use std::collections::HashMap;
use std::iter::zip;

use super::entry::EntryValue;
use super::inner::models::Entry;
use super::inner::schema::data;
use super::lang::{PatternQuery, Query, QueryComponent, QueryPart, QueryQualifier};
use crate::database::inner::models;
use diesel::IntoSql;
use diesel::RunQueryDsl;
use diesel::{ExpressionMethods, TextExpressionMethods};
use anyhow::Result;
use diesel::expression::grouped::Grouped;
use diesel::expression::operators::{And, Not, Or};
use diesel::sql_types::Bool;
use diesel::sqlite::Sqlite;
use diesel::{
    r2d2::{ConnectionManager, PooledConnection},
    SqliteConnection,
};
use diesel::{BoxableExpression, QueryDsl};

#[derive(Debug, Clone)]
pub struct QueryExecutionError(String);

impl std::fmt::Display for QueryExecutionError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

impl std::error::Error for QueryExecutionError {}

pub fn execute(
    connection: &PooledConnection<ConnectionManager<SqliteConnection>>,
    query: Query,
) -> Result<Vec<Entry>, QueryExecutionError> {
    use crate::database::inner::schema::data::dsl::*;

    if let Some(predicates) = to_sqlite_predicates(query.clone())? {
        let db_query = data.filter(predicates);
        db_query
            .load::<models::Entry>(connection)
            .map_err(|e| QueryExecutionError(e.to_string()))
    } else {
        match query {
            Query::SingleQuery(_) => Err(QueryExecutionError(
                "Forced manual evaluation of an atomic query, this should never happen.".into(),
            )),
            Query::MultiQuery(mq) => match mq.qualifier {
                QueryQualifier::Not => Err(QueryExecutionError(
                    "Stopped manual evaluation at NOT sub-query due to performance limits. Please \
                     rework your query."
                        .into(),
                )),
                _ => {
                    let subquery_results = mq
                        .queries
                        .iter()
                        .map(|q| execute(connection, *q.clone()))
                        .collect::<Result<Vec<Vec<Entry>>, QueryExecutionError>>()?;
                    match mq.qualifier {
                        QueryQualifier::Not => unreachable!(),
                        QueryQualifier::And => Ok(subquery_results
                            .into_iter()
                            .reduce(|acc, cur| {
                                acc.into_iter()
                                    .filter(|e| {
                                        cur.iter().map(|e| &e.identity).any(|x| x == &e.identity)
                                    })
                                    .collect()
                            })
                            .unwrap()), // TODO
                        QueryQualifier::Or => Ok(subquery_results.into_iter().flatten().collect()),
                        QueryQualifier::Join => {
                            let pattern_queries = mq
                                .queries
                                .into_iter()
                                .map(|q| match *q {
                                    Query::SingleQuery(QueryPart::Matches(pq)) => Some(pq),
                                    _ => None,
                                })
                                .collect::<Option<Vec<_>>>();

                            if let Some(pattern_queries) = pattern_queries {
                                let entries = zip(pattern_queries, subquery_results)
                                    .into_iter()
                                    .map(|(query, results)| {
                                        results
                                            .into_iter()
                                            .map(|e| EntryWithVars::new(&query, e))
                                            .collect::<Vec<EntryWithVars>>()
                                    });

                                let joined = entries
                                    .reduce(|acc, cur| {
                                        acc.into_iter()
                                            .filter(|tested_entry| {
                                                tested_entry.vars.iter().any(|(k1, v1)| {
                                                    cur.iter().any(|other_entry| {
                                                        other_entry
                                                            .vars
                                                            .iter()
                                                            .any(|(k2, v2)| k1 == k2 && v1 == v2)
                                                    })
                                                })
                                            })
                                            .collect()
                                    })
                                    .unwrap(); // TODO

                                Ok(joined.into_iter().map(|ev| ev.entry).collect())
                            } else {
                                Err(QueryExecutionError(
                                    "Cannot join on non-atomic queries.".into(),
                                ))
                            }
                        }
                    }
                }
            },
        }
    }
}

struct EntryWithVars {
    entry: Entry,
    vars: HashMap<String, String>,
}

impl EntryWithVars {
    pub fn new(query: &PatternQuery, entry: Entry) -> Self {
        let mut vars = HashMap::new();

        if let QueryComponent::Variable(Some(var_name)) = &query.entity {
            vars.insert(
                var_name.clone(),
                crate::util::hash::b58_encode(&entry.entity),
            );
        }

        if let QueryComponent::Variable(Some(var_name)) = &query.attribute {
            vars.insert(var_name.clone(), entry.attribute.clone());
        }

        if let QueryComponent::Variable(Some(var_name)) = &query.value {
            if let Some(value_str) = &entry.value_str {
                vars.insert(var_name.clone(), value_str.clone());
            }
        }

