use crate::{NativeUpsert, WriteArgs};
use async_trait::async_trait;
use prisma_value::PrismaValue;
use query_structure::{ast::FieldArity, *};
use std::collections::HashMap;

#[async_trait]
pub trait Connector {
    /// Returns a connection to a data source.
    async fn get_connection(&self) -> crate::Result<Box<dyn Connection + Send + Sync>>;

    /// Returns the name of the connector.
    fn name(&self) -> &'static str;

    /// Returns whether a connector should retry an entire transaction when that transaction failed during its execution
    /// because of a transient transaction error. Note: This is specific to MongoDB for now.
    fn should_retry_on_transient_error(&self) -> bool;
}

#[async_trait]
pub trait Connection: ConnectionLike {
    async fn start_transaction<'a>(
        &'a mut self,
        isolation_level: Option<String>,
    ) -> crate::Result<Box<dyn Transaction + 'a>>;

    /// Explicit upcast.
    fn as_connection_like(&mut self) -> &mut dyn ConnectionLike;
}

#[async_trait]
pub trait Transaction: ConnectionLike {
    async fn commit(&mut self) -> crate::Result<()>;
    async fn rollback(&mut self) -> crate::Result<()>;

    /// Explicit upcast of self reference. Rusts current vtable layout doesn't allow for an upcast if
    /// `trait A`, `trait B: A`, so that `Box<dyn B> as Box<dyn A>` works. This is a simple, explicit workaround.
    fn as_connection_like(&mut self) -> &mut dyn ConnectionLike;
}

/// Marker trait required by the query core executor to abstract connections and
/// transactions into something that can is capable of writing to or reading from the database.
pub trait ConnectionLike: ReadOperations + WriteOperations + Send + Sync {}

/// A wrapper struct allowing to either filter for records or for the core to
/// communicate already known record selectors to connectors.
///
/// Connector implementations should use known selectors to skip unnecessary fetch operations
/// if the query core already determined the selectors in a previous step. Simply put,
/// `selectors` should always have precendence over `filter`.
#[derive(Debug, Clone)]
pub struct RecordFilter {
    pub filter: Filter,
    pub selectors: Option<Vec<SelectionResult>>,
}

impl RecordFilter {
    pub fn empty() -> Self {
        Self {
            filter: Filter::empty(),
            selectors: None,
        }
    }

    pub fn has_selectors(&self) -> bool {
        self.selectors.is_some()
    }
}

impl From<Filter> for RecordFilter {
    fn from(filter: Filter) -> Self {
        Self {
            filter,
            selectors: None,
        }
    }
}

impl From<Vec<SelectionResult>> for RecordFilter {
    fn from(selectors: Vec<SelectionResult>) -> Self {
        Self {
            filter: Filter::empty(),
            selectors: Some(selectors),
        }
    }
}

impl From<SelectionResult> for RecordFilter {
    fn from(selector: SelectionResult) -> Self {
        Self {
            filter: Filter::empty(),
            selectors: Some(vec![selector]),
        }
    }
}

/// Selections for aggregation queries.
#[derive(Debug, Clone)]
pub enum AggregationSelection {
    /// Single field selector. Only valid in the context of group by statements.
    Field(ScalarFieldRef),

    /// Counts records of the model that match the query.
    /// `all` indicates that an all-records selection has been made (e.g. SQL *).
    /// `fields` are specific fields to count on. By convention, if `all` is true,
    /// it will always be the last of the count results.
    Count { all: bool, fields: Vec<ScalarFieldRef> },

    /// Compute average for each field contained.
    Average(Vec<ScalarFieldRef>),

    /// Compute sum for each field contained.
    Sum(Vec<ScalarFieldRef>),

    /// Compute mininum for each field contained.
    Min(Vec<ScalarFieldRef>),

    /// Compute maximum for each field contained.
    Max(Vec<ScalarFieldRef>),
}

impl AggregationSelection {
    /// Returns (field_db_name, TypeIdentifier, FieldArity)
    pub fn identifiers(&self) -> Vec<(String, TypeIdentifier, FieldArity)> {
        match self {
            AggregationSelection::Field(field) => {
                vec![(field.db_name().to_owned(), field.type_identifier(), field.arity())]
            }

