from __future__ import annotations

from rest_framework import serializers

from apps.groups.models import (
    GroupBook,
    MemberProgress,
    ReadingGroup,
    ReadingGroupMembership,
    ReadingSchedule,
    Section,
)
from apps.books.serializers import EBookListSerializer


class ReadingGroupMembershipSerializer(serializers.ModelSerializer):
    user_email = serializers.CharField(source="user.email", read_only=True)
    user_username = serializers.CharField(source="user.username", read_only=True)

    class Meta:
        model = ReadingGroupMembership
        fields = [
            "id", "user", "user_email", "user_username",
            "role", "joined_at",
        ]
        read_only_fields = ["id", "joined_at"]


class ReadingGroupListSerializer(serializers.ModelSerializer):
    member_count = serializers.SerializerMethodField()
    admin_email = serializers.CharField(source="admin.email", read_only=True)

    class Meta:
        model = ReadingGroup
        fields = [
            "id", "name", "description", "admin", "admin_email",
            "member_count", "created_at", "updated_at",
        ]

    def get_member_count(self, obj: ReadingGroup) -> int:
        return obj.memberships.count()


class ReadingGroupDetailSerializer(serializers.ModelSerializer):
    admin_email = serializers.CharField(source="admin.email", read_only=True)
    members = ReadingGroupMembershipSerializer(source="memberships", many=True, read_only=True)

    class Meta:
        model = ReadingGroup
        fields = [
            "id", "name", "description", "admin", "admin_email",
            "members", "created_at", "updated_at",
        ]


class ReadingGroupCreateSerializer(serializers.ModelSerializer):
    class Meta:
        model = ReadingGroup
        fields = ["name", "description"]


class AddMemberSerializer(serializers.Serializer):
    user_id = serializers.IntegerField()

    def validate_user_id(self, value: int) -> int:
        from django.conf import settings
        User = settings.AUTH_USER_MODEL
        if not User.objects.filter(id=value).exists():
            raise serializers.ValidationError("User not found.")
        return value


class SectionSerializer(serializers.ModelSerializer):
    class Meta:
        model = Section
        fields = [
            "id", "title", "order", "start_chapter_index",
            "end_chapter_index", "estimated_reading_minutes", "created_at",
        ]
        read_only_fields = ["id", "created_at"]


class SectionAdjustSerializer(serializers.Serializer):
    """Payload for manual section adjustments (merge/split)."""
    operation = serializers.ChoiceField(choices=["merge", "split"])
    section_ids = serializers.ListField(
        child=serializers.IntegerField(), min_length=1,
        help_text="For merge: list of section IDs to merge. For split: [section_id] to split."
    )
    split_at = serializers.IntegerField(
        required=False, default=2, min_value=2,
        help_text="Number of new sections when splitting"
    )


class ReadingScheduleSerializer(serializers.ModelSerializer):
    section_details = serializers.SerializerMethodField()

    class Meta:
        model = ReadingSchedule
        fields = [
            "id", "meeting_number", "week_date", "section_ids",
            "section_details", "created_at",
        ]
        read_only_fields = ["id", "created_at"]

    def get_section_details(self, obj: ReadingSchedule) -> list[dict]:
        sections = Section.objects.filter(
            id__in=obj.section_ids, group_book=obj.group_book
        ).order_by("order")
        return SectionSerializer(sections, many=True).data


class MemberProgressSerializer(serializers.ModelSerializer):
    user_email = serializers.CharField(source="user.email", read_only=True)
    user_username = serializers.CharField(source="user.username", read_only=True)
    current_section_title = serializers.SerializerMethodField()

    class Meta:
        model = MemberProgress
        fields = [
            "id", "user", "user_email", "user_username",
            "current_section", "current_section_title",
            "completed_sections", "updated_at",
        ]
        read_only_fields = ["id", "updated_at"]

    def get_current_section_title(self, obj: MemberProgress) -> str | None:
        if obj.current_section:
            return obj.current_section.title
        return None


class GroupBookListSerializer(serializers.ModelSerializer):
    ebook = EBookListSerializer(read_only=True)
    uploaded_by_email = serializers.CharField(source="uploaded_by.email", read_only=True)
    section_count = serializers.SerializerMethodField()

    class Meta:
        model = GroupBook
        fields = [
            "id", "title", "status", "ebook", "uploaded_by",
            "uploaded_by_email", "section_count", "created_at", "updated_at",
        ]

    def get_section_count(self, obj: GroupBook) -> int:
        return obj.sections.count()


class GroupBookDetailSerializer(serializers.ModelSerializer):
    ebook = EBookListSerializer(read_only=True)
    uploaded_by_email = serializers.CharField(source="uploaded_by.email", read_only=True)
    sections = SectionSerializer(many=True, read_only=True)
    schedules = ReadingScheduleSerializer(source="schedules", many=True, read_only=True)

    class Meta:
        model = GroupBook
        fields = [
            "id", "group", "title", "status", "ebook",
            "uploaded_by", "uploaded_by_email",
            "sections", "schedules", "created_at", "updated_at",
        ]


class GroupBookCreateSerializer(serializers.Serializer):
    ebook_id = serializers.IntegerField()
    title = serializers.CharField(max_length=512, required=False)

    def validate_ebook_id(self, value: int) -> int:
        from apps.books.models import EBook
        if not EBook.objects.filter(id=value).exists():
            raise serializers.ValidationError("EBook not found.")
        # Check format is EPUB
        ebook = EBook.objects.get(id=value)
        if ebook.format != "epub":
            raise serializers.ValidationError("Only EPUB format is supported for group books.")
        return value

    def validate(self, data: dict) -> dict:
        request = self.context.get("request")
        if request and not data.get("title"):
            from apps.books.models import EBook
            ebook = EBook.objects.get(id=data["ebook_id"])
            data["title"] = ebook.title
        return data