muse2 2.1.0

//! Code for reading process flows from a CSV file.
use super::super::{input_err_msg, read_csv};
use crate::commodity::{CommodityID, CommodityMap, CommodityType};
use crate::process::{
    FlowDirection, FlowType, ProcessFlow, ProcessFlowsMap, ProcessID, ProcessMap,
};
use crate::region::{RegionID, parse_region_str};
use crate::units::{FlowPerActivity, MoneyPerFlow};
use crate::year::parse_year_str;
use anyhow::{Context, Result, bail, ensure};
use indexmap::{IndexMap, IndexSet};
use itertools::iproduct;
use serde::Deserialize;
use std::collections::HashMap;
use std::path::Path;
use std::rc::Rc;

const PROCESS_FLOWS_FILE_NAME: &str = "process_flows.csv";

#[derive(PartialEq, Debug, Deserialize)]
struct ProcessFlowRaw {
    process_id: String,
    commodity_id: String,
    commission_years: String,
    regions: String,
    coeff: FlowPerActivity,
    #[serde(default)]
    #[serde(rename = "type")]
    kind: FlowType,
    cost: Option<MoneyPerFlow>,
}

impl ProcessFlowRaw {
    fn validate(&self) -> Result<()> {
        // Check that flow is not infinity or nan.
        ensure!(
            self.coeff.is_finite(),
            "Invalid value for coeff ({})",
            self.coeff
        );

        // **TODO**: https://github.com/EnergySystemsModellingLab/MUSE2/issues/300
        ensure!(
            self.kind == FlowType::Fixed,
            "Commodity flexible assets are not currently supported"
        );

        // Check that flow cost is non-negative
        if let Some(cost) = self.cost {
            ensure!(
                (cost.value() >= 0.0),
                "Invalid value for flow cost ({cost}). Must be >=0."
            );
        }

        Ok(())
    }
}

/// Read process flows from a CSV file.
///
/// # Arguments
///
/// * `model_dir` - Folder containing model configuration files
/// * `processes` - Mutable map of known processes (may be updated)
/// * `commodities` - Map of known commodities
/// * `milestone_years` - Milestone years used by the model
///
/// # Returns
///
/// A `HashMap<ProcessID, ProcessFlowsMap>` mapping process IDs to their flows.
pub fn read_process_flows(
    model_dir: &Path,
    processes: &mut ProcessMap,
    commodities: &CommodityMap,
    milestone_years: &[u32],
) -> Result<HashMap<ProcessID, ProcessFlowsMap>> {
    let file_path = model_dir.join(PROCESS_FLOWS_FILE_NAME);
    let process_flow_csv = read_csv(&file_path)?;
    read_process_flows_from_iter(process_flow_csv, processes, commodities, milestone_years)
        .with_context(|| input_err_msg(&file_path))
}

/// Validates that all SED/SVD outputs from each process have consistent units.
///
/// For processes with multiple SED/SVD outputs, the annual fixed costs are distributed
/// proportionally based on flow coefficients. This only makes sense if all outputs share
/// the same units.
fn validate_output_flows_units(flows_map: &HashMap<ProcessID, ProcessFlowsMap>) -> Result<()> {
    // Collect all validation errors so that the error reported is deterministic,
    // this is needed because ProcessFlows are stored in a HashMap.
    let mut errors: Vec<(ProcessID, RegionID, u32, Vec<&str>)> = Vec::new();

    for (process_id, process_flows) in flows_map {
        for ((region_id, year), flows) in process_flows {
            let sed_svd_output_units: IndexSet<&str> = flows
                .values()
                .filter_map(|flow| {
                    let commodity = &flow.commodity;
                    (flow.coeff.value() > 0.0
                        && matches!(
                            commodity.kind,
                            CommodityType::ServiceDemand | CommodityType::SupplyEqualsDemand
                        ))
                    .then_some(commodity.units.as_str())
                })
                .collect();

