// Copyright 2019 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package markdown

import (
	"fmt"
	"regexp"
	"strings"

	"forgejo.org/modules/markup"
	"forgejo.org/modules/markup/common"
	markdownutil "forgejo.org/modules/markup/markdown/util"
	"forgejo.org/modules/setting"

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

var byteMailto = []byte("mailto:")

// ASTTransformer is a default transformer of the goldmark tree.
type ASTTransformer struct{}

func (g *ASTTransformer) applyElementDir(n ast.Node) {
	if markup.DefaultProcessorHelper.ElementDir != "" {
		n.SetAttributeString("dir", []byte(markup.DefaultProcessorHelper.ElementDir))
	}
}

// Transform transforms the given AST tree.
func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
	firstChild := node.FirstChild()
	tocMode := ""
	ctx := pc.Get(markdownutil.RenderContextKey).(*markup.RenderContext)
	rc := pc.Get(markdownutil.RenderConfigKey).(*RenderConfig)

	tocList := make([]markup.Header, 0, 20)
	if rc.yamlNode != nil {
		metaNode := rc.toMetaNode()
		if metaNode != nil {
			node.InsertBefore(node, firstChild, metaNode)
		}
		tocMode = rc.TOC
	}

	_ = ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
		if !entering {
			return ast.WalkContinue, nil
		}

		switch v := n.(type) {
		case *ast.Heading:
			g.transformHeading(ctx, v, reader, &tocList)
		case *ast.Paragraph:
			g.applyElementDir(v)
		case *ast.Image:
			g.transformImage(ctx, v)
		case *ast.Link:
			g.transformLink(ctx, v)
		case *ast.List:
			g.transformList(ctx, v, rc)
		case *ast.Text:
			if v.SoftLineBreak() && !v.HardLineBreak() {
				if ctx.Metas["mode"] != "document" {
					v.SetHardLineBreak(setting.Markdown.EnableHardLineBreakInComments)
				} else {
					v.SetHardLineBreak(setting.Markdown.EnableHardLineBreakInDocuments)
				}
			}
		case *ast.CodeSpan:
			g.transformCodeSpan(ctx, v, reader)
		case *common.Footnote:
			if scope, found := ctx.Metas["scope"]; found {
				v.Name = fmt.Appendf(v.Name, "-%s", scope)
			}
		case *common.FootnoteLink:
			if scope, found := ctx.Metas["scope"]; found {
				v.Name = fmt.Appendf(v.Name, "-%s", scope)
			}
		case *common.FootnoteBackLink:
			if scope, found := ctx.Metas["scope"]; found {
				v.Name = fmt.Appendf(v.Name, "-%s", scope)
			}
		}
		return ast.WalkContinue, nil
	})

	showTocInMain := tocMode == "true" /* old behavior, in main view */ || tocMode == "main"
	showTocInSidebar := !showTocInMain && tocMode != "false" // not hidden, not main, then show it in sidebar
	if len(tocList) > 0 && (showTocInMain || showTocInSidebar) {
		if showTocInMain {
			tocNode := createTOCNode(tocList, rc.Lang, nil)
			node.InsertBefore(node, firstChild, tocNode)
		} else {
			tocNode := createTOCNode(tocList, rc.Lang, map[string]string{"open": "open"})
			ctx.SidebarTocNode = tocNode
		}
	}

	if len(rc.Lang) > 0 {
		node.SetAttributeString("lang", []byte(rc.Lang))
	}
}

// NewHTMLRenderer creates a HTMLRenderer to render
// in the gitea form.
func NewHTMLRenderer(opts ...html.Option) renderer.NodeRenderer {
	r := &HTMLRenderer{
		Config: html.NewConfig(),
	}
	for _, opt := range opts {
		opt.SetHTMLOption(&r.Config)
	}
	return r
}

// HTMLRenderer is a renderer.NodeRenderer implementation that
// renders gitea specific features.
type HTMLRenderer struct {
	html.Config
}

// RegisterFuncs implements renderer.NodeRenderer.RegisterFuncs.
func (r *HTMLRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
	reg.Register(ast.KindDocument, r.renderDocument)
	reg.Register(KindDetails, r.renderDetails)
	reg.Register(KindSummary, r.renderSummary)
	reg.Register(KindIcon, r.renderIcon)
	reg.Register(ast.KindCodeSpan, r.renderCodeSpan)
	reg.Register(KindTaskCheckBoxListItem, r.renderTaskCheckBoxListItem)
	reg.Register(east.KindTaskCheckBox, r.renderTaskCheckBox)
}

func (r *HTMLRenderer) renderDocument(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
	n := node.(*ast.Document)

	if val, has := n.AttributeString("lang"); has {
		var err error
		if entering {
			_, err = w.WriteString("<div")
			if err == nil {
				_, err = fmt.Fprintf(w, ` lang=%q`, val)
			}
			if err == nil {
				_, err = w.WriteRune('>')
			}
		} else {
			_, err = w.WriteString("</div>")
		}

		if err != nil {
			return ast.WalkStop, err
		}
	}

	return ast.WalkContinue, nil
}

func (r *HTMLRenderer) renderDetails(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
	var err error
	if entering {
		if _, err = w.WriteString("<details"); err != nil {
			return ast.WalkStop, err
		}
		html.RenderAttributes(w, node, nil)
		_, err = w.WriteString(">")
	} else {
		_, err = w.WriteString("</details>")
	}

	if err != nil {
		return ast.WalkStop, err
	}

	return ast.WalkContinue, nil
}

func (r *HTMLRenderer) renderSummary(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
	var err error
	if entering {
		_, err = w.WriteString("<summary>")
	} else {
		_, err = w.WriteString("</summary>")
	}

	if err != nil {
		return ast.WalkStop, err
	}

	return ast.WalkContinue, nil
}

var validNameRE = regexp.MustCompile("^[a-z ]+$")

func (r *HTMLRenderer) renderIcon(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
	if !entering {
		return ast.WalkContinue, nil
	}

	n := node.(*Icon)

	name := strings.TrimSpace(strings.ToLower(string(n.Name)))

	if len(name) == 0 {
		// skip this
		return ast.WalkContinue, nil
	}

	if !validNameRE.MatchString(name) {
		// skip this
		return ast.WalkContinue, nil
	}

	_, err := fmt.Fprintf(w, `<i class="icon %s"></i>`, name)
	if err != nil {
		return ast.WalkStop, err
	}

	return ast.WalkContinue, nil
}
