'use client'

import React, { useState, useEffect, useMemo } from 'react'
import { useSDK } from '@/lib/sdk'
import { StepHeader, STEP_EXPLANATIONS } from '@/components/sdk/StepHeader'
import {
  Course,
  CourseCategory,
  Enrollment,
  EnrollmentStatus,
  AcademyStatistics,
  isEnrollmentOverdue,
  getDaysUntilDeadline
} from '@/lib/sdk/academy/types'
import {
  fetchSDKAcademyList, generateAllCourses, fetchCertificates,
  deleteEnrollment, completeEnrollment
} from '@/lib/sdk/academy/api'
import type { Certificate } from '@/lib/sdk/academy/types'
import { Tab, TabId } from './_types'
import { TabNavigation, StatCard, FilterBar } from './_components/shared'
import { CourseCard } from './_components/CourseCard'
import { EnrollmentCard } from './_components/EnrollmentCard'
import { CertificatesTab } from './_components/CertificatesTab'
import { EnrollmentEditModal } from './_components/EnrollmentEditModal'
import { CourseEditModal } from './_components/CourseEditModal'
import { SettingsTab } from './_components/SettingsTab'
import {
  HeaderActions,
  GenerationResultBar,
  LoadingSpinner,
  OverdueAlert,
  InfoBox,
  EmptyCourses,
  EmptyEnrollments
} from './_components/PageSections'

// =============================================================================
// MAIN PAGE
// =============================================================================

export default function AcademyPage() {
  const { state } = useSDK()
  const [activeTab, setActiveTab] = useState<TabId>('overview')
  const [courses, setCourses] = useState<Course[]>([])
  const [enrollments, setEnrollments] = useState<Enrollment[]>([])
  const [certificates, setCertificates] = useState<Certificate[]>([])
  const [statistics, setStatistics] = useState<AcademyStatistics | null>(null)
  const [isLoading, setIsLoading] = useState(true)
  const [isGenerating, setIsGenerating] = useState(false)
  const [generateResult, setGenerateResult] = useState<{ generated: number; skipped: number; errors: string[] } | null>(null)

  // Modal states
  const [editingEnrollment, setEditingEnrollment] = useState<Enrollment | null>(null)
  const [editingCourse, setEditingCourse] = useState<Course | null>(null)
  const [settingsSaved, setSettingsSaved] = useState(false)

  // Filters
  const [selectedCategory, setSelectedCategory] = useState<CourseCategory | 'all'>('all')
  const [selectedStatus, setSelectedStatus] = useState<EnrollmentStatus | 'all'>('all')
  const [certSearch, setCertSearch] = useState('')

  // Load data from SDK backend
  useEffect(() => {
    loadData()
  }, [])

  // Calculate tab counts
  const tabCounts = useMemo(() => {
    return {
      courses: courses.length,
      enrollments: enrollments.filter(e => e.status !== 'completed').length,
      certificates: certificates.length || enrollments.filter(e => e.certificateId).length,
      overdue: enrollments.filter(e => isEnrollmentOverdue(e)).length
    }
  }, [courses, enrollments, certificates])

  // Filtered courses
  const filteredCourses = useMemo(() => {
    let filtered = [...courses]

    if (selectedCategory !== 'all') {
      filtered = filtered.filter(c => c.category === selectedCategory)
    }

    return filtered.sort((a, b) => new Date(b.updatedAt).getTime() - new Date(a.updatedAt).getTime())
  }, [courses, selectedCategory])

  // Filtered enrollments
  const filteredEnrollments = useMemo(() => {
    let filtered = [...enrollments]

    if (selectedStatus !== 'all') {
      filtered = filtered.filter(e => e.status === selectedStatus)
    }

    // Sort: overdue first, then by deadline
    return filtered.sort((a, b) => {
      const aOverdue = isEnrollmentOverdue(a) ? -1 : 0
      const bOverdue = isEnrollmentOverdue(b) ? -1 : 0
      if (aOverdue !== bOverdue) return aOverdue - bOverdue
      return getDaysUntilDeadline(a.deadline) - getDaysUntilDeadline(b.deadline)
    })
  }, [enrollments, selectedStatus])

