use crate::ast::*;
use crate::lexer::{Token, TokenKind};
use crate::error::RuntimeError;

pub struct Parser {
    tokens: Vec<Token>,
    current: usize,
}

impl Parser {
    pub fn new(tokens: Vec<Token>) -> Self {
        Self { tokens, current: 0 }
    }

    pub fn parse(&mut self) -> Vec<Stmt> {
        let mut statements = Vec::new();

        while !self.is_at_end() {
            statements.push(self.declaration());
        }

        statements
    }

    fn declaration(&mut self) -> Stmt {
        if self.match_kind(&[TokenKind::Let]) {
            self.let_declaration()
        } else if self.match_kind(&[TokenKind::Fn]) {
            self.fn_declaration()
        } else {
            self.statement()
        }
    }

    fn statement(&mut self) -> Stmt {
        if self.match_kind(&[TokenKind::If]) {
            self.if_statement()
        } else if self.match_kind(&[TokenKind::While]) {
            self.while_statement()
        } else if self.match_kind(&[TokenKind::Return]) {
            self.return_statement()
        } else if self.match_kind(&[TokenKind::LeftBrace]) {
            Stmt::Block(self.block())
        } else {
            self.expression_statement()
        }
    }

    fn let_declaration(&mut self) -> Stmt {
        let name = self.consume_ident("Expected variable name.").unwrap();
        self.consume(TokenKind::Equal, "Expected '=' after variable name.").unwrap();
        let initializer = self.expression();
        self.match_kind(&[TokenKind::Semicolon]); // 分号可选

        Stmt::Let { name, initializer }
    }

    fn fn_declaration(&mut self) -> Stmt {
        let name = self.consume_ident("Expected function name.").unwrap();
        self.consume(TokenKind::LeftParen, "Expected '(' after function name.").unwrap();

        let mut params = Vec::new();
        if !self.check(&TokenKind::RightParen) {
            loop {
                params.push(self.consume_ident("Expected parameter name.").unwrap());
                if !self.match_kind(&[TokenKind::Comma]) {
                    break;
                }
            }
        }

        self.consume(TokenKind::RightParen, "Expected ')' after parameters.").unwrap();
        self.consume(TokenKind::LeftBrace, "Expected '{' before function body.").unwrap();
        let body = self.block();

        Stmt::Function { name, params, body }
    }

    fn lambda_expr(&mut self) -> Expr {
        self.consume(TokenKind::LeftParen, "Expected '(' after 'fn'.").unwrap();
        let mut params = Vec::new();
        if !self.check(&TokenKind::RightParen) {
            loop {
                params.push(self.consume_ident("Expected parameter name.").unwrap());
                if !self.match_kind(&[TokenKind::Comma]) {
                    break;
                }
            }
        }
        self.consume(TokenKind::RightParen, "Expected ')' after parameters.").unwrap();
        self.consume(TokenKind::LeftBrace, "Expected '{' before function body.").unwrap();
        let body = self.block();
        Expr::Lambda { params, body }
    }

    fn if_statement(&mut self) -> Stmt {
        self.consume(TokenKind::LeftParen, "Expected '(' after 'if'.").unwrap();
        let condition = self.expression();
        self.consume(TokenKind::RightParen, "Expected ')' after condition.").unwrap();

        let then_branch = Box::new(self.statement());
        let else_branch = if self.match_kind(&[TokenKind::Else]) {
            Some(Box::new(self.statement()))
        } else {
            None
        };

        Stmt::If { condition, then_branch, else_branch }
    }

    fn while_statement(&mut self) -> Stmt {
        self.consume(TokenKind::LeftParen, "Expected '(' after 'while'.").unwrap();
        let condition = self.expression();
        self.consume(TokenKind::RightParen, "Expected ')' after condition.").unwrap();

        let body = Box::new(self.statement());
        Stmt::While { condition, body }
    }

    fn return_statement(&mut self) -> Stmt {
        let value = if !self.check(&TokenKind::Semicolon) && !self.check(&TokenKind::RightBrace) {
            Some(self.expression())
        } else {
            None
        };

        self.match_kind(&[TokenKind::Semicolon]); // 分号可选
        Stmt::Return(value)
    }

    fn block(&mut self) -> Vec<Stmt> {
        let mut statements = Vec::new();

        while !self.check(&TokenKind::RightBrace) && !self.is_at_end() {
            statements.push(self.declaration());
        }

