const { MongoClient } = require("mongodb")
const { database_url, database_name } = require('../../config')
const crypto = require("crypto")
const time = require('../../lib/src/time')
let max_database_connection_timeout = 1000

const client = new MongoClient(database_url, {
    serverSelectionTimeoutMS: max_database_connection_timeout, 
    useUnifiedTopology: true
})

const get_db = async () => {
    try {
        await client.connect()
        await client.db(database_name).command({ ping: 1 })
        return client.db(database_name)
    } catch (err) {
        console.error('can not connect to database')
        await client.close()
        return null
    }
}

const get_titles = async (start, count) => {
    let db = await get_db()
    if (!db) {
        return null
    }
    let titles = await db.collection('title').find().skip(parseInt(start)).limit(parseInt(count)).toArray()
    return (!titles.length) ? null : titles
}

const get_titles_for_language = async (start, count, language) => {
    let db = await get_db()
    if (!db) {
        return null
    }
    let titles = await db.collection('title').find({language:language}).skip(parseInt(start)).limit(parseInt(count)).toArray()
    return (!titles.length) ? null : titles
}

const get_private_titles_with_key = async (key) => {
    let db = await get_db()
    if (!db) {
        return null
    }
    let titles = await db.collection('private_title').find({key:key}).toArray()
    return (!titles.length) ? null : titles
}

const get_free_session_servers = async (title) => {
    let db = await get_db()
    if (!db) {
        return null
    }

    let servers = await db.collection('session_server').find({title:title}).toArray()

    if (!servers.length) {
        return null
    }

    let active_session = db.collection('active_session')
    
    let free_servers = []

    for (const server of servers) {
        let sessions = await active_session.find({server_url:server.url}).toArray()
        if (server.limit > sessions.length) {
            free_servers.push(server)
        }
    }
    return (free_servers.length) ? free_servers : null
}

const add_active_session = async (title, server_url, session_id, websocket_url) => {
    let db = await get_db()
    if (!db) {
        return false
    }

    let active_session = db.collection('active_session')

    await active_session.insertOne({
        title: title,
        server_url: server_url,
        session_id: session_id,
        websocket_url: websocket_url
    })

    return true
}

const generate_session_id = async () => {
    let db = await get_db()
    if (!db) {
        return null
    }

    let active_session = db.collection('active_session')
    let session_id = {}

    let max_id_len = 6
    let sessions_with_id = 0
    while(true) {
        session_id = crypto.randomBytes(max_id_len/2).toString('hex').toUpperCase()
        sessions_with_id = await active_session.find({session_id:session_id}).toArray().length
        if (!sessions_with_id) {
            return session_id
        }
    }
}

const get_active_session = async (session_id) => {
    let db = await get_db()
    if (!db) {
        return null
    }
    
    let active_session = await db.collection('active_session').findOne({session_id:session_id})
    return active_session
}

const remove_active_session = async (session_id) => {
    let db = await get_db()
    if (!db) {
        return false
    }
    
    await db.collection('active_session').deleteOne({session_id:{$in:[session_id]}})
    return true
}

const get_session_websocket_url = async (session_id) => {
    let db = await get_db()
    if (!db) {
        return null
    }
    let active_session = db.collection('active_session')
    let session = await active_session.findOne({session_id:session_id})
    if (!session) {
        return null
    }
    return session.websocket_url
}

const get_statuses = async () => {
    let db = await get_db()
    if (!db) {
        return null
    }
    let statuses = await db.collection('status').find().toArray()
    return (!statuses.length) ? null : statuses
}

const get_all_session_servers = async () => {
    let db = await get_db()
    if (!db) {
        return null
    }

    let servers = await db.collection('session_server').find().toArray()

    if (!servers.length) {
        return null
    }
    return servers
}

const add_error = async (error_message) => {
    let db = await get_db()
    if (!db) {
        return false
    }

    let error_collection = db.collection('error_history')

    await error_collection.insertOne({error_message:error_message, time: time.get_date_time(), unix_timestamp: time.get_unix_timestamp()})
    return true
}

const get_errors = async () => {
    let db = await get_db()
    if (!db) {
        return null
    }
    let errors = await db.collection('error_history').find().toArray()
    return (!errors.length) ? null : errors
}

const get_all_active_sessions = async () => {
    let db = await get_db()
    if (!db) {
        return null
    }

    let active_sessions = await db.collection('active_session').find().toArray()

    if (!active_sessions.length) {
        return null
    }
    return active_sessions
}

const add_session_to_history = async (session_id, 
    title, 
    server_url, 
    websocket_url, 
    max_uniq_users, 
    users_at_close, 
    time_start, 
    unix_timestamp_start, 
    time_end, 
    unix_timestamp_end
    ) => {

    let db = await get_db()
    if (!db) {
        return false
    }

    let session_history = db.collection('session_history')

    let duration_in_seconds = unix_timestamp_end - unix_timestamp_start
    await session_history.insertOne({
        session_id: session_id,
        title: title,
        server_url: server_url,
        websocket_url: websocket_url,
        max_uniq_users: max_uniq_users,
        users_at_close: users_at_close,
        time_start: time_start,
        unix_timestamp_start: unix_timestamp_start,
        time_end: time_end,
        unix_timestamp_end: unix_timestamp_end,
        duration_in_seconds: duration_in_seconds,
        duration_in_minutes: duration_in_seconds / 60
    })
    return true
}

const get_all_session_history = async () => {
    let db = await get_db()
    if (!db) {
        return null
    }

    let session_history = await db.collection('session_history').find().toArray()

    if (!session_history.length) {
        return null
    }
    return session_history
}

module.exports = {
    get_titles,
    get_free_session_servers,
    add_active_session,
    generate_session_id,
    remove_active_session,
    get_active_session,
    get_session_websocket_url,
    get_titles_for_language,
    get_private_titles_with_key,
    get_statuses,
    get_all_session_servers,
    add_error,
    get_errors,
    get_all_active_sessions,
    add_session_to_history,
    get_all_session_history
}