// Copyright (c) 2015 Shawn Goertzen

// Copyright (c) 2017 Mikael Berthe

//

// This code mostly comes from github.com/sgoertzen/html2text,

// with some specific but intrusive changes for Mastodon HTML messages.

// For example, links are not displayed for hashtags and mentions,

// and links alone are displayed for the other cases.

//

// Licensed under the MIT license.

// Please see the LICENSE file is this directory.

package html2text

import (

	"bytes"

	"errors"

	"golang.org/x/net/html"

	"strings"

)

var breakers = map[string]bool{

	"br":  true,

	"div": true,

	"tr":  true,

	"li":  true,

	"p":   true,

}

// Textify turns an HTML body into a text string

func Textify(body string) (string, error) {

	r := strings.NewReader(body)

	doc, err := html.Parse(r)

	if err != nil {

		return "", errors.New("unable to parse the html")

	}

	var buffer bytes.Buffer

	process(doc, &buffer, "")

	s := strings.TrimSpace(buffer.String())

	return s, nil

}

func process(n *html.Node, b *bytes.Buffer, class string) {

	processChildren := true

	if n.Type == html.ElementNode && n.Data == "head" {

		return

	} else if n.Type == html.ElementNode && n.Data == "a" && n.FirstChild != nil {

		anchor(n, b, class)

		processChildren = false

	} else if n.Type == html.TextNode {

		// Clean up data

		cleanData := strings.Replace(strings.Trim(n.Data, " \t"), "\u00a0", " ", -1)

		// Heuristics to add a whitespace character...

		var prevSpace, nextSpace bool // hint if previous/next char is a space

		var last byte

		bl := b.Len()

		if bl > 0 {

			last = b.Bytes()[bl-1]

			if last == ' ' {

				prevSpace = true

			}

		}

		if len(cleanData) > 0 && cleanData[0] == ' ' {

			nextSpace = true

		}

		if prevSpace && nextSpace {

			b.WriteString(cleanData[1:]) // Trim 1 space

		} else {

			if bl > 0 && last != '\n' && last != '@' && last != '#' && !prevSpace && !nextSpace {

				b.WriteString(" ")

			}

			b.WriteString(cleanData)

		}

	}

	if processChildren {

		var class string

		if n.Type == html.ElementNode && n.Data == "span" {

			for _, attr := range n.Attr {

				if attr.Key == "class" {

					class = attr.Val

					break

				}

			}

		}

		for c := n.FirstChild; c != nil; c = c.NextSibling {

			process(c, b, class)

		}

	}

	if b.Len() > 0 {

		bl := b.Len()

		last := b.Bytes()[bl-1]

		if last != '\n' && n.Type == html.ElementNode && breakers[n.Data] {

			// Remove previous space

			for last == ' ' {

				bl--

				b.Truncate(bl)

				if bl > 0 {

					last = b.Bytes()[bl-1]

				} else {

					last = '\x00'

				}

			}

			b.WriteString("\n")

		}

	}

}

func anchor(n *html.Node, b *bytes.Buffer, class string) {

	bl := b.Len()

	var last byte

	if bl > 0 {

		last = b.Bytes()[bl-1]

	}

	var tmpbuf bytes.Buffer

	for c := n.FirstChild; c != nil; c = c.NextSibling {

		process(c, &tmpbuf, class)

	}

	if class == "tag" || class == "h-card" || last == '@' {

		b.Write(tmpbuf.Bytes())

		return

	}

	// Add heading space if needed

	if last != ' ' && last != '\n' {

		b.WriteString(" ")

	}

	s := tmpbuf.String()

	if strings.HasPrefix(s, "#") || strings.HasPrefix(s, "@") {

		b.WriteString(s) // Tag or mention: display content

		return

	}

	// Display href link

	for _, attr := range n.Attr {

		if attr.Key == "href" {

			link := n.Attr[0].Val

			b.WriteString(link)

			break

		}

	}

}