// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.

module compiler

import(
	strings
)

const (
	MaxLocalVars = 50
)

pub
struct Fn {
	// addr int
pub:
mut:
	name          string
	mod           string
	//local_vars    []Var
	//var_idx       int
	args          []Var
	is_interface  bool
	// called_fns    []string
	// idx           int
	scope_level   int
	typ           string // return type
	receiver_typ  string
	is_c          bool
	is_public     bool
	is_method     bool
	is_decl       bool // type myfn fn(int, int)
	is_unsafe     bool
	is_deprecated bool
	is_variadic   bool
	is_generic    bool
	returns_error bool
	defer_text    []string
	type_pars 	  []string
	type_inst 	  []TypeInst
	dispatch_of	  TypeInst	// current type inst of this generic instance
	body_idx	  int		// idx of the first body statement
	fn_name_token_idx int // used by error reporting
	comptime_define string
	is_used bool // so that we can skip unused fns in resulting C code
}

struct TypeInst {
mut:
	// an instantiation of generic params (e.g. ["int","int","double"])
	inst 	map[string]string
	done	bool
}

const (
	EmptyFn = Fn{}
	MainFn = Fn{ name: 'main' }
)

fn (a []TypeInst) str() string {
	mut r := []string
	for t in a {
		mut s := ' | '
		for k in t.inst.keys() {
			s += k+' -> '+ t.inst[k] +' | '
		}
		r << s
	}
	return r.str()
}

fn (p &Parser) find_var(name string) ?Var {
	for i in 0 .. p.var_idx {
		if p.local_vars[i].name == name {
			return p.local_vars[i]
		}
	}
	return none
}

fn (p &Parser) find_var_check_new_var(name string) ?Var {
	for i in 0 .. p.var_idx {
		if p.local_vars[i].name == name {
			return p.local_vars[i]
		}
	}
	// A hack to allow `newvar := Foo{ field: newvar }`
	// Declare the variable so that it can be used in the initialization
	if name == 'main__' + p.var_decl_name {
		return Var{
			name : p.var_decl_name
			typ : 'voidptr'
			is_mut : true
		}
	}
	return none
}

fn (p mut Parser) open_scope() {
	p.cur_fn.defer_text << ''
	p.cur_fn.scope_level++
}

fn (p mut Parser) mark_var_used(v Var) {
	if v.idx == -1 || v.idx >= p.local_vars.len {
		return
	}
	p.local_vars[v.idx].is_used = true
}

fn (p mut Parser) mark_var_returned(v Var) {
	if v.idx == -1 || v.idx >= p.local_vars.len {
		return
	}
	p.local_vars[v.idx].is_returned = true
}

fn (p mut Parser) mark_var_changed(v Var) {
	if v.idx == -1 || v.idx >= p.local_vars.len {
		return
	}
	p.local_vars[v.idx].is_changed = true
}

fn (p mut Parser) mark_arg_moved(v Var) {
	for i, arg in p.cur_fn.args {
		if arg.name == v.name {
			//println('setting f $p.cur_fn.name arg $arg.name to is_mut')
			p.cur_fn.args[i].is_moved = true
			break
		}
	}
	p.table.fns[p.cur_fn.name] = p.cur_fn
}

fn (p mut Parser) known_var(name string) bool {
	_ = p.find_var(name) or {
		return false
	}
	return true
}

fn (p mut Parser) known_var_check_new_var(name string) bool {
	_ = p.find_var_check_new_var(name) or {
		return false
	}
	return true
}

fn (p mut Parser) register_var(v Var) {
	mut new_var := {v | idx: p.var_idx, scope_level: p.cur_fn.scope_level}
	if v.line_nr == 0 {
		new_var.token_idx = p.cur_tok_index()
		new_var.line_nr = p.cur_tok().line_nr
	}
	// Expand the array
	if p.var_idx >= p.local_vars.len {
		p.local_vars << new_var
	}
	else {
		p.local_vars[p.var_idx] = new_var
	}
	p.var_idx++
}

fn (p mut Parser) clear_vars() {
	// shared a := [1, 2, 3]
	p.var_idx = 0
	if p.local_vars.len > 0 {
		if p.pref.autofree {
			//p.local_vars.free()
		}
		p.local_vars = []Var
	}
	
}

// Function signatures are added to the top of the .c file in the first run.
fn (p mut Parser) fn_decl() {
	p.clear_vars() // clear local vars every time a new fn is started
	p.fgen('fn ')

	//defer { p.fgenln('\n') }
	// If we are in the first pass, create a new function.
	// In the second pass fetch the one we created.
	/*
	mut f := if p.first_pass {
		Fn{
			mod: p.mod
			is_public: p.tok == .key_pub
		}
	else {
	}
	*/
	is_pub := p.tok == .key_pub
	mut f := Fn{
		mod: p.mod
		is_public: is_pub || p.is_vh // functions defined in .vh are always public
		is_unsafe: p.attr == 'unsafe_fn'
		is_deprecated: p.attr == 'deprecated'
		comptime_define: if p.attr.starts_with('if ') { p.attr.right(3) } else { '' }
	}
	is_live := p.attr == 'live' && !p.pref.is_so  && p.pref.is_live
	if p.attr == 'live' &&  p.first_pass() && !p.pref.is_live && !p.pref.is_so {
		println('INFO: run `v -live program.v` if you want to use [live] functions')
	}
	if is_pub {
		p.next()
	}
	p.returns = false
	//p.gen('/* returns $p.returns */')
	p.next()
	
