//! Helper traits and methods for strings.

use std::fmt::Write;

use gtk::glib::markup_escape_text;
use linkify::{LinkFinder, LinkKind};
use ruma::{MatrixUri, RoomAliasId, RoomId, UserId};
use url::Url;

#[cfg(test)]
mod tests;

use super::matrix::{find_at_room, MatrixIdUri, AT_ROOM};
use crate::{
    components::{LabelWithWidgets, Pill},
    prelude::*,
    session::model::Room,
};

/// The prefix for an email URI.
const EMAIL_URI_PREFIX: &str = "mailto:";
/// The prefix for a HTTPS URL.
const HTTPS_URI_PREFIX: &str = "https://";
/// The scheme for a `matrix:` URI.
const MATRIX_URI_SCHEME: &str = "matrix";

/// Common extensions to strings.
pub trait StrExt {
    /// Escape markup for compatibility with Pango.
    fn escape_markup(&self) -> String;

    /// Remove newlines from the string.
    fn remove_newlines(&self) -> String;
}

impl<T> StrExt for T
where
    T: AsRef<str>,
{
    fn escape_markup(&self) -> String {
        markup_escape_text(self.as_ref()).into()
    }

    fn remove_newlines(&self) -> String {
        self.as_ref().replace('\n', "")
    }
}

/// Common extensions to mutable strings.
pub trait StrMutExt {
    /// Truncate this string at the first newline.
    ///
    /// Appends an ellipsis if the string was truncated.
    ///
    /// Returns `true` if the string was truncated.
    fn truncate_newline(&mut self) -> bool;

    /// Truncate whitespaces at the end of the string.
    fn truncate_end_whitespaces(&mut self);

    /// Append an ellipsis, except if this string already ends with an ellipsis.
    fn append_ellipsis(&mut self);
}

impl StrMutExt for String {
    fn truncate_newline(&mut self) -> bool {
        let newline = self.find('\n');

        if let Some(newline) = newline {
            self.truncate(newline);
            self.append_ellipsis();
        }

        newline.is_some()
    }

    fn truncate_end_whitespaces(&mut self) {
        if self.is_empty() {
            return;
        }

        let rspaces_idx = self
            .rfind(|c: char| !c.is_whitespace())
            .map(|idx| {
                // We have the position of the last non-whitespace character, so the first
                // whitespace character is the next one.
                let mut idx = idx + 1;

                while !self.is_char_boundary(idx) {
                    idx += 1;
                }

                idx
            })
            // 0 means that there are only whitespaces in the string.
            .unwrap_or_default();

        if rspaces_idx < self.len() {
            self.truncate(rspaces_idx);
        }
    }

    fn append_ellipsis(&mut self) {
        if !self.ends_with('…') && !self.ends_with("..") {
            self.push('…');
        }
    }
}

/// Common extensions for adding Pango markup to mutable strings.
pub trait PangoStrMutExt {
    /// Append the opening Pango markup link tag of the given URI parts.
    ///
    /// The URI is also used as a title, so users can preview the link on hover.
    fn append_link_opening_tag(&mut self, uri: impl AsRef<str>);

    /// Append the given emote's sender name and consumes it, if it is set.
    fn maybe_append_emote_name(&mut self, name: &mut Option<&str>);

    /// Append the given URI as a mention, if it is one.
    ///
    /// Returns the created [`Pill`], it the URI was added as a mention.
    fn maybe_append_mention(&mut self, uri: impl TryInto<MatrixIdUri>, room: &Room)
        -> Option<Pill>;

    /// Append the given string and replace `@room` with a mention.
    ///
    /// Returns the created [`Pill`], it `@room` was found.
    fn append_and_replace_at_room(&mut self, s: &str, room: &Room) -> Option<Pill>;
}

impl PangoStrMutExt for String {
    fn append_link_opening_tag(&mut self, uri: impl AsRef<str>) {
        let uri = uri.escape_markup();
        // We need to escape the title twice because GTK doesn't take care of it.
        let title = uri.escape_markup();

        let _ = write!(self, r#"<a href="{uri}" title="{title}">"#);
    }

    fn maybe_append_emote_name(&mut self, name: &mut Option<&str>) {
        if let Some(name) = name.take() {
            let _ = write!(self, "<b>{}</b> ", name.escape_markup());
        }
    }

    fn maybe_append_mention(
        &mut self,
        uri: impl TryInto<MatrixIdUri>,
        room: &Room,
    ) -> Option<Pill> {
        let pill = uri.try_into().ok().and_then(|uri| uri.into_pill(room))?;

        self.push_str(LabelWithWidgets::DEFAULT_PLACEHOLDER);

