const { Sequelize } = require('sequelize')

/**
 * Strips a key from every element in a JSONB array using PostgreSQL's
 * jsonb_agg + #- operator in a subquery.
 *
 * @param {string} column - JSONB column e.g. "personal_info"
 * @param {string} arrayField - array field name e.g. "addresses"
 * @param {string[]} keys - keys to strip from each array element e.g. ["street", "zip"]
 * @returns {string} SQL fragment
 */
function buildArrayStrip(column, arrayField, keys) {
    const keyRemovals = keys.reduce(
        (acc, key) => `(${acc} #- '{${key}}')`,
        "elem"
    );

    return `(
    SELECT jsonb_agg(${keyRemovals})
    FROM jsonb_array_elements("${column}"->'${arrayField}') AS elem
  )`;
}

/**
 * Builds a Sequelize literal that strips JSONB paths at the DB level.
 * Supports:
 *  - nested keys:        "personal_info.name.given_name"
 *  - array item keys:    "personal_info.addresses[].street"
 *
 * @param {string} column - JSONB column name e.g. "personal_info"
 * @param {string[]} excludePaths - dot-notation paths
 * @returns {Array|null} Sequelize literal attribute tuple
 */
function excludeJsonbPaths(column, excludePaths = []) {
    // Separate nested paths from array paths
    const nestedPaths = excludePaths.filter(
        (p) => p.startsWith(`${column}.`) && !p.includes("[]")
    );
    const arrayPaths = excludePaths.filter(
        (p) => p.startsWith(`${column}.`) && p.includes("[]")
    );

    // Group array paths by their field name
    // e.g. { addresses: ["street", "zip"], phone_number: ["country_code"] }
    const arrayGroups = {};
    for (const path of arrayPaths) {
        const stripped = path.replace(`${column}.`, "");          // addresses[].street
        const [arrayField, key] = stripped.split("[].");           // ["addresses", "street"]
        if (!arrayGroups[arrayField]) arrayGroups[arrayField] = [];
        arrayGroups[arrayField].push(key);
    }

    if (!nestedPaths.length && !Object.keys(arrayGroups).length) return null;

    // Start with the column and chain #- for nested paths
    let literal = `"${column}"`;

    // Strip nested keys first
    for (const path of nestedPaths) {
        const keys = path.replace(`${column}.`, "").split(".");
        literal = `(${literal} #- '{${keys.join(",")}}')`;
    }

    // Then rebuild array fields with stripped keys using jsonb_set
    for (const [arrayField, keys] of Object.entries(arrayGroups)) {
        const arrayStrip = buildArrayStrip(column, arrayField, keys);
        literal = `jsonb_set(${literal}, '{${arrayField}}', COALESCE(${arrayStrip}, '[]'))`;
    }

    return [Sequelize.literal(literal), column];
}

module.exports = { excludeJsonbPaths };