package docsite

import (
	"bytes"
	"fmt"

	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/ast"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/text"
	"github.com/yuin/goldmark/util"
)

// newMarkdown returns the one goldmark pipeline every page goes through:
// CommonMark plus GFM, heading IDs, and the page transformers. The html
// renderer keeps its default safe mode, so raw HTML in Markdown is never
// passed through.
func newMarkdown() goldmark.Markdown {
	return goldmark.New(
		goldmark.WithExtensions(extension.GFM),
		goldmark.WithParserOptions(
			parser.WithAutoHeadingID(),
			parser.WithASTTransformers(
				util.Prioritized(h1Stripper{}, 100),
			),
		),
	)
}

// h1Stripper removes the page's leading "# Title" heading; the template
// renders the title once.
type h1Stripper struct{}

func (h1Stripper) Transform(doc *ast.Document, _ text.Reader, _ parser.Context) {
	if h, ok := doc.FirstChild().(*ast.Heading); ok && h.Level == 1 {
		doc.RemoveChild(doc, h)
	}
}

// renderedPage is one page after parsing and rendering.
type renderedPage struct {
	html []byte
}

// renderPage parses and renders a page body to HTML.
func (s *site) renderPage(md goldmark.Markdown, p *Page) (renderedPage, error) {
	ctx := parser.NewContext()
	doc := md.Parser().Parse(text.NewReader(p.Body), parser.WithContext(ctx))
	var buf bytes.Buffer
	if err := md.Renderer().Render(&buf, p.Body, doc); err != nil {
		return renderedPage{}, fmt.Errorf("docsite: render %s: %w", p.Source, err)
	}
	return renderedPage{html: buf.Bytes()}, nil
}