package engine

type sequenceItemProjectionIndex struct {
	outputByInput []int
	inputByOutput []int
}

func newSequenceItemProjectionIndex(projections []sequenceItemProjection) sequenceItemProjectionIndex {
	maxInput := -1
	maxOutput := -1
	for _, projection := range projections {
		if projection.inputIndex > maxInput {
			maxInput = projection.inputIndex
		}
		if projection.outputIndex > maxOutput {
			maxOutput = projection.outputIndex
		}
	}
	index := sequenceItemProjectionIndex{
		outputByInput: make([]int, maxInput+1),
		inputByOutput: make([]int, maxOutput+1),
	}
	for input := range index.outputByInput {
		index.outputByInput[input] = -1
	}
	for output := range index.inputByOutput {
		index.inputByOutput[output] = -1
	}
	for _, projection := range projections {
		if projection.inputIndex >= 0 && projection.inputIndex < len(index.outputByInput) && projection.outputIndex >= 0 && projection.outputIndex < len(index.inputByOutput) {
			index.outputByInput[projection.inputIndex] = projection.outputIndex
			index.inputByOutput[projection.outputIndex] = projection.inputIndex
		}
	}
	return index
}

func (index sequenceItemProjectionIndex) outputForInput(inputIndex int) (int, bool) {
	if inputIndex < 0 || inputIndex >= len(index.outputByInput) || index.outputByInput[inputIndex] < 0 {
		return 0, false
	}
	return index.outputByInput[inputIndex], true
}

func (index sequenceItemProjectionIndex) inputForOutput(outputIndex int) (int, bool) {
	if outputIndex < 0 || outputIndex >= len(index.inputByOutput) || index.inputByOutput[outputIndex] < 0 {
		return 0, false
	}
	return index.inputByOutput[outputIndex], true
}