using System.Collections;
using System.Collections.Generic;
using System.Text;
namespace MLEM.Font {
///
/// A code point source is a wrapper around a or that allows retrieving UTF-32 code points at a given index using . Additionally, it allows enumerating every code point in the underlying or .
///
public readonly struct CodePointSource : IEnumerable {
private readonly string strg;
private readonly StringBuilder builder;
private char this[int index] => this.strg?[index] ?? this.builder[index];
///
/// The length of this code point, in characters.
/// Note that this is not representative of the amount of code points in this source.
///
public int Length => this.strg?.Length ?? this.builder.Length;
///
/// Creates a new code point source from the given .
///
/// The whose code points to inspect.
public CodePointSource(string strg) {
this.strg = strg;
this.builder = null;
}
///
/// Creates a new code point source from the given .
///
/// The whose code points to inspect.
public CodePointSource(StringBuilder builder) {
this.strg = null;
this.builder = builder;
}
///
/// Returns the code point at the given in this code point source's underlying string, where the index is measured in characters and not code points.
/// The resulting code point will either be a single cast to an , at which point the returned length will be 1, or a UTF-32 character made up of two values, at which point the returned length will be 2.
///
/// The index at which to return the code point, which is measured in characters.
/// Whether the represents a low surrogate. If this is , the represents a high surrogate and the low surrogate will be looked for in the following character. If this is , the represents a low surrogate and the high surrogate will be looked for in the previous character.
///
public (int CodePoint, int Length) GetCodePoint(int index, bool indexLowSurrogate = false) {
var curr = this[index];
if (indexLowSurrogate) {
if (index > 0) {
var high = this[index - 1];
if (char.IsSurrogatePair(high, curr))
return (char.ConvertToUtf32(high, curr), 2);
}
} else {
if (index < this.Length - 1) {
var low = this[index + 1];
if (char.IsSurrogatePair(curr, low))
return (char.ConvertToUtf32(curr, low), 2);
}
}
return (curr, 1);
}
/// Returns an enumerator that iterates through the collection.
/// A that can be used to iterate through the collection.
/// 1
public IEnumerator GetEnumerator() {
var index = 0;
while (index < this.Length) {
var (codePoint, length) = this.GetCodePoint(index);
yield return codePoint;
index += length;
}
}
/// Returns an enumerator that iterates through a collection.
/// An object that can be used to iterate through the collection.
/// 2
IEnumerator IEnumerable.GetEnumerator() {
return this.GetEnumerator();
}
}
}