在JavaScript中实现无数据库URL参数短链：一种客户端压缩编码方案

// 假设原始参数字符串
const originalParamsString = "urgency=all&impact=widespread&contentType=mine";

// 经过Gzip压缩和Base64编码后（此处仅为概念性示例，实际需引入压缩库）
// 结果可能类似：eNorLUpPzUuutE3MyVHLzC1ITC6xLc9MSS0uKEpNTFFLzs8rSc0rCaksSLXNzcxLBQCqJxIm
// 长度通常在50-100字符之间
const encodedString = "eNorLUpPzUuutE3MyVHLzC1ITC6xLc9MSS0uKEpNTFFLzs8rSc0rCaksSLXNzcxLBQCqJxIm";

// 1. 定义参数映射表
const paramMappings = {
    urgency: {
        all: 'a',
        high: 'h',
        medium: 'm',
        low: 'l'
    },
    impact: {
        widespread: 'w',
        local: 'o',
        minor: 'i'
    },
    contentType: {
        'image/jpeg': 'j', // 注意这里是完整的字符串值
        'document/pdf': 'd',
        'video/mp4': 'v'
    }
};

// 2. 定义参数的固定顺序
const paramOrder = ['urgency', 'impact', 'contentType'];

/**
 * 编码函数：将原始参数对象转换为压缩后的短字符串
 * @param {object} params - 包含原始参数键值对的对象
 * @returns {string} - 压缩后的短字符串
 */
function encodeParams(params) {
    let shortString = '';
    for (const key of paramOrder) {
        const value = params[key];
        if (paramMappings[key] && paramMappings[key][value]) {
            shortString += paramMappings[key][value];
        } else {
            // 处理未定义或未知参数值的情况
            // 策略1: 抛出错误 (严格模式)
            // throw new Error(`Unknown value '${value}' for parameter '${key}'`);
            // 策略2: 使用一个占位符 (如果允许部分编码)
            console.warn(`Warning: Unknown value '${value}' for parameter '${key}'. Using placeholder.`);
            shortString += '_'; // 使用下划线作为未知值的占位符
        }
    }
    return shortString;
}

/**
 * 解码函数：将压缩后的短字符串还原为原始参数对象
 * @param {string} shortString - 压缩后的短字符串
 * @returns {object} - 还原后的原始参数对象
 */
function decodeParams(shortString) {
    const params = {};
    for (let i = 0; i < shortString.length; i++) {
        const char = shortString[i];
        const paramName = paramOrder[i];

        if (!paramName) {
            console.warn(`Warning: Unexpected character '${char}' at position ${i}. Ignoring.`);
            continue; // 超出预设参数顺序的字符
        }

        let foundValue = null;
        const mappingForParam = paramMappings[paramName];
        if (mappingForParam) {
            for (const valueKey in mappingForParam) {
                if (mappingForParam[valueKey] === char) {
                    foundValue = valueKey;
                    break;
                }
            }
        }

        if (foundValue) {
            params[paramName] = foundValue;
        } else if (char === '_') {
            // 如果是占位符，可以设置为null或默认值
            params[paramName] = null;
        } else {
            console.warn(`Warning: Unknown encoded character '${char}' for parameter '${paramName}'.`);
            params[paramName] = null; // 或者设置为 undefined
        }
    }
    return params;
}

// 示例使用
const originalParams = {
    urgency: 'all',
    impact: 'widespread',
    contentType: 'image/jpeg'
};

// 编码
const encodedString = encodeParams(originalParams);
console.log("原始参数对象:", originalParams);
console.log("编码结果:", encodedString); // 预期输出: "awj"

// 构造短URL
const baseUrl = "https://www.someurl.com";
const shortUrl = `${baseUrl}?params=${encodedString}`;
console.log("生成的短URL:", shortUrl);

// 解码 (模拟从短URL中获取参数并解码)
const url = new URL(shortUrl);
const paramsFromUrl = url.searchParams.get('params');
const decodedParams = decodeParams(paramsFromUrl);
console.log("解码结果:", decodedParams);
// 预期输出: { urgency: 'all', impact: 'widespread', contentType: 'image/jpeg' }

// 带有未知值的编码示例
const paramsWithUnknown = {
    urgency: 'all',
    impact: 'critical', // 假设 'critical' 不在映射中
    contentType: 'image/jpeg'
};
const encodedWithUnknown = encodeParams(paramsWithUnknown);
console.log("编码结果 (含未知值):", encodedWithUnknown); // 预期输出: "a_j"
const decodedWithUnknown = decodeParams(encodedWithUnknown);
console.log("解码结果 (含未知值):", decodedWithUnknown); // 预期输出: { urgency: 'all', impact: null, contentType: 'image/jpeg' }