import assert from "minimalistic-assert";

import * as resolved_topic from "../shared/src/resolved_topic.ts";

import * as hash_util from "./hash_util.ts";
import * as narrow_state from "./narrow_state.ts";
import * as stream_topic_history from "./stream_topic_history.ts";
import * as sub_store from "./sub_store.ts";
import * as unread from "./unread.ts";
import * as user_topics from "./user_topics.ts";
import * as util from "./util.ts";

const max_topics = 8;
const max_topics_with_unread = 12;

export type TopicInfo = {
    stream_id: number;
    topic_name: string;
    topic_resolved_prefix: string;
    topic_display_name: string;
    unread: number;
    is_zero: boolean;
    is_muted: boolean;
    is_followed: boolean;
    is_unmuted_or_followed: boolean;
    is_active_topic: boolean;
    url: string;
    contains_unread_mention: boolean;
};

type TopicChoiceState = {
    active_topic: string | undefined;
    topics_with_unread_mentions: Set<string>;
    more_topics_unmuted_unreads: number;
    more_topics_have_unread_mention_messages: boolean;
    more_topics_muted_unreads: number;
    more_topics_have_muted_unread_mention_messages: boolean;
    topics_selected: number;
    items: TopicInfo[];
};

function choose_topics(
    stream_id: number,
    topic_names: string[],
    zoomed: boolean,
    topic_choice_state: TopicChoiceState,
): void {
    for (const [idx, topic_name] of topic_names.entries()) {
        const num_unread = unread.num_unread_for_topic(stream_id, topic_name);
        const is_active_topic = topic_choice_state.active_topic === topic_name.toLowerCase();
        const is_topic_muted = user_topics.is_topic_muted(stream_id, topic_name);
        const is_topic_followed = user_topics.is_topic_followed(stream_id, topic_name);
        const is_topic_unmuted_or_followed = user_topics.is_topic_unmuted_or_followed(
            stream_id,
            topic_name,
        );
        const [topic_resolved_prefix, topic_display_name] =
            resolved_topic.display_parts(topic_name);
        // Important: Topics are lower-case in this set.
        const contains_unread_mention = topic_choice_state.topics_with_unread_mentions.has(
            topic_name.toLowerCase(),
        );

        if (!zoomed) {
            function should_show_topic(topics_selected: number): boolean {
                // This function exists just for readability, to
                // avoid long chained conditionals to determine
                // which topics to include.

                // We always show the active topic.  Ideally, this
                // logic would first check whether the active
                // topic is in the set of those with unreads to
                // avoid ending up with max_topics_with_unread + 1
                // total topics if the active topic comes after
                // the first several topics with unread messages.
                if (is_active_topic) {
                    return true;
                }

                // We unconditionally skip showing muted topics
                // when not zoomed, even if they have unread
                // messages.
                if (is_topic_muted) {
                    return false;
                }

                // We include the most recent max_topics topics,
                // even if there are no unread messages.
                if (idx < max_topics && topics_selected < max_topics) {
                    return true;
                }

                // We include older topics with unread messages up
                // until max_topics_with_unread total topics have
                // been included.
                if (num_unread > 0 && topics_selected < max_topics_with_unread) {
                    return true;
                }

                // Otherwise, we don't show the topic in the
                // unzoomed view.  We might display its unread
                // count in "show all topics" if it is not muted.
                return false;
            }

            const show_topic = should_show_topic(topic_choice_state.topics_selected);
            if (!show_topic) {
                if (!is_topic_muted) {
                    topic_choice_state.more_topics_unmuted_unreads += num_unread;
                    if (contains_unread_mention) {
                        topic_choice_state.more_topics_have_unread_mention_messages = true;
                    }
                } else {
                    topic_choice_state.more_topics_muted_unreads += num_unread;
                    if (contains_unread_mention) {
                        topic_choice_state.more_topics_have_muted_unread_mention_messages = true;
                    }
                }
                continue;
            }
            topic_choice_state.topics_selected += 1;
            // We fall through to rendering the topic, using the
            // same code we do when zoomed.
        }

