Refactor: Decouple style from segment

[JordanMartinez]

The base area's type signature is:

public GenericStyledArea<ParagraphStyle, SegmentType, SegmentStyle>

When writing custom objects, we have to write the following code:

public CustomArea extends 
    GenericStyledArea<
        ParagraphStyle, 
        Either<
            TextObject<TextStyle>, 
            CustomObject<TextStyle>
        >, 
        TextStyle
    >

You'll notice that the styles are embedded into the custom objects. this doesn't make sense for two reasons:

1. What if the custom object doesn't need a style (e.g. a hyperlink should always be styled as a hyperlink)

public CustomArea extends 
    GenericStyledArea<
        ParagraphStyle, 
        Either<
            TextObject<TextStyle>, 
            CustomObject<
                TextStyle   // This is useless for the custom object
            > 
        >, 
        TextStyle
    >

2. What if one wanted to use a style objects for each object? In other words, Text could have TextStyle and CustomObject could have CustomObjectStyle? If so, we'd have to write this hairy code:

public CustomArea extends 
    GenericStyledArea<
        ParagraphStyle, 
        Either<
            TextObject<
                Either<
                    TextStyle, 
                    CustomObjectStyle
                >
            >, 
            CustomObject<
                Either<
                    TextStyle, 
                    CustomObjectStyle
                >
            >, 
        Either<
            TextStyle, 
            CustomObjectStyle
        >
    >
{}

I propose we separate the two, so that an segment type no longer knows its own style. Thus, the type signature would become:

public Case1Area extends 
    GenericStyledArea<
        ParagraphStyle, 
        Either<
            // stores the text, nothing more
            Text,
            // stores the displayed text and its actual link, nothing more
            Hyperlink 
        >, 
        // Text will render node using TextStyle. 
        // Hyperlink will ignore its associated TextStyle object 
        //    and set its node's style class to "hyperlink"
        TextStyle 
    >

public Case2Area extends 
    GenericStyledArea<
        ParagraphStyle, 
        Either<
            TextObject, 
            CustomObject
        >, 
        Either<
            TextStyle, 
            CustomStyle
        >
    >

// maybe a class like this that adds helper methods to work with the Eithers?
public GenericStyledEitherArea<PS, Seg1, Seg2, Style1, Style2> extends
    GenericStyledArea<PS, Either<Seg1, Seg2>, Either<Style1, Style2>>

Case2AreaAgain<ParagraphStyle, TextObject, CustomObject, TextStyle, CustomStyle>
    extends GenericStyledEitherArea< /* the types */ >

[JordanMartinez]

One issue that can arise with this: setting the style of an Either.left object with an Either.right style.

[JordanMartinez]

To me, the best way this should be resolved is by refactoring Paragraph, so that it stores the segments styles outside of them by having a separate StyleSpans<S> object. Then, the concat/subsequence/etc methods would call the corresponding methods on the List<SEG> segments object and StyleSpans<S> styles object each and pass their results into the Paragraph's constructor: Paragraph(paragraphStyle, segmentOps, segments, styles).

SegmentOps would need to refactored as well. TextExt would need to convert Paragraph<PS, SEG, S> into a List<StyledSegment<SEG, S>> to properly render the segments to the screen as a single style could be used throughout multiple segments, or a single segment, could have multiple styles.