// Copyright 2018 Grove Enterprises LLC
//
// 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 std::collections::HashMap;
use std::io::Error;
use std::io::BufReader;
use std::io::prelude::*;
use std::iter::Iterator;
use std::fs::File;
use std::string::String;
use std::convert::*;

extern crate csv;

use super::csv::StringRecord;

use super::api::*;
use super::rel::*;
use super::parser::*;
use super::sqltorel::*;
use super::dataframe::*;
use super::functions::math::*;
use super::functions::geospatial::*;

#[derive(Debug)]
pub enum ExecutionError {
    IoError(Error),
    CsvError(csv::Error),
    Custom(String)
}

impl From<Error> for ExecutionError {
    fn from(e: Error) -> Self {
        ExecutionError::IoError(e)
    }
}

impl From<String> for ExecutionError {
    fn from(e: String) -> Self {
        ExecutionError::Custom(e)
    }
}

/// Represents a csv file with a known schema
#[derive(Debug)]
pub struct CsvRelation {
    file: File,
    schema: TupleType
}

pub struct FilterRelation {
    schema: TupleType,
    input: Box<SimpleRelation>,
    expr: Rex
}

pub struct ProjectRelation {
    schema: TupleType,
    input: Box<SimpleRelation>,
    expr: Vec<Rex>
}

impl<'a> CsvRelation {

    pub fn open(file: File, schema: TupleType) -> Result<Self,ExecutionError> {
        Ok(CsvRelation { file, schema })
    }

    /// Convert StringRecord into our internal tuple type based on the known schema
    fn create_tuple(&self, r: &StringRecord) -> Result<Tuple,ExecutionError> {
        assert_eq!(self.schema.columns.len(), r.len());
        let values = self.schema.columns.iter().zip(r.into_iter()).map(|(c,s)| match c.data_type {
            //TODO: remove unwrap use here
            DataType::UnsignedLong => Value::UnsignedLong(s.parse::<u64>().unwrap()),
            DataType::String => Value::String(s.to_string()),
            DataType::Double => Value::Double(s.parse::<f64>().unwrap()),
        }).collect();
        Ok(Tuple::new(values))
    }
}

/// trait for all relations (a relation is essentially just an iterator over tuples with
/// a known schema)
pub trait SimpleRelation {
    /// scan all records in this relation
    fn scan<'a>(&'a self, ctx: &'a ExecutionContext) -> Box<Iterator<Item=Result<Tuple,ExecutionError>> + 'a>;
    /// get the schema for this relation
    fn schema<'a>(&'a self) -> &'a TupleType;
}

impl SimpleRelation for CsvRelation {

    fn scan<'a>(&'a self, _ctx: &'a ExecutionContext) -> Box<Iterator<Item=Result<Tuple,ExecutionError>> + 'a> {

        let buf_reader = BufReader::new(&self.file);
        let csv_reader = csv::Reader::from_reader(buf_reader);
        let record_iter = csv_reader.into_records();

        let tuple_iter = record_iter.map(move|r| match r {
            Ok(record) => self.create_tuple(&record),
            Err(e) => Err(ExecutionError::CsvError(e))
        });

        Box::new(tuple_iter)
    }

    fn schema<'a>(&'a self) -> &'a TupleType {
        &self.schema
    }

}

impl SimpleRelation for FilterRelation {

    fn scan<'a>(&'a self, ctx: &'a ExecutionContext) -> Box<Iterator<Item=Result<Tuple, ExecutionError>> + 'a> {
        Box::new(self.input.scan(ctx).filter(move|t|
            match t {
                &Ok(ref tuple) => match ctx.evaluate(tuple, &self.schema, &self.expr) {
                    Ok(Value::Boolean(b)) => b,
                    _ => panic!("Predicate expression evaluated to non-boolean value")
                },
                _ => true // let errors through the filter so they can be handled later
            }
        ))
    }

    fn schema<'a>(&'a self) -> &'a TupleType {
        &self.schema
    }
}

impl SimpleRelation for ProjectRelation {

    fn scan<'a>(&'a self, ctx: &'a ExecutionContext) -> Box<Iterator<Item=Result<Tuple, ExecutionError>> + 'a> {
        let foo = self.input.scan(ctx).map(move|r| match r {
            Ok(tuple) => {
                let values = self.expr.iter()
                    .map(|e| match e {
                        &Rex::TupleValue(i) => tuple.values[i].clone(),
                        //TODO: relation delegating back to execution context seems wrong way around
                        _ => ctx.evaluate(&tuple,&self.schema, e).unwrap() //TODO: remove unwrap
                        //unimplemented!("Unsupported expression for projection")
                    })
                    .collect();
                Ok(Tuple::new(values))
            },
            Err(_) => r
        });

