import { Exam } from "@/interfaces/exam";
import { diff, Diff } from "deep-diff";

const EXCLUDED_FIELDS = new Set(["_id", "id", "createdAt", "createdBy", "entities", "isDiagnostic", "private"]);

export function generateExamDifferences(oldExam: Exam, newExam: Exam): string[] {
    const differences = diff(oldExam, newExam) || [];
    return differences.map((change) => formatDifference(change)).filter(Boolean) as string[];
}

function formatDifference(change: Diff<any, any>): string | undefined {
    if (!change.path) {
        return;
    }

    if (change.path.some((segment) => EXCLUDED_FIELDS.has(segment))) {
        return;
    }

    // Convert path array to something human-readable
    const pathString = change.path.join(" \u2192 "); // e.g. "parts → 0 → exercises → 1 → prompt"

    switch (change.kind) {
        case "N":
            // A new property/element was added
            return `\u{2022} Added \`${pathString}\` with value: ${formatValue(change.rhs)}`;

        case "D":
            // A property/element was deleted
            return `\u{2022} Removed \`${pathString}\` which had value: ${formatValue(change.lhs)}`;

        case "E":
            // A property/element was edited
            return `\u{2022} Changed \`${pathString}\` from ${formatValue(change.lhs)} to ${formatValue(change.rhs)}`;

        case "A":
            // An array change; change.item describes what happened at array index change.index
            return formatArrayChange(change);

        default:
            return;
    }
}

function formatArrayChange(change: Diff<any, any>): string | undefined {
    if (!change.path) return;
    if (change.path.some((segment) => EXCLUDED_FIELDS.has(segment))) {
        return;
    }
    
    const pathString = change.path.join(" \u2192 ");

    const arrayChange = (change as any).item;
    const idx = (change as any).index;

    if (!arrayChange) return;

    switch (arrayChange.kind) {
        case "N":
            return `\u{2022} Added an item at index [${idx}] in \`${pathString}\`: ${formatValue(arrayChange.rhs)}`;
        case "D":
            return `\u{2022} Removed an item at index [${idx}] in \`${pathString}\`: ${formatValue(arrayChange.lhs)}`;
        case "E":
            return `\u{2022} Edited an item at index [${idx}] in \`${pathString}\` from ${formatValue(arrayChange.lhs)} to ${formatValue(arrayChange.rhs)}`;
        case "A":
            // Nested array changes could happen theoretically; handle or ignore similarly
            return `\u{2022} Complex array change at index [${idx}] in \`${pathString}\`: ${JSON.stringify(arrayChange)}`;
        default:
            return;
    }
}

function formatValue(value: any): string {
    if (value === null) return "null";
    if (value === undefined) return "undefined";
    if (typeof value === "object") {
        try {
            return JSON.stringify(value);
        } catch {
            return String(value);
        }
    }
    return JSON.stringify(value);
}