import { useState, useEffect, useRef } from 'react';
import { useParams, useNavigate } from 'react-router-dom';
import { Card } from '../../components/ui/card';
import { Button } from '../../components/ui/button';
import { Input } from '../../components/ui/input';
import { Label } from '../../components/ui/label';
import { Textarea } from '../../components/ui/textarea';
import { Switch } from '../../components/ui/switch';
import { Separator } from '../../components/ui/separator';
import { toast } from 'sonner';
import {
  HiOutlineArrowLeft,
  HiOutlineBookOpen,
  HiOutlineChevronRight,
  HiOutlinePhoto,
  HiOutlineTrash,
} from 'react-icons/hi2';
import courseService from '@/services/courseService';
import fileService from '@/services/fileService';

const MAX_IMAGE_BYTES = 5 * 1024 * 1024;

function CourseFormPage() {
  const { courseId } = useParams();
  const navigate = useNavigate();
  const isEditing = Boolean(courseId);
  const fileInputRef = useRef(null);

  const [form, setForm] = useState({
    courseCode: '',
    title: '',
    slug: '',
    description: '',
    image: '',
    isPublished: false,
  });
  const [imageUrl, setImageUrl] = useState('');
  const [uploading, setUploading] = useState(false);
  const [loading, setLoading] = useState(isEditing);
  const [saving, setSaving] = useState(false);
  const [error, setError] = useState(null);

  useEffect(() => {
    if (!isEditing) return;
    const fetchCourse = async () => {
      try {
        const data = await courseService.getById(courseId);
        setForm({
          courseCode: data.courseCode || '',
          title: data.title || '',
          slug: data.slug || '',
          description: data.description || '',
          image: data.image || '',
          isPublished: data.isPublished || false,
        });
        setImageUrl(data.imageUrl || data.image || '');
      } catch (err) {
        setError(err.message || 'Failed to load course');
      } finally {
        setLoading(false);
      }
    };
    fetchCourse();
  }, [courseId, isEditing]);

  const handleChange = (field, value) => {
    setForm((prev) => ({ ...prev, [field]: value }));
  };

  const handleImagePick = async (event) => {
    const file = event.target.files?.[0];
    event.target.value = '';
    if (!file) return;
    if (!file.type.startsWith('image/')) {
      toast.error('Only image files are allowed');
      return;
    }
    if (file.size > MAX_IMAGE_BYTES) {
      toast.error('Image must not exceed 5MB');
      return;
    }
    setUploading(true);
    try {
      const uploaded = await fileService.upload(file, 'courses');
      handleChange('image', uploaded.objectKey);
      setImageUrl(uploaded.url);
    } catch {
      // global API interceptor already surfaced the error toast
    } finally {
      setUploading(false);
    }
  };

  const handleRemoveImage = () => {
    handleChange('image', '');
    setImageUrl('');
  };

  const generateSlug = () => {
    const slug = form.title
      .toLowerCase()
      .normalize('NFD')
      .replace(/[\u0300-\u036f]/g, '')
      .replace(/đ/g, 'd')
      .replace(/[^a-z0-9\s-]/g, '')
      .replace(/\s+/g, '-')
      .replace(/-+/g, '-')
      .trim();
    handleChange('slug', slug);
  };

  const handleSave = async (publish) => {
    if (!form.courseCode.trim() || !form.title.trim()) {
      setError('Course code and title are required');
      return;
    }
    setSaving(true);
    setError(null);
    try {
      const payload = { ...form, isPublished: publish };
      if (isEditing) {
        await courseService.update(courseId, payload);
      } else {
        const created = await courseService.create(payload);
        navigate(`/courses/detail/${created.id}`);
        return;
      }
      navigate(`/courses/detail/${courseId}`);
    } catch (err) {
      setError(err.message || 'Failed to save course');
    } finally {
      setSaving(false);
    }
  };

  if (loading) {
    return (
      <>
        <div className="flex items-center justify-center py-20 text-app-text-muted">Loading course...</div>
      </>
    );
  }

  return (
    <>
      <div className="max-w-4xl mx-auto px-6 py-8">
        {/* Breadcrumb */}
        <div className="flex items-center gap-2 text-sm text-app-text-muted mb-4">
          <button
            onClick={() => navigate('/courses')}
            className="hover:text-app-primary transition-colors flex items-center gap-1"
          >
            <HiOutlineBookOpen className="w-4 h-4" />
            Courses
          </button>
          <HiOutlineChevronRight className="w-3.5 h-3.5" />
          <span className="font-medium text-app-text">
            {isEditing ? 'Edit Course' : 'New Course'}
          </span>
        </div>

        {/* Header */}
        <div className="flex flex-row items-center justify-between mb-6">
          <h2 className="text-xl font-bold text-app-text">
            {isEditing ? 'Edit Course' : 'Create New Course'}
          </h2>
          <div className="flex items-center gap-2">
            <Button
              variant="outline"
              className="rounded-xl bg-app-surface-muted text-app-text hover:bg-app-interactive-hover"
              onClick={() => navigate(isEditing ? `/courses/detail/${courseId}` : '/courses')}
              disabled={saving}
            >
              <HiOutlineArrowLeft className="w-4 h-4 mr-2" />
              Cancel
            </Button>
            <Button
              variant="outline"
              className="rounded-xl bg-app-surface-muted text-app-text hover:bg-app-interactive-hover"
              onClick={() => handleSave(false)}
              disabled={saving || uploading}
            >
              {saving ? 'Saving...' : 'Save Draft'}
            </Button>
            <Button
              className="rounded-xl bg-app-primary text-white hover:bg-app-primary-dark"
              onClick={() => handleSave(true)}
              disabled={saving || uploading}
            >
              {saving ? 'Saving...' : isEditing ? 'Update & Publish' : 'Save & Publish'}
            </Button>
          </div>
        </div>

