from __future__ import annotations
from collections import defaultdict
from dataclasses import dataclass
from datetime import date
from decimal import Decimal
from typing import Any, Optional

from two_way_match import (
    InvoiceHeader,
    InvoiceLine,
    MatchExceptionRecord,
    POLine,
    TwoWayConfig,
    TwoWayMatchResult,
    _cfg_from_dict,
    _qty_bands,
    to_decimal,
)

D0 = Decimal("0")

# ── New input dataclass ────────────────────────────────────────────────────────

@dataclass
class GRLineItem:
    id:                 int
    po_line_id:         Optional[int]
    gr_date:            date             # DATE column, no timezone
    inspection_status:  str              # 'accepted'|'partial_accept'|'rejected'|'pending'|'returned'
    quantity_accepted:  Optional[Decimal]
    quantity_received:  Optional[Decimal]
    deleted_at:         Optional[Any] = None   # non-None → soft-deleted; excluded everywhere


# ── Zone rank (adds 'critical' above 'red' for integrity signals) ──────────────

_ZONE_RANK: dict[str, int] = {"green": 0, "amber": 1, "red": 2, "critical": 3}


def _worse(a: Optional[str], b: str) -> str:
    """Worst-wins comparator. critical > red > amber > green."""
    return b if _ZONE_RANK.get(b, 0) > _ZONE_RANK.get(a or "green", 0) else (a or "green")


def _push_zone(result: TwoWayMatchResult, inv_line_id: Optional[int], zone: str) -> None:
    """Update a specific matched line's zone and the overall match_zone, worst-wins."""
    if inv_line_id is not None:
        for mlr in result.match_line_results:
            if mlr.invoice_line_id == inv_line_id:
                mlr.line_zone = _worse(mlr.line_zone, zone)
    result.match_zone = _worse(result.match_zone, zone)


# ── Private helpers ────────────────────────────────────────────────────────────

def _uninvoiced_qty(
    po_line: POLine,
    accepted_by_po: dict[int, list[GRLineItem]],
) -> Decimal:
    """
    SUM(quantity_accepted for accepted/partial_accept GRs on po_line) − po_line.invoiced_qty.
    Raises RuntimeError on IDP17: quantity_accepted IS NULL on an accepted row.
    Callers must NOT fall back to quantity_received — that would silently mask the violation.
    """
    rows = accepted_by_po.get(po_line.id, [])
    for g in rows:
        if g.quantity_accepted is None:
            raise RuntimeError(
                f"IDP17 violation: GR line id={g.id} inspection_status={g.inspection_status!r} "
                "has quantity_accepted IS NULL."
            )
    total_accepted = sum((g.quantity_accepted for g in rows), D0)
    return total_accepted - (to_decimal(po_line.invoiced_qty) or D0)


def _band_verdict(
    qty_over_pct: Decimal,
    item_type: Optional[str],
    cfg: TwoWayConfig,
) -> Optional[str]:
    """Return failing zone ('amber'|'red') if qty_over_pct exceeds tolerance, else None (pass)."""
    qty_green, qty_amber = _qty_bands(item_type, cfg)   # reuses existing 2-way helper
    if qty_over_pct == D0 or qty_over_pct <= qty_green:
        return None
    return "amber" if qty_over_pct <= qty_amber else "red"


def _qty_check_single(
    *,
    inv_line: InvoiceLine,
    po_line: POLine,
    accepted_by_po: dict[int, list[GRLineItem]],
    result: TwoWayMatchResult,
    cfg: TwoWayConfig,
) -> None:
    """§5.3 quantity-over-received check for one Tier 1-3 (inv_line, po_line) direct match."""

