#include <stdexcept>
#include <cstring>
#include <cctype>
#include "ast.h"

using namespace std;


ParseError::ParseError(const string &what_arg)
	:runtime_error(what_arg){}
ParseError::ParseError(const char *what_arg)
	:runtime_error(what_arg){}


Lambda::Lambda(){}
Lambda::Lambda(const Name &arg,const AST &ast)
	:arg(arg),body(ast){}


AST::AST()
	:type(Type::tuple){}

AST AST::makeNumber(Number numval){
	AST ast; ast.type=AST::Type::number; ast.numval=numval; return ast;
}
AST AST::makeString(String strval){
	AST ast; ast.type=AST::Type::string; ast.strval=strval; return ast;
}
AST AST::makeName(Name nameval){
	AST ast; ast.type=AST::Type::name; ast.nameval=nameval; return ast;
}
AST AST::makeIndex(Index indexval){
	AST ast; ast.type=AST::Type::index; ast.indexval=indexval; return ast;
}
AST AST::makeTuple(Terms terms){
	AST ast; ast.type=AST::Type::tuple; ast.terms=terms; return ast;
}
AST AST::makeLambda(Lambda lambdaval){
	AST ast; ast.type=AST::Type::lambda; ast.lambdaval=lambdaval; return ast;
}
AST AST::makeLambda(const Name &arg,const AST &body){
	AST ast; ast.type=AST::Type::lambda; ast.lambdaval.arg=arg; ast.lambdaval.body=body; return ast;
}
AST AST::makeNative(const Native &native){
	AST ast; ast.type=AST::Type::native; ast.nativeval=native; return ast;
}


bool iswordchar(char c){
	return isalpha(c)||isdigit(c)||strchr("!$%&*+,-./:;<=>?@^_|~",c)!=nullptr;
}

class AST::Tokeniser{
	const string source;
	const i64 size;
	i64 index=0,nextat=0;

public:
	Tokeniser(const string &source)
			:source(source),size(source.size()){
		// cerr<<"Tokeniser: initialised with <<"<<source<<">>"<<endl;
		advance();
	}

	bool eof() const {
		return index==-1;
	}

	string get(){
		if(index==-1)throw logic_error("Tokeniser::get() after last token");
		if(nextat==index)throw logic_error("Tokeniser::get() before advance()");
		// cerr<<"Tokeniser: got <<"<<source.substr(index,nextat-index)<<">>"<<endl;
		// cerr<<"           left: <<"<<source.substr(nextat)<<">>"<<endl;
		return source.substr(index,nextat-index);
	}

	bool advance(){
		index=nextat;
		// cerr<<"advance: reading from <<"<<source.substr(index)<<">>"<<endl;

		do {
			while(index<size&&isspace(source[index])){
				index++;
			}
			if(index==size){
				index=nextat=-1;
				return false;
			}
			if(source[index]!='#')break;
			while(index<size&&source[index]!='\n'){
				index++;
			}
			if(index==size){
				index=nextat=-1;
				return false;
			}
		} while(isspace(source[index])||source[index]=='#');

		if(strchr("'()\\",source[index])!=nullptr){
			nextat=index+1;
			return true;
		} else if(index<size-1&&source[index]=="λ"[0]&&source[index+1]=="λ"[1]){
			nextat=index+2;
			return true;
		} else if(isdigit(source[index])||(index<size-1&&source[index]=='-'&&isdigit(source[index+1]))){
			nextat=index+1;
			while(nextat<size&&isdigit(source[nextat])){
				nextat++;
			}
			return true;
		} else if(iswordchar(source[index])){
			nextat=index+1;
			while(nextat<size&&iswordchar(source[nextat])){
				nextat++;
			}
			return true;
		} else if(source[index]=='"'){
			for(nextat=index+1;nextat<size;nextat++){
				if(source[nextat]=='\\'){
					nextat++;
					if(nextat==size){
						throw ParseError("Unexpected end of file after '\\' in string");
					}
				} else if(source[nextat]=='"'){
					break;
				}
			}
			if(nextat==size){
				throw ParseError("Unexpected end of file in string");
			}
			nextat++;
			return true;
		} else {
			throw ParseError(string("Invalid token starting with '")+source[index]+"'");
		}
	}
};

static char parseHex(char c){
	if(c>='0'&&c<='9'){
		return c-'0';
	} else if(c>='a'&&c<='f'){
		return c-'a'+10;
	} else if(c>='A'&&c<='F'){
		return c-'A'+10;
	} else {
		return -1;
	}
}

