use std::{
    path::Path,
    sync::{Arc, Mutex},
    time::{SystemTime, UNIX_EPOCH},
};

use rand::{RngCore, rngs::OsRng};
use rusqlite::{Connection, OptionalExtension, params};
use sha2::{Digest, Sha256};
use thiserror::Error;

#[derive(Debug, Error)]
pub enum DbError {
    #[error("database error: {0}")]
    Message(String),
    #[error("record not found")]
    NotFound,
    #[error("record already exists")]
    Conflict,
    #[error("database worker failed: {0}")]
    Worker(String),
}

pub type DbResult<T> = Result<T, DbError>;

#[derive(Clone)]
pub struct Database {
    connection: Arc<Mutex<Connection>>,
}

#[derive(Clone, Debug)]
pub struct User {
    pub id: i64,
    pub email: String,
    pub display_name: String,
}

#[derive(Clone, Debug)]
pub struct SessionUser {
    pub user: User,
    pub csrf_token: String,
}

#[derive(Clone, Debug)]
pub struct GroceryList {
    pub id: i64,
    pub name: String,
    pub revision: i64,
}

#[derive(Clone, Debug)]
pub struct Item {
    pub id: i64,
    pub list_id: i64,
    pub name: String,
    pub quantity: String,
    pub note: String,
    pub category_id: Option<i64>,
    pub checked: bool,
    pub version: i64,
}

#[derive(Clone, Debug)]
pub struct Category {
    pub id: i64,
    pub name: String,
}

impl Database {
    pub fn open(path: impl AsRef<Path>) -> DbResult<Self> {
        let connection = Connection::open(path).map_err(sql_error)?;
        configure(&connection)?;
        migrate(&connection)?;

        Ok(Self {
            connection: Arc::new(Mutex::new(connection)),
        })
    }

    #[cfg(test)]
    pub fn open_in_memory() -> DbResult<Self> {
        Self::open(":memory:")
    }

    async fn call<T, F>(&self, operation: F) -> DbResult<T>
    where
        T: Send + 'static,
        F: FnOnce(&mut Connection) -> DbResult<T> + Send + 'static,
    {
        let connection = Arc::clone(&self.connection);
        tokio::task::spawn_blocking(move || {
            let mut connection = connection
                .lock()
                .map_err(|error| DbError::Worker(error.to_string()))?;
            operation(&mut connection)
        })
        .await
        .map_err(|error| DbError::Worker(error.to_string()))?
    }

    pub async fn create_user(
        &self,
        email: String,
        display_name: String,
        password_hash: String,
    ) -> DbResult<User> {
        self.call(move |connection| {
            let result = connection.execute(
                "INSERT INTO users (email, display_name, password_hash, created_at)
                 VALUES (?1, ?2, ?3, ?4)",
                params![email, display_name, password_hash, now()],
            );

            match result {
                Ok(_) => {
                    let id = connection.last_insert_rowid();
                    Ok(User {
                        id,
                        email,
                        display_name,
                    })
                }
                Err(error) if error.to_string().contains("UNIQUE") => Err(DbError::Conflict),
                Err(error) => Err(sql_error(error)),
            }
        })
        .await
    }

    pub async fn find_user_by_email(&self, email: String) -> DbResult<Option<(User, String)>> {
        self.call(move |connection| {
            connection
                .query_row(
                    "SELECT id, email, display_name, password_hash
                     FROM users WHERE email = ?1 COLLATE NOCASE",
                    params![email],
                    |row| {
                        Ok((
                            User {
                                id: row.get(0)?,
                                email: row.get(1)?,
                                display_name: row.get(2)?,
                            },
                            row.get(3)?,
                        ))
                    },
                )
                .optional()
                .map_err(sql_error)
        })
        .await
    }