    # Pre-band guard 1: missing invoice qty — Cat 2 incomplete_fields already owns this flag
    if inv_line.quantity is None:
        result.skipped_steps.append({
            "step": "qty_over_received",
            "skip_reason": "inv_qty_null",
            "line_id": inv_line.id,
            "po_line_id": po_line.id,
        })
        return

    uninvoiced = _uninvoiced_qty(po_line, accepted_by_po)

    # Pre-band guard 2: negative uninvoiced → IDP17 forensic exception, zone red
    if uninvoiced < D0:
        result.match_exceptions.append(MatchExceptionRecord(
            exception_type="qty_over_received",
            line_id=inv_line.id,
            po_line_id=po_line.id,
            exception_detail={
                "reason": "uninvoiced_accepted_qty_negative",
                "uninvoiced_accepted_qty": str(uninvoiced),
            },
        ))
        _push_zone(result, inv_line.id, "red")
        result.overall_status = "exception"
        return

    inv_qty = inv_line.quantity

    # Pre-band guard 3/4: uninvoiced == 0
    if uninvoiced == D0:
        if inv_qty > D0:
            # All accepted GR qty already consumed by prior approved invoices
            result.match_exceptions.append(MatchExceptionRecord(
                exception_type="gr_fully_consumed",
                line_id=inv_line.id,
                po_line_id=po_line.id,
                exception_detail={"reason": "gr_fully_consumed", "inv_qty": str(inv_qty)},
            ))
            _push_zone(result, inv_line.id, "red")
            result.overall_status = "exception"
        # inv_qty == 0 → noise line ($0 line), skip silently
        return

    # Band evaluation
    qty_over_pct = max(D0, (inv_qty - uninvoiced) / uninvoiced * Decimal("100"))
    zone = _band_verdict(qty_over_pct, po_line.item_type, cfg)
    if zone:
        result.match_exceptions.append(MatchExceptionRecord(
            exception_type="qty_over_received",
            line_id=inv_line.id,
            po_line_id=po_line.id,
            exception_detail={
                "reason": "qty_over_received",
                "qty_over_pct": str(qty_over_pct),
                "inv_qty": str(inv_qty),
                "uninvoiced_accepted_qty": str(uninvoiced),
            },
        ))
        _push_zone(result, inv_line.id, zone)
        result.overall_status = "exception"


def _qty_check_tier4_group(
    *,
    gl_account: Optional[str],
    group_inv_lines: list[InvoiceLine],
    group_po_lines: list[POLine],
    accepted_by_po: dict[int, list[GRLineItem]],
    accepted_gr: list[GRLineItem],        # full accepted list — needed to detect no-GR vs consumed
    result: TwoWayMatchResult,
    cfg: TwoWayConfig,
) -> None:
    """
    §5.6 aggregate GR quantity check for one Tier-4 GL group.
    Partitions PO lines into goods / services subsets.
    NULL-item-type PO lines are excluded from both (no GR obligation by default).
    The quantity comparison is conservative: ALL inv-line qty (goods+services) vs
    ONLY the goods-subset uninvoiced accepted qty.
    """
    po_goods    = [pl for pl in group_po_lines if pl.item_type == "goods"]
    po_services = [pl for pl in group_po_lines if pl.item_type == "services"]

    if not po_goods:
        return      # 100 % services or all NULL item_type → no GR obligation for this group

    goods_ids = {pl.id for pl in po_goods}

    # IDP17 violations surface here via RuntimeError from _uninvoiced_qty
    uninvoiced_goods = sum((_uninvoiced_qty(pl, accepted_by_po) for pl in po_goods), D0)

    # Total invoice qty over the WHOLE group (conservative: includes services portion)
    inv_qty_total = sum(
        (il.quantity for il in group_inv_lines if il.quantity is not None), D0
    )

    inv_ids = [il.id for il in group_inv_lines]

    base_detail: dict[str, Any] = {
        "group_gl_account":              gl_account,
        "po_lines_goods":                sorted(goods_ids),
        "po_lines_services":             [pl.id for pl in po_services],
        "uninvoiced_accepted_qty_goods": str(uninvoiced_goods),
        "inv_qty_total":                 str(inv_qty_total),
    }

    # Pre-band guard: negative uninvoiced_goods → IDP17 forensic
    if uninvoiced_goods < D0:
        result.match_exceptions.append(MatchExceptionRecord(
            exception_type="qty_over_received",
            exception_detail={**base_detail, "reason": "uninvoiced_accepted_qty_negative"},
        ))
        for il_id in inv_ids:
            _push_zone(result, il_id, "red")
        result.overall_status = "exception"
        return

