const std = @import("std");
const Loc = @import("loc.zig").Loc;
const BlockStmt = @import("stmt.zig").BlockStmt;
const Pat = @import("pat.zig").Pat;
const Regex = @import("lit.zig").Regex;
const Parser = @import("../parser.zig").Parser;
const Formatter = @import("../formatter.zig").Formatter;
const ParseError = @import("../parser.zig").ParseError;
const BP = @import("../parser.zig").BP;

pub const ExprType = union(enum) {
    identifier: []const u8,
    this: void,
    super: void,
    null: void,
    bool: bool,
    number: f64,
    string: []const u8,
    regex: Regex,
    array: ArrayExpr,
    object: ObjectExpr,
    func: FnExpr,
    arrow: ArrowFn,
    class: ClassExpr,
    template: TemplateLit,
    tagged_template: TaggedTemplate,
    member: MemberExpr,
    computed_member: ComputedMember,
    call: CallExpr,
    new: NewExpr,
    chain: ChainExpr,
    unary: UnaryExpr,
    binary: BinaryExpr,
    update: UpdateExpr,
    conditional: IfExpr,
    assign: AssignExpr,
    sequence: SeqExpr,
    spread: SpreadElem,
    yield: YieldExpr,
    await: AwaitExpr,
    meta_prop: MetaProp,
    parenthesized: *const Expr,
    private_ident: []const u8,
};

pub const Expr = struct {
    loc: Loc,
    data: ExprType,

    pub fn parse(p: *Parser, min_bp: u32) ParseError!*const Expr {
        var left = try p.parsePrimaryExpr();

        while (true) {
            const cur_bp = p.bp(p.peek());
            if (cur_bp <= min_bp) break;

            switch (p.peek()) {
                .@"=",
                .@"+=",
                .@"-=",
                .@"*=",
                .@"/=",
                .@"%=",
                .@"**=",
                .@"<<=",
                .@">>=",
                .@">>>=",
                .@"&=",
                .@"|=",
                .@"^=",
                .@"&&=",
                .@"||=",
                .@"??=",
                => {
                    p.advance();
                    const op = p.assignOpFromToken();
                    const right = try Expr.parse(p, BP.assign);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .assign = .{ .loc = loc, .op = op, .left = left, .right = right } }, loc);
                },

                .@"?" => {
                    p.advance();
                    const consequent = try Expr.parse(p, 0);
                    try p.expect(.@":");
                    const alternate = try Expr.parse(p, BP.conditional);
                    const loc: Loc = .{ .start = left.loc.start, .end = alternate.loc.end };
                    left = p.arena.exprPtr(.{ .conditional = .{ .loc = loc, .condition = left, .consequent = consequent, .alternate = alternate } }, loc);
                },

                .@"??" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.coalesce);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"??", .left = left, .right = right } }, loc);
                },

                .@"||" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.log_or);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"||", .left = left, .right = right } }, loc);
                },

                .@"&&" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.log_and);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"&&", .left = left, .right = right } }, loc);
                },

                .@"|" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.bit_or);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"|", .left = left, .right = right } }, loc);
                },

                .@"^" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.bit_xor);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"^", .left = left, .right = right } }, loc);
                },

                .@"&" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.bit_and);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"&", .left = left, .right = right } }, loc);
                },

                .@"==" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.equality);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"==", .left = left, .right = right } }, loc);
                },

                .@"!=" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.equality);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"!=", .left = left, .right = right } }, loc);
                },

                .@"===" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.equality);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"===", .left = left, .right = right } }, loc);
                },

                .@"!==" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.equality);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"!==", .left = left, .right = right } }, loc);
                },

                .@"<" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.relational);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"<", .left = left, .right = right } }, loc);
                },

                .@">" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.relational);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@">", .left = left, .right = right } }, loc);
                },

                .@"<=" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.relational);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"<=", .left = left, .right = right } }, loc);
                },

                .@">=" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.relational);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@">=", .left = left, .right = right } }, loc);
                },

                .in => {
                    p.advance();
                    const right = try Expr.parse(p, BP.relational);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .in, .left = left, .right = right } }, loc);
                },

                .instanceof => {
                    p.advance();
                    const right = try Expr.parse(p, BP.relational);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .instanceof, .left = left, .right = right } }, loc);
                },

                .@"<<" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.shift);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"<<", .left = left, .right = right } }, loc);
                },

                .@">>" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.shift);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@">>", .left = left, .right = right } }, loc);
                },

                .@">>>" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.shift);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@">>>", .left = left, .right = right } }, loc);
                },

