func diff()

in MobiusTest/Source/SimpleDiff.swift [55:95]

• 37 lines of code
• 8 McCabe index (conditional complexity)

func diff(lhs: ArraySlice<Substring>, rhs: ArraySlice<Substring>) -> [Difference] {
    var lhsIndexMap = [String: [Int]]()
    for (index, value) in zip(lhs.indices, lhs) {
        lhsIndexMap[String(value), default: []].append(index)
    }

    var lhsSubStart = lhs.startIndex
    var rhsSubStart = rhs.startIndex
    var subLength = 0
    var overlap = [Int: Int]()

    for (indexRhs, value) in zip(rhs.indices, rhs) {
        var innerOverlap = [Int: Int]()

        for indexLhs in lhsIndexMap[String(value), default: []] {
            let innerSubLength = (overlap[indexLhs - 1] ?? 0) + 1
            innerOverlap[indexLhs] = innerSubLength
            if innerSubLength > subLength {
                subLength = innerSubLength
                lhsSubStart = indexLhs - subLength + 1
                rhsSubStart = indexRhs - subLength + 1
            }
        }
        overlap = innerOverlap
    }

    var diffs = [Difference]()
    if subLength == 0 {
        if !lhs.isEmpty {
            diffs.append(.delete(lhs))
        }
        if !rhs.isEmpty {
            diffs.append(.insert(rhs))
        }
    } else {
        diffs.append(contentsOf: diff(lhs: lhs.prefix(upTo: lhsSubStart), rhs: rhs.prefix(upTo: rhsSubStart)))
        diffs.append(.same(rhs.suffix(from: rhsSubStart).prefix(subLength)))
        diffs.append(contentsOf: diff(lhs: lhs.suffix(from: lhsSubStart + subLength), rhs: rhs.suffix(from: rhsSubStart + subLength)))
    }
    return diffs
}