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)* }

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

top_level = _{ import | function_decl | struct_decl }

export = { "export" }

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

param_list = { param ~ ("," ~ param)* ~ ","? }
param      = { identifier ~ ":" ~ type_expr }

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

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

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

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

statement_list = { statement* }

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

// --- basic statements ---

expr_stmt = { expr ~ ";" }

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

break_stmt = { "break" ~ ";" }

continue_stmt = { "continue" ~ ";" }

// --- variable declarations ---

var_decl_kind = { "let" | "const" | "var" }

var_decl = {
    var_decl_kind ~ identifier ~ ("=" ~ expr)? ~ ";"
}

// --- control flow ---

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

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

for_stmt = {
    "for" ~ "(" ~ (var_decl_no_semicolon | expr_stmt | ";") ~ expr? ~ ";" ~ expr? ~ ")" ~ statement
}

// helper (same as var_decl but no trailing ;)
var_decl_no_semicolon = {
    var_decl_kind ~ identifier ~ ("=" ~ expr)?
}

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

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

postfix = {
    field_px
  | call_px
  | index_px
  | binary_px
}

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

expr = {
    primary ~ postfix*
}