/**
 * @param contextSize
 *        How many lines of context around each changed line should be included.
 */
class DiffFactory(private val contextSize: Int) {

    companion object {

        private const val LINE_SEPARATOR = "\n"
    }

    /**
     * Creates a git-apply compatible diff.
     */
    fun computeDiff(
        filename: String,
        originalContent: String,
        newContent: String
    ): String = UnifiedDiffUtils.generateUnifiedDiff(
        "a/$filename", // a/ and b/ required for git-apply compatibility
        "b/$filename",
        originalContent.split(LINE_SEPARATOR),
        DiffUtils.diff(
            originalContent, newContent,
            NullDiffAlgorithmListener
        ),
        contextSize
    ).joinToString(LINE_SEPARATOR)
}