typedef enum {
			  TYPE_BUILTIN
} TypeKind;

typedef enum {
			  BUILTIN_INT,
			  BUILTIN_I8,
			  BUILTIN_I16,
			  BUILTIN_I32,
			  BUILTIN_I64,
			  BUILTIN_U8,
			  BUILTIN_U16,
			  BUILTIN_U32,
			  BUILTIN_U64,
			  BUILTIN_FLOAT,
			  BUILTIN_F32,
			  BUILTIN_F64,
			  BUILTIN_TYPE_COUNT
} BuiltinType;


typedef struct {
	Location where;
	TypeKind kind;
	union {
	    BuiltinType builtin;
	};
} Type;

typedef enum {
			  EXPR_INT_LITERAL,
			  EXPR_FLOAT_LITERAL,
			  EXPR_BINARY_OP,
			  EXPR_UNARY_OP
} ExprKind;

typedef enum {
			  UNARY_MINUS
} UnaryOp;

typedef enum {
			  BINARY_PLUS,
			  BINARY_MINUS
} BinaryOp;

#define EXPR_FLAG_FLEXIBLE 0x01

typedef struct Expression {
	Location where;
	ExprKind kind;
	Type type;
	uint16_t flags;
	union {
		FloatLiteral floatl;
		IntLiteral intl;
		struct {
			UnaryOp op;
			struct Expression *of;
		} unary;
		struct {
			BinaryOp op;
			struct Expression *lhs;
			struct Expression *rhs;
		} binary;
	};
} Expression;

#define DECL_FLAG_INFER_TYPE 0x01
#define DECL_FLAG_CONST 0x02
#define DECL_FLAG_HAS_EXPR 0x04
typedef struct {
	Location where;
	Identifier var;
	Type type;
	Expression expr;
	uint16_t flags;
} Declaration;

/* OPTIM: Instead of using dynamic arrays, do two passes. */

typedef enum {
			  STMT_DECLS
} StatementKind;
	
typedef struct {
	Location where;
	StatementKind kind;
	union {
		Array decls;
	};
} Statement;

typedef struct {
	Array stmts;
} ParsedFile;

typedef struct {
	Tokenizer *tokr;
	BlockArr exprs; /* a dynamic array of expressions, so that we don't need to call malloc every time we make an expression */
} Parser;

/* 
allocate a new expression.
IMPORTANT: This invalidates all other parser-allocated Expression pointers.
 */
static Expression *parser_new_expr(Parser *p) {
	return block_arr_add(&p->exprs);
}

/* returns BUILTIN_TYPE_COUNT on failure */
static BuiltinType kw_to_builtin_type(Keyword kw) {
	switch (kw) {
	case KW_INT: return BUILTIN_INT;
	case KW_I8: return BUILTIN_I8;
	case KW_I16: return BUILTIN_I16;
	case KW_I32: return BUILTIN_I32;
	case KW_I64: return BUILTIN_I64;
	case KW_U8: return BUILTIN_U8;
	case KW_U16: return BUILTIN_U16;
	case KW_U32: return BUILTIN_U32;
	case KW_U64: return BUILTIN_U64;
	case KW_FLOAT: return BUILTIN_FLOAT;
	case KW_F32: return BUILTIN_F32;
	case KW_F64: return BUILTIN_F64;
	default: return BUILTIN_TYPE_COUNT;
	}
}

static Keyword builtin_type_to_kw(BuiltinType t) {
	switch (t) {
	case BUILTIN_INT: return KW_INT;
	case BUILTIN_I8: return KW_I8;
	case BUILTIN_I16: return KW_I16;
	case BUILTIN_I32: return KW_I32;
	case BUILTIN_I64: return KW_I64;
	case BUILTIN_U8: return KW_U8;
	case BUILTIN_U16: return KW_U16;
	case BUILTIN_U32: return KW_U32;
	case BUILTIN_U64: return KW_U64;
	case BUILTIN_FLOAT: return KW_FLOAT;
	case BUILTIN_F32: return KW_F32;
	case BUILTIN_F64: return KW_F64;
	case BUILTIN_TYPE_COUNT: break;
	}
	assert(0);
	return KW_COUNT;
}

static bool type_parse(Type *type, Parser *p) {
	Tokenizer *t = p->tokr;
	type->where = t->token->where;
	switch (t->token->kind) {
	case TOKEN_KW:
		type->kind = TYPE_BUILTIN;
		type->builtin = kw_to_builtin_type(t->token->kw);
		if (type->builtin == BUILTIN_TYPE_COUNT) {
			tokr_err(t, "Expected type.");
			return false;
		} else {
			t->token++;
			return true;
		}
		break;
	default: break;
	}
	tokr_err(t, "Unrecognized type.");
	return false;
}