            // Record error if validation fails
            if sed_svd_output_units.len() > 1 {
                errors.push((
                    process_id.clone(),
                    region_id.clone(),
                    *year,
                    sed_svd_output_units.into_iter().collect(),
                ));
            }
        }
    }

    // Sort errors for deterministic ordering
    errors.sort_by_key(|(process_id, region_id, year, _)| {
        (process_id.clone(), region_id.clone(), *year)
    });

    // Return first error if any exist
    if let Some((process_id, region_id, year, units)) = errors.first() {
        bail!(
            "Process {process_id} has SED/SVD outputs with different units: [{}] \
             in region: {region_id} and year: {year}",
            units.join(", ")
        );
    }

    Ok(())
}

/// Read `ProcessFlowRaw` records from an iterator and convert them into `ProcessFlow` records.
///
/// # Arguments
///
/// * `iter` - Iterator over `ProcessFlowRaw` records
/// * `processes` - Mutable map of known processes used for validation and updates
/// * `commodities` - Map of known commodities
/// * `milestone_years` - Milestone years used by the model
///
/// # Returns
///
/// A `HashMap<ProcessID, ProcessFlowsMap>` mapping process IDs to their flows.
fn read_process_flows_from_iter<I>(
    iter: I,
    processes: &mut ProcessMap,
    commodities: &CommodityMap,
    milestone_years: &[u32],
) -> Result<HashMap<ProcessID, ProcessFlowsMap>>
where
    I: Iterator<Item = ProcessFlowRaw>,
{
    let mut flows_map: HashMap<ProcessID, ProcessFlowsMap> = HashMap::new();
    for record in iter {
        record.validate()?;

        // Get process
        let (id, process) = processes
            .get_key_value(record.process_id.as_str())
            .with_context(|| format!("Process {} not found", record.process_id))?;

        // Get regions
        let process_regions = &process.regions;
        let record_regions =
            parse_region_str(&record.regions, process_regions).with_context(|| {
                format!("Invalid region for process {id}. Valid regions are {process_regions:?}")
            })?;

        // Get years
        let process_years: Vec<u32> = process.years.clone().collect();
        let record_years =
            parse_year_str(&record.commission_years, &process_years).with_context(|| {
                format!("Invalid year for process {id}. Valid years are {process_years:?}")
            })?;

        // Get commodity
        let commodity = commodities
            .get(record.commodity_id.as_str())
            .with_context(|| format!("{} is not a valid commodity ID", &record.commodity_id))?;

        // Create ProcessFlow object
        let process_flow = ProcessFlow {
            commodity: Rc::clone(commodity),
            coeff: record.coeff,
            kind: FlowType::Fixed,
            cost: record.cost.unwrap_or(MoneyPerFlow(0.0)),
        };

        // Insert flow into the map
        let region_year_map = flows_map.entry(id.clone()).or_default();
        for (year, region_id) in iproduct!(record_years, record_regions.iter()) {
            let flows_map = region_year_map
                .entry((region_id.clone(), year))
                .or_default();
            let existing = Rc::get_mut(flows_map)
                .unwrap() // safe: there will only be one copy
                .insert(commodity.id.clone(), process_flow.clone())
                .is_some();
            ensure!(
                !existing,
                "Duplicate process flow entry for region {}, year {} and commodity {}",
                region_id,
                year,
                commodity.id
            );
        }
    }

    validate_flows_and_update_primary_output(processes, &flows_map, milestone_years)?;
    validate_secondary_flows(processes, &flows_map, milestone_years)?;
    validate_output_flows_units(&flows_map)?;

    Ok(flows_map)
}

fn validate_flows_and_update_primary_output(
    processes: &mut ProcessMap,
    flows_map: &HashMap<ProcessID, ProcessFlowsMap>,
    milestone_years: &[u32],
) -> Result<()> {
    for (process_id, process) in processes.iter_mut() {
        let map = flows_map
            .get(process_id)
            .with_context(|| format!("Missing flows map for process {process_id}"))?;

