Project sequence evidence through item mappings

internal/engine/sequence_projection.go

@@ -0,0 +1,50 @@
+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
+}