datasynth-group 5.35.2

//! Per-subsidiary NCI rollforward — Task 7.1.
//!
//! Implements the IFRS 10 / ASC 810 non-controlling-interest
//! rollforward identity for one fully-consolidated, non-wholly-owned
//! subsidiary at a time:
//!
//! ```text
//! closing_nci = opening_nci
//!             + (1 - ownership_percent) * net_income
//!             + (1 - ownership_percent) * oci
//!             - (1 - ownership_percent) * dividends_paid
//! ```
//!
//! # Standards reference
//!
//! - **IFRS 10.B94** — profit or loss and each component of OCI is
//!   attributed to the owners of the parent and to the NCI in
//!   proportion to their ownership interest (no current-period
//!   reallocation when the proportion changes).
//! - **IFRS 10.22** — the parent presents NCI in the consolidated
//!   statement of financial position within equity, separately from the
//!   equity of the owners of the parent.
//! - **ASC 810-10-45-15** — the US GAAP equivalent: the share of net
//!   income attributable to the NCI is presented separately on the
//!   consolidated income statement.
//!
//! # Validation
//!
//! - `consolidation_method` **must** be
//!   [`crate::config::ConsolidationMethod::Full`].  All other methods
//!   are rejected with [`GroupError::Aggregate`] naming the entity and
//!   the offending method.  NCI is not meaningful for `Parent` entities
//!   (wholly owned), `EquityMethod` / `Proportional` / `FairValue`
//!   investees (one-line investment treatment).
//! - `ownership_percent` **must** be present and `< 1.0`.  A `Full`
//!   entity with `ownership_percent == 1.0` is a caller bug — that
//!   entity should be `Parent` so the wholly-owned-subsidiary path is
//!   used.  We surface this with a precise error message rather than
//!   silently generating a zero NCI.
//! - All amounts use [`rust_decimal::Decimal`] — never `f64`.  The
//!   final `closing_nci` is rounded to **2 decimal places** so the
//!   on-disk JSON is human-readable and the rollforward identity is
//!   verifiable in a spreadsheet.

use chrono::NaiveDate;
use rust_decimal::Decimal;
use serde::{Deserialize, Serialize};

use crate::config::ConsolidationMethod;
use crate::errors::{GroupError, GroupResult};
use crate::manifest::ManifestEntity;

// ── Public types ──────────────────────────────────────────────────────────────

/// One subsidiary's NCI rollforward record for the period.
///
/// All amounts are denominated in `currency` (the group presentation
/// currency for the consolidated rollforward — translation per Chunk 6
/// must already have been applied to the contributing P&L / OCI /
/// dividend numbers).
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct NciRollforward {
    /// Subsidiary entity code (matches
    /// [`crate::manifest::ManifestEntity::code`]).
    pub entity_code: String,
    /// Code of the parent entity that holds the controlling interest.
    /// Mirrors [`crate::manifest::ManifestEntity::parent_code`].
    pub parent_entity_code: String,
    /// Parent's ownership share of the subsidiary's equity, in `[0, 1)`.
    pub ownership_percent: Decimal,
    /// Non-controlling interest's share of the subsidiary's equity =
    /// `1 - ownership_percent`.  Stored separately for downstream
    /// consumers so they don't have to recompute it.
    pub nci_percent: Decimal,
    /// Carrying balance of the NCI brought forward from the prior
    /// period (zero on the first period of an engagement).
    pub opening_nci: Decimal,
    /// NCI's share of the period's net income =
    /// `(1 - ownership_percent) * net_income`.
    pub nci_share_of_profit: Decimal,
    /// NCI's share of the period's OCI =
    /// `(1 - ownership_percent) * oci`.
    pub nci_share_of_oci: Decimal,
    /// NCI's share of dividends paid by the subsidiary =
    /// `(1 - ownership_percent) * total_dividends_paid`.  Reduces the
    /// NCI carrying balance.
    pub nci_dividends: Decimal,
    /// **v5.2** — IFRS 10.23 equity-transaction adjustment to NCI for
    /// mid-period ownership changes that don't affect control.  Signed:
    /// positive = NCI grew (parent sold to NCI per `ControlDecreased`);
    /// negative = NCI shrank (parent acquired from NCI per
    /// `ControlIncreased`).  Zero when the entity has no
    /// `ControlIncreased` / `ControlDecreased` events for the period.
    /// `#[serde(default)]` so v5.0–v5.1 archives without the field
    /// load to zero.
    #[serde(default)]
    pub equity_transaction_adjustments: Decimal,
    /// **v5.4** — IFRS 3 § 42 P&L remeasurement gain/loss recognised
    /// when control is gained mid-period (i.e. the parent's previously
    /// held interest is re-measured to acquisition-date fair value).
    /// Computed as `previously_held_interest_fair_value
    /// − previously_held_interest_carrying`.  Zero when the entity has
    /// no `ControlGained` event for the period.
    /// `#[serde(default)]` keeps v5.0–v5.3 archives loading byte-
    /// identically.
    #[serde(default)]
    pub pl_remeasurement_gain_or_loss: Decimal,
    /// Closing NCI =
    /// `opening_nci + nci_share_of_profit + nci_share_of_oci - nci_dividends + equity_transaction_adjustments`,
    /// rounded to 2dp (banker's rounding).
    pub closing_nci: Decimal,
    /// Period end date the rollforward is as of.
    pub period_end: NaiveDate,
    /// Currency the amounts are denominated in (group presentation
    /// currency).
    pub currency: String,
}

