*! version 2.41.0 02nov2020
program ms_parse_absvars, sclass
	syntax [anything(id="absvars" name=absvars equalok everything)], /// Allow for no absvars
		[NOIsily] /// passed to -ms_fvunab-
		[SAVEfe Generate] /// Synonyms
		[REPLACE] ///
		[*] /// more options, that are returned in s(options)

	loc save_all_fe = ("`savefe'" != "") | ("`generate'" != "")

* Constant-only
	if (`"`absvars'"' == "") {
		sreturn clear
		sreturn loc extended_absvars ""
		sreturn loc num_slopes = "0"
		sreturn loc intercepts = "1"
		sreturn loc targets = `" """'
		sreturn loc cvars = `" """'
		sreturn loc ivars = `"_cons"'
		sreturn loc basevars = `""'
		sreturn loc absvars = `" """'
		sreturn loc save_all_fe = 0
		sreturn loc save_any_fe = 0
		sreturn loc has_intercept = 1
		sreturn loc G = 1
		sreturn loc options = `"`options'"'
		exit
	}

* Unabbreviate variables and trim spaces
	UnabAbsvars `absvars', `noisily' target stringok `replace'
	loc basevars `s(basevars)'
	loc absvars `s(varlist)'

* Count the number of absvars
	loc G 0
	loc absvars_copy `absvars'
	while ("`absvars_copy'" != "") {
		loc ++G
		gettoken absvar absvars_copy : absvars_copy, bind
	}

* For each absvar, get the ivars and cvars (slope variables),
* and whether the absvar has an intercept or is slopes-only

	loc g 0
	loc any_has_intercept 0
	loc save_any_fe 0

	while ("`absvars'" != "") {
		loc ++g
		gettoken absvar absvars : absvars, bind

		* Extract or create the target variable for the FE (optional)
		ParseTarget `absvar' // updates `target' and `absvar'
		if (`save_all_fe' & "`target'" == "") loc target __hdfe`g'__

		* Extract intercept and slope elements of the absvar
		cap conf str var `absvar'
		if (c(rc)) {
			ParseAbsvar `absvar' // updates `ivars' `cvars' `has_intercept'
		}
		else {
			ParseStringAbsvar `absvar'
		}
		if (`has_intercept') loc any_has_intercept 1
		loc num_slopes : word count `cvars'

		* Create a nice canonical label for the absvar
		loc baselabel : subinstr loc ivars " " "#", all
		loc sep = cond(`has_intercept', "##", "#")
		if (`num_slopes' == 1) {
			loc label `baselabel'`sep'c.`cvars'
		}
		else if (`num_slopes' > 1) {
			loc label `baselabel'`sep'c.(`cvars')
		}
		else {
			loc label `baselabel'
		}

		* Construct expanded labels (used by the output tables)
		* EXAMPLE: i.x##c.(y z) --> i.x i.x#c.y i.x#c.z
		// note: we can't have i. with st_matrixrowstripe
		// Hack: 1. ensures an ivar doesn't end up with a c. prefix
		loc ebaselabel : subinstr loc ivars " " "#1.", all
		loc ebaselabel 1.`ebaselabel'
		if (`has_intercept') loc extended `extended' `ebaselabel'
		foreach cvar of local cvars {
			loc extended `extended' `ebaselabel'#c.`cvar'
		}

		* Update locals
		loc all_num_slopes "`all_num_slopes' `num_slopes'"
		loc all_has_intercept "`all_has_intercept' `has_intercept'"
		loc all_ivars `"`all_ivars' "`ivars'""'
		loc all_cvars `"`all_cvars' "`cvars'""'
		loc all_absvars `"`all_absvars' "`absvar'""'

		* Store target variables including slopes
		if ("`target'" != "") {
			loc save_any_fe 1

			loc targetleft
			loc targetright
			if (`has_intercept') loc targetleft `target'
			if (`num_slopes' > 0) {
				mata: st_local("targetright", invtokens(J(1, `num_slopes', "`target'Slope") + strofreal(1..`num_slopes')))
			}
			loc all_targets `"`all_targets' "`targetleft' `targetright'""'