            AggregationSelection::Count { all, fields } => {
                let mut mapped = Self::map_field_types(fields, Some(TypeIdentifier::Int));

                if *all {
                    mapped.push(("all".to_owned(), TypeIdentifier::Int, FieldArity::Required));
                }

                mapped
            }

            AggregationSelection::Average(fields) => Self::map_field_types(fields, Some(TypeIdentifier::Float)),
            AggregationSelection::Sum(fields) => Self::map_field_types(fields, None),
            AggregationSelection::Min(fields) => Self::map_field_types(fields, None),
            AggregationSelection::Max(fields) => Self::map_field_types(fields, None),
        }
    }

    fn map_field_types(
        fields: &[ScalarFieldRef],
        fixed_type: Option<TypeIdentifier>,
    ) -> Vec<(String, TypeIdentifier, FieldArity)> {
        fields
            .iter()
            .map(|f| {
                (
                    f.db_name().to_owned(),
                    fixed_type.unwrap_or_else(|| f.type_identifier()),
                    FieldArity::Required,
                )
            })
            .collect()
    }
}

pub type AggregationRow = Vec<AggregationResult>;

/// Result of an aggregation operation on a model or field.
/// A `Field` return type is only interesting for aggregations involving
/// group bys, as they return field values alongside group aggregates.
#[derive(Debug, Clone)]
pub enum AggregationResult {
    Field(ScalarFieldRef, PrismaValue),
    Count(Option<ScalarFieldRef>, PrismaValue),
    Average(ScalarFieldRef, PrismaValue),
    Sum(ScalarFieldRef, PrismaValue),
    Min(ScalarFieldRef, PrismaValue),
    Max(ScalarFieldRef, PrismaValue),
}

#[async_trait]
pub trait ReadOperations {
    /// Gets a single record or `None` back from the database.
    ///
    /// - The `ModelRef` represents the datamodel and its relations.
    /// - The `Filter` defines what item we want back and is guaranteed to be
    ///   defined to filter at most one item by the core.
    /// - The `FieldSelection` defines the values to be returned.
    async fn get_single_record(
        &mut self,
        model: &Model,
        filter: &Filter,
        selected_fields: &FieldSelection,
        relation_load_strategy: RelationLoadStrategy,
        trace_id: Option<String>,
    ) -> crate::Result<Option<SingleRecord>>;

    /// Gets multiple records from the database.
    ///
    /// - The `ModelRef` represents the datamodel and its relations.
    /// - The `QueryArguments` defines various constraints (see docs for detailed explanation).
    /// - The `FieldSelection` defines the fields (e.g. columns or document fields)
    ///   to be returned as a projection of fields of the model it queries.
    async fn get_many_records(
        &mut self,
        model: &Model,
        query_arguments: QueryArguments,
        selected_fields: &FieldSelection,
        relation_load_strategy: RelationLoadStrategy,
        trace_id: Option<String>,
    ) -> crate::Result<ManyRecords>;

    /// Retrieves pairs of IDs that belong together from a intermediate join
    /// table.
    ///
    /// Given the field from parent, and the projections, return the given
    /// projections with the corresponding child projections fetched from the
    /// database. The IDs returned will be used to perform a in-memory join
    /// between two datasets.
    async fn get_related_m2m_record_ids(
        &mut self,
        from_field: &RelationFieldRef,
        from_record_ids: &[SelectionResult],
        trace_id: Option<String>,
    ) -> crate::Result<Vec<(SelectionResult, SelectionResult)>>;

