/*
	File: Keywords
*/
var/const/KW_FAIL = 0 //Fatal error; stop parsing entire script.
var/const/KW_PASS = 1 //OK
var/const/KW_ERR  = 2 //Non-fatal error, keyword couldn't be handled properly. Ignore keyword but continue on.
var/const/KW_WARN = 3 //Warning

/*
var/const/Class: n_Keyword
var/const/Represents a special statement in the code triggered by a keyword.
*/
/datum/n_Keyword
/*
	Var: inline
	1 if the keyword is in an expression (e.g. the new keyword in many languages), 0 otherwise (such as the if and else keywords).
*/
	var/inline

/datum/n_Keyword/New(inline = 0)
	src.inline = inline
	return ..()

/*
	Proc: Parse
	Called when the parser finds a keyword in the code.

	Parameters:
	parser - The parser that created this object. You can use the parameter to manipulate the parser in order to add statements and blocks
	to its AST.
*/
/datum/n_Keyword/proc/Parse(var/datum/n_Parser/parser)
	return
/*
	Class: nS_Keyword
	A keyword in n_Script. By default these include return, if, else, while, and def. To enable or disable a keyword, change the
	<nS_Options.keywords> list.

	Behavior:
	When a parser is expecting a new statement, and a keyword listed in <nS_Options.keywords> is found, it will call the keyword's
	<n_Keyword.Parse()> proc.
*/
/datum/n_Keyword/nS_Keyword/New(var/inline = 0)
	if(inline)
		del src

/datum/n_Keyword/nS_Keyword/kwReturn/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	if(istype(parser.curBlock, /datum/node/BlockDefinition/GlobalBlock)) // Exit out of the program by setting the tokens list size to the same as index.
		parser.tokens.len = parser.index
		return

	var/datum/node/statement/ReturnStatement/stmt = new
	parser.NextToken()   //skip 'return' token
	stmt.value = parser.ParseExpression()
	parser.curBlock.statements += stmt

/datum/n_Keyword/nS_Keyword/kwIf/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	var/datum/node/statement/IfStatement/stmt = new
	parser.NextToken()  //skip 'if' token
	stmt.cond = parser.ParseParenExpression()
	if(!parser.CheckToken(")", /datum/token/symbol))
		return KW_FAIL

	if(!parser.CheckToken("{", /datum/token/symbol, skip=0)) //Token needs to be preserved for parse loop, so skip=0
		return KW_ERR

	parser.curBlock.statements += stmt
	stmt.block = new
	parser.AddBlock(stmt.block)

/datum/n_Keyword/nS_Keyword/kwElseIf/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	var/list/L = parser.curBlock.statements
	var/datum/node/statement/IfStatement/ifstmt

	if(L && L.len)
		ifstmt = L[L.len] //Get the last statement in the current block

	if(!ifstmt || !istype(ifstmt) || ifstmt.else_if)
		to_chat(usr, "NTSL: ELSE IF FAILED: [!ifstmt], [!istype(ifstmt)], [!istype(ifstmt) || ifstmt.else_if]")// Usr is unsafe as SHIT but JUST incase I forget this debug line like the fucking asset cache...

		parser.errors += new/datum/scriptError/ExpectedToken("if statement", parser.curToken)
		return KW_FAIL

	var/datum/node/statement/IfStatement/ElseIf/stmt = new
	parser.NextToken()  //skip 'if' token
	stmt.cond = parser.ParseParenExpression()
	if(!parser.CheckToken(")", /datum/token/symbol))
		return KW_FAIL

	if(!parser.CheckToken("{", /datum/token/symbol, skip = 0)) //Token needs to be preserved for parse loop, so skip=0
		return KW_ERR

	parser.curBlock.statements += stmt
	stmt.block = new
	ifstmt.else_if = stmt
	parser.AddBlock(stmt.block)