    # Pre-band guard: uninvoiced_goods == 0
    if uninvoiced_goods == D0:
        # Distinguish "no accepted GRs for goods lines yet" from "fully consumed"
        has_accepted_gr_for_goods = any(g.po_line_id in goods_ids for g in accepted_gr)
        exc_type = "gr_fully_consumed" if has_accepted_gr_for_goods else "no_accepted_gr"
        if inv_qty_total > D0:
            result.match_exceptions.append(MatchExceptionRecord(
                exception_type=exc_type,
                exception_detail={**base_detail, "reason": exc_type},
            ))
            for il_id in inv_ids:
                _push_zone(result, il_id, "red")
            result.overall_status = "exception"
        # inv_qty_total == 0 → noise group, skip silently
        return

    # Band evaluation (always uses "goods" tolerance for mixed groups — §5.6 conservative choice)
    qty_over_pct = max(D0, (inv_qty_total - uninvoiced_goods) / uninvoiced_goods * Decimal("100"))
    zone = _band_verdict(qty_over_pct, "goods", cfg)
    if zone:
        result.match_exceptions.append(MatchExceptionRecord(
            exception_type="qty_over_received",
            exception_detail={
                **base_detail,
                "subset_breakdown": {"qty_over_pct": str(qty_over_pct)},
            },
        ))
        for il_id in inv_ids:
            _push_zone(result, il_id, zone)
        result.overall_status = "exception"


# ── Public entry point ─────────────────────────────────────────────────────────

def run_three_way_match(
    two_way_result: TwoWayMatchResult,
    invoice: InvoiceHeader,           # must have invoice_date: Optional[date]
    inv_lines: list[InvoiceLine],
    po_lines: list[POLine],
    gr_lines: list[GRLineItem],
    *,
    matching_configs: Optional[dict] = None,
) -> TwoWayMatchResult:
    """
    Layers GR checks (§5.1–5.6) on top of an already-completed 2-way match result.
    Always sets match_type='three_way'.

    Check order (stop-on-fire for checks 1-3):
        1. no_accepted_gr        — stop if no accepted/partial_accept GRs exist
        2. invoice_before_gr     — stop if invoice pre-dates earliest accepted GR; zone→critical
        3. gr_inspection_rejected — stop if any routed GR row has status='rejected'
        4. qty_over_received     — per matched PO line (Tier 1-3) or GL group (Tier 4)

    2-way line counts (lines_total / lines_matched / lines_in_exception) are never modified;
    only match_zone, individual line_zone fields, match_exceptions, and overall_status change.
    """
    cfg = _cfg_from_dict(matching_configs or {})

    result = two_way_result
    result.match_type = "three_way"

    inv_by_id: dict[int, InvoiceLine] = {il.id: il for il in inv_lines}
    po_by_id:  dict[int, POLine]      = {pl.id: pl for pl in po_lines}

    # Collect matched pairs from 2-way, split by tier
    tier1_3: list[tuple[int, int]] = []
    tier4:   list[tuple[int, int]] = []
    for mlr in result.match_line_results:
        if mlr.line_status != "matched":
            continue
        (tier4 if mlr.match_tier == 4 else tier1_3).append(
            (mlr.invoice_line_id, mlr.po_line_id)
        )

    all_po_ids: set[int] = {po_id for _, po_id in tier1_3 + tier4}
    if not all_po_ids:
        return result   # nothing matched in 2-way; nothing to GR-check

    # Route GR rows to matched PO lines.
    # Exclude: soft-deleted rows, and 'returned' rows (those belong to credit-note matching §5.5).
    routed = [
        g for g in gr_lines
        if g.po_line_id in all_po_ids
        and g.deleted_at is None
        and g.inspection_status != "returned"
    ]

    # ── Check 1: no accepted GR ────────────────────────────────────────────────
    # Timing-fraud source set: accepted / partial_accept only (§5.1)
    accepted = [g for g in routed if g.inspection_status in ("accepted", "partial_accept")]
    if not accepted:
        result.match_exceptions.append(MatchExceptionRecord(
            exception_type="no_accepted_gr",
            exception_detail={"reason": "no_accepted_gr",
                              "matched_po_line_ids": sorted(all_po_ids)},
        ))
        result.overall_status = "exception"
        return result