        // Flows are required for all milestone years within the process years of activity
        let required_years = milestone_years
            .iter()
            .filter(|&y| process.years.contains(y));
        let region_year: Vec<(&RegionID, &u32)> =
            iproduct!(process.regions.iter(), required_years).collect();

        ensure!(
            region_year
                .iter()
                .all(|(region_id, year)| map.contains_key(&((*region_id).clone(), **year))),
            "Flows map for process {process_id} does not cover all regions and required years"
        );

        let primary_output = if let Some(primary_output) = &process.primary_output {
            Some(primary_output.clone())
        } else {
            let (region_id, year) = region_year[0];
            infer_primary_output(&map[&(region_id.clone(), *year)]).with_context(|| {
                format!("Could not infer primary_output for process {process_id}")
            })?
        };

        for (region_id, &year) in region_year {
            let flows = &map[&(region_id.clone(), year)];

            // Check that the process has flows for this region/year
            check_flows_primary_output(flows, primary_output.as_ref()).with_context(|| {
                format!(
                    "Invalid primary output configuration for process {process_id} \
                    (region: {region_id}, year: {year})"
                )
            })?;
        }

        // Update primary output if needed
        if process.primary_output != primary_output {
            // Safe: There should only be one ref to process
            Rc::get_mut(process).unwrap().primary_output = primary_output;
        }
    }

    Ok(())
}

/// Infer the primary output.
///
/// This is only possible if there is only one output flow for the process.
fn infer_primary_output(map: &IndexMap<CommodityID, ProcessFlow>) -> Result<Option<CommodityID>> {
    let mut iter = map.iter().filter_map(|(commodity_id, flow)| {
        (flow.direction() == FlowDirection::Output).then_some(commodity_id)
    });

    let Some(first_output) = iter.next() else {
        // If there are only input flows, then the primary output should be None
        return Ok(None);
    };

    ensure!(
        iter.next().is_none(),
        "Need to specify primary_output explicitly if there are multiple output flows"
    );

    Ok(Some(first_output.clone()))
}

/// Check the flows are correct for the specified primary output (or lack thereof)
fn check_flows_primary_output(
    flows_map: &IndexMap<CommodityID, ProcessFlow>,
    primary_output: Option<&CommodityID>,
) -> Result<()> {
    if let Some(primary_output) = primary_output {
        let flow = flows_map.get(primary_output).with_context(|| {
            format!("Primary output commodity '{primary_output}' isn't a process flow")
        })?;

        ensure!(
            flow.direction() == FlowDirection::Output,
            "Primary output commodity '{primary_output}' isn't an output flow",
        );
    } else {
        ensure!(
            flows_map
                .values()
                .all(|x| x.direction() == FlowDirection::Input
                    || x.direction() == FlowDirection::Zero),
            "First year is only inputs, but subsequent years have outputs, although no primary \
            output is specified"
        );
    }

    Ok(())
}

/// Checks that non-primary io are defined for all milestone years, at least, (within a region) and
/// that they are only inputs or only outputs in all years.
fn validate_secondary_flows(
    processes: &mut ProcessMap,
    flows_map: &HashMap<ProcessID, ProcessFlowsMap>,
    milestone_years: &[u32],
) -> Result<()> {
    for (process_id, process) in processes.iter() {
        // Get the flows for this process - there should be no error, as was checked already
        let map = flows_map
            .get(process_id)
            .with_context(|| format!("Missing flows map for process {process_id}"))?;

        // Flows are required for all milestone years within the process years of activity
        let required_years: Vec<&u32> = milestone_years
            .iter()
            .filter(|&y| process.years.contains(y))
            .collect();

