public SpanRider(SpanVector spans, SpanPosition latestPosition = new SpanPosition(), int cp = 0)
{
_spans = spans;
_spanPosition = new SpanPosition();
CurrentPosition = 0;
Length = 0;
At(latestPosition, cp);
}
/// <summary>
/// Delete n elements of vector
/// </summary>
internal virtual void Delete(int index, int count, ref SpanPosition latestPosition)
{
DeleteInternal(index, count);
if (index <= latestPosition.Index)
{
latestPosition = new SpanPosition();
}
}
public bool At(SpanPosition latestPosition, int cp)
{
var inRange = _spans.FindSpan(cp, latestPosition, out _spanPosition);
if (inRange)
{
// cp is in range:
// - Length is the distance to the end of the span
// - CurrentPosition is cp
Length = _spans[_spanPosition.Index].length - (cp - _spanPosition.Offset);
CurrentPosition = cp;
}
else
{
// cp is out of range:
// - Length is the default span length
// - CurrentPosition is the end of the last span
Length = int.MaxValue;
CurrentPosition = _spanPosition.Offset;
}
return(inRange);
}
private SpanPosition _spanPosition; // index and cp of current span
public SpanRider(SpanVector spans, SpanPosition latestPosition) : this(spans, latestPosition, latestPosition.Offset)
{
}
private SpanPosition Set(int first, int length, object?element, Equals equals, SpanPosition spanPosition)
{
var inRange = FindSpan(first, spanPosition, out spanPosition);
// fs = index of first span partly or completely updated
// fc = character index at start of fs
var fs = spanPosition.Index;
var fc = spanPosition.Offset;
// Find the span that contains the first affected cp
if (!inRange)
{
// The first cp is past the end of the last span
if (fc < first)
{
// Create default run up to first
Add(new Span(Default, first - fc));
}
if (Count > 0 &&
equals(_spans[Count - 1].element, element))
{
// New Element matches end Element, just extend end Element
_spans[Count - 1].length += length;
// Make sure fs and fc still agree
if (fs == Count)
{
fc += length;
}
}
else
{
Add(new Span(element, length));
}
}
else
{
// Now find the last span affected by the update
var ls = fs;
var lc = fc;
while (ls < Count &&
lc + _spans[ls].length <= first + length)
{
lc += _spans[ls].length;
ls++;
}
// ls = first span following update to remain unchanged in part or in whole
// lc = character index at start of ls
// expand update region backwards to include existing Spans of identical
// Element type
if (first == fc)
{
// Item at [fs] is completely replaced. Check prior item
if (fs > 0 &&
equals(_spans[fs - 1].element, element))
{
// Expand update area over previous run of equal classification
fs--;
fc -= _spans[fs].length;
first = fc;
length += _spans[fs].length;
}
}
else
{
// Item at [fs] is partially replaced. Check if it is same as update
if (equals(_spans[fs].element, element))
{
// Expand update area back to start of first affected equal valued run
length = first + length - fc;
first = fc;
}
}
// Expand update region forwards to include existing Spans of identical
// Element type
if (ls < Count &&
equals(_spans[ls].element, element))
{
// Extend update region to end of existing split run
length = lc + _spans[ls].length - first;
lc += _spans[ls].length;
ls++;
}
// If no old Spans remain beyond area affected by update, handle easily:
if (ls >= Count)
{
// None of the old span list extended beyond the update region
if (fc < first)
{
// Updated region leaves some of [fs]
if (Count != fs + 2)
{
if (!Resize(fs + 2))
{
throw new OutOfMemoryException();
}
}
_spans[fs].length = first - fc;
_spans[fs + 1] = new Span(element, length);
}
else
{
// Updated item replaces [fs]
if (Count != fs + 1)
{
if (!Resize(fs + 1))
{
throw new OutOfMemoryException();
}
}
_spans[fs] = new Span(element, length);
}
}
else
{
// Record partial element type at end, if any
object?trailingElement = null;
var trailingLength = 0;
if (first + length > lc)
{
trailingElement = _spans[ls].element;
trailingLength = lc + _spans[ls].length - (first + length);
}
// Calculate change in number of Spans
var spanDelta = 1 // The new span
+ (first > fc ? 1 : 0) // part span at start
- (ls - fs); // existing affected span count
// Note part span at end doesn't affect the calculation - the run may need
// updating, but it doesn't need creating.
