# =============================================================================
# Projet : AIR — Accounting Intermediate Representation
# Auteur : Simon-Pierre Boucher
# Contact : contact@spboucher.ai
# Fichier : tax.py
# Description : Tax pass — applies ALSL tax policies deterministically (no rates in code).
# =============================================================================
"""Tax pass.

For each taxable event, evaluates the ALSL tax policies matching the event's
jurisdiction and computes each tax component on its base with the policy
set's rounding mode. Every computed tax amount becomes a provenance node
derived from the event subtotal.

NO tax rate exists in this file — rates live in versioned ALSL policy sets
with mandatory source citations (see docs/research/canada-gst-qst.md).
"""
from __future__ import annotations

from aic.diagnostics import Diagnostic, Severity
from aic.passes.base import Pass
from aic.unit import CompilationUnit, TaxLineState
from alsl.evaluator import applicable_tax_policies
from core.events import EventType

TAXABLE_TYPES = (EventType.SALE, EventType.PURCHASE, EventType.REFUND)


class TaxPass(Pass):
    name = "tax"

    def run(self, unit: CompilationUnit) -> list[Diagnostic]:
        diags: list[Diagnostic] = []
        rounding = unit.policies.rounding.mode

        for event in unit.document.events:
            if event.type not in TAXABLE_TYPES:
                continue
            if event.tax is None or event.tax.exempt:
                continue
            state = unit.event_state(event.id)
            if state.subtotal is None or state.subtotal_node is None:
                continue  # validation already failed this event

            policies = applicable_tax_policies(unit.policies, event, state.subtotal)
            if not policies:
                diags.append(Diagnostic(
                    code="AIR-E400", severity=Severity.ERROR,
                    message=(
                        f"no tax policy in set '{unit.policies.name}' matches "
                        f"jurisdiction '{event.tax.jurisdiction}'"
                    ),
                    location=f"event {event.id}, field tax.jurisdiction",
                    suggestion="add an ALSL tax policy for this jurisdiction "
                               "or mark the event tax.exempt: true",
                    origin_pass=self.name,
                ))
                continue

            wanted = set(event.tax.codes)  # optional explicit filter
            produced: set[str] = set()
            for policy in policies:
                for comp in policy.components:
                    if wanted and comp.code not in wanted:
                        continue
                    if comp.base != "subtotal":
                        diags.append(Diagnostic(
                            code="AIR-E401", severity=Severity.ERROR,
                            message=f"unsupported tax base '{comp.base}' in policy "
                                    f"'{policy.name}' (ALSL v0.1 supports 'subtotal')",
                            location=f"policy {policy.name}, component {comp.code}",
                            suggestion="use base: subtotal",
                            origin_pass=self.name,
                        ))
                        continue
                    raw = state.subtotal.multiply(comp.rate)
                    amount = raw.quantized(rounding)
                    node = unit.provenance.define(
                        kind="tax",
                        operation=f"tax:{comp.code}@{comp.rate}~{rounding.value}",
                        amount=amount,
                        inputs=(state.subtotal_node,),
                        source_ref=policy.source,
                    )
                    state.taxes.append(TaxLineState(
                        code=comp.code,
                        amount=amount,
                        node_id=node.id,
                        payable_role=comp.payable_role,
                        receivable_role=comp.receivable_role,
                        recoverable=comp.recoverable_on_purchase,
                        policy=policy.name,
                    ))
                    produced.add(comp.code)

            for missing in wanted - produced:
                diags.append(Diagnostic(
                    code="AIR-W400", severity=Severity.WARNING,
                    message=f"event requested tax code '{missing}' but no policy "
                            "produced it",
                    location=f"event {event.id}, field tax.codes",
                    suggestion="check the policy set covers this code for the jurisdiction",
                    origin_pass=self.name,
                ))
        return diags