WHITESPACE = _{ " " | "\t" | "\r" | "\n" }
COMMENT    = _{ "//" ~ (!"\n" ~ ANY)* }

program = { SOI ~ top_level* ~ EOI }

// primitives
identifier = @{ (ASCII_ALPHA | "_") ~ (ASCII_ALPHANUMERIC | "_")* }
integer    = @{ ASCII_DIGIT+ }
float      = @{ ASCII_DIGIT+ ~ "." ~ ASCII_DIGIT+ }
boolean    =  { "true" | "false" }
string_lit =  { "\"" ~ inner_str ~ "\"" }
inner_str  = @{ (!"\"" ~ ANY)* }

export     = { "public" }
mutable    = { "mut" }
var_decl_1 = { type_expr ~ mutable? ~ identifier }

// ================= TOP LEVEL =================

top_level = _{ import | function_decl | struct_decl }

import = { "import" ~ string_lit ~ ";" }

field_list = { field ~ ("," ~ field)* ~ ","? }
field      = { export? ~ type_expr ~ identifier }

param_list = { var_decl_1 ~ ("," ~ var_decl_1)* ~ ","? }

struct_decl = {
    export? ~ "struct" ~ identifier ~ "{" ~ field_list? ~ "}"
}

function_decl = {
    export? ~ type_expr ~ identifier ~ "(" ~ param_list? ~ ")" ~ block
}

// ================= STATEMENTS =================

block = { "{" ~ statement_list ~ "}" }

statement_list = { statement* }

statement = _{
    expr_stmt
  | var_decl_statement
  | if_stmt
  | while_stmt
  | return_stmt
  | break_stmt
  | continue_stmt
  | block
}

// --- basic statements ---

expr_stmt = { expr ~ ";" }

return_stmt = { "return" ~ expr? ~ ";" }

break_stmt = { "break" ~ ";" }

continue_stmt = { "continue" ~ ";" }

var_decl_statement = { var_decl_1 ~ ";" }

if_stmt = {
    "if" ~ "(" ~ expr ~ ")" ~ statement ~ ("else" ~ statement)?
}

while_stmt = {
    "while" ~ "(" ~ expr ~ ")" ~ statement
}

// ================= EXPRESSIONS =================
type_expr = { identifier }

primary = {
    integer
  | float
  | boolean
  | string_lit
  | identifier
}

postfix = {
    field_px
  | call_px
  | struct_px
  | index_px
  | binary_px
}

field_px          = { "." ~ identifier }
call_px           = { "(" ~ (expr ~ ("," ~ expr)*)? ~ ")" }
struct_px         = { "{" ~ (struct_field_decl ~ ("," ~ struct_field_decl)*)? ~ "}" }
index_px          = { "[" ~ expr ~ "]" }
binary_px         = { bin_op ~ expr }
bin_op            = { "+" | "-" | "*" | "/" | "%" | "==" | "!=" | "<" | ">" | "<=" | ">=" }
struct_field_decl = { identifier ~ ":" ~ expr }

expr = {
    primary ~ postfix*
}