/// Inputs required to derive an [`NciRollforward`].
///
/// The caller is responsible for already having translated
/// `period_net_income`, `period_oci`, and `total_dividends_paid` into
/// the group presentation currency (Chunk 6).  This function does not
/// know about FX rates.
pub struct NciInputs<'a> {
    /// Reference to the subsidiary's manifest entity.  Provides the
    /// entity code, parent code, ownership percent, and consolidation
    /// method used to validate the inputs.
    pub entity: &'a ManifestEntity,
    /// Subsidiary's period net income (after tax), in the same currency
    /// as `currency`.  Sign convention: profit positive, loss negative.
    pub period_net_income: Decimal,
    /// Subsidiary's period OCI (other comprehensive income), in the
    /// same currency as `currency`.
    pub period_oci: Decimal,
    /// Subsidiary's total dividends paid for the period (gross — both
    /// to controlling and non-controlling shareholders).  Always
    /// non-negative; the NCI share will be subtracted from the closing
    /// balance.
    pub total_dividends_paid: Decimal,
    /// Opening NCI carrying value brought forward from the prior period
    /// (zero on the first period of an engagement).
    pub opening_nci: Decimal,
    /// v5.2: IFRS 3 § 19(a) / ASC 805-30-30-1 acquisition-date NCI
    /// fair value.  Used **only** on the first period of an engagement
    /// (when `opening_nci == 0`).  When supplied, the rollforward uses
    /// this fair value as the opening NCI instead of zero, implementing
    /// the full-goodwill measurement basis where NCI is recognised at
    /// its acquisition-date fair value rather than its proportionate
    /// share of net assets.  `None` defaults to the v5.0–v5.1
    /// behaviour (proportionate basis: opening NCI starts at zero on
    /// the first period and grows via share-of-profit / OCI in
    /// subsequent periods).
    pub acquisition_date_nci_fair_value: Option<Decimal>,
    /// **v5.2** — IFRS 10.23 / IFRS 10.B96 mid-period ownership-change
    /// events affecting this subsidiary.  The rollforward consumes
    /// these to compute the equity-transaction adjustment to NCI.
    /// Empty by default — engagements without ownership-change events
    /// see no behaviour change.  Driver-side wiring reads each entity's
    /// `intercompany/ownership_change_events.json` file (PR #155) and
    /// threads the parsed events here.
    pub ownership_changes: &'a [datasynth_core::models::intercompany::OwnershipChangeEvent],
    /// **v5.4** — Period start date.  Used to pro-rate `period_net_income`,
    /// `period_oci`, and `total_dividends_paid` for `ControlGained` mid-
    /// period events: the entity contributes only the post-acquisition
    /// fraction `(period_end - effective_date + 1) / (period_end -
    /// period_start + 1)` to consolidated profit.  When no
    /// `ControlGained` event applies, `period_start` is unused and the
    /// rollforward applies the full period numbers.
    pub period_start: NaiveDate,
    /// Period end date.
    pub period_end: NaiveDate,
    /// Group presentation currency.
    pub currency: String,
}

// ── Public API ────────────────────────────────────────────────────────────────

