app.js

// app.js
const express = require("express");
const path = require("path");
require("dotenv").config();
const { GoogleGenAI } = require("@google/genai");

const app = express();

// Middleware
app.use(express.static(path.join(__dirname, "public")));
app.use(express.urlencoded({ extended: true }));
app.use(express.json());

// Homepage
app.get("/", (req, res) => {
    res.sendFile(path.join(__dirname, "public", "Homepage.html"));
});

// Main page
app.get("/mainpage", (req, res) => {
    res.sendFile(path.join(__dirname, "public", "Mainpage.html"));

});

/**
 * Generate fallback roadmap for technical or non-technical goals
 */
function generateFallbackRoadmap(goal) {
    const baseSteps = [
        {
            title: "Understand the Basics",
            description: `Learn and master the fundamental concepts of ${goal}.`,
            duration: `${2 + Math.floor(Math.random() * 3)} weeks`,
        },
        {
            title: "Explore Intermediate Topics",
            description: `Dive deeper into ${goal} concepts and techniques to build a solid foundation.`,
            duration: `${3 + Math.floor(Math.random() * 3)} weeks`,
        },
        {
            title: "Practice & Apply",
            description: `Work on exercises, mini-projects, or practical tasks to apply your ${goal} knowledge.`,
            duration: `${3 + Math.floor(Math.random() * 4)} weeks`,
        },
        {
            title: "Create a Portfolio",
            description: `Build real-world projects, presentations, or reports to showcase your skills in ${goal}.`,
            duration: `${4 + Math.floor(Math.random() * 4)} weeks`,
        },
        {
            title: "Review & Expand",
            description: `Evaluate progress, refine skills, and explore advanced resources to master ${goal}.`,
            duration: `${2 + Math.floor(Math.random() * 3)} weeks`,
        },
    ];

    return baseSteps.map((step, idx) => ({ id: idx + 1, ...step }));
}

/**
 * Gemini-based Learning Roadmap Endpoint
 */
app.post("/api/roadmap", async (req, res) => {
    const { goal } = req.body;
    if (!goal) {
        return res.status(400).json({ error: "Goal is required" });
    }

    //  Fallback roadmap (NO LINKS, NO RESOURCES)
    function generateFallbackRoadmap(goal) {
        const steps = [
            {
                title: "Understand the Fundamentals",
                description: `Learn the basic concepts and foundations of ${goal}.`,
                duration: `${2 + Math.floor(Math.random() * 3)} weeks`
            },
            {
                title: "Build Core Knowledge",
                description: `Strengthen your understanding by exploring core areas of ${goal}.`,
                duration: `${3 + Math.floor(Math.random() * 3)} weeks`
            },
            {
                title: "Apply What You Learn",
                description: `Practice ${goal} through exercises, tasks, or hands-on activities.`,
                duration: `${3 + Math.floor(Math.random() * 4)} weeks`
            },
            {
                title: "Create Real-World Work",
                description: `Build projects, case studies, or real examples related to ${goal}.`,
                duration: `${4 + Math.floor(Math.random() * 4)} weeks`
            },
            {
                title: "Refine & Advance",
                description: `Improve your skills, fix gaps, and explore advanced concepts in ${goal}.`,
                duration: `${2 + Math.floor(Math.random() * 3)} weeks`
            }
        ];

        return steps.map((step, idx) => ({
            id: idx + 1,
            ...step
        }));
    }

    const fallbackRoadmap = generateFallbackRoadmap(goal);

    try {
        const apiKey = process.env.GEMINI_API_KEY?.trim();

        //  If no API key → fallback only
        if (!apiKey) {
            return res.json({ roadmap: fallbackRoadmap });
        }

        const gemini = new GoogleGenAI({ apiKey });

        const prompt = `
Generate a 5-step actionable learning roadmap for mastering "${goal}".

Rules:
- Return ONLY a valid JSON array
- No markdown, no explanations, no code fences
- Each step must include: id, title, description, duration
- Do NOT include links or resources

Example format:
[
  { "id": 1, "title": "...", "description": "...", "duration": "3 weeks" }
]
        `;

        const response = await gemini.models.generateContent({
            model: "gemini-2.5-flash",
            contents: prompt
        });

        let text = response.text?.trim() || "";
        text = text.replace(/^```json/, "")
            .replace(/^```/, "")
            .replace(/```$/, "")
            .trim();

        let roadmap;

        try {
            roadmap = JSON.parse(text);

            if (!Array.isArray(roadmap) || roadmap.length === 0) {
                roadmap = fallbackRoadmap;
            } else {
                // ✅ Normalize response
                roadmap = roadmap.map((step, idx) => ({
                    id: step.id || idx + 1,
                    title: step.title || fallbackRoadmap[idx].title,
                    description: step.description || fallbackRoadmap[idx].description,
                    duration: step.duration || fallbackRoadmap[idx].duration
                }));
            }
        } catch {
            roadmap = fallbackRoadmap;
        }

        res.json({ roadmap });

    } catch (err) {
        console.error("Gemini API error:", err);
        res.status(500).json({
            roadmap: fallbackRoadmap,
            error: "AI generation failed, fallback used"
        });
    }
});

// Start server
app.listen(3000, () => {
    console.log("Server is running on http://localhost:3000");
});