"""FCC Form 499-A shared utilities.

De minimis calculator (Appendix A), safe-harbor percentage lookup, Line 612
filing-type detection, and Line 105 box-tick derivation.

Used by form_499a.py, form_499_initial.py, and the /validate endpoint's
Python counterpart (if we ever move validation server-side).
"""

from __future__ import annotations

import logging
from dataclasses import dataclass, field
from typing import Optional

import psycopg2
import os

logger = logging.getLogger(__name__)


# ── Line 105 box-tick derivation ────────────────────────────────────────
# Mirrors site/src/lib/line_105_catalog.ts::derivedLine105Boxes. When a
# CLEC/IXC/Wireless has infra_type='reseller' or 'mvno', the handler
# automatically ticks the corresponding derived Line 105 box on the form.

LINE_105_BOX_NUMBERS = {
    "voip_interconnected":      1,
    "voip_non_interconnected":  2,
    "clec":                     3,
    "ilec":                     4,
    "local_reseller":           5,   # derived from clec + reseller
    "toll_reseller":            6,   # derived from ixc + reseller
    "ixc":                      7,
    "wireless":                 8,
    "mvno":                     9,   # derived from wireless + mvno
    "prepaid_calling_card":    10,
    "private_line":            11,
    "satellite":               12,
    "payphone":                13,
    "osp":                     14,
    "shared_tenant":           15,
    "audio_bridging":          16,
    "toll_free":               17,
    "paging":                  18,
    "smr":                     19,
    "fixed_wireless":          20,
    "mobile_satellite":        21,
    "other":                   22,
}


def derived_line_105_boxes(category_id: str, infra_type: Optional[str]) -> list[int]:
    """Return extra Line 105 boxes to tick because of the infra_type flag."""
    boxes: list[int] = []
    if infra_type == "reseller":
        if category_id == "clec":
            boxes.append(5)
        elif category_id == "ixc":
            boxes.append(6)
    if infra_type == "mvno" and category_id == "wireless":
        boxes.append(9)
    return boxes


def all_line_105_boxes_to_tick(line_105_categories: list[dict]) -> list[int]:
    """Return every Line 105 box number to tick for this filer."""
    boxes: set[int] = set()
    for cat in line_105_categories or []:
        cat_id = cat.get("id")
        if cat_id and cat_id in LINE_105_BOX_NUMBERS:
            boxes.add(LINE_105_BOX_NUMBERS[cat_id])
        boxes.update(derived_line_105_boxes(cat_id, cat.get("infra_type")))
    return sorted(boxes)


# ── Safe harbor lookup ──────────────────────────────────────────────────

SAFE_HARBOR_DISALLOWED_CATEGORIES = {"voip_non_interconnected"}


def _db_connect():
    return psycopg2.connect(os.environ.get("DATABASE_URL", ""))


def load_safe_harbor_pct(form_year: int, category_id: str) -> Optional[float]:
    """Return the safe-harbor interstate % for (year, category), or None.

    None is returned for categories that have no safe harbor (e.g.,
    non-interconnected VoIP) or if the year/category combination isn't in
    the fcc_safe_harbor_percentages seed table.
    """
    if category_id in SAFE_HARBOR_DISALLOWED_CATEGORIES:
        return None
    try:
        conn = _db_connect()
        with conn.cursor() as cur:
            cur.execute(
                "SELECT interstate_pct FROM fcc_safe_harbor_percentages "
                "WHERE form_year = %s AND line_105_category = %s",
                (form_year, category_id),
            )
            row = cur.fetchone()
        conn.close()
        return float(row[0]) if row else None
    except Exception as exc:
        logger.warning("safe-harbor lookup failed: %s", exc)
        return None


def safe_harbor_allowed(category_id: str) -> bool:
    return category_id not in SAFE_HARBOR_DISALLOWED_CATEGORIES


# ── De minimis calculator (Appendix A, 11-line worksheet) ───────────────


@dataclass
class DeMinimisWorksheet:
    """Appendix A de minimis determination worksheet.

