import hashlib
import re
import sqlite3
from freepost import random, settings

db = sqlite3.connect(settings['sqlite']['database'])

# Returns SQLite rows as dictionaries instead of tuples.
# https://docs.python.org/3/library/sqlite3.html#sqlite3.Connection.row_factory
db.row_factory = sqlite3.Row

# A custom function to compute SHA-512 because it's not built into SQLite
db.create_function('SHA512', 1, lambda text:
                                    None if text is None else hashlib.sha512(text.encode('UTF-8')).hexdigest())

# The REGEXP operator is a special syntax for the regexp() user function. No
# regexp() user function is defined by default and so use of the REGEXP operator
# will normally result in an error message. If an application-defined SQL
# function named "regexp" is added at run-time, then the "X REGEXP Y" operator
# will be implemented as a call to "regexp(Y,X)".
db.create_function('REGEXP', 2, lambda pattern, string:
                                    re.search(pattern, string, flags=re.IGNORECASE) is not None)

# Store a new session_id for a user that has logged in
# The session token is stored in the user cookies during login, here
# we store the hash value of that token.
def new_session(user_id, session_token):
    with db:
        db.execute(
            """
            UPDATE user
            SET    session = SHA512(:session)
            WHERE  id = :user
            """,
            {
                'user': user_id,
                'session': session_token
            }
        )

# Delete user session token on logout
def delete_session (user_id):
    with db:
        db.execute (
            """
            UPDATE user
            SET    session = NULL
            WHERE  id = :user
            """,
            {
                'user': user_id
            }
        )

# Check user login credentials
# 
# @return None if bad credentials, otherwise return the user
def check_user_credentials (username, password):
    with db:
        cursor = db.execute (
            """
            SELECT *
            FROM   user
            WHERE  username = :username
                   AND password = SHA512(:password || salt)
                   AND isActive = 1
            """,
            {
                'username': username,
                'password': password
            }
        )
    
        return cursor.fetchone ()

# Check if username exists
def username_exists (username, case_sensitive = True):
    if not username:
        return None
    
    if case_sensitive:
        where = 'WHERE username = :username'
    else:
        where = 'WHERE LOWER(username) = LOWER(:username)'
    
    with db:
        cursor = db.execute(
            """
            SELECT *
            FROM user
            """ +
            where,
            {
                'username': username
            }
        )
            
        return cursor.fetchone() is not None

# Create new user account
def new_user (username, password):
    # Create a hash_id for the new post
    hash_id = random.alphanumeric_string (10)
    
    # Create a salt for user's password
    salt = random.ascii_string (16)
    
    # Add user to database
    with db:
        db.execute (
            """
            INSERT INTO user (hashId, isActive, password, registered, salt, username)
                   VALUES (:hash_id, 1, SHA512(:password || :salt), DATE(), :salt, :username)
            """,
            {
                'hash_id': hash_id,
                'password': password,
                'salt': salt,
                'username': username
            }
        )

# Check if session token exists
def is_valid_session (token):
    return get_user_by_session_token (token) is not None

# Return the number of unread replies
def count_unread_messages (user_id):
    with db:
        cursor = db.execute (
            """
            SELECT COUNT(1) AS new_messages
            FROM   comment
            WHERE  parentUserId = :user AND userId != :user AND `read` = 0
            """,
            {
                'user': user_id
            }
        )
        
        return cursor.fetchone ()['new_messages']

# Retrieve a user
def get_user_by_username (username):
    if not username:
        return None
    
    with db:
        cursor = db.execute(
            """
            SELECT *
            FROM   user
            WHERE  username = :username
            """,
            {
                'username': username
            }
        )
            
        return cursor.fetchone()

# Retrieve a user from a session cookie
def get_user_by_session_token(session_token):
    with db:
        cursor = db.execute(
            """
            SELECT *
            FROM   user
            WHERE  session = SHA512(:session)
            """,
            {
                'session': session_token
            }
        )
        
        return cursor.fetchone()

