// 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 parser

import (
	v.scanner
	v.ast
	v.token
	v.table
	v.types
	term
	os
)

struct Parser {
	scanner     &scanner.Scanner
	file_name   string
mut:
	tok         token.Token
	peek_tok    token.Token
	// vars []string
	table       &table.Table
	return_type types.Type
}

pub fn parse_stmt(text string, table &table.Table) ast.Stmt {
	s := scanner.new_scanner(text)
	mut p := Parser{
		scanner: s
		table: table
	}
	p.read_first_token()
	return p.stmt()
}

pub fn parse_file(path string, table &table.Table) ast.File {
	println('parse file "$path"')
	text := os.read_file(path) or {
		panic(err)
	}
	mut stmts := []ast.Stmt
	mut p := Parser{
		scanner: scanner.new_scanner(text)
		table: table
		file_name: path
	}
	p.read_first_token()
	for {
		// res := s.scan()
		if p.tok.kind == .eof {
			break
		}
		// println('expr at ' + p.tok.str())
		s := p.stmt()
		// println(s)
		stmts << s // p.stmt()
	}
	p.check_fn_calls()
	// println('nr stmts = $stmts.len')
	// println(stmts[0])
	return ast.File{
		stmts: stmts
	}
}

pub fn parse_files(paths []string, table &table.Table) []ast.File {
	mut files := []ast.File
	for path in paths {
		files << parse_file(path, table)
	}
	return files
}

// former get_type()
pub fn (p mut Parser) parse_type() types.Type {
	typ := p.table.types[p.tok.lit]
	if isnil(typ.name.str) || typ.name == '' {
		p.error('undefined type `$p.tok.lit`')
	}
	p.next()
	return typ
}

pub fn (p mut Parser) read_first_token() {
	// need to call next() twice to get peek token and current token
	p.next()
	p.next()
}

pub fn (p mut Parser) parse_block() []ast.Stmt {
	p.check(.lcbr)
	mut stmts := []ast.Stmt
	for {
		// res := s.scan()
		if p.tok.kind in [.eof, .rcbr] {
			break
		}
		// println('expr at ' + p.tok.str())
		stmts << p.stmt()
	}
	p.check(.rcbr)
	// println('nr exprs in block = $exprs.len')
	return stmts
}

fn (p mut Parser) next() {
	p.tok = p.peek_tok
	p.peek_tok = p.scanner.scan()
	// println(p.tok.str())
}

fn (p mut Parser) check(expected token.Kind) {
	if p.tok.kind != expected {
		s := 'syntax error: unexpected `${p.tok.kind.str()}`, expecting `${expected.str()}`'
		p.error(s)
	}
	p.next()
}

fn (p mut Parser) check_name() string {
	name := p.tok.lit
	p.check(.name)
	return name
}

pub fn (p mut Parser) stmt() ast.Stmt {
	// println('stmt at ' + p.tok.str())
	// `x := ...`
	if p.tok.kind == .name {
		if p.peek_tok.kind == .decl_assign {
			return p.var_decl()
		}
		else if p.peek_tok.is_assign() {
			return p.assign_stmt()
		}
	}
	match p.tok.kind {
		.key_module {
			return p.module_decl()
		}
		.key_import {
			return p.import_stmt()
		}
		.key_pub {
			match p.peek_tok.kind {
				.key_fn {
					return p.fn_decl()
				}
				.key_struct, .key_union, .key_interface {
					return p.struct_decl()
				}
				else {
					p.error('wrong pub keyword usage')
					return ast.Stmt{}
				}
	}
			// .key_const {
			// return p.const_decl()
			// }
			// .key_enum {
			// return p.enum_decl()
			// }
			// .key_type {
			// return p.type_decl()
			// }
		}
		.key_fn {
			return p.fn_decl()
		}
		.key_struct {
			return p.struct_decl()
		}
		.key_return {
			return p.return_stmt()
		}
		.key_mut {
			return p.var_decl()
		}
		.key_for {
			return p.for_statement()
		}
		else {
			expr,_ := p.expr(0)
			return ast.ExprStmt{
				expr: expr
			}
		}
	}
}

pub fn (p mut Parser) assign_stmt() ast.AssignStmt {
	name := p.tok.lit
	// println('looking for $name')
	var := p.table.find_var(name) or {
		p.error('unknown variable `$name`')
		exit(1)
	}
	if !var.is_mut {
		p.error('`$var.name` is immutable, declare it with `mut $var.name := ...`')
	}
	left_expr,left_type := p.expr(0)
	op := p.tok.kind
	// println('assignn_stmt() ' + op.str())
	p.next()
	right_expr,right_type := p.expr(0)
	if !types.check(left_type, right_type) {
		p.error('oops')
	}
	return ast.AssignStmt{
		left: left_expr
		right: right_expr
		op: op
	}
}

pub fn (p &Parser) error(s string) {
	println(term.bold(term.red('$p.file_name:$p.tok.line_nr: $s')))
	exit(1)
}

pub fn (p &Parser) error_at_line(s string, line_nr int) {
	println(term.bold(term.red('$p.file_name:$line_nr: $s')))
	exit(1)
}

pub fn (p &Parser) warn(s string) {
	println(term.blue('x.v:$p.tok.line_nr: $s'))
}

