/*
 * Emit and parse JSON
 */

autoload Sort;
autoload Ctype;

namespace JSON {

    string quote(string a) {
	string result = "\"";
	for (int i = 0; i < String::length(a); i++) {
	    int c = a[i];
	    switch (c) {
	    case '"':
	    case '\\':
		result = result + "\\" + String::new(c);
		break;
	    case '\n':
		result = result + "\\n";
		break;
	    default:
		result = result + String::new(c);
		break;
	    }
	}
	return result + "\"";
    }

    public string to_json(poly arg)
    {
	string do_indent(int indent) {
	    string result = "\n";
	    for (int i = 0; i < indent; i++)
		result = result + "\t";
	    return result;
	}

	string json(poly arg, int indent);

	string json_hash(poly[string] a, int indent) {
	    string[] keys = hash_keys(a);
	    string result = "{";
	    bool first = true;

	    Sort::qsort(&keys, bool func(poly a, poly b) { return a > b; });
	    for (int i = 0; i < dim(keys); i++) {
		string key = keys[i];
		string value = json(a[key], indent+1);

		if (!first)
		    result = result + ",";
		first = false;
		result = result + do_indent(indent+1);
		result = result + quote(key) + ": " + value;
	    }
	    result = result + do_indent(indent) + "}";
	    return result;
	}

	string json_array(poly[] a, int indent) {
	    string result = "[";
	    bool first = true;

	    for (int i = 0; i < dim(a); i++) {
		if (!first)
		    result = result + ",";
		first = false;
		result = result + do_indent(indent+1);
		result = result + to_json(a[i]);
	    }
	    result = result + do_indent(indent) + "]";
	    return result;
	}

	string json_string(string arg) {
	    return quote(arg);
	}

	string json_int(int arg) {
	    return sprintf ("%d", arg);
	}

	json = string func(poly arg, int indent) {
	    if (is_hash(arg))
		return json_hash(arg, indent);
	    if (is_array(arg))
		return json_array(arg, indent);
	    if (is_string(arg))
		return json_string(arg);
	    if (is_int(arg))
		return json_int(arg);
	    return "";
	};

	return json(arg, 0);
    }

    typedef enum {
	_string,
	_int,
	_oc,
	_cc,
	_os,
	_cs,
	_comma,
	_colon,
	_end,
	_error
    } term_t;

    typedef struct {
	union {
	    int	ival;
	    string	sval;
	} val;
	term_t	token;
    } token_t;

    typedef struct {
	file	f;
	int	line;
	string	token;
    } json_input_t;

    json_input_t start_json(string s) {
	return (json_input_t) { .f = File::string_read(s), .line = 1 };
    }

    token_t lex(*json_input_t f) {

	int ch() {
	    int c = File::getc(f->f);
	    if (c == '\n')
		f->line++;
	    f->token = f->token + String::new(c);
	    return c;
	}

	void unch(int c) {
	    if (c == '\n')
		f->line--;
	    f->token = String::substr(f->token, 0, String::length(f->token) - 1);
	    File::ungetc(c, f->f);
	}

	try {
	    f->token = "";
	    for (;;) {
		int	c = ch();

		switch (c) {
		case '\n':
		case ' ':
		case '\t':
		    continue;
		case '{':
		    return (token_t) { .token = term_t._oc };
		case '}':
		    return (token_t) { .token = term_t._cc };
		case '[':
		    return (token_t) { .token = term_t._os };
		case ']':
		    return (token_t) { .token = term_t._cs };
		case ',':
		    return (token_t) { .token = term_t._comma };
		case ':':
		    return (token_t) { .token = term_t._colon };
		case '0': case '1': case '2': case '3': case '4':
		case '5': case '6': case '7': case '8': case '9':
		    int ival = 0;
		    while (Ctype::isdigit(c)) {
			ival = ival * 10 + c - '0';
			c = ch();
		    }
		    unch(c);
		    return (token_t) { .val = { .ival = ival }, .token = term_t._int };
		case '"':
		    string sval = "";
		    for (;;) {
			c = ch();
			if (c == '"')
			    break;
			if (c == '\\') {
			    c = ch();
			    switch (c) {
			    case 'n':
				c = '\n';
				break;
			    case 't':
				c = '\t';
				break;
			    default:
				break;
			    }
			}
			sval = sval + String::new(c);
		    }
		    return (token_t) { .val = { .sval = sval }, .token = term_t._string };
		default:
		    break;
		}
		break;
	    }
	}
	catch File::io_eof(file f) {
	    return (token_t) { .token = term_t._end };
	}
	return (token_t) { .token = term_t._error };
    }

    public exception json_parse_error(int line, string token);

    public poly from_json(string arg) {
	json_input_t f = start_json(arg);

	token_t	token;

	void next() {
	    token = lex(&f);
	}

	void expect(term_t t) {
	    if (token.token != t)
		raise json_parse_error(f.line, f.token);
	}

	poly value();

	poly[string] hash() {
	    poly[string] ret = {};
	    for (;;) {
		expect(term_t._string);
		string name = token.val.sval;
		next();
		expect(term_t._colon);
		next();
		poly val = value();
		ret[name] = val;
		switch (token.token) {
		case term_t._comma:
		    next();
		    continue;
		case term_t._cc:
		    next();
		    return ret;
		default:
		    raise json_parse_error(f.line, f.token);
		}
	    }
	}

	poly[] array() {
	    poly[...] ret = {};
	    for (;;) {
		poly val = value();
		ret[dim(ret)] = val;
		switch (token.token) {
		case term_t._comma:
		    next();
		    continue;
		case term_t._cs:
		    next();
		    return ret;
		default:
		    raise json_parse_error(f.line, f.token);
		}
	    }
	}

	value = poly func() {
	    switch (token.token) {
	    case term_t._oc:
	    next();
	    return hash();
	    case term_t._os:
	    next();
	    return array();
	    case term_t._int:
	    int ival = token.val.ival;
	    next();
	    return ival;
	    case term_t._string:
	    string sval = token.val.sval;
	    next();
	    return sval;
	    }
	};

	next();
	return value();
    }
}