    Every field corresponds to a line in the 2026 Form 499-A Appendix A.
    Mirrors the PDF layout exactly so auditors can follow along.
    """
    form_year: int
    # Lines 1-4 — interstate/intl contribution bases for filer + affiliates
    line_1_filer_interstate_cents:     int = 0
    line_2_filer_intl_cents:           int = 0
    line_3_affiliates_interstate_cents: int = 0
    line_4_affiliates_intl_cents:      int = 0
    # Line 5 — consolidated interstate
    line_5_consolidated_interstate_cents: int = 0
    # Line 6 — consolidated interstate+intl (pre-LIRE exclusion)
    line_6_consolidated_total_cents:   int = 0
    # Line 7 — interstate as % of consolidated total (LIRE test)
    line_7_interstate_pct:             float = 0.0
    # Line 8 — LIRE exempt? (line_7 ≤ 12%)
    line_8_lire_exempt:                bool = False
    # Line 9 — contribution base to test
    line_9_contribution_base_cents:    int = 0
    # Line 10 — year-specific factor (0.256 for 2026)
    line_10_factor:                    float = 0.0
    # Line 11 — estimated annual contribution = line_9 × line_10
    line_11_estimated_contrib_cents:   int = 0
    # Result
    is_de_minimis:                     bool = False
    threshold_usd:                     int = 10000
    notes:                             list[str] = field(default_factory=list)

    def to_dict(self) -> dict:
        return {
            "form_year": self.form_year,
            "line_1_filer_interstate_cents":     self.line_1_filer_interstate_cents,
            "line_2_filer_intl_cents":           self.line_2_filer_intl_cents,
            "line_3_affiliates_interstate_cents": self.line_3_affiliates_interstate_cents,
            "line_4_affiliates_intl_cents":      self.line_4_affiliates_intl_cents,
            "line_5_consolidated_interstate_cents": self.line_5_consolidated_interstate_cents,
            "line_6_consolidated_total_cents":   self.line_6_consolidated_total_cents,
            "line_7_interstate_pct":             self.line_7_interstate_pct,
            "line_8_lire_exempt":                self.line_8_lire_exempt,
            "line_9_contribution_base_cents":    self.line_9_contribution_base_cents,
            "line_10_factor":                    self.line_10_factor,
            "line_11_estimated_contrib_cents":   self.line_11_estimated_contrib_cents,
            "is_de_minimis":                     self.is_de_minimis,
            "threshold_usd":                     self.threshold_usd,
            "notes":                             self.notes,
        }


def load_deminimis_factor(form_year: int) -> float:
    """Return the Appendix A Line 10 factor for a form year.

    Raises ValueError if the year isn't in the seed table — an unknown
    form year is a code bug, not a graceful-fallback situation.
    """
    try:
        conn = _db_connect()
        with conn.cursor() as cur:
            cur.execute(
                "SELECT factor FROM fcc_deminimis_factors WHERE form_year = %s",
                (form_year,),
            )
            row = cur.fetchone()
        conn.close()
    except Exception as exc:
        logger.error("deminimis factor lookup failed: %s", exc)
        raise
    if not row:
        raise ValueError(f"No de minimis factor configured for form year {form_year}")
    return float(row[0])


def calculate_de_minimis(
    *,
    form_year: int,
    filer_total_revenue_cents: int,
    filer_interstate_pct: float,
    filer_international_pct: float,
    affiliates: Optional[list[dict]] = None,
) -> DeMinimisWorksheet:
    """Compute the Appendix A de minimis worksheet.

    affiliates is a list of {total_revenue_cents, interstate_pct,
    international_pct} records for each affiliated filer. Empty list =
    no affiliates.
    """
    affiliates = affiliates or []
    w = DeMinimisWorksheet(form_year=form_year)

    # Line 1: filer interstate revenue
    w.line_1_filer_interstate_cents = int(
        filer_total_revenue_cents * (filer_interstate_pct / 100.0)
    )
    # Line 2: filer international revenue
    w.line_2_filer_intl_cents = int(
        filer_total_revenue_cents * (filer_international_pct / 100.0)
    )

    # Lines 3-4: affiliates
    for a in affiliates:
        tot = int(a.get("total_revenue_cents", 0))
        ipct = float(a.get("interstate_pct", 0))
        intl = float(a.get("international_pct", 0))
        w.line_3_affiliates_interstate_cents += int(tot * ipct / 100.0)
        w.line_4_affiliates_intl_cents       += int(tot * intl / 100.0)