        // Get the non-primary io flows for all years, if any, arranged by (commodity, region)
        let iter = iproduct!(process.years.clone(), process.regions.iter());
        let mut flows: HashMap<(CommodityID, RegionID), Vec<&ProcessFlow>> = HashMap::new();
        let mut number_of_years: HashMap<(CommodityID, RegionID), u32> = HashMap::new();
        for (year, region_id) in iter {
            if let Some(commodity_map) = map.get(&(region_id.clone(), year)) {
                let flow = commodity_map.iter().filter_map(|(commodity_id, flow)| {
                    (Some(commodity_id) != process.primary_output.as_ref())
                        .then_some(((commodity_id.clone(), region_id.clone()), flow))
                });

                for (key, value) in flow {
                    flows.entry(key.clone()).or_default().push(value);
                    if required_years.contains(&&year) {
                        *number_of_years.entry(key).or_default() += 1;
                    }
                }
            }
        }

        // Finally we check that the flows for a given commodity and region are defined for all
        // milestone years and that they are all inputs or all outputs. This later check is done
        // for all years in the process range, required or not.
        for ((commodity_id, region_id), value) in &flows {
            ensure!(
                number_of_years[&(commodity_id.clone(), region_id.clone())]
                    == required_years.len().try_into().unwrap(),
                "Flow of commodity {commodity_id} in region {region_id} for process {process_id} \
                does not cover all milestone years within the process range of activity."
            );
            let input_or_zero = value
                .iter()
                .all(|&x| [FlowDirection::Input, FlowDirection::Zero].contains(&x.direction()));
            let output_or_zero = value
                .iter()
                .all(|&x| [FlowDirection::Output, FlowDirection::Zero].contains(&x.direction()));
            ensure!(
                input_or_zero || output_or_zero,
                "Flow of commodity {commodity_id} in region {region_id} for process {process_id} \
                behaves as input or output in different years."
            );
        }
    }

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::commodity::Commodity;
    use crate::commodity::{CommodityLevyMap, DemandMap, PricingStrategy};
    use crate::fixture::{
        assert_error, assert_validate_fails_with_simple, assert_validate_ok_simple,
        other_commodity, process, sed_commodity, svd_commodity,
    };
    use crate::patch::FilePatch;
    use crate::process::{FlowType, Process, ProcessFlow, ProcessMap};
    use crate::time_slice::TimeSliceLevel;
    use crate::units::{FlowPerActivity, MoneyPerFlow};
    use indexmap::IndexMap;
    use itertools::Itertools;
    use map_macro::hash_map;
    use rstest::{fixture, rstest};
    use std::iter;
    use std::rc::Rc;

    fn flow(commodity: Rc<Commodity>, coeff: f64) -> ProcessFlow {
        ProcessFlow {
            commodity,
            coeff: FlowPerActivity(coeff),
            kind: FlowType::Fixed,
            cost: MoneyPerFlow(0.0),
        }
    }

    fn build_maps<I>(
        process: Process,
        flows: I,
        years: Option<Vec<u32>>,
    ) -> (ProcessMap, HashMap<ProcessID, ProcessFlowsMap>)
    where
        I: Clone + Iterator<Item = (CommodityID, ProcessFlow)>,
    {
        let years = years.unwrap_or(process.years.clone().collect());
        let map: Rc<IndexMap<_, _>> = Rc::new(flows.collect());
        let flows_inner = iproduct!(&process.regions, years)
            .map(|(region_id, year)| ((region_id.clone(), year), map.clone()))
            .collect();
        let flows = hash_map! {process.id.clone() => flows_inner};
        let processes = iter::once((process.id.clone(), process.into())).collect();

        (processes, flows)
    }

    #[fixture]
    pub fn sed_commodity_pj() -> Commodity {
        Commodity {
            id: "sed_pj".into(),
            description: "Test SED commodity (PJ)".into(),
            kind: CommodityType::SupplyEqualsDemand,
            time_slice_level: TimeSliceLevel::DayNight,
            pricing_strategy: PricingStrategy::Shadow,
            levies_prod: CommodityLevyMap::new(),
            levies_cons: CommodityLevyMap::new(),
            demand: DemandMap::new(),
            units: "PJ".into(),
        }
    }