        Some(pill)
    }

    fn append_and_replace_at_room(&mut self, s: &str, room: &Room) -> Option<Pill> {
        if let Some(pos) = find_at_room(s) {
            self.push_str(&(&s[..pos]).escape_markup());
            self.push_str(LabelWithWidgets::DEFAULT_PLACEHOLDER);
            self.push_str(&(&s[pos + AT_ROOM.len()..]).escape_markup());

            Some(room.at_room().to_pill())
        } else {
            self.push_str(&s.escape_markup());
            None
        }
    }
}

/// Linkify the given text.
///
/// The text will also be escaped with [`StrExt::escape_markup()`].
pub fn linkify(text: &str) -> String {
    let mut linkified = String::with_capacity(text.len());
    Linkifier::new(&mut linkified).linkify(text);
    linkified
}

/// A helper type to linkify text.
pub struct Linkifier<'a> {
    /// The string containing the result.
    inner: &'a mut String,
    /// The mentions detection setting and results.
    mentions: MentionsMode<'a>,
}

impl<'a> Linkifier<'a> {
    /// Construct a new linkifier that will add text in the given string.
    pub fn new(inner: &'a mut String) -> Self {
        Self {
            inner,
            mentions: MentionsMode::NoMentions,
        }
    }

    /// Enable mentions detection in the given room and add pills to the given
    /// list.
    ///
    /// If `detect_at_room` is `true`, it will also try to detect `@room`
    /// mentions.
    pub fn detect_mentions(
        mut self,
        room: &'a Room,
        pills: &'a mut Vec<Pill>,
        detect_at_room: bool,
    ) -> Self {
        self.mentions = MentionsMode::WithMentions {
            pills,
            room,
            detect_at_room,
        };
        self
    }

    /// Search and replace links in the given text.
    ///
    /// Returns the list of mentions, if any where found.
    pub fn linkify(mut self, text: &str) {
        let mut finder = LinkFinder::new();
        // Allow URLS without a scheme.
        finder.url_must_have_scheme(false);

        let mut prev_span = None;

        for span in finder.spans(text) {
            let span_text = span.as_str();

            match span.kind() {
                Some(LinkKind::Url) => {
                    let is_valid_url = self.append_detected_url(span_text, prev_span);

                    if is_valid_url {
                        prev_span = None;
                    } else {
                        prev_span = Some(span_text);
                    }
                }
                Some(LinkKind::Email) => {
                    self.inner
                        .append_link_opening_tag(format!("{EMAIL_URI_PREFIX}{span_text}"));
                    self.inner.push_str(&span_text.escape_markup());
                    self.inner.push_str("</a>");

                    // The span was a valid email so we will not need to check it for the next span.
                    prev_span = None;
                }
                _ => {
                    if let MentionsMode::WithMentions {
                        pills,
                        room,
                        detect_at_room: true,
                    } = &mut self.mentions
                    {
                        if let Some(pill) = self.inner.append_and_replace_at_room(span_text, room) {
                            pills.push(pill);
                        }

                        prev_span = Some(span_text);
                        continue;
                    }

                    self.append_string(span_text);
                    prev_span = Some(span_text);
                }
            }
        }
    }

    /// Append the given string.
    ///
    /// Escapes the markup of the string.
    fn append_string(&mut self, s: &str) {
        self.inner.push_str(&s.escape_markup());
    }

    /// Append the given URI with the given link content.
    fn append_uri(&mut self, uri: &str, content: &str) {
        if let MentionsMode::WithMentions { pills, room, .. } = &mut self.mentions {
            if let Some(pill) = self.inner.maybe_append_mention(uri, room) {
                pills.push(pill);

                return;
            }
        }

        self.inner.append_link_opening_tag(uri);
        self.append_string(content);
        self.inner.push_str("</a>");
    }

    /// Append the given string detected as a URL.
    ///
    /// Appends false positives as normal strings, otherwise appends it as a
    /// URI.
    ///
    /// Returns `true` if it was detected as a valid URL.
    fn append_detected_url(&mut self, detected_url: &str, prev_span: Option<&str>) -> bool {
        if Url::parse(detected_url).is_ok() {
            // This is a full URL with a scheme, we can trust that it is valid.
            self.append_uri(detected_url, detected_url);
            return true;
        }