        Box::new(foo)
    }

    fn schema<'a>(&'a self) -> &'a TupleType {
        &self.schema
    }
}

#[derive(Debug,Clone)]
pub struct ExecutionContext {
    schemas: HashMap<String, TupleType>,
    functions: HashMap<String, FunctionMeta>,

}

impl ExecutionContext {

    pub fn new(schemas: HashMap<String, TupleType>) -> Self {
        ExecutionContext { schemas: schemas, functions: HashMap::new() }
    }

    pub fn define_function(&mut self, fm: FunctionMeta) {
        self.functions.insert(fm.name.to_lowercase(), fm);
    }

    pub fn sql(&self, sql: &str) -> Result<Box<DataFrame>, ExecutionError> {

        // parse SQL into AST
        let ast = Parser::parse_sql(String::from(sql)).unwrap();

        // create a query planner
        let query_planner = SqlToRel::new(self.schemas.clone()); //TODO: pass reference to schemas

        // plan the query (create a logical relational plan)
        let plan = query_planner.sql_to_rel(&ast).unwrap(); //TODO: remove unwrap

        // return the DataFrame
        Ok(Box::new(DF { ctx: Box::new(self.clone()), plan: plan })) //TODO: don't clone context
    }

    /// Open a CSV file
    ///TODO: this is building a relational plan not an execution plan so shouldn't really be here
    pub fn load(&self, filename: &str, schema: &TupleType) -> Result<Box<DataFrame>, ExecutionError> {
        let plan = Rel::CsvFile { filename: filename.to_string(), schema: schema.clone() };
        Ok(Box::new(DF { ctx: Box::new((*self).clone()), plan: Box::new(plan) }))
    }

    pub fn register_table(&mut self, name: String, schema: TupleType) {
        self.schemas.insert(name, schema);
    }

    pub fn create_execution_plan(&self, plan: &Rel) -> Result<Box<SimpleRelation>,ExecutionError> {
        match *plan {

            Rel::EmptyRelation => {
                panic!()
            },

            Rel::TableScan { ref table_name, ref schema, .. } => {
                // for now, tables are csv files
                let file = File::open(format!("test/data/{}.csv", table_name))?;
                let rel = CsvRelation::open(file, schema.clone())?;
                Ok(Box::new(rel))
            },

            Rel::CsvFile { ref filename, ref schema } => {
                let file = File::open(filename)?;
                let rel = CsvRelation::open(file, schema.clone())?;
                Ok(Box::new(rel))
            },

            Rel::Selection { ref expr, ref input, ref schema } => {
                let input_rel = self.create_execution_plan(input)?;
                let rel = FilterRelation {
                    input: input_rel,
                    expr: expr.clone(),
                    schema: schema.clone()
                };
                Ok(Box::new(rel))
            },

            Rel::Projection { ref expr, ref input, .. } => {
                let input_rel = self.create_execution_plan(&input)?;
                let input_schema = input_rel.schema().clone();

                //TODO: seems to be duplicate of sql_to_rel code
                let project_columns: Vec<Field> = expr.iter().map(|e| {
                    match e {
                        &Rex::TupleValue(i) => input_schema.columns[i].clone(),
                        &Rex::ScalarFunction {ref name, .. } => Field {
                            name: name.clone(),
                            data_type: DataType::Double, //TODO: hard-coded .. no function metadata yet
                            nullable: true
                        },
                        _ => unimplemented!("Unsupported projection expression")
                    }
                }).collect();

                let project_schema = TupleType { columns: project_columns };

                let rel = ProjectRelation {
                    input: input_rel,
                    expr: expr.clone(),
                    schema: project_schema,

                };

                Ok(Box::new(rel))
            }
        }
    }

    /// Evaluate a relational expression against a tuple
    pub fn evaluate(&self, tuple: &Tuple, tt: &TupleType, rex: &Rex) -> Result<Value, Box<ExecutionError>> {

        match rex {
            &Rex::BinaryExpr { ref left, ref op, ref right } => {
                let left_value = self.evaluate(tuple, tt, left)?;
                let right_value = self.evaluate(tuple, tt, right)?;
                match op {
                    &Operator::Eq => Ok(Value::Boolean(left_value == right_value)),
                    &Operator::NotEq => Ok(Value::Boolean(left_value != right_value)),
                    &Operator::Lt => Ok(Value::Boolean(left_value < right_value)),
                    &Operator::LtEq => Ok(Value::Boolean(left_value <= right_value)),
                    &Operator::Gt => Ok(Value::Boolean(left_value > right_value)),
                    &Operator::GtEq => Ok(Value::Boolean(left_value >= right_value)),
                }
            },
            &Rex::TupleValue(index) => Ok(tuple.values[index].clone()),
            &Rex::Literal(ref value) => Ok(value.clone()),
            &Rex::ScalarFunction { ref name, ref args } => {