if (spanDelta < 0)
{
DeleteInternal(fs + 1, -spanDelta);
}
else if (spanDelta > 0)
{
Insert(fs + 1, spanDelta);
// Initialize inserted Spans
for (var i = 0; i < spanDelta; i++)
{
_spans[fs + 1 + i] = new Span(null, 0);
}
}
// Assign Element values
// Correct Length of split span before updated range
if (fc < first)
{
_spans[fs].length = first - fc;
fs++;
fc = first;
}
// Record Element type for updated range
_spans[fs] = new Span(element, length);
fs++;
fc += length;
// Correct Length of split span following updated range
if (lc < first + length)
{
_spans[fs] = new Span(trailingElement, trailingLength);
}
}
}
// Return a known valid span position.
return(new SpanPosition(fs, fc));
}
/// <summary>
/// Set an element as a reference to a character range; takes a SpanPosition of a recently accessed
/// span for performance and returns a known valid SpanPosition
/// </summary>
public SpanPosition SetReference(int first, int length, object element, SpanPosition spanPosition)
{
return(Set(first, length, element, SpanVector.s_referenceEquals, spanPosition));
}
/// <summary>
/// Set an element as a value to a character range; takes a SpanPosition of a recently accessed
/// span for performance and returns a known valid SpanPosition
/// </summary>
public SpanPosition SetValue(int first, int length, object element, SpanPosition spanPosition)
{
return(Set(first, length, element, SpanVector.s_equals, spanPosition));
}
/// <summary>
/// Finds the span that contains the specified character position.
/// </summary>
/// <param name="cp">position to find</param>
/// <param name="latestPosition">Position of the most recently accessed span (e.g., the current span
/// of a SpanRider) for performance; FindSpan runs in O(1) time if the specified cp is in the same span
/// or an adjacent span.</param>
/// <param name="spanPosition">receives the index and first cp of the span that contains the specified
/// position or, if the position is past the end of the vector, the index and cp just past the end of
/// the last span.</param>
/// <returns>Returns true if cp is in range or false if not.</returns>
internal bool FindSpan(int cp, SpanPosition latestPosition, out SpanPosition spanPosition)
{
Debug.Assert(cp >= 0);
var spanCount = _spans.Count;
int spanIndex, spanCP;
if (cp == 0)
{
// CP zero always corresponds to span index zero
spanIndex = 0;
spanCP = 0;
}
else if (cp >= latestPosition.Offset || cp * 2 < latestPosition.Offset)
{
// One of the following is true:
// 1. cp is after the latest position (the most recently accessed span)
// 2. cp is closer to zero than to the latest position
if (cp >= latestPosition.Offset)
{
// case 1: scan forward from the latest position
spanIndex = latestPosition.Index;
spanCP = latestPosition.Offset;
}
else
{
// case 2: scan forward from the start of the span vector
spanIndex = 0;
spanCP = 0;
}
// Scan forward until we find the Span that contains the specified CP or
// reach the end of the SpanVector
for (; spanIndex < spanCount; ++spanIndex)
{
var spanLength = _spans[spanIndex].length;
if (cp < spanCP + spanLength)
{
break;
}
spanCP += spanLength;
}
}
else
{
// The specified CP is before the latest position but closer to it than to zero;
// therefore scan backwards from the latest position
spanIndex = latestPosition.Index;
spanCP = latestPosition.Offset;
while (spanCP > cp)
{
Debug.Assert(spanIndex > 0);
spanCP -= _spans[--spanIndex].length;
}
}
// Return index and cp of span in out param.
spanPosition = new SpanPosition(spanIndex, spanCP);
// Return true if the span is in range.
return(spanIndex != spanCount);
}
