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	//! De-HTML.
	//!
	//! A module to remove HTML tags from the email text

	use std::io::BufRead;

	use once_cell::sync::Lazy;
	use quick_xml::{
	events::{BytesEnd, BytesStart, BytesText},
	Reader,
	};

	use crate::simplify::{simplify_quote, SimplifiedText};

	struct Dehtml {
	strbuilder: String,
	quote: String,
	add_text: AddText,
	last_href: Option<String>,
	/// GMX wraps a quote in `<div name="quote">`. After a `<div name="quote">`, this count is
	/// increased at each `<div>` and decreased at each `</div>`. This way we know when the quote ends.
	/// If this is > `0`, then we are inside a `<div name="quote">`
	divs_since_quote_div: u32,
	/// Everything between `<div name="quote">` and `<div name="quoted-content">` is usually metadata
	/// If this is > `0`, then we are inside a `<div name="quoted-content">`.
	divs_since_quoted_content_div: u32,
	/// All-Inkl just puts the quote into `<blockquote> </blockquote>`. This count is
	/// increased at each `<blockquote>` and decreased at each `</blockquote>`.
	blockquotes_since_blockquote: u32,
	}

	impl Dehtml {
	/// Returns true if HTML parser is currently inside the quote.
	fn is_quote(&self) -> bool {
	self.divs_since_quoted_content_div > 0 \|\| self.blockquotes_since_blockquote > 0
	}

	/// Returns the buffer where the text should be written.
	///
	/// If the parser is inside the quote, returns the quote buffer.
	fn get_buf(&mut self) -> &mut String {
	if self.is_quote() {
	&mut self.quote
	} else {
	&mut self.strbuilder
	}
	}

	fn get_add_text(&self) -> AddText {
	if self.divs_since_quote_div > 0 && self.divs_since_quoted_content_div == 0 {
	AddText::No // Everything between `<div name="quoted">` and `<div name="quoted_content">` is metadata which we don't want
	} else {
	self.add_text
	}
	}
	}

	#[derive(Debug, PartialEq, Clone, Copy)]
	enum AddText {
	/// Inside `<script>`, `<style>` and similar tags
	/// which contents should not be displayed.
	No,

	YesRemoveLineEnds,

	/// Inside `<pre>`.
	YesPreserveLineEnds,
	}

	pub(crate) fn dehtml(buf: &str) -> Option<SimplifiedText> {
	let (s, quote) = dehtml_quick_xml(buf);
	if !s.trim().is_empty() {
	let text = dehtml_cleanup(s);
	let top_quote = if !quote.trim().is_empty() {
	Some(dehtml_cleanup(simplify_quote(&quote).0))
	} else {
	None
	};
	return Some(SimplifiedText {
	text,
	top_quote,
	..Default::default()
	});
	}
	let s = dehtml_manually(buf);
	if !s.trim().is_empty() {
	let text = dehtml_cleanup(s);
	return Some(SimplifiedText {
	text,
	..Default::default()
	});
	}
	None
	}

	fn dehtml_cleanup(mut text: String) -> String {
	text.retain(\|c\| c != '\r');
	let lines = text.trim().split('\n');
	let mut text = String::new();
	let mut linebreak = false;
	for line in lines {
	if line.chars().all(char::is_whitespace) {
	linebreak = true;
	} else {
	if !text.is_empty() {
	text += "\n";
	if linebreak {
	text += "\n";
	}
	}
	text += line.trim_end();
	linebreak = false;
	}
	}
	text
	}

	fn dehtml_quick_xml(buf: &str) -> (String, String) {
	let buf = buf.trim().trim_start_matches("<!doctype html>");

	let mut dehtml = Dehtml {
	strbuilder: String::with_capacity(buf.len()),
	quote: String::new(),
	add_text: AddText::YesRemoveLineEnds,
	last_href: None,
	divs_since_quote_div: 0,
	divs_since_quoted_content_div: 0,
	blockquotes_since_blockquote: 0,
	};

	let mut reader = quick_xml::Reader::from_str(buf);
	reader.check_end_names(false);

	let mut buf = Vec::new();

