from django.contrib import admin, messages
from django.forms import ModelForm, ValidationError as FormValidationError
from django.utils.html import format_html

from links.models import Click, ShortLink
from links.services import ValidationError, generate_code, validate_target_url

admin.site.site_header = "URL shortener"
admin.site.site_title = "Shortener admin"
admin.site.index_title = "Links and clicks"


class ShortLinkAdminForm(ModelForm):
    class Meta:
        model = ShortLink
        fields = "__all__"

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if "code" in self.fields:
            self.fields["code"].required = False
        if "created_by_token" in self.fields:
            self.fields["created_by_token"].required = False

    def clean_target_url(self):
        raw = self.cleaned_data.get("target_url") or ""
        try:
            return validate_target_url(raw)
        except ValidationError as exc:
            raise FormValidationError(str(exc)) from exc

    def clean(self):
        cleaned = super().clean()
        if not self.instance.pk and not cleaned.get("code"):
            cleaned["code"] = generate_code()
        if not cleaned.get("created_by_token"):
            cleaned["created_by_token"] = "admin"
        return cleaned


class ClickInline(admin.TabularInline):
    model = Click
    extra = 0
    can_delete = False
    show_change_link = True
    max_num = 0
    readonly_fields = ("occurred_at", "ip_hash", "user_agent", "referrer")
    fields = ("occurred_at", "ip_hash", "user_agent", "referrer")

    def has_add_permission(self, request, obj=None):
        return False


@admin.register(ShortLink)
class ShortLinkAdmin(admin.ModelAdmin):
    form = ShortLinkAdminForm
    list_display = (
        "code",
        "short_url_display",
        "target_url",
        "title",
        "is_active",
        "click_count",
        "created_by_token",
        "expires_at",
        "created_at",
    )
    list_filter = ("is_active", "created_by_token", "created_at")
    search_fields = ("code", "target_url", "external_ref", "title")
    date_hierarchy = "created_at"
    ordering = ("-created_at",)
    list_per_page = 50
    actions = ("disable_links",)
    inlines = (ClickInline,)
    readonly_fields = (
        "id",
        "code",
        "created_by_token",
        "click_count",
        "created_at",
        "updated_at",
        "short_url_display",
    )
    fieldsets = (
        (
            None,
            {
                "fields": (
                    "code",
                    "short_url_display",
                    "target_url",
                    "title",
                    "external_ref",
                    "is_active",
                    "expires_at",
                )
            },
        ),
        (
            "Attribution",
            {"fields": ("created_by_token", "click_count", "created_at", "updated_at", "id")},
        ),
    )

    def get_readonly_fields(self, request, obj=None):
        if obj:
            return self.readonly_fields + ("target_url",)
        return self.readonly_fields

    @admin.display(description="Short URL")
    def short_url_display(self, obj: ShortLink) -> str:
        if not obj.code:
            return "—"
        return format_html('<a href="{0}">{0}</a>', obj.public_short_url)

    def save_model(self, request, obj, form, change):
        if not change:
            if not obj.code:
                obj.code = generate_code()
            if not obj.created_by_token:
                obj.created_by_token = (
                    request.user.get_username() if request.user.is_authenticated else "admin"
                )
        super().save_model(request, obj, form, change)

    @admin.action(description="Disable selected links")
    def disable_links(self, request, queryset):
        updated = queryset.filter(is_active=True).update(is_active=False)
        self.message_user(
            request,
            f"Disabled {updated} link(s).",
            messages.SUCCESS if updated else messages.INFO,
        )


@admin.register(Click)
class ClickAdmin(admin.ModelAdmin):
    list_display = ("link", "occurred_at", "ip_hash_short", "user_agent_short")
    list_filter = ("occurred_at",)
    search_fields = ("link__code", "ip_hash", "user_agent", "referrer")
    date_hierarchy = "occurred_at"
    readonly_fields = ("id", "link", "occurred_at", "ip_hash", "user_agent", "referrer")
    ordering = ("-occurred_at",)

    def has_add_permission(self, request):
        return False

    def has_change_permission(self, request, obj=None):
        return False

    @admin.display(description="IP hash")
    def ip_hash_short(self, obj: Click) -> str:
        return (obj.ip_hash[:12] + "…") if obj.ip_hash else "—"

    @admin.display(description="User agent")
    def user_agent_short(self, obj: Click) -> str:
        ua = obj.user_agent or ""
        return (ua[:48] + "…") if len(ua) > 48 else (ua or "—")