// Copyright 2016 Mozilla
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
// this file except in compliance with the License. You may obtain a copy of the
// License at http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

use rusqlite;
use rusqlite::types::ToSql;

use std::rc::Rc;

use core_traits::{Binding, Entid, KnownEntid, TypedValue};

use mentat_core::{HasSchema, Schema};

use mentat_query_algebrizer::{
    algebrize_with_inputs, parse_find_string, AlgebraicQuery, EmptyBecause, FindQuery,
};

pub use mentat_query_algebrizer::QueryInputs;

pub use edn::query::{Keyword, PlainSymbol, Variable};

use edn::query::{
    Element, FindSpec, Pattern, PatternNonValuePlace, PatternValuePlace, WhereClause,
};

use mentat_query_projector::{ConstantProjector, Projector};

use mentat_query_projector::translate::{query_to_select, ProjectedSelect};

use mentat_sql::SQLQuery;

pub use mentat_query_algebrizer::Known;

pub use mentat_query_projector::{
    QueryOutput,  // Includes the columns/find spec.
    QueryResults, // The results themselves.
    RelResult,
};

use public_traits::errors::{MentatError, Result};

pub type QueryExecutionResult = Result<QueryOutput>;
pub type PreparedResult<'sqlite> = Result<PreparedQuery<'sqlite>>;

pub enum PreparedQuery<'sqlite> {
    Empty {
        find_spec: Rc<FindSpec>,
    },
    Constant {
        select: ConstantProjector,
    },
    Bound {
        statement: rusqlite::Statement<'sqlite>,
        schema: Schema,
        connection: &'sqlite rusqlite::Connection,
        args: Vec<(String, Rc<rusqlite::types::Value>)>,
        projector: Box<dyn Projector>,
    },
}

impl<'sqlite> PreparedQuery<'sqlite> {
    pub fn run<T>(&mut self, _inputs: T) -> QueryExecutionResult
    where
        T: Into<Option<QueryInputs>>,
    {
        match self {
            PreparedQuery::Empty { ref find_spec } => Ok(QueryOutput::empty(find_spec)),
            PreparedQuery::Constant { ref select } => {
                select.project_without_rows().map_err(|e| e.into())
            }
            PreparedQuery::Bound {
                ref mut statement,
                ref schema,
                ref connection,
                ref args,
                ref projector,
            } => {
                let rows = run_statement(statement, args)?;
                projector
                    .project(schema, connection, rows)
                    .map_err(|e| e.into())
            }
        }
    }
}

pub trait IntoResult {
    fn into_scalar_result(self) -> Result<Option<Binding>>;
    fn into_coll_result(self) -> Result<Vec<Binding>>;
    fn into_tuple_result(self) -> Result<Option<Vec<Binding>>>;
    fn into_rel_result(self) -> Result<RelResult<Binding>>;
}

impl IntoResult for QueryExecutionResult {
    fn into_scalar_result(self) -> Result<Option<Binding>> {
        self?.into_scalar().map_err(|e| e.into())
    }

    fn into_coll_result(self) -> Result<Vec<Binding>> {
        self?.into_coll().map_err(|e| e.into())
    }

    fn into_tuple_result(self) -> Result<Option<Vec<Binding>>> {
        self?.into_tuple().map_err(|e| e.into())
    }

    fn into_rel_result(self) -> Result<RelResult<Binding>> {
        self?.into_rel().map_err(|e| e.into())
    }
}

/// A struct describing information about how Mentat would execute a query.
pub enum QueryExplanation {
    /// A query known in advance to be empty, and why we believe that.
    KnownEmpty(EmptyBecause),

    /// A query known in advance to return a constant value.
    KnownConstant,

    /// A query that takes actual work to execute.
    ExecutionPlan {
        /// The translated query and any bindings.
        query: SQLQuery,
        /// The output of SQLite's `EXPLAIN QUERY PLAN`.
        steps: Vec<QueryPlanStep>,
    },
}

/// A single row in the output of SQLite's `EXPLAIN QUERY PLAN`.
/// See https://www.sqlite.org/eqp.html for an explanation of each field.
pub struct QueryPlanStep {
    pub select_id: i32,
    pub order: i32,
    pub from: i32,
    pub detail: String,
}

fn algebrize_query<T>(known: Known, query: FindQuery, inputs: T) -> Result<AlgebraicQuery>
where
    T: Into<Option<QueryInputs>>,
{
    let algebrized = algebrize_with_inputs(known, query, 0, inputs.into().unwrap_or_default())?;
    let unbound = algebrized.unbound_variables();
    // Because we are running once, we can check that all of our `:in` variables are bound at this point.
    // If they aren't, the user has made an error -- perhaps writing the wrong variable in `:in`, or
    // not binding in the `QueryInput`.
    if !unbound.is_empty() {
        bail!(MentatError::UnboundVariables(
            unbound.into_iter().map(|v| v.to_string()).collect()
        ));
    }
    Ok(algebrized)
}

fn fetch_values<'sqlite>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    entity: Entid,
    attribute: Entid,
    only_one: bool,
) -> QueryExecutionResult {
    let v = Variable::from_valid_name("?v");