	// Method receiver
	mut receiver_typ := ''
	if p.tok == .lpar {
		f.is_method = true
		p.check(.lpar)
		receiver_name := p.check_name()
		is_mut := p.tok == .key_mut
		is_amp := p.tok == .amp
		if is_mut || is_amp {
			p.check_space(p.tok)
		}
		receiver_typ = p.get_type()
		t := p.table.find_type(receiver_typ)
		if (t.name == '' || t.is_placeholder) && !p.first_pass() {
			p.error('unknown receiver type `$receiver_typ`')
		}	
		if t.cat == .interface_ {
			p.error('invalid receiver type `$receiver_typ` (`$receiver_typ` is an interface)')
		}
		// Don't allow modifying types from a different module
		if !p.first_pass() && !p.builtin_mod && t.mod != p.mod &&
			!p.is_vgen // allow .str()
		{
			//println('T.mod=$T.mod')
			//println('p.mod=$p.mod')
			p.error('cannot define new methods on non-local type `$receiver_typ`')
		}
		// `(f *Foo)` instead of `(f mut Foo)` is a common mistake
		if receiver_typ.ends_with('*') {
			tt := receiver_typ.replace('*', '')
			p.error('use `($receiver_name mut $tt)` instead of `($receiver_name *$tt)`')
		}
		f.receiver_typ = receiver_typ
		if is_mut || is_amp {
			receiver_typ += '*'
		}
		p.check(.rpar)
		p.fspace()
		receiver := Var {
			name: receiver_name
			is_arg: true
			typ: receiver_typ
			is_mut: is_mut
			ref: is_amp
			ptr: is_mut
			line_nr: p.scanner.line_nr
			token_idx: p.cur_tok_index()
		}
		f.args << receiver
		p.register_var(receiver)
	}
	// +-/* methods
	if p.tok in [.plus, .minus, .mul, .div, .mod] {
		f.name = p.tok.str()
		p.next()
	}
	else {
		f.name = p.check_name()
	}
	f.fn_name_token_idx = p.cur_tok_index()
	// init fn
	if f.name == 'init' && !f.is_method && f.is_public && !p.is_vh {
		p.error('init function cannot be public')
	}
	// C function header def? (fn C.NSMakeRect(int,int,int,int))
	is_c := f.name == 'C' && p.tok == .dot
	// Just fn signature? only builtin.v + default build mode
	if p.is_vh {
	//println('\n\nfn_decl() name=$f.name receiver_typ=$receiver_typ nogen=$p.cgen.nogen')
	}
	if is_c {
		p.check(.dot)
		f.name = p.check_name()
		f.is_c = true
	}
	else if !p.pref.translated {
		if contains_capital(f.name) && !p.fileis('view.v') {
			println('`$f.name`')
			p.error('function names cannot contain uppercase letters, use snake_case instead')
		}
		if f.name[0] == `_` {
			p.error('function names cannot start with `_`, use snake_case instead')
		}
		if f.name.contains('__') {
			p.error('function names cannot contain double underscores, use single underscores instead')
		}
	}
	// simple_name := f.name
	// user.register() => User_register()
	has_receiver := receiver_typ.len > 0
	if receiver_typ != '' {
		// f.name = '${receiver_typ}_${f.name}'
	}
	// full mod function name
	// `os.exit()` ==> `os__exit()`
	// if !is_c && !p.builtin_mod && receiver_typ.len == 0 {
	if !is_c && !has_receiver &&
(!p.builtin_mod || (p.builtin_mod && f.name == 'init')) {
		f.name = p.prepend_mod(f.name)
	}
	if p.first_pass() && receiver_typ.len == 0 {
		if existing_fn := p.table.find_fn(f.name) {
			// This existing function could be defined as C decl before
			// (no body), then we don't need to throw an error.
			if !existing_fn.is_decl {
				p.error('redefinition of `$f.name`')
			}
		}
	}
	// Generic?
	if p.tok == .lt {
		f.is_generic = true
		p.next()
		for {
			type_par := p.check_name()
			if type_par.len > 1 || !(type_par in reserved_type_param_names) {
				p.error('type parameters must be single-character, upper-case letters of the following set: $reserved_type_param_names')
			}
			if type_par in f.type_pars {
				p.error('redeclaration of type parameter `$type_par`')
			}
			f.type_pars << type_par
			if p.tok == .gt { break }
			p.check(.comma)
		}
		p.set_current_fn(f)
		p.check(.gt)
	}
	// Args (...)
	p.fn_args(mut f)
	// Returns an error?
	if p.tok == .not {
		p.next()
		f.returns_error = true
	}
	// Returns a type?
	mut typ := 'void'
	if p.tok in [.name, .mul, .amp, .lsbr, .question, .lpar] {
		p.fgen(' ')
		typ = p.get_type()
	}
	// V allows empty functions (just definitions)
	is_fn_header := !is_c && !p.is_vh &&		p.tok != .lcbr
	if is_fn_header {
		f.is_decl = true
	}
	// `{` required only in normal function declarations
	if !is_c && !p.is_vh && !is_fn_header {
		p.fgen(' ')
		p.check(.lcbr)
	}
	// Register ?option type
	if typ.starts_with('Option_') {
		p.cgen.typedefs << 'typedef Option $typ;'
	}
	// Register function
	f.typ = typ
	str_args := f.str_args(p.table)
	// Special case for main() args
	if f.name == 'main__main' && !has_receiver {
		if str_args != '' || typ != 'void' {
			p.error_with_token_index('fn main must have no arguments and no return values', f.fn_name_token_idx)
		}
	}
	dll_export_linkage := p.get_linkage_prefix()
	if !p.is_vweb {
		p.set_current_fn( f )
	}
	// Generate `User_register()` instead of `register()`
	// Internally it's still stored as "register" in type User
	mut fn_name_cgen := p.table.fn_gen_name(f)
	// Start generation of the function body
	skip_main_in_test := false
	if !is_c && !is_live && !p.is_vh && !is_fn_header && !skip_main_in_test {
		if p.pref.obfuscate {
			p.genln('; // $f.name')
		}
		// Generic functions are inserted as needed from the call site
		if f.is_generic {
			if p.first_pass() {
				f.body_idx = p.cur_tok_index()+1
				if f.is_method {
					rcv := p.table.find_type(receiver_typ)
					if p.first_pass() && rcv.name == '' {
						r := Type {
							name: rcv.name.replace('*', '')
							mod: p.mod
							is_placeholder: true
						}
						p.table.register_type2(r)
					}
					// println('added generic method $rcv.name $f.name')
					p.add_method(rcv.name, f)
				} else {
					p.table.register_fn(f)
				}
			}
			if f.is_method { p.mark_var_changed(f.args[0]) }
			p.check_unused_variables()
			p.set_current_fn( EmptyFn )
			p.returns = false
			p.skip_fn_body()
			return
		} else {
			p.gen_fn_decl(f, typ, str_args)
		}
	}

