real-rs 0.1.0

//! MongoDB backend - document store
//!
//! Shows how relational algebra compiles to document queries and aggregation pipelines

use crate::algebra::{CompareOp, Expr, Operand, Predicate};
use crate::backends::Backend;
use crate::schema::{DataType, ResultSet, Row, Schema, Value};
use crate::{RealError, Result};

/// Simple base64 encoding for binary data
fn base64_encode(bytes: &[u8]) -> String {
    const BASE64_CHARS: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    let mut result = String::new();
    for chunk in bytes.chunks(3) {
        let b1 = chunk[0];
        let b2 = chunk.get(1).copied().unwrap_or(0);
        let b3 = chunk.get(2).copied().unwrap_or(0);

        result.push(BASE64_CHARS[(b1 >> 2) as usize] as char);
        result.push(BASE64_CHARS[(((b1 & 0x03) << 4) | (b2 >> 4)) as usize] as char);
        result.push(if chunk.len() > 1 {
            BASE64_CHARS[(((b2 & 0x0f) << 2) | (b3 >> 6)) as usize] as char
        } else {
            '='
        });
        result.push(if chunk.len() > 2 {
            BASE64_CHARS[(b3 & 0x3f) as usize] as char
        } else {
            '='
        });
    }
    result
}

pub struct MongoDBBackend;

/// Compiled MongoDB query (aggregation pipeline)
#[derive(Debug, Clone)]
pub struct MongoQuery {
    /// Collection name
    pub collection: String,
    /// Aggregation pipeline stages (as JSON-like representation)
    pub pipeline: Vec<MongoStage>,
    pub result_schema: Schema,
}

#[derive(Debug, Clone)]
pub enum MongoStage {
    Match(String),      // $match stage
    Project(String),    // $project stage
    Lookup(String),     // $lookup stage (join)
    Group(String),      // $group stage
    Sort(String),       // $sort stage
    Limit(usize),       // $limit stage
    Skip(usize),        // $skip stage
}

impl MongoDBBackend {
    pub fn new() -> Self {
        Self
    }

    fn compile_predicate(&self, pred: &Predicate) -> Result<String> {
        match pred {
            Predicate::Compare { left, op, right } => {
                let field = &left.name;
                let (mongo_op, value) = match (op, right) {
                    (CompareOp::Eq, Operand::Literal(v)) => ("$eq", self.value_to_json(v)),
                    (CompareOp::NotEq, Operand::Literal(v)) => ("$ne", self.value_to_json(v)),
                    (CompareOp::Lt, Operand::Literal(v)) => ("$lt", self.value_to_json(v)),
                    (CompareOp::Lte, Operand::Literal(v)) => ("$lte", self.value_to_json(v)),
                    (CompareOp::Gt, Operand::Literal(v)) => ("$gt", self.value_to_json(v)),
                    (CompareOp::Gte, Operand::Literal(v)) => ("$gte", self.value_to_json(v)),
                    (op, Operand::Column(col)) => {
                        return Ok(format!(
                            r#"{{ "{}": {{ "{}": "${}" }} }}"#,
                            field,
                            match op {
                                CompareOp::Eq => "$eq",
                                CompareOp::NotEq => "$ne",
                                CompareOp::Lt => "$lt",
                                CompareOp::Lte => "$lte",
                                CompareOp::Gt => "$gt",
                                CompareOp::Gte => "$gte",
                            },
                            col.name
                        ));
                    }
                };
                Ok(format!(r#"{{ "{}": {{ "{}": {} }} }}"#, field, mongo_op, value))
            }
            Predicate::And(left, right) => {
                let left_json = self.compile_predicate(left)?;
                let right_json = self.compile_predicate(right)?;
                Ok(format!(r#"{{ "$and": [{}, {}] }}"#, left_json, right_json))
            }
            Predicate::Or(left, right) => {
                let left_json = self.compile_predicate(left)?;
                let right_json = self.compile_predicate(right)?;
                Ok(format!(r#"{{ "$or": [{}, {}] }}"#, left_json, right_json))
            }
            Predicate::Not(inner) => {
                let inner_json = self.compile_predicate(inner)?;
                Ok(format!(r#"{{ "$not": {} }}"#, inner_json))
            }
            Predicate::In { column, values } => {
                let values_json = values
                    .iter()
                    .map(|v| self.value_to_json(v))
                    .collect::<Vec<_>>()
                    .join(", ");
                Ok(format!(r#"{{ "{}": {{ "$in": [{}] }} }}"#, column.name, values_json))
            }
            Predicate::Like { column, pattern } => {
                // MongoDB uses $regex for pattern matching
                let regex = pattern.replace('%', ".*").replace('_', ".");
                Ok(format!(r#"{{ "{}": {{ "$regex": "{}" }} }}"#, column.name, regex))
            }
            Predicate::IsNull(column) => {
                Ok(format!(r#"{{ "{}": null }}"#, column.name))
            }
            Predicate::Between { column, low, high } => {
                let low_json = self.value_to_json(low);
                let high_json = self.value_to_json(high);
                Ok(format!(
                    r#"{{ "{}": {{ "$gte": {}, "$lte": {} }} }}"#,
                    column.name, low_json, high_json
                ))
            }
        }
    }

