// 处理数组diff 返回数组变更
import { uniqueArr } from "./util";

export interface Add {
    before: {
        key: any,
        arr: any[],
    },
    after: {
        key: any,
        arr: any[],
    },
}

export default function diff(oldArr = [], newArr = [], isKeyExist = true) {
    newArr = uniqueArr(newArr)
    // getDelete
    let deleteArr = []
    let keepArr = []
    let deleteAll = false // 是否删除所有元素
    let addAll = false
    let prevIndex = -2
    let add: Add

    if (!isKeyExist) {
        return {
            del: {
                arr: oldArr,
            },
            add: {
                before: {
                    key: null,
                    arr: newArr,
                },
                after: {
                    key: null,
                    arr: [],
                }
            }
        }
    }

    for (let i= 0; i < oldArr.length; i++) {
        const item = oldArr[i]
        const INDEX = newArr.indexOf(item)
        // console.log(INDEX, item)
        if (INDEX < 0) {
            deleteArr.push(item)
        } else {
            // 判断是否在newArr中连续出现
            if (prevIndex !== -2 && prevIndex+1 !== INDEX) {
                deleteAll = true
                addAll = true
                deleteArr = oldArr
                keepArr = []
                break
            } else {
                keepArr.push(item)
            }
            prevIndex = INDEX
        }
    }

    if (addAll || !keepArr.length) {
        add = {
            before: {
                key: null,
                arr: newArr,
            },
            after: {
                key: 0,
                arr: [],
            }
        }
    } else {
        const start = newArr.indexOf(keepArr[0])
        const end = newArr.indexOf(keepArr[keepArr.length - 1])
        add = {
            before: {
                key: keepArr[0],
                arr: newArr.slice(0, start)
            },
            after: {
                key: keepArr[keepArr.length - 1],
                arr: newArr.slice(end + 1)
            },
        }
    }
    
    // 计算新增数组
    return {
        del: {
            arr: deleteArr,
        }, 
        add,
    }
}