	if is_fn_header {
		p.genln('$typ $fn_name_cgen($str_args);')
		p.fgenln('')
	}
	if is_c {
		p.fgenln('\n')
	}
	// Register the method
	if receiver_typ != '' {
		mut receiver_t := p.table.find_type(receiver_typ)
		// No such type yet? It could be defined later. Create a new type.
		// struct declaration later will modify it instead of creating a new one.
		if p.first_pass() && receiver_t.name == '' {
			//println('fn decl ! registering placeholder $receiver_typ')
			receiver_t = Type {
				name: receiver_typ.replace('*', '')
				mod: p.mod
				is_placeholder: true
			}
			p.table.register_type2(receiver_t)
		}
		p.add_method(receiver_t.name, f)
	}
	else if p.first_pass(){
		// println('register_fn $f.name typ=$typ isg=$is_generic pass=$p.pass ' +
//'$p.file_name')
		p.table.register_fn(f)
	}
	if p.is_vh || p.first_pass() || is_live || is_fn_header || skip_main_in_test {
		// First pass? Skip the body for now
		// Look for generic calls.
		if !p.is_vh && !is_fn_header {
			p.skip_fn_body()
		}
		// Live code reloading? Load all fns from .so
		if is_live && p.first_pass() && p.mod == 'main' {
			//println('ADDING SO FN $fn_name_cgen')
			p.cgen.so_fns << fn_name_cgen
			fn_name_cgen = '(* $fn_name_cgen )'
		}
		// Function definition that goes to the top of the C file.
		mut fn_decl := '$dll_export_linkage$typ $fn_name_cgen($str_args)'
		if p.pref.obfuscate {
			fn_decl += '; // $f.name'
		}
		// Add function definition to the top
		if !is_c && p.first_pass() {
			p.cgen.fns << fn_decl + ';'
		}
		return
	}
	if p.attr == 'live' && p.pref.is_so {
		//p.genln('// live_function body start')
		p.genln('pthread_mutex_lock(&live_fn_mutex);')
	}

	if f.name in ['main__main', 'main', 'WinMain'] {
		if p.pref.is_test {
			p.error_with_token_index('tests cannot have function `main`', f.fn_name_token_idx)
		}
	}
	// println('is_c=$is_c name=$f.name')
	if is_c || p.is_vh || is_fn_header {
		return
	}
	// Profiling mode? Start counting at the beginning of the function (save current time).
	if p.pref.is_prof && f.name != 'time__ticks' {
		p.genln('double _PROF_START = time__ticks();//$f.name')
		cgen_name := p.table.fn_gen_name(f)
		if f.defer_text.len > f.scope_level {
			f.defer_text[f.scope_level] = '  ${cgen_name}_time += time__ticks() - _PROF_START;'
		}
	}
	p.statements_no_rcbr()
	//p.cgen.nogen = false
	// Print counting result after all statements in main
	if p.pref.is_prof && f.name == 'main' {
		p.genln(p.print_prof_counters())
	}
	// Counting or not, always need to add defer before the end
	if !p.is_vweb {
		if f.defer_text.len > f.scope_level {
		p.genln(f.defer_text[f.scope_level])
		}
	}
	if typ != 'void' && !p.returns {
		p.error_with_token_index('$f.name must return "$typ"', f.fn_name_token_idx)
	}
	if p.attr == 'live' && p.pref.is_so {
		//p.genln('// live_function body end')
		p.genln('pthread_mutex_unlock(&live_fn_mutex);')
	}
	// {} closed correctly? scope_level should be 0
	if p.mod == 'main' {
		// println(p.cur_fn.scope_level)
	}
	if p.cur_fn.scope_level > 2 {
		// p.error('unclosed {')
	}
	// Make sure all vars in this function are used (only in main for now)
	if p.mod != 'main' {
		p.genln('}')
		return
	}
	p.genln('}')
	p.check_unused_variables()
	p.set_current_fn( EmptyFn )
	p.returns = false
}

[inline]
// Skips the entire function's body in the first pass.
fn (p mut Parser) skip_fn_body() {
	mut opened_scopes := 0
	mut closed_scopes := 0
	for {
		if p.tok == .lcbr {
			opened_scopes++
		}
		if p.tok == .rcbr {
			closed_scopes++
		}
		// find `foo<Bar>()` in function bodies and register generic types
		// TODO
		// ...
		// Reached a declaration token? (fn, struct, const etc) Stop.
		if p.tok.is_decl() {
			break
		}
		// fn body ended, and a new fn attribute declaration like [live] is starting?
		if closed_scopes > opened_scopes && p.prev_tok == .rcbr {
			if p.tok == .lsbr {
				break
			}
		}
		p.next()
	}
}

fn (p Parser) get_linkage_prefix() string {
	return if p.pref.ccompiler == 'msvc' && p.attr == 'live' && p.pref.is_so {
		'__declspec(dllexport) '
	} else if p.attr == 'inline' {
		'static inline '
	} else {
		''
	}
}

fn (p mut Parser) check_unused_variables() {
	for var in p.local_vars {
		if var.name == '' {
			break
		}
		if !var.is_used && !p.pref.is_repl && !var.is_arg && !p.pref.translated {
			p.production_error_with_token_index('`$var.name` declared and not used', var.token_idx )
		}
		if !var.is_changed && var.is_mut && !p.pref.is_repl &&
			!p.pref.translated && var.typ != 'T*'
		{
			p.error_with_token_index('`$var.name` is declared as mutable, but it was never changed', var.token_idx )
		}
	}
}