/// Derive an [`NciRollforward`] for one subsidiary.
///
/// Pure function: no I/O, no allocation beyond the record itself, no
/// dependence on global state.  Two calls with the same input produce
/// equal records.
///
/// # Validation
///
/// 1. `entity.consolidation_method` **must** be
///    [`ConsolidationMethod::Full`].  Returns
///    [`GroupError::Aggregate`] otherwise (NCI is meaningless for any
///    other consolidation method).
/// 2. `entity.ownership_percent` **must** be present and `< 1.0`.
///    Wholly-owned entities should be modelled as `Parent` so the
///    wholly-owned-subsidiary path applies; an entity that is `Full`
///    but `100%` owned is a caller bug.
///
/// # Math
///
/// ```text
/// nci_percent           = 1 - ownership_percent
/// nci_share_of_profit   = nci_percent * period_net_income
/// nci_share_of_oci      = nci_percent * period_oci
/// nci_dividends         = nci_percent * total_dividends_paid
/// closing_nci           = (opening_nci + nci_share_of_profit
///                          + nci_share_of_oci - nci_dividends).round_dp(2)
/// ```
///
/// # Errors
///
/// - [`GroupError::Aggregate`] if `consolidation_method` is not
///   `Full` — names the entity and the offending method.
/// - [`GroupError::Aggregate`] if `ownership_percent` is missing or
///   `>= 1.0` — names the entity.
pub fn compute_nci_rollforward(inputs: &NciInputs) -> GroupResult<NciRollforward> {
    let entity = inputs.entity;

    // 1. Reject any non-Full consolidation method up front — NCI is
    //    not meaningful for Parent / EquityMethod / Proportional /
    //    FairValue entities.
    if entity.consolidation_method != ConsolidationMethod::Full {
        return Err(GroupError::Aggregate(format!(
            "compute_nci_rollforward: entity `{}` has consolidation_method=\
             {:?} — NCI is only meaningful for ConsolidationMethod::Full \
             (Parent is wholly owned; EquityMethod / Proportional / \
             FairValue use one-line investment treatment)",
            entity.code, entity.consolidation_method,
        )));
    }

    // 2. Ownership must be present and < 1.0 for a Full entity to
    //    have any NCI to measure.
    let ownership_percent = entity.ownership_percent.ok_or_else(|| {
        GroupError::Aggregate(format!(
            "compute_nci_rollforward: entity `{}` is consolidation_method=\
             Full but has no ownership_percent set — supply ownership_percent \
             < 1.0 or change the method to Parent for wholly-owned",
            entity.code,
        ))
    })?;

    if ownership_percent >= Decimal::ONE {
        return Err(GroupError::Aggregate(format!(
            "compute_nci_rollforward: entity `{}` is consolidation_method=\
             Full but has no ownership_percent < 1.0 — use Parent for \
             wholly-owned",
            entity.code,
        )));
    }

    // Derive the parent code from the manifest.  Required for the
    // rollforward record so downstream consumers (consolidation note
    // disclosure, IFRS 12 § 12 schedule) can attribute the NCI to a
    // controlling parent without re-walking the manifest.
    let parent_entity_code = entity.parent_code.clone().ok_or_else(|| {
        GroupError::Aggregate(format!(
            "compute_nci_rollforward: entity `{}` has no parent_code in the \
             manifest — every Full subsidiary must declare its parent",
            entity.code,
        ))
    })?;

    let nci_percent = Decimal::ONE - ownership_percent;

    // v5.2: when this is the first period of an engagement (i.e.
    // `opening_nci == 0`) AND the caller supplied an
    // `acquisition_date_nci_fair_value`, seed the opening NCI from
    // the fair value rather than starting at zero.  This implements
    // IFRS 3 § 19(a) / ASC 805-30-30-1 full-goodwill measurement
    // (NCI recognised at acquisition-date fair value) — the fair
    // value rolls forward through the standard share-of-equity
    // allocation in subsequent periods.
    //
    // For non-first-period rollforwards (`opening_nci != 0`) the
    // fair value is ignored — the prior period's closing balance has
    // already absorbed it via the period-1 calculation.  For
    // proportionate measurement (no fair value supplied) the rollforward
    // works as in v5.0–v5.1: opening starts at zero, share of profit
    // grows it.
    let effective_opening_nci = match (
        inputs.opening_nci.is_zero(),
        inputs.acquisition_date_nci_fair_value,
    ) {
        (true, Some(fv)) => fv,
        _ => inputs.opening_nci,
    };