  // Enrollment counts per course
  const enrollmentCountByCourseId = useMemo(() => {
    const counts: Record<string, number> = {}
    enrollments.forEach(e => {
      counts[e.courseId] = (counts[e.courseId] || 0) + 1
    })
    return counts
  }, [enrollments])

  // Course name lookup
  const courseNameById = useMemo(() => {
    const map: Record<string, string> = {}
    courses.forEach(c => { map[c.id] = c.title })
    return map
  }, [courses])

  const tabs: Tab[] = [
    { id: 'overview', label: 'Uebersicht' },
    { id: 'courses', label: 'Kurse', count: tabCounts.courses, countColor: 'bg-blue-100 text-blue-600' },
    { id: 'enrollments', label: 'Einschreibungen', count: tabCounts.enrollments, countColor: 'bg-yellow-100 text-yellow-600' },
    { id: 'certificates', label: 'Zertifikate', count: tabCounts.certificates, countColor: 'bg-green-100 text-green-600' },
    { id: 'settings', label: 'Einstellungen' }
  ]

  const stepInfo = STEP_EXPLANATIONS['academy']

  const loadData = async () => {
    setIsLoading(true)
    try {
      const [data, certs] = await Promise.allSettled([
        fetchSDKAcademyList(),
        fetchCertificates(),
      ])
      if (data.status === 'fulfilled') {
        setCourses(data.value.courses)
        setEnrollments(data.value.enrollments)
        setStatistics(data.value.statistics)
      } else {
        console.error('Failed to load Academy data:', data.reason)
      }
      if (certs.status === 'fulfilled') {
        setCertificates(certs.value)
      }
    } finally {
      setIsLoading(false)
    }
  }

  const handleCompleteEnrollment = async (id: string) => {
    try {
      await completeEnrollment(id)
      await loadData()
    } catch (e) {
      console.error('Failed to complete enrollment:', e)
    }
  }

  const handleDeleteEnrollment = async (id: string) => {
    if (!window.confirm('Einschreibung wirklich loeschen?')) return
    try {
      await deleteEnrollment(id)
      await loadData()
    } catch (e) {
      console.error('Failed to delete enrollment:', e)
    }
  }

  const handleGenerateAll = async () => {
    setIsGenerating(true)
    setGenerateResult(null)
    try {
      const result = await generateAllCourses()
      setGenerateResult({ generated: result.generated, skipped: result.skipped, errors: result.errors || [] })
      // Reload data to show new courses
      await loadData()
    } catch (error) {
      console.error('Failed to generate courses:', error)
      setGenerateResult({ generated: 0, skipped: 0, errors: [error instanceof Error ? error.message : 'Fehler bei der Generierung'] })
    } finally {
      setIsGenerating(false)
    }
  }

  const clearFilters = () => {
    setSelectedCategory('all')
    setSelectedStatus('all')
  }

  return (
    <div className="space-y-6">
      {/* Step Header */}
      <StepHeader
        stepId="academy"
        title={stepInfo?.title || 'Compliance Academy'}
        description={stepInfo?.description || 'E-Learning Plattform fuer Compliance-Schulungen'}
        explanation={stepInfo?.explanation}
        tips={stepInfo?.tips}
      >
        <HeaderActions isGenerating={isGenerating} onGenerateAll={handleGenerateAll} />
      </StepHeader>

      {/* Generation Result */}
      {generateResult && <GenerationResultBar result={generateResult} />}

      {/* Tab Navigation */}
      <TabNavigation
        tabs={tabs}
        activeTab={activeTab}
        onTabChange={setActiveTab}
      />