// Implementation of Pratt Precedence
pub fn (p mut Parser) expr(rbp int) (ast.Expr,types.Type) {
	// println('expr at ' + p.tok.str())
	// null denotation (prefix)
	mut node := ast.Expr{}
	mut typ := types.void_type
	match p.tok.kind {
		.name {
			/*
			sym := p.table.find_symbol(p.tok.lit)
			if sym.cat == .function {
				return
			}
			*/

			// fn call
			if p.peek_tok.kind == .lpar {
				x,typ2 := p.call_expr() // TODO `node,typ :=` should work
				node = x
				typ = typ2
			}
			// struct init
			else if p.peek_tok.kind == .lcbr {
				typ = p.parse_type()
				// println('sturct init typ=$typ.name')
				p.check(.lcbr)
				mut field_names := []string
				mut exprs := []ast.Expr
				for p.tok.kind != .rcbr {
					field_name := p.check_name()
					field_names << field_name
					p.check(.colon)
					// expr,field_type := p.expr(0)
					expr,_ := p.expr(0)
					// if !types.check(   ,field_type
					exprs << expr
				}
				node = ast.StructInit{
					typ: typ
					exprs: exprs
					fields: field_names
				}
				p.check(.rcbr)
			}
			else {
				// name expr
				node = ast.Ident{
					name: p.tok.lit
				}
				var := p.table.find_var(p.tok.lit) or {
					p.error('unknown variable `$p.tok.lit`')
					exit(0)
				}
				typ = var.typ
				// ///typ = types.int_type
				p.next()
			}
		}
		.lsbr {
			node,typ = p.array_init()
		}
		.key_true, .key_false {
			node = ast.BoolLiteral{
				val: p.tok.kind == .key_true
			}
			typ = types.bool_type
			p.next()
		}
		.str {
			node,typ = p.parse_string_literal()
		}
		.number {
			node,typ = p.parse_number_literal()
		}
		.key_if {
			node,typ = p.if_expr()
		}
		.lpar {
			p.check(.lpar)
			p.next()
			node,typ = p.expr(token.lowest_prec)
			p.check(.rpar)
		}
		else {
			if p.tok.is_unary() {
				pt := p.tok
				p.next()
				expr,t2 := p.expr(token.lowest_prec)
				node = ast.UnaryExpr{
					left: expr
					op: pt.kind
				}
				typ = t2
			}
			else {
				p.error('!unknown token ' + p.tok.str())
			}
		}
	}
	// left binding power
	for rbp < p.tok.precedence() {
		prev_tok := p.tok
		p.next()
		mut t2 := types.Type{}
		// left denotation (infix / postfix)
		if prev_tok.is_right_assoc() {
			mut expr := ast.Expr{}
			expr,t2 = p.expr(prev_tok.precedence() - 1)
			node = ast.BinaryExpr{
				left: node
				op: prev_tok.kind
				right: expr
			}
			// println(t2.name + 'OOO')
			if !types.check(&typ, &t2) {
				println('tok: $prev_tok.str()')
				p.error('cannot convert `$t2.name` to `$typ.name`')
			}
		}
		else if prev_tok.is_left_assoc() {
			// postfix (`++` | `--`)
			if prev_tok.kind in [.inc, .dec] {
				node = ast.UnaryExpr{
					left: node
					op: prev_tok.kind
				}
			}
			else {
				mut expr := ast.Expr{}
				expr,t2 = p.expr(prev_tok.precedence() - 1)
				if prev_tok.is_relational() {
					typ = types.bool_type
				}
				else {
					typ = t2
				}
				// println(t2.name + '222')
				node = ast.BinaryExpr{
					left: node
					op: prev_tok.kind
					right: expr
				}
			}
		}
	}
	return node,typ
}

fn (p mut Parser) for_statement() ast.ForStmt {
	p.check(.key_for)
	// `for i in start .. end`
	if p.peek_tok.kind == .key_in {
		var := p.check_name()
		p.check(.key_in)
		start := p.tok.lit.int()
		p.check(.number)
		p.check(.dotdot)
		end := p.tok.lit.int()
		// println('for start=$start $end')
		p.check(.number)
		stmts := p.parse_block()
		// println('nr stmts=$stmts.len')
		return ast.ForStmt{
			stmts: stmts
			is_in: true
		}
	}
	// `for cond {`
	cond,typ := p.expr(0)
	if !types.check(types.bool_type, typ) {
		p.error('non-bool used as for condition')
	}
	stmts := p.parse_block()
	return ast.ForStmt{
		cond: cond
		stmts: stmts
	}
}