    // 3. **v5.4** — Walk ownership-change events to determine
    //    effective semantics for the period:
    //
    //    - `ControlIncreased` / `ControlDecreased` (within control):
    //      equity transactions per IFRS 10.23.  NCI carrying adjusted
    //      by approximately `-consideration_paid_or_received`.
    //    - `ControlGained` (mid-period acquisition): IFRS 3 § 42 re-
    //      measurement of the parent's previously-held interest at
    //      acquisition-date FV with P&L gain/loss = `FV - carrying`.
    //      Profit attribution is **time-weighted** by the post-
    //      acquisition fraction of the period, since the entity was
    //      not in consolidation pre-acquisition.  Opening NCI seeded
    //      from `acquisition_date_nci_fair_value` regardless of the
    //      caller's `opening_nci` (period-1 of consolidation for this
    //      entity).
    //    - `ControlLost` (mid-period deconsolidation): still rejected
    //      as v5.5+ follow-up — requires removing the entity from
    //      consolidation and IFRS 10.B97 retained-interest re-measurement.
    //
    //    Multiple `ControlGained` events on a single entity for one
    //    period are treated as the latest applying — engagements can't
    //    really have two mid-period acquisitions of the same entity in
    //    one reporting period without intervening `ControlLost`.
    use datasynth_core::models::intercompany::OwnershipChangeType;
    let mut equity_transaction_adjustments = Decimal::ZERO;
    let mut control_gained_event: Option<
        &datasynth_core::models::intercompany::OwnershipChangeEvent,
    > = None;
    for ev in inputs.ownership_changes {
        match ev.event_type {
            OwnershipChangeType::ControlIncreased | OwnershipChangeType::ControlDecreased => {
                equity_transaction_adjustments -= ev.consideration_paid_or_received;
            }
            OwnershipChangeType::ControlGained => {
                // Latest event wins if multiple supplied (rare).
                control_gained_event = Some(ev);
            }
            OwnershipChangeType::ControlLost => {
                return Err(GroupError::Aggregate(format!(
                    "compute_nci_rollforward: entity `{}`: ControlLost \
                     mid-period deconsolidation events are not yet supported \
                     by the rollforward — this is a v5.5+ follow-up.",
                    entity.code,
                )));
            }
        }
    }

    // 4. **v5.4** — Time-weight + opening-NCI override for ControlGained.
    //
    //    Time-weight = (period_end - effective_date + 1) / (period_end - period_start + 1).
    //    Both numerator and denominator are inclusive day counts.  When
    //    `effective_date == period_start`, the weight is 1.0 (full
    //    period contributes — the acquisition occurred exactly at
    //    period start, equivalent to a period-1 baseline).  When
    //    `effective_date == period_end`, the weight is 1 day / N days
    //    (only the final day's activity counts).
    //
    //    The IFRS 3 § 42 re-measurement gain/loss is independent of
    //    time-weighting: it's the one-time effect of revaluing the
    //    prior interest to FV at the acquisition date.
    let mut time_weight = Decimal::ONE;
    let mut pl_remeasurement_gain_or_loss = Decimal::ZERO;
    let mut control_gained_opening_override: Option<Decimal> = None;
    if let Some(ev) = control_gained_event {
        // Validate effective_date is in [period_start, period_end].
        if ev.effective_date < inputs.period_start || ev.effective_date > inputs.period_end {
            return Err(GroupError::Aggregate(format!(
                "compute_nci_rollforward: entity `{}`: ControlGained \
                 effective_date {} is outside the period [{}, {}] — \
                 the manifest builder normally rejects this; surface it \
                 here as a defence-in-depth check",
                entity.code, ev.effective_date, inputs.period_start, inputs.period_end,
            )));
        }
        let total_days = (inputs.period_end - inputs.period_start).num_days() + 1;
        let post_days = (inputs.period_end - ev.effective_date).num_days() + 1;
        time_weight = Decimal::from(post_days) / Decimal::from(total_days);

        // IFRS 3 § 42: gain/loss = FV - carrying.  Both fields are
        // optional on the event; if either is missing the gain/loss
        // is zero (engagement explicitly opted out of the IFRS 3.42
        // P&L recognition for this acquisition, e.g. a fresh-buy with
        // no prior interest).
        if let (Some(fv), Some(carrying)) = (
            ev.previously_held_interest_fair_value,
            ev.previously_held_interest_carrying,
        ) {
            pl_remeasurement_gain_or_loss = fv - carrying;
        }