    // This should never fail.
    // TODO: it should be possible to algebrize with variable entity and attribute,
    // particularly with known type, allowing the use of prepared statements.
    let pattern = Pattern::simple(
        PatternNonValuePlace::Entid(entity),
        PatternNonValuePlace::Entid(attribute),
        PatternValuePlace::Variable(v.clone()),
    )
    .unwrap();

    let element = Element::Variable(v);
    let spec = if only_one {
        FindSpec::FindScalar(element)
    } else {
        FindSpec::FindColl(element)
    };
    let query = FindQuery::simple(spec, vec![WhereClause::Pattern(pattern)]);

    let algebrized = algebrize_query(known, query, None)?;

    run_algebrized_query(known, sqlite, algebrized)
}

fn lookup_attribute(schema: &Schema, attribute: &Keyword) -> Result<KnownEntid> {
    schema
        .get_entid(attribute)
        .ok_or_else(|| MentatError::UnknownAttribute(attribute.name().into()))
}

/// Return a single value for the provided entity and attribute.
/// If the attribute is multi-valued, an arbitrary value is returned.
/// If no value is present for that entity, `None` is returned.
/// If `attribute` isn't an attribute, `None` is returned.
#[allow(clippy::extra_unused_lifetimes)]
pub fn lookup_value<'sqlite, 'schema, 'cache, E, A>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    entity: E,
    attribute: A,
) -> Result<Option<TypedValue>>
where
    E: Into<Entid>,
    A: Into<Entid>,
{
    let entid = entity.into();
    let attrid = attribute.into();

    if known.is_attribute_cached_forward(attrid) {
        Ok(known
            .get_value_for_entid(known.schema, attrid, entid)
            .cloned())
    } else {
        fetch_values(sqlite, known, entid, attrid, true)
            .into_scalar_result()
            // Safe to unwrap: we never retrieve structure.
            .map(|r| r.map(|v| v.into_scalar().unwrap()))
    }
}

pub fn lookup_values<'sqlite, E, A>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    entity: E,
    attribute: A,
) -> Result<Vec<TypedValue>>
where
    E: Into<Entid>,
    A: Into<Entid>,
{
    let entid = entity.into();
    let attrid = attribute.into();

    if known.is_attribute_cached_forward(attrid) {
        Ok(known
            .get_values_for_entid(known.schema, attrid, entid)
            .cloned()
            .unwrap_or_else(Vec::new))
    } else {
        fetch_values(sqlite, known, entid, attrid, false)
            .into_coll_result()
            // Safe to unwrap: we never retrieve structure.
            .map(|v| v.into_iter().map(|x| x.into_scalar().unwrap()).collect())
    }
}

/// Return a single value for the provided entity and attribute.
/// If the attribute is multi-valued, an arbitrary value is returned.
/// If no value is present for that entity, `None` is returned.
/// If `attribute` doesn't name an attribute, an error is returned.
pub fn lookup_value_for_attribute<'sqlite, 'attribute, E>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    entity: E,
    attribute: &'attribute Keyword,
) -> Result<Option<TypedValue>>
where
    E: Into<Entid>,
{
    let attribute = lookup_attribute(known.schema, attribute)?;
    lookup_value(sqlite, known, entity.into(), attribute)
}

pub fn lookup_values_for_attribute<'sqlite, 'attribute, E>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    entity: E,
    attribute: &'attribute Keyword,
) -> Result<Vec<TypedValue>>
where
    E: Into<Entid>,
{
    let attribute = lookup_attribute(known.schema, attribute)?;
    lookup_values(sqlite, known, entity.into(), attribute)
}

fn run_statement<'sqlite, 'stmt, 'bound>(
    statement: &'stmt mut rusqlite::Statement<'sqlite>,
    bindings: &'bound [(String, Rc<rusqlite::types::Value>)],
) -> Result<rusqlite::Rows<'stmt>> {
    let rows = if bindings.is_empty() {
        statement.query(rusqlite::params![])?
    } else {
        let refs: Vec<(&str, &dyn ToSql)> = bindings
            .iter()
            .map(|&(ref k, ref v)| (k.as_str(), v.as_ref() as &dyn ToSql))
            .collect();
        statement.query_named(&refs)?
    };
    Ok(rows)
}

fn run_sql_query<'sqlite, 'sql, 'bound, T, F>(
    sqlite: &'sqlite rusqlite::Connection,
    sql: &'sql str,
    bindings: &'bound [(String, Rc<rusqlite::types::Value>)],
    mut mapper: F,
) -> Result<Vec<T>>
where
    F: FnMut(&rusqlite::Row) -> T,
{
    let mut statement = sqlite.prepare(sql)?;
    let mut rows = run_statement(&mut statement, &bindings)?;
    let mut result = vec![];
    while let Some(row_or_error) = rows.next().unwrap() {
        result.push(mapper(&row_or_error));
    }
    Ok(result)
}

