/*
	File: Parser
*/
/*
	Class: n_Parser
	An object that reads tokens and produces an AST (abstract syntax tree).
*/
/datum/n_Parser
/*
	Var: index
	The parser's current position in the token's list.
*/
	var/index = 1
/*
	Var: tokens
	A list of tokens in the source code generated by a scanner.
*/
	var/list/tokens   = new
/*
	Var: errors
	A list of fatal errors found by the parser. If there are any items in this list, then it is not safe to run the returned AST.

	See Also:
	- <scriptError>
*/
	var/list/errors   = new
/*
	Var: warnings
	A list of non-fatal problems in the script.
*/
	var/list/warnings = new
/*
	Var: curToken
	The token at <index> in <tokens>.
*/
	var/datum/token/curToken
	var/datum/stack/blocks = new
	var/datum/node/BlockDefinition/GlobalBlock/global_block = new
	var/datum/node/BlockDefinition/GlobalBlock/curBlock

/*
	Proc: Parse
	Reads the tokens and returns the AST's <GlobalBlock> node. Be sure to populate the tokens list before calling this procedure.
*/
/datum/n_Parser/proc/Parse()
	return
/*
	Proc: NextToken
	Sets <curToken> to the next token in the <tokens> list, or null if there are no more tokens.
*/
/datum/n_Parser/proc/NextToken()
	if(index >= tokens.len)
		curToken = null
	else
		curToken = tokens[++index]
	return curToken

/*
	Class: nS_Parser
	An implmentation of a parser for n_Script.
*/
/datum/n_Parser/nS_Parser
	var/datum/n_scriptOptions/nS_Options/options
/*
	Constructor: New

	Parameters:
	tokens  - A list of tokens to parse.
	options - An object used for configuration.
*/
/datum/n_Parser/nS_Parser/New(tokens[], var/datum/n_scriptOptions/options)
	src.tokens = tokens
	src.options = options
	curBlock = global_block
	return ..()

/datum/n_Parser/nS_Parser/Parse()
	ASSERT(tokens)
	for(,src.index <= src.tokens.len, src.index++)
		curToken = tokens[index]
		switch(curToken.type)
			if(/datum/token/keyword)
				var/datum/n_Keyword/kw = options.keywords[curToken.value]
				kw = new kw()
				if(kw)
					if(!kw.Parse(src))
						return

			if(/datum/token/word)
				var/datum/token/ntok
				if(index + 1 > tokens.len)
					errors += new/datum/scriptError/BadToken(curToken)
					continue

				ntok = tokens[index + 1]

				if(!istype(ntok, /datum/token/symbol))
					errors += new/datum/scriptError/BadToken(ntok)
					continue

				if(ntok.value == "(")
					ParseFunctionStatement()

				else if(options.assign_operators.Find(ntok.value))
					ParseAssignment()

				else
					errors += new/datum/scriptError/BadToken(ntok)
					continue

				if(!istype(curToken, /datum/token/end))
					errors += new/datum/scriptError/ExpectedToken(";", curToken)
					continue

			if(/datum/token/symbol)
				if(curToken.value == "}")
					if(!EndBlock())
						errors += new/datum/scriptError/BadToken(curToken)
						continue

				else
					errors += new/datum/scriptError/BadToken(curToken)
					continue

			if(/datum/token/end)
				warnings += new/datum/scriptError/BadToken(curToken)
				continue

			else
				errors += new/datum/scriptError/BadToken(curToken)
				return

	return global_block

/datum/n_Parser/nS_Parser/proc/CheckToken(val, type, err = 1, skip = 1)
	if(curToken.value != val || !istype(curToken, type))
		if(err)
			errors += new/datum/scriptError/ExpectedToken(val, curToken)
		return 0
	if(skip)
		NextToken()

	return 1

/datum/n_Parser/nS_Parser/proc/AddBlock(var/datum/node/BlockDefinition/B)
	blocks.Push(curBlock)
	curBlock = B

/datum/n_Parser/nS_Parser/proc/EndBlock()
	if(curBlock == global_block)
		return 0

	curBlock = blocks.Pop()
	return 1

/datum/n_Parser/nS_Parser/proc/ParseAssignment()
	var/name = curToken.value
	if(!options.IsValidID(name))
		errors += new/datum/scriptError/InvalidID(curToken)
		return

	NextToken()
	var/t = options.binary_operators[options.assign_operators[curToken.value]]
	var/datum/node/statement/VariableAssignment/stmt = new()
	stmt.var_name = new(name)
	NextToken()

	if(t)
		stmt.value = new t()
		stmt.value:exp = new/datum/node/expression/value/variable(stmt.var_name)
		stmt.value:exp2 = ParseExpression()
	else
		stmt.value = ParseExpression()

	curBlock.statements += stmt

/datum/n_Parser/nS_Parser/proc/ParseFunctionStatement()
	if(!istype(curToken, /datum/token/word))
		errors += new/datum/scriptError("Bad identifier in function call.")
		return

	var/datum/node/statement/FunctionCall/stmt=new
	stmt.func_name = curToken.value
	NextToken() //skip function name
	if(!CheckToken("(", /datum/token/symbol)) //Check for and skip open parenthesis
		return
	var/loops = 0
	for()
		loops++
		if(loops >= 800)
			errors +=new/datum/scriptError("Cannot find ending params.")
			return

		if(!curToken)
			errors+=new/datum/scriptError/EndOfFile()
			return
		if(istype(curToken, /datum/token/symbol) && curToken.value == ")")
			curBlock.statements += stmt
			NextToken() //Skip close parenthesis
			return

		var/datum/node/expression/P = ParseParamExpression(check_functions = 1)
		stmt.parameters += P
		if(istype(curToken, /datum/token/symbol) && curToken.value == ",")
			NextToken()