        // Opening NCI overrides to acquisition-date fair value when
        // supplied.  Falls back to the input's
        // `acquisition_date_nci_fair_value`, then to zero (proportionate
        // basis at acquisition).
        control_gained_opening_override = ev
            .acquisition_date_nci_fair_value
            .or(inputs.acquisition_date_nci_fair_value);
    }

    // 5. Apply the IFRS 10.B94 / ASC 810 share-of-equity allocation
    //    with time-weighting (1.0 if no ControlGained mid-period).
    let nci_share_of_profit = nci_percent * inputs.period_net_income * time_weight;
    let nci_share_of_oci = nci_percent * inputs.period_oci * time_weight;
    let nci_dividends = nci_percent * inputs.total_dividends_paid * time_weight;

    // 6. Pick the effective opening NCI: ControlGained override wins,
    //    then the existing period-1 fair-value seed logic, otherwise
    //    the caller's `opening_nci`.
    let effective_opening_nci = match control_gained_opening_override {
        Some(fv) => fv,
        None => effective_opening_nci,
    };

    let closing_nci = (effective_opening_nci + nci_share_of_profit + nci_share_of_oci
        - nci_dividends
        + equity_transaction_adjustments)
        .round_dp(2);

    Ok(NciRollforward {
        entity_code: entity.code.clone(),
        parent_entity_code,
        ownership_percent,
        nci_percent,
        opening_nci: effective_opening_nci.round_dp(2),
        nci_share_of_profit: nci_share_of_profit.round_dp(2),
        nci_share_of_oci: nci_share_of_oci.round_dp(2),
        nci_dividends: nci_dividends.round_dp(2),
        equity_transaction_adjustments: equity_transaction_adjustments.round_dp(2),
        pl_remeasurement_gain_or_loss: pl_remeasurement_gain_or_loss.round_dp(2),
        closing_nci,
        period_end: inputs.period_end,
        currency: inputs.currency.clone(),
    })
}

// ── Unit tests ────────────────────────────────────────────────────────────────

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

    fn make_entity(
        code: &str,
        method: ConsolidationMethod,
        ownership: Option<Decimal>,
    ) -> ManifestEntity {
        ManifestEntity {
            code: code.to_string(),
            name: None,
            country: "DE".to_string(),
            functional_currency: "EUR".to_string(),
            scoping_profile: "significant".to_string(),
            consolidation_method: method,
            ownership_percent: ownership,
            parent_code: Some("PARENT".to_string()),
            accounting_framework: None,
            industry: None,
            hyperinflation_status:
                datasynth_core::models::HyperinflationStatus::NotHyperinflationary,
            ownership_changes: Vec::new(),
            entity_seed: "00".to_string(),
            shard_id: "S_DEFAULT_0001".to_string(),
        }
    }

    fn period_end() -> NaiveDate {
        NaiveDate::from_ymd_opt(2024, 3, 31).unwrap()
    }

    #[test]
    fn happy_path_eighty_percent_owned() {
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(1000),
            period_oci: dec!(200),
            total_dividends_paid: dec!(500),
            opening_nci: dec!(800),
            acquisition_date_nci_fair_value: None,
            ownership_changes: &[],
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };

        let rf = compute_nci_rollforward(&inputs).expect("must succeed");

        assert_eq!(rf.entity_code, "SUB");
        assert_eq!(rf.parent_entity_code, "PARENT");
        assert_eq!(rf.ownership_percent, dec!(0.80));
        assert_eq!(rf.nci_percent, dec!(0.20));
        assert_eq!(rf.nci_share_of_profit, dec!(200.00));
        assert_eq!(rf.nci_share_of_oci, dec!(40.00));
        assert_eq!(rf.nci_dividends, dec!(100.00));
        // 800 + 200 + 40 - 100 = 940
        assert_eq!(rf.closing_nci, dec!(940.00));
    }