                .@"+" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.additive);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"+", .left = left, .right = right } }, loc);
                },

                .@"-" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.additive);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"-", .left = left, .right = right } }, loc);
                },

                .@"*" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.multiplicative);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"*", .left = left, .right = right } }, loc);
                },

                .@"/" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.multiplicative);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"/", .left = left, .right = right } }, loc);
                },

                .@"%" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.multiplicative);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"%", .left = left, .right = right } }, loc);
                },

                .@"**" => {
                    p.advance();
                    const right = try Expr.parse(p, BP.exponentiation - 1);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    left = p.arena.exprPtr(.{ .binary = .{ .loc = loc, .op = .@"**", .left = left, .right = right } }, loc);
                },

                .lparen => {
                    p.advance();
                    var args: [256]Expr = undefined;
                    var arg_count: usize = 0;

                    if (p.peek() != .rparen) {
                        while (true) {
                            if (p.peek() == .@"...") {
                                p.advance();
                                const arg = try Expr.parse(p, 0);
                                args[arg_count] = Expr{ .loc = arg.loc, .data = .{ .spread = .{ .loc = arg.loc, .arg = p.arena.exprPtr(arg.data, arg.loc) } } };
                                arg_count += 1;
                            } else {
                                const arg = try Expr.parse(p, 0);
                                args[arg_count] = arg.*;
                                arg_count += 1;
                            }
                            if (!p.match(.comma)) break;
                        }
                    }

                    try p.expect(.rparen);
                    const loc: Loc = .{ .start = left.loc.start, .end = p.tok().loc.start };
                    left = p.arena.exprPtr(.{ .call = .{ .loc = loc, .callee = left, .args = args[0..arg_count], .optional = false } }, loc);
                },

                .@"?." => {
                    p.advance();
                    if (p.peek() == .lparen) {
                        p.advance();
                        var args: [256]Expr = undefined;
                        var arg_count: usize = 0;
                        if (p.peek() != .rparen) {
                            while (true) {
                                const arg = try Expr.parse(p, 0);
                                args[arg_count] = arg.*;
                                arg_count += 1;
                                if (!p.match(.comma)) break;
                            }
                        }
                        try p.expect(.rparen);
                        const loc: Loc = .{ .start = left.loc.start, .end = p.tok().loc.start };
                        left = p.arena.exprPtr(.{ .call = .{ .loc = loc, .callee = left, .args = args[0..arg_count], .optional = true } }, loc);
                    } else if (p.peek() == .lbracket) {
                        p.advance();
                        const expr = try Expr.parse(p, 0);
                        try p.expect(.rbracket);
                        const loc: Loc = .{ .start = left.loc.start, .end = p.tok().loc.start };
                        left = p.arena.exprPtr(.{ .computed_member = .{ .loc = loc, .obj = left, .expr = expr } }, loc);
                    } else if (p.peek() == .identifier or p.peek().isKeyword()) {
                        const prop_tok = p.advanceTok();
                        const prop = p.tokenSlice(prop_tok);
                        const loc: Loc = .{ .start = left.loc.start, .end = prop_tok.loc.end };
                        left = p.arena.exprPtr(.{ .member = .{ .loc = loc, .obj = left, .prop = .{ .ident = prop } } }, loc);
                    } else if (p.peek() == .private_identifier) {
                        const prop_tok = p.advanceTok();
                        const prop = p.tokenSlice(prop_tok);
                        const loc: Loc = .{ .start = left.loc.start, .end = prop_tok.loc.end };
                        left = p.arena.exprPtr(.{ .member = .{ .loc = loc, .obj = left, .prop = .{ .private = prop } } }, loc);
                    }
                },

                .lbracket => {
                    p.advance();
                    const expr = try Expr.parse(p, 0);
                    try p.expect(.rbracket);
                    const loc: Loc = .{ .start = left.loc.start, .end = p.tok().loc.start };
                    left = p.arena.exprPtr(.{ .computed_member = .{ .loc = loc, .obj = left, .expr = expr } }, loc);
                },

                .@"." => {
                    p.advance();
                    if (p.peek() == .private_identifier) {
                        const prop_tok = p.advanceTok();
                        const prop = p.tokenSlice(prop_tok);
                        const loc: Loc = .{ .start = left.loc.start, .end = prop_tok.loc.end };
                        left = p.arena.exprPtr(.{ .member = .{ .loc = loc, .obj = left, .prop = .{ .private = prop } } }, loc);
                    } else {
                        const prop_tok = try p.expectTok(.identifier);
                        const prop = p.tokenSlice(prop_tok);
                        const loc: Loc = .{ .start = left.loc.start, .end = prop_tok.loc.end };
                        left = p.arena.exprPtr(.{ .member = .{ .loc = loc, .obj = left, .prop = .{ .ident = prop } } }, loc);
                    }
                },