        self.consume(TokenKind::RightBrace, "Expected '}' after block.").unwrap();
        statements
    }

    fn expression_statement(&mut self) -> Stmt {
        let expr = self.expression();
        self.match_kind(&[TokenKind::Semicolon]); // 分号可选
        Stmt::ExprStmt(expr)
    }

    fn expression(&mut self) -> Expr {
        self.assignment()
    }

    fn assignment(&mut self) -> Expr {
        let expr = self.logical_or();

        if self.match_kind(&[TokenKind::Equal]) {
            let value = self.assignment();
            return match expr {
                Expr::Variable(name) => Expr::Assign { name, value: Box::new(value) },
                Expr::Get { object, name } => Expr::Set { object, name, value: Box::new(value) },
                _ => panic!("Invalid assignment target."),
            };
        }

        expr
    }

    fn logical_or(&mut self) -> Expr {
        let mut expr = self.logical_and();

        while self.match_kind(&[TokenKind::OrOr]) {
            let right = self.logical_and();
            expr = Expr::Logical {
                left: Box::new(expr),
                op: LogicalOp::Or,
                right: Box::new(right),
            };
        }

        expr
    }

    fn logical_and(&mut self) -> Expr {
        let mut expr = self.equality();

        while self.match_kind(&[TokenKind::AndAnd]) {
            let right = self.equality();
            expr = Expr::Logical {
                left: Box::new(expr),
                op: LogicalOp::And,
                right: Box::new(right),
            };
        }

        expr
    }

    fn equality(&mut self) -> Expr {
        let mut expr = self.comparison();

        while self.match_kind(&[TokenKind::EqualEqual, TokenKind::BangEqual]) {
            let op = match self.previous().kind {
                TokenKind::EqualEqual => BinaryOp::Equal,
                TokenKind::BangEqual => BinaryOp::NotEqual,
                _ => unreachable!(),
            };
            let right = self.comparison();
            expr = Expr::Binary {
                left: Box::new(expr),
                op,
                right: Box::new(right),
            };
        }

        expr
    }

    fn comparison(&mut self) -> Expr {
        let mut expr = self.term();

        while self.match_kind(&[TokenKind::Greater, TokenKind::GreaterEqual, TokenKind::Less, TokenKind::LessEqual]) {
            let op = match self.previous().kind {
                TokenKind::Greater => BinaryOp::Greater,
                TokenKind::GreaterEqual => BinaryOp::GreaterEqual,
                TokenKind::Less => BinaryOp::Less,
                TokenKind::LessEqual => BinaryOp::LessEqual,
                _ => unreachable!(),
            };
            let right = self.term();
            expr = Expr::Binary {
                left: Box::new(expr),
                op,
                right: Box::new(right),
            };
        }

        expr
    }

    fn term(&mut self) -> Expr {
        let mut expr = self.factor();

        while self.match_kind(&[TokenKind::Plus, TokenKind::Minus]) {
            let op = match self.previous().kind {
                TokenKind::Plus => BinaryOp::Add,
                TokenKind::Minus => BinaryOp::Sub,
                _ => unreachable!(),
            };
            let right = self.factor();
            expr = Expr::Binary {
                left: Box::new(expr),
                op,
                right: Box::new(right),
            };
        }

        expr
    }

    fn factor(&mut self) -> Expr {
        let mut expr = self.unary();

        while self.match_kind(&[TokenKind::Star, TokenKind::Slash]) {
            let op = match self.previous().kind {
                TokenKind::Star => BinaryOp::Mul,
                TokenKind::Slash => BinaryOp::Div,
                _ => unreachable!(),
            };
            let right = self.unary();
            expr = Expr::Binary {
                left: Box::new(expr),
                op,
                right: Box::new(right),
            };
        }

        expr
    }

    fn unary(&mut self) -> Expr {
        if self.match_kind(&[TokenKind::Bang, TokenKind::Minus]) {
            let op = match self.previous().kind {
                TokenKind::Bang => UnaryOp::Not,
                TokenKind::Minus => UnaryOp::Negate,
                _ => unreachable!(),
            };
            let right = self.unary();
            return Expr::Unary {
                op,
                right: Box::new(right),
            };
        }

        self.call()
    }

    fn call(&mut self) -> Expr {
        let mut expr = self.primary();