    #[fixture]
    pub fn sed_commodity_tonnes() -> Commodity {
        Commodity {
            id: "sed_tonnes".into(),
            description: "Test SED commodity (tonnes)".into(),
            kind: CommodityType::SupplyEqualsDemand,
            time_slice_level: TimeSliceLevel::DayNight,
            pricing_strategy: PricingStrategy::Shadow,
            levies_prod: CommodityLevyMap::new(),
            levies_cons: CommodityLevyMap::new(),
            demand: DemandMap::new(),
            units: "tonnes".into(),
        }
    }

    #[rstest]
    fn output_flows_matching_units(
        svd_commodity: Commodity,
        sed_commodity: Commodity,
        process: Process,
    ) {
        // Both commodities have the same units
        assert_eq!(svd_commodity.units, sed_commodity.units);

        let commodity1 = Rc::new(svd_commodity);
        let commodity2 = Rc::new(sed_commodity);
        let (_, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), 1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), 2.0)),
            ]
            .into_iter(),
            None,
        );

        // Validation should pass since the units are the same
        validate_output_flows_units(&flows_map).unwrap();
    }

    #[rstest]
    fn output_flows_mismatched_units(
        sed_commodity_pj: Commodity,
        sed_commodity_tonnes: Commodity,
        process: Process,
    ) {
        // Ensure the two commodities have different units
        assert_ne!(sed_commodity_pj.units, sed_commodity_tonnes.units);

        let commodity1 = Rc::new(sed_commodity_pj);
        let commodity2 = Rc::new(sed_commodity_tonnes);
        let (_, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), 1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), 2.0)),
            ]
            .into_iter(),
            None,
        );

        // Different units should cause validation to fail
        let result = validate_output_flows_units(&flows_map);
        // Note that the error contents are sorted so we should deterministically get
        // this exact error message.
        assert_error!(
            result,
            "Process process1 has SED/SVD outputs with different units: [PJ, tonnes] in region: GBR and year: 2010"
        );
    }

    #[rstest]
    fn output_flows_other_commodity_ignored(
        sed_commodity_pj: Commodity,
        other_commodity: Commodity,
        process: Process,
    ) {
        // Modify OTH commodity to have different units
        let mut other_commodity = other_commodity;
        other_commodity.units = "tonnes".into();
        assert_ne!(sed_commodity_pj.units, other_commodity.units);

        let sed_commodity = Rc::new(sed_commodity_pj);
        let oth_commodity = Rc::new(other_commodity);

        let (_, flows_map) = build_maps(
            process,
            [
                (sed_commodity.id.clone(), flow(sed_commodity.clone(), 1.0)),
                (oth_commodity.id.clone(), flow(oth_commodity.clone(), 2.0)),
            ]
            .into_iter(),
            None,
        );

        // OTH commodity should be ignored, validation should pass
        validate_output_flows_units(&flows_map).unwrap();
    }

    #[rstest]
    fn single_sed_svd_output(svd_commodity: Commodity, process: Process) {
        let commodity = Rc::new(svd_commodity);
        let (_, flows_map) = build_maps(
            process,
            std::iter::once((commodity.id.clone(), flow(commodity.clone(), 1.0))),
            None,
        );

        // Single output should always pass validation
        validate_output_flows_units(&flows_map).unwrap();
    }

    #[rstest]
    fn no_sed_svd_outputs(other_commodity: Commodity, process: Process) {
        let oth_commodity_1 = Rc::new(other_commodity.clone());
        let oth_commodity_2 = Rc::new(other_commodity.clone());
        let (_, flows_map) = build_maps(
            process,
            [
                (CommodityID("oth1".into()), flow(oth_commodity_1, 1.0)),
                (CommodityID("oth2".into()), flow(oth_commodity_2, 2.0)),
            ]
            .into_iter(),
            None,
        );