// user.register() => "User_register(user)"
// method_ph - where to insert "user_register("
// receiver_var - "user" (needed for pthreads)
// receiver_type - "User"
fn (p mut Parser) async_fn_call(f Fn, method_ph int, receiver_var, receiver_type string) {
	// println('\nfn_call $f.name is_method=$f.is_method receiver_type=$f.receiver_type')
	// p.print_tok()
	mut thread_name := ''
	// Normal function => just its name, method => TYPE_FN.name
	mut fn_name := f.name
	if f.is_method {
		fn_name = receiver_type.replace('*', '') + '_' + f.name
		//fn_name = '${receiver_type}_${f.name}'
	}
	// Generate tmp struct with args
	arg_struct_name := 'thread_arg_$fn_name'
	tmp_struct := p.get_tmp()
	p.genln('$arg_struct_name * $tmp_struct = malloc(sizeof($arg_struct_name));')
	mut arg_struct := 'typedef struct  $arg_struct_name   { '
	p.next()
	p.check(.lpar)
	// str_args contains the args for the wrapper function:
	// wrapper(arg_struct * arg) { fn("arg->a, arg->b"); }
	mut str_args := ''
	mut did_gen_something := false
	for i, arg in f.args {
		arg_struct += '$arg.typ $arg.name ;'// Add another field (arg) to the tmp struct definition
		str_args += 'arg $dot_ptr $arg.name'
		if i == 0 && f.is_method {
			p.genln('$tmp_struct $dot_ptr $arg.name =  $receiver_var ;')
			if i < f.args.len - 1 {
				str_args += ','
			}
			did_gen_something = true
			continue
		}
		// Set the struct values (args)
		p.genln('$tmp_struct $dot_ptr $arg.name =  ')
		p.expression()
		p.genln(';')
		if i < f.args.len - 1 {
			p.check(.comma)
			str_args += ','
		}
		did_gen_something = true
	}

	if !did_gen_something {
		// Msvc doesnt like empty struct
		arg_struct += 'EMPTY_STRUCT_DECLARATION;'
	}

	arg_struct += '} $arg_struct_name ;'
	// Also register the wrapper, so we can use the original function without modifying it
	fn_name = p.table.fn_gen_name(f)
	wrapper_name := '${fn_name}_thread_wrapper'
	mut wrapper_type := 'void*'
	if p.os == .windows {
		wrapper_type = 'void* __stdcall'
	}
	wrapper_text := '$wrapper_type $wrapper_name($arg_struct_name * arg) {$fn_name( /*f*/$str_args ); return NULL; }'
	p.cgen.register_thread_fn(wrapper_name, wrapper_text, arg_struct)
	// Create thread object
	tmp_nr := p.get_tmp_counter()
	thread_name = '_thread$tmp_nr'
	if p.os != .windows {
		p.genln('pthread_t $thread_name;')
	}
	tmp2 := p.get_tmp()
	mut parg := 'NULL'
	if f.args.len > 0 {
		parg = ' $tmp_struct'
	}
	// Call the wrapper
	if p.os == .windows {
		p.genln(' CreateThread(0,0, $wrapper_name, $parg, 0,0);')
	}
	else {
		p.genln('int $tmp2 = pthread_create(& $thread_name, NULL, (void *)$wrapper_name, $parg);')
	}
	p.check(.rpar)
}

// p.tok == fn_name
fn (p mut Parser) fn_call(f mut Fn, method_ph int, receiver_var, receiver_type string) {
	if f.is_unsafe && !p.builtin_mod && !p.inside_unsafe {
		p.warn('you are calling an unsafe function outside of an unsafe block')
	}	
	if f.is_deprecated {
		p.warn('$f.name is deprecated')
	}	
	if !f.is_public &&  !f.is_c && !p.pref.is_test && !f.is_interface && f.mod != p.mod {
		if f.name == 'contains' {
			println('use `value in numbers` instead of `numbers.contains(value)`')
		}
		p.error('function `$f.name` is private')
	}
	is_comptime_define := f.comptime_define != '' && f.comptime_define != p.pref.comptime_define
	if is_comptime_define {
		p.cgen.nogen = true
	}	
	p.calling_c = f.is_c
	if f.is_c && !p.builtin_mod {
		if f.name == 'free' {
			p.error('use `free()` instead of `C.free()`')
		} else if f.name == 'malloc' {
			p.error('use `malloc()` instead of `C.malloc()`')
		}
	}
	f.is_used = true
	cgen_name := p.table.fn_gen_name(f)
	p.next()		// fn name
	if p.tok == .lt {
		mut i := p.token_idx
		for {
			if p.tokens[i].tok == .gt {
				p.error('explicit type arguments are not allowed; remove `<...>`')
			} else if p.tokens[i].tok == .lpar {
				// probably a typo, do not concern the user with the above error message
				break
			}
			i += 1
		}
	}
	// if p.pref.is_prof {
	// p.cur_fn.called_fns << cgen_name
	// }

	// If we have a method placeholder,
	// we need to preappend "method(receiver, ...)"
	if f.is_method {
		receiver := f.args.first()
		//println('r=$receiver.typ RT=$receiver_type')
		if receiver.is_mut && !p.expr_var.is_mut {
			//println('$method_call  recv=$receiver.name recv_mut=$receiver.is_mut')
			if p.expr_var.is_for_var {
				p.error('`$p.expr_var.name` is immutable, `for` variables' +
					' always are')
			}	 else {
				p.error('`$p.expr_var.name` is immutable, declare it with `mut`')
			}
		}
		if !p.expr_var.is_changed && receiver.is_mut {
			p.mark_var_changed(p.expr_var)
		}
		p.gen_method_call(receiver, receiver_type, cgen_name, f.typ, method_ph)
	} else {
		// Normal function call
		p.gen('$cgen_name (')
	}
	
	// `foo<Bar>()`
	// if f is generic, the name is changed to a suitable instance in dispatch_generic_fn_instance()
	// we then replace `cgen_name` with the instance's name
	generic := f.is_generic
	p.fn_call_args(mut f)
	if generic {
		p.cgen.resetln(p.cgen.cur_line.replace('$cgen_name (', '$f.name ('))
		// println('calling inst $f.name: $p.cgen.cur_line')
	}

	p.gen(')')
	p.calling_c = false
	if is_comptime_define {
		p.cgen.nogen = false
		p.cgen.resetln('')
	}
	// println('end of fn call typ=$f.typ')
}