#define NOT_AN_OP -1
static int op_precedence(Keyword op) {
	switch (op) {
	case KW_PLUS:
		return 10;
	case KW_MINUS:
		return 20;
	default:
		return NOT_AN_OP;
	}
}

static bool expr_parse(Expression *e, Parser *p, Token *end) {
	Tokenizer *t = p->tokr;
	if (end == NULL) return false;
	e->flags = 0;
	e->where = t->token->where;
	if (end <= t->token) {
		tokr_err(t, "Empty expression.");
		return false;
	}
	if (end - t->token == 1) {
		/* 1-token expression */
		switch (t->token->kind) {
		case TOKEN_NUM_LITERAL: {
			NumLiteral *num = &t->token->num;
			switch (num->kind) {
			case NUM_LITERAL_FLOAT:
				e->kind = EXPR_FLOAT_LITERAL;
				e->type.kind = TYPE_BUILTIN;
				e->type.builtin = BUILTIN_FLOAT;
				e->floatl = num->floatval;
				break;
			case NUM_LITERAL_INT:
				e->kind = EXPR_INT_LITERAL;
				e->flags |= EXPR_FLAG_FLEXIBLE;
				e->type.kind = TYPE_BUILTIN;
				e->type.builtin = BUILTIN_INT; /* TODO: if it's too big, use a u64 instead. */
				e->intl = num->intval;
				break;
			}
		} break;
		default:
			tokr_err(t, "Unrecognized expression.");
			return false;
		}
		t->token = end;
		return true;
	}
	/* Find the lowest-precedence operator not in parentheses */
	int paren_level = 0;
	int lowest_precedence = NOT_AN_OP;
	Token *lowest_precedence_op;
	for (Token *token = t->token; token < end; token++) {
		if (token->kind == TOKEN_KW) {
			switch (token->kw) {
			case KW_LPAREN:
				paren_level++;
				break;
			case KW_RPAREN:
				paren_level--;
				if (paren_level < 0) {
					t->token = token;
					tokr_err(t, "Excessive closing parenthesis.");
				}
				break;
			default: { /* OPTIM: use individual cases for each op */
				int precedence = op_precedence(token->kw);
				if (precedence == NOT_AN_OP) break; /* nvm it's not an operator */
				if (lowest_precedence == NOT_AN_OP || precedence <= lowest_precedence) {
					lowest_precedence = precedence;
					lowest_precedence_op = token;
				}
			} break;
			}
		}
	}
	if (lowest_precedence == NOT_AN_OP) {
		/* function calls, array accesses, etc. OR
		 something like (5+3)*/
		tokr_err(t, "Not implemented yet.");
		return false;
	}
	
	/* This is a unary op not a binary one. */
	while (lowest_precedence_op != t->token
		   && lowest_precedence_op[-1].kind == TOKEN_KW
		   && op_precedence(lowest_precedence_op[-1].kw) != NOT_AN_OP) {
		lowest_precedence_op--;
	}

	/* Unary */
	if (lowest_precedence_op == t->token) {
		UnaryOp op;
		bool is_unary;
		switch (lowest_precedence_op->kw) {
		case KW_PLUS:
			/* unary + is ignored entirely */
			t->token++;
			/* re-parse this expression without + */
			return expr_parse(e, p, end);
		case KW_MINUS:
			is_unary = true;
			op = UNARY_MINUS;
			break;
		default:
			is_unary = false;
			break;
		}
		if (!is_unary) {
			tokr_err(t, "%s is not a unary operator.", keywords[lowest_precedence_op->kw]);
			return false;
		}
		e->unary.op = op;
		e->kind = EXPR_UNARY_OP;
		t->token++;
		Expression *of = parser_new_expr(p);
		e->unary.of = of;
		return expr_parse(of, p, end);
	}
	
