package parser

import (
	"fmt"

	"gointerpreter/ast"
	"gointerpreter/lexer"
	"gointerpreter/token"
)

type Parser struct {
	l      *lexer.Lexer
	errors []string

	currToken token.Token
	peekToken token.Token
}

func New(l *lexer.Lexer) *Parser {
	p := &Parser{
		l:      l,
		errors: []string{},
	}

	p.nextToken()
	p.nextToken()

	return p
}

func (p *Parser) nextToken() {
	p.currToken = p.peekToken
	p.peekToken = p.l.NextToken()
}

func (p *Parser) ParseProgram() *ast.Program {
	program := &ast.Program{
		Statements: []ast.Statement{},
	}

	for p.currToken.Type != token.EOF {
		statement := p.parseStatement()
		if statement != nil {
			program.Statements = append(program.Statements, statement)
		}

		p.nextToken()
	}

	return program
}

func (p *Parser) parseStatement() ast.Statement {
	switch p.currToken.Type {
	case token.LET:
		return p.parseLetStatement()
	case token.RETURN:
		return p.parseReturnStatement()
	default:
		return nil
	}
}

func (p *Parser) parseReturnStatement() *ast.ReturnStatement {
	stmt := &ast.ReturnStatement{Token: p.currToken}

	p.nextToken()

	for !p.currTokenIs(token.SEMICOLON) {
		p.nextToken()
	}

	return stmt
}

func (p *Parser) parseLetStatement() *ast.LetStatement {
	stmt := &ast.LetStatement{Token: p.currToken}

	if !p.expectPeek(token.IDENT) {
		return nil
	}

	stmt.Name = &ast.Identifier{Token: p.currToken, Value: p.currToken.Literal}

	if !p.expectPeek(token.ASSIGN) {
		return nil
	}

	for !p.currTokenIs(token.SEMICOLON) {
		p.nextToken()
	}

	return stmt
}

func (p *Parser) currTokenIs(t token.TokenType) bool {
	return p.currToken.Type == t
}

func (p *Parser) peekTokenIs(t token.TokenType) bool {
	return p.peekToken.Type == t
}

func (p *Parser) expectPeek(t token.TokenType) bool {
	if p.peekTokenIs(t) {
		p.nextToken()
		return true
	}

	p.peekError(t)
	return false
}

func (p *Parser) Errors() []string {
	return p.errors
}

func (p *Parser) peekError(t token.TokenType) {
	msg := fmt.Sprintf("expected next token to be [%s], got [%s] instead", t, p.peekToken.Type)
	p.errors = append(p.errors, msg)
}