function Token *
token_get(S64 i = 0){
  i += pctx->token_iter;
  if(i >= pctx->tokens.len){
    return &pctx->empty_token;
  }
  Token *result = &pctx->tokens[i];
  if(result->kind == TK_NewLine){
    pctx->indent = result->indent;
  }
  
  return result;
}

function Token *
token_next(){ 
  Token *token = token_get();
  pctx->token_iter++;
  return token;
}

function Token *
token_is(Token_Kind kind){
  Token *token = token_get();
  if(token->kind == kind){
    return token;
  }
  return 0;
}

function Token *
token_match(Token_Kind kind){
  Token *token = token_get();
  if(token->kind == kind){
    return token_next();
  }
  return 0;
}

function Token *
token_match_keyword(Intern_String string){
  Token *token = token_get();
  if(token->kind == TK_Keyword){
    if(string.str == token->intern_val.str){
      token = token_next();
      return token;
    }
  }
  return 0;
}

function void
parsing_error(Token *token, const char *str, ...){ 
  Scratch scratch;
  STRING_FMT(scratch, str, string);
  
  // @Note(Krzosa): Print nice error message
  printf("\nError: %s", string.str);
  if(token){
    printf(" %s:%d\n", token->file.str, (S32)token->line);
    
    // @Note(Krzosa): Print error line
    {
      int i = 0;
      while(token->line_begin[i]!='\n' && token->line_begin[i]!=0) i++;
      printf("%.*s\n", i, token->line_begin);
      
      // @Note(Krzosa): Print error marker
      int token_i = token->str - token->line_begin;
      for(int i = 0; i < token_i-2; i++) printf(" ");
      printf("^^^^^^\n");
    }
  }
  
  __debugbreak();
}

function Token *
token_expect(Token_Kind kind){
  Token *token = token_get();
  if(token->kind == kind){
    token = token_next();
    return token;
  }
  parsing_error(token, "Expected token of kind: [%s], got instead token of kind: [%s]", token_kind_string(kind).str, token_kind_string(token->kind).str);
  return 0;
}

//-----------------------------------------------------------------------------
// Expression parsing
//-----------------------------------------------------------------------------
/*
add = [+-]
mul = [/%*]
compare = == | != | >= | > | <= | <
logical = [&|^] | && | ||
unary = [&*-!~+] | ++ | --

atom_expr = Int 
| Float 
| String 
| Identifier
| 'cast' '(' typespec ',' expr ')'
| 'size_type' '(' typespec ')'
| 'size_expr' '(' expr ')'
| '{' compound_expr '}'
| '(' expr ')' 
| '(' ':' typespec ')' '{' compound_expr '}'
postfix_expr = atom_expr ('[' expr ']' | '.' Identifier | ++ | -- | '(' expr_list ')')*
unary_expr = unary ? unary_expr : atom_expr
mul_expr = atom_expr (mul atom_expr)*
add_expr = mul_expr (add mul_expr)*
logical_expr = add_expr (logical add_expr)*
compare_expr = logical_expr (compare logical_expr)*
ternary_expr = compare_expr ('?' ternary_expr ':' ternary_expr)?
expr = logical_expr

Compound literals
- (:[23]*Type){}
 - Type{}
- { }
*/
function Ast_Expr *parse_expr(S64 rbp = 0);
function Ast_Typespec *parse_typespec();

function Ast_Expr *
parse_expr_compound(){
  Scratch scratch;
  Token *pos = token_get();
  Array<Ast_Expr *> exprs = {scratch};
  while(!token_is(TK_CloseBrace)){
    Token *token = token_get();
    Ast_Expr *index = 0;
    Ast_Expr *name  = 0;
    if(token_match(TK_OpenBracket)){
      index = parse_expr();
      token_expect(TK_CloseBracket);
      token_expect(TK_Assign);
    }
    else if(token_is(TK_Identifier)){
      token = token_next();
      name = ast_expr_identifier(token, token->intern_val);
      token_expect(TK_Assign);
    }
    
    Ast_Expr *item = parse_expr();
    Ast_Expr *item_comp = ast_expr_compound_item(token, index, name, item);
    exprs.add(item_comp);
    
    if(!token_match(TK_Comma)){
      break;
    }
  }
  token_expect(TK_CloseBrace);
  
  Ast_Expr *result = ast_expr_compound(pos, 0, exprs);
  return result;
}

function Ast_Expr *
parse_expr_nud(Token *token){
  switch(token->kind){
    case TK_StringLit: return ast_expr_string(token, token->intern_val);
    case TK_Identifier: return ast_expr_identifier(token, token->intern_val);
    case TK_Integer: return ast_expr_integer(token, token->int_val);
    case TK_Keyword: {
      if(token->intern_val == keyword_cast){
        token_expect(TK_OpenParen);
        Ast_Expr *expr = parse_expr();
        token_expect(TK_Colon);
        Ast_Typespec *typespec = parse_typespec();
        token_expect(TK_CloseParen);
        return ast_expr_cast(token, expr, typespec);
      }
      else {
        parsing_error(token, "Unexpected keyword: [%s], expected keyword [cast]", token->intern_val.str); 
        return 0;
      }
    }break;
    case TK_OpenBrace: return parse_expr_compound();
    case TK_OpenParen: {Ast_Expr *result = parse_expr(); token_expect(TK_CloseParen); return result;}
    default: parsing_error(token, "Unexpected token of kind: [%s] in expression", token_kind_string(token->kind).str); return 0;
  }
}

function S64
op_precedence(Token_Kind kind){ 
  S64 result = pctx->pt[kind];
  return result;
}