                .template_head, .no_sub_template => {
                    const template = try TemplateLit.parse(p);
                    const loc: Loc = .{ .start = left.loc.start, .end = template.loc.end };
                    left = p.arena.exprPtr(.{ .tagged_template = .{ .loc = loc, .tag = left, .quasi = template } }, loc);
                },

                .@"++" => {
                    if (!p.isLineTerminatorBeforeNext()) {
                        p.advance();
                        const loc: Loc = .{ .start = left.loc.start, .end = left.loc.end + 2 };
                        left = p.arena.exprPtr(.{ .update = .{ .loc = loc, .op = .@"++", .arg = left, .prefix = false } }, loc);
                    } else break;
                },

                .@"--" => {
                    if (!p.isLineTerminatorBeforeNext()) {
                        p.advance();
                        const loc: Loc = .{ .start = left.loc.start, .end = left.loc.end + 2 };
                        left = p.arena.exprPtr(.{ .update = .{ .loc = loc, .op = .@"--", .arg = left, .prefix = false } }, loc);
                    } else break;
                },

                .comma => {
                    p.advance();
                    const right = try Expr.parse(p, BP.comma);
                    const loc: Loc = .{ .start = left.loc.start, .end = right.loc.end };
                    var exprs: [2]Expr = .{ left.*, right.* };
                    left = p.arena.exprPtr(.{ .sequence = .{ .loc = loc, .exprs = &exprs } }, loc);
                },

                else => break,
            }
        }

        return left;
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        switch (self.data) {
            .identifier => |name| f.write(name),
            .this => f.write("this"),
            .super => f.write("super"),
            .null => f.write("null"),
            .bool => |b| f.write(if (b) "true" else "false"),
            .number => |n| {
                var buf: [64]u8 = undefined;
                f.write(std.fmt.bufPrint(&buf, "{d}", .{n}) catch "0");
            },
            .string => |s| {
                f.writeChar('"');
                f.write(s);
                f.writeChar('"');
            },
            .regex => |r| {
                f.writeChar('/');
                f.write(r.pattern);
                f.writeChar('/');
                f.write(r.flags);
            },
            .array => |a| a.fmt(f),
            .object => |o| o.fmt(f),
            .func => |fn_expr| fn_expr.fmt(f),
            .arrow => |arrow| arrow.fmt(f),
            .class => |c| c.fmt(f),
            .template => |t| t.fmt(f),
            .tagged_template => |tt| tt.fmt(f),
            .member => |m| m.fmt(f),
            .computed_member => |cm| cm.fmt(f),
            .call => |call| call.fmt(f),
            .new => |n| {
                f.write("new ");
                n.callee.*.fmt(f);
                f.writeChar('(');
                for (n.args, 0..) |a, i| {
                    if (i > 0) f.write(", ");
                    a.fmt(f);
                }
                f.writeChar(')');
            },
            .chain => |c| c.expr.*.fmt(f),
            .unary => |u| {
                if (u.prefix) {
                    f.write(@tagName(u.op));
                    u.arg.*.fmt(f);
                } else {
                    u.arg.*.fmt(f);
                    f.write(@tagName(u.op));
                }
            },
            .binary => |b| {
                f.writeChar('(');
                b.left.*.fmt(f);
                f.writeSpace();
                f.write(@tagName(b.op));
                f.writeSpace();
                b.right.*.fmt(f);
                f.writeChar(')');
            },
            .update => |u| {
                const s = if (u.op == .@"++") "++" else "--";
                if (u.prefix) {
                    f.write(s);
                    u.arg.*.fmt(f);
                } else {
                    u.arg.*.fmt(f);
                    f.write(s);
                }
            },
            .conditional => |c| {
                c.condition.*.fmt(f);
                f.write(" ? ");
                c.consequent.*.fmt(f);
                f.write(" : ");
                c.alternate.*.fmt(f);
            },
            .assign => |a| {
                a.left.*.fmt(f);
                f.writeSpace();
                f.write(@tagName(a.op));
                f.writeSpace();
                a.right.*.fmt(f);
            },
            .sequence => |s| {
                for (s.exprs, 0..) |e, i| {
                    if (i > 0) f.write(", ");
                    e.fmt(f);
                }
            },
            .spread => |s| {
                f.write("...");
                s.arg.*.fmt(f);
            },
            .yield => |y| {
                f.write("yield");
                if (y.delegate) f.write("*");
                if (y.arg) |a| {
                    f.writeSpace();
                    a.*.fmt(f);
                }
            },
            .await => |a| {
                f.write("await ");
                a.arg.*.fmt(f);
            },
            .meta_prop => |m| {
                f.write(m.meta);
                f.writeChar('.');
                f.write(m.prop);
            },
            .parenthesized => |p| {
                f.writeChar('(');
                p.*.fmt(f);
                f.writeChar(')');
            },
            .private_ident => |name| f.write(name),
        }
    }
};