	loop {
	match reader.read_event_into(&mut buf) {
	Ok(quick_xml::events::Event::Start(ref e)) => {
	dehtml_starttag_cb(e, &mut dehtml, &reader)
	}
	Ok(quick_xml::events::Event::End(ref e)) => dehtml_endtag_cb(e, &mut dehtml),
	Ok(quick_xml::events::Event::Text(ref e)) => dehtml_text_cb(e, &mut dehtml),
	Ok(quick_xml::events::Event::CData(e)) => match e.escape() {
	Ok(e) => dehtml_text_cb(&e, &mut dehtml),
	Err(e) => {
	eprintln!(
	"CDATA escape error at position {}: {:?}",
	reader.buffer_position(),
	e,
	);
	}
	},
	Ok(quick_xml::events::Event::Empty(ref e)) => {
	// Handle empty tags as a start tag immediately followed by end tag.
	// For example, `<p/>` is treated as `<p></p>`.
	dehtml_starttag_cb(e, &mut dehtml, &reader);
	dehtml_endtag_cb(
	&BytesEnd::new(String::from_utf8_lossy(e.name().as_ref())),
	&mut dehtml,
	);
	}
	Err(e) => {
	eprintln!(
	"Parse html error: Error at position {}: {:?}",
	reader.buffer_position(),
	e
	);
	}
	Ok(quick_xml::events::Event::Eof) => break,
	_ => (),
	}
	buf.clear();
	}

	(dehtml.strbuilder, dehtml.quote)
	}

	fn dehtml_text_cb(event: &BytesText, dehtml: &mut Dehtml) {
	static LINE_RE: Lazy<regex::Regex> = Lazy::new(\|\| regex::Regex::new(r"(\r?\n)+").unwrap());

	if dehtml.get_add_text() == AddText::YesPreserveLineEnds
	\|\| dehtml.get_add_text() == AddText::YesRemoveLineEnds
	{
	let event = event as &[_];
	let event_str = std::str::from_utf8(event).unwrap_or_default();
	let mut last_added = escaper::decode_html_buf_sloppy(event).unwrap_or_default();
	if event_str.starts_with(&last_added) {
	last_added = event_str.to_string();
	}

	if dehtml.get_add_text() == AddText::YesRemoveLineEnds {
	// Replace all line ends with spaces.
	// E.g. `\r\n\r\n` is replaced with one space.
	let last_added = LINE_RE.replace_all(&last_added, " ");

	// Add a space if `last_added` starts with a space
	// and there is no whitespace at the end of the buffer yet.
	// Trim the rest of leading whitespace from `last_added`.
	let buf = dehtml.get_buf();
	if !buf.ends_with(' ') && !buf.ends_with('\n') && last_added.starts_with(' ') {
	*buf += " ";
	}

	*buf += last_added.trim_start();
	} else {
	*dehtml.get_buf() += LINE_RE.replace_all(&last_added, "\n").as_ref();
	}
	}
	}

	fn dehtml_endtag_cb(event: &BytesEnd, dehtml: &mut Dehtml) {
	let tag = String::from_utf8_lossy(event.name().as_ref())
	.trim()
	.to_lowercase();

	match tag.as_str() {
	"style" \| "script" \| "title" \| "pre" => {
	*dehtml.get_buf() += "\n\n";
	dehtml.add_text = AddText::YesRemoveLineEnds;
	}
	"div" => {
	pop_tag(&mut dehtml.divs_since_quote_div);
	pop_tag(&mut dehtml.divs_since_quoted_content_div);

	*dehtml.get_buf() += "\n\n";
	dehtml.add_text = AddText::YesRemoveLineEnds;
	}
	"a" => {
	if let Some(ref last_href) = dehtml.last_href.take() {
	let buf = dehtml.get_buf();
	if buf.ends_with('[') {
	buf.truncate(buf.len() - 1);
	} else {
	*buf += "](";
	*buf += last_href;
	*buf += ")";
	}
	}
	}
	"b" \| "strong" => {
	if dehtml.get_add_text() != AddText::No {
	dehtml.get_buf() += "";
	}
	}
	"i" \| "em" => {
	if dehtml.get_add_text() != AddText::No {
	*dehtml.get_buf() += "_";
	}
	}
	"blockquote" => pop_tag(&mut dehtml.blockquotes_since_blockquote),
	_ => {}
	}
	}

	fn dehtml_starttag_cb<B: std::io::BufRead>(
	event: &BytesStart,
	dehtml: &mut Dehtml,
	reader: &quick_xml::Reader<B>,
	) {
	let tag = String::from_utf8_lossy(event.name().as_ref())
	.trim()
	.to_lowercase();

	match tag.as_str() {
	"p" \| "table" \| "td" => {
	if !dehtml.strbuilder.is_empty() {
	*dehtml.get_buf() += "\n\n";
	}
	dehtml.add_text = AddText::YesRemoveLineEnds;
	}
	#[rustfmt::skip]
	"div" => {
	maybe_push_tag(event, reader, "quote", &mut dehtml.divs_since_quote_div);
	maybe_push_tag(event, reader, "quoted-content", &mut dehtml.divs_since_quoted_content_div);

