use axum::extract::State;
use conduwuit::{
	Result, at, err,
	matrix::{
		Event,
		event::RelationTypeEqual,
		pdu::{PduCount, ShortEventId},
	},
	utils::{IterStream, ReadyExt, result::FlatOk, stream::WidebandExt},
};
use conduwuit_service::Services;
use futures::StreamExt;
use ruma::{
	EventId, RoomId, UInt, UserId,
	api::{
		Direction,
		client::relations::{
			get_relating_events, get_relating_events_with_rel_type,
			get_relating_events_with_rel_type_and_event_type,
		},
	},
	events::{TimelineEventType, relation::RelationType},
};

use crate::Ruma;

/// Parse a pagination token, trying ShortEventId first, then falling back to
/// PduCount
async fn parse_pagination_token(
	services: &Services,
	room_id: &RoomId,
	token: Option<&str>,
	default: PduCount,
) -> Result<PduCount> {
	let Some(token) = token else {
		return Ok(default);
	};

	// Try parsing as ShortEventId first
	if let Ok(shorteventid) = token.parse::<ShortEventId>() {
		// ShortEventId maps directly to a PduCount in our database
		// The shorteventid IS the count value, just need to wrap it
		Ok(PduCount::Normal(shorteventid))
	} else if let Ok(count) = token.parse::<u64>() {
		// Fallback to PduCount for backwards compatibility
		Ok(PduCount::Normal(count))
	} else if let Ok(count) = token.parse::<i64>() {
		// Also handle negative counts for backfilled events
		Ok(PduCount::from_signed(count))
	} else {
		Err(err!(Request(InvalidParam("Invalid pagination token"))))
	}
}

/// Convert a PduCount to a token string (using the underlying ShortEventId)
fn count_to_token(count: PduCount) -> String {
	// The PduCount's unsigned value IS the ShortEventId
	count.into_unsigned().to_string()
}

/// # `GET /_matrix/client/r0/rooms/{roomId}/relations/{eventId}/{relType}/{eventType}`
pub(crate) async fn get_relating_events_with_rel_type_and_event_type_route(
	State(services): State<crate::State>,
	body: Ruma<get_relating_events_with_rel_type_and_event_type::v1::Request>,
) -> Result<get_relating_events_with_rel_type_and_event_type::v1::Response> {
	paginate_relations_with_filter(
		&services,
		body.sender_user(),
		&body.room_id,
		&body.event_id,
		body.event_type.clone().into(),
		body.rel_type.clone().into(),
		body.from.as_deref(),
		body.to.as_deref(),
		body.limit,
		body.recurse,
		body.dir,
	)
	.await
	.map(|res| get_relating_events_with_rel_type_and_event_type::v1::Response {
		chunk: res.chunk,
		next_batch: res.next_batch,
		prev_batch: res.prev_batch,
		recursion_depth: res.recursion_depth,
	})
}

/// # `GET /_matrix/client/r0/rooms/{roomId}/relations/{eventId}/{relType}`
pub(crate) async fn get_relating_events_with_rel_type_route(
	State(services): State<crate::State>,
	body: Ruma<get_relating_events_with_rel_type::v1::Request>,
) -> Result<get_relating_events_with_rel_type::v1::Response> {
	paginate_relations_with_filter(
		&services,
		body.sender_user(),
		&body.room_id,
		&body.event_id,
		None,
		body.rel_type.clone().into(),
		body.from.as_deref(),
		body.to.as_deref(),
		body.limit,
		body.recurse,
		body.dir,
	)
	.await
	.map(|res| get_relating_events_with_rel_type::v1::Response {
		chunk: res.chunk,
		next_batch: res.next_batch,
		prev_batch: res.prev_batch,
		recursion_depth: res.recursion_depth,
	})
}

/// # `GET /_matrix/client/r0/rooms/{roomId}/relations/{eventId}`
pub(crate) async fn get_relating_events_route(
	State(services): State<crate::State>,
	body: Ruma<get_relating_events::v1::Request>,
) -> Result<get_relating_events::v1::Response> {
	paginate_relations_with_filter(
		&services,
		body.sender_user(),
		&body.room_id,
		&body.event_id,
		None,
		None,
		body.from.as_deref(),
		body.to.as_deref(),
		body.limit,
		body.recurse,
		body.dir,
	)
	.await
}