			* Build the absvar equation; assert that we can create the new vars
			if (`has_intercept') {
				conf new var `target'
			}
			forval h = 1/`num_slopes' {
				conf new var `target'Slope`h'
				loc cvar : word `h' of `cvars'
			}
		}
		else {
			loc all_targets `"`all_targets' """'
		}

	}

	sreturn clear
	sreturn loc extended_absvars "`extended'"
	sreturn loc num_slopes = "`all_num_slopes'"
	sreturn loc intercepts = "`all_has_intercept'"
	sreturn loc targets = `"`all_targets'"'
	sreturn loc cvars = `"`all_cvars'"'
	sreturn loc ivars = `"`all_ivars'"'
	sreturn loc basevars = `"`basevars'"'
	sreturn loc absvars = `"`all_absvars'"'
	sreturn loc save_all_fe = `save_all_fe'
	sreturn loc save_any_fe = `save_any_fe'
	sreturn loc has_intercept = `any_has_intercept'
	sreturn loc G = `G'
	sreturn loc options = `"`options'"'
end


program ParseTarget
	if strpos("`0'", "=") {
		gettoken target 0 : 0, parse("=")
		_assert ("`target'" != "")
		conf new var `target'
		gettoken eqsign 0 : 0, parse("=")
	}
	c_local absvar `0'
	c_local target `target'
end


program ParseStringAbsvar
	syntax varname(str)
	c_local ivars `varlist'
	c_local cvars
	c_local has_intercept 1
end


program ParseAbsvar
	* Add i. prefix in case there is none
	loc hasdot = strpos("`0'", ".")
	loc haspound = strpos("`0'", "#")
	if (!`hasdot' & !`haspound') loc 0 i.`0'

	* Expand absvar:
	* x#c.z			--->							i.x#c.z
	* x##c.z		--->	i.x			z			i.x#c.z
	* x##c.(z w) 	--->	i.x			z		w 	i.x#c.z		i.x#c.w
	* x#y##c.z		--->	i.x#i.y 	z			i.x#i.y#c.z
	* x#y##c.(z w)	--->	i.x#i.y 	z		w	i.x#i.y#c.z	i.x#i.y#c.w
	syntax varlist(numeric fv ts)

	* Iterate over every factor of the extended absvar
	loc has_intercept 0 // 1 if there is a "factor" w/out a "c." part
	foreach factor of loc varlist {
		if (!strpos("`factor'", ".")) continue // ignore the "z", "w" cases
		ParseFactor `factor' // updates `factor_ivars' `factor_cvars'
		loc ivars `ivars' `factor_ivars'
		loc cvars `cvars' `factor_cvars'
		if ("`factor_cvars'" == "") loc has_intercept 1
	}

	loc ivars : list uniq ivars
	loc unique_cvars : list uniq cvars
	_assert ("`ivars'" != ""), ///
		msg("no indicator variables in absvar <`0'> (extended to `varlist')")
	_assert (`: list unique_cvars == cvars'), ///
		msg("duplicated c. variable in absvar <`0'> unique(`cvars') == <`unique_cvars'>)")

	c_local ivars `ivars'
	c_local cvars `cvars'
	c_local has_intercept `has_intercept'
end


program ParseFactor
	loc 0 : subinstr loc 0 "#" " ", all
	if ("`noisily'"!="") di as result "    ParseFactor: parts=<`0'>"
	foreach part of loc 0 {
		if ("`noisily'"!="") di as result "        ParseFactor: part=<`part'>"
		_assert strpos("`part'", ".")
		loc first_char = substr("`part'", 1, 1)
		_assert inlist("`first_char'", "c", "i"), ///
			msg("got `part'; expected c or i") // every part must start with "i" or "c"


		if (substr("`part'", 1, 2)=="i." | substr("`part'", 1, 2)=="ib") {
			* Standard case: i.var or c.var - just remove i. or c.

