use std::collections::HashSet;

use sqlite as sql;
use thiserror::Error;

use crate::node::Database;
use crate::{
    prelude::Timestamp,
    prelude::{Id, NodeId},
    sql::transaction,
};

/// Result of inserting into the routing table.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum InsertResult {
    /// Nothing was updated.
    NotUpdated,
    /// The entry's timestamp was updated.
    TimeUpdated,
    /// A new entry was inserted.
    SeedAdded,
}

/// An error occuring in peer-to-peer networking code.
#[derive(Error, Debug)]
pub enum Error {
    /// An Internal error.
    #[error("internal error: {0}")]
    Internal(#[from] sql::Error),
    /// Internal unit overflow.
    #[error("the unit overflowed")]
    UnitOverflow,
}

/// Backing store for a routing table.
pub trait Store {
    /// Get the nodes seeding the given id.
    fn get(&self, id: &Id) -> Result<HashSet<NodeId>, Error>;
    /// Get the resources seeded by the given node.
    fn get_resources(&self, node_id: &NodeId) -> Result<HashSet<Id>, Error>;
    /// Get a specific entry.
    fn entry(&self, id: &Id, node: &NodeId) -> Result<Option<Timestamp>, Error>;
    /// Checks if any entries are available.
    fn is_empty(&self) -> Result<bool, Error> {
        Ok(self.len()? == 0)
    }
    /// Add a new node seeding the given id.
    fn insert<'a>(
        &mut self,
        ids: impl IntoIterator<Item = &'a Id>,
        node: NodeId,
        time: Timestamp,
    ) -> Result<Vec<(Id, InsertResult)>, Error>;
    /// Remove a node for the given id.
    fn remove(&mut self, id: &Id, node: &NodeId) -> Result<bool, Error>;
    /// Iterate over all entries in the routing table.
    fn entries(&self) -> Result<Box<dyn Iterator<Item = (Id, NodeId)>>, Error>;
    /// Get the total number of routing entries.
    fn len(&self) -> Result<usize, Error>;
    /// Prune entries older than the given timestamp.
    fn prune(&mut self, oldest: Timestamp, limit: Option<usize>) -> Result<usize, Error>;
    /// Count the number of routes for a specific repo RID.
    fn count(&self, id: &Id) -> Result<usize, Error>;
}

impl Store for Database {
    fn get(&self, id: &Id) -> Result<HashSet<NodeId>, Error> {
        let mut stmt = self
            .db
            .prepare("SELECT (node) FROM routing WHERE repo = ?")?;
        stmt.bind((1, id))?;

        let mut nodes = HashSet::new();
        for row in stmt.into_iter() {
            nodes.insert(row?.read::<NodeId, _>("node"));
        }
        Ok(nodes)
    }

    fn get_resources(&self, node: &NodeId) -> Result<HashSet<Id>, Error> {
        let mut stmt = self.db.prepare("SELECT repo FROM routing WHERE node = ?")?;
        stmt.bind((1, node))?;

        let mut resources = HashSet::new();
        for row in stmt.into_iter() {
            resources.insert(row?.read::<Id, _>("repo"));
        }
        Ok(resources)
    }

    fn entry(&self, id: &Id, node: &NodeId) -> Result<Option<Timestamp>, Error> {
        let mut stmt = self
            .db
            .prepare("SELECT (timestamp) FROM routing WHERE repo = ? AND node = ?")?;

        stmt.bind((1, id))?;
        stmt.bind((2, node))?;

        if let Some(Ok(row)) = stmt.into_iter().next() {
            return Ok(Some(row.read::<i64, _>("timestamp") as Timestamp));
        }
        Ok(None)
    }

    fn insert<'a>(
        &mut self,
        ids: impl IntoIterator<Item = &'a Id>,
        node: NodeId,
        time: Timestamp,
    ) -> Result<Vec<(Id, InsertResult)>, Error> {
        let time: i64 = time.try_into().map_err(|_| Error::UnitOverflow)?;
        let mut results = Vec::new();

        transaction(&self.db, |db| {
            for id in ids.into_iter() {
                let mut stmt =
                    db.prepare("SELECT (timestamp) FROM routing WHERE repo = ? AND node = ?")?;

                stmt.bind((1, id))?;
                stmt.bind((2, &node))?;

                let existed = stmt.into_iter().next().is_some();
                let mut stmt = db.prepare(
                    "INSERT INTO routing (repo, node, timestamp)
                     VALUES (?, ?, ?)
                     ON CONFLICT DO UPDATE
                     SET timestamp = ?3
                     WHERE timestamp < ?3",
                )?;

                stmt.bind((1, id))?;
                stmt.bind((2, &node))?;
                stmt.bind((3, time))?;
                stmt.next()?;

