//! std.io.Writer drop in replacement that uses function pointer instead of
//! compile time construct. Analogous to std.io.AnyReader.

const std = @import("std");
const AnyWriter = @This();
pub const Error = anyerror;

context: *const anyopaque,
writeFn: *const fn (context: *const anyopaque, buffer: []const u8) anyerror!usize,

// Must create a wrapper around the original writer in order to add a typeErasedWriteFn
// and keep a reference to it alive until we're done writing to it
// Usage might look like this:
//  var wrap = AnyWriter.wrapper(myWriter);
//  var aw = wrap.any();
pub fn wrapper(writer: anytype) Wrapper(@TypeOf(writer)) {
    return .{ .ww = writer };
}
pub fn Wrapper(comptime writerType: type) type {
    return struct {
        ww: writerType,
        fn typeErasedWriteFn(context: *const anyopaque, buffer: []const u8) anyerror!usize {
            const self: *const @This() = @alignCast(@ptrCast(context));
            return self.ww.write(buffer);
        }
        pub fn any(self: *@This()) AnyWriter {
            return .{
                .context = @ptrCast(self),
                .writeFn = &typeErasedWriteFn,
            };
        }
    };
}

pub fn write(self: AnyWriter, bytes: []const u8) anyerror!usize {
    return self.writeFn(self.context, bytes);
}

pub fn writeAll(self: AnyWriter, bytes: []const u8) anyerror!void {
    var index: usize = 0;
    while (index != bytes.len) {
        index += try self.write(bytes[index..]);
    }
}

pub fn print(self: AnyWriter, comptime format: []const u8, args: anytype) anyerror!void {
    return std.fmt.format(self, format, args);
}

pub fn writeByte(self: AnyWriter, byte: u8) anyerror!void {
    const array = [1]u8{byte};
    return self.writeAll(&array);
}

pub fn writeByteNTimes(self: AnyWriter, byte: u8, n: usize) anyerror!void {
    var bytes: [256]u8 = undefined;
    @memset(bytes[0..], byte);

    var remaining: usize = n;
    while (remaining > 0) {
        const to_write = @min(remaining, bytes.len);
        try self.writeAll(bytes[0..to_write]);
        remaining -= to_write;
    }
}

pub inline fn writeInt(self: AnyWriter, comptime T: type, value: T, endian: std.builtin.Endian) anyerror!void {
    var bytes: [@divExact(@typeInfo(T).Int.bits, 8)]u8 = undefined;
    std.mem.writeInt(std.math.ByteAlignedInt(@TypeOf(value)), &bytes, value, endian);
    return self.writeAll(&bytes);
}

pub fn writeStruct(self: AnyWriter, value: anytype) anyerror!void {
    // Only extern and packed structs have defined in-memory layout.
    comptime std.debug.assert(@typeInfo(@TypeOf(value)).Struct.layout != .Auto);
    return self.writeAll(std.mem.asBytes(&value));
}