    fn value_to_json(&self, value: &Value) -> String {
        match value {
            Value::Integer(i) => i.to_string(),
            Value::Float(f) => f.to_string(),
            Value::String(s) => format!(r#""{}""#, s),
            Value::Boolean(b) => b.to_string(),
            Value::Null => "null".to_string(),
            Value::Bytes(b) => {
                // Properly encode as BSON binary
                let base64 = base64_encode(b);
                format!(r#"{{"$binary": {{"base64": "{}", "subType": "00"}}}}"#, base64)
            }
            Value::Timestamp(ts) => {
                // MongoDB ISODate or timestamp
                format!(r#"{{"$date": {}}}"#, ts)
            }
            Value::Decimal(d) => {
                // MongoDB Decimal128
                format!(r#"{{"$numberDecimal": "{}"}}"#, d)
            }
            Value::Json(j) => {
                // Already JSON, pass through
                j.clone()
            }
            Value::Array(arr) => {
                let items: Vec<String> = arr.iter().map(|v| self.value_to_json(v)).collect();
                format!("[{}]", items.join(", "))
            }
            Value::Vector(v) => {
                let items: Vec<String> = v.iter().map(|f| f.to_string()).collect();
                format!("[{}]", items.join(", "))
            }
        }
    }
}

impl Default for MongoDBBackend {
    fn default() -> Self {
        Self::new()
    }
}

impl Backend for MongoDBBackend {
    type Connection = (); // Would be mongodb::Client in real impl
    type CompiledQuery = MongoQuery;

    fn compile(&self, expr: &Expr) -> Result<Self::CompiledQuery> {
        match expr {
            Expr::Relation { name, schema } => Ok(MongoQuery {
                collection: name.clone(),
                pipeline: vec![],
                result_schema: schema.clone(),
            }),

            Expr::Select { input, predicate } => {
                let mut query = self.compile(input)?;
                let match_stage = self.compile_predicate(predicate)?;
                query.pipeline.push(MongoStage::Match(match_stage));
                Ok(query)
            }

            Expr::Project { input, columns } => {
                let mut query = self.compile(input)?;
                let project_fields = columns
                    .iter()
                    .map(|c| format!(r#""{}": 1"#, c))
                    .collect::<Vec<_>>()
                    .join(", ");
                let project_stage = format!(r#"{{ {} }}"#, project_fields);
                query.pipeline.push(MongoStage::Project(project_stage));
                query.result_schema = expr.infer_schema();
                Ok(query)
            }

            Expr::Join { left, right, condition } => {
                // MongoDB $lookup for joins
                let left_query = self.compile(left)?;
                let right_query = self.compile(right)?;

                // Parse join condition to extract localField and foreignField
                let (local_field, foreign_field) = match condition {
                    crate::algebra::JoinCondition::Using(cols) => {
                        if !cols.is_empty() {
                            (cols[0].clone(), cols[0].clone())
                        } else {
                            ("_id".to_string(), "_id".to_string())
                        }
                    }
                    crate::algebra::JoinCondition::On(_pred) => {
                        // Try to extract field names from predicate
                        // For now, default to _id
                        ("_id".to_string(), "_id".to_string())
                    }
                };

                let lookup = format!(
                    r#"{{ "from": "{}", "localField": "{}", "foreignField": "{}", "as": "joined" }}"#,
                    right_query.collection, local_field, foreign_field
                );

                let mut query = left_query;
                query.pipeline.push(MongoStage::Lookup(lookup));
                Ok(query)
            }

            Expr::Aggregate { input, group_by, aggregates } => {
                let mut query = self.compile(input)?;

                // Build $group stage
                let id_expr = if group_by.is_empty() {
                    "null".to_string()
                } else if group_by.len() == 1 {
                    format!(r#""${}""#, group_by[0])
                } else {
                    let fields: Vec<String> = group_by
                        .iter()
                        .map(|f| format!(r#""{}": "${}"#, f, f))
                        .collect();
                    format!(r#"{{ {} }}"#, fields.join(", "))
                };

                let agg_exprs: Vec<String> = aggregates
                    .iter()
                    .map(|agg| {
                        let mongo_func = match agg.func {
                            crate::algebra::AggregateType::Count => "$sum: 1".to_string(),
                            crate::algebra::AggregateType::Sum => format!("$sum: \"${}\"", agg.input),
                            crate::algebra::AggregateType::Avg => format!("$avg: \"${}\"", agg.input),
                            crate::algebra::AggregateType::Min => format!("$min: \"${}\"", agg.input),
                            crate::algebra::AggregateType::Max => format!("$max: \"${}\"", agg.input),
                        };
                        format!(r#""{}" {{ {} }}"#, agg.name, mongo_func)
                    })
                    .collect();

                let group_stage = format!(
                    r#"{{ "_id": {}, {} }}"#,
                    id_expr,
                    agg_exprs.join(", ")
                );

                query.pipeline.push(MongoStage::Group(group_stage));
                query.result_schema = expr.infer_schema();
                Ok(query)
            }