pub const FnType = union(enum) {
    normal: void,
    generator: void,
    async: void,
    async_generator: void,
};

pub const FnExpr = struct {
    loc: Loc,
    fn_type: FnType,
    id: ?[]const u8,
    params: []const Pat,
    body: BlockStmt,

    pub fn parse(p: *Parser) ParseError!*const Expr {
        const start = p.advanceTok().loc.start;

        var fn_type: FnType = .normal;
        if (p.peek() == .@"*") {
            fn_type = .generator;
            p.advance();
        }

        var id: ?[]const u8 = null;
        if (p.peek() == .identifier or p.peek().isKeywordButNotLet()) {
            const id_tok = p.advanceTok();
            id = p.tokenSlice(id_tok);
        }

        const params = try p.parseParams();
        const body = try p.parseFunctionBody();

        return p.arena.exprPtr(
            .{ .func = .{ .loc = .{ .start = start, .end = body.loc.end }, .fn_type = fn_type, .id = id, .params = params, .body = body } },
            .{ .start = start, .end = body.loc.end },
        );
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.write("function");
        if (self.fn_type == .generator or self.fn_type == .async_generator) {
            f.write("*");
        }
        if (self.fn_type == .async or self.fn_type == .async_generator) {
            f.write(" async");
        }
        if (self.id) |id| {
            f.writeSpace();
            f.write(id);
        }
        f.writeChar('(');
        for (self.params, 0..) |p, i| {
            if (i > 0) f.write(", ");
            p.fmt(f);
        }
        f.write(") ");
        self.body.fmt(f);
    }
};

pub const ArrowFn = struct {
    loc: Loc,
    async_token: bool,
    params: []const Pat,
    body: union(enum) {
        block: BlockStmt,
        expr: *const Expr,
    },

    pub fn parse(p: *Parser, params_info: struct { loc: Loc, params: []const Pat }) ParseError!*const Expr {
        try p.expect(.@"=>");
        const async_token = false;

        if (p.peek() == .lbrace) {
            const body = try p.parseFunctionBody();
            return p.arena.exprPtr(
                .{ .arrow = .{ .loc = .{ .start = params_info.loc.start, .end = body.loc.end }, .async_token = async_token, .params = params_info.params, .body = .{ .block = body } } },
                .{ .start = params_info.loc.start, .end = body.loc.end },
            );
        }

        const expr = try Expr.parse(p, 0);
        return p.arena.exprPtr(
            .{ .arrow = .{ .loc = .{ .start = params_info.loc.start, .end = expr.loc.end }, .async_token = async_token, .params = params_info.params, .body = .{ .expr = expr } } },
            .{ .start = params_info.loc.start, .end = expr.loc.end },
        );
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        if (self.async_token) f.write("async ");
        f.writeChar('(');
        for (self.params, 0..) |p, i| {
            if (i > 0) f.write(", ");
            p.fmt(f);
        }
        f.write(") => ");
        switch (self.body) {
            .block => |b| b.fmt(f),
            .expr => |e| e.*.fmt(f),
        }
    }
};

pub const ClassExpr = struct {
    loc: Loc,
    id: ?[]const u8,
    super_class: ?*const Expr,
    body: []const ClassElem,

    pub fn parse(p: *Parser) ParseError!*const Expr {
        const start = p.advanceTok().loc.start;

        var id: ?[]const u8 = null;
        if (p.peek() == .identifier) {
            const id_tok = p.advanceTok();
            id = p.tokenSlice(id_tok);
        }

        var super_class: ?*const Expr = null;
        if (p.matchKeyword(.extends)) {
            super_class = try Expr.parse(p, 0);
        }

        try p.expect(.lbrace);
        var elems: [128]ClassElem = undefined;
        var elem_count: usize = 0;

