use serde::{Deserialize, Serialize};
use uuid::Uuid;

use crate::rooms::RM_COLUMNS;
use crate::{ChannelError, ChannelResult};

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MessagePage {
    pub messages: Vec<MessageItem>,
    pub has_more: bool,
    pub next_cursor: Option<String>,
    pub prev_cursor: Option<String>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MessageItem {
    pub id: Uuid,
    pub room_id: Uuid,
    pub seq: i64,
    pub thread: Option<Uuid>,
    pub parent: Option<Uuid>,
    pub content: String,
    pub content_type: String,
    pub pinned: bool,
    pub system_type: Option<String>,
    pub metadata: serde_json::Value,
    pub sender_id: Uuid,
    pub send_at: chrono::DateTime<chrono::Utc>,
    pub edited_at: Option<chrono::DateTime<chrono::Utc>>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PaginationParams {
    pub room_id: Uuid,
    pub limit: u64,
    pub cursor: Option<String>,
    pub direction: PaginationDirection,
}

#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum PaginationDirection {
    Before,
    After,
}

pub struct MessagePagination {
    db: db::AppDatabase,
}

impl MessagePagination {
    pub fn new(db: db::AppDatabase) -> Self {
        Self { db }
    }

    pub async fn get_messages(
        &self,
        params: PaginationParams,
    ) -> ChannelResult<MessagePage> {
        let limit = std::cmp::Ord::min(params.limit, 100) as i64;
        let cursor_seq = params.cursor.and_then(|c| c.parse::<i64>().ok());

        let messages = match (params.direction, cursor_seq) {
            (PaginationDirection::Before, Some(seq)) => {
                db::sqlx::query_as::<_, model::room::RoomMessageModel>(
                    db::sqlx::AssertSqlSafe(format!(
                        "SELECT {RM_COLUMNS} FROM room_message \
                     WHERE room = $1 AND seq < $2 AND deleted_at IS NULL AND thread IS NULL \
                     ORDER BY seq DESC LIMIT $3"
                    )),
                )
                .bind(params.room_id)
                .bind(seq)
                .bind(limit + 1)
                .fetch_all(self.db.reader())
                .await?
            }
            (PaginationDirection::After, Some(seq)) => {
                db::sqlx::query_as::<_, model::room::RoomMessageModel>(
                    db::sqlx::AssertSqlSafe(format!(
                        "SELECT {RM_COLUMNS} FROM room_message \
                     WHERE room = $1 AND seq > $2 AND deleted_at IS NULL AND thread IS NULL \
                     ORDER BY seq ASC LIMIT $3"
                    )),
                )
                .bind(params.room_id)
                .bind(seq)
                .bind(limit + 1)
                .fetch_all(self.db.reader())
                .await?
            }
            _ => {
                db::sqlx::query_as::<_, model::room::RoomMessageModel>(
                    db::sqlx::AssertSqlSafe(format!(
                        "SELECT {RM_COLUMNS} FROM room_message \
                     WHERE room = $1 AND deleted_at IS NULL AND thread IS NULL \
                     ORDER BY seq DESC LIMIT $2"
                    )),
                )
                .bind(params.room_id)
                .bind(limit + 1)
                .fetch_all(self.db.reader())
                .await?
            }
        };

        let has_more = messages.len() > limit as usize;
        let messages: Vec<_> =
            messages.into_iter().take(limit as usize).collect();

        let next_cursor = if has_more {
            messages.last().map(|m| m.seq.to_string())
        } else {
            None
        };
        let prev_cursor = messages.first().map(|m| m.seq.to_string());

        let items: Vec<MessageItem> = messages
            .into_iter()
            .map(|m| MessageItem {
                id: m.id,
                room_id: m.room,
                seq: m.seq,
                thread: m.thread,
                parent: m.parent,
                content: m.content,
                content_type: m.content_type,
                pinned: m.pinned,
                system_type: m.system_type,
                metadata: m.metadata,
                sender_id: m.author,
                send_at: m.created_at,
                edited_at: m.edited_at,
            })
            .collect();

        Ok(MessagePage {
            messages: items,
            has_more,
            next_cursor,
            prev_cursor,
        })
    }

    pub async fn get_messages_around(
        &self,
        room_id: Uuid,
        message_id: Uuid,
        context_size: i64,
    ) -> ChannelResult<MessagePage> {
        let target = db::sqlx::query_as::<_, model::room::RoomMessageModel>(
            db::sqlx::AssertSqlSafe(format!(
                "SELECT {RM_COLUMNS} FROM room_message \
                 WHERE id = $1 AND room = $2 AND deleted_at IS NULL"
            )),
        )
        .bind(message_id)
        .bind(room_id)
        .fetch_optional(self.db.reader())
        .await?
        .ok_or(ChannelError::Internal("message not found".to_string()))?;

        let before = db::sqlx::query_as::<_, model::room::RoomMessageModel>(
            db::sqlx::AssertSqlSafe(format!(
                "SELECT {RM_COLUMNS} FROM room_message \
                 WHERE room = $1 AND seq < $2 AND deleted_at IS NULL \
                 ORDER BY seq DESC LIMIT $3"
            )),
        )
        .bind(room_id)
        .bind(target.seq)
        .bind(context_size)
        .fetch_all(self.db.reader())
        .await?;

        let after = db::sqlx::query_as::<_, model::room::RoomMessageModel>(
            db::sqlx::AssertSqlSafe(format!(
                "SELECT {RM_COLUMNS} FROM room_message \
                 WHERE room = $1 AND seq > $2 AND deleted_at IS NULL \
                 ORDER BY seq ASC LIMIT $3"
            )),
        )
        .bind(room_id)
        .bind(target.seq)
        .bind(context_size)
        .fetch_all(self.db.reader())
        .await?;

        let mut all_messages = before;
        all_messages.reverse();
        all_messages.push(target);
        all_messages.extend(after);

        let items: Vec<MessageItem> = all_messages
            .into_iter()
            .map(|m| MessageItem {
                id: m.id,
                room_id: m.room,
                seq: m.seq,
                thread: m.thread,
                parent: m.parent,
                content: m.content,
                content_type: m.content_type,
                pinned: m.pinned,
                system_type: m.system_type,
                metadata: m.metadata,
                sender_id: m.author,
                send_at: m.created_at,
                edited_at: m.edited_at,
            })
            .collect();

        Ok(MessagePage {
            messages: items,
            has_more: false,
            next_cursor: None,
            prev_cursor: None,
        })
    }
}