// Copyright 2023 GoEdge CDN goedge.cdn@gmail.com. All rights reserved. Official site: https://goedge.cn .

package docutils

import (
	"bytes"
	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"
	"os"
	"path/filepath"
	"regexp"
	"sync"
)

type cacheItem struct {
	ModifiedAt int64
	Data       []byte
}

var cacheMap = map[string]*cacheItem{} // path => *cacheItem
var cacheLocker = &sync.RWMutex{}

func ReadMarkdownFile(path string, productName string, rootURL string) ([]byte, error) {
	stat, err := os.Stat(path)
	if err != nil {
		return nil, err
	}

	if stat.IsDir() {
		return nil, os.ErrNotExist
	}
	var modifiedAt = stat.ModTime().Unix()

	cacheLocker.RLock()
	item, ok := cacheMap[path]
	if ok && item.ModifiedAt == modifiedAt {
		cacheLocker.RUnlock()
		return item.Data, nil
	}
	cacheLocker.RUnlock()

	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}

	// keywords
	data = bytes.ReplaceAll(data, []byte("GoEdge"), []byte(productName))
	data = bytes.ReplaceAll(data, []byte("GOEDGE"), []byte(productName))
	data = bytes.ReplaceAll(data, []byte("http://goedge.cn"), []byte("http://example.com"))
	data = bytes.ReplaceAll(data, []byte("https://goedge.cn"), []byte("https://example.com"))

	var markdown = goldmark.New(
		goldmark.WithParserOptions(
			parser.WithAutoHeadingID(), // read note
		),
		goldmark.WithExtensions(extension.Table,
			extension.Strikethrough,
			highlighting.NewHighlighting(highlighting.WithStyle("github"), highlighting.WithFormatOptions(chromahtml.TabWidth(4))),
		),
		goldmark.WithRendererOptions(html.WithHardWraps()),
	)

	var buf = &bytes.Buffer{}
	err = markdown.Convert(data, buf)
	if err != nil {
		return nil, err
	}
	data = buf.Bytes()

	// convert links
	{
		var reg = regexp.MustCompile(`(?U)<a href="(.+\.md)">`)
		data = reg.ReplaceAllFunc(data, func(link []byte) []byte {
			var pieces = reg.FindSubmatch(link)
			if len(pieces) > 1 {
				var newLink = append([]byte(rootURL), bytes.TrimSuffix(pieces[1], []byte(".md"))...)
				newLink = append(newLink, []byte(".html")...)
				newLink = []byte(filepath.Clean(string(newLink)))
				return bytes.ReplaceAll(link, pieces[1], newLink)
			}
			return link
		})
	}

	// convert images
	{
		var reg = regexp.MustCompile(`(?U)<img src="(.+)"[^>]*>`)
		data = reg.ReplaceAllFunc(data, func(link []byte) []byte {
			var pieces = reg.FindSubmatch(link)
			if len(pieces) > 1 {
				var newLink = append([]byte(rootURL), pieces[1]...)
				newLink = []byte(filepath.Clean(string(newLink)))
				return []byte("<a href=\"" + string(newLink) + "\" target=\"_blank\">" + string(bytes.ReplaceAll(link, pieces[1], newLink)) + "</a>")
			}
			return link
		})
	}

	// put into cache
	item = &cacheItem{
		ModifiedAt: modifiedAt,
		Data:       data,
	}
	cacheLocker.Lock()
	cacheMap[path] = item
	cacheLocker.Unlock()

	return data, nil
}