        while (p.peek() != .rbrace and p.peek() != .eof) {
            const elem = try ClassElem.parse(p);
            elems[elem_count] = elem;
            elem_count += 1;
        }

        const end_tok = try p.expectTok(.rbrace);
        return p.arena.exprPtr(
            .{ .class = .{ .loc = .{ .start = start, .end = end_tok.loc.end }, .id = id, .super_class = super_class, .body = elems[0..elem_count] } },
            .{ .start = start, .end = end_tok.loc.end },
        );
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.write("class");
        if (self.id) |id| {
            f.writeSpace();
            f.write(id);
        }
        if (self.super_class) |sc| {
            f.write(" extends ");
            sc.*.fmt(f);
        }
        f.write(" {");
        f.newline();
        f.indent_level += 1;
        for (self.body) |elem| {
            f.writeIndent();
            elem.fmt(f);
            f.newline();
        }
        f.indent_level -= 1;
        f.writeIndent();
        f.writeChar('}');
    }
};

pub const ClassElem = union(enum) {
    method: FnExpr,
    get: PropGet,
    set: PropSet,
    field: FieldDef,
    static_block: BlockStmt,
    static_method: FnExpr,
    static_get: PropGet,
    static_set: PropSet,
    static_field: FieldDef,

    pub fn parse(p: *Parser) ParseError!ClassElem {
        const start = p.tok().loc.start;
        const is_static = p.matchKeyword(.static);

        if (is_static and p.peek() == .lbrace) {
            const body = try p.parseFunctionBody();
            return ClassElem{ .static_block = body };
        }

        if (p.matchKeyword(.get)) {
            const key = try p.parsePropKey();
            try p.expect(.lparen);
            try p.expect(.rparen);
            const body = try p.parseFunctionBody();
            if (is_static) return ClassElem{ .static_get = .{ .key = key, .body = body } };
            return ClassElem{ .get = .{ .key = key, .body = body } };
        }

        if (p.matchKeyword(.set)) {
            const key = try p.parsePropKey();
            try p.expect(.lparen);
            const param = try Pat.parse(p);
            try p.expect(.rparen);
            const body = try p.parseFunctionBody();
            if (is_static) return ClassElem{ .static_set = .{ .key = key, .param = param, .body = body } };
            return ClassElem{ .set = .{ .key = key, .param = param, .body = body } };
        }

        if (p.match(.@"*")) {
            _ = try p.parsePropKey();
            try p.expect(.lparen);
            const params = try p.parseParams();
            const body = try p.parseFunctionBody();
            const fn_expr = FnExpr{ .loc = .{ .start = start, .end = body.loc.end }, .fn_type = .generator, .id = null, .params = params, .body = body };
            if (is_static) return ClassElem{ .static_method = fn_expr };
            return ClassElem{ .method = fn_expr };
        }

        const key = try p.parsePropKey();

        if (p.peek() == .lparen) {
            const params = try p.parseParams();
            const body = try p.parseFunctionBody();
            const fn_expr = FnExpr{ .loc = .{ .start = start, .end = body.loc.end }, .fn_type = .normal, .id = null, .params = params, .body = body };
            if (is_static) return ClassElem{ .static_method = fn_expr };
            return ClassElem{ .method = fn_expr };
        }

        var value: ?*const Expr = null;
        if (p.match(.@"=")) {
            value = try Expr.parse(p, 0);
        }
        if (p.peek() == .semicolon) p.advance();

        const field = FieldDef{ .loc = .{ .start = start, .end = if (value) |v| v.loc.end else p.tok().loc.start }, .key = key, .value = value };
        if (is_static) return ClassElem{ .static_field = field };
        return ClassElem{ .field = field };
    }
};

pub const FieldDef = struct {
    loc: Loc,
    key: PropKey,
    value: ?*const Expr,
};

pub const ArrayExpr = struct {
    loc: Loc,
    elems: []const ?Expr,

    pub fn parse(p: *Parser) ParseError!*const Expr {
        const start = p.advanceTok().loc.start;
        var elems: [256]?Expr = undefined;
        var count: usize = 0;

        while (p.peek() != .rbracket and p.peek() != .eof) {
            if (p.match(.comma)) {
                elems[count] = null;
                count += 1;
            } else if (p.peek() == .@"...") {
                p.advance();
                const arg = try Expr.parse(p, 0);
                elems[count] = Expr{ .loc = arg.loc, .data = .{ .spread = .{ .loc = arg.loc, .arg = arg } } };
                count += 1;
                if (!p.match(.comma)) break;
            } else {
                const expr = try Expr.parse(p, 0);
                elems[count] = expr.*;
                count += 1;
                if (!p.match(.comma)) break;
            }
        }