                // evaluate the arguments to the function
                let arg_values : Vec<Value> = args.iter()
                    .map(|a| self.evaluate(tuple, tt, &a))
                    .collect::<Result<Vec<Value>, Box<ExecutionError>>>()?;

                let func = self.load_function_impl(name.as_ref())?;

                match func.execute(arg_values) {
                    Ok(value) => Ok(value),
                    Err(_) => Err(Box::new(ExecutionError::Custom("TBD".to_string()))) //TODO: fix
                }
            }
        }

    }

    /// load a function implementation ... eventually do this dyanmically to allow for UDFs
    fn load_function_impl(&self, function_name: &str) -> Result<Box<ScalarFunction>,Box<ExecutionError>> {
        match function_name {
            "sqrt" => Ok(Box::new(SqrtFunction {})),
            "latlng" => Ok(Box::new(LatLngFunc {})),
            _ => Err(Box::new(ExecutionError::Custom(format!("Unknown function {}", function_name))))
        }
    }

}




pub struct DF {
    ctx: Box<ExecutionContext>,
    plan: Box<Rel>
}

impl DataFrame for DF {

    fn repartition(&self, _n: u32) -> Result<Box<DataFrame>, DataFrameError> {
        unimplemented!()
    }

    fn select(&self, _expr: Vec<Rex>) -> Result<Box<DataFrame>, DataFrameError> {
        unimplemented!()
    }

    fn filter(&self, expr: Rex) -> Result<Box<DataFrame>, DataFrameError> {

        let plan = Rel::Selection {
            expr: expr,
            input: self.plan.clone(),
            schema: self.plan.schema().clone()
        };

        Ok(Box::new(DF { ctx: self.ctx.clone(), plan: Box::new(plan) }))
    }

    fn write(&self, filename: &str) -> Result<(), DataFrameError> {
        let execution_plan = self.ctx.create_execution_plan(&self.plan)?;

        // create output file
        println!("Writing csv to {}", filename);
        let mut file = File::create(filename)?;

        // implement execution here for now but should be a common method for processing a plan
        let it = execution_plan.scan(&self.ctx);
        it.for_each(|t| {
            match t {
                Ok(tuple) => {
                    let csv = format!("{}\n", tuple.to_string());
                    file.write(&csv.into_bytes()).unwrap(); //TODO: remove unwrap
                },
                Err(e) => panic!(format!("Error processing tuple: {:?}", e)) //TODO: error handling
            }
        });

        Ok(())
    }

    fn col(&self, column_name: &str) -> Result<Rex, DataFrameError> {
        match &self.plan.as_ref() {
            &&Rel::CsvFile { ref schema, .. } => match schema.column(column_name) {
                Some((i,_)) => Ok(Rex::TupleValue(i)),
                _ => Err(DataFrameError::InvalidColumn(column_name.to_string()))
            },
            _ => Err(DataFrameError::NotImplemented)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_sqrt() {

        let mut ctx = create_context();

        ctx.define_function( FunctionMeta {
            name: "sqrt".to_string(),
            args: vec![ Field::new("value", DataType::Double, false) ],
            return_type: DataType::Double
        });

        let df = ctx.sql(&"SELECT id, sqrt(id) FROM people").unwrap();

        df.write("_sqrt_out.csv").unwrap();

        //TODO: check that generated file has expected contents
    }

    #[test]
    fn test_complex_type() {

        let mut ctx = create_context();

        ctx.define_function( FunctionMeta {
            name: "latlng".to_string(),
            args: vec![
                Field::new("lat", DataType::Double, false),
                Field::new("lng", DataType::Double, false)
            ],
            return_type: DataType::Double
        });

        let df = ctx.sql(&"SELECT latlng(lat, lng) FROM uk_cities").unwrap();

        df.write("_uk_cities_out.csv").unwrap();

        //TODO: check that generated file has expected contents
    }

    fn create_context() -> ExecutionContext {

        // create a schema registry
        let mut schemas : HashMap<String, TupleType> = HashMap::new();

        // define schemas for test data
        schemas.insert("people".to_string(), TupleType::new(vec![
            Field::new("id", DataType::UnsignedLong, false),
            Field::new("name", DataType::String, false)]));

        schemas.insert("uk_cities".to_string(), TupleType::new(vec![
            Field::new("city", DataType::String, false),
            Field::new("lat", DataType::Double, false),
            Field::new("lng", DataType::Double, false)]));

        // create execution context
        ExecutionContext::new(schemas.clone())
    }
}