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//
// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See License.txt in the project root for license information.
//
namespace Microsoft.VisualStudio.Text.Utilities
{
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Microsoft.VisualStudio.Text.Differencing;
using Microsoft.VisualStudio.Text.Projection;
internal class ProjectionSpanDiffer
{
private readonly IDifferenceService diffService;
private readonly ReadOnlyCollection<SnapshotSpan> inputDeletedSnapSpans;
private readonly ReadOnlyCollection<SnapshotSpan> inputInsertedSnapSpans;
// exposed to unit tests
internal List<SnapshotSpan>[] deletedSurrogates;
internal List<SnapshotSpan>[] insertedSurrogates;
public ProjectionSpanDiffer(IDifferenceService diffService,
ReadOnlyCollection<SnapshotSpan> deletedSnapSpans,
ReadOnlyCollection<SnapshotSpan> insertedSnapSpans)
{
this.diffService = diffService;
this.inputDeletedSnapSpans = deletedSnapSpans;
this.inputInsertedSnapSpans = insertedSnapSpans;
}
private IDifferenceCollection<SnapshotSpan> differences;
public IDifferenceCollection<SnapshotSpan> GetDifferences()
{
if (this.differences == null)
{
DecomposeSpans();
var deletedSpans = new List<SnapshotSpan>();
var insertedSpans = new List<SnapshotSpan>();
for (int s = 0; s < deletedSurrogates.Length; ++s)
{
deletedSpans.AddRange(deletedSurrogates[s]);
}
for (int s = 0; s < insertedSurrogates.Length; ++s)
{
insertedSpans.AddRange(insertedSurrogates[s]);
}
differences = this.diffService.DifferenceSequences(deletedSpans, insertedSpans);
}
return differences;
}
#region Internal (for testing) helpers
internal void DecomposeSpans()
{
// Prepare spans for diffing. The basic idea is this: suppose we have input spans from some source snapshot as follows:
//
// deleted: 0..10
// inserted: 0..3 7..10
//
// We would like to raise a text change event that indicates that the text from 3..7 was deleted, rather than
// an event indicating that all the text from 0..10 was deleted and replaced. We could simply compute a string
// difference of the before & after text, but there might be a lot of text (so that would be expensive), and we
// also don't want to suppress eventing when identical text comes from different source buffers (which might have
// different content types). So, this routine converts the input spans into a form suitable for diffing:
//
// deleted: 0..3 3..7 7..10
// inserted 0..3 7..10
//
// then we compute the differences of the spans qua spans, which in this case will indicate that the span named "3..7"
// was deleted, and that's what we use to generate text change events.
// what to substitute for input spans during diffing
this.deletedSurrogates = new List<SnapshotSpan>[this.inputDeletedSnapSpans.Count];
this.insertedSurrogates = new List<SnapshotSpan>[this.inputInsertedSnapSpans.Count];
// collect spans by text buffer
Dictionary<ITextSnapshot, List<Thing>> buffer2DeletedThings = new Dictionary<ITextSnapshot, List<Thing>>();
for (int ds = 0; ds < this.inputDeletedSnapSpans.Count; ++ds)
{
SnapshotSpan ss = this.inputDeletedSnapSpans[ds];
List<Thing> things;
if (!buffer2DeletedThings.TryGetValue(ss.Snapshot, out things))
{
things = new List<Thing>();
buffer2DeletedThings.Add(ss.Snapshot, things);
}
things.Add(new Thing(ss.Span, ds));
// unrelated
deletedSurrogates[ds] = new List<SnapshotSpan>();
}
Dictionary<ITextSnapshot, List<Thing>> buffer2InsertedThings = new Dictionary<ITextSnapshot, List<Thing>>();
for (int ns = 0; ns < this.inputInsertedSnapSpans.Count; ++ns)
{
SnapshotSpan ss = this.inputInsertedSnapSpans[ns];
List<Thing> things;
if (!buffer2InsertedThings.TryGetValue(ss.Snapshot, out things))
{
things = new List<Thing>();
buffer2InsertedThings.Add(ss.Snapshot, things);
}
things.Add(new Thing(ss.Span, ns));
// unrelated
insertedSurrogates[ns] = new List<SnapshotSpan>();
}
foreach (KeyValuePair<ITextSnapshot, List<Thing>> pair in buffer2DeletedThings)
{
List<Thing> insertedThings;
ITextSnapshot snapshot = pair.Key;
if (buffer2InsertedThings.TryGetValue(snapshot, out insertedThings))
{
List<Thing> deletedThings = pair.Value;
insertedThings.Sort(Comparison);
deletedThings.Sort(Comparison);
int i = 0;
int d = 0;
do
{
Span inserted = insertedThings[i].span;
Span deleted = deletedThings[d].span;
Span? overlap = inserted.Overlap(deleted);
if (overlap == null)
{
if (inserted.Start < deleted.Start)
{
i++;
}
else
{
d++;
}
}
else
{
NormalizedSpanCollection insertedResidue = NormalizedSpanCollection.Difference(new NormalizedSpanCollection(inserted),
new NormalizedSpanCollection(overlap.Value)); // todo add overload to normalizedspancollection
if (insertedResidue.Count > 0)
{
int pos = insertedThings[i].position;
insertedThings.RemoveAt(i);
bool didOverlap = false;
int ir = 0;
while (ir < insertedResidue.Count)
{
Span r = insertedResidue[ir];
if (didOverlap || r.Start < overlap.Value.Start)
{
insertedThings.Insert(i++, new Thing(r, pos));
ir++;
}
else
{
insertedThings.Insert(i++, new Thing(overlap.Value, pos));
didOverlap = true;
}
}
if (!didOverlap)
{
insertedThings.Insert(i++, new Thing(overlap.Value, pos));
}
i--;
}
NormalizedSpanCollection deletedResidue = NormalizedSpanCollection.Difference(new NormalizedSpanCollection(deleted),
new NormalizedSpanCollection(overlap.Value));
if (deletedResidue.Count > 0)
{
int pos = deletedThings[d].position;
deletedThings.RemoveAt(d);
bool didOverlap = false;
int dr = 0;
while (dr < deletedResidue.Count)
{
Span r = deletedResidue[dr];
if (didOverlap || r.Start < overlap.Value.Start)
{
deletedThings.Insert(d++, new Thing(r, pos));
dr++;
}
else
{
deletedThings.Insert(d++, new Thing(overlap.Value, pos));
didOverlap = true;
}
}
if (!didOverlap)
{
deletedThings.Insert(d++, new Thing(overlap.Value, pos));
}
d--;
}
}
if (inserted.End <= deleted.End)
{
i++;
}
if (deleted.End <= inserted.End)
{
d++;
}
} while (i < insertedThings.Count && d < deletedThings.Count);
}
}
foreach (KeyValuePair<ITextSnapshot, List<Thing>> pair in buffer2DeletedThings)
{
foreach (Thing t in pair.Value)
{
deletedSurrogates[t.position].Add(new SnapshotSpan(pair.Key, t.span));
}
}
foreach (KeyValuePair<ITextSnapshot, List<Thing>> pair in buffer2InsertedThings)
{
foreach (Thing t in pair.Value)
{
insertedSurrogates[t.position].Add(new SnapshotSpan(pair.Key, t.span));
}
}
}
#endregion
#region Private helpers
private class Thing
{
public Span span;
public int position;
public Thing(Span span, int position)
{
this.span = span;
this.position = position;
}
}
private static int Comparison(Thing left, Thing right)
{
return left.span.Start - right.span.Start;
}
#endregion
}
}
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