// for declaration
// return an updated Fn object with args[] field set
fn (p mut Parser) fn_args(f mut Fn) {
	p.check(.lpar)
	defer { p.check(.rpar) }
	if f.is_interface {
		int_arg := Var {
			typ: f.receiver_typ
			token_idx: p.cur_tok_index()
		}
		f.args << int_arg
	}
	// `(int, string, int)`
	// Just register fn arg types
	types_only := p.tok == .mul || p.tok == .amp || (p.peek() == .comma && p.table.known_type(p.lit)) || p.peek() == .rpar// (int, string)
	if types_only {
		for p.tok != .rpar {
			typ := p.get_type()
			p.check_and_register_used_imported_type(typ)
			v := Var {
				typ: typ
				is_arg: true
				// is_mut: is_mut
				line_nr: p.scanner.line_nr
				token_idx: p.cur_tok_index()
			}
			// f.register_var(v)
			f.args << v
			if p.tok == .comma {
				p.next()
			}
		}
	}
	// `(a int, b, c string)` syntax
	for p.tok != .rpar {
		mut names := [	p.check_name()	]
		// `a,b,c int` syntax
		for p.tok == .comma {
			p.check(.comma)
			p.fspace()
			names << p.check_name()
		}
		p.fspace()
		is_mut := p.tok == .key_mut
		if is_mut {
			p.check(.key_mut)
		}
		// variadic arg
		if p.tok == .ellipsis {
			p.check(.ellipsis)
			if p.tok == .rpar {
				p.error('you must provide a type for vargs: eg `...string`. multiple types `...` are not supported yet.')
			}
			f.is_variadic = true
		}
		mut typ := p.get_type()
		if !p.first_pass() && !p.table.known_type(typ) {
			p.error('fn_args: unknown type $typ')
		}
		if f.is_variadic {
			if !f.is_c {
				// register varg struct, incase function is never called
				if p.first_pass() && !f.is_generic {
					p.register_vargs_stuct(typ, 0)
				}
				typ = 'varg_$typ'
			} else {
				typ = '...$typ' // TODO: fix, this is invalid in C
			}
		}
		p.check_and_register_used_imported_type(typ)
		if is_mut && is_primitive_type(typ) {
			p.error('mutable arguments are only allowed for arrays, maps, and structs.' +
			'\nreturn values instead: `foo(n mut int)` => `foo(n int) int`')
		}
		for name in names {
			if is_mut {
				typ += '*'
			}
			v := Var{
				name: name
				typ: typ
				is_arg: true
				is_mut: is_mut
				ptr: is_mut
				line_nr: p.scanner.line_nr
				token_idx: p.cur_tok_index()
			}
			p.register_var(v)
			f.args << v
		}
		if p.tok == .comma {
			p.check(.comma)
		}
		// unnamed (C definition)
		if p.tok == .ellipsis {
			if !f.is_c {
				p.error('variadic argument syntax must be `arg_name ...type` eg `argname ...string`.')
			}
			f.args << Var {
				// name: '...'
				typ: '...'
			}
			p.next()
		}
	}
}