      {/* Loading State */}
      {isLoading ? (
        <LoadingSpinner />
      ) : activeTab === 'settings' ? (
        <SettingsTab onSaved={() => { setSettingsSaved(true); setTimeout(() => setSettingsSaved(false), 2000) }} saved={settingsSaved} />
      ) : activeTab === 'certificates' ? (
        <CertificatesTab certificates={certificates} certSearch={certSearch} onSearchChange={setCertSearch} />
      ) : (
        <>
          {/* Statistics (Overview Tab) */}
          {activeTab === 'overview' && statistics && (
            <div className="grid grid-cols-1 md:grid-cols-4 gap-4">
              <StatCard
                label="Kurse gesamt"
                value={statistics.totalCourses}
                color="gray"
              />
              <StatCard
                label="Aktive Teilnehmer"
                value={(statistics.byStatus?.in_progress || 0) + (statistics.byStatus?.not_started || 0)}
                color="blue"
              />
              <StatCard
                label="Abschlussrate"
                value={`${statistics.completionRate}%`}
                color="green"
              />
              <StatCard
                label="Ueberfaellig"
                value={statistics.overdueCount}
                color={statistics.overdueCount > 0 ? 'red' : 'green'}
              />
            </div>
          )}

          {/* Overdue Alert */}
          {tabCounts.overdue > 0 && (
            <OverdueAlert
              count={tabCounts.overdue}
              onShow={() => {
                setActiveTab('enrollments')
                setSelectedStatus('all')
              }}
            />
          )}

          {/* Info Box (Overview Tab) */}
          {activeTab === 'overview' && <InfoBox />}

          {/* Filters */}
          <FilterBar
            selectedCategory={selectedCategory}
            selectedStatus={selectedStatus}
            onCategoryChange={setSelectedCategory}
            onStatusChange={setSelectedStatus}
            onClear={clearFilters}
          />

          {/* Courses Tab */}
          {(activeTab === 'overview' || activeTab === 'courses') && (
            <div className="space-y-4">
              {activeTab === 'courses' && (
                <h2 className="text-lg font-semibold text-gray-900">Kurse ({filteredCourses.length})</h2>
              )}
              {filteredCourses.map(course => (
                <CourseCard
                  key={course.id}
                  course={course}
                  enrollmentCount={enrollmentCountByCourseId[course.id] || 0}
                  onEdit={setEditingCourse}
                />
              ))}
            </div>
          )}

          {/* Enrollments Tab */}
          {activeTab === 'enrollments' && (
            <div className="space-y-4">
              <h2 className="text-lg font-semibold text-gray-900">Einschreibungen ({filteredEnrollments.length})</h2>
              {filteredEnrollments.map(enrollment => (
                <EnrollmentCard
                  key={enrollment.id}
                  enrollment={enrollment}
                  courseName={courseNameById[enrollment.courseId] || 'Unbekannter Kurs'}
                  onEdit={setEditingEnrollment}
                  onComplete={handleCompleteEnrollment}
                  onDelete={handleDeleteEnrollment}
                />
              ))}
            </div>
          )}

          {/* Empty States */}
          {activeTab === 'courses' && filteredCourses.length === 0 && (
            <EmptyCourses selectedCategory={selectedCategory} onClearFilters={clearFilters} />
          )}

          {activeTab === 'enrollments' && filteredEnrollments.length === 0 && (
            <EmptyEnrollments selectedStatus={selectedStatus} onClearFilters={clearFilters} />
          )}
        </>
      )}

      {/* Enrollment Edit Modal */}
      {editingEnrollment && (
        <EnrollmentEditModal
          enrollment={editingEnrollment}
          onClose={() => setEditingEnrollment(null)}
          onSaved={() => { setEditingEnrollment(null); loadData() }}
        />
      )}

      {/* Course Edit Modal */}
      {editingCourse && (
        <CourseEditModal
          course={editingCourse}
          onClose={() => setEditingCourse(null)}
          onSaved={() => { setEditingCourse(null); loadData() }}
        />
      )}
    </div>
  )
}