fn (p mut Parser) if_expr() (ast.Expr,types.Type) {
	mut node := ast.Expr{}
	p.check(.key_if)
	cond,typ := p.expr(0)
	if !types.check(types.bool_type, typ) {
		p.error('non-bool used as if condition')
	}
	stmts := p.parse_block()
	mut else_stmts := []ast.Stmt
	if p.tok.kind == .key_else {
		println('GOT ELSE')
		p.check(.key_else)
		else_stmts = p.parse_block()
	}
	node = ast.IfExpr{
		cond: cond
		stmts: stmts
		else_stmts: else_stmts
	}
	return node,types.void_type
}

fn (p mut Parser) parse_string_literal() (ast.Expr,types.Type) {
	mut node := ast.Expr{}
	node = ast.StringLiteral{
		val: p.tok.lit
	}
	p.next()
	return node,types.string_type
}

fn (p mut Parser) array_init() (ast.Expr,types.Type) {
	p.check(.lsbr)
	mut val_type := types.void_type
	mut exprs := []ast.Expr
	mut i := 0
	for p.tok.kind != .rsbr {
		expr,typ := p.expr(0)
		// The first element's type
		if i == 0 {
			val_type = typ
		}
		else if !types.check(val_type, typ) {
			p.error('expected array element with type `$val_type.name`')
		}
		exprs << expr
		i++
		if p.tok.kind == .comma {
			p.check(.comma)
		}
	}
	mut node := ast.Expr{}
	node = ast.ArrayInit{
		typ: val_type
		exprs: exprs
	}
	p.check(.rsbr)
	return node,val_type
}

fn (p mut Parser) parse_number_literal() (ast.Expr,types.Type) {
	lit := p.tok.lit
	mut node := ast.Expr{}
	mut typ := types.int_type
	if lit.contains('.') {
		node = ast.FloatLiteral{
			// val: lit.f64()
			val: lit
		}
		typ = types.f64_type
	}
	else {
		node = ast.IntegerLiteral{
			val: lit.int()
		}
		typ = types.int_type
	}
	p.next()
	return node,typ
}

fn (p mut Parser) module_decl() ast.Module {
	p.check(.key_module)
	p.next()
	return ast.Module{}
}

fn (p mut Parser) import_stmt() ast.Import {
	p.check(.key_import)
	name := p.check_name()
	return ast.Import{
		mods: [name]
	}
}

fn (p mut Parser) struct_decl() ast.StructDecl {
	is_pub := p.tok.kind == .key_pub
	if is_pub {
		p.next()
	}
	p.check(.key_struct)
	name := p.check_name()
	p.check(.lcbr)
	mut fields := []ast.Field
	for p.tok.kind != .rcbr {
		if p.tok.kind == .key_pub {
			p.check(.key_pub)
			p.check(.colon)
		}
		field_name := p.check_name()
		typ := p.parse_type()
		fields << ast.Field{
			name: field_name
			typ: typ
		}
	}
	p.check(.rcbr)
	p.table.register_type(types.Type{
		name: name
	})
	return ast.StructDecl{
		name: name
		is_pub: is_pub
		fields: fields
	}
}

fn (p mut Parser) return_stmt() ast.Return {
	p.next()
	expr,t := p.expr(0)
	if !types.check(p.return_type, t) {
		p.error('cannot use `$t.name` as type `$p.return_type.name` in return argument')
	}
	return ast.Return{
		expr: expr
	}
}

fn (p mut Parser) var_decl() ast.VarDecl {
	is_mut := p.tok.kind == .key_mut // || p.prev_tok == .key_for
	// is_static := p.tok.kind == .key_static
	if p.tok.kind == .key_mut {
		p.check(.key_mut)
		// p.fspace()
	}
	if p.tok.kind == .key_static {
		p.check(.key_static)
		// p.fspace()
	}
	name := p.tok.lit
	p.read_first_token()
	expr,t := p.expr(token.lowest_prec)
	if _ := p.table.find_var(name) {
		p.error('redefinition of `$name`')
	}
	p.table.register_var(table.Var{
		name: name
		typ: t
		is_mut: is_mut
	})
	// println(p.table.names)
	// println('added $name')
	return ast.VarDecl{
		name: name
		expr: expr // p.expr(token.lowest_prec)
		
		typ: t
	}
}

fn verror(s string) {
	println(s)
	exit(1)
}