        try p.expect(.rbracket);
        return p.arena.exprPtr(.{ .array = .{ .loc = .{ .start = start, .end = p.tok().loc.start }, .elems = elems[0..count] } }, .{ .start = start, .end = p.tok().loc.start });
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.writeChar('[');
        for (self.elems, 0..) |elem, i| {
            if (i > 0) f.write(", ");
            if (elem) |e| e.fmt(f);
        }
        f.writeChar(']');
    }
};

pub const ObjectExpr = struct {
    loc: Loc,
    props: []const Prop,

    pub fn parse(p: *Parser) ParseError!*const Expr {
        const start = p.advanceTok().loc.start;
        var props: [128]Prop = undefined;
        var count: usize = 0;

        while (p.peek() != .rbrace and p.peek() != .eof) {
            if (p.peek() == .@"...") {
                p.advance();
                const arg = try Expr.parse(p, 0);
                props[count] = .{ .loc = arg.loc, .key = .{ .ident = "" }, .data = .{ .spread = .{ .loc = arg.loc, .arg = arg } } };
                count += 1;
            } else if (p.peek() == .identifier) {
                const name_tok = p.tok();
                const name = p.tokenSlice(name_tok);
                p.advance();
                if (p.peek() == .@":") {
                    p.advance();
                    const value = try Expr.parse(p, 0);
                    props[count] = .{ .loc = .{ .start = name_tok.loc.start, .end = value.loc.end }, .key = .{ .ident = name }, .data = .{ .init = .{ .key = .{ .ident = name }, .value = value } } };
                    count += 1;
                } else if (p.peek() == .lparen) {
                    const params = try p.parseParams();
                    const body = try p.parseFunctionBody();
                    props[count] = .{ .loc = .{ .start = name_tok.loc.start, .end = body.loc.end }, .key = .{ .ident = name }, .data = .{ .method = .{ .loc = .{ .start = name_tok.loc.start, .end = body.loc.end }, .fn_type = .normal, .id = null, .params = params, .body = body } } };
                    count += 1;
                } else if (p.peek() == .@"=") {
                    p.advance();
                    const value = try Expr.parse(p, 0);
                    props[count] = .{ .loc = .{ .start = name_tok.loc.start, .end = value.loc.end }, .key = .{ .ident = name }, .data = .{ .init = .{ .key = .{ .ident = name }, .value = value } } };
                    count += 1;
                } else if (p.peek() == .comma or p.peek() == .rbrace) {
                    props[count] = .{ .loc = .{ .start = name_tok.loc.start, .end = name_tok.loc.end }, .key = .{ .ident = name }, .data = .{ .shorthand = name } };
                    count += 1;
                }
            } else if (p.peek() == .number or p.peek() == .string) {
                const key = try p.parsePropKey();
                try p.expect(.@":");
                const value = try Expr.parse(p, 0);
                props[count] = .{ .loc = .{ .start = start, .end = value.loc.end }, .key = key, .data = .{ .init = .{ .key = key, .value = value } } };
                count += 1;
            } else if (p.peek() == .lbracket) {
                const key = try p.parsePropKey();
                try p.expect(.@":");
                const value = try Expr.parse(p, 0);
                props[count] = .{ .loc = .{ .start = start, .end = value.loc.end }, .key = key, .data = .{ .init = .{ .key = key, .value = value } } };
                count += 1;
            } else if (p.matchKeyword(.get)) {
                const key = try p.parsePropKey();
                try p.expect(.lparen);
                try p.expect(.rparen);
                const body = try p.parseFunctionBody();
                props[count] = .{ .loc = .{ .start = start, .end = body.loc.end }, .key = key, .data = .{ .get = .{ .key = key, .body = body } } };
                count += 1;
            } else if (p.matchKeyword(.set)) {
                const key = try p.parsePropKey();
                try p.expect(.lparen);
                const param = try Pat.parse(p);
                try p.expect(.rparen);
                const body = try p.parseFunctionBody();
                props[count] = .{ .loc = .{ .start = start, .end = body.loc.end }, .key = key, .data = .{ .set = .{ .key = key, .param = param, .body = body } } };
                count += 1;
            } else if (p.match(.@"*")) {
                const key = try p.parsePropKey();
                const params = try p.parseParams();
                const body = try p.parseFunctionBody();
                props[count] = .{ .loc = .{ .start = start, .end = body.loc.end }, .key = key, .data = .{ .method = .{ .loc = .{ .start = start, .end = body.loc.end }, .fn_type = .generator, .id = null, .params = params, .body = body } } };
                count += 1;
            } else {
                break;
            }