    #[test]
    fn full_goodwill_acquisition_date_fair_value_seeds_period_one_opening() {
        // v5.2: IFRS 3.19(a) full-goodwill measurement.  Period 1
        // (opening_nci == 0) with a fair value of 850 → effective
        // opening = 850, then standard period activity rolls forward.
        //
        // Subsidiary:
        //   - 75% owned (NCI = 25%)
        //   - period net income = 1000 → NCI share = 250
        //   - period OCI = 200 → NCI share = 50
        //   - dividends paid = 400 → NCI share = 100
        // Closing = 850 + 250 + 50 - 100 = 1050
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.75)));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(1000),
            period_oci: dec!(200),
            total_dividends_paid: dec!(400),
            opening_nci: Decimal::ZERO,
            acquisition_date_nci_fair_value: Some(dec!(850)),
            ownership_changes: &[],
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).expect("must succeed");

        assert_eq!(
            rf.opening_nci,
            dec!(850.00),
            "opening must be seeded from fair value, not zero"
        );
        assert_eq!(rf.nci_share_of_profit, dec!(250.00));
        assert_eq!(rf.nci_share_of_oci, dec!(50.00));
        assert_eq!(rf.nci_dividends, dec!(100.00));
        assert_eq!(rf.closing_nci, dec!(1050.00));
    }

    #[test]
    fn full_goodwill_fair_value_ignored_when_opening_nci_nonzero() {
        // v5.2: in subsequent periods (opening_nci != 0) the fair
        // value is ignored — the prior period already absorbed it
        // via its own period-1 calculation.  Effective opening must
        // come from `opening_nci`, not the fair value.
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(500),
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: dec!(940), // brought forward from a prior period
            acquisition_date_nci_fair_value: Some(dec!(1000)), // stale FV
            ownership_changes: &[],
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).expect("must succeed");

        assert_eq!(
            rf.opening_nci,
            dec!(940.00),
            "fair value must not override a non-zero opening_nci"
        );
        // Closing = 940 + 100 (20% of 500) = 1040
        assert_eq!(rf.closing_nci, dec!(1040.00));
    }

    #[test]
    fn proportionate_basis_unchanged_when_no_fair_value() {
        // v5.2 sanity: when no fair value is supplied (None), the
        // rollforward must produce byte-identical output to v5.0–v5.1.
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(1000),
            period_oci: dec!(200),
            total_dividends_paid: dec!(500),
            opening_nci: dec!(800),
            acquisition_date_nci_fair_value: None, // proportionate basis
            ownership_changes: &[],
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).expect("must succeed");

        // Same numbers as `happy_path_eighty_percent_owned`.
        assert_eq!(rf.opening_nci, dec!(800.00));
        assert_eq!(rf.closing_nci, dec!(940.00));
    }

    #[test]
    fn rejects_parent_method() {
        let entity = make_entity("PARENT_CO", ConsolidationMethod::Parent, None);
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: Decimal::ZERO,
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: Decimal::ZERO,
            acquisition_date_nci_fair_value: None,
            ownership_changes: &[],
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };

        let err = compute_nci_rollforward(&inputs).expect_err("must reject parent");
        match err {
            GroupError::Aggregate(msg) => {
                assert!(msg.contains("PARENT_CO"));
                assert!(msg.contains("Parent"));
            }
            other => panic!("expected Aggregate, got {other:?}"),
        }
    }

    // ── v5.2 IFRS 10.23 equity-transaction tests ─────────────────────────

    fn equity_event(
        ty: datasynth_core::models::intercompany::OwnershipChangeType,
        before: Decimal,
        after: Decimal,
        consideration: Decimal,
    ) -> datasynth_core::models::intercompany::OwnershipChangeEvent {
        datasynth_core::models::intercompany::OwnershipChangeEvent {
            entity_code: "SUB".to_string(),
            parent_entity_code: "PARENT".to_string(),
            event_type: ty,
            effective_date: NaiveDate::from_ymd_opt(2024, 2, 15).unwrap(),
            ownership_percent_before: before,
            ownership_percent_after: after,
            previously_held_interest_carrying: None,
            previously_held_interest_fair_value: None,
            consideration_paid_or_received: consideration,
            acquisition_date_nci_fair_value: None,
            nci_measurement_method: Default::default(),
            currency: "CHF".to_string(),
        }
    }