// foo *(1, 2, 3, mut bar)*
fn (p mut Parser) fn_call_args(f mut Fn) {
	// println('fn_call_args() name=$f.name args.len=$f.args.len')
	// C func. # of args is not known
	p.check(.lpar)
	if f.is_c {
		for p.tok != .rpar {
			//C.func(var1, var2.method())
			//If the parameter calls a function or method that is not C,
			//the value of p.calling_c is changed
			p.calling_c = true
			ph := p.cgen.add_placeholder()
			typ := p.bool_expression()
			// Cast V byteptr to C char* (byte is unsigned in V, that led to C warnings)
			if typ == 'byte*' {
				p.cgen.set_placeholder(ph, '(char*)')
			}
			if p.tok == .comma {
				p.gen(', ')
				p.check(.comma)
			}
		}
		p.check(.rpar)
		return
	}
	// add debug information to panic when -g arg is passed
	if p.v.pref.is_debug && f.name == 'panic' && !p.is_js {
		mod_name := p.mod.replace('_dot_', '.')
		fn_name := p.cur_fn.name.replace('${p.mod}__', '')
		file_path := cescaped_path(p.file_path)
		p.cgen.resetln(p.cgen.cur_line.replace(
			'v_panic (',
			'panic_debug ($p.scanner.line_nr, tos3("$file_path"), tos3("$mod_name"), tos2((byte *)"$fn_name"), '
		))
	}
	mut saved_args := []string
	for i, arg in f.args {
		// Receiver is the first arg
		// Skip the receiver, because it was already generated in the expression
		if i == 0 && f.is_method {
			if f.args.len > 1 { // && !p.is_js {
				p.gen(',')
			}
			continue
		}
		// Reached the final vararg? Quit
		if i == f.args.len - 1 && arg.typ.starts_with('varg_') {
			break
		}
		ph := p.cgen.add_placeholder()
		// `)` here means that not enough args were provided
		if p.tok == .rpar {
			str_args := f.str_args(p.table)// TODO this is C args
			p.error('not enough arguments in call to `$f.name ($str_args)`')
		}
		// If `arg` is mutable, the caller needs to provide `mut`:
		// `mut numbers := [1,2,3]; reverse(mut numbers);`
		if arg.is_mut {
			if p.tok != .key_mut && p.tok == .name {
				mut dots_example :=  'mut $p.lit'
				if i > 0 {
					dots_example = '.., ' + dots_example
				}
				if i < f.args.len - 1 {
					dots_example = dots_example + ',..'
				}
				p.error('`$arg.name` is a mutable argument, you need to provide `mut`: `$f.name($dots_example)`')
			}
			if p.peek() != .name {
				p.error('`$arg.name` is a mutable argument, you need to provide a variable to modify: `$f.name(... mut a...)`')
			}
			p.check(.key_mut)
			var_name := p.lit
			v := p.find_var(var_name) or {
				p.error('`$arg.name` is a mutable argument, you need to provide a variable to modify: `$f.name(... mut a...)`')
				exit(1)
			}
			if !v.is_changed {
				p.mark_var_changed(v)
			}
		}
		p.expected_type = arg.typ
		clone := p.pref.autofree && arg.typ == 'string' && arg.is_moved && p.mod != 'builtin'
		if clone {
			p.gen('/*YY f=$f.name arg=$arg.name is_moved=$arg.is_moved*/string_clone(')
		}
		mut typ := p.bool_expression()
		if clone {
			p.gen(')')
		}
		// Optimize `println`: replace it with `printf` to avoid extra allocations and
		// function calls.
		// `println(777)` => `printf("%d\n", 777)`
		// (If we don't check for void, then V will compile `println(func())`)
		if i == 0 && (f.name == 'println' || f.name == 'print') && typ == 'ustring' {
			if typ == 'ustring' {
				p.gen('.s')
			}
			typ = 'string'
		}
		if i == 0 && (f.name == 'println' || f.name == 'print')  &&
			!(typ in ['string', 'ustring', 'void' ])
		{
			T := p.table.find_type(typ)
			$if !windows {
			$if !js {
				fmt := p.typ_to_fmt(typ, 0)
				if fmt != '' && typ != 'bool' {
					nl := if f.name == 'println' { '\\n' } else { '' }
					p.cgen.resetln(p.cgen.cur_line.replace(f.name +
					' (', '/*opt*/printf ("' + fmt + '$nl", '))
					continue
				}
			}
			}
			if typ.ends_with('*') {
				p.cgen.set_placeholder(ph, 'ptr_str(')
				p.gen(')')
				continue
			}
			// Make sure this type has a `str()` method
			$if !js {
			if !T.has_method('str') {
				// varg
				if T.name.starts_with('varg_') {
					p.gen_varg_str(T)
					p.cgen.set_placeholder(ph, '${typ}_str(')
					p.gen(')')
					continue
				}
				// Arrays have automatic `str()` methods
				else if T.name.starts_with('array_') {
					p.gen_array_str(T)
					p.cgen.set_placeholder(ph, '${typ}_str(')
					p.gen(')')
					continue
				}
				// struct
				else if T.cat == .struct_ {
					p.gen_struct_str(T)
					p.cgen.set_placeholder(ph, '${typ}_str(')
					p.gen(')')
					continue
				}
				error_msg := ('`$typ` needs to have method `str() string` to be printable')
				p.error(error_msg)
			}
			p.cgen.set_placeholder(ph, '${typ}_str(')
			p.gen(')')
			}
			continue
		}
		got := typ
		expected := arg.typ
		got_ptr := got.ends_with('*')
		exp_ptr := expected.ends_with('*')
		// println('fn arg got="$got" exp="$expected"')
		type_mismatch := !p.check_types_no_throw(got, expected)
		if type_mismatch && f.is_generic {
			// println("argument `$arg.name` is generic")
			saved_args << got
		} else if type_mismatch {
			mut j := i
			if f.is_method {
				j--
			}
			mut nr := '${i+1}th'
			if j == 0 {
				nr = 'first'
			} else if j == 1 {
				nr = 'second'
			}	 else if j == 2 {
				nr = 'third'
			}
			p.error('cannot use type `$typ` as type `$arg.typ` in $nr ' +
				'argument to `$f.name()`')
		} else {
			saved_args << ''
		}
		is_interface := p.table.is_interface(arg.typ)
		// Automatically add `&` or `*` before an argument.
		// V, unlike C and Go, simplifies this aspect:
		// `foo(bar)` is allowed where `foo(&bar)` is expected.
		// The argument is not mutable, so it won't be changed by the function.
		// It doesn't matter whether it's passed by referencee or by value
		// to the end user.
		if !is_interface {
			// Dereference
			if got_ptr && !exp_ptr {
				p.cgen.set_placeholder(ph, '*')
			}
			// Reference
			// TODO ptr hacks. DOOM hacks, fix please.
			if !got_ptr && exp_ptr && got != 'voidptr' {
				// Special case for mutable arrays. We can't `&` function
				// results,
				// have to use `(array[]){ expr }` hack.
				if expected.starts_with('array_') && exp_ptr { //&& !arg.is_mut{
					p.cgen.set_placeholder(ph, '& /*111*/ (array[]){')
					p.gen('}[0] ')
				}
				// println('\ne:"$expected" got:"$got"')
				else if ! (expected == 'void*' && got == 'int') &&
				! (expected == 'byte*' && got.contains(']byte')) &&
				! (expected == 'byte*' && got == 'string') &&
				//! (expected == 'void*' && got == 'array_int') {
				! (expected == 'byte*' && got == 'byteptr') {
					p.cgen.set_placeholder(ph, '& /*112 EXP:"$expected" GOT:"$got" */')
				}
			}
		}
		else if is_interface {
			if !got_ptr {
				p.cgen.set_placeholder(ph, '&')
			}
			// Pass all interface methods
			interface_type := p.table.find_type(arg.typ)
			for method in interface_type.methods {
				p.gen(', ${typ}_${method.name} ')
			}
		}
		// Check for commas
		if i < f.args.len - 1 {
			// Handle 0 args passed to varargs
			if p.tok != .comma && !f.is_variadic {
				p.error('wrong number of arguments for $i,$arg.name fn `$f.name`: expected $f.args.len, but got less')
			}
			if p.tok == .comma && (!f.is_variadic || (f.is_variadic && i < f.args.len-2 )) {
				p.check(.comma)
				p.gen(',')
			}
		}
	}
	// varargs
	varg_type, varg_values := p.fn_call_vargs(f)
	if f.is_variadic {
		saved_args << varg_type
	}
	if p.tok == .comma {
		p.error('wrong number of arguments for fn `$f.name`: expected $f.args.len, but got more')
	}
	p.check(.rpar)
	if f.is_generic {
		type_map := p.extract_type_inst(f, saved_args)
		p.dispatch_generic_fn_instance(mut f, type_map)
	}
	if f.is_variadic {
		p.fn_gen_caller_vargs(f, varg_type, varg_values)
	}
}