AST& AST::parse(AST::Tokeniser &tokeniser){
	if(tokeniser.eof()){
		throw ParseError("No tokens to parse");
	}
	const string &token=tokeniser.get();
	if(token.size()==0){
		throw logic_error("Unexpected empty token from tokeniser");
	}
	if(isdigit(token[0])||(token.size()>1&&token[0]=='-'&&isdigit(token[1]))){
		type=Type::number;
		numval=strtol(token.data(),NULL,10);
	} else if(iswordchar(token[0])){
		type=Type::name;
		nameval=token;
	} else if(token=="("){
		type=Type::tuple;
		while(true){
			if(!tokeniser.advance()){
				throw ParseError("List opened with '(' not closed");
			}
			if(tokeniser.get()==")")break;
			terms.push_back(AST().parse(tokeniser));
		}
	} else if(token=="'"){
		if(!tokeniser.advance()){
			throw ParseError("Unexpected EOF after quote");
		}
		parse(tokeniser);
		quoted=true;
	} else if(token=="\\"||token=="λ"){
		type=Type::lambda;
		if(!tokeniser.advance()){
			throw ParseError("Unexpected EOF after '\\'");
		}
		const string &arg=tokeniser.get();
		if(!iswordchar(arg[0])){
			throw ParseError("Name expected after '\\'");
		}
		lambdaval.arg=arg;
		if(!tokeniser.advance()){
			throw ParseError("Body expected after argument of '\\'");
		}
		lambdaval.body=AST().parse(tokeniser);
	} else if(token[0]=='"'){
		if(token.back()!='"'){
			throw logic_error("No string terminator at end of string token from tokeniser");
		}
		type=Type::string;
		for(i64 i=1;i<(i64)token.size()-1;i++){
			if(token[i]=='\\'){
				switch(token[i+1]){
					case 't': strval+='\t'; break;
					case 'n': strval+='\n'; break;
					case 'r': strval+='\r'; break;
					case 'x':{
						if(i+3>=(i64)token.size()-1){
							throw ParseError("Not enough characters after hexadecimal"
							                 " escape sequence");
						}
						char hex1=parseHex(token[i+2]),
						     hex2=parseHex(token[i+3]);
						if(hex1==-1||hex2==-1){
							throw ParseError("Invalid characters in hexadecimal"
							                 " escape sequence");
						}
						strval+=(hex1<<4)|hex2;
						i+=2;
						break;
					}
					default: strval+=token[i+1]; break;
				}
				i++;
			} else {
				strval+=token[i];
			}
		}
	} else if(token==")"){
		throw ParseError("Unexpected token '"+token+"'");
	} else {
		throw logic_error("Unrecognised token from tokeniser: '"+token+"'");
	}
	return *this;
}

AST::AST(const string &source)
	:AST(source.data()){};

AST::AST(const char *source){
	Tokeniser tokeniser(source);
	parse(tokeniser);
	if(tokeniser.advance()){
		throw ParseError("Trailing content in source");
	}
}


ostream& operator<<(ostream &os,const AST &ast){
	if(ast.quoted){
		os<<"'";
	}

	switch(ast.type){
		case AST::Type::number:
			os<<ast.numval;
			break;

		case AST::Type::string:
			os<<'"';
			for(char c : ast.strval){
				switch(c){
					case '\t': os<<"\\t"; break;
					case '\n': os<<"\\n"; break;
					case '\r': os<<"\\r"; break;
					case '"': os<<"\\\""; break;
					default:
						if(c>=32&&c<=126){
							os<<c;
						} else {
							os<<"\\x"
							  <<"0123456789abcdef"[(unsigned char)c/16]
							  <<"0123456789abcdef"[(unsigned char)c%16];
						}
				}
			}
			os<<'"';
			break;

		case AST::Type::name:
			os<<ast.nameval;
			break;

		case AST::Type::index:
			os<<'['<<ast.indexval<<']';
			break;

		case AST::Type::tuple:
			os<<'(';
			for(i64 i=0;i<(i64)ast.terms.size();i++){
				if(i!=0)os<<' ';
				os<<ast.terms[i];
			}
			os<<')';
			break;

		case AST::Type::lambda:
			os<<"\\"<<ast.lambdaval.arg<<' '<<*ast.lambdaval.body;
			break;

		case AST::Type::native:
			os<<"\\ [native]";
			break;
	}
	return os;
}