        // Processes with only OTH outputs should pass validation
        validate_output_flows_units(&flows_map).unwrap();
    }

    #[rstest]
    fn sed_svd_inputs_different_units_ignored(
        sed_commodity_pj: Commodity,
        sed_commodity_tonnes: Commodity,
        svd_commodity: Commodity,
        process: Process,
    ) {
        // Ensure input commodities have different units
        assert_ne!(sed_commodity_pj.units, sed_commodity_tonnes.units);

        // Output commodity shares units with one input
        assert_eq!(svd_commodity.units, sed_commodity_pj.units);

        let input1 = Rc::new(sed_commodity_pj);
        let input2 = Rc::new(sed_commodity_tonnes);
        let output = Rc::new(svd_commodity);

        let (_, flows_map) = build_maps(
            process,
            [
                // Two inputs with different units (negative coefficients)
                (input1.id.clone(), flow(input1.clone(), -1.0)),
                (input2.id.clone(), flow(input2.clone(), -2.0)),
                // Single output (positive coefficient)
                (output.id.clone(), flow(output.clone(), 3.0)),
            ]
            .into_iter(),
            None,
        );

        // Validation should pass because only outputs are checked
        validate_output_flows_units(&flows_map).unwrap();
    }

    #[rstest]
    fn single_output_infer_primary(#[from(svd_commodity)] commodity: Commodity, process: Process) {
        let milestone_years = vec![2010, 2020];
        let commodity = Rc::new(commodity);
        let (mut processes, flows_map) = build_maps(
            process,
            std::iter::once((commodity.id.clone(), flow(commodity.clone(), 1.0))),
            None,
        );
        validate_flows_and_update_primary_output(&mut processes, &flows_map, &milestone_years)
            .unwrap();
        assert_eq!(
            processes.values().exactly_one().unwrap().primary_output,
            Some(commodity.id.clone())
        );
    }

    #[rstest]
    fn multiple_outputs_error(
        #[from(svd_commodity)] commodity1: Commodity,
        #[from(sed_commodity)] commodity2: Commodity,
        process: Process,
    ) {
        let milestone_years: Vec<u32> = vec![2010, 2020];
        let commodity1 = Rc::new(commodity1);
        let commodity2 = Rc::new(commodity2);
        let (mut processes, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), 1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), 2.0)),
            ]
            .into_iter(),
            None,
        );
        let res =
            validate_flows_and_update_primary_output(&mut processes, &flows_map, &milestone_years);
        assert_error!(res, "Could not infer primary_output for process process1");
    }

    #[rstest]
    fn explicit_primary_output(
        #[from(svd_commodity)] commodity1: Commodity,
        #[from(sed_commodity)] commodity2: Commodity,
        process: Process,
    ) {
        let milestone_years = vec![2010, 2020];
        let commodity1 = Rc::new(commodity1);
        let commodity2 = Rc::new(commodity2);
        let mut process = process;
        process.primary_output = Some(commodity2.id.clone());
        let (mut processes, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), 1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), 2.0)),
            ]
            .into_iter(),
            None,
        );
        validate_flows_and_update_primary_output(&mut processes, &flows_map, &milestone_years)
            .unwrap();
        assert_eq!(
            processes.values().exactly_one().unwrap().primary_output,
            Some(commodity2.id.clone())
        );
    }

    #[rstest]
    fn all_inputs_no_primary(
        #[from(svd_commodity)] commodity1: Commodity,
        #[from(sed_commodity)] commodity2: Commodity,
        process: Process,
    ) {
        let milestone_years = vec![2010, 2020];
        let commodity1 = Rc::new(commodity1);
        let commodity2 = Rc::new(commodity2);
        let (mut processes, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), -1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), -2.0)),
            ]
            .into_iter(),
            None,
        );
        validate_flows_and_update_primary_output(&mut processes, &flows_map, &milestone_years)
            .unwrap();
        assert_eq!(
            processes.values().exactly_one().unwrap().primary_output,
            None
        );
    }