// From a given generic function and an argument list matching its signature,
// create a type instantiation
fn (p mut Parser) extract_type_inst(f &Fn, args_ []string) TypeInst {
	mut r := TypeInst{}
	mut i := 0
	mut args := args_
	if f.typ != 'void' { args << f.typ }
	for e in args {
		if e == '' { continue }
		tp := f.type_pars[i]
		mut ti := e
		if ti.starts_with('fn (') {
			fn_args := ti[4..].all_before(') ').split(',')
			mut found := false
			for fa_ in fn_args {
				mut fa := fa_
				for fa.starts_with('array_') { fa = fa[6..] }
				if fa == tp {
					r.inst[tp] = fa
					found = true
					i += 1
					break
				}
			}
			if found { continue }
			ti = ti.all_after(') ')
		}
		for ti.starts_with('array_') { ti = ti[6..] }
		if r.inst[tp] != '' {
			if r.inst[tp] != ti {
				p.error('type parameter `$tp` has type ${r.inst[tp]}, not `$ti`')
			}
			continue
		}
		// println("extracted $tp => $ti")
		r.inst[tp] = ti
		i += 1
		if i >= f.type_pars.len { break }
	}
	if r.inst[f.typ] == '' && f.typ in f.type_pars {
		r.inst[f.typ] = '_ANYTYPE_'
	}
	for tp in f.type_pars {
		if r.inst[tp] == '' {
			p.error_with_token_index('unused type parameter `$tp`', f.body_idx-2)
		}
	}
	return r
}

// Replace type params of a given generic function using a TypeInst
fn (p mut Parser) replace_type_params(f &Fn, ti TypeInst) []string {
	mut sig := []string
	for a in f.args {
		sig << a.typ
	}
	sig << f.typ
	mut r := []string
	for _, a in sig {
		mut fi := a
		mut fr := ''
		if fi.starts_with('fn (') {
			fr += 'fn ('
			mut fn_args := fi[4..].all_before(') ').split(',')
			fn_args << fi.all_after(') ')
			for i, fa_ in fn_args {
				mut fna := fa_.trim_space()
				for fna.starts_with('array_') {
					fna = fna[6..]
					fr += 'array_'
				}
				if fna in ti.inst.keys() {
					fr += ti.inst[fna]
				} else {
					fr += fna
				}
				if i <= fn_args.len-3 {
					fr += ','
				} else if i == fn_args.len-2 {
					fr += ') '
				}
			}
			r << fr
			continue
		}
		for fi.starts_with('array_') {
			fi = fi[6..]
			fr += 'array_'
		}
		if fi.starts_with('varg_') {
			fi = fi[5..]
			fr += 'varg_'
		}
		if fi in ti.inst.keys() {
			mut t := ti.inst[fi]
			fr += t
			// println("replaced $a => $fr")
		} else {
			fr += fi
		}
		r << fr
	}
	return r
}

fn (p mut Parser) register_vargs_stuct(typ string, len int) string {
	vargs_struct := 'varg_$typ'
	varg_type := Type{
		cat: .struct_,
		name: vargs_struct,
		mod: p.mod
	}
	mut varg_len := len
	if !p.table.known_type(vargs_struct) {
		p.table.register_type2(varg_type)
		p.cgen.typedefs << 'typedef struct $vargs_struct $vargs_struct;\n'
	} else {
		ex_typ := p.table.find_type(vargs_struct)
		ex_len := ex_typ.fields[1].name[5..ex_typ.fields[1].name.len-1].int()
		if ex_len > varg_len { varg_len = ex_len }
		p.table.rewrite_type(varg_type)
	}
	p.table.add_field(vargs_struct, 'len', 'int', false, '', .public)
	p.table.add_field(vargs_struct, 'args[$varg_len]', typ, false, '', .public)
	
	return vargs_struct
}

fn (p mut Parser) fn_call_vargs(f Fn) (string, []string) {
	if !f.is_variadic {
		return '', []string
	}
	last_arg := f.args.last()
	mut varg_def_type := last_arg.typ[3..]
	mut types := []string
	mut values := []string
	for p.tok != .rpar {
		if p.tok == .comma {
			p.check(.comma)
		}
		p.cgen.start_tmp()
		mut varg_type := p.bool_expression()
		varg_value := p.cgen.end_tmp()
		if varg_type.starts_with('varg_') &&
			(values.len > 0 || p.tok == .comma) {
				p.error('You cannot pass additional vargs when forwarding vargs to another function/method')
			}
		if !f.is_generic {
			p.check_types(last_arg.typ, varg_type)
		} else {
			if types.len > 0 {
				for t in types {
					p.check_types(varg_type, t)
				}
			}
		}
		ref_deref := if last_arg.typ.ends_with('*') && !varg_type.ends_with('*') { '&' }
			else if !last_arg.typ.ends_with('*') && varg_type.ends_with('*') { '*' }
			else { '' }
		types << varg_type
		values << '$ref_deref$varg_value'
	}
	for va in p.table.varg_access {
		if va.fn_name != f.name { continue }
		if va.index >= values.len {
			p.error_with_token_index('variadic arg index out of range: $va.index/${values.len-1}, vargs are 0 indexed', va.tok_idx)
		}
	}
	if !f.is_method && f.args.len > 1 {
		p.cgen.gen(',')
	}
	return types[0], values
}

fn (p mut Parser) fn_gen_caller_vargs(f &Fn, varg_type string, values []string) {
	is_varg := varg_type.starts_with('varg_')
	if is_varg { // forwarding varg
		p.cgen.gen('${values[0]}')
	} else {
		vargs_struct := p.register_vargs_stuct(varg_type, values.len)
		p.cgen.gen('&($vargs_struct){.len=$values.len,.args={'+values.join(',')+'}}')
	}
}

fn (p mut Parser) register_multi_return_stuct(types []string) string {
	typ := '_V_MulRet_' + types.join('_V_').replace('*', '_PTR_')
	if p.table.known_type(typ) { return typ }
	p.table.register_type2(Type{
		cat: .struct_,
		name: typ,
		mod: p.mod
	})
	for i, t in typ.replace('_V_MulRet_', '').replace('_PTR_', '*').split('_V_') {
		p.table.add_field(typ, 'var_$i', t, false, '', .public)
	}
	p.cgen.typedefs << 'typedef struct $typ $typ;'
	return typ
}

fn (p mut Parser) rename_generic_fn_instance(f mut Fn, ti TypeInst) {
	if f.is_method {
		f.name = f.receiver_typ + '_' + f.name
	}
	f.name = f.name + '_T'
	for k in ti.inst.keys() {
		f.name = f.name + '_' + type_to_safe_str(ti.inst[k])
	}
}