    pub async fn has_users(&self) -> DbResult<bool> {
        self.call(|connection| {
            connection
                .query_row("SELECT EXISTS(SELECT 1 FROM users)", [], |row| {
                    Ok(row.get::<_, i64>(0)? != 0)
                })
                .map_err(sql_error)
        })
        .await
    }

    pub async fn create_session(&self, user_id: i64) -> DbResult<(String, String)> {
        self.call(move |connection| {
            let session_token = new_secret();
            let csrf_token = new_secret();
            connection
                .execute(
                    "INSERT INTO sessions (token_hash, user_id, csrf_token, expires_at)
                     VALUES (?1, ?2, ?3, ?4)",
                    params![
                        hash_secret(&session_token),
                        user_id,
                        csrf_token,
                        now() + 60 * 60 * 24 * 30
                    ],
                )
                .map_err(sql_error)?;
            Ok((session_token, csrf_token))
        })
        .await
    }

    pub async fn session_user(&self, session_token: String) -> DbResult<Option<SessionUser>> {
        self.call(move |connection| {
            connection
                .query_row(
                    "SELECT u.id, u.email, u.display_name, s.csrf_token
                     FROM sessions s
                     JOIN users u ON u.id = s.user_id
                     WHERE s.token_hash = ?1 AND s.expires_at > ?2",
                    params![hash_secret(&session_token), now()],
                    |row| {
                        Ok(SessionUser {
                            user: User {
                                id: row.get(0)?,
                                email: row.get(1)?,
                                display_name: row.get(2)?,
                            },
                            csrf_token: row.get(3)?,
                        })
                    },
                )
                .optional()
                .map_err(sql_error)
        })
        .await
    }

    pub async fn delete_session(&self, session_token: String) -> DbResult<()> {
        self.call(move |connection| {
            connection
                .execute(
                    "DELETE FROM sessions WHERE token_hash = ?1",
                    params![hash_secret(&session_token)],
                )
                .map_err(sql_error)?;
            Ok(())
        })
        .await
    }

    pub async fn list_summaries(&self) -> DbResult<Vec<GroceryList>> {
        self.call(move |connection| {
            let mut statement = connection
                .prepare(
                    "SELECT l.id, l.name, l.revision
                     FROM lists l
                     ORDER BY l.created_at DESC",
                )
                .map_err(sql_error)?;
            let rows = statement
                .query_map([], |row| {
                    Ok(GroceryList {
                        id: row.get(0)?,
                        name: row.get(1)?,
                        revision: row.get(2)?,
                    })
                })
                .map_err(sql_error)?;

            rows.collect::<Result<Vec<_>, _>>().map_err(sql_error)
        })
        .await
    }

    pub async fn create_list(&self, name: String) -> DbResult<GroceryList> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            transaction
                .execute(
                    "INSERT INTO lists (name, revision, created_at)
                     VALUES (?1, 0, ?2)",
                    params![name, now()],
                )
                .map_err(sql_error)?;
            let list_id = transaction.last_insert_rowid();
            for (position, category_name) in DEFAULT_CATEGORIES.iter().enumerate() {
                transaction
                    .execute(
                        "INSERT INTO categories (list_id, name, position, created_at)
                         VALUES (?1, ?2, ?3, ?4)",
                        params![list_id, category_name, position as i64, now()],
                    )
                    .map_err(sql_error)?;
            }
            transaction.commit().map_err(sql_error)?;
            Ok(GroceryList {
                id: list_id,
                name,
                revision: 0,
            })
        })
        .await
    }

    pub async fn list_access(&self, list_id: i64) -> DbResult<Option<GroceryList>> {
        self.call(move |connection| {
            connection
                .query_row(
                    "SELECT l.id, l.name, l.revision
                     FROM lists l
                     WHERE l.id = ?1",
                    params![list_id],
                    |row| {
                        Ok(GroceryList {
                            id: row.get(0)?,
                            name: row.get(1)?,
                            revision: row.get(2)?,
                        })
                    },
                )
                .optional()
                .map_err(sql_error)
        })
        .await
    }