# Get posts by date (for homepage)
def get_posts (page = 0, session_user_id = None, sort = 'hot', topic = None):
    if sort == 'new':
        sort = 'ORDER BY P.created DESC'
    else:
        sort = 'ORDER BY P.dateCreated DESC, P.vote DESC, P.commentsCount DESC'
    
    if topic:
        topic_name = 'WHERE T.name = :topic'
    else:
        topic_name = ''
    
    with db:
        cursor = db.execute (
            """
            SELECT P.*,
                   U.username,
                   V.vote AS user_vote,
                   GROUP_CONCAT(T.name, " ") AS topics
            FROM   post AS P
            JOIN   user AS U ON P.userId = U.id
            LEFT JOIN vote_post as V ON V.postId = P.id AND V.userId = :user
            LEFT JOIN topic as T ON T.post_id = P.id
            {topic}
            GROUP BY P.id
            {order}
            LIMIT  :limit
            OFFSET :offset
            """.format (topic=topic_name, order=sort),
            {
                'user': session_user_id,
                'limit': settings['defaults']['items_per_page'],
                'offset': page * settings['defaults']['items_per_page'],
                'topic': topic
            }
        )
        
        return cursor.fetchall ()

# Retrieve user's own posts
def get_user_posts (user_id):
    with db:
        cursor = db.execute (
            """
            SELECT *
            FROM   post
            WHERE  userId = :user
            ORDER BY created DESC
            LIMIT  50
            """,
            {
                'user': user_id
            }
        )
        
        return cursor.fetchall()

# Retrieve user's own comments
def get_user_comments (user_id):
    with db:
        cursor = db.execute (
            """
            SELECT C.*,
                   P.title AS postTitle,
                   P.hashId AS postHashId
            FROM   comment AS C
            JOIN   post AS P ON P.id = C.postId
            WHERE  C.userId = :user
            ORDER BY C.created DESC
            LIMIT  50
            """,
            {
                'user': user_id
            }
        )
        
        return cursor.fetchall()

# Retrieve user's own replies to other people
def get_user_replies (user_id):
    with db:
        cursor = db.execute(
            """
            SELECT C.*,
                   P.title AS postTitle,
                   P.hashId AS postHashId,
                   U.username AS username
            FROM   comment AS C
            JOIN   post AS P ON P.id = C.postId
            JOIN   user AS U ON U.id = C.userId
            WHERE  C.parentUserId = :user AND C.userId != :user
            ORDER BY C.created DESC
            LIMIT  50
            """,
            {
                'user': user_id
            }
        )
        
        return cursor.fetchall()

# Update user information
def update_user (user_id, about, email, email_notifications, preferred_feed):
    with db:
        # Update user info, but not email address
        db.execute(
            """
            UPDATE user
            SET    about = :about,
                   email_notifications = :notifications,
                   preferred_feed = :preferred_feed
            WHERE  id = :user
            """,
            {
                'about': about,
                'notifications': email_notifications,
                'user': user_id,
                'preferred_feed': preferred_feed
            }
        )
        
        # Update email address. Convert all addresses to LOWER() case. This
        # prevents two users from using the same address with different case.
        # IGNORE update if the email address is already specified. This is
        # necessary to avoid an "duplicate key" exception when updating value.
        db.execute (
            """
            UPDATE OR IGNORE user
            SET email = LOWER(:email)
            WHERE id = :user
            """,
            {
                'email': email,
                'user': user_id
            }
        )

# Set user replies as read
def set_replies_as_read (user_id):
    with db:
        db.execute(
            """
            UPDATE comment
            SET    `read` = 1
            WHERE  parentUserId = :user AND `read` = 0
            """,
            {
                'user': user_id
            }
        )

# Submit a new post/link
def new_post (title, link, text, user_id):
    # Create a hash_id for the new post
    hash_id = random.alphanumeric_string (10)
    
    with db:
        db.execute(
            """
            INSERT INTO post (hashId, created, dateCreated, title,
                              link, text, vote, commentsCount, userId)
            VALUES (:hash_id, DATETIME(), DATE(), :title, :link,
                    :text, 0, 0, :user)
            """,
            {
                'hash_id': hash_id,
                'title': title,
                'link': link,
                'text': text,
                'user': user_id
            }
        )
    
    return hash_id

# Set topics post. Deletes existing ones.
def replace_post_topics (post_id, topics = ''):
    if not topics:
        return
    
    # Normalize topics
    # 1. Split topics by space
    # 2. Remove empty strings
    # 3. Lower case topic name
    topics = [ topic.lower () for topic in topics.split (' ') if topic ]
    
    if len (topics) == 0:
        return
    
    # Remove extra topics if the list is too long
    topics = topics[:settings['defaults']['topics_per_post']]
    
    with db:
        # First we delete the existing topics
        db.execute (
            """
            DELETE
            FROM   topic
            WHERE  post_id = :post
            """,
            {
                'post': post_id
            }
        )
        
