    const std = @import("../std.zig");
    const io = std.io;
    const assert = std.debug.assert;
    const testing = std.testing;

    pub fn BufferedReader(comptime buffer_size: usize, comptime ReaderType: type) type {
        return struct {
            unbuffered_reader: ReaderType,
            fifo: FifoType = FifoType.init(),

            pub const Error = ReaderType.Error;
            pub const Reader = io.Reader(*Self, Error, read);

            const Self = @This();
            const FifoType = std.fifo.LinearFifo(u8, std.fifo.LinearFifoBufferType{ .Static = buffer_size });

            pub fn read(self: *Self, dest: []u8) Error!usize {
                var dest_index: usize = 0;
                while (dest_index < dest.len) {
                    const written = self.fifo.read(dest[dest_index..]);
                    if (written == 0) {
                        // fifo empty, fill it

                        const writable = self.fifo.writableSlice(0);
                        assert(writable.len > 0);
                        const n = try self.unbuffered_reader.read(writable);
                        if (n == 0) {
                            // reading from the unbuffered stream returned nothing

                            // so we have nothing left to read.

                            return dest_index;
                        }
                        self.fifo.update(n);
                    }
                    dest_index += written;
                }
                return dest.len;
            }

            pub fn reader(self: *Self) Reader {
                return .{ .context = self };
            }
        };
    }

    pub fn bufferedReader(underlying_stream: anytype) BufferedReader(4096, @TypeOf(underlying_stream)) {
        return .{ .unbuffered_reader = underlying_stream };
    }

    test "io.BufferedReader" {
        const OneByteReadReader = struct {
            str: []const u8,
            curr: usize,

            const Error = error{NoError};
            const Self = @This();
            const Reader = io.Reader(*Self, Error, read);

            fn init(str: []const u8) Self {
                return Self{
                    .str = str,
                    .curr = 0,
                };
            }

            fn read(self: *Self, dest: []u8) Error!usize {
                if (self.str.len <= self.curr or dest.len == 0)
                    return 0;

                dest[0] = self.str[self.curr];
                self.curr += 1;
                return 1;
            }

            fn reader(self: *Self) Reader {
                return .{ .context = self };
            }
        };

        const str = "This is a test";
        var one_byte_stream = OneByteReadReader.init(str);
        var buf_reader = bufferedReader(one_byte_stream.reader());
        const stream = buf_reader.reader();

        const res = try stream.readAllAlloc(testing.allocator, str.len + 1);
        defer testing.allocator.free(res);
        try testing.expectEqualSlices(u8, str, res);
    }