    pub async fn items(&self, list_id: i64) -> DbResult<Vec<Item>> {
        self.call(move |connection| {
            let mut statement = connection
                .prepare(
                    "SELECT id, list_id, name, quantity, note, category_id, checked, version
                     FROM items
                     WHERE list_id = ?1
                     ORDER BY position ASC, created_at ASC",
                )
                .map_err(sql_error)?;
            let rows = statement
                .query_map(params![list_id], |row| {
                    Ok(Item {
                        id: row.get(0)?,
                        list_id: row.get(1)?,
                        name: row.get(2)?,
                        quantity: row.get(3)?,
                        note: row.get(4)?,
                        category_id: row.get(5)?,
                        checked: row.get::<_, i64>(6)? != 0,
                        version: row.get(7)?,
                    })
                })
                .map_err(sql_error)?;
            rows.collect::<Result<Vec<_>, _>>().map_err(sql_error)
        })
        .await
    }

    pub async fn categories(&self, list_id: i64) -> DbResult<Vec<Category>> {
        self.call(move |connection| {
            let mut statement = connection
                .prepare(
                    "SELECT id, name
                     FROM categories
                     WHERE list_id = ?1
                     ORDER BY position ASC, name COLLATE NOCASE ASC",
                )
                .map_err(sql_error)?;
            let rows = statement
                .query_map(params![list_id], |row| {
                    Ok(Category {
                        id: row.get(0)?,
                        name: row.get(1)?,
                    })
                })
                .map_err(sql_error)?;
            rows.collect::<Result<Vec<_>, _>>().map_err(sql_error)
        })
        .await
    }

    pub async fn create_category(&self, list_id: i64, name: String) -> DbResult<i64> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            let position: i64 = transaction
                .query_row(
                    "SELECT COALESCE(MAX(position), -1) + 1
                     FROM categories WHERE list_id = ?1",
                    params![list_id],
                    |row| row.get(0),
                )
                .map_err(sql_error)?;
            let result = transaction.execute(
                "INSERT INTO categories (list_id, name, position, created_at)
                 VALUES (?1, ?2, ?3, ?4)",
                params![list_id, name, position, now()],
            );
            match result {
                Ok(_) => {}
                Err(error) if error.to_string().contains("UNIQUE") => {
                    return Err(DbError::Conflict);
                }
                Err(error) => return Err(sql_error(error)),
            }
            let revision = bump_revision(&transaction, list_id)?;
            transaction.commit().map_err(sql_error)?;
            Ok(revision)
        })
        .await
    }

    pub async fn add_item(
        &self,
        list_id: i64,
        name: String,
        quantity: String,
        note: String,
        category_id: Option<i64>,
    ) -> DbResult<i64> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            ensure_category(&transaction, list_id, category_id)?;
            let position: i64 = transaction
                .query_row(
                    "SELECT COALESCE(MAX(position), -1) + 1 FROM items WHERE list_id = ?1",
                    params![list_id],
                    |row| row.get(0),
                )
                .map_err(sql_error)?;
            transaction
                .execute(
                    "INSERT INTO items
                     (list_id, name, quantity, note, category_id, checked, version, position, created_at, updated_at)
                     VALUES (?1, ?2, ?3, ?4, ?5, 0, 1, ?6, ?7, ?7)",
                    params![list_id, name, quantity, note, category_id, position, now()],
                )
                .map_err(sql_error)?;
            let revision = bump_revision(&transaction, list_id)?;
            transaction.commit().map_err(sql_error)?;
            Ok(revision)
        })
        .await
    }

    pub async fn set_item_checked(
        &self,
        list_id: i64,
        item_id: i64,
        checked: bool,
    ) -> DbResult<i64> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            let changed = transaction
                .execute(
                    "UPDATE items
                     SET checked = ?1, version = version + 1, updated_at = ?2
                     WHERE id = ?3 AND list_id = ?4",
                    params![checked as i64, now(), item_id, list_id],
                )
                .map_err(sql_error)?;
            if changed == 0 {
                return Err(DbError::NotFound);
            }
            let revision = bump_revision(&transaction, list_id)?;
            transaction.commit().map_err(sql_error)?;
            Ok(revision)
        })
        .await
    }

