package render

import (
	"bytes"
	"fmt"
	"regexp"

	chromahtml "github.com/alecthomas/chroma/v2/formatters/html"
	"github.com/yuin/goldmark"
	highlighting "github.com/yuin/goldmark-highlighting/v2"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
)

var (
	md         goldmark.Markdown
	platformRe = regexp.MustCompile("^```(\\w+)\\s+(pico|esp32s3|esp32c3)\\s*$")
)

func init() {
	md = goldmark.New(
		goldmark.WithExtensions(
			extension.GFM,
			highlighting.NewHighlighting(
				highlighting.WithFormatOptions(
					chromahtml.WithClasses(true),
					chromahtml.ClassPrefix("hl-"),
				),
			),
		),
		goldmark.WithParserOptions(
			parser.WithAutoHeadingID(),
		),
		goldmark.WithRendererOptions(
			html.WithUnsafe(),
		),
	)
}

// preprocessPlatformBlocks rewrites fenced code blocks tagged with a platform
// (e.g. ```cpp pico) into an HTML wrapper div + untagged fence so Goldmark
// renders them normally while preserving the data-platform attribute.
func preprocessPlatformBlocks(src []byte) []byte {
	lines := bytes.Split(src, []byte("\n"))
	var out [][]byte
	inFence := false
	platformFence := false

	for _, line := range lines {
		trimmed := bytes.TrimSpace(line)

		if !inFence {
			if m := platformRe.FindSubmatch(trimmed); m != nil {
				out = append(out, []byte(fmt.Sprintf(`<div data-platform="%s">`, m[2])))
				out = append(out, []byte{})
				out = append(out, []byte("```"+string(m[1])))
				inFence = true
				platformFence = true
				continue
			}
			if bytes.HasPrefix(trimmed, []byte("```")) {
				inFence = true
			}
		} else if bytes.Equal(trimmed, []byte("```")) {
			inFence = false
			if platformFence {
				out = append(out, line)
				out = append(out, []byte{})
				out = append(out, []byte("</div>"))
				platformFence = false
				continue
			}
		}

		out = append(out, line)
	}

	return bytes.Join(out, []byte("\n"))
}

func Markdown(src []byte) ([]byte, error) {
	src = preprocessPlatformBlocks(src)
	var buf bytes.Buffer
	if err := md.Convert(src, &buf); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}