from django import forms
from django.contrib import admin, messages
from django.db import transaction
from django.db.models import Max

from .models import Resource, ResourceCheckpoint, SkillResource


class SkillResourceInline(admin.TabularInline):
    model = SkillResource
    extra = 1
    autocomplete_fields = ['skill']


class ResourceCheckpointInline(admin.TabularInline):
    model = ResourceCheckpoint
    extra = 0
    fields = ('order_index', 'title', 'url_fragment', 'estimated_minutes', 'source')
    ordering = ('order_index',)


class ResourceAdminForm(forms.ModelForm):
    bulk_checkpoints = forms.CharField(
        required=False,
        widget=forms.Textarea(attrs={'rows': 12, 'cols': 80}),
        label='Bulk add checkpoints',
        help_text=(
            'Paste module/lesson titles, one per line (source=manual). '
            'Only applied when this resource has NO checkpoints yet; if it '
            'already has any, the paste is ignored — edit the inline rows '
            'below instead. Blank lines ignored.'
        ),
    )

    class Meta:
        model = Resource
        exclude = ['skills']


@admin.register(Resource)
class ResourceAdmin(admin.ModelAdmin):
    form = ResourceAdminForm
    list_display = ('title', 'provider', 'type', 'difficulty_level', 'duration', 'rating')
    list_filter = ('provider', 'type', 'difficulty_level')
    search_fields = ('title', 'provider', 'url')
    inlines = [SkillResourceInline, ResourceCheckpointInline]
    fieldsets = (
        (None, {
            'fields': ('title', 'provider', 'url', 'type', 'difficulty_level',
                       'duration', 'rating'),
        }),
        ('Bulk checkpoint paste', {
            'classes': ('collapse',),
            'fields': ('bulk_checkpoints',),
            'description': 'Optional shortcut for adding multiple checkpoints at once.',
        }),
    )

    def save_model(self, request, obj, form, change):
        bulk = (form.cleaned_data.get('bulk_checkpoints') or '').strip()
        lines = [line.strip() for line in bulk.splitlines() if line.strip()] if bulk else []

        with transaction.atomic():
            super().save_model(request, obj, form, change)
            if not lines:
                return
            # Refuse to append when checkpoints already exist — the admin
            # should use the inline to edit existing rows. This prevents
            # accidental duplication and silent orphaning of
            # UserCheckpointProgress rows when the admin re-edits the list.
            if obj.checkpoints.exists():
                self.message_user(
                    request,
                    "Bulk paste ignored: this resource already has checkpoints. "
                    "Edit them via the inline below instead.",
                    level=messages.WARNING,
                )
                return
            current_max = obj.checkpoints.aggregate(m=Max('order_index'))['m'] or 0
            ResourceCheckpoint.objects.bulk_create([
                ResourceCheckpoint(
                    resource=obj,
                    order_index=current_max + offset,
                    title=line,
                    source='manual',
                )
                for offset, line in enumerate(lines, start=1)
            ])
            self.message_user(
                request,
                f"Added {len(lines)} checkpoint(s) via bulk paste.",
                level=messages.SUCCESS,
            )


@admin.register(ResourceCheckpoint)
class ResourceCheckpointAdmin(admin.ModelAdmin):
    list_display = ('resource', 'order_index', 'title', 'source', 'estimated_minutes')
    list_filter = ('source', 'resource__provider')
    search_fields = ('title', 'resource__title')
    ordering = ('resource', 'order_index')


@admin.register(SkillResource)
class SkillResourceAdmin(admin.ModelAdmin):
    list_display = ('skill', 'resource', 'relevance_score')
    list_filter = ('skill__category',)
    search_fields = ('skill__skill_name', 'resource__title')
    autocomplete_fields = ['skill', 'resource']