fn (p mut Parser) dispatch_generic_fn_instance(f mut Fn, ti TypeInst) {
	mut new_inst := true
	for e in f.type_inst {
		if e.inst.str() == ti.inst.str() {
			new_inst = false
			break
		}
	}

	if !new_inst {
		p.rename_generic_fn_instance(mut f, ti)
		_f := p.table.find_fn(f.name) or {
			p.error('function instance `$f.name` not found')
			return
		}
		f.args = _f.args
		f.typ = _f.typ
		f.is_generic = false
		f.type_inst = []TypeInst
		f.dispatch_of = ti
		// println('using existing inst $f.name(${f.str_args(p.table)}) $f.typ')
		return
	}

	f.type_inst << ti
	p.table.register_fn(f)
	// Remember current scanner position, go back here for each type instance
	// TODO remove this once tokens are cached in `new_parser()`
	saved_tok_idx := p.cur_tok_index()
	saved_fn := p.cur_fn
	saved_var_idx := p.var_idx
	saved_local_vars := p.local_vars
	p.clear_vars()
	saved_line := p.cgen.cur_line
	saved_lines := p.cgen.lines
	saved_is_tmp := p.cgen.is_tmp
	saved_tmp_line := p.cgen.tmp_line
	returns := p.returns		// should be always false

	p.rename_generic_fn_instance(mut f, ti)
	f.is_generic = false		// the instance is a normal function
	f.type_inst = []TypeInst
	f.scope_level = 0
	f.dispatch_of = ti

	// TODO this is done to prevent a crash as a result of this not being
	// properly initialised. This is a bug somewhere futher upstream
	f.defer_text = []string

	old_args := f.args
	new_types := p.replace_type_params(f, ti)
	f.args = []Var
	for i in 0..new_types.len-1 {
		mut v := old_args[i]
		v.typ = new_types[i]
		f.args << v
	}
	f.typ = new_types.last()
	if f.typ in f.type_pars { f.typ = '_ANYTYPE_' }

	if f.typ in ti.inst {
		f.typ = ti.inst[f.typ]
	}

	if f.is_method {
		p.add_method(f.args[0].name, f)
	} else {
		p.table.register_fn(f)
	}
	// println("generating gen inst $f.name(${f.str_args(p.table)}) $f.typ : $ti.inst")

	p.cgen.is_tmp = false
	p.returns = false
	p.cgen.tmp_line = ''
	p.cgen.cur_line = ''
	p.cgen.lines = []string
	p.cur_fn = *f
	for arg in f.args {
		p.register_var(arg)
	}
	p.token_idx = f.body_idx-1
	p.next()	// re-initializes the parser properly
	str_args := f.str_args(p.table)

	p.in_dispatch = true
	p.genln('${p.get_linkage_prefix()}$f.typ $f.name($str_args) {')
	// p.genln('/* generic fn instance $f.name : $ti.inst */')
	p.statements()
	p.in_dispatch = false

	if f.typ == '_ANYTYPE_' {
		f.typ = p.cur_fn.typ
		f.name = f.name.replace('_ANYTYPE_', type_to_safe_str(f.typ))
		p.cgen.lines[0] = p.cgen.lines[0].replace('_ANYTYPE_', f.typ)
		p.table.register_fn(f)
	}
	for l in p.cgen.lines {
		p.cgen.fns << l
	}

	p.token_idx = saved_tok_idx-1
	p.next()
	p.check(.rpar)		// end of the arg list which caused this dispatch
	p.cur_fn = saved_fn
	p.var_idx = saved_var_idx
	p.local_vars = saved_local_vars
	p.cgen.lines = saved_lines
	p.cgen.cur_line = saved_line
	p.cgen.is_tmp = saved_is_tmp
	p.cgen.tmp_line = saved_tmp_line
	p.returns = false
}

// "fn (int, string) int"
fn (f &Fn) typ_str() string {
	mut sb := strings.new_builder(50)
	sb.write('fn (')
	for i, arg in f.args {
		sb.write(arg.typ)
		if i < f.args.len - 1 {
			sb.write(',')
		}
	}
	sb.write(')')
	if f.typ != 'void' {
		sb.write(' $f.typ')
	}
	return sb.str()
}

// f.args => "int a, string b"
fn (f &Fn) str_args(table &Table) string {
	mut s := ''
	for i, arg in f.args {
		// Interfaces are a special case. We need to pass the object + pointers
		// to all methods:
		// fn handle(r Runner) { =>
		// void handle(void *r, void (*Runner_run)(void*)) {
		if table.is_interface(arg.typ) {
			// First the object (same name as the interface argument)
			s += ' void* $arg.name'
			// Now  all methods
			interface_type := table.find_type(arg.typ)
			for method in interface_type.methods {
				s += ', $method.typ (*${arg.typ}_${method.name})(void*'
				if method.args.len > 1 {
					for a in method.args[1..] {
						s += ', $a.typ'
					}
				}
				s += ')'
			}
		}
		else if arg.typ.starts_with('varg_') {
			s += '$arg.typ *$arg.name'
		}
		else {
			// s += '$arg.typ $arg.name'
			s += table.cgen_name_type_pair(arg.name, arg.typ)// '$arg.typ $arg.name'
		}
		if i < f.args.len - 1 {
			s += ', '
		}
	}
	return s
}

// find local function variable with closest name to `name`
fn (p &Parser) find_misspelled_local_var(name string, min_match f32) string {
	mut closest := f32(0)
	mut closest_var := ''
	for var in p.local_vars {
		if var.scope_level > p.cur_fn.scope_level {
			continue
		}
		n := name.all_after('.')
		if var.name == '' || (n.len - var.name.len > 2 || var.name.len - n.len > 2) { continue }
		c := strings.dice_coefficient(var.name, n)
		if c > closest {
			closest = c
			closest_var = var.name
		}
	}
	return if closest >= min_match { closest_var } else { '' }
}

fn (fns []Fn) contains(f Fn) bool {
	for ff in fns {
		if ff.name == f.name {
			return true
		}
	}
	return false
}

pub fn (f Fn) v_fn_module() string {
	return f.mod
}

pub fn (f Fn) v_fn_name() string {
	return f.name.replace('${f.mod}__', '')
}