    pub async fn update_item(
        &self,
        list_id: i64,
        item_id: i64,
        name: String,
        quantity: String,
        note: String,
        category_id: Option<i64>,
    ) -> DbResult<i64> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            ensure_category(&transaction, list_id, category_id)?;
            let changed = transaction
                .execute(
                    "UPDATE items
                     SET name = ?1, quantity = ?2, note = ?3, category_id = ?4,
                         version = version + 1, updated_at = ?5
                     WHERE id = ?6 AND list_id = ?7",
                    params![name, quantity, note, category_id, now(), item_id, list_id],
                )
                .map_err(sql_error)?;
            if changed == 0 {
                return Err(DbError::NotFound);
            }
            let revision = bump_revision(&transaction, list_id)?;
            transaction.commit().map_err(sql_error)?;
            Ok(revision)
        })
        .await
    }

    pub async fn delete_item(&self, list_id: i64, item_id: i64) -> DbResult<i64> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            let changed = transaction
                .execute(
                    "DELETE FROM items WHERE id = ?1 AND list_id = ?2",
                    params![item_id, list_id],
                )
                .map_err(sql_error)?;
            if changed == 0 {
                return Err(DbError::NotFound);
            }
            let revision = bump_revision(&transaction, list_id)?;
            transaction.commit().map_err(sql_error)?;
            Ok(revision)
        })
        .await
    }

    pub async fn create_invitation(&self, created_by: i64, token: String) -> DbResult<i64> {
        self.call(move |connection| {
            let expires_at = now() + 60 * 60 * 24 * 7;
            connection
                .execute(
                    "INSERT INTO invitations (token_hash, created_by, expires_at)
                     VALUES (?1, ?2, ?3)",
                    params![hash_secret(&token), created_by, expires_at],
                )
                .map_err(sql_error)?;
            Ok(expires_at)
        })
        .await
    }

    pub async fn invitation(&self, token: String) -> DbResult<bool> {
        self.call(move |connection| {
            let valid = connection
                .query_row(
                    "SELECT 1 FROM invitations
                     WHERE token_hash = ?1 AND expires_at > ?2",
                    params![hash_secret(&token), now()],
                    |_| Ok(()),
                )
                .optional()
                .map_err(sql_error)?
                .is_some();
            Ok(valid)
        })
        .await
    }

    pub async fn accept_invitation(&self, token: String) -> DbResult<()> {
        self.call(move |connection| {
            let transaction = connection.transaction().map_err(sql_error)?;
            let valid = transaction
                .query_row(
                    "SELECT 1 FROM invitations
                     WHERE token_hash = ?1 AND expires_at > ?2",
                    params![hash_secret(&token), now()],
                    |_| Ok(()),
                )
                .optional()
                .map_err(sql_error)?
                .is_some();
            if !valid {
                return Err(DbError::NotFound);
            }
            transaction
                .execute(
                    "DELETE FROM invitations WHERE token_hash = ?1",
                    params![hash_secret(&token)],
                )
                .map_err(sql_error)?;
            transaction.commit().map_err(sql_error)?;
            Ok(())
        })
        .await
    }
}

fn configure(connection: &Connection) -> DbResult<()> {
    connection
        .pragma_update(None, "foreign_keys", true)
        .map_err(sql_error)?;
    connection
        .pragma_update(None, "journal_mode", "WAL")
        .map_err(sql_error)?;
    connection
        .busy_timeout(std::time::Duration::from_secs(5))
        .map_err(sql_error)?;
    Ok(())
}