            if (!p.match(.comma)) break;
        }

        try p.expect(.rbrace);
        return p.arena.exprPtr(.{ .object = .{ .loc = .{ .start = start, .end = p.tok().loc.start }, .props = props[0..count] } }, .{ .start = start, .end = p.tok().loc.start });
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.writeChar('{');
        for (self.props, 0..) |p, i| {
            if (i > 0) f.write(", ");
            p.fmt(f);
        }
        f.writeChar('}');
    }
};

pub const PropType = union(enum) {
    init: PropInit,
    get: PropGet,
    set: PropSet,
    shorthand: []const u8,
    spread: SpreadElem,
    method: FnExpr,
};

pub const Prop = struct {
    loc: Loc,
    key: PropKey,
    data: PropType,

    pub fn fmt(self: @This(), f: *Formatter) void {
        switch (self.data) {
            .init => |p_init| {
                self.key.fmt(f);
                f.write(": ");
                p_init.value.*.fmt(f);
            },
            .get => |g| g.fmt(f),
            .set => |s| s.fmt(f),
            .shorthand => |name| f.write(name),
            .spread => |sp| {
                f.write("...");
                sp.arg.*.fmt(f);
            },
            .method => |m| m.fmt(f),
        }
    }
};

pub const PropKey = union(enum) {
    ident: []const u8,
    string: []const u8,
    number: f64,
    computed: *const Expr,
    private: []const u8,
};

pub const PropInit = struct {
    key: PropKey,
    value: *const Expr,
};

pub const PropGet = struct {
    key: PropKey,
    body: BlockStmt,

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.write("get ");
        self.key.fmt(f);
        f.write("() ");
        self.body.fmt(f);
    }
};

pub const PropSet = struct {
    key: PropKey,
    param: Pat,
    body: BlockStmt,

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.write("set ");
        self.key.fmt(f);
        f.writeChar('(');
        self.param.fmt(f);
        f.write(") ");
        self.body.fmt(f);
    }
};

pub const SpreadElem = struct {
    loc: Loc,
    arg: *const Expr,
};

pub const MemberExpr = struct {
    loc: Loc,
    obj: *const Expr,
    prop: union(enum) {
        ident: []const u8,
        private: []const u8,
    },

    pub fn fmt(self: @This(), f: *Formatter) void {
        self.obj.*.fmt(f);
        switch (self.prop) {
            .ident => |name| {
                f.writeChar('.');
                f.write(name);
            },
            .private => |name| {
                f.writeChar('.');
                f.write(name);
            },
        }
    }
};

pub const ComputedMember = struct {
    loc: Loc,
    obj: *const Expr,
    expr: *const Expr,

    pub fn fmt(self: @This(), f: *Formatter) void {
        self.obj.*.fmt(f);
        f.writeChar('[');
        self.expr.*.fmt(f);
        f.writeChar(']');
    }
};

pub const CallExpr = struct {
    loc: Loc,
    callee: *const Expr,
    args: []const Expr,
    optional: bool,

    pub fn fmt(self: @This(), f: *Formatter) void {
        self.callee.*.fmt(f);
        if (self.optional) {
            f.write("?.(");
        } else {
            f.writeChar('(');
        }
        for (self.args, 0..) |a, i| {
            if (i > 0) f.write(", ");
            a.fmt(f);
        }
        f.writeChar(')');
    }
};

pub const NewExpr = struct {
    loc: Loc,
    callee: *const Expr,
    args: []const Expr,
};

pub const ChainExpr = struct {
    loc: Loc,
    expr: *const Expr,
};

pub const UnaryOp = enum {
    @"-",
    @"+",
    @"!",
    @"~",
    typeof,
    void,
    delete,
};

pub const UnaryExpr = struct {
    loc: Loc,
    op: UnaryOp,
    arg: *const Expr,
    prefix: bool,
};

pub const BinaryOp = enum {
    @"==",
    @"!=",
    @"===",
    @"!==",
    @"<",
    @"<=",
    @">",
    @">=",
    @"<<",
    @">>",
    @">>>",
    @"+",
    @"-",
    @"*",
    @"/",
    @"%",
    @"**",
    @"|",
    @"^",
    @"&",
    in,
    instanceof,
    @"||",
    @"&&",
    @"??",
};