        // It does not have a scheme, try to split it to get only the domain.
        let domain = if let Some((domain, _)) = detected_url.split_once('/') {
            // This is a URL with a path component.
            domain
        } else if let Some((domain, _)) = detected_url.split_once('?') {
            // This is a URL with a query component.
            domain
        } else if let Some((domain, _)) = detected_url.split_once('#') {
            // This is a URL with a fragment.
            domain
        } else {
            // It should only contain the full domain.
            detected_url
        };

        // Check that the top-level domain is known.
        if !domain.rsplit_once('.').is_some_and(|(_, d)| tld::exist(d)) {
            // This is a false positive, treat it like a regular string.
            self.append_string(detected_url);
            return false;
        }

        // The LinkFinder detects the homeserver part of `matrix:` URIs and Matrix
        // identifiers, e.g. it detects `example.org` in `matrix:r/somewhere:
        // example.org` or in `#somewhere:matrix.org`. We can use that to detect the
        // full URI or identifier with the previous span.

        // First, detect if the previous character is `:`, this is common to URIs and
        // identifiers.
        if let Some(prev_span) = prev_span.filter(|s| s.ends_with(':')) {
            // Most identifiers in Matrix do not have a list of allowed characters, so all
            // characters are allowed… which makes it difficult to find where they start.
            // We have to set arbitrary rules for the localpart to match most cases:
            // - No whitespaces
            // - No `:`, as it is the separator between localpart and server name, and after
            //   the scheme in URIs
            // - As soon as we encounter a known sigil, we assume we have the full ID. We
            //   ignore event IDs because we need a room to be able to generate a link.
            if let Some((pos, c)) = prev_span[..]
                .char_indices()
                .rev()
                // Skip the `:` we detected earlier.
                .skip(1)
                .find(|(_, c)| c.is_whitespace() || matches!(c, ':' | '!' | '#' | '@'))
            {
                let maybe_id_start = &prev_span[pos..];

                match c {
                    ':' if prev_span[..pos].ends_with(MATRIX_URI_SCHEME) => {
                        // This should be a matrix URI.
                        let maybe_full_uri =
                            format!("{MATRIX_URI_SCHEME}{maybe_id_start}{detected_url}");
                        if MatrixUri::parse(&maybe_full_uri).is_ok() {
                            // Remove the start of the URI from the string.
                            self.inner.truncate(
                                self.inner.len() - maybe_id_start.len() - MATRIX_URI_SCHEME.len(),
                            );
                            self.append_uri(&maybe_full_uri, &maybe_full_uri);

                            return true;
                        }
                    }
                    '!' => {
                        // This should be a room ID.
                        if let Ok(room_id) =
                            RoomId::parse(format!("{maybe_id_start}{detected_url}"))
                        {
                            // Remove the start of the ID from the string.
                            self.inner.truncate(self.inner.len() - maybe_id_start.len());
                            // Transform it into a link.
                            self.append_uri(&room_id.matrix_to_uri().to_string(), room_id.as_str());
                            return true;
                        }
                    }
                    '#' => {
                        // This should be a room alias.
                        if let Ok(room_alias) =
                            RoomAliasId::parse(format!("{maybe_id_start}{detected_url}"))
                        {
                            // Remove the start of the ID from the string.
                            self.inner.truncate(self.inner.len() - maybe_id_start.len());
                            // Transform it into a link.
                            self.append_uri(
                                &room_alias.matrix_to_uri().to_string(),
                                room_alias.as_str(),
                            );
                            return true;
                        }
                    }
                    '@' => {
                        // This should be a user ID.
                        if let Ok(user_id) =
                            UserId::parse(format!("{maybe_id_start}{detected_url}"))
                        {
                            // Remove the start of the ID from the string.
                            self.inner.truncate(self.inner.len() - maybe_id_start.len());
                            // Transform it into a link.
                            self.append_uri(&user_id.matrix_to_uri().to_string(), user_id.as_str());
                            return true;
                        }
                    }
                    _ => {
                        // We reached a whitespace without a sigil or URI
                        // scheme, this must be a regular URL.
                    }
                }
            }
        }

        self.append_uri(&format!("{HTTPS_URI_PREFIX}{detected_url}"), detected_url);
        true
    }
}

/// The mentions mode of the [`Linkifier`].
#[derive(Debug, Default)]
enum MentionsMode<'a> {
    /// The builder will not detect mentions.
    #[default]
    NoMentions,
    /// The builder will detect mentions.
    WithMentions {
        /// The pills for the detected mentions.
        pills: &'a mut Vec<Pill>,
        /// The room containing the mentions.
        room: &'a Room,
        /// Whether to detect `@room` mentions.
        detect_at_room: bool,
    },
}
