# 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]" | "[@" [0-9]+ ("," ws? "@" [0-9]+)* "]"

# Vector strings support flat numbers, expressions, nested matrices, or config parameters
# Enforces a valid item before and after every comma to break on double commas ,,
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)* "]"

# Captures both taper=(z,0.5) and functional variations like taper(z,0.7) or noise(0.4)
parameter_assignment ::= [a-zA-Z_-]+ "=(" ws? [xyz] ws? "," ws? signed_num ws? ")" | [a-zA-Z_-]+ "(" ws? [xyz] ws? "," ws? num ws? ")" | [a-zA-Z_-]+ "(" num ")"

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

# Fully parses 'fw * 4', implicit coefficients like '-4fw', '-4fd', or solo variables
# FIX: Added sign? variable to cleanly handle prefixed variables like -fd or -hh
term ::= variable ("*" (variable | signed_num))? | signed_num variable? | sign? variable | "sym(" ws? expression ws? ")"
variable ::= "fw" | "hw" | "fd" | "hd" | "fh" | "hh" | "bd" | "bh" | "@idx" | "@" [0-9]+

boolean_flag ::= "surf" | "-%"

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

# STRICT number definition - only one sign character allowed total
positive_num ::= [0-9]+ ("." [0-9]+)?
negative_num ::= "-" [0-9]+ ("." [0-9]+)?
num ::= positive_num | negative_num

# FIX: Changed to sign? positive_num to allow 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 ::= "+" | "-" | "*" | "/"

ws ::= [ \t]+
ws_or_nl ::= [ \t\r\n]+