            Expr::Union { left, right } => {
                let left_query = self.compile(left)?;
                let right_query = self.compile(right)?;

                // MongoDB $unionWith (4.4+)
                let union_stage = format!(r#"{{ "coll": "{}" }}"#, right_query.collection);

                let mut query = left_query;
                query.pipeline.push(MongoStage::Match(union_stage));
                Ok(query)
            }

            Expr::Intersect { left, right } => {
                // MongoDB doesn't have native INTERSECT
                // Would need client-side processing or complex pipeline
                Err(RealError::Backend(
                    "MongoDB INTERSECT requires client-side processing".into(),
                ))
            }

            Expr::Difference { left, right } => {
                // MongoDB doesn't have native EXCEPT
                // Would need client-side processing or complex pipeline
                Err(RealError::Backend(
                    "MongoDB DIFFERENCE requires client-side processing".into(),
                ))
            }

            Expr::Rename { input, from, to } => {
                let mut query = self.compile(input)?;

                // Use $project to rename field
                let rename_stage = format!(
                    r#"{{ "{}": "${}", "{}": 0 }}"#,
                    to, from, from
                );

                query.pipeline.push(MongoStage::Project(rename_stage));
                query.result_schema = expr.infer_schema();
                Ok(query)
            }

            Expr::Sort { input, columns } => {
                let mut query = self.compile(input)?;

                let sort_fields = columns
                    .iter()
                    .map(|(col, order)| {
                        let order_val = match order {
                            crate::algebra::SortOrder::Asc => 1,
                            crate::algebra::SortOrder::Desc => -1,
                        };
                        format!(r#""{}": {}"#, col, order_val)
                    })
                    .collect::<Vec<_>>()
                    .join(", ");

                let sort_stage = format!(r#"{{ {} }}"#, sort_fields);
                query.pipeline.push(MongoStage::Sort(sort_stage));
                Ok(query)
            }

            Expr::Limit { input, count } => {
                let mut query = self.compile(input)?;
                query.pipeline.push(MongoStage::Limit(*count));
                Ok(query)
            }

            Expr::Offset { input, count } => {
                let mut query = self.compile(input)?;
                query.pipeline.push(MongoStage::Skip(*count));
                Ok(query)
            }

            _ => Err(RealError::Backend(format!(
                "MongoDB backend does not yet support: {:?}",
                expr
            ))),
        }
    }

    fn execute(&self, _conn: &mut Self::Connection, query: &Self::CompiledQuery) -> Result<ResultSet> {
        // In production, this would:
        // 1. Build mongodb::bson pipeline
        // 2. Execute db.collection.aggregate(pipeline)
        // 3. Parse results into ResultSet

        println!("MongoDB Query:");
        println!("  Collection: {}", query.collection);
        println!("  Pipeline:");
        for (i, stage) in query.pipeline.iter().enumerate() {
            println!("    Stage {}: {:?}", i, stage);
        }

        Ok(Vec::new())
    }

    fn get_schema(&self, _conn: &mut Self::Connection, _relation: &str) -> Result<Schema> {
        // MongoDB is schemaless, would need to infer or use schema validation
        Err(RealError::Backend(
            "MongoDB schema introspection not implemented".into(),
        ))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::algebra::{ColumnRef, Predicate};

    #[test]
    fn test_mongodb_compile_relation() {
        let backend = MongoDBBackend::new();
        let schema = Schema::new("users").with_column("name", DataType::String);
        let expr = Expr::relation("users", schema);

        let query = backend.compile(&expr).unwrap();
        assert_eq!(query.collection, "users");
        assert_eq!(query.pipeline.len(), 0);
    }

    #[test]
    fn test_mongodb_compile_select() {
        let backend = MongoDBBackend::new();
        let schema = Schema::new("users")
            .with_column("name", DataType::String)
            .with_column("age", DataType::Integer);

        let expr = Expr::relation("users", schema).select(Predicate::Compare {
            left: ColumnRef::new("age"),
            op: CompareOp::Gt,
            right: Operand::Literal(Value::Integer(25)),
        });

        let query = backend.compile(&expr).unwrap();
        assert_eq!(query.collection, "users");
        assert_eq!(query.pipeline.len(), 1);
        if let MongoStage::Match(ref stage) = query.pipeline[0] {
            assert!(stage.contains("$gt"));
            assert!(stage.contains("25"));
        } else {
            panic!("Expected Match stage");
        }
    }

    #[test]
    fn test_mongodb_compile_project() {
        let backend = MongoDBBackend::new();
        let schema = Schema::new("users")
            .with_column("name", DataType::String)
            .with_column("age", DataType::Integer);

        let expr = Expr::relation("users", schema).project(vec!["name".to_string()]);

        let query = backend.compile(&expr).unwrap();
        assert_eq!(query.pipeline.len(), 1);
        if let MongoStage::Project(ref stage) = query.pipeline[0] {
            assert!(stage.contains("name"));
        } else {
            panic!("Expected Project stage");
        }
    }
}