        # Now insert the new topics.
        # IGNORE duplicates that trigger UNIQUE constraint.
        db.executemany (
            """
            INSERT OR IGNORE INTO topic (post_id, name)
            VALUES (?, ?)
            """,
            [ (post_id, topic) for topic in topics ]
        )

# Retrieve a post
def get_post (hash, session_user_id = None):
    with db:
        cursor = db.execute (
            """
            SELECT P.*,
                   U.username,
                   V.vote AS user_vote
            FROM   post AS P
            JOIN   user AS U ON P.userId = U.id
            LEFT JOIN vote_post as V ON V.postId = P.id AND V.userId = :user
            WHERE  P.hashId = :post
            """,
            {
                'user': session_user_id,
                'post': hash
            }
        )
        
        return cursor.fetchone ()

# Update a post
def update_post (title, link, text, post_hash_id, user_id):
    with db:
        db.execute (
            """
            UPDATE post
            SET    title = :title,
                   link  = :link,
                   text  = :text
            WHERE  hashId = :hash_id
                   AND userId = :user
            """,
            {
                'title': title,
                'link': link,
                'text': text,
                'hash_id': post_hash_id,
                'user': user_id
            }
        )

# Retrieve all comments for a specific post
def get_post_comments (post_id, session_user_id = None):
    with db:
        cursor = db.execute (
            """
            SELECT C.*,
                   U.username,
                   V.vote AS user_vote
            FROM   comment AS C
            JOIN   user AS U ON C.userId = U.id
            LEFT JOIN vote_comment as V ON V.commentId = C.id AND V.userId = :user
            WHERE  C.postId = :post
            ORDER BY C.vote DESC,
                     C.created ASC
            """,
            {
                'user': session_user_id,
                'post': post_id
            }
        )
        
        return cursor.fetchall ()

# Retrieve all topics for a specific post
def get_post_topics (post_id):
    with db:
        cursor = db.execute (
            """
            SELECT T.name
            FROM   topic AS T
            WHERE  T.post_id = :post
            ORDER BY T.name ASC
            """,
            {
                'post': post_id
            }
        )
        
        return cursor.fetchall ()

# Submit a new comment to a post
def new_comment (comment_text, post_hash_id, user_id, parent_user_id = None, parent_comment_id = None):
    # Create a hash_id for the new comment
    hash_id = random.alphanumeric_string (10)
    
    # Retrieve post
    post = get_post (post_hash_id)
    
    with db:
        db.execute (
            """
            INSERT INTO comment (hashId, created, dateCreated, `read`, text, vote,
                                 parentId, parentUserId, postId, userId)
            VALUES (:hash_id, DATETIME(), DATE(), 0, :text, 0, :parent_id,
                    :parent_user_id, :post_id, :user)
            """,
            {
                'hash_id': hash_id,
                'text': comment_text,
                'parent_id': parent_comment_id,
                'parent_user_id': parent_user_id,
                'post_id': post['id'],
                'user': user_id
            }
        )
        
        # Increase comments count for post
        db.execute (
            """
            UPDATE post
            SET    commentsCount = commentsCount + 1
            WHERE  id = :post
            """,
            {
                'post': post['id']
            }
        )
    
    return hash_id

# Retrieve a single comment
def get_comment (hash_id, session_user_id = None):
    with db:
        cursor = db.execute(
            """
            SELECT C.*,
                   P.hashId AS postHashId,
                   P.title AS postTitle,
                   U.username,
                   V.vote AS user_vote
            FROM   comment AS C
            JOIN   user AS U ON C.userId = U.id
            JOIN   post AS P ON P.id = C.postId
            LEFT JOIN vote_comment as V ON V.commentId = C.id AND V.userId = :user
            WHERE  C.hashId = :comment
            """,
            {
                'user': session_user_id,
                'comment': hash_id
            }
        )
        
        return cursor.fetchone()

# Retrieve last N newest comments
def get_latest_comments ():
    with db:
        cursor = db.execute (
            """
            SELECT C.*,
                   P.hashId AS postHashId,
                   P.title AS postTitle,
                   U.username
            FROM   comment AS C
            JOIN   user AS U ON C.userId = U.id
            JOIN   post AS P ON P.id = C.postId
            ORDER BY C.id DESC
            LIMIT  50
            """,
            {
            }
        )
        
        return cursor.fetchall ()

# Update a comment
def update_comment (text, comment_hash_id, user_id):
    with db:
        db.execute (
            """
            UPDATE comment
            SET    text = :text
            WHERE  hashId = :comment AND userId = :user
            """,
            {
                'text': text,
                'comment': comment_hash_id,
                'user': user_id
            }
        )