                let result = match (self.db.change_count() > 0, existed) {
                    (true, true) => InsertResult::TimeUpdated,
                    (true, false) => InsertResult::SeedAdded,
                    (false, _) => InsertResult::NotUpdated,
                };
                results.push((*id, result));
            }
            Ok(results)
        })
        .map_err(Error::from)
    }

    fn entries(&self) -> Result<Box<dyn Iterator<Item = (Id, NodeId)>>, Error> {
        let mut stmt = self
            .db
            .prepare("SELECT repo, node FROM routing ORDER BY repo")?
            .into_iter();
        let mut entries = Vec::new();

        while let Some(Ok(row)) = stmt.next() {
            let id = row.read("repo");
            let node = row.read("node");

            entries.push((id, node));
        }
        Ok(Box::new(entries.into_iter()))
    }

    fn remove(&mut self, id: &Id, node: &NodeId) -> Result<bool, Error> {
        let mut stmt = self
            .db
            .prepare("DELETE FROM routing WHERE repo = ? AND node = ?")?;

        stmt.bind((1, id))?;
        stmt.bind((2, node))?;
        stmt.next()?;

        Ok(self.db.change_count() > 0)
    }

    fn len(&self) -> Result<usize, Error> {
        let stmt = self.db.prepare("SELECT COUNT(1) FROM routing")?;
        let count: i64 = stmt
            .into_iter()
            .next()
            .expect("COUNT will always return a single row")?
            .read(0);
        let count: usize = count.try_into().map_err(|_| Error::UnitOverflow)?;
        Ok(count)
    }

    fn prune(&mut self, oldest: Timestamp, limit: Option<usize>) -> Result<usize, Error> {
        let oldest: i64 = oldest.try_into().map_err(|_| Error::UnitOverflow)?;
        let limit: i64 = limit
            .unwrap_or(i64::MAX as usize)
            .try_into()
            .map_err(|_| Error::UnitOverflow)?;

        let mut stmt = self.db.prepare(
            "DELETE FROM routing WHERE rowid IN
            (SELECT rowid FROM routing WHERE timestamp < ? LIMIT ?)",
        )?;
        stmt.bind((1, oldest))?;
        stmt.bind((2, limit))?;
        stmt.next()?;

        Ok(self.db.change_count())
    }

    fn count(&self, id: &Id) -> Result<usize, Error> {
        let mut stmt = self
            .db
            .prepare("SELECT COUNT(*) FROM routing WHERE repo = ?")?;

        stmt.bind((1, id))?;

        let count: i64 = stmt
            .into_iter()
            .next()
            .expect("COUNT will always return a single row")?
            .read(0);

        let count: usize = count.try_into().map_err(|_| Error::UnitOverflow)?;

        Ok(count)
    }
}

#[cfg(test)]
mod test {
    use localtime::LocalTime;

    use super::*;
    use crate::test::arbitrary;

    #[test]
    fn test_insert_and_get() {
        let ids = arbitrary::set::<Id>(5..10);
        let nodes = arbitrary::set::<NodeId>(5..10);
        let mut db = Database::open(":memory:").unwrap();

        for node in &nodes {
            assert_eq!(
                db.insert(&ids, *node, 0).unwrap(),
                ids.iter()
                    .map(|id| (*id, InsertResult::SeedAdded))
                    .collect::<Vec<_>>()
            );
        }

        for id in &ids {
            let seeds = db.get(id).unwrap();
            for node in &nodes {
                assert!(seeds.contains(node));
            }
        }
    }

    #[test]
    fn test_insert_and_get_resources() {
        let ids = arbitrary::set::<Id>(5..10);
        let nodes = arbitrary::set::<NodeId>(5..10);
        let mut db = Database::open(":memory:").unwrap();

        for node in &nodes {
            db.insert(&ids, *node, 0).unwrap();
        }

        for node in &nodes {
            let projects = db.get_resources(node).unwrap();
            for id in &ids {
                assert!(projects.contains(id));
            }
        }
    }

    #[test]
    fn test_entries() {
        let ids = arbitrary::set::<Id>(6..9);
        let nodes = arbitrary::set::<NodeId>(6..9);
        let mut db = Database::open(":memory:").unwrap();

        for node in &nodes {
            assert!(db
                .insert(&ids, *node, 0)
                .unwrap()
                .iter()
                .all(|(_, r)| *r == InsertResult::SeedAdded));
        }

        let results = db.entries().unwrap().collect::<Vec<_>>();
        assert_eq!(results.len(), ids.len() * nodes.len());

        let mut results_ids = results.iter().map(|(id, _)| *id).collect::<Vec<_>>();
        results_ids.dedup();

        assert_eq!(results_ids.len(), ids.len(), "Entries are grouped by id");
    }

    #[test]
    fn test_insert_and_remove() {
        let ids = arbitrary::set::<Id>(5..10);
        let nodes = arbitrary::set::<NodeId>(5..10);
        let mut db = Database::open(":memory:").unwrap();

        for node in &nodes {
            db.insert(&ids, *node, 0).unwrap();
        }
        for id in &ids {
            for node in &nodes {
                assert!(db.remove(id, node).unwrap());
            }
        }
        for id in &ids {
            assert!(db.get(id).unwrap().is_empty());
        }
    }