    #[test]
    fn control_increased_shrinks_nci_by_consideration() {
        // Parent buys 10% from NCI for 100 — NCI shrinks by ~100.
        // Opening NCI 800, share of profit 200 (1000 × 20% pre-event
        // simplification), share of OCI 0, dividends 0,
        // equity-transaction adjustment = -100.
        // Closing = 800 + 200 + 0 - 0 - 100 = 900.
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let event = equity_event(
            OwnershipChangeType::ControlIncreased,
            dec!(0.80),
            dec!(0.90),
            dec!(100),
        );
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(1000),
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: dec!(800),
            acquisition_date_nci_fair_value: None,
            ownership_changes: std::slice::from_ref(&event),
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        assert_eq!(rf.equity_transaction_adjustments, dec!(-100.00));
        assert_eq!(rf.closing_nci, dec!(900.00));
    }

    #[test]
    fn control_decreased_grows_nci_by_consideration_received() {
        // Parent sells 10% to NCI for 100 (negative sign — inflow).
        // NCI grows by ~100.  Opening 800, profit 200, dividends 0,
        // adjustment = -(-100) = +100.  Closing = 800+200+0-0+100 = 1100.
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let event = equity_event(
            OwnershipChangeType::ControlDecreased,
            dec!(0.90),
            dec!(0.80),
            dec!(-100),
        );
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(1000),
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: dec!(800),
            acquisition_date_nci_fair_value: None,
            ownership_changes: std::slice::from_ref(&event),
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        assert_eq!(rf.equity_transaction_adjustments, dec!(100.00));
        assert_eq!(rf.closing_nci, dec!(1100.00));
    }

    #[test]
    fn multiple_equity_transactions_sum() {
        // Two equity transactions: +50 (decrease) then -30 (increase).
        // Total adjustment: -(-50) + -(30) = +50 - 30 = +20.
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.75)));
        let events = vec![
            equity_event(
                OwnershipChangeType::ControlDecreased,
                dec!(0.80),
                dec!(0.75),
                dec!(-50),
            ),
            equity_event(
                OwnershipChangeType::ControlIncreased,
                dec!(0.75),
                dec!(0.78),
                dec!(30),
            ),
        ];
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: Decimal::ZERO,
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: dec!(500),
            acquisition_date_nci_fair_value: None,
            ownership_changes: &events,
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        assert_eq!(rf.equity_transaction_adjustments, dec!(20.00));
        assert_eq!(rf.closing_nci, dec!(520.00));
    }

    /// **v5.4** — ControlGained mid-period at the period start is the
    /// degenerate case: time_weight = 1.0 (full period contributes),
    /// matching what `acquisition_date_nci_fair_value` does for period-1.
    #[test]
    fn control_gained_at_period_start_is_full_period_contribution() {
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        // ControlGained at period_start with FV = 1000 (NCI) + carrying
        // = 0 + FV = 0 (no remeasurement gain).
        let mut ev = equity_event(
            OwnershipChangeType::ControlGained,
            Decimal::ZERO,
            dec!(0.80),
            dec!(5000),
        );
        ev.effective_date = NaiveDate::from_ymd_opt(2024, 1, 1).unwrap();
        ev.acquisition_date_nci_fair_value = Some(dec!(1000));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(2000),
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: Decimal::ZERO,
            acquisition_date_nci_fair_value: None,
            ownership_changes: std::slice::from_ref(&ev),
            period_start: NaiveDate::from_ymd_opt(2024, 1, 1).unwrap(),
            period_end: NaiveDate::from_ymd_opt(2024, 3, 31).unwrap(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        // Full period: time_weight = 1.0
        // Opening = 1000 (FV from event), share_of_profit = 0.20 × 2000 × 1.0 = 400
        // Closing = 1000 + 400 = 1400
        assert_eq!(rf.opening_nci, dec!(1000));
        assert_eq!(rf.nci_share_of_profit, dec!(400.00));
        assert_eq!(rf.closing_nci, dec!(1400.00));
        assert_eq!(rf.pl_remeasurement_gain_or_loss, Decimal::ZERO);
    }