/datum/n_Keyword/nS_Keyword/kwElse/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	var/list/L = parser.curBlock.statements
	var/datum/node/statement/IfStatement/stmt

	if(L && L.len)
		stmt = L[L.len] //Get the last statement in the current block

	if(!stmt || !istype(stmt) || stmt.else_block) //Ensure that it is an if statement
		to_chat(usr, "NTSL: ELSE IF FAILED: [!stmt], [!istype(stmt)], [!istype(stmt) || stmt.else_block]")// Usr is unsafe as SHIT but JUST incase I forget this debug line like the fucking asset cache...

		parser.errors += new/datum/scriptError/ExpectedToken("if statement", parser.curToken)
		return KW_FAIL

	parser.NextToken()         //skip 'else' token
	if(!parser.CheckToken("{", /datum/token/symbol, skip = 0))
		return KW_ERR

	stmt.else_block = new()
	parser.AddBlock(stmt.else_block)

/datum/n_Keyword/nS_Keyword/kwWhile/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	var/datum/node/statement/WhileLoop/stmt = new
	parser.NextToken()  //skip 'while' token
	stmt.cond = parser.ParseParenExpression()
	if(!parser.CheckToken(")", /datum/token/symbol))
		return KW_FAIL

	if(!parser.CheckToken("{", /datum/token/symbol, skip=0))
		return KW_ERR

	parser.curBlock.statements += stmt
	stmt.block = new
	parser.AddBlock(stmt.block)

/datum/n_Keyword/nS_Keyword/kwBreak/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	if(istype(parser.curBlock, /datum/node/BlockDefinition/GlobalBlock))
		parser.errors += new/datum/scriptError/BadToken(parser.curToken)
		. = KW_WARN

	var/datum/node/statement/BreakStatement/stmt = new
	parser.NextToken()   //skip 'break' token
	parser.curBlock.statements += stmt

/datum/n_Keyword/nS_Keyword/kwContinue/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	if(istype(parser.curBlock, /datum/node/BlockDefinition/GlobalBlock))
		parser.errors += new/datum/scriptError/BadToken(parser.curToken)
		. = KW_WARN

	var/datum/node/statement/ContinueStatement/stmt = new
	parser.NextToken()   //skip 'break' token
	parser.curBlock.statements += stmt

/datum/n_Keyword/nS_Keyword/kwDef/Parse(var/datum/n_Parser/nS_Parser/parser)
	. = KW_PASS
	var/datum/node/statement/FunctionDefinition/def = new
	parser.NextToken() //skip 'def' token

	if(!parser.options.IsValidID(parser.curToken.value))
		parser.errors += new/datum/scriptError/InvalidID(parser.curToken)
		return KW_FAIL

	def.func_name = parser.curToken.value
	parser.NextToken()

	if(!parser.CheckToken("(", /datum/token/symbol))
		return KW_FAIL

	for() //for now parameters can be separated by whitespace - they don't need a comma in between
		if(istype(parser.curToken, /datum/token/symbol))
			switch(parser.curToken.value)
				if(",")
					parser.NextToken()
				if(")")
					break
				else
					parser.errors += new/datum/scriptError/BadToken(parser.curToken)
					return KW_ERR

		else if(istype(parser.curToken, /datum/token/word))
			def.parameters += parser.curToken.value
			parser.NextToken()

		else
			parser.errors += new/datum/scriptError/InvalidID(parser.curToken)
			return KW_ERR

	if(!parser.CheckToken(")", /datum/token/symbol))
		return KW_FAIL

	if(istype(parser.curToken, /datum/token/end)) //Function prototype
		parser.curBlock.statements += def

	else if(parser.curToken.value == "{" && istype(parser.curToken, /datum/token/symbol))
		def.block = new
		parser.curBlock.statements += def
		parser.curBlock.functions[def.func_name] = def
		parser.AddBlock(def.block)
	else
		parser.errors += new/datum/scriptError/BadToken(parser.curToken)
		return KW_FAIL