fn algebrize_query_str<'query, T>(
    known: Known,
    query: &'query str,
    inputs: T,
) -> Result<AlgebraicQuery>
where
    T: Into<Option<QueryInputs>>,
{
    let parsed = parse_find_string(query)?;
    algebrize_query(known, parsed, inputs)
}

fn run_algebrized_query<'sqlite>(
    known: Known,
    sqlite: &'sqlite rusqlite::Connection,
    algebrized: AlgebraicQuery,
) -> QueryExecutionResult {
    assert!(
        algebrized.unbound_variables().is_empty(),
        "Unbound variables should be checked by now"
    );
    if algebrized.is_known_empty() {
        // We don't need to do any SQL work at all.
        return Ok(QueryOutput::empty(&algebrized.find_spec));
    }

    let select = query_to_select(known.schema, algebrized)?;
    match select {
        ProjectedSelect::Constant(constant) => {
            constant.project_without_rows().map_err(|e| e.into())
        }
        ProjectedSelect::Query { query, projector } => {
            let SQLQuery { sql, args } = query.to_sql_query()?;

            let mut statement = sqlite.prepare(sql.as_str())?;
            let rows = run_statement(&mut statement, &args)?;

            projector
                .project(known.schema, sqlite, rows)
                .map_err(|e| e.into())
        }
    }
}

/// Take an EDN query string, a reference to an open SQLite connection, a Mentat schema, and an
/// optional collection of input bindings (which should be keyed by `"?varname"`), and execute the
/// query immediately, blocking the current thread.
/// Returns a structure that corresponds to the kind of input query, populated with `TypedValue`
/// instances.
/// The caller is responsible for ensuring that the SQLite connection has an open transaction if
/// isolation is required.
pub fn q_once<'sqlite, 'query, T>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    query: &'query str,
    inputs: T,
) -> QueryExecutionResult
where
    T: Into<Option<QueryInputs>>,
{
    let algebrized = algebrize_query_str(known, query, inputs)?;
    run_algebrized_query(known, sqlite, algebrized)
}

/// Just like `q_once`, but doesn't use any cached values.
pub fn q_uncached<T>(
    sqlite: &rusqlite::Connection,
    schema: &Schema,
    query: &str,
    inputs: T,
) -> QueryExecutionResult
where
    T: Into<Option<QueryInputs>>,
{
    let known = Known::for_schema(schema);
    let algebrized = algebrize_query_str(known, query, inputs)?;

    run_algebrized_query(known, sqlite, algebrized)
}

pub fn q_prepare<'sqlite, 'schema, 'cache, 'query, T>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known<'schema, 'cache>,
    query: &'query str,
    inputs: T,
) -> PreparedResult<'sqlite>
where
    T: Into<Option<QueryInputs>>,
{
    let algebrized = algebrize_query_str(known, query, inputs)?;

    let unbound = algebrized.unbound_variables();
    if !unbound.is_empty() {
        // TODO: Allow binding variables at execution time, not just
        // preparation time.
        bail!(MentatError::UnboundVariables(
            unbound.into_iter().map(|v| v.to_string()).collect()
        ));
    }

    if algebrized.is_known_empty() {
        // We don't need to do any SQL work at all.
        return Ok(PreparedQuery::Empty {
            find_spec: algebrized.find_spec,
        });
    }

    let select = query_to_select(known.schema, algebrized)?;
    match select {
        ProjectedSelect::Constant(constant) => Ok(PreparedQuery::Constant { select: constant }),
        ProjectedSelect::Query { query, projector } => {
            let SQLQuery { sql, args } = query.to_sql_query()?;
            let statement = sqlite.prepare(sql.as_str())?;

            Ok(PreparedQuery::Bound {
                statement,
                schema: known.schema.clone(),
                connection: sqlite,
                args,
                projector,
            })
        }
    }
}

pub fn q_explain<'sqlite, 'query, T>(
    sqlite: &'sqlite rusqlite::Connection,
    known: Known,
    query: &'query str,
    inputs: T,
) -> Result<QueryExplanation>
where
    T: Into<Option<QueryInputs>>,
{
    let algebrized = algebrize_query_str(known, query, inputs)?;
    if algebrized.is_known_empty() {
        return Ok(QueryExplanation::KnownEmpty(
            algebrized.cc.empty_because.unwrap(),
        ));
    }
    match query_to_select(known.schema, algebrized)? {
        ProjectedSelect::Constant(_constant) => Ok(QueryExplanation::KnownConstant),
        ProjectedSelect::Query {
            query,
            projector: _projector,
        } => {
            let query = query.to_sql_query()?;

            let plan_sql = format!("EXPLAIN QUERY PLAN {}", query.sql);

            let steps = run_sql_query(sqlite, &plan_sql, &query.args, |row| QueryPlanStep {
                select_id: row.get(0).unwrap(),
                order: row.get(1).unwrap(),
                from: row.get(2).unwrap(),
                detail: row.get(3).unwrap(),
            })?;

            Ok(QueryExplanation::ExecutionPlan { query, steps })
        }
    }
}