        EntryWithVars { entry, vars }
    }
}

type SqlPredicate = dyn BoxableExpression<data::table, Sqlite, SqlType = Bool>;

type SqlResult = Option<Box<SqlPredicate>>;

fn to_sqlite_predicates(query: Query) -> Result<SqlResult, QueryExecutionError> {
    match query {
        Query::SingleQuery(qp) => match qp {
            QueryPart::Matches(eq) => {
                let mut subqueries: Vec<Box<SqlPredicate>> = vec![];

                match &eq.entity {
                    QueryComponent::Exact(q_entity) => {
                        subqueries.push(Box::new(data::entity.eq(q_entity.encode().map_err(
                            |e| QueryExecutionError(format!("failed producing sql: {e}")),
                        )?)))
                    }
                    QueryComponent::In(q_entities) => {
                        let entities: Result<Vec<_>, _> =
                            q_entities.iter().map(|t| t.encode()).collect();
                        subqueries.push(Box::new(data::entity.eq_any(entities.map_err(|e| {
                            QueryExecutionError(format!("failed producing sql: {e}"))
                        })?)))
                    }
                    QueryComponent::Contains(q_entity) => subqueries.push(Box::new(
                        data::entity_searchable.like(format!("%{}%", q_entity)),
                    )),
                    QueryComponent::Variable(_) => {}
                };

                match &eq.attribute {
                    QueryComponent::Exact(q_attribute) => {
                        subqueries.push(Box::new(data::attribute.eq(q_attribute.0.clone())))
                    }
                    QueryComponent::In(q_attributes) => subqueries.push(Box::new(
                        data::attribute.eq_any(q_attributes.iter().map(|a| &a.0).cloned()),
                    )),
                    QueryComponent::Contains(q_attribute) => subqueries
                        .push(Box::new(data::attribute.like(format!("%{}%", q_attribute)))),
                    QueryComponent::Variable(_) => {}
                };

                match &eq.value {
                    QueryComponent::Exact(q_value) => match q_value {
                        EntryValue::Number(n) => subqueries.push(Box::new(data::value_num.eq(*n))),
                        _ => subqueries.push(Box::new(data::value_str.eq(
                            q_value.to_string().map_err(|e| {
                                QueryExecutionError(format!("failed producing sql: {e}"))
                            })?,
                        ))),
                    },
                    QueryComponent::In(q_values) => {
                        let first = q_values.first().ok_or_else(|| {
                            QueryExecutionError(
                                "Malformed expression: Inner value cannot be empty.".into(),
                            )
                        })?;

                        match first {
                            EntryValue::Number(_) => subqueries.push(Box::new(
                                data::value_num.eq_any(
                                    q_values
                                        .iter()
                                        .map(|v| {
                                            if let EntryValue::Number(n) = v {
                                                Ok(*n)
                                            } else {
                                                Err(QueryExecutionError(format!(
                                                    "IN queries must not combine numeric and \
                                                     string values! ({v} is not a number)"
                                                )))
                                            }
                                        })
                                        .collect::<Result<Vec<f64>, QueryExecutionError>>()?,
                                ),
                            )),
                            _ => subqueries.push(Box::new(
                                data::value_str.eq_any(
                                    q_values
                                        .iter()
                                        .map(|v| {
                                            if let EntryValue::Number(_) = v {
                                                Err(QueryExecutionError(format!(
                                                    "IN queries must not combine numeric and \
                                                     string values! (Found {v})"
                                                )))
                                            } else {
                                                v.to_string().map_err(|e| {
                                                    QueryExecutionError(format!(
                                                        "failed producing sql: {e}"
                                                    ))
                                                })
                                            }
                                        })
                                        .collect::<Result<Vec<String>, QueryExecutionError>>()?,
                                ),
                            )),
                        }
                    }
                    QueryComponent::Contains(q_value) => {
                        subqueries.push(Box::new(data::value_str.like(format!("S%{}%", q_value))))
                    }
                    QueryComponent::Variable(_) => {}
                };

                match subqueries.len() {
                    0 => Ok(Some(Box::new(true.into_sql::<Bool>()))),
                    1 => Ok(Some(subqueries.remove(0))),
                    _ => {
                        let mut result: Box<And<Box<SqlPredicate>, Box<SqlPredicate>>> =
                            Box::new(And::new(subqueries.remove(0), subqueries.remove(0)));
                        while !subqueries.is_empty() {
                            result = Box::new(And::new(result, subqueries.remove(0)));
                        }
                        Ok(Some(Box::new(result)))
                    }
                }
            }
            QueryPart::Type(_) => unimplemented!("Type queries are not yet implemented."),
        },
        Query::MultiQuery(mq) => {
            let mq_result = mq
                .queries
                .into_iter()
                .map(|sq| to_sqlite_predicates(*sq))
                .collect::<Result<Vec<SqlResult>, QueryExecutionError>>()?;

            let mq_result: Option<Vec<Box<SqlPredicate>>> = mq_result.into_iter().collect();

            if let Some(mut subqueries) = mq_result {
                match subqueries.len() {
                    0 => Ok(Some(Box::new(true.into_sql::<Bool>()))),
                    1 => {
                        if let QueryQualifier::Not = mq.qualifier {
                            Ok(Some(Box::new(Not::new(subqueries.remove(0)))))
                        } else {
                            Ok(Some(subqueries.remove(0)))
                        }
                    }
                    _ => match mq.qualifier {
                        QueryQualifier::Join => Ok(None),
                        QueryQualifier::And => {
                            let mut result: Box<And<Box<SqlPredicate>, Box<SqlPredicate>>> =
                                Box::new(And::new(subqueries.remove(0), subqueries.remove(0)));
                            while !subqueries.is_empty() {
                                result = Box::new(And::new(result, subqueries.remove(0)));
                            }
                            Ok(Some(Box::new(Grouped(result))))
                        }
                        QueryQualifier::Or => {
                            let mut result =
                                Box::new(Or::new(subqueries.remove(0), subqueries.remove(0)));
                            while !subqueries.is_empty() {
                                result = Box::new(Or::new(result, subqueries.remove(0)));
                            }
                            Ok(Some(Box::new(Grouped(result))))
                        }
                        QueryQualifier::Not => {
                            Err(QueryExecutionError("NOT only takes one subquery.".into()))
                        }
                    },
                }
            } else {
                Ok(None)
            }
        }
    }
}