        <Separator className="mb-6" />

        {error && (
          <div className="mb-4 p-3 rounded-xl bg-red-50 border border-red-200 text-red-700 text-sm">
            {error}
          </div>
        )}

        <Card
          className="rounded-xl border border-app-border bg-white overflow-hidden"
          style={{ boxShadow: 'rgba(0,0,0,0.03) 0px 4px 24px' }}
        >
          <div className="p-5 border-b border-app-border">
            <h4 className="font-semibold text-app-text">Course Details</h4>
          </div>
          <div className="p-5 space-y-4">
            <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
              <div>
                <Label className="mb-1.5 block text-app-text text-xs font-semibold uppercase tracking-wider">
                  Course Code <span className="text-red-500">*</span>
                </Label>
                <Input
                  placeholder="e.g. LDR-101"
                  value={form.courseCode}
                  onChange={(e) => handleChange('courseCode', e.target.value)}
                  className="rounded-xl bg-app-surface-muted border-0 focus:bg-white focus:ring-2 focus:ring-app-primary"
                />
              </div>
              <div>
                <Label className="mb-1.5 block text-app-text text-xs font-semibold uppercase tracking-wider">
                  Title <span className="text-red-500">*</span>
                </Label>
                <Input
                  placeholder="Course title"
                  value={form.title}
                  onChange={(e) => handleChange('title', e.target.value)}
                  className="rounded-xl bg-app-surface-muted border-0 focus:bg-white focus:ring-2 focus:ring-app-primary"
                />
              </div>
            </div>

            <div>
              <div className="flex items-center justify-between mb-1.5">
                <Label className="block text-app-text text-xs font-semibold uppercase tracking-wider">
                  Slug
                </Label>
                <button
                  type="button"
                  onClick={generateSlug}
                  className="text-app-primary hover:underline text-xs font-medium"
                >
                  Auto-generate from title
                </button>
              </div>
              <div className="flex rounded-xl overflow-hidden bg-app-surface-muted">
                <span className="px-4 py-2 text-app-text-muted font-mono text-sm bg-app-border/30 flex items-center select-none">
                  /courses/
                </span>
                <Input
                  value={form.slug}
                  onChange={(e) => handleChange('slug', e.target.value)}
                  className="border-0 bg-transparent font-mono focus:ring-0 focus:bg-transparent"
                />
              </div>
            </div>

            <div>
              <Label className="mb-1.5 block text-app-text text-xs font-semibold uppercase tracking-wider">
                Description
              </Label>
              <Textarea
                placeholder="Course description..."
                rows={4}
                value={form.description}
                onChange={(e) => handleChange('description', e.target.value)}
                className="rounded-xl bg-app-surface-muted border-0 focus:bg-white focus:ring-2 focus:ring-app-primary resize-none"
              />
            </div>

            <div>
              <Label className="mb-1.5 block text-app-text text-xs font-semibold uppercase tracking-wider">
                Image
              </Label>
              <div
                role="button"
                tabIndex={0}
                aria-label="Upload course image"
                onClick={() => !uploading && fileInputRef.current?.click()}
                onKeyDown={(e) => {
                  if ((e.key === 'Enter' || e.key === ' ') && !uploading) {
                    e.preventDefault();
                    fileInputRef.current?.click();
                  }
                }}
                className="group relative h-48 w-full cursor-pointer overflow-hidden rounded-xl border border-dashed border-app-border bg-app-surface-muted"
              >
                {imageUrl ? (
                  <>
                    <img src={imageUrl} alt="Course" className="h-full w-full object-cover" />
                    {!uploading && (
                      <div className="absolute inset-0 hidden items-center justify-center bg-black/40 text-sm font-medium text-white group-hover:flex">
                        Replace
                      </div>
                    )}
                    <button
                      type="button"
                      aria-label="Remove image"
                      onClick={(e) => {
                        e.stopPropagation();
                        handleRemoveImage();
                      }}
                      className="absolute right-3 top-3 flex h-8 w-8 items-center justify-center rounded-lg bg-white/90 text-red-500 shadow-sm hover:bg-white"
                    >
                      <HiOutlineTrash className="h-4 w-4" />
                    </button>
                  </>
                ) : (
                  <div className="flex h-full flex-col items-center justify-center gap-1 text-app-text-muted">
                    <HiOutlinePhoto className="h-8 w-8" />
                    <span className="text-sm font-medium text-app-text">Click to upload image</span>
                    <span className="text-xs">PNG, JPG, WEBP — max 5MB</span>
                  </div>
                )}
                {uploading && (
                  <div className="absolute inset-0 flex items-center justify-center bg-black/40 text-sm font-medium text-white">
                    Uploading...
                  </div>
                )}
                <input
                  ref={fileInputRef}
                  type="file"
                  accept="image/*"
                  className="hidden"
                  onChange={handleImagePick}
                />
              </div>
            </div>

            <div className="flex items-center justify-between p-4 rounded-xl bg-app-surface-muted">
              <div className="flex flex-col">
                <span className="font-medium text-sm text-app-text">Published</span>
                <span className="text-xs text-app-text-muted">Make this course visible to students</span>
              </div>
              <Switch
                checked={form.isPublished}
                onCheckedChange={(checked) => handleChange('isPublished', checked)}
              />
            </div>
          </div>
        </Card>
      </div>
    </>
  );
}

export default CourseFormPage;