    # ── Check 2: timing fraud ─────────────────────────────────────────────────
    # Skip if invoice_date IS NULL (Cat 2 incomplete_fields already owns missing date).
    if invoice.invoice_date is not None:
        earliest_gr_date = min(g.gr_date for g in accepted)   # DATE-level comparison
        if invoice.invoice_date < earliest_gr_date:
            result.match_exceptions.append(MatchExceptionRecord(
                exception_type="invoice_before_gr",
                exception_detail={
                    "reason":             "invoice_before_gr",
                    "invoice_date":       str(invoice.invoice_date),
                    "earliest_gr_date":   str(earliest_gr_date),
                },
            ))
            result.risk_flags.append("invoice_before_gr")
            result.match_zone     = "critical"    # §8.3 — integrity signal overrides normal zones
            result.overall_status = "exception"
            return result

    # ── Check 3: inspection rejection ─────────────────────────────────────────
    # Source set: ALL routed non-returned GR rows (§5.1) — rejected status fires regardless of
    # whether the PO line also has accepted GRs.
    rejected = [g for g in routed if g.inspection_status == "rejected"]
    if rejected:
        result.match_exceptions.append(MatchExceptionRecord(
            exception_type="gr_inspection_rejected",
            exception_detail={
                "reason":           "gr_inspection_rejected",
                "rejected_gr_ids":  sorted(g.id for g in rejected),
            },
        ))
        result.overall_status = "exception"
        return result

    # ── Check 4: quantity over-received ───────────────────────────────────────
    # Build accepted-GR index per PO line, FIFO-ordered (gr_date ASC, id ASC).
    # This ordering is analytical only — nothing is physically decremented (§5.4).
    accepted_by_po: dict[int, list[GRLineItem]] = defaultdict(list)
    for g in accepted:
        if g.po_line_id is not None:
            accepted_by_po[g.po_line_id].append(g)
    for rows in accepted_by_po.values():
        rows.sort(key=lambda g: (g.gr_date, g.id))

    # Tier 1-3: one check per direct (inv_line, po_line) match
    for inv_id, po_id in tier1_3:
        il = inv_by_id.get(inv_id)
        pl = po_by_id.get(po_id)
        if il is None or pl is None:
            continue
        if pl.item_type in (None, "services"):
            continue    # services and NULL-typed lines have no GR obligation
        try:
            _qty_check_single(
                inv_line=il, po_line=pl,
                accepted_by_po=accepted_by_po,
                result=result, cfg=cfg,
            )
        except RuntimeError as exc:
            result.match_exceptions.append(MatchExceptionRecord(
                exception_type="data_integrity_violation",
                line_id=inv_id,
                po_line_id=po_id,
                exception_detail={"reason": "idp17_quantity_accepted_null", "detail": str(exc)},
            ))
            _push_zone(result, inv_id, "red")
            result.overall_status = "exception"

    # Tier 4: aggregate check per GL group (§5.6)
    if tier4:
        # Reconstruct GL groups from inv_line.gl_account
        gl_groups: dict[str, dict[str, set]] = defaultdict(
            lambda: {"inv": set(), "po": set()}
        )
        for inv_id, po_id in tier4:
            il = inv_by_id.get(inv_id)
            if il is None:
                continue
            key = il.gl_account or "__null__"
            gl_groups[key]["inv"].add(inv_id)
            gl_groups[key]["po"].add(po_id)

        for gl_key, ids in gl_groups.items():
            try:
                _qty_check_tier4_group(
                    gl_account     = None if gl_key == "__null__" else gl_key,
                    group_inv_lines= [inv_by_id[i] for i in ids["inv"] if i in inv_by_id],
                    group_po_lines = [po_by_id[i]  for i in ids["po"]  if i in po_by_id],
                    accepted_by_po = accepted_by_po,
                    accepted_gr    = accepted,
                    result=result, cfg=cfg,
                )
            except RuntimeError as exc:
                result.match_exceptions.append(MatchExceptionRecord(
                    exception_type="data_integrity_violation",
                    exception_detail={
                        "reason": "idp17_quantity_accepted_null",
                        "gl_account": None if gl_key == "__null__" else gl_key,
                        "detail": str(exc),
                    },
                ))
                result.overall_status = "exception"

    return result