| impulseFile sf impulseResponse impulseLength sourceFile sampleCount inBuffer destFile outBuffer |

"Ask for the impulse response file and read the samples into RAM. The samples file must be mono."
impulseFile := 
	HostDriverInterface
		getFileWithPrompt: 'Select the impulse response file:'
		fileTypes: (Array with: HostDriverInterface sampleFileType)
		ifCancel: [^ self].
sf := SamplesFile for: impulseFile ifAbsent: [^ self].
impulseLength := sf sampleFrames.
impulseResponse := sf getSamplesFromMonoWavetableFileStartingAt: 0 length: impulseLength.

"Ask for the file to be convolved."
sourceFile := 
	HostDriverInterface
		getFileWithPrompt: 'Select the source file:'
		fileTypes: (Array with: HostDriverInterface sampleFileType)
		ifCancel: [^ self].
sf := SamplesFile for: sourceFile ifAbsent: [^ self].
sampleCount := sf sampleFrames.
inBuffer := sf readBuffer.

"Ask for the name of the output file."
destFile := 
	HostDriverInterface
		putFileWithPrompt: 'Select the source file:'
		initially: sf filename
		fileTypes: (Array with: HostDriverInterface sampleFileType)
		ifCancel: [^ self].
sf := sf copyForFilename: destFile asFilename.
sf writeHeader.
outBuffer := sf writeBuffer.

"Now, convolve. (This processes left channel only.)"
self dialogClass displayStringWithThermometer: 'Now computing convolution...' while: [
	| pastInputSamples samplePair progressScale sampleScale |

	pastInputSamples := Array new: impulseLength withAll: 0.
	samplePair := Array new: 2.
	progressScale := 1.0 / sampleCount.
	sampleScale := (impulseResponse inject: 0 into: [ :sum :x | sum + x abs]) inverse.

	1 to: sampleCount do: [ :x | | sum |
		(x bitAnd: 16rFF) = 0 ifTrue: [self dialogClass thermometerSignal raiseRequestWith: x * progressScale].
		pastInputSamples replaceFrom: 2 to: impulseLength with: pastInputSamples startingAt: 1.
		inBuffer nextSampleInto: samplePair.
		pastInputSamples at: 1 put: (samplePair at: 1).
		sum := 0.
		1 to: impulseLength do: [ :i | sum := (impulseResponse at: i) * (pastInputSamples at: i) + sum].
		sum := sum * sampleScale.
		outBuffer writeLeftSample: sum rightSample: sum]].

"Close the files, we are done."
inBuffer close.
outBuffer close.