use std::{
    collections::HashMap,
    io::{Read, Write},
};

use chrono::NaiveDateTime;
use csv::Position;
// inluding dsl works better for completion with rust analyzer
use polars::lazy::dsl::*;
use polars::prelude::*;
use serde::Serialize;

use super::csv::{read_definitions, BuildFrom, Component, ConstraintType, Definition, SourceType};

// TODO: Polars suggests this, but docs suggest it doesn't have very good platform support
//use jemallocator::Jemalloc;
// #[global_allocator]
// static GLOBAL: Jemalloc = Jemalloc;

#[derive(Debug, Serialize, Default)]
struct Product {
    // Parse datetime from string: https://rust-lang-nursery.github.io/rust-cookbook/datetime/parse.html#parse-string-into-datetime-struct
    // TODO: Serialisers.
    start_date_time: NaiveDateTime,
    end_date_time: NaiveDateTime,
    encounter_start_date_time: Option<NaiveDateTime>,
    encounter: Option<String>,
    service: Option<String>,
    transfer: Option<String>,
    quantity: Option<f64>,
    duration: Option<f64>,
    actual_charge: Option<f64>,
    standard_cost: Option<f64>,
    // TODO: Enum this?
    day_of_stay: Option<u8>,
    source_allocated_amount: Option<f64>,
}

pub struct CreateProductInputs<E, S, T, P, Di>
where
    E: Read,
    S: Read,
    T: Read,
    P: Read,
    Di: Read,
{
    pub encounters: csv::Reader<E>,
    pub services: csv::Reader<S>,
    pub transfers: csv::Reader<T>,
    pub procedures: csv::Reader<P>,
    pub diagnoses: csv::Reader<Di>,
}

pub fn create_products_polars(
    definitions_path: String,
    patients_path: String,
    encounters_path: String,
    services_path: String,
    transfers_path: String,
    procedures_path: String,
    diagnoses_path: String,
    output_path: String,
) -> anyhow::Result<()> {
    let mut all_definitions: HashMap<String, Definition> =
        read_definitions(&mut csv::Reader::from_path(definitions_path)?)?;

    for (key, definition) in all_definitions {
        match definition.build_from {
            BuildFrom::Encounter => build_encounters_polars(
                definition,
                encounters_path.clone(),
                patients_path.clone(),
                output_path.clone(),
            ),
            BuildFrom::Service => todo!(),
            BuildFrom::Transfer => todo!(),
            BuildFrom::CodingProcedure => todo!(),
            BuildFrom::CodingDiagnosis => todo!(),
            BuildFrom::LinkedDataset => todo!(),
            BuildFrom::Revenue => todo!(),
        }?;
    }

    Ok(())
}

// TODO: Build from linked dataset is pretty hard, it potentially requires knowing everything abuot the previous year's
// cosing run (BSCO, Dataset_Encounter_Cache, etc).
pub fn create_products<D, E, S, T, P, Di, O>(
    definitions: &mut csv::Reader<D>,
    product_inputs: CreateProductInputs<E, S, T, P, Di>,
    // TODO: Looks kind of bad, any other way around it? I'd rather not have to depend on crossbeam as well
    output: &mut csv::Writer<O>,
    // TODO: Default to 10 million or something sane
    batch_size: usize,
) -> anyhow::Result<()>
where
    D: Read,
    E: Read,
    S: Read,
    T: Read,
    P: Read,
    Di: Read,
    // TODO: Looks kind of bad, any other way around it? I'd rather not have to depend on crossbeam as well
    O: Write + Send + 'static,
{
    let mut all_definitions: HashMap<String, Definition> = read_definitions(definitions)?;
    // Partition the rules by the build from type, so that we'll run all the rules at once for a particular file, which should be much faster
    // then opening files and scanning one at a time. Could also do batches in files

    let mut mapped_definitions: HashMap<BuildFrom, Vec<Definition>> = HashMap::new();
    for (_, definition) in all_definitions {
        mapped_definitions
            .entry(definition.build_from)
            .or_insert(vec![])
            .push(definition);
    }

    // Now whenever we want to produce a built service, just write it to tx.

    // Note that rust csv can seek to a certain position, so we can read in a batch from a reader, then
    // seek to that position in the reader (or position 0) if we couldn't find a particular record.
    // Alternatively, we could store an index of all records (e.g. encounter numbers) that map to their position in the reader,
    // so we can quickly seek to the appropriate index and read the record.
    // https://docs.rs/csv/latest/csv/struct.Reader.html#method.seek
    // Store encounter positions in file, so that later when we read through transfers/whatever we can easily
    // seak to the correct position quickly in case we have a cache miss
    let mut encounter_positions: HashMap<String, Position> = HashMap::new();
    // TODO: Consider just using polars for this, can use streaming so don't need to worry about
    // running out of memory or being super efficient, can just focus on the code and let the query
    // optimiser sort things out (main reason I don't like this though is it may be inderterminate in
    // runtime speed, will just need to see how it performs I guess, so maybe just make a seperate implementation)

    // TODO: Alternative to storing encounter positions would be to sort portions of the file bits at a time (I think it's called a merge sort?).

