"""Request validation and response shaping for the search endpoints."""

from __future__ import annotations

from dataclasses import asdict
from typing import Any

from django.conf import settings
from rest_framework import serializers

from apps.search.types import SORT_OPTIONS, SORT_RELEVANCE, SearchRequest, SearchResult

MAX_QUERY_LENGTH = 200
MAX_FILTER_VALUES = 20


class CommaSeparatedField(serializers.CharField):
    """
    Accepts ``?skills=python,django`` **and** repeated ``?skills=python&skills=django``.

    Both spellings are common in the wild; normalising here keeps the views and
    both backends free of query-string trivia.
    """

    def __init__(self, **kwargs: Any) -> None:
        kwargs.setdefault("required", False)
        kwargs.setdefault("allow_blank", True)
        super().__init__(**kwargs)

    def get_value(self, dictionary: Any) -> Any:
        # ``QueryDict.get`` silently keeps only the last occurrence, which would
        # turn ``?skills=a&skills=b`` into ``b``.  ``getlist`` keeps both.
        if hasattr(dictionary, "getlist"):
            values = dictionary.getlist(self.field_name)
            if values:
                return values
        return super().get_value(dictionary)

    def to_internal_value(self, data: Any) -> tuple[str, ...]:
        raw: list[str] = []
        if isinstance(data, list | tuple):
            raw = [str(item) for item in data]
        elif data:
            raw = [str(data)]

        values: list[str] = []
        for chunk in raw:
            for item in chunk.split(","):
                cleaned = item.strip().lower()[:128]
                if cleaned and cleaned not in values:
                    values.append(cleaned)
        if len(values) > MAX_FILTER_VALUES:
            raise serializers.ValidationError(
                f"At most {MAX_FILTER_VALUES} values are allowed per filter."
            )
        return tuple(values)


class SearchRequestSerializer(serializers.Serializer):
    """Validates and normalises the query string of ``GET /api/v1/search/``."""

    q = serializers.CharField(
        required=False, allow_blank=True, max_length=MAX_QUERY_LENGTH, trim_whitespace=True,
        help_text="Free-text keyword. Supports quoted phrases and -exclusions.",
    )  # fmt: skip
    skills = CommaSeparatedField(help_text="Skill names, OR-combined.")
    roles = CommaSeparatedField(help_text="Job family, e.g. engineering, human_resources.")
    seniority = CommaSeparatedField(help_text="Seniority level, e.g. senior, manager, cxo.")
    countries = CommaSeparatedField(help_text="Country of residence.")
    industries = CommaSeparatedField(help_text="Industry of the current employer.")
    companies = CommaSeparatedField(help_text="Current employer name.")
    min_experience = serializers.IntegerField(required=False, min_value=0, max_value=70)
    max_experience = serializers.IntegerField(required=False, min_value=0, max_value=70)
    sort = serializers.ChoiceField(choices=SORT_OPTIONS, required=False, default=SORT_RELEVANCE)
    page = serializers.IntegerField(required=False, min_value=1, default=1)
    page_size = serializers.IntegerField(required=False, min_value=1, max_value=100, default=20)
    facets = serializers.BooleanField(required=False, default=True)

    def validate(self, attrs: dict[str, Any]) -> dict[str, Any]:
        low, high = attrs.get("min_experience"), attrs.get("max_experience")
        if low is not None and high is not None and low > high:
            raise serializers.ValidationError(
                {"min_experience": "min_experience cannot be greater than max_experience."}
            )

        page, page_size = attrs.get("page", 1), attrs.get("page_size", 20)
        # Deep pagination is both useless to a human and expensive for the
        # engine, so it is rejected instead of silently truncated.
        if page * page_size > settings.SEARCH["MAX_RESULT_WINDOW"]:
            raise serializers.ValidationError(
                {"page": f"Cannot page beyond {settings.SEARCH['MAX_RESULT_WINDOW']} results."}
            )
        return attrs

    def to_search_request(self) -> SearchRequest:
        data = self.validated_data
        return SearchRequest(
            q=data.get("q", "").strip(),
            skills=data.get("skills", ()),
            roles=data.get("roles", ()),
            seniority=data.get("seniority", ()),
            countries=data.get("countries", ()),
            industries=data.get("industries", ()),
            companies=data.get("companies", ()),
            min_experience=data.get("min_experience"),
            max_experience=data.get("max_experience"),
            sort=data.get("sort", SORT_RELEVANCE),
            page=data.get("page", 1),
            page_size=data.get("page_size", 20),
            include_facets=data.get("facets", True),
        )


# ---------------------------------------------------------------------------
# Response serializers (declared explicitly so the OpenAPI schema is accurate)
# ---------------------------------------------------------------------------
class SearchHitSerializer(serializers.Serializer):
    id = serializers.IntegerField()
    score = serializers.FloatField()
    full_name = serializers.CharField()
    headline = serializers.CharField()
    job_title = serializers.CharField()
    job_title_role = serializers.CharField()
    seniority_levels = serializers.ListField(child=serializers.CharField())
    company = serializers.CharField()
    industry = serializers.CharField()
    location_name = serializers.CharField()
    location_country = serializers.CharField()
    years_experience = serializers.IntegerField(allow_null=True)
    linkedin_url = serializers.CharField()
    skills = serializers.ListField(child=serializers.CharField())
    highlight = serializers.DictField(child=serializers.ListField(child=serializers.CharField()))


class FacetBucketSerializer(serializers.Serializer):
    key = serializers.CharField()
    count = serializers.IntegerField()


class SearchResponseSerializer(serializers.Serializer):
    count = serializers.IntegerField()
    page = serializers.IntegerField()
    page_size = serializers.IntegerField()
    total_pages = serializers.IntegerField()
    took_ms = serializers.IntegerField()
    backend = serializers.CharField()
    results = SearchHitSerializer(many=True)
    facets = serializers.DictField(child=FacetBucketSerializer(many=True))

    @staticmethod
    def from_result(result: SearchResult, request: SearchRequest) -> dict[str, Any]:
        total_pages = max(1, -(-result.total // request.page_size))
        return {
            "count": result.total,
            "page": request.page,
            "page_size": request.page_size,
            "total_pages": total_pages,
            "took_ms": result.took_ms,
            "backend": result.backend,
            "results": [asdict(hit) for hit in result.hits],
            "facets": {
                name: [asdict(bucket) for bucket in buckets]
                for name, buckets in result.facets.items()
            },
        }


class SuggestResponseSerializer(serializers.Serializer):
    suggestions = serializers.ListField(child=serializers.CharField())