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package rendering

import (
    "bytes"
    "html/template"

    chromalib "github.com/alecthomas/chroma/v2"
    chromahtml "github.com/alecthomas/chroma/v2/formatters/html"
    "github.com/alecthomas/chroma/v2/lexers"
    "github.com/alecthomas/chroma/v2/styles"
)

func HighlightCode(content, filename string) (string, string) {
    lexer := lexers.Match(filename)
    if lexer == nil {
        lexer = lexers.Analyse(content)
    }
    if lexer == nil {
        lexer = lexers.Fallback
    }
    lexer = chromalib.Coalesce(lexer)

    style := styles.Get("onedark")
    if style == nil {
        style = styles.Fallback
    }

    formatter := chromahtml.New(
        chromahtml.WithClasses(true),
        chromahtml.TabWidth(4),
        chromahtml.WithLineNumbers(true),
        chromahtml.LineNumbersInTable(true),
    )

    var cssBuf bytes.Buffer
    if err := formatter.WriteCSS(&cssBuf, style); err != nil {
        return plainFallback(content), ""
    }
    chromaCSS := cssBuf.String()

    iterator, err := lexer.Tokenise(nil, content)
    if err != nil {
        return plainFallback(content), chromaCSS
    }

    var hlBuf bytes.Buffer
    if err := formatter.Format(&hlBuf, style, iterator); err != nil {
        return plainFallback(content), chromaCSS
    }

    return hlBuf.String(), chromaCSS
}

func plainFallback(content string) string {
    return `<pre style="padding:1rem;overflow:auto;font-size:0.82rem;line-height:1.65">` +
        template.HTMLEscapeString(content) + `</pre>`
}