			* Sanity check
			gettoken left part : part, parse(".")
			gettoken dot part : part, parse(".")
			_assert ("`dot'" == ".")
			if ("`noisily'"!="") di as result "                     part=<`part'>"
		}
		else {
			* c.L.var -> received as cL.var
			_assert ("`first_char'"=="c")

			* try to get "var" from "c.var" and "L2.var" from "cL2.var"
			if (substr("`part'", 1, 2)=="c.") {
				loc part = substr("`part'", 3, .)
			}
			else {
				loc part = substr("`part'", 2, .)
			}

			if ("`noisily'"!="") di as result "                     part=<`part'>"
		}

		if ("`first_char'" == "c") {
			loc cvars `cvars' `part'
		}
		else {
			loc ivars `ivars' `part'
		}
	}
	c_local factor_ivars `ivars'
	c_local factor_cvars `cvars'
end


program UnabAbsvars, sclass
/* Description:
Like -fvunab- but with three exceptions:
- Doesn't expand "x##y" into "x y x#y"
- Doesn't expand x#y into i.x#i.y
- Doesn't expand x#c.(y z) into x#c.y and x#c.z
*/
	sreturn clear
	syntax anything(name=remainder equalok) [, NOIsily TARGET STRingok REPLACE]

	* Trim spaces around equal signs ("= ", " =", "  =   ", etc)
	while (regexm("`remainder'", "[ ][ ]+")) {
		loc remainder : subinstr loc remainder "  " " ", all
	}
	loc remainder : subinstr loc remainder " =" "=", all
	loc remainder : subinstr loc remainder "= " "=", all

	* Expand variable names
	loc is_numlist 0 // Will match inside L(1 2 3) or L(-1/1)
	while ("`remainder'" != "") {
		* gettoken won't place spaces in 0;
		* but we can see if a space is coming with `next_char'
		gettoken 0 remainder: remainder, parse(" #.()=")

		// bug in Stata v12 and older
		// version 12
		// loc x = substr(" ", 1, 1)
		// assert "`x'"==" "

		// bugged code in v12:
		// loc next_char = substr("`remainder'", 1, 1)

		// workaround:
		loc next_char `"`=substr("`remainder'", 1, 1)'"'

		* Match common delimiters
		loc delim1 = inlist("`0'", "#", ".", "(", ")", "=")

		* Match "i" and "L" in "i.turn L(1 2)"
		loc delim2 = inlist("`next_char'", ".", "(")

		* deal with newvar
		if ("`target'" != "") & ("`next_char'" == "=") {
			if ("`replace'" != "") novarabbrev cap drop `0'
			syntax newvarname
			loc 0 `varlist'
		}
		* If we know its a variable, parse it
		else if !(`delim1' | `delim2' | `is_numlist') {

			if ("`stringok'" != "") {
				cap syntax varlist(numeric fv ts)
				if (c(rc)==109) {
					syntax varlist
				}
				else {
					syntax varlist(numeric fv ts) // will raise error
				}
				loc stringvars `stringvars' `varlist'
			}
			else {
				syntax varlist(numeric fv ts)
			}

			loc 0 `varlist'
			loc unique `unique' `varlist'
		}
		if ("`0'" == ")") loc is_numlist 0
		if ("`0'" != "." & "`next_char'" == "(") loc is_numlist 1

		if ("`next_char'" != " ") loc next_char // add back spaces
		loc answer "`answer'`0'`next_char'"
		if ("`noisily'" != "") di as result "{bf:`answer'}"
	}
	local unique : list uniq unique
	local stringvars : list uniq stringvars
	sreturn local basevars `unique' // similar to fvrevar,list
	sreturn local stringvars `stringvars'
	sreturn local varlist `answer'
end