	
	BinaryOp op; 
	switch (lowest_precedence_op->kw) {
	case KW_PLUS:
		op = BINARY_PLUS;
		break;
	case KW_MINUS:
		op = BINARY_MINUS;
		break;
	default: assert(0); break;
	}
	e->binary.op = op;
	e->kind = EXPR_BINARY_OP;

	Expression *lhs = parser_new_expr(p);
	e->binary.lhs = lhs;
	if (!expr_parse(lhs, p, lowest_precedence_op))
		return false;
	
	Expression *rhs = parser_new_expr(p);
	t->token = lowest_precedence_op + 1;
	e->binary.rhs = rhs;
	if (!expr_parse(rhs, p, end))
		return false;
	
	return true;
}

/*
ends_with = which keyword does this expression end with?
if it's KW_RPAREN, this will match parentheses properly.
*/
typedef enum {
	  EXPR_END_RPAREN_OR_COMMA,
	  EXPR_END_SEMICOLON
} ExprEndKind;
static Token *expr_find_end(Parser *p, ExprEndKind ends_with) {
	Tokenizer *t = p->tokr;
	long bracket_level = 0;
	Token *token = t->token;
	while (1) {
		switch (ends_with) {
		case EXPR_END_RPAREN_OR_COMMA:
			if (token->kind == TOKEN_KW) {
				if (token->kw == KW_COMMA && bracket_level == 0)
					return token;
				if (token->kw == KW_LPAREN)
					bracket_level++;
				if (token->kw == KW_RPAREN) {
					bracket_level--;
					if (bracket_level == 0) {
						return token;
					}
				}
			}
			break;
		case EXPR_END_SEMICOLON:
			if (token_is_kw(token, KW_SEMICOLON))
				return token;
			break;
		}
		if (token->kind == TOKEN_EOF) {
			switch (ends_with) {
			case EXPR_END_SEMICOLON:
				tokr_err(t, "Could not find ';' at end of expression.");
				return NULL;
			case EXPR_END_RPAREN_OR_COMMA:
				if (bracket_level > 0) {
					tokr_err(t, "Opening parenthesis was never closed."); /* FEATURE: Find out where this is */
					return NULL;
				} else {
					tokr_err(t, "Could not find ')' or ',' at end of expression.");
					return NULL;
				}
				return NULL;
			}
		}
		token++;
	}
}

static bool decls_parse(Array *ds, Parser *p) {
	Tokenizer *t = p->tokr;
	arr_create(ds, sizeof(Declaration));
	while (1) {
		Declaration *decl = arr_add(ds);
		if (t->token->kind != TOKEN_IDENT) {
			tokr_err(t, "Cannot declare non-identifier.");
			return false;
		}

		decl->where = t->token->where;
		decl->var = t->token->ident;
		decl->flags = 0;
		t->token++;

		if (!token_is_kw(t->token, KW_COLON)) {
			tokr_err(t, "Expected ':' in declaration.");
			return false;
		}
		t->token++;

		if (!token_is_kw(t->token, KW_MINUS)
			&& !token_is_kw(t->token, KW_EQ)
			&& !token_is_kw(t->token, KW_SEMICOLON)) {
			if (!type_parse(&decl->type, p))
				return false;
		} else {
			decl->flags |= DECL_FLAG_INFER_TYPE;
		}
		
		if (token_is_kw(t->token, KW_SEMICOLON)) {
			if (decl->flags & DECL_FLAG_INFER_TYPE) {
				tokr_err(t, "Cannot infer type without expression.");
				return false;
			}
		} else if (token_is_kw(t->token, KW_EQ)) {
			t->token++;
			if (!expr_parse(&decl->expr, p, expr_find_end(p, EXPR_END_SEMICOLON)))
				return false;
			decl->flags |= DECL_FLAG_HAS_EXPR;
		} else if (token_is_kw(t->token, KW_MINUS)) {
			t->token++;
			if (!expr_parse(&decl->expr, p, expr_find_end(p, EXPR_END_SEMICOLON)))
				return false;
			decl->flags |= DECL_FLAG_HAS_EXPR | DECL_FLAG_CONST;
		} else {
			tokr_err(t, "Expected ';', '=', or '-' in delaration.");
			return false;
		}
		if (token_is_kw(t->token, KW_SEMICOLON)) {
			t->token++;
			break;
		}
		if (!token_is_kw(t->token, KW_COMMA)) {
			tokr_err(t, "Expected ';' or ',' to finish or continue declaration.");
			return false;
		}
		t->token++; /* move past comma */
	}
	return true;
}