function Ast_Expr *
parse_expr_led(Token *op, Ast_Expr *left){
  enum{ Left_Associative, Right_Associative };
  S64 assoc = Left_Associative;
  Ast_Expr *right = parse_expr(op_precedence(op->kind) - assoc);
  switch(op->kind){
    case TK_Add: case TK_Mul: case TK_Sub: case TK_Div: return ast_expr_binary(left, right, op);
    default: parsing_error(op, "Unexpected token of kind: [%s] in expression", token_kind_string(op->kind).str); return 0;
  }
}

function Ast_Expr *
parse_expr(S64 rbp){
  Token *token = token_next();
  Ast_Expr *left = parse_expr_nud(token);
  while(rbp < op_precedence(token_get()->kind)){
    token = token_next();
    left  = parse_expr_led(token, left);
  }
  return left;
}

function S64
expr_eval(Ast_Expr *expr){
  switch(expr->kind){
    case AK_Expr_Int: return expr->int_val;
    case AK_Expr_Binary : {
      S64 left = expr_eval(expr->binary.left);
      S64 right = expr_eval(expr->binary.right);
      switch(expr->binary.op){
        case TK_Add: return left + right;
        case TK_Sub: return left - right;
        case TK_Mul: return left * right;
        case TK_Div: return left / right;
        default: invalid_codepath;
      }
    }break;
    default: invalid_codepath;
  }
  return 0;
}

#define TEST_PARSER()                 \
Scratch scratch(thread_ctx.scratch);\
Parse_Ctx ctx = {};                 \
ctx.init(scratch, scratch);         \
pctx = &ctx

function void
test_parse_expr(){
  TEST_PARSER();
  struct Test{String str;S64 val;};
  Array<Test> exprs = {scratch};
  exprs.add({"(4+5)*2"_s, (4+5)*2});
  exprs.add({"4+5*2"_s, 4+5*2});
  exprs.add({"4*5+5"_s, 4*5+5});
  exprs.add({"4+5+5+3"_s, 4+5+5+3});
  
  Iter(exprs){
    lex_restream(&ctx, it->str, "test_expr"_s);
    Ast_Expr *result = parse_expr();
    S64 val = expr_eval(result);
    assert(val == it->val);
  }
}

//-----------------------------------------------------------------------------
// Parsing declarations
//-----------------------------------------------------------------------------
function Ast_Typespec *
parse_optional_type(){
  Ast_Typespec *result = 0;
  if(token_match(TK_Colon)) result = parse_typespec();
  return result;
}

function Ast_Typespec *
parse_typespec_function(Token *token){
  Scratch scratch;
  Array<Ast_Typespec *> args = {scratch};
  if(!token_is(TK_CloseParen)) {
    for(;;) {
      args.add(parse_typespec());
      if(!token_match(TK_Comma)){
        break;
      }
    }
  }
  token_expect(TK_CloseParen);
  Ast_Typespec *ret = parse_optional_type();
  Ast_Typespec *result = ast_typespec_func(token, ret, args);
  return result;
}

// [10]*int - Array of 10 pointers to ints
function Ast_Typespec *
parse_typespec_recurse(){
  Token *token = token_get();
  if(token_match(TK_Mul)){
    Ast_Typespec *result = parse_typespec_recurse();
    result = ast_typespec_pointer(token, result);
    return result;
  }
  else if(token_match(TK_OpenBracket)){
    Ast_Expr *expr = parse_expr();
    token_expect(TK_CloseBracket);
    Ast_Typespec *result = parse_typespec_recurse();
    result = ast_typespec_array(token, result, expr);
    return result;
  }
  else if(token_match(TK_OpenParen)){
    Ast_Typespec *result = parse_typespec_function(token);
    return result;
  }
  else if(token_match(TK_Identifier)){
    Ast_Typespec *result = ast_typespec_name(token, token->intern_val);
    return result;
  }
  else{
    parsing_error(token, "Failed to parse type, unexpected token of kind", token_kind_string(token->kind).str);
    return 0;
  }
}

function Ast_Typespec *
parse_typespec(){
  Ast_Typespec *result = parse_typespec_recurse();
  return result;
}

function Ast_Expr *
parse_assign_expr(){
  Ast_Expr *result = 0;
  if(token_match(TK_Assign)) result = parse_expr();
  return result;
}

function Ast_Decl *
parse_decl(){
  Ast_Decl *result = 0;
  if(token_is(TK_Identifier)){
    if(pctx->indent != 0) parsing_error(token_get(), "Top level declarations shouldn't be indented");
    Token *name = token_next();
    if(token_match(TK_DoubleColon)){ // Constant
      Ast_Expr *expr = parse_expr();
      result = ast_decl_const(name, name->intern_val, expr);
    }
    else if(token_match(TK_Colon)){ 
      Ast_Typespec *typespec = 0;
      Ast_Expr     *expr     = 0;
      if(!token_is(TK_Assign))   typespec = parse_typespec();
      if(token_match(TK_Assign)) expr     = parse_expr();
      if(!expr && !typespec) parsing_error(name, "invalid declaration, no type or value");
      
      result = ast_decl_var(name, typespec, name->intern_val, expr);
    }
    else{
      Token *token = token_get();
      parsing_error(token, "Unexpected token: [%s] when parsing a declaration", token_kind_string(token->kind).str);
    }
    
  }
  return result;
}

function Ast_Package *
parse_file(){
  Scratch scratch;
  Token *token = token_get();
  Array<Ast_Decl *>decls = {scratch};
  while(!token_is(TK_End)){
    while(token_match(TK_NewLine));
    Ast_Decl *decl = parse_decl();
    if(!decl) break;
    decls.add(decl);
  }
  Ast_Package *result = ast_package(token, token->file, decls);
  return result;
}