        loop {
            if self.match_kind(&[TokenKind::LeftParen]) {
                let mut arguments = Vec::new();
                if !self.check(&TokenKind::RightParen) {
                    loop {
                        arguments.push(self.expression());
                        if !self.match_kind(&[TokenKind::Comma]) {
                            break;
                        }
                    }
                }
                self.consume(TokenKind::RightParen, "Expected ')' after arguments.").unwrap();
                expr = Expr::Call {
                    callee: Box::new(expr),
                    arguments,
                };
            } else if self.match_kind(&[TokenKind::Dot]) {
                let name = self.consume_ident("Expected property name after '.'.").unwrap();
                expr = Expr::Get {
                    object: Box::new(expr),
                    name,
                };
            } else {
                break;
            }
        }

        expr
    }

    fn primary(&mut self) -> Expr {
        // 布尔值
        if self.match_kind(&[TokenKind::True]) {
            return Expr::Literal(Literal::Bool(true));
        }
        if self.match_kind(&[TokenKind::False]) {
            return Expr::Literal(Literal::Bool(false));
        }
        if self.match_kind(&[TokenKind::Nil]) {
            return Expr::Literal(Literal::Nil);
        }

        // 数字
        if let TokenKind::Number(n) = self.peek().kind {
            self.advance();
            return Expr::Literal(Literal::Number(n));
        }

        // 字符串
        if let TokenKind::String(s) = &self.peek().kind {
            let s = s.clone();
            self.advance();
            return Expr::Literal(Literal::String(s));
        }

        // 标识符（变量）
        if let TokenKind::Identifier(name) = &self.peek().kind {
            let name = name.clone();
            self.advance();
            return Expr::Variable(name);
        }

        // 匿名函数（闭包）: fn(params) { body }
        if self.match_kind(&[TokenKind::Fn]) {
            return self.lambda_expr();
        }

        // 括号表达式
        if self.match_kind(&[TokenKind::LeftParen]) {
            let expr = self.expression();
            self.consume(TokenKind::RightParen, "Expected ')' after expression.").unwrap();
            return expr;
        }

        if self.match_kind(&[TokenKind::LeftBrace]) {
            return self.object_literal();
        }

        panic!("Expected expression at line {}", self.peek().line);
    }

    fn match_kind(&mut self, kinds: &[TokenKind]) -> bool {
        for kind in kinds {
            if self.check(kind) {
                self.advance();
                return true;
            }
        }
        false
    }

    fn consume(&mut self, kind: TokenKind, msg: &str) -> Result<(), RuntimeError> {
        if self.check(&kind) {
            self.advance();
            Ok(())
        } else {
            Err(RuntimeError::ParseError {
                message: msg.to_string(),
                token: self.peek().clone(),
            })
        }
    }

    fn consume_ident(&mut self, msg: &str) -> Result<String, RuntimeError> {
        match &self.peek().kind {
            TokenKind::Identifier(name) => {
                let name = name.clone();
                self.advance();
                Ok(name)
            }
            _ => Err(RuntimeError::ParseError {
                message: msg.to_string(),
                token: self.peek().clone(),
            }),
        }
    }

    fn check(&self, kind: &TokenKind) -> bool {
        if self.is_at_end() {
            return false;
        }
        std::mem::discriminant(&self.peek().kind)
            == std::mem::discriminant(kind)
    }

    fn advance(&mut self) -> &Token {
        if !self.is_at_end() {
            self.current += 1;
        }
        self.previous()
    }

    fn is_at_end(&self) -> bool {
        matches!(self.peek().kind, TokenKind::EOF)
    }

    fn peek(&self) -> &Token {
        &self.tokens[self.current]
    }

    fn previous(&self) -> &Token {
        &self.tokens[self.current - 1]
    }

    fn object_literal(&mut self) -> Expr {
        let mut properties = Vec::new();
        if !self.check(&TokenKind::RightBrace) {
            loop {
                let name = self.consume_ident("Expected property name in object literal").unwrap();
                self.consume(TokenKind::Colon, "Expected ':' after property name in object literal").unwrap();
                let value = self.expression();
                properties.push((name, value));
                if !self.match_kind(&[TokenKind::Comma]) {
                    break;
                }
            }
        }
        self.consume(TokenKind::RightBrace, "Expected '}' after object literal").unwrap();
        Expr::ObjectLiteral { properties }
    }
}