fn migrate(connection: &Connection) -> DbResult<()> {
    connection
        .execute_batch(
            "CREATE TABLE IF NOT EXISTS users (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                email TEXT NOT NULL UNIQUE COLLATE NOCASE,
                display_name TEXT NOT NULL,
                password_hash TEXT NOT NULL,
                created_at INTEGER NOT NULL
            );
            CREATE TABLE IF NOT EXISTS sessions (
                token_hash TEXT PRIMARY KEY,
                user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
                csrf_token TEXT NOT NULL,
                expires_at INTEGER NOT NULL
            );
            CREATE TABLE IF NOT EXISTS lists (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                name TEXT NOT NULL,
                revision INTEGER NOT NULL DEFAULT 0,
                created_at INTEGER NOT NULL
            );
            CREATE TABLE IF NOT EXISTS categories (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                list_id INTEGER NOT NULL REFERENCES lists(id) ON DELETE CASCADE,
                name TEXT NOT NULL COLLATE NOCASE,
                position INTEGER NOT NULL DEFAULT 0,
                created_at INTEGER NOT NULL,
                UNIQUE (list_id, name)
            );
            CREATE TABLE IF NOT EXISTS invitations (
                token_hash TEXT PRIMARY KEY,
                created_by INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
                expires_at INTEGER NOT NULL
            );
            CREATE TABLE IF NOT EXISTS items (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                list_id INTEGER NOT NULL REFERENCES lists(id) ON DELETE CASCADE,
                name TEXT NOT NULL,
                quantity TEXT NOT NULL DEFAULT '',
                note TEXT NOT NULL DEFAULT '',
                category_id INTEGER REFERENCES categories(id) ON DELETE SET NULL,
                checked INTEGER NOT NULL DEFAULT 0,
                version INTEGER NOT NULL DEFAULT 1,
                position INTEGER NOT NULL DEFAULT 0,
                created_at INTEGER NOT NULL,
                updated_at INTEGER NOT NULL
            );
            CREATE INDEX IF NOT EXISTS items_list_idx ON items(list_id);
            CREATE INDEX IF NOT EXISTS categories_list_idx ON categories(list_id);
            CREATE INDEX IF NOT EXISTS sessions_user_idx ON sessions(user_id);",
        )
        .map_err(sql_error)?;

    Ok(())
}

fn ensure_category(
    transaction: &rusqlite::Transaction<'_>,
    list_id: i64,
    category_id: Option<i64>,
) -> DbResult<()> {
    let Some(category_id) = category_id else {
        return Ok(());
    };
    let exists = transaction
        .query_row(
            "SELECT 1 FROM categories WHERE id = ?1 AND list_id = ?2",
            params![category_id, list_id],
            |_| Ok(()),
        )
        .optional()
        .map_err(sql_error)?;
    if exists.is_none() {
        return Err(DbError::NotFound);
    }
    Ok(())
}

const DEFAULT_CATEGORIES: &[&str] = &[
    "Produce",
    "Meat & seafood",
    "Dairy & eggs",
    "Pantry",
    "Frozen",
    "Household",
];

fn bump_revision(transaction: &rusqlite::Transaction<'_>, list_id: i64) -> DbResult<i64> {
    transaction
        .execute(
            "UPDATE lists SET revision = revision + 1 WHERE id = ?1",
            params![list_id],
        )
        .map_err(sql_error)?;
    transaction
        .query_row(
            "SELECT revision FROM lists WHERE id = ?1",
            params![list_id],
            |row| row.get(0),
        )
        .map_err(sql_error)
}

fn sql_error(error: impl std::fmt::Display) -> DbError {
    DbError::Message(error.to_string())
}

fn now() -> i64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs() as i64
}

pub fn new_secret() -> String {
    let mut bytes = [0_u8; 32];
    OsRng.fill_bytes(&mut bytes);
    hex::encode(bytes)
}