    #[test]
    fn test_insert_duplicate() {
        let id = arbitrary::gen::<Id>(1);
        let node = arbitrary::gen::<NodeId>(1);
        let mut db = Database::open(":memory:").unwrap();

        assert_eq!(
            db.insert([&id], node, 0).unwrap(),
            vec![(id, InsertResult::SeedAdded)]
        );
        assert_eq!(
            db.insert([&id], node, 0).unwrap(),
            vec![(id, InsertResult::NotUpdated)]
        );
        assert_eq!(
            db.insert([&id], node, 0).unwrap(),
            vec![(id, InsertResult::NotUpdated)]
        );
    }

    #[test]
    fn test_insert_existing_updated_time() {
        let id = arbitrary::gen::<Id>(1);
        let node = arbitrary::gen::<NodeId>(1);
        let mut db = Database::open(":memory:").unwrap();

        assert_eq!(
            db.insert([&id], node, 0).unwrap(),
            vec![(id, InsertResult::SeedAdded)]
        );
        assert_eq!(
            db.insert([&id], node, 1).unwrap(),
            vec![(id, InsertResult::TimeUpdated)]
        );
        assert_eq!(db.entry(&id, &node).unwrap(), Some(1));
    }

    #[test]
    fn test_update_existing_multi() {
        let id1 = arbitrary::gen::<Id>(1);
        let id2 = arbitrary::gen::<Id>(1);
        let node = arbitrary::gen::<NodeId>(1);
        let mut db = Database::open(":memory:").unwrap();

        assert_eq!(
            db.insert([&id1], node, 0).unwrap(),
            vec![(id1, InsertResult::SeedAdded)]
        );
        assert_eq!(
            db.insert([&id1, &id2], node, 0).unwrap(),
            vec![
                (id1, InsertResult::NotUpdated),
                (id2, InsertResult::SeedAdded)
            ]
        );
        assert_eq!(
            db.insert([&id1, &id2], node, 1).unwrap(),
            vec![
                (id1, InsertResult::TimeUpdated),
                (id2, InsertResult::TimeUpdated)
            ]
        );
    }

    #[test]
    fn test_remove_redundant() {
        let id = arbitrary::gen::<Id>(1);
        let node = arbitrary::gen::<NodeId>(1);
        let mut db = Database::open(":memory:").unwrap();

        assert_eq!(
            db.insert([&id], node, 0).unwrap(),
            vec![(id, InsertResult::SeedAdded)]
        );
        assert!(db.remove(&id, &node).unwrap());
        assert!(!db.remove(&id, &node).unwrap());
    }

    #[test]
    fn test_len() {
        let mut db = Database::open(":memory:").unwrap();
        let ids = arbitrary::vec::<Id>(10);
        let node = arbitrary::gen(1);

        db.insert(&ids, node, LocalTime::now().as_millis()).unwrap();

        assert_eq!(10, db.len().unwrap(), "correct number of rows in table");
    }

    #[test]
    fn test_prune() {
        let mut rng = fastrand::Rng::new();
        let now = LocalTime::now();
        let ids = arbitrary::vec::<Id>(10);
        let nodes = arbitrary::vec::<NodeId>(10);
        let mut db = Database::open(":memory:").unwrap();

        for node in &nodes {
            let time = rng.u64(..now.as_millis());
            db.insert(&ids, *node, time).unwrap();
        }

        let ids = arbitrary::vec::<Id>(10);
        let nodes = arbitrary::vec::<NodeId>(10);

        for node in &nodes {
            let time = rng.u64(now.as_millis()..i64::MAX as u64);
            db.insert(&ids, *node, time).unwrap();
        }

        let pruned = db.prune(now.as_millis(), None).unwrap();
        assert_eq!(pruned, ids.len() * nodes.len());

        for id in &ids {
            for node in &nodes {
                let t = db.entry(id, node).unwrap().unwrap();
                assert!(t >= now.as_millis());
            }
        }
    }

    #[test]
    fn test_count() {
        let id = arbitrary::gen::<Id>(1);
        let nodes = arbitrary::set::<NodeId>(5..10);
        let mut db = Database::open(":memory:").unwrap();

        for node in &nodes {
            db.insert([&id], *node, 0).unwrap();
        }
        assert_eq!(db.count(&id).unwrap(), nodes.len());
    }
}