func validateCSV(s *testSuite, l types.List) {
	s.Equal(uint64(100), l.Len())

	i := uint64(0)
	l.IterAll(func(v types.Value, j uint64) {
		s.Equal(i, j)
		st := v.(types.Struct)
		s.Equal(types.String(fmt.Sprintf("a%d", i)), st.Get("a"))
		s.Equal(types.Number(i), st.Get("b"))
		i++
	})
}

// Write takes a types.List l of structs (described by sd) and writes it to output as comma-delineated values.
func Write(l types.List, sd types.StructDesc, comma rune, output io.Writer) {
	structChan := make(chan types.Struct, 1024)
	go func() {
		l.IterAll(func(v types.Value, index uint64) {
			structChan <- v.(types.Struct)
		})
		close(structChan)
	}()

	fieldNames := getFieldNamesFromStruct(sd)
	csvWriter := csv.NewWriter(output)
	csvWriter.Comma = comma
	d.Exp.NoError(csvWriter.Write(fieldNames), "Failed to write header %v", fieldNames)
	record := make([]string, len(fieldNames))
	for s := range structChan {
		for i, f := range fieldNames {
			record[i] = fmt.Sprintf("%v", s.Get(f))
		}
		d.Exp.NoError(csvWriter.Write(record), "Failed to write record %v", record)
	}

	csvWriter.Flush()
	d.Exp.NoError(csvWriter.Error(), "error flushing csv")
}

func diffSummaryList(ch chan<- diffSummaryProgress, v1, v2 types.List) {
	ch <- diffSummaryProgress{OldSize: v1.Len(), NewSize: v2.Len()}

	spliceChan := make(chan types.Splice)
	stopChan := make(chan struct{}, 1) // buffer size of 1, so this won't block if diff already finished

	go func() {
		v2.Diff(v1, spliceChan, stopChan)
		close(spliceChan)
	}()

	for splice := range spliceChan {
		if splice.SpRemoved == splice.SpAdded {
			ch <- diffSummaryProgress{Changes: splice.SpRemoved}
		} else {
			ch <- diffSummaryProgress{Adds: splice.SpAdded, Removes: splice.SpRemoved}
		}
	}
}

func diffLists(dq *diffQueue, w io.Writer, p types.Path, v1, v2 types.List) {
	wroteHeader := false
	splices := v2.Diff(v1)
	for _, splice := range splices {
		if splice.SpRemoved == splice.SpAdded {
			for i := uint64(0); i < splice.SpRemoved; i++ {
				lastEl := v1.Get(splice.SpAt + i)
				newEl := v2.Get(splice.SpFrom + i)
				if canCompare(lastEl, newEl) {
					idx := types.Number(splice.SpAt + i)
					p1 := p.AddIndex(idx)
					dq.PushBack(diffInfo{p1, idx, lastEl, newEl})
				} else {
					wroteHeader = writeHeader(w, wroteHeader, p)
					line(w, subPrefix, nil, v1.Get(splice.SpAt+i))
					line(w, addPrefix, nil, v2.Get(splice.SpFrom+i))
				}
			}
		} else {
			for i := uint64(0); i < splice.SpRemoved; i++ {
				wroteHeader = writeHeader(w, wroteHeader, p)
				line(w, subPrefix, nil, v1.Get(splice.SpAt+i))
			}
			for i := uint64(0); i < splice.SpAdded; i++ {
				wroteHeader = writeHeader(w, wroteHeader, p)
				line(w, addPrefix, nil, v2.Get(splice.SpFrom+i))
			}
		}
	}
	writeFooter(w, wroteHeader)
}

func diffLists(w io.Writer, p types.Path, v1, v2 types.List) (err error) {
	spliceChan := make(chan types.Splice)
	stopChan := make(chan struct{}, 1) // buffer size of 1, so this won't block if diff already finished

	go func() {
		v2.Diff(v1, spliceChan, stopChan)
		close(spliceChan)
	}()

	wroteHdr := false

	for splice := range spliceChan {
		if err != nil {
			break
		}

		if splice.SpRemoved == splice.SpAdded {
			// Heuristic: list only has modifications.
			for i := uint64(0); i < splice.SpRemoved; i++ {
				lastEl := v1.Get(splice.SpAt + i)
				newEl := v2.Get(splice.SpFrom + i)
				if shouldDescend(lastEl, newEl) {
					idx := types.Number(splice.SpAt + i)
					writeFooter(w, &wroteHdr)
					err = diff(w, p.AddIndex(idx), idx, lastEl, newEl)
				} else {
					writeHeader(w, p, &wroteHdr)
					line(w, DEL, nil, v1.Get(splice.SpAt+i))
					err = line(w, ADD, nil, v2.Get(splice.SpFrom+i))
				}
			}
			continue
		}

		// Heuristic: list only has additions/removals.
		for i := uint64(0); i < splice.SpRemoved && err == nil; i++ {
			writeHeader(w, p, &wroteHdr)
			err = line(w, DEL, nil, v1.Get(splice.SpAt+i))
		}
		for i := uint64(0); i < splice.SpAdded && err == nil; i++ {
			writeHeader(w, p, &wroteHdr)
			err = line(w, ADD, nil, v2.Get(splice.SpFrom+i))
		}
	}

	err = writeFooter(w, &wroteHdr)

	if err != nil {
		stopChan <- struct{}{}
		// Wait for diff to stop.
		for range spliceChan {
		}
	}
	return
}

func diffLists(w io.Writer, p types.Path, v1, v2 types.List) {
	spliceChan := make(chan types.Splice)
	stopChan := make(chan struct{}, 1) // buffer size of 1, so this won't block if diff already finished

	defer stop(stopChan)
	go func() {
		v2.Diff(v1, spliceChan, stopChan)
		close(spliceChan)
	}()

	wroteHeader := false

	for splice := range spliceChan {
		if splice.SpRemoved == splice.SpAdded {
			for i := uint64(0); i < splice.SpRemoved; i++ {
				lastEl := v1.Get(splice.SpAt + i)
				newEl := v2.Get(splice.SpFrom + i)
				if shouldDescend(lastEl, newEl) {
					idx := types.Number(splice.SpAt + i)
					diff(w, p.AddIndex(idx), idx, lastEl, newEl)
				} else {
					wroteHeader = writeHeader(w, wroteHeader, p)
					line(w, DEL, nil, v1.Get(splice.SpAt+i))
					line(w, ADD, nil, v2.Get(splice.SpFrom+i))
				}
			}
		} else {
			for i := uint64(0); i < splice.SpRemoved; i++ {
				wroteHeader = writeHeader(w, wroteHeader, p)
				line(w, DEL, nil, v1.Get(splice.SpAt+i))
			}
			for i := uint64(0); i < splice.SpAdded; i++ {
				wroteHeader = writeHeader(w, wroteHeader, p)
				line(w, ADD, nil, v2.Get(splice.SpFrom+i))
			}
		}
	}

	writeFooter(w, wroteHeader)
}