# Add or update vote to a post
def vote_post (post_id, user_id, vote):
    with db:
        # Create a new vote for this post, if one doesn't already exist
        db.execute(
            """
            INSERT OR IGNORE INTO vote_post (vote, datetime, postId, userId)
            VALUES (0, DATETIME(), :post, :user)
            """,
            {
                'post': post_id,
                'user': user_id
            }
        )
        
        # Update user vote (+1 or -1)
        db.execute(
            """
            UPDATE vote_post
            SET    vote = vote + :vote
            WHERE  postId = :post AND userId = :user
            """,
            {
                'vote': vote,
                'post': post_id,
                'user': user_id
            }
        )
        
        # Update post's total
        db.execute (
            """
            UPDATE post
            SET    vote = vote + :vote
            WHERE  id = :post
            """,
            {
                'vote': vote,
                'post': post_id
            }
        )

# Add or update vote to a comment
def vote_comment (comment_id, user_id, vote):
    with db:
        # Create a new vote for this post, if one doesn't already exist
        db.execute (
            """
            INSERT INTO vote_comment (vote, datetime, commentId, userId)
            VALUES (0, DATETIME(), :comment, :user)
            """,
            {
                'comment': comment_id,
                'user': user_id
            }
        )
        
        # Update user vote (+1 or -1)
        db.execute (
            """
            UPDATE vote_comment
            SET    vote = vote + :vote
            WHERE  commentId = :comment AND userId = :user
            """,
            {
                'vote': vote,
                'comment': comment_id,
                'user': user_id
            }
        )
        
        # Update comment's total
        db.execute (
            """
            UPDATE comment
            SET    vote = vote + :vote
            WHERE  id = :comment
            """,
            {
                'vote': vote,
                'comment': comment_id
            }
        )

# Search posts
def search (query, sort='newest', page=0):
    if not query:
        return []
    
    # Remove multiple white spaces and replace with '|' (for query REGEXP)
    query = re.sub (' +', '|', query.strip ())
    
    if len (query) == 0:
        return []
    
    if sort == 'newest':
        sort = 'P.created DESC'
    if sort == 'points':
        sort = 'P.vote DESC'
    
    with db:
        cursor = db.execute (
            """
            SELECT P.*,
                   U.username
            FROM   post AS P
            JOIN   user AS U ON P.userId = U.id
            WHERE  P.title REGEXP :query
            ORDER BY {sort}
            LIMIT  :limit
            OFFSET :offset
            """.format (sort=sort),
            {
                'query': query,
                'sort': sort,
                'limit': settings['defaults']['search_results_per_page'],
                'offset': page * settings['defaults']['search_results_per_page']
            }
        )
        
        return cursor.fetchall ()

# Set reset token for user email
def set_password_reset_token (user_id = None, token = None):
    if not user_id or not token:
        return
    
    with db:
        db.execute (
            """
            UPDATE user
            SET    passwordResetToken = SHA512(:token),
                   passwordResetTokenExpire = DATETIME('now', '+1 HOUR')
            WHERE  id = :user
            """,
            {
                'user': user_id,
                'token': token
            }
        )

# Delete the password reset token for a user
def delete_password_reset_token (user_id = None):
    with db:
        db.execute (
            """
            UPDATE user
            SET    passwordResetToken = NULL,
                   passwordResetTokenExpire = NULL
            WHERE  id = :user
            """,
            {
                'user': user_id
            }
        )

# Check if a reset token has expired.
def is_password_reset_token_valid (user_id = None):
    with db:
        cursor = db.execute(
            """
            SELECT COUNT(1) AS valid
            FROM   user
            WHERE  id = :user
                   AND passwordResetToken IS NOT NULL
                   AND passwordResetTokenExpire IS NOT NULL
                   AND passwordResetTokenExpire > DATETIME('now')
            """,
            {
                'user': user_id
            }
        )
        
        return cursor.fetchone()['valid'] == 1

# Reset user password
def reset_password (username = None, email = None, new_password = None, secret_token = None):
    if not new_password:
        return
    
    with db:
        db.execute (
            """
            UPDATE user
            SET    password = SHA512(:password || salt),
                   passwordResetToken = NULL,
                   passwordResetTokenExpire = NULL
            WHERE username = :user
                  AND email = :email
                  AND passwordResetToken = SHA512(:token)
                  AND passwordResetTokenExpire > DATE()
            """,
            {
                'password': new_password,
                'user': username,
                'email': email,
                'token': secret_token
            }
        )