Abbrev

const Abbrev = struct {
    operands: []const Operand,

    const Builtin = enum(u2) {
        end_block,
        enter_subblock,
        define_abbrev,
        unabbrev_record,

        const first_record_id: u32 = std.math.maxInt(u32) - @typeInfo(Builtin).@"enum".field_names.len + 1;
        fn toRecordId(builtin: Builtin) u32 {
            return first_record_id + @backingInt(builtin);
        }
    };

    const Operand = union(enum) {
        literal: u64,
        encoding: union(Encoding) {
            fixed: u7,
            vbr: u6,
            array: u3,
            char6,
            blob: u3,
        },
        align_32_bits,
        block_len,
        abbrev_op,

        const literal_id = std.math.maxInt(u64);
        const Encoding = enum(u3) {
            fixed = 1,
            vbr = 2,
            array = 3,
            char6 = 4,
            blob = 5,
            _,
        };
    };

    const Store = struct {
        abbrevs: std.ArrayList(Abbrev),

        fn deinit(store: *Store, allocator: std.mem.Allocator) void {
            for (store.abbrevs.items) |abbrev| allocator.free(abbrev.operands);
            store.abbrevs.deinit(allocator);
            store.* = undefined;
        }

        fn addAbbrev(store: *Store, allocator: std.mem.Allocator, abbrev: Abbrev) !void {
            try store.ensureUnusedCapacity(allocator, 1);
            store.addAbbrevAssumeCapacity(abbrev);
        }

        fn addAbbrevAssumeCapacity(store: *Store, allocator: std.mem.Allocator, abbrev: Abbrev) !void {
            store.abbrevs.appendAssumeCapacity(.{
                .operands = try allocator.dupe(Abbrev.Operand, abbrev.operands),
            });
        }

        fn addOwnedAbbrev(store: *Store, allocator: std.mem.Allocator, abbrev: Abbrev) !void {
            try store.abbrevs.ensureUnusedCapacity(allocator, 1);
            store.addOwnedAbbrevAssumeCapacity(abbrev);
        }

        fn addOwnedAbbrevAssumeCapacity(store: *Store, abbrev: Abbrev) void {
            store.abbrevs.appendAssumeCapacity(abbrev);
        }
    };
}