    /// Aggregates records for a specific model based on the given selections.
    /// Whether or not the aggregations can be executed in a single query or
    /// requires multiple roundtrips to the underlying data source is at the
    /// discretion of the implementing connector.
    /// `having` can only be a scalar filter. Relation elements can be safely ignored.
    async fn aggregate_records(
        &mut self,
        model: &Model,
        query_arguments: QueryArguments,
        selections: Vec<AggregationSelection>,
        group_by: Vec<ScalarFieldRef>,
        having: Option<Filter>,
        trace_id: Option<String>,
    ) -> crate::Result<Vec<AggregationRow>>;
}

#[async_trait]
pub trait WriteOperations {
    /// Insert a single record to the database.
    async fn create_record(
        &mut self,
        model: &Model,
        args: WriteArgs,
        selected_fields: FieldSelection,
        trace_id: Option<String>,
    ) -> crate::Result<SingleRecord>;

    /// Inserts many records at once into the database.
    async fn create_records(
        &mut self,
        model: &Model,
        args: Vec<WriteArgs>,
        skip_duplicates: bool,
        trace_id: Option<String>,
    ) -> crate::Result<usize>;

    /// Update records in the `Model` with the given `WriteArgs` filtered by the
    /// `Filter`.
    async fn update_records(
        &mut self,
        model: &Model,
        record_filter: RecordFilter,
        args: WriteArgs,
        trace_id: Option<String>,
    ) -> crate::Result<usize>;

    /// Update record in the `Model` with the given `WriteArgs` filtered by the
    /// `Filter`.
    async fn update_record(
        &mut self,
        model: &Model,
        record_filter: RecordFilter,
        args: WriteArgs,
        selected_fields: Option<FieldSelection>,
        trace_id: Option<String>,
    ) -> crate::Result<Option<SingleRecord>>;

    /// Native upsert
    /// Use the connectors native upsert to upsert the `Model`
    async fn native_upsert_record(
        &mut self,
        upsert: NativeUpsert,
        trace_id: Option<String>,
    ) -> crate::Result<SingleRecord>;

    /// Delete records in the `Model` with the given `Filter`.
    async fn delete_records(
        &mut self,
        model: &Model,
        record_filter: RecordFilter,
        trace_id: Option<String>,
    ) -> crate::Result<usize>;

    /// Delete single record in the `Model` with the given `Filter`.
    /// Return selected fields of the deleted record, if the connector
    /// supports it. If the connector does not support it, error is returned.
    async fn delete_record(
        &mut self,
        model: &Model,
        record_filter: RecordFilter,
        selected_fields: FieldSelection,
        trace_id: Option<String>,
    ) -> crate::Result<SingleRecord>;

    // We plan to remove the methods below in the future. We want emulate them with the ones above. Those should suffice.

    /// Connect the children to the parent (m2m relation only).
    async fn m2m_connect(
        &mut self,
        field: &RelationFieldRef,
        parent_id: &SelectionResult,
        child_ids: &[SelectionResult],
        trace_id: Option<String>,
    ) -> crate::Result<()>;

    /// Disconnect the children from the parent (m2m relation only).
    async fn m2m_disconnect(
        &mut self,
        field: &RelationFieldRef,
        parent_id: &SelectionResult,
        child_ids: &[SelectionResult],
        trace_id: Option<String>,
    ) -> crate::Result<()>;

    /// Execute the raw query in the database as-is.
    /// The parsing of the query arguments is deferred to the connectors.
    ///
    /// Returns the number of rows affected.
    async fn execute_raw(&mut self, inputs: HashMap<String, PrismaValue>) -> crate::Result<usize>;

    /// Execute the raw query in the database as-is.
    /// The parsing of the query arguments is deferred to the connectors.
    ///
    /// Returns resulting rows as JSON.
    async fn query_raw(
        &mut self,
        model: Option<&Model>,
        inputs: HashMap<String, PrismaValue>,
        query_type: Option<String>,
    ) -> crate::Result<serde_json::Value>;
}