#[allow(clippy::too_many_arguments)]
async fn paginate_relations_with_filter(
	services: &Services,
	sender_user: &UserId,
	room_id: &RoomId,
	target: &EventId,
	filter_event_type: Option<TimelineEventType>,
	filter_rel_type: Option<RelationType>,
	from: Option<&str>,
	to: Option<&str>,
	limit: Option<UInt>,
	recurse: bool,
	dir: Direction,
) -> Result<get_relating_events::v1::Response> {
	let start: PduCount = parse_pagination_token(services, room_id, from, match dir {
		| Direction::Forward => PduCount::min(),
		| Direction::Backward => PduCount::max(),
	})
	.await?;

	let to: Option<PduCount> = if let Some(to_str) = to {
		Some(parse_pagination_token(services, room_id, Some(to_str), PduCount::min()).await?)
	} else {
		None
	};

	// Use limit or else 30, with maximum 100
	let limit: usize = limit
		.map(TryInto::try_into)
		.flat_ok()
		.unwrap_or(30)
		.min(100);

	// Spec (v1.10) recommends depth of at least 3
	let depth: u8 = if recurse { 3 } else { 1 };

	// Check if this is a thread request
	let is_thread = filter_rel_type
		.as_ref()
		.is_some_and(|rel| *rel == RelationType::Thread);

	let mut events: Vec<_> = services
		.rooms
		.pdu_metadata
		.get_relations(sender_user, room_id, target, start, limit, depth, dir)
		.await
		.into_iter()
		.filter(|(_, pdu)| {
			filter_event_type
				.as_ref()
				.is_none_or(|kind| kind == pdu.kind())
		})
		.filter(|(_, pdu)| {
			filter_rel_type
				.as_ref()
				.is_none_or(|rel_type| rel_type.relation_type_equal(pdu))
		})
		.stream()
		.ready_take_while(|(count, _)| Some(*count) != to)
		.wide_filter_map(|item| visibility_filter(services, sender_user, item))
		.take(limit)
		.collect()
		.await;

	// For threads, check if we should include the root event
	let mut at_thread_beginning = false;
	if is_thread && dir == Direction::Backward {
		// Check if we've reached the beginning of the thread
		// (fewer events than requested means we've exhausted the thread)
		if events.len() < limit {
			// Try to get the thread root event
			if let Ok(root_pdu) = services.rooms.timeline.get_pdu(target).await {
				// Check visibility
				if services
					.rooms
					.state_accessor
					.user_can_see_event(sender_user, room_id, target)
					.await
				{
					// Get the PduCount for the root event
					if let Ok(root_count) = services.rooms.timeline.get_pdu_count(target).await {
						// Insert the root at the beginning (for backwards pagination)
						events.insert(0, (root_count, root_pdu));
						at_thread_beginning = true;
					}
				}
			}
		}
	}

	// Determine if there are more events to fetch
	let has_more = if at_thread_beginning {
		false // We've included the root, no more events
	} else {
		// Check if we got a full page of results (might be more)
		events.len() >= limit
	};

	let next_batch = if has_more {
		match dir {
			| Direction::Forward => events.last(),
			| Direction::Backward => events.first(),
		}
		.map(|(count, _)| count_to_token(*count))
	} else {
		None
	};

	Ok(get_relating_events::v1::Response {
		next_batch,
		prev_batch: from.map(Into::into),
		recursion_depth: recurse.then_some(depth.into()),
		chunk: events
			.into_iter()
			.map(at!(1))
			.map(Event::into_format)
			.collect(),
	})
}

async fn visibility_filter<Pdu: Event + Send + Sync>(
	services: &Services,
	sender_user: &UserId,
	item: (PduCount, Pdu),
) -> Option<(PduCount, Pdu)> {
	let (_, pdu) = &item;

	services
		.rooms
		.state_accessor
		.user_can_see_event(sender_user, pdu.room_id(), pdu.event_id())
		.await
		.then_some(item)
}