<len;i++)ast_free(nodes[i]);
					free(nodes);
					return pr_err_c("Unexpected end-of-file while parsing list");
				}

				ParseRet pr=parse_(cursor);
				if(pr.errstr){
					for(int i=0;i<len;i++)ast_free(nodes[i]);
					free(nodes);
					return pr;
				}
				if(len==sz){
					sz*=2;
					nodes=realloc(nodes,sz,AST*);
				}
				nodes[len++]=pr.ast;
			}
			return pr_ast(ast_list(len,nodes));
		}

		case TT_WORD:
			return pr_ast(ast_word(copybufasstring(tok.str,tok.len)));

		case TT_QUOTEDWORD:
			return pr_ast(ast_symbol(copybufasstring(tok.str,tok.len)));

		case TT_NUMBER:
			return pr_ast(ast_number(strtod(tok.str,NULL)));

		case TT_STRING:{
			assert(tok.len>=2&&tok.str[0]=='"'&&tok.str[tok.len-1]=='"');
			int len=0;
			for(int i=1;i<tok.len-1;i++){
				if(tok.str[i]=='\\'){
					i++;
					assert(i<tok.len-1);
					if(tok.str[i]=='x'){
						if(i>=tok.len-3||!ishexdigit(tok.str[i+1])||!ishexdigit(tok.str[i+2])){
							return pr_err_c("\"\\x\" in string needs two hexadecimal digits");
						}
						i+=2;
					}
				}
				len++;
			}
			char *buf=malloc(len==0?1:len,char);
			int j=0;
			for(int i=1;i<tok.len-1;i++){
				if(tok.str[i]=='\\'){
					i++;
					switch(tok.str[i]){
						case 'x':
							buf[j++]=16*hexnum(tok.str[i+1])+hexnum(tok.str[i+2]);
							i+=2;
							break;

						case 'n': buf[j++]='\n'; break;
						case 't': buf[j++]='\t'; break;
						case 'r': buf[j++]='\r'; break;
						case 'b': buf[j++]='\b'; break;
						case 'a': buf[j++]='\a'; break;
						default: buf[j++]=tok.str[i]; break;
					}
				} else {
					buf[j++]=tok.str[i];
				}
			}
			return pr_ast(ast_string(buf,len));
		}

		case TT_ERR:
			return pr_err_c(tok.str);

		default:
			assert(false);
	}
}


ParseRet parse(const char *source,int length){
	Cursor cursor={source,length};
	return parse_(&cursor);
}