compose-highlight/dev.hossain.highlight.engine/ThemeParser

ThemeParser

Parses Highlight.js CSS theme files into a map of hljs class names ->SpanStyle.

Why this exists

Highlight.js tokenizes source code into HTML where each token is wrapped in a <span class="hljs-keyword"> (or similar class). It assigns class names only - it does not apply colors. Colors come from the companion CSS theme file, where rules like .hljs-keyword { color: #7928a1 } define the appearance of each token type.

Compose cannot consume CSS directly, so ThemeParser bridges the gap: it reads the CSS file and produces a Map<String, SpanStyle> (e.g. "hljs-keyword" -> SpanStyle(color=...)) that HtmlToAnnotatedString uses to apply the correct color to each token when building the final androidx.compose.ui.text.AnnotatedString.

hljs theme CSS files follow a strict, predictable flat-rule format so a regex-based parser is sufficient. At-rule blocks (e.g. @media, @supports) are stripped before parsing to prevent inner rules from overwriting top-level color declarations.

Functions

parse

fun parse(cssText: String): Map<String, SpanStyle>

Parses CSS text directly into a color map. Extracts SpanStyle for each .hljs-* selector block.

fun parse(context: Context, cssAssetPath: String): Map<String, SpanStyle>

Parses a CSS theme file from assets into a color map. Results are not cached here - callers should use lazy to cache per theme.

parseAsset

fun parseAsset(context: Context, cssAssetPath: String): Map<String, SpanStyle>

Parses a CSS theme file from assets into a color map. Unlike parse, this overload throws if the file cannot be opened, so callers can distinguish a missing file from a successfully-parsed (but empty) theme.