// Copyright 2017 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package orgmode

import (
	"fmt"
	"html/template"
	"io"
	"strings"

	"code.gitea.io/gitea/modules/highlight"
	"code.gitea.io/gitea/modules/htmlutil"
	"code.gitea.io/gitea/modules/log"
	"code.gitea.io/gitea/modules/markup"
	"code.gitea.io/gitea/modules/setting"

	"github.com/alecthomas/chroma/v2"
	"github.com/niklasfasching/go-org/org"
)

func init() {
	markup.RegisterRenderer(renderer{})
}

// Renderer implements markup.Renderer for orgmode
type renderer struct{}

var (
	_ markup.Renderer            = (*renderer)(nil)
	_ markup.PostProcessRenderer = (*renderer)(nil)
)

func (renderer) Name() string {
	return "orgmode"
}

func (renderer) NeedPostProcess() bool { return true }

func (renderer) FileNamePatterns() []string {
	return []string{"*.org"}
}

func (renderer) SanitizerRules() []setting.MarkupSanitizerRule {
	return []setting.MarkupSanitizerRule{}
}

// Render renders orgmode raw bytes to HTML
func Render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
	htmlWriter := org.NewHTMLWriter()
	htmlWriter.HighlightCodeBlock = func(source, lang string, inline bool, params map[string]string) string {
		defer func() {
			if err := recover(); err != nil {
				// catch the panic, log the error and return empty result
				log.Error("Panic in HighlightCodeBlock: %v\n%s", err, log.Stack(2))
			}
		}()

		lexer := highlight.GetChromaLexerWithFallback("", lang, nil) // don't use content to detect, it is too slow
		lexer = chroma.Coalesce(lexer)

		sb := &strings.Builder{}
		// include language-x class as part of commonmark spec
		_ = ctx.RenderInternal.FormatWithSafeAttrs(sb, `<pre><code class="chroma language-%s">`, strings.ToLower(lexer.Config().Name))
		_, _ = sb.WriteString(string(highlight.RenderCodeByLexer(lexer, source)))
		_, _ = sb.WriteString("</code></pre>")
		return sb.String()
	}

	w := &orgWriter{rctx: ctx, HTMLWriter: htmlWriter}
	htmlWriter.ExtendingWriter = w

	// Parse the document first to extract outline for TOC
	doc := org.New().Silent().Parse(input, "")
	if doc.Error != nil {
		return fmt.Errorf("orgmode.Parse failed: %w", doc.Error)
	}

	// Extract headers from the document outline for sidebar TOC
	ctx.SidebarTocHeaders = extractHeadersFromOutline(doc.Outline)

	res, err := doc.Write(w)
	if err != nil {
		return fmt.Errorf("orgmode.Render failed: %w", err)
	}
	_, err = io.Copy(output, strings.NewReader(res))
	return err
}

// extractHeadersFromOutline recursively extracts headers from org document outline
func extractHeadersFromOutline(outline org.Outline) []markup.Header {
	var headers []markup.Header
	collectHeaders(outline.Section, &headers)
	return headers
}

// collectHeaders recursively collects headers from sections
func collectHeaders(section *org.Section, headers *[]markup.Header) {
	if section == nil {
		return
	}

	// Process current section's headline
	if section.Headline != nil {
		h := section.Headline
		// Convert headline title nodes to plain text
		titleText := org.String(h.Title...)
		*headers = append(*headers, markup.Header{
			Level: h.Lvl,
			Text:  titleText,
			ID:    h.ID(),
		})
	}

	// Process child sections
	for _, child := range section.Children {
		collectHeaders(child, headers)
	}
}

// RenderString renders orgmode string to HTML string
func RenderString(ctx *markup.RenderContext, content string) (string, error) {
	var buf strings.Builder
	if err := Render(ctx, strings.NewReader(content), &buf); err != nil {
		return "", err
	}
	return buf.String(), nil
}

// Render renders orgmode string to HTML string
func (renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
	return Render(ctx, input, output)
}

type orgWriter struct {
	*org.HTMLWriter
	rctx *markup.RenderContext
}

var _ org.Writer = (*orgWriter)(nil)

func (r *orgWriter) resolveLink(link string) string {
	return strings.TrimPrefix(link, "file:")
}

// WriteRegularLink renders images, links or videos
func (r *orgWriter) WriteRegularLink(l org.RegularLink) {
	link := r.resolveLink(l.URL)

	printHTML := func(html template.HTML, a ...any) {
		_, _ = fmt.Fprint(r, htmlutil.HTMLFormat(html, a...))
	}
	// Inspired by https://github.com/niklasfasching/go-org/blob/6eb20dbda93cb88c3503f7508dc78cbbc639378f/org/html_writer.go#L406-L427
	switch l.Kind() {
	case "image":
		if l.Description == nil {
			printHTML(`<img src="%s" alt="%s">`, link, link)
		} else {
			imageSrc := r.resolveLink(org.String(l.Description...))
			printHTML(`<a href="%s"><img src="%s" alt="%s"></a>`, link, imageSrc, imageSrc)
		}
	case "video":
		if l.Description == nil {
			printHTML(`<video src="%s">%s</video>`, link, link)
		} else {
			videoSrc := r.resolveLink(org.String(l.Description...))
			printHTML(`<a href="%s"><video src="%s">%s</video></a>`, link, videoSrc, videoSrc)
		}
	default:
		var description any = link
		if l.Description != nil {
			description = template.HTML(r.WriteNodesAsString(l.Description...)) // orgmode HTMLWriter outputs HTML content
		}
		printHTML(`<a href="%s">%s</a>`, link, description)
	}
}