	*dehtml.get_buf() += "\n\n";
	dehtml.add_text = AddText::YesRemoveLineEnds;
	}
	"br" => {
	*dehtml.get_buf() += "\n";
	dehtml.add_text = AddText::YesRemoveLineEnds;
	}
	"style" \| "script" \| "title" => {
	dehtml.add_text = AddText::No;
	}
	"pre" => {
	*dehtml.get_buf() += "\n\n";
	dehtml.add_text = AddText::YesPreserveLineEnds;
	}
	"a" => {
	if let Some(href) = event
	.html_attributes()
	.filter_map(\|attr\| attr.ok())
	.find(\|attr\| {
	String::from_utf8_lossy(attr.key.as_ref())
	.trim()
	.to_lowercase()
	== "href"
	})
	{
	let href = href
	.decode_and_unescape_value(reader)
	.unwrap_or_default()
	.to_string();

	if !href.is_empty() {
	dehtml.last_href = Some(href);
	*dehtml.get_buf() += "[";
	}
	}
	}
	"b" \| "strong" => {
	if dehtml.get_add_text() != AddText::No {
	dehtml.get_buf() += "";
	}
	}
	"i" \| "em" => {
	if dehtml.get_add_text() != AddText::No {
	*dehtml.get_buf() += "_";
	}
	}
	"blockquote" => dehtml.blockquotes_since_blockquote += 1,
	_ => {}
	}
	}

	/// In order to know when a specific tag is closed, we need to count the opening and closing tags.
	/// The `counts`s are stored in the `Dehtml` struct.
	fn pop_tag(count: &mut u32) {
	if *count > 0 {
	*count -= 1;
	}
	}

	/// In order to know when a specific tag is closed, we need to count the opening and closing tags.
	/// The `counts`s are stored in the `Dehtml` struct.
	fn maybe_push_tag(
	event: &BytesStart,
	reader: &Reader<impl BufRead>,
	tag_name: &str,
	count: &mut u32,
	) {
	if *count > 0 \|\| tag_contains_attr(event, reader, tag_name) {
	*count += 1;
	}
	}

	fn tag_contains_attr(event: &BytesStart, reader: &Reader<impl BufRead>, name: &str) -> bool {
	event.attributes().any(\|r\| {
	r.map(\|a\| {
	a.decode_and_unescape_value(reader)
	.map(\|v\| v == name)
	.unwrap_or(false)
	})
	.unwrap_or(false)
	})
	}

	pub fn dehtml_manually(buf: &str) -> String {
	// Just strip out everything between "<" and ">"
	let mut strbuilder = String::new();
	let mut show_next_chars = true;
	for c in buf.chars() {
	match c {
	'<' => show_next_chars = false,
	'>' => show_next_chars = true,
	_ => {
	if show_next_chars {
	strbuilder.push(c)
	}
	}
	}
	}
	strbuilder
	}

	#[cfg(test)]
	mod tests {
	use super::*;

	#[test]
	fn test_dehtml() {
	let cases = vec![
	(
	"<a href='https://example.com'> Foo </a>",
	"[ Foo ](https://example.com)",
	),
	("<b> bar </b>", "* bar *"),
	("<i>foo</i>", "_foo_"),
	("<b> bar <i> foo", "* bar _ foo"),
	("& bar", "& bar"),
	// Despite missing ', this should be shown:
	("<a href='/foo.png>Hi</a> ", "Hi"),
	("No link: <a href='https://get.delta.chat/'/>", "No link:"),
	(
	"No link: <a href='https://get.delta.chat/'></a>",
	"No link:",
	),
	("<!doctype html>\n<b>fat text</b>", "fat text"),
	// Invalid html (at least DC should show the text if the html is invalid):
	("<!some invalid html code>\n<b>some text</b>", "some text"),
	];
	for (input, output) in cases {
	assert_eq!(dehtml(input).unwrap().text, output);
	}
	let none_cases = vec!["<html> </html>", ""];
	for input in none_cases {
	assert_eq!(dehtml(input), None);
	}
	}

	#[test]
	fn test_dehtml_parse_br() {
	let html = "line1<br>line2";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "line1\nline2");

	let html = "line1<br> line2";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "line1\nline2");

	let html = "line1 <br><br> line2";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "line1\n\nline2");

	let html = "\r\r\nline1<br>\r\n\r\n\r\rline2<br/>line3\n\r";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "line1\nline2\nline3");
	}