    // TODO: Try with and without rayon, should be able to help I think as we're going through so much data sequentially,
    // although we're still likely to be bottlenecked by just write-speed
    let mut encounters = product_inputs.encounters;
    let headers = encounters.headers()?.clone();

    for encounter in encounters.records() {
        let encounter = encounter?;
        let position = encounter.position().unwrap();
        let encounter: HashMap<String, String> = encounter.deserialize(Some(&headers))?;
        encounter_positions.insert(
            encounter.get("EncounterNumber").unwrap().to_string(),
            position.clone(),
        );
        // TODO: For each encounter definition, check this fits the filter criteria/constraints,
        // and
        let definitions = mapped_definitions.get(&BuildFrom::Encounter).unwrap();
        for definition in definitions {
            let matching_filter = (definition.filters.is_empty()
                || definition.filters.iter().any(|filter| {
                    let field = encounter.get(filter.field.as_str());
                    if field.is_none() {
                        return false;
                    }
                    let field = field.unwrap();
                    if filter.equal {
                        filter.value == *field
                    } else {
                        filter.value != *field
                    }
                }))
                && (definition.constraints.is_empty()
                    || definition.constraints.iter().any(|constraint| {
                        let field = encounter.get(constraint.field.as_str());
                        if field.is_none() {
                            return false;
                        }
                        let field = field.unwrap();
                        // TODO: Is this just number/datetime? Should probably be an enum? It's not, seems to be E in the test data
                        let field_type = &constraint.source_type;
                        match constraint.constraint_type {
                            ConstraintType::Equal => *field == constraint.value,
                            _ => false,
                        }
                    }));
            if matching_filter {
                // Generate the service code
            }
        }

        // TODO: Generate the built service
        output.serialize(Product::default())?;
    }

    // Now do the same with transfers, services, etc, referencing the encounter reader by using the
    // indexes in encounter_positions
    Ok(())
}

//TODO: This will iterate over the file multiple times, which could technically be
// slower than just going through the file once since reading from disk is slower
// than reading from memory. However, reading from
pub fn build_encounters_polars(
    definition: Definition,
    encounters_path: String,
    patients_path: String,
    output_path: String,
) -> anyhow::Result<()> {
    // 1. Apply filters/constraints to limit encounters
    let filter = definition
        .filters
        .iter()
        .map(|filter| {
            // TODO: Filter field depends on type, as extra/classificiation need to append extra/classification
            //  but how do we check this?
            let col = col(&filter.field);
            if filter.equal {
                col.eq(lit(filter.value.clone()))
            } else {
                col.neq(lit(filter.value.clone()))
            }
        })
        .reduce(|prev, next| prev.and(next))
        .unwrap();

    let constraint = definition
        .constraints
        .iter()
        .map(|constraint| {
            let col = col(&constraint.field);

            // TODO: Might need to do a cast here
            match constraint.constraint_type {
                ConstraintType::Equal => col.eq(lit(constraint.value.clone())),
                ConstraintType::GreaterThan => col.gt(lit(constraint.value.clone())),
                ConstraintType::GreaterThanOrEqualTo => col.gt_eq(lit(constraint.value.clone())),
                ConstraintType::LessThan => col.lt(lit(constraint.value.clone())),
                ConstraintType::LessThanOrEqualTo => col.lt_eq(lit(constraint.value.clone())),
                ConstraintType::NotEqualTo => col.neq(lit(constraint.value.clone())),
            }
        })
        .reduce(|prev, next| prev.and(next))
        .unwrap();

    // TODO: If constraints or components include patient field, then we need to join onto
    //  the patient file.
    let mut reader = LazyCsvReader::new(encounters_path)
        .has_header(true)
        .finish()?;
    // TODO: Refactor me
    if definition
        .constraints
        .iter()
        .any(|c| c.source_type == SourceType::Patient)
        || definition
            .filters
            .iter()
            .any(|f| f.source_type == SourceType::Patient)
        || definition.components.iter().any(|c| match c {
            Component::Field(source, _) => source == "P",
            _ => false,
        })
    {
        let patient_reader = LazyCsvReader::new(patients_path)
            .has_header(true)
            .finish()?;
        reader = reader.join(
            patient_reader,
            [col("Id")],
            [col("Patient_Id")],
            JoinArgs::new(JoinType::Inner),
        );
    }
    let filtered = reader
        .filter(filter.and(constraint))
        .with_streaming(true)
        .collect()?;

    // TODO: Now for each of the filtered records, create a new record that is the built record, based on the components
    //  quantity, etc. from the definition

    let mut file = std::fs::File::create("output_path").unwrap();
    let mut writer = CsvWriter::new(&mut file);

    // 2. Create the built services and write to disk
    // TODO: Kind of sucks we need to colelct into memory, see if there's a better way to do this later (otherwise can't use polars)
    // writer
    //     .finish(&mut reader.with_streaming(true).collect()?)
    //     .unwrap();

    Ok(())
}