const e = require('express')
const database = require('./database.js')
const con = require('./console')

const NO_VALUE = null
const NO_CACHE = undefined

const users = {}
const email_links = {}
const password_links = {}
const session_links = {}
var newest_user = database.getNewestUserId();

const getUserByEmail = (email) => {
    const fast = email_links[email]
    if (fast === NO_VALUE) {
        return undefined
    }
    if (fast === NO_CACHE) {
        const slow = database.getUserByEmail(email)
        if (slow === undefined) {
            email_links[email] = NO_VALUE
        } else {
            email_links[email] = slow.id
            if (users[slow.id] === NO_CACHE) {
                users[slow.id] = slow
            }
        }
        return slow
    }
    return users[fast]
}

const getUserByPassword = (password) => {
    const fast = password_links[password]
    if (fast === NO_VALUE) {
        return undefined
    }
    if (fast === NO_CACHE) {
        const slow = database.getUserByPassword(password)
        if (slow === undefined) {
            password_links[password] = NO_VALUE
        } else {
            password_links[password] = slow.id
            if (users[slow.id] === NO_CACHE) {
                users[slow.id] = slow
            }
        }
        return slow
    }
    return users[fast]
}

const getUsers = (ids) => {
    const fast = {}
    const batch = []
    for (const id of ids) {
        if (users[id] === NO_CACHE) {
            batch.push(id)
        } else {
            fast[id] = users[id]
        }
    }
    if (batch.length > 0) {
        const slow = database.getUsers(batch)
        for(const [id, user] of Object.entries(slow)) {
            fast[id] = user
        }
    }
    return fast
}

const getUsersPage = (page) => {
    const COUNT = 10
    const INDEX = newest_user - page * COUNT
    const batch = []
    for (let i = INDEX; i > INDEX - COUNT && i >= 0; i--) {
        batch.push(i)
    }
    const users = getUsers(batch)
    return batch.map(i => users[i]).filter(u => u !== undefined)
}

const register = (first, last, email, password, gender, month, day, year) => {
    const data = database.register(first, last, email, password, gender, month, day, year)
    if (data === undefined) {
        return undefined
    }
    newest_user = data.user.id
    session_links[data.key] = data.user.id
    users[data.user.id] = data.user
    return data.key
}

const login = (email, pass) => {
    const data = database.login(email, pass)
    if (data === undefined) {
        return undefined
    }
    session_links[data.key] = data.user.id
    users[data.user.id] = data.user
    return data.key
}

const logout = (token) => {

    if (session_links[token] === NO_VALUE) {
        return false
    }

    if (!database.deleteSession(token)) {
        return false
    }

    delete session_links[token]
    return true
}

const auth = (token) => {
    const fast = session_links[token]
    if (fast === NO_VALUE) {
        return undefined
    }
    if (fast === NO_CACHE) {
        const slow = database.auth(token)
        if (slow === undefined) {
            session_links[token] = NO_VALUE
        } else {
            session_links[token] = slow.id
            if (users[slow.id] === NO_CACHE) {
                users[slow.id] = slow
            }
        }
        return slow
    }
    return users[fast]
}

const posts = {}
const users_posts = {}
const updated_posts = {}
var newest_post = database.getNewestPostId();

const addPost = (user, content) => {
    const id = database.addPost(user, content)
    if (id === undefined) {
        return -1
    }
    newest_post = id
    if (users_posts[user] === NO_VALUE) {
        users[posts] = [id]
    } else if (users_posts[user] === NO_CACHE) {
        getUsersPosts(user)
    } else {
        users_posts[user].unshift(id)
    }
    return id
}

const getPosts = (ids) => {
    const fast = {}
    const batch = []
    for (const id of ids) {
        if (posts[id] === NO_CACHE) {
            batch.push(id)
        } else {
            fast[id] = posts[id]
        }
    }
    if (batch.length > 0) {
        const slow = database.getPosts(batch)
        for(const [id, post] of Object.entries(slow)) {
            fast[id] = post
        }
    }
    return fast
}

const getUsersPosts = (user) => {
    const fast = users_posts[user] 
    if (fast === NO_CACHE) {
        const posts = database.getUsersPosts(user)
        if (posts === undefined) {
            users_posts[user] = NO_VALUE
        } else {
            const slow = []
            for (const post in posts) {
                slow.push[post.id]
                if (posts[post.id] === NO_CACHE) {
                    posts[post.id] = post
                }
            }
            users_posts[user] = slow
        }
        return posts
    } else {
        return getPosts(fast)
    }
}

const getPostsPage = (page) => {
    const COUNT = 10
    const INDEX = newest_post - page * COUNT
    const batch = []
    for (let i = INDEX; i > INDEX - COUNT && i >= 0; i--) {
        batch.push(i)
    }
    const posts = getPosts(batch)
    return batch.map(i => posts[i]).filter(p => p !== undefined)
}

const comment = (id, user, content) => {
    var fast = posts[id]
    if (fast === NO_VALUE) {
        return false
    } else if (fast === NO_CACHE) {
        const slow = getPosts([id])
        if (slow[id] === undefined) {
            return false
        } else {
            fast = slow[id]
        }
    }
    fast.comments.push({user, content})
    posts[id] = fast
    updated_posts[id] = true
    return true
}

const like = (id, user, state) => {
    var fast = posts[id]
    if (fast === NO_VALUE) {
        return false
    } else if (fast === NO_CACHE) {
        const slow = getPosts([id])
        if (slow[id] === undefined) {
            return false
        } else {
            fast = slow[id]
        }
    }
    fast.likes[user] = state
    posts[id] = fast
    updated_posts[id] = true
    return true
}

const dump = () => {
    for (id in updated_posts) {
        const post = posts[id]
        if (post === NO_CACHE || post === NO_VALUE) continue;
        if (!database.updatePost(post.id, JSON.stringify(post.likes), JSON.stringify(post.comments))) {
            con.error(`Failed to saved cached post id ${id}`)
        } else {
            delete updated_posts.id
        }
    }
    con.msg('Saved cache successfully')
}

module.exports = { 
    getUserByEmail, 
    getUserByPassword, 
    getUsers,
    getUsersPage, 
    register, 
    login,
    logout,
    auth, 
    addPost, 
    getPosts, 
    getUsersPosts, 
    getPostsPage, 
    comment,
    like, 
    dump 
}