# Root: Handles empty arrays, loose lists, or coordinate blocks
root ::= (block-sequence | empty-scene)? ws?

empty-scene ::= "[]"

block-sequence ::= block (ws-or-nl+ block)*

# A block is a raw tag name or a fully positioned layout primitive
block ::= primitive (anchor? vector)?

primitive ::= "[" [a-zA-Z0-9_-]+ "]"

anchor ::= "[abs]" | "[@" digits ("," ws? "@" digits)* "]"

# Vector strings support flat numbers, expressions, nested matrices, or config parameters
vector ::= "[" value ("," ws? value)* "]"

value ::= nested-array | parameter-assignment | expression | attribute | signed-num | boolean-flag | variable

# Captures matrices like [1,1,1.5] or [-0.6,0.6,-0.4] cleanly
nested-array ::= "[" value ("," ws? value)* "]"

# Layout modifier keywords or attributes
attribute ::= "noise=" signed-num | "mesh" | "surf" | "-%"

# Fixed: Explicitly wrapped multi-line assignment alternates in parentheses
parameter-assignment ::= (
                         tag-name "=(" ws? [xyz] ws? "," ws? signed-num ws? ")" 
                       | tag-name "(" ws? [xyz] ws? "," ws? num ws? ")" 
                       | tag-name "(" num ")"
)

# Expressions handle explicit signs directly adjacent to implicit multi-variables
expression ::= term (op term)*

# Fix: Explicitly wrapped the multi-line term rule alternates in parentheses to resolve the parsing error
term ::= (
         variable multiplication-suffix? 
       | signed-num variable? 
       | sign? variable 
       | "sym(" ws? expression ws? ")"
)

multiplication-suffix ::= "*" (variable | signed-num)

variable ::= "fw" | "hw" | "fd" | "hd" | "fh" | "hh" | "bd" | "bh" | "@idx" | "@" digits

boolean-flag ::= "surf" | "-%"

# STRICT number definition - only one sign character allowed total
positive-num ::= digits ("." digits)?
negative-num ::= "-" digits ("." digits)?
num ::= positive-num | negative-num

# Allows things like +5 or -5 without doubling up a negative_num's minus sign
signed-num ::= sign? positive-num | negative-num

# SINGLE sign only - completely kills any '--' variants instantly
sign ::= "+" | "-"

op ::= "+" | "-" | "*" | "/"

# Explicit named primitives to ensure perfect alignment with the GBNF compiler loop
tag-name ::= [a-zA-Z_-]+
digits ::= [0-9]+
ws ::= [ \t]+
ws-or-nl ::= [ \t\r\n]+