writer.go

// {{{ Copyright (c) Paul R. Tagliamonte <paul@k3xec.com>, 2020
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE. }}}

package sdr

import (
	"errors"
)

// ErrShortWrite will be returned when a write was aborted halfway through.
var ErrShortWrite = errors.New("sdr: short write")

// Writer is the interface that wraps the basic Write method.
type Writer interface {
	// Write IQ Samples into the target Samples buffer. There are two return
	// values, an int representing the **IQ** samples (not bytes) read by this
	// function, and any error conditions encountered.
	Write(Samples) (int, error)

	// Get the sdr.SampleFormat
	SampleFormat() SampleFormat

	// SampleRate will get the number of samples per second that this
	// stream is communicating at.
	SampleRate() uint
}

// WriteCloser is the interface that groups the basic Read and Close methods.
type WriteCloser interface {
	Writer
	Closer
}

type multiWriter struct {
	writers          []Writer
	samplesPerSecond uint
	sampleFormat     SampleFormat
}

// MultiWriter creates a writer that duplicates its writes to all the
// provided writers, similar to the Unix tee(1) command, or io.MultiWriter.
//
// This has the same behavior as an io.MultiWriter, but will copy between
// IQ streams.
func MultiWriter(
	writers ...Writer,
) (Writer, error) {

	switch len(writers) {
	case 0:
		return nil, errors.New("sdr.MultiWriter: No writers passed to MultiWriter")
	case 1:
		return writers[0], nil
	}

	var (
		samplesPerSecond = writers[0].SampleRate()
		sampleFormat     = writers[0].SampleFormat()
	)

	allWriters := make([]Writer, 0, len(writers))
	for _, w := range writers {

		if w.SampleRate() != samplesPerSecond {
			return nil, errors.New("sdr.MultiWriter: Sample rate mismatch")
		}

		if w.SampleFormat() != sampleFormat {
			return nil, ErrSampleFormatMismatch
		}

		if mw, ok := w.(*multiWriter); ok {
			allWriters = append(allWriters, mw.writers...)
		} else {
			allWriters = append(allWriters, w)
		}
	}
	return &multiWriter{
		sampleFormat:     sampleFormat,
		samplesPerSecond: samplesPerSecond,
		writers:          allWriters,
	}, nil
}

func (mw *multiWriter) SampleRate() uint {
	return mw.samplesPerSecond
}

// SampleFormat implements the sdr.Writer interface.
func (mw *multiWriter) SampleFormat() SampleFormat {
	return mw.sampleFormat
}

// Write implements the sdr.Writer interface.
func (mw *multiWriter) Write(buf Samples) (int, error) {
	var (
		i   int
		err error
	)

	for _, w := range mw.writers {
		i, err = w.Write(buf)
		if err != nil {
			return i, err
		}
		if i != buf.Length() {
			return i, ErrShortWrite
		}
	}
	return buf.Length(), nil
}

type writerWithCloser struct {
	Writer
	closer func() error
}

func (rwc writerWithCloser) Close() error {
	return rwc.closer()
}

// WriterWithCloser will add a closer to a writer to make an sdr.WriteCloser
func WriterWithCloser(w Writer, c func() error) WriteCloser {
	return writerWithCloser{
		Writer: w,
		closer: c,
	}
}

type discard struct {
	sampleFormat SampleFormat
	sampleRate   uint
}

func (d discard) SampleFormat() SampleFormat {
	return d.sampleFormat
}

func (d discard) SampleRate() uint {
	return d.sampleRate
}

func (d discard) Write(s Samples) (int, error) {
	return s.Length(), nil
}

// Discard will accept writes, and store them safely... nowhere. This is
// a highly optimized and very fast writer. Just don't expect to get your
// data back.
func Discard(sampleRate uint, sampleFormat SampleFormat) Writer {
	return discard{
		sampleFormat: sampleFormat,
		sampleRate:   sampleRate,
	}
}

// vim: foldmethod=marker