import type { StudentRecord } from '@/stores/students'
import { computed, type ComputedRef, ref, type Ref } from 'vue'

interface GradeOption {
  title: string
  value: number
}

interface StudentFormState {
  studentId: string
  name: string
  department: string
  grade: number
  enrollYear: number
  credits: number
  advisor: string
  email: string
  phone: string
  status: string
}

interface UseStudentMaintenanceFormOptions {
  departments: string[]
  gradeOptions: GradeOption[]
  enrollYears: number[]
  statuses: string[]
  students: ComputedRef<StudentRecord[]>
  editingId: Ref<number | null>
  highlightedId: Ref<number | null>
}

type SaveSummaryItem = {
  key: string
  label: string
  before: string | null
  after: string
}

const fieldLabels: Record<keyof StudentFormState, string> = {
  studentId: '學號',
  name: '姓名',
  department: '系所',
  grade: '年級',
  enrollYear: '入學年度',
  credits: '已修學分',
  advisor: '指導老師',
  email: 'Email',
  phone: '電話',
  status: '狀態',
}

function createDefaultForm(
  departments: string[],
  gradeOptions: GradeOption[],
  enrollYears: number[],
  statuses: string[]
): StudentFormState {
  return {
    studentId: '',
    name: '',
    department: departments[0] ?? '',
    grade: gradeOptions[0]?.value ?? 1,
    enrollYear: enrollYears[0] ?? 2024,
    credits: 0,
    advisor: '',
    email: '',
    phone: '',
    status: statuses[0] ?? '',
  }
}

function createEmptyFieldErrors() {
  return {
    studentId: [],
    name: [],
    department: [],
    grade: [],
    enrollYear: [],
    credits: [],
    advisor: [],
    email: [],
    phone: [],
    status: [],
  } as Record<keyof StudentFormState, string[]>
}

export function useStudentMaintenanceForm(options: UseStudentMaintenanceFormOptions) {
  const form = ref<StudentFormState>(
    createDefaultForm(
      options.departments,
      options.gradeOptions,
      options.enrollYears,
      options.statuses
    )
  )
  const initialForm = ref<StudentFormState>({ ...form.value })
  const fieldErrors = ref(createEmptyFieldErrors())

  const isDirty = computed(() => JSON.stringify(form.value) !== JSON.stringify(initialForm.value))

  function gradeLabel(grade: number) {
    return options.gradeOptions.find((option) => option.value === grade)?.title ?? `年級 ${grade}`
  }

  function formatSummaryValue(key: string, value: string | number | null | undefined) {
    if (value === null || value === undefined || value === '') return '—'
    if (key === 'grade') return gradeLabel(Number(value))
    return String(value)
  }

  const saveSummary = computed<SaveSummaryItem[]>(() => {
    const before = initialForm.value
    const after = form.value
    const entries = Object.keys(fieldLabels).map((key) => {
      const fieldKey = key as keyof StudentFormState
      return {
        key,
        label: fieldLabels[fieldKey],
        before: options.editingId.value ? formatSummaryValue(key, before[fieldKey]) : null,
        after: formatSummaryValue(key, after[fieldKey]),
      }
    })

    if (!options.editingId.value) return entries
    return entries.filter((entry) => entry.before !== entry.after)
  })

  const errorSummary = computed(() => {
    const entries = Object.entries(fieldErrors.value).flatMap(([field, messages]) =>
      messages.map((message) => ({ field, message }))
    )
    return entries.slice(0, 3)
  })

  function setForm(nextForm: StudentFormState) {
    form.value = { ...nextForm }
  }

  function syncInitialForm() {
    initialForm.value = { ...form.value }
  }

  function resetForm() {
    form.value = createDefaultForm(
      options.departments,
      options.gradeOptions,
      options.enrollYears,
      options.statuses
    )
    syncInitialForm()
    clearAllErrors()
  }

  function clearAllErrors() {
    fieldErrors.value = createEmptyFieldErrors()
  }

  function clearFieldError(field: keyof StudentFormState | string) {
    if (!fieldErrors.value[field as keyof StudentFormState]?.length) return
    fieldErrors.value[field as keyof StudentFormState] = []
  }

  function validateForm() {
    const errors: Array<{ field: keyof StudentFormState; message: string }> = []
    const studentId = form.value.studentId.trim()
    const name = form.value.name.trim()
    const email = form.value.email.trim()
    const credits = form.value.credits

    if (!studentId) errors.push({ field: 'studentId', message: '請輸入學號' })
    if (!name) errors.push({ field: 'name', message: '請輸入姓名' })
    if (!form.value.department) errors.push({ field: 'department', message: '請選擇系所' })
    if (!form.value.grade) errors.push({ field: 'grade', message: '請選擇年級' })
    if (!form.value.enrollYear) errors.push({ field: 'enrollYear', message: '請選擇入學年度' })
    if (credits === null || Number.isNaN(credits)) {
      errors.push({ field: 'credits', message: '請輸入已修學分' })
    } else if (credits < 0) {
      errors.push({ field: 'credits', message: '已修學分不可小於 0' })
    }
    if (!form.value.status) errors.push({ field: 'status', message: '請選擇狀態' })
    if (email && !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email)) {
      errors.push({ field: 'email', message: 'Email 格式不正確' })
    }

    const duplicate = options.students.value.find(
      (item) => item.studentId === studentId && item.id !== options.editingId.value
    )
    if (studentId && duplicate) {
      errors.push({ field: 'studentId', message: '學號已存在，請確認是否重複' })
    }

    return errors
  }

  function statusColor(status: string) {
    if (status === '在學') return 'success'
    if (status === '休學') return 'warning'
    if (status === '畢業') return 'secondary'
    return 'default'
  }

  function rowProps(data: { item: StudentRecord }) {
    return {
      class: data.item.id === options.highlightedId.value ? 'is-highlighted' : '',
    }
  }

  const isPlaceholderValue = (value: string | null) => value === '—'

  return {
    errorSummary,
    fieldErrors,
    form,
    initialForm,
    isDirty,
    isPlaceholderValue,
    saveSummary,
    clearAllErrors,
    clearFieldError,
    formatSummaryValue,
    gradeLabel,
    resetForm,
    rowProps,
    setForm,
    statusColor,
    syncInitialForm,
    validateForm,
  }
}

export type { SaveSummaryItem, StudentFormState }