"""Reliability verifier — writes `provenance_verified` + `text_agreement`.

Implements the dispatch table from spec §6 ReliabilityStep. The normalisers
in :mod:`ix.provenance.normalize` do the actual string/number/date work; this
module chooses which one to run for each field based on its Pydantic
annotation, and writes the two reliability flags onto the existing
:class:`FieldProvenance` records in place.

The summary counters (``verified_fields``, ``text_agreement_fields``) land in
``provenance.quality_metrics`` alongside the existing coverage metrics.
"""

from __future__ import annotations

import re
import types
from datetime import date, datetime
from decimal import Decimal, InvalidOperation
from typing import Any, Literal, Union, get_args, get_origin, get_type_hints

from pydantic import BaseModel

from ix.contracts.provenance import FieldProvenance, ProvenanceData
from ix.provenance.normalize import (
    normalize_date,
    normalize_iban,
    normalize_number,
    normalize_string,
    should_skip_text_agreement,
)


def _unwrap_optional(tp: Any) -> Any:
    """Return the non-None arm of ``Optional[X]`` / ``X | None``.

    Handles both ``typing.Union`` and ``types.UnionType`` (PEP 604 ``X | Y``
    unions), which ``get_type_hints`` returns on Python 3.12+.
    """
    origin = get_origin(tp)
    if origin is Union or origin is types.UnionType:
        args = [a for a in get_args(tp) if a is not type(None)]
        if len(args) == 1:
            return args[0]
    return tp


def _is_literal(tp: Any) -> bool:
    return get_origin(tp) is Literal


def _is_iban_field(field_path: str) -> bool:
    return "iban" in field_path.lower()


def _compare_string(value: str, snippet: str) -> bool:
    try:
        return normalize_string(value) in normalize_string(snippet)
    except Exception:
        return False


_NUMBER_TOKEN_RE = re.compile(r"[+\-]?[\d][\d',.\s]*\d|[+\-]?\d+")


def _compare_number(value: Any, snippet: str) -> bool:
    try:
        canonical = normalize_number(value)
    except (InvalidOperation, ValueError):
        return False
    # Try the whole snippet first (cheap path when the snippet IS the number).
    try:
        if normalize_number(snippet) == canonical:
            return True
    except (InvalidOperation, ValueError):
        pass
    # Fall back to scanning numeric substrings — OCR snippets commonly carry
    # labels ("Closing balance CHF 1'234.56") that confuse a whole-string
    # numeric parse.
    for match in _NUMBER_TOKEN_RE.finditer(snippet):
        token = match.group()
        try:
            if normalize_number(token) == canonical:
                return True
        except (InvalidOperation, ValueError):
            continue
    return False


def _compare_date(value: Any, snippet: str) -> bool:
    try:
        iso_value = normalize_date(value)
    except (ValueError, TypeError):
        return False
    # Find any date-like chunk in snippet; try normalising each token segment.
    # Simplest heuristic: try snippet as a whole; on failure, scan tokens.
    try:
        if normalize_date(snippet) == iso_value:
            return True
    except (ValueError, TypeError):
        pass
    # Token scan — dateutil will raise on the non-date tokens, which is fine.
    for token in _tokenise_for_date(snippet):
        try:
            if normalize_date(token) == iso_value:
                return True
        except (ValueError, TypeError):
            continue
    return False


def _tokenise_for_date(s: str) -> list[str]:
    """Split on whitespace + common punctuation so date strings survive whole.

    Keeps dots / slashes / dashes inside tokens (they're valid date
    separators); splits on spaces, commas, semicolons, colons, brackets.
    """
    return [t for t in re.split(r"[\s,;:()\[\]]+", s) if t]


def _compare_iban(value: str, snippet: str) -> bool:
    try:
        return normalize_iban(value) in normalize_iban(snippet)
    except Exception:
        return False


def _compare_for_type(value: Any, field_type: Any, snippet: str, field_path: str) -> bool:
    unwrapped = _unwrap_optional(field_type)

    # Date / datetime.
    if unwrapped in (date, datetime):
        return _compare_date(value, snippet)

    # Numeric.
    if unwrapped in (int, float, Decimal):
        return _compare_number(value, snippet)

    # IBAN (detected by field name).
    if _is_iban_field(field_path):
        return _compare_iban(str(value), snippet)

    # Default: string substring.
    return _compare_string(str(value), snippet)


def verify_field(
    field_provenance: FieldProvenance,
    field_type: Any,
    texts: list[str],
) -> tuple[bool | None, bool | None]:
    """Compute the two reliability flags for one field.

    Returns ``(provenance_verified, text_agreement)``. See spec §6 for the
    dispatch rules. ``None`` on either slot means the check was skipped
    (Literal, None value, or short-value for text_agreement).
    """
    value = field_provenance.value
    unwrapped = _unwrap_optional(field_type)

    # Skip Literal / None value entirely — both flags None.
    if _is_literal(unwrapped) or value is None:
        return (None, None)

    # provenance_verified: scan cited segments.
    provenance_verified: bool | None
    if not field_provenance.sources:
        provenance_verified = False
    else:
        provenance_verified = any(
            _compare_for_type(value, field_type, s.text_snippet, field_provenance.field_path)
            for s in field_provenance.sources
        )

    # text_agreement: None if no texts, else apply short-value rule.
    text_agreement: bool | None
    if not texts or should_skip_text_agreement(value, field_type):
        text_agreement = None
    else:
        concatenated = "\n".join(texts)
        text_agreement = _compare_for_type(
            value, field_type, concatenated, field_provenance.field_path
        )

    return provenance_verified, text_agreement


def apply_reliability_flags(
    provenance_data: ProvenanceData,
    use_case_response: type[BaseModel],
    texts: list[str],
) -> None:
    """Apply :func:`verify_field` to every field in ``provenance_data``.

    Mutates ``provenance_data`` in place:

    * Each ``FieldProvenance``'s ``provenance_verified`` and
      ``text_agreement`` slots are filled.
    * ``quality_metrics['verified_fields']`` is set to the number of fields
      whose ``provenance_verified`` is True.
    * ``quality_metrics['text_agreement_fields']`` is set likewise for
      ``text_agreement``.

    ``use_case_response`` is the Pydantic class for the extraction schema
    (e.g. :class:`~ix.use_cases.bank_statement_header.BankStatementHeader`).
    Type hints are resolved via ``get_type_hints`` so forward-refs and
    ``str | None`` unions are normalised consistently.
    """
    type_hints = get_type_hints(use_case_response)

    verified_count = 0
    text_agreement_count = 0
    for fp in provenance_data.fields.values():
        # Field path is something like "result.bank_name" — the part after
        # the first dot is the attribute name on the response schema.
        leaf = fp.field_path.split(".", 1)[-1]
        # For nested shapes we only resolve the top-level name; MVP use cases
        # are flat so that's enough. When we ship nested schemas we'll walk
        # the annotation tree here.
        top_attr = leaf.split(".")[0]
        field_type: Any = type_hints.get(top_attr, str)

        pv, ta = verify_field(fp, field_type, texts)
        fp.provenance_verified = pv
        fp.text_agreement = ta
        if pv is True:
            verified_count += 1
        if ta is True:
            text_agreement_count += 1

    provenance_data.quality_metrics["verified_fields"] = verified_count
    provenance_data.quality_metrics["text_agreement_fields"] = text_agreement_count