"""Select replayable demo scenarios from the shared scenario catalog."""

import re
import unicodedata
from dataclasses import dataclass
from difflib import SequenceMatcher
from functools import lru_cache
from pathlib import Path

import yaml

_REPOSITORY_ROOT = Path(__file__).parents[4]
SCENARIO_PATH = _REPOSITORY_ROOT / "eval" / "scenarios.yaml"
FIXTURE_ROOT = _REPOSITORY_ROOT / "eval" / "fixtures"
_WORD_PATTERN = re.compile(r"[a-z0-9]+")


@dataclass(frozen=True)
class Scenario:
    """One shared suggestion and its optional parent scenario."""

    key: str
    chip: str
    query: str
    after: str | None = None

    @property
    def is_refinement(self) -> bool:
        """Return whether this scenario refines an earlier result."""
        return self.after is not None


@dataclass(frozen=True)
class ScenarioMatch:
    """Describe which recorded scenario will answer a demo request."""

    key: str
    is_exact: bool
    scenario_query: str
    chip: str


@lru_cache(maxsize=1)
def load_scenarios() -> tuple[Scenario, ...]:
    """Load and validate the shared scenario catalog once."""
    payload = yaml.safe_load(SCENARIO_PATH.read_text(encoding="ascii"))
    if not isinstance(payload, dict) or payload.get("version") != 1:
        raise ValueError("Scenario catalog must have version 1")
    entries = payload.get("scenarios")
    if not isinstance(entries, list) or not entries:
        raise ValueError("Scenario catalog must contain scenarios")
    scenarios = tuple(_parse_scenario(entry) for entry in entries)
    keys = {scenario.key for scenario in scenarios}
    if len(keys) != len(scenarios):
        raise ValueError("Scenario keys must be unique")
    if any(scenario.after not in keys for scenario in scenarios if scenario.after is not None):
        raise ValueError("Scenario catalog contains an unknown parent")
    return scenarios


def select_scenario(query: str) -> ScenarioMatch:
    """Select an exact scenario or the nearest available recorded fixture."""
    scenarios = _replayable_scenarios()
    normalized_query = normalize_text(query)
    for scenario in scenarios:
        if normalized_query in {normalize_text(scenario.query), normalize_text(scenario.chip)}:
            return _to_match(scenario, is_exact=True)

    selected = max(
        scenarios,
        key=lambda scenario: max(
            SequenceMatcher(None, normalized_query, normalize_text(scenario.query)).ratio(),
            SequenceMatcher(None, normalized_query, normalize_text(scenario.chip)).ratio(),
        ),
    )
    return _to_match(selected, is_exact=False)


def select_replay_scenario(
    query: str,
    has_previous_recommendations: bool,
) -> ScenarioMatch:
    """Map a request with prior results to its recorded refinement when available."""
    selected = select_scenario(query)
    scenarios = _replayable_scenarios()
    selected_scenario = next(scenario for scenario in scenarios if scenario.key == selected.key)
    if selected_scenario.is_refinement or not has_previous_recommendations:
        return selected
    refinement = next(
        (scenario for scenario in scenarios if scenario.after == selected_scenario.key),
        None,
    )
    return _to_match(refinement, is_exact=False) if refinement is not None else selected


def suggestion_items() -> list[dict[str, str]]:
    """Return chip and query pairs for non-refinement scenarios."""
    return [
        {"chip": scenario.chip, "query": scenario.query}
        for scenario in load_scenarios()
        if not scenario.is_refinement
    ]


def normalize_text(value: str) -> str:
    """Normalize text for exact and similarity matching."""
    decomposed = unicodedata.normalize("NFKD", value.casefold())
    ascii_text = decomposed.encode("ascii", errors="ignore").decode("ascii")
    return " ".join(_WORD_PATTERN.findall(ascii_text))


@lru_cache(maxsize=1)
def _replayable_scenarios() -> tuple[Scenario, ...]:
    fixture_keys = {path.name for path in FIXTURE_ROOT.iterdir() if path.is_dir()}
    scenarios = tuple(scenario for scenario in load_scenarios() if scenario.key in fixture_keys)
    if not scenarios:
        raise ValueError("Demo mode requires at least one scenario fixture")
    return scenarios


def _parse_scenario(payload: object) -> Scenario:
    if not isinstance(payload, dict):
        raise ValueError("Each scenario must be a mapping")
    required = {"key", "chip", "query", "facets"}
    if not required <= set(payload):
        raise ValueError("Scenario is missing a required field")
    after = payload.get("after")
    if after is not None and not isinstance(after, str):
        raise ValueError("Scenario parent must be a key")
    return Scenario(
        key=_required_string(payload, "key"),
        chip=_required_string(payload, "chip"),
        query=_required_string(payload, "query"),
        after=after,
    )


def _required_string(payload: dict[object, object], key: str) -> str:
    value = payload.get(key)
    if not isinstance(value, str) or not value:
        raise ValueError(f"Scenario {key} must be a non-empty string")
    return value


def _to_match(scenario: Scenario, is_exact: bool) -> ScenarioMatch:
    return ScenarioMatch(
        key=scenario.key,
        is_exact=is_exact,
        scenario_query=scenario.query,
        chip=scenario.chip,
    )