        const topic_info: TopicInfo = {
            stream_id,
            topic_name,
            topic_resolved_prefix,
            topic_display_name,
            unread: num_unread,
            is_zero: num_unread === 0,
            is_muted: is_topic_muted,
            is_followed: is_topic_followed,
            is_unmuted_or_followed: is_topic_unmuted_or_followed,
            is_active_topic,
            url: hash_util.by_stream_topic_url(stream_id, topic_name),
            contains_unread_mention,
        };

        topic_choice_state.items.push(topic_info);
    }
}

function contains_topic(topic_names: string[], narrowed_topic: string): boolean {
    const lower_cased_topics = topic_names.map((name) => name.toLowerCase());
    return lower_cased_topics.includes(narrowed_topic.toLowerCase());
}

type TopicListInfo = {
    items: TopicInfo[];
    num_possible_topics: number;
    more_topics_unreads: number;
    more_topics_have_unread_mention_messages: boolean;
    more_topics_unread_count_muted: boolean;
};

export function get_list_info(
    stream_id: number,
    zoomed: boolean,
    search_term: string,
): TopicListInfo {
    const narrowed_topic = narrow_state.topic();
    const topic_choice_state: TopicChoiceState = {
        items: [],
        topics_selected: 0,
        more_topics_muted_unreads: 0,
        more_topics_unmuted_unreads: 0,
        more_topics_have_unread_mention_messages: false,
        more_topics_have_muted_unread_mention_messages: false,
        active_topic: narrow_state.topic()?.toLowerCase(),
        topics_with_unread_mentions: unread.get_topics_with_unread_mentions(stream_id),
    };

    const sub = sub_store.get(stream_id);
    assert(sub !== undefined);
    const stream_muted = sub.is_muted;

    let topic_names = stream_topic_history.get_recent_topic_names(stream_id);

    if (
        stream_id === narrow_state.stream_id() &&
        narrowed_topic &&
        !contains_topic(topic_names, narrowed_topic)
    ) {
        topic_names.unshift(narrowed_topic);
    }

    if (zoomed) {
        const word_separator_regex = /[\s/:_-]/; // Use -, _, :, / as word separators in addition to spaces.
        topic_names = util.filter_by_word_prefix_match(
            topic_names,
            search_term,
            (topic) => topic,
            word_separator_regex,
        );
    }

    if (stream_muted && !zoomed) {
        const unmuted_or_followed_topics = topic_names.filter((topic) =>
            user_topics.is_topic_unmuted_or_followed(stream_id, topic),
        );
        choose_topics(stream_id, unmuted_or_followed_topics, zoomed, topic_choice_state);

        const other_topics = topic_names.filter(
            (topic) => !user_topics.is_topic_unmuted_or_followed(stream_id, topic),
        );
        choose_topics(stream_id, other_topics, zoomed, topic_choice_state);
    } else {
        choose_topics(stream_id, topic_names, zoomed, topic_choice_state);
    }

    if (
        topic_choice_state.more_topics_unmuted_unreads === 0 &&
        topic_choice_state.more_topics_muted_unreads > 0 &&
        stream_muted
    ) {
        // For muted streams, if the only unreads are in muted topics,
        // we have a muted styling "all topics" row.
        return {
            items: topic_choice_state.items,
            num_possible_topics: topic_names.length,
            more_topics_unreads: topic_choice_state.more_topics_muted_unreads,
            more_topics_have_unread_mention_messages:
                topic_choice_state.more_topics_have_muted_unread_mention_messages,
            more_topics_unread_count_muted: true,
        };
    }
    return {
        items: topic_choice_state.items,
        num_possible_topics: topic_names.length,
        more_topics_unreads: topic_choice_state.more_topics_unmuted_unreads,
        more_topics_have_unread_mention_messages:
            // Because mentions are important, and get displayed in the
            // overall summary, we display the mention indicator even if
            // they are in muted streams.
            topic_choice_state.more_topics_have_unread_mention_messages ||
            topic_choice_state.more_topics_have_muted_unread_mention_messages,
        more_topics_unread_count_muted: false,
    };
}