    # Line 5: consolidated interstate
    w.line_5_consolidated_interstate_cents = (
        w.line_1_filer_interstate_cents + w.line_3_affiliates_interstate_cents
    )
    # Line 6: consolidated interstate + intl
    w.line_6_consolidated_total_cents = w.line_5_consolidated_interstate_cents + (
        w.line_2_filer_intl_cents + w.line_4_affiliates_intl_cents
    )

    # Line 7: interstate as % of consolidated total (guard /0)
    if w.line_6_consolidated_total_cents > 0:
        w.line_7_interstate_pct = round(
            100.0 * w.line_5_consolidated_interstate_cents /
            w.line_6_consolidated_total_cents,
            4,
        )
    else:
        w.line_7_interstate_pct = 0.0

    # Line 8: LIRE exempt if interstate ≤ 12% of combined
    w.line_8_lire_exempt = w.line_7_interstate_pct <= 12.0

    # Line 9: contribution base to test — interstate + (0 if LIRE else intl)
    intl_total = w.line_2_filer_intl_cents + w.line_4_affiliates_intl_cents
    w.line_9_contribution_base_cents = (
        w.line_5_consolidated_interstate_cents +
        (0 if w.line_8_lire_exempt else intl_total)
    )

    # Line 10: year factor
    w.line_10_factor = load_deminimis_factor(form_year)

    # Line 11: estimated annual contribution
    w.line_11_estimated_contrib_cents = int(
        w.line_9_contribution_base_cents * w.line_10_factor
    )

    # Result: de minimis if < $10,000
    w.is_de_minimis = w.line_11_estimated_contrib_cents < (w.threshold_usd * 100)

    if w.is_de_minimis:
        w.notes.append(
            f"De minimis: estimated contribution ${w.line_11_estimated_contrib_cents/100:,.2f}"
            f" < ${w.threshold_usd:,.0f} threshold."
        )
    else:
        w.notes.append(
            f"NOT de minimis: estimated contribution ${w.line_11_estimated_contrib_cents/100:,.2f}"
            f" ≥ ${w.threshold_usd:,.0f} threshold."
        )
    if w.line_8_lire_exempt:
        w.notes.append(
            f"LIRE exempt: interstate ({w.line_7_interstate_pct:.2f}%) ≤ 12% "
            f"of combined interstate+intl — international revenue excluded."
        )
    return w


# ── Line 612 filing-type detection ──────────────────────────────────────


def detect_filing_type(
    *,
    entity: dict,
    current_year_filing_exists: bool = False,
    revised_reason: Optional[str] = None,
) -> str:
    """Return one of: original_april_1, registration_new_filer,
    revised_registration, revised_revenue.
    """
    if not entity.get("filer_id_499"):
        return "registration_new_filer"
    if current_year_filing_exists:
        if revised_reason == "registration":
            return "revised_registration"
        if revised_reason == "revenue":
            return "revised_revenue"
    return "original_april_1"


# ── TRS contribution base (Lines 512-514) ───────────────────────────────

# Revenue lines that roll up into the TRS contribution base.
# Line 418.4 (non-interconnected VoIP) is included ONLY in TRS base —
# it's excluded from USF/NANPA/LNP/ITSP bases. Line 511 subtracts.
TRS_BASE_LINE_KEYS = [
    "line_403", "line_404", "line_404_1", "line_404_3",
    "line_405", "line_406", "line_407", "line_408",
    "line_409", "line_410", "line_411", "line_412",
    "line_413", "line_414_1", "line_414_2",
    "line_415", "line_416", "line_417",
    "line_418_4",  # TRS-only
]


def compute_trs_contribution_base(revenue_lines: dict) -> tuple[int, int, int]:
    """Return (line_512, line_513, line_514) in cents.

    line_512 = Σ(TRS_BASE_LINE_KEYS) - line_511
    line_513 = line_513 (uncollectible for TRS, provided by filer)
    line_514 = line_512 - line_513
    """
    line_512 = sum(int(revenue_lines.get(k, 0) or 0) for k in TRS_BASE_LINE_KEYS)
    line_512 -= int(revenue_lines.get("line_511", 0) or 0)
    line_513 = int(revenue_lines.get("line_513", 0) or 0)
    line_514 = line_512 - line_513
    return line_512, line_513, line_514