from __future__ import annotations

from rest_framework import serializers

from books.models import Book, ReadingStatus


class BookListSerializer(serializers.ModelSerializer):
    """Lightweight serializer for list views — avoids heavy field serialization."""

    reading_progress = serializers.FloatField(read_only=True)

    class Meta:
        model = Book
        fields = [
            "id",
            "title",
            "author",
            "genre",
            "reading_status",
            "reading_progress",
            "cover_image_url",
            "created_at",
            "updated_at",
        ]


class BookDetailSerializer(serializers.ModelSerializer):
    """Full serializer for book detail views including all metadata."""

    reading_progress = serializers.FloatField(read_only=True)
    owner = serializers.ReadOnlyField(source="owner.username")

    class Meta:
        model = Book
        fields = [
            "id",
            "title",
            "author",
            "genre",
            "description",
            "cover_image_url",
            "isbn",
            "total_pages",
            "current_page",
            "reading_status",
            "reading_progress",
            "owner",
            "created_at",
            "updated_at",
        ]
        read_only_fields = ["owner", "created_at", "updated_at", "reading_progress"]

    def validate_title(self, value: str) -> str:
        """Ensure title is not just whitespace."""
        stripped = value.strip()
        if not stripped:
            msg = "Title cannot be empty."
            raise serializers.ValidationError(msg)
        return stripped

    def validate_author(self, value: str) -> str:
        """Ensure author is not just whitespace."""
        stripped = value.strip()
        if not stripped:
            msg = "Author cannot be empty."
            raise serializers.ValidationError(msg)
        return stripped

    def validate(self, attrs: dict) -> dict:
        """Business rules — handles both full creates and partial updates."""
        # Resolve effective values: use provided attrs, fall back to instance
        current_total = getattr(self.instance, "total_pages", None)
        current_current = getattr(self.instance, "current_page", None)
        total_pages = attrs.get("total_pages", current_total) or 0
        current_page = attrs.get("current_page", current_current) or 0
        reading_status = attrs.get("reading_status", None)

        if current_page > total_pages > 0:
            msg = "Current page cannot exceed total pages."
            raise serializers.ValidationError({"current_page": msg})

        if reading_status == ReadingStatus.FINISHED:
            if total_pages > 0:
                attrs["current_page"] = total_pages
            elif self.instance and self.instance.total_pages > 0:
                attrs["current_page"] = self.instance.total_pages

        return attrs


class BookWriteSerializer(BookDetailSerializer):
    """Alias for detail serializer — used for write operations with full validation."""

    pass