//go:build ignore

// Command gen_chroma_css regenerates assets/chroma.css, the syntax-highlighting
// stylesheet for fenced code blocks (see internal/parser/markdown.go). Run it
// via `go generate ./web` whenever the chosen Chroma styles should change.
package main

import (
	"bytes"
	"fmt"
	"os"

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

// lightStyleName and darkStyleName are the Chroma styles used for syntax
// highlighting in, respectively, light and dark mode. "github"/"github-dark"
// is a matched light/dark pair, mirroring the codebase's own light/dark
// palette in web/assets/style.css.
const (
	lightStyleName = "github"
	darkStyleName  = "github-dark"
)

func main() {
	formatter := chromahtml.New(chromahtml.WithClasses(true))

	var out bytes.Buffer
	out.WriteString("/* Generated by web/gen_chroma_css.go via `go generate ./web` — do not edit by hand. */\n\n")

	if err := writeStyle(&out, formatter, lightStyleName); err != nil {
		fail(err)
	}

	out.WriteString("\n@media (prefers-color-scheme: dark) {\n")
	if err := writeStyle(&out, formatter, darkStyleName); err != nil {
		fail(err)
	}
	out.WriteString("}\n")

	// pre already carries the slide deck's own code background
	// (--color-code-bg, matching plain, non-highlighted code blocks); this
	// overrides Chroma's own background class so highlighted blocks look
	// consistent with the rest of the deck instead of introducing a second
	// background color.
	out.WriteString("\npre.chroma, pre.chroma code {\n  background: var(--color-code-bg);\n}\n")

	if err := os.WriteFile("assets/vendor/chroma.css", out.Bytes(), 0o644); err != nil {
		fail(err)
	}
}

func writeStyle(w *bytes.Buffer, formatter *chromahtml.Formatter, name string) error {
	style := styles.Get(name)
	if style == nil {
		return fmt.Errorf("unknown chroma style %q", name)
	}
	return formatter.WriteCSS(w, style)
}

func fail(err error) {
	fmt.Fprintln(os.Stderr, "gen_chroma_css:", err)
	os.Exit(1)
}