    /// **v5.4** — ControlGained mid-period at the midpoint pro-rates
    /// profit by the post-acquisition fraction.
    #[test]
    fn control_gained_mid_period_pro_rates_profit() {
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        // Period: Q1 2024 (90 days).  Acquisition date: Feb 15
        // (~46 days remaining; weight ≈ 46/90).
        let mut ev = equity_event(
            OwnershipChangeType::ControlGained,
            Decimal::ZERO,
            dec!(0.80),
            dec!(5000),
        );
        ev.effective_date = NaiveDate::from_ymd_opt(2024, 2, 15).unwrap();
        ev.acquisition_date_nci_fair_value = Some(dec!(1000));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(2000),
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: Decimal::ZERO,
            acquisition_date_nci_fair_value: None,
            ownership_changes: std::slice::from_ref(&ev),
            period_start: NaiveDate::from_ymd_opt(2024, 1, 1).unwrap(),
            period_end: NaiveDate::from_ymd_opt(2024, 3, 31).unwrap(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        // total_days = 91 (Jan 1 to Mar 31 inclusive).
        // post_days = 46 (Feb 15 to Mar 31 inclusive).
        // weight = 46/91 ≈ 0.50549...
        // share_of_profit = 0.20 × 2000 × (46/91) = 400 × 0.50549 ≈ 202.20
        // Closing = 1000 + 202.20 = 1202.20
        let weight = Decimal::from(46) / Decimal::from(91);
        let expected_share = (dec!(0.20) * dec!(2000) * weight).round_dp(2);
        assert_eq!(rf.opening_nci, dec!(1000));
        assert_eq!(rf.nci_share_of_profit, expected_share);
        let expected_close = (dec!(1000) + dec!(0.20) * dec!(2000) * weight).round_dp(2);
        assert_eq!(rf.closing_nci, expected_close);
    }

    /// **v5.4** — ControlGained P&L re-measurement gain/loss = FV - carrying.
    #[test]
    fn control_gained_records_ifrs_3_42_remeasurement_gain() {
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let mut ev = equity_event(
            OwnershipChangeType::ControlGained,
            Decimal::ZERO,
            dec!(0.80),
            dec!(5000),
        );
        ev.effective_date = NaiveDate::from_ymd_opt(2024, 1, 1).unwrap();
        ev.previously_held_interest_carrying = Some(dec!(800));
        ev.previously_held_interest_fair_value = Some(dec!(1500));
        ev.acquisition_date_nci_fair_value = Some(dec!(500));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: Decimal::ZERO,
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: Decimal::ZERO,
            acquisition_date_nci_fair_value: None,
            ownership_changes: std::slice::from_ref(&ev),
            period_start: NaiveDate::from_ymd_opt(2024, 1, 1).unwrap(),
            period_end: NaiveDate::from_ymd_opt(2024, 3, 31).unwrap(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        // Re-measurement gain = 1500 - 800 = 700
        assert_eq!(rf.pl_remeasurement_gain_or_loss, dec!(700));
    }

    /// **v5.5+ follow-up** — ControlLost mid-period still rejected.
    #[test]
    fn control_lost_mid_period_rejected_with_v55_pointer() {
        use datasynth_core::models::intercompany::OwnershipChangeType;
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let event = equity_event(
            OwnershipChangeType::ControlLost,
            dec!(0.80),
            Decimal::ZERO,
            dec!(-500),
        );
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: Decimal::ZERO,
            period_oci: Decimal::ZERO,
            total_dividends_paid: Decimal::ZERO,
            opening_nci: dec!(800),
            acquisition_date_nci_fair_value: None,
            ownership_changes: std::slice::from_ref(&event),
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let err = compute_nci_rollforward(&inputs).unwrap_err();
        let msg = format!("{err}");
        assert!(msg.contains("ControlLost"));
        assert!(msg.contains("v5.5"));
    }

    #[test]
    fn empty_ownership_changes_byte_identical_to_baseline() {
        // With no events, the rollforward must produce the same numbers
        // as the v5.0–v5.1 baseline — equity_transaction_adjustments is
        // exactly zero and closing_nci has no contribution from events.
        let entity = make_entity("SUB", ConsolidationMethod::Full, Some(dec!(0.80)));
        let inputs = NciInputs {
            entity: &entity,
            period_net_income: dec!(1000),
            period_oci: dec!(200),
            total_dividends_paid: dec!(500),
            opening_nci: dec!(800),
            acquisition_date_nci_fair_value: None,
            ownership_changes: &[],
            period_start: period_end(),
            period_end: period_end(),
            currency: "CHF".to_string(),
        };
        let rf = compute_nci_rollforward(&inputs).unwrap();
        assert_eq!(rf.equity_transaction_adjustments, Decimal::ZERO);
        // 800 + 200 + 40 - 100 = 940 (same as happy_path_eighty_percent_owned)
        assert_eq!(rf.closing_nci, dec!(940.00));
    }
}