pub const BinaryExpr = struct {
    loc: Loc,
    op: BinaryOp,
    left: *const Expr,
    right: *const Expr,
};

pub const UpdateOp = enum {
    @"++",
    @"--",
};

pub const UpdateExpr = struct {
    loc: Loc,
    op: UpdateOp,
    arg: *const Expr,
    prefix: bool,
};

pub const IfExpr = struct {
    loc: Loc,
    condition: *const Expr,
    consequent: *const Expr,
    alternate: *const Expr,
};

pub const AssignOp = enum {
    @"=",
    @"+=",
    @"-=",
    @"*=",
    @"/=",
    @"%=",
    @"**=",
    @"<<=",
    @">>=",
    @">>>=",
    @"|=",
    @"^=",
    @"&=",
    @"||=",
    @"&&=",
    @"??=",
};

pub const AssignExpr = struct {
    loc: Loc,
    op: AssignOp,
    left: *const Expr,
    right: *const Expr,
};

pub const SeqExpr = struct {
    loc: Loc,
    exprs: []const Expr,
};

pub const YieldExpr = struct {
    loc: Loc,
    arg: ?*const Expr,
    delegate: bool,
};

pub const AwaitExpr = struct {
    loc: Loc,
    arg: *const Expr,
};

pub const MetaProp = struct {
    loc: Loc,
    meta: []const u8,
    prop: []const u8,
};

pub const TemplateLit = struct {
    loc: Loc,
    quasis: []const TemplateElem,
    exprs: []const Expr,

    pub fn parse(p: *Parser) ParseError!TemplateLit {
        const start = p.tok().loc.start;
        var quasis: [64]TemplateElem = undefined;
        var exprs: [64]Expr = undefined;
        var q_count: usize = 0;
        var e_count: usize = 0;

        while (true) {
            switch (p.peek()) {
                .no_sub_template => {
                    const t = p.advanceTok();
                    const slice = p.tokenSlice(t);
                    quasis[q_count] = .{ .loc = .{ .start = t.loc.start, .end = t.loc.end }, .value = slice, .tail = true };
                    q_count += 1;
                    break;
                },
                .template_head => {
                    const t = p.advanceTok();
                    const slice = p.tokenSlice(t);
                    quasis[q_count] = .{ .loc = .{ .start = t.loc.start, .end = t.loc.end }, .value = slice, .tail = false };
                    q_count += 1;
                    const expr = try Expr.parse(p, 0);
                    exprs[e_count] = expr.*;
                    e_count += 1;
                    try p.expect(.rbrace);
                },
                .template_middle => {
                    const t = p.advanceTok();
                    const slice = p.tokenSlice(t);
                    quasis[q_count] = .{ .loc = .{ .start = t.loc.start, .end = t.loc.end }, .value = slice, .tail = false };
                    q_count += 1;
                    const expr = try Expr.parse(p, 0);
                    exprs[e_count] = expr.*;
                    e_count += 1;
                    try p.expect(.rbrace);
                },
                .template_tail => {
                    const t = p.advanceTok();
                    const slice = p.tokenSlice(t);
                    quasis[q_count] = .{ .loc = .{ .start = t.loc.start, .end = t.loc.end }, .value = slice, .tail = true };
                    q_count += 1;
                    break;
                },
                else => break,
            }
        }

        return .{ .loc = .{ .start = start, .end = p.tok().loc.start }, .quasis = quasis[0..q_count], .exprs = exprs[0..e_count] };
    }

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.writeChar('`');
        var ei: usize = 0;
        for (self.quasis, 0..) |q, i| {
            if (i > 0 and ei < self.exprs.len) {
                f.write("${");
                self.exprs[ei].fmt(f);
                f.writeChar('}');
                ei += 1;
            }
            f.write(q.value);
        }
        f.writeChar('`');
    }
};

pub const TemplateElem = struct {
    loc: Loc,
    value: []const u8,
    tail: bool,
};

pub const TaggedTemplate = struct {
    loc: Loc,
    tag: *const Expr,
    quasi: TemplateLit,

    pub fn fmt(self: @This(), f: *Formatter) void {
        self.tag.*.fmt(f);
        self.quasi.fmt(f);
    }
};

pub const Decorator = struct {
    loc: Loc,
    expr: *const Expr,

    pub fn fmt(self: @This(), f: *Formatter) void {
        f.writeChar('@');
        self.expr.*.fmt(f);
    }
};