    #[rstest]
    fn flows_not_in_all_milestone_years(
        #[from(svd_commodity)] commodity1: Commodity,
        #[from(sed_commodity)] commodity2: Commodity,
        process: Process,
    ) {
        let milestone_years = vec![2010, 2015, 2020];
        let flow_years = vec![2010, 2020];
        let commodity1 = Rc::new(commodity1);
        let commodity2 = Rc::new(commodity2);
        let (mut processes, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), 1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), 2.0)),
            ]
            .into_iter(),
            Some(flow_years),
        );
        let res =
            validate_flows_and_update_primary_output(&mut processes, &flows_map, &milestone_years);
        assert_error!(
            res,
            "Flows map for process process1 does not cover all regions and required years"
        );
    }

    #[rstest]
    fn flows_only_milestone_years(
        #[from(svd_commodity)] commodity1: Commodity,
        #[from(sed_commodity)] commodity2: Commodity,
        process: Process,
    ) {
        let milestone_years = vec![2010, 2015, 2020];
        let commodity1 = Rc::new(commodity1);
        let commodity2 = Rc::new(commodity2);
        let (mut processes, flows_map) = build_maps(
            process,
            [
                (commodity1.id.clone(), flow(commodity1.clone(), 1.0)),
                (commodity2.id.clone(), flow(commodity2.clone(), -2.0)),
            ]
            .into_iter(),
            Some(milestone_years.clone()),
        );
        validate_flows_and_update_primary_output(&mut processes, &flows_map, &milestone_years)
            .unwrap();
    }

    #[test]
    fn flows_different_direction_different_years() {
        let patch = FilePatch::new("process_flows.csv")
            .with_deletion("GASPRC,GASPRD,all,all,-1.05,fixed,")
            .with_addition("GASPRC,GASPRD,all,2020;2030,-1.05,fixed,")
            .with_addition("GASPRC,GASPRD,all,2040,1.05,fixed,");
        assert_validate_fails_with_simple!(
            vec![patch],
            "Flow of commodity GASPRD in region GBR for process GASPRC behaves as input or output in different years."
        );
    }

    #[test]
    fn missing_flow() {
        let patch = FilePatch::new("process_flows.csv")
            .with_deletion("GASPRC,GASPRD,all,all,-1.05,fixed,")
            .with_addition("GASPRC,GASPRD,all,2020;2030,-1.05,fixed,");
        assert_validate_fails_with_simple!(
            vec![patch],
            "Flow of commodity GASPRD in region GBR for process GASPRC does not cover all milestone years within the process range of activity."
        );
    }

    #[test]
    fn coeff_zero() {
        let patch = FilePatch::new("process_flows.csv")
            .with_deletion("GASPRC,GASPRD,all,all,-1.05,fixed,")
            .with_addition("GASPRC,GASPRD,all,2020;2030,-1.05,fixed,")
            .with_addition("GASPRC,GASPRD,all,2040,0,fixed,");
        assert_validate_ok_simple!(vec![patch]);
    }

    #[test]
    fn flows_not_needed_before_time_horizon() {
        // NB: Time horizon starts at 2020 for simple example
        //
        // Flows are only needed for milestone years. Check that users can omit them for
        // non-milestone years.
        let patches = vec![
            FilePatch::new("processes.csv")
                .with_deletion("GASDRV,Dry gas extraction,all,GASPRD,2020,2040,1.0,")
                .with_addition("GASDRV,Dry gas extraction,all,GASPRD,1980,2040,1.0,"),
            FilePatch::new("process_flows.csv")
                .with_deletion("GASPRC,GASPRD,all,all,-1.05,fixed,")
                .with_addition("GASPRC,GASPRD,all,2020;2030;2040,-1.05,fixed,"),
        ];
        assert_validate_ok_simple!(patches);
    }
}