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 = []) {
    const nestedPaths = excludePaths.filter(
        (p) => p.startsWith(`${column}.`) && !p.includes("[]")
    );

    const arrayPaths = excludePaths.filter(
        (p) => p.startsWith(`${column}.`) && p.includes("[]")
    );

    // ─── Group array paths ──────────────────────────────────────────────────────
    // Separate bare array strips  → "personal_info.addresses[]"
    // from key-level strips       → "personal_info.addresses[].city"
    const bareArrayStrips = new Set();   // fields to remove entirely e.g. "addresses"
    const arrayGroups = {};          // fields to partially strip e.g. { addresses: ["city"] }

    for (const path of arrayPaths) {
        const stripped = path.replace(`${column}.`, "");   // "addresses[].city" or "addresses[]"

        if (stripped.endsWith("[]")) {
            // ─── Bare array strip — remove the whole field ─────────────────────────
            const arrayField = stripped.replace("[]", "");
            bareArrayStrips.add(arrayField);
        } else {
            // ─── Key-level strip — remove specific keys inside each element ────────
            const [arrayPart, key] = stripped.split("[].");   // ["addresses", "city"]
            const arrayField = arrayPart.replace("[]", "");

            // Skip if the whole array is already being stripped entirely
            if (bareArrayStrips.has(arrayField)) continue;

            if (!arrayGroups[arrayField]) arrayGroups[arrayField] = [];
            arrayGroups[arrayField].push(key);
        }
    }

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

    let literal = `"${column}"`;

    // ─── 1. Strip nested keys ───────────────────────────────────────────────────
    for (const path of nestedPaths) {
        const keys = path.replace(`${column}.`, "").split(".");
        literal = `(${literal} #- '{${keys.join(",")}}')`;
    }

    // ─── 2. Strip entire array fields ──────────────────────────────────────────
    for (const arrayField of bareArrayStrips) {
        literal = `(${literal} #- '{${arrayField}}')`;
    }

    // ─── 3. Strip specific keys inside array elements ──────────────────────────
    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 };