static bool stmt_parse(Statement *s, Parser *p) {
	Tokenizer *t = p->tokr;
	s->where = t->token->where;
	if (token_is_kw(t->token + 1, KW_COLON)) {
		s->kind = STMT_DECLS;
		return decls_parse(&s->decls, p);
	} else {
		tokr_err(t, "Unreocgnized statement.");
		return false;
	}
}

static void parser_from_tokenizer(Parser *p, Tokenizer *t) {
	p->tokr = t;
	block_arr_create(&p->exprs, 10, sizeof(Expression)); /* block size = 1024 */
}

static bool file_parse(ParsedFile *f, Parser *p) {
	Tokenizer *t = p->tokr;
	arr_create(&f->stmts, sizeof(Statement));
	bool ret = true;
	while (t->token->kind != TOKEN_EOF) {
		Statement *stmt = arr_add(&f->stmts);
		if (!stmt_parse(stmt, p))
			ret = false;
	}
	return ret;
}

#define PARSE_PRINT_LOCATION(l) //fprintf(out, "[l%lu]", (unsigned long)(l).line);

static void expr_fprint(FILE *out, Expression *e) {
	PARSE_PRINT_LOCATION(e->where);
	switch (e->kind) {
	case EXPR_INT_LITERAL:
		fprintf(out, "%lld", (long long)e->intl);
		break;
	case EXPR_FLOAT_LITERAL:
		fprintf(out, "%f", (double)e->floatl);
		break;
	case EXPR_BINARY_OP:
		switch (e->binary.op) {
		case BINARY_PLUS:
			fprintf(out, "add");
			break;
		case BINARY_MINUS:
			fprintf(out, "subtract");
			break;
		}
		fprintf(out, "(");
		expr_fprint(out, e->binary.lhs);
		fprintf(out, ",");
		expr_fprint(out, e->binary.rhs);
		fprintf(out, ")");
		break;
	case EXPR_UNARY_OP:
		switch (e->unary.op) {
		case UNARY_MINUS:
			fprintf(out, "negate");
			break;
		}
		fprintf(out, "(");
		expr_fprint(out, e->unary.of);
		fprintf(out, ")");
	}
}

static void type_fprint(FILE *out, Type *t) {
	PARSE_PRINT_LOCATION(t->where);
	switch (t->kind) {
	case TYPE_BUILTIN:
		fprintf(out, "%s", keywords[builtin_type_to_kw(t->builtin)]);
		break;
	}
}

static void decl_fprint(FILE *out, Declaration *d) {
	PARSE_PRINT_LOCATION(d->where);
	ident_fprint(out, d->var);
	if (d->flags & DECL_FLAG_CONST) {
		fprintf(out, "[const]");
	}
	fprintf(out, ":");
	if (!(d->flags & DECL_FLAG_INFER_TYPE)) {
		type_fprint(out, &d->type);
	}
	if (d->flags & DECL_FLAG_HAS_EXPR) {
		fprintf(out, "=");
		expr_fprint(out, &d->expr);
	}
}

static void stmt_fprint(FILE *out, Statement *s) {
	PARSE_PRINT_LOCATION(s->where);
	switch (s->kind) {
	case STMT_DECLS:
		arr_foreach(&s->decls, Declaration, decl) {
			if (decl != s->decls.data) {
				fprintf(out, ", ");
			}
			decl_fprint(out, decl);
		}
		fprintf(out, ";\n");
		break;
	}
}

static void parsed_file_fprint(FILE *out, ParsedFile *f) {
	arr_foreach(&f->stmts, Statement, stmt) {
		stmt_fprint(out, stmt);
	}
}

/* TODO: Freeing parser */