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

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

const PATH_LABELS: Record<string, string> = {
    parts: "Parts",
    exercises: "Exercises",
    userSolutions: "User Solutions",
    words: "Words",
    options: "Options",
    prompt: "Prompt",
    text: "Text",
    audio: "Audio",
    script: "Script",
    difficulty: "Difficulty",
    shuffle: "Shuffle",
    solutions: "Solutions",
    variant: "Variant",
    prefix: "Prefix",
    suffix: "Suffix",
    topic: "Topic",
};

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_KEYS.has(segment))) {
        return;
    }

    const pathString = pathToHumanReadable(change.path);

    switch (change.kind) {
        case "N": // New property/element
            return `• Added ${pathString} with value: ${formatValue(change.rhs)}\n`;
        case "D": // Deleted property/element
            return `• Removed ${pathString} which had value: ${formatValue(change.lhs)}\n`;
        case "E": // Edited property/element
            return `• Changed ${pathString} from ${formatValue(change.lhs)} to ${formatValue(change.rhs)}\n`;
        case "A": // Array change
            return formatArrayChange(change);
        default:
            return;
    }
}

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

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

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

    if (!arrayChange) return;

    switch (arrayChange.kind) {
        case "N":
            return `• Added an item at [#${idx + 1}] in ${pathString}: ${formatValue(arrayChange.rhs)}\n`;
        case "D":
            return `• Removed an item at [#${idx + 1}] in ${pathString}: ${formatValue(arrayChange.lhs)}\n`;
        case "E":
            return `• Edited an item at [#${idx + 1}] in ${pathString} from ${formatValue(arrayChange.lhs)} to ${formatValue(arrayChange.rhs)}\n`;
        case "A":
            return `• Complex array change at [#${idx + 1}] in ${pathString}: ${JSON.stringify(arrayChange)}\n`;
        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,
                (key, val) => {
                    if (EXCLUDED_KEYS.has(key)) {
                        return undefined;
                    }
                    return val;
                },
                2 // optional indentation for readability
            );
        } catch {
            return String(value);
        }
    }

    return JSON.stringify(value);
}

/**
 * Convert an array of path segments into a friendlier string.
 * Example:
 *   ["parts", 0, "exercises", 1, "prompt"]
 * becomes:
 *   "Parts → [#1] → Exercises → [#2] → Prompt"
 */
function pathToHumanReadable(pathSegments: Array<string | number>): string {
    return pathSegments
        .map((seg) => {
            if (typeof seg === "number") {
                return `[#${seg + 1}]`;
            }
            return PATH_LABELS[seg] ?? seg;
        })
        .join(" → ");
}