pub fn hash_secret(secret: &str) -> String {
    let mut hasher = Sha256::new();
    hasher.update(secret.as_bytes());
    hex::encode(hasher.finalize())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[tokio::test]
    async fn creates_a_list_and_item() {
        let database = Database::open_in_memory().unwrap();
        let list = database
            .create_list("Weekly shop".into())
            .await
            .unwrap();
        database
            .add_item(
                list.id.clone(),
                "Milk".into(),
                "2 litres".into(),
                String::new(),
                None,
            )
            .await
            .unwrap();

        let items = database.items(list.id).await.unwrap();
        assert_eq!(items.len(), 1);
        assert_eq!(items[0].name, "Milk");
    }

    #[tokio::test]
    async fn sessions_and_invitations_are_scoped_to_users() {
        let database = Database::open_in_memory().unwrap();
        let owner = database
            .create_user("owner@example.com".into(), "Owner".into(), "hash".into())
            .await
            .unwrap();
        let list = database
            .create_list("Household".into())
            .await
            .unwrap();
        assert_eq!(database.categories(list.id.clone()).await.unwrap().len(), 6);
        let (session_token, csrf_token) = database.create_session(owner.id.clone()).await.unwrap();

        let session = database
            .session_user(session_token.clone())
            .await
            .unwrap()
            .unwrap();
        assert_eq!(session.user.id, owner.id);
        assert_eq!(session.csrf_token, csrf_token);

        // Any registered account can access every list.
        assert_eq!(
            database
                .list_access(list.id.clone())
                .await
                .unwrap()
                .unwrap()
                .name,
            "Household"
        );

        let invitation_token = "test-invitation".to_owned();
        database
            .create_invitation(owner.id.clone(), invitation_token.clone())
            .await
            .unwrap();
        assert!(
            database
                .invitation(invitation_token.clone())
                .await
                .unwrap()
        );

        database
            .accept_invitation(invitation_token.clone())
            .await
            .unwrap();
        assert!(
            !database
                .invitation(invitation_token)
                .await
                .unwrap()
        );

        // A list created later is also accessible to every account.
        let future_list = database
            .create_list("Future shop".into())
            .await
            .unwrap();
        assert_eq!(
            database
                .list_access(future_list.id)
                .await
                .unwrap()
                .unwrap()
                .name,
            "Future shop"
        );
    }

    #[tokio::test]
    async fn checked_state_is_set_not_toggled() {
        let database = Database::open_in_memory().unwrap();
        let list = database.create_list("List".into()).await.unwrap();
        database
            .add_item(
                list.id.clone(),
                "Coffee".into(),
                String::new(),
                String::new(),
                None,
            )
            .await
            .unwrap();
        let item = database.items(list.id.clone()).await.unwrap().remove(0);

        database
            .set_item_checked(list.id.clone(), item.id.clone(), true)
            .await
            .unwrap();
        database
            .set_item_checked(list.id.clone(), item.id.clone(), true)
            .await
            .unwrap();

        let item = database.items(list.id).await.unwrap().remove(0);
        assert!(item.checked);
        assert_eq!(item.version, 3);
    }

    #[tokio::test]
    async fn checking_an_item_does_not_change_list_order() {
        let database = Database::open_in_memory().unwrap();
        let list = database.create_list("List".into()).await.unwrap();
        database
            .add_item(
                list.id.clone(),
                "First".into(),
                String::new(),
                String::new(),
                None,
            )
            .await
            .unwrap();
        database
            .add_item(
                list.id.clone(),
                "Second".into(),
                String::new(),
                String::new(),
                None,
            )
            .await
            .unwrap();
        let first_item = database.items(list.id.clone()).await.unwrap().remove(0);

        database
            .set_item_checked(list.id.clone(), first_item.id, true)
            .await
            .unwrap();

        let items = database.items(list.id).await.unwrap();
        assert_eq!(items[0].name, "First");
        assert!(items[0].checked);
        assert_eq!(items[1].name, "Second");
    }
}