import { ref, watch, type Ref } from 'vue'

/** 是否为可提交的完整非负小数（空字符串视为清空） */
export function isCompleteDecimalInput(raw: string): boolean {
  const trimmed = raw.trim()
  return trimmed === '' || /^\d+(\.\d+)?$/.test(trimmed)
}

export function parseDecimalInput(raw: string, precision?: number): number | null {
  const trimmed = raw.trim()
  if (!trimmed) return null
  if (!/^\d+(\.\d+)?$/.test(trimmed)) return null
  const num = Number(trimmed)
  if (!Number.isFinite(num) || num < 0) return null
  if (precision == null) return num
  return Number(num.toFixed(precision))
}

function formatDecimalDisplay(val: number, precision?: number): string {
  if (precision == null) return String(val)
  return Number(val.toFixed(precision)).toString()
}

function sanitizeDecimalText(raw: string): string {
  let text = raw.replace(/[^\d.]/g, '')
  const dotIndex = text.indexOf('.')
  if (dotIndex >= 0) {
    text = text.slice(0, dotIndex + 1) + text.slice(dotIndex + 1).replace(/\./g, '')
  }
  return text
}

/**
 * 将 number | null 与 el-input 文本双向绑定；
 * 仅在完整小数或清空时写入 source，避免打断输入，同时保证运费计算 watch 能触发。
 */
export function useDecimalInputBinding(
  source: Ref<number | null>,
  options?: { precision?: number; onCommit?: () => void }
) {
  const text = ref('')

  watch(
    source,
    (val) => {
      const next =
        val == null || Number.isNaN(Number(val))
          ? ''
          : formatDecimalDisplay(Number(val), options?.precision)
      if (text.value !== next) text.value = next
    },
    { immediate: true }
  )

  function commitFromText(raw: string, force = false) {
    const sanitized = sanitizeDecimalText(raw)
    text.value = sanitized
    if (!force && !isCompleteDecimalInput(sanitized)) return
    const parsed = parseDecimalInput(sanitized, options?.precision)
    const prev = source.value
    const changed =
      parsed == null ? prev != null : prev == null || Math.abs(Number(prev) - parsed) > 1e-9
    source.value = parsed
    if (parsed != null) {
      text.value = formatDecimalDisplay(parsed, options?.precision)
    } else if (force) {
      text.value = ''
    }
    if (changed) options?.onCommit?.()
  }

  function handleInput(val: string) {
    commitFromText(val, false)
  }

  function handleBlur() {
    commitFromText(text.value, true)
  }

  return { text, handleInput, handleBlur }
}