	#[test]
	fn test_dehtml_parse_span() {
	assert_eq!(dehtml("<span>Foo</span>bar").unwrap().text, "Foobar");
	assert_eq!(dehtml("<span>Foo</span> bar").unwrap().text, "Foo bar");
	assert_eq!(dehtml("<span>Foo </span>bar").unwrap().text, "Foo bar");
	assert_eq!(dehtml("<span>Foo</span>\nbar").unwrap().text, "Foo bar");
	assert_eq!(dehtml("\n<span>Foo</span> bar").unwrap().text, "Foo bar");
	assert_eq!(dehtml("<span>Foo</span>\n\nbar").unwrap().text, "Foo bar");
	assert_eq!(dehtml("Foo\n<span>bar</span>").unwrap().text, "Foo bar");
	assert_eq!(dehtml("Foo<span>\nbar</span>").unwrap().text, "Foo bar");
	}

	#[test]
	fn test_dehtml_parse_p() {
	let html = "<p>Foo</p><p>Bar</p>";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "Foo\n\nBar");

	let html = "<p>Foo<p>Bar";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "Foo\n\nBar");

	let html = "<p>Foo</p><p>Bar<p>Baz";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "Foo\n\nBar\n\nBaz");
	}

	#[test]
	fn test_dehtml_parse_href() {
	let html = "<a href=url>text</a";
	let plain = dehtml(html).unwrap().text;

	assert_eq!(plain, "[text](url)");
	}

	#[test]
	fn test_dehtml_case_sensitive_link() {
	let html = "<html><A HrEf=\"https://foo.bar/Data\">case in URLs matter</A></html>";
	let plain = dehtml(html).unwrap().text;
	assert_eq!(plain, "[case in URLs matter](https://foo.bar/Data)");
	}

	#[test]
	fn test_dehtml_bold_text() {
	let html = "<!DOCTYPE name [<!DOCTYPE ...>]><!-- comment -->text <b><?php echo ... ?>bold</b><![CDATA[<>]]>";
	let plain = dehtml(html).unwrap().text;

	assert_eq!(plain, "text bold<>");
	}

	#[test]
	fn test_dehtml_html_encoded() {
	let html =
	"<>"'& äÄöÖüÜß fooÆçÇ &diams;&lrm;&rlm;&zwnj;&noent;&zwj;";

	let plain = dehtml(html).unwrap().text;

	assert_eq!(
	plain,
	"<>\"\'& äÄöÖüÜß fooÆçÇ \u{2666}\u{200e}\u{200f}\u{200c}&noent;\u{200d}"
	);
	}

	#[test]
	fn test_unclosed_tags() {
	let input = r##"
	<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.01 Transitional//EN'
	'http://www.w3.org/TR/html4/loose.dtd'>
	<html>
	<head>
	<title>Hi</title>
	<meta http-equiv='Content-Type' content='text/html; charset=iso-8859-1'>
	</head>
	<body>
	lots of text
	</body>
	</html>
	"##;
	let txt = dehtml(input).unwrap();
	assert_eq!(txt.text.trim(), "lots of text");
	}

	#[test]
	fn test_pre_tag() {
	let input = "<html><pre>\ntwo\nlines\n</pre></html>";
	let txt = dehtml(input).unwrap();
	assert_eq!(txt.text.trim(), "two\nlines");
	}

	#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
	async fn test_quote_div() {
	let input = include_str!("../test-data/message/gmx-quote-body.eml");
	let dehtml = dehtml(input).unwrap();
	let SimplifiedText {
	text,
	is_forwarded,
	is_cut,
	top_quote,
	footer,
	} = dehtml;
	assert_eq!(text, "Test");
	assert_eq!(is_forwarded, false);
	assert_eq!(is_cut, false);
	assert_eq!(top_quote.as_deref(), Some("test"));
	assert_eq!(footer, None);
	}

	#[test]
	fn test_spaces() {
	let input = include_str!("../test-data/spaces.html");
	let txt = dehtml(input).unwrap();
	assert_eq!(txt.text, "Welcome back to Strolling!\n\nHey there,\n\nWelcome back! Use this link to securely sign in to your Strolling account:\n\nSign in to Strolling\n\nFor your security, the link will expire in 24 hours time.\n\nSee you soon!\n\nYou can also copy & paste this URL into your browser:\n\nhttps://strolling.rosano.ca/members/?token=XXX&action=signin&r=https%3A%2F%2Fstrolling.rosano.ca%2F\n\nIf you did not make this request, you can safely ignore this email.\n\nThis message was sent from [strolling.rosano.ca](https://strolling.rosano.ca/) to [alice@example.org](mailto:alice@example.org)");
	}
	}