"use client";

import { useEffect, useState, useRef } from "react";
import { Html5QrcodeScanner, Html5QrcodeSupportedFormats } from "html5-qrcode";
import { Scan as ScanIcon, Check, Minus, Plus, AlertTriangle, X } from "lucide-react";

export default function ScanPage() {
  const [scannedData, setScannedData] = useState(null);
  const [item, setItem] = useState(null);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);
  
  const [quantityAdjust, setQuantityAdjust] = useState(0);
  const [updating, setUpdating] = useState(false);

  const scannerRef = useRef(null);

  useEffect(() => {
    // Only initialize scanner if not already scanning a specific item
    if (scannedData) return;

    const onScanSuccess = (decodedText) => {
      setScannedData(decodedText);
      scannerRef.current?.clear();
    };

    scannerRef.current = new Html5QrcodeScanner(
      "reader",
      { 
        fps: 10, 
        qrbox: { width: 250, height: 250 },
        formatsToSupport: [ Html5QrcodeSupportedFormats.QR_CODE ] 
      },
      /* verbose= */ false
    );
    scannerRef.current.render(onScanSuccess, () => {});

    return () => {
      scannerRef.current?.clear().catch(e => console.error("Failed to clear scanner", e));
    };
  }, [scannedData]);

  useEffect(() => {
    if (!scannedData) return;

    const lookupItem = async () => {
      setLoading(true);
      setError(null);
      try {
        // Fetch items and find the matched one
        const res = await fetch("/api/inventory");
        const list = await res.json();
        
        const matchedItem = list.find(i => i.qrCodeId === scannedData || i.id === scannedData);
        if (matchedItem) {
          setItem(matchedItem);
          setQuantityAdjust(0);
        } else {
          setError(`No item found in database matching: ${scannedData}`);
        }
      } catch (err) {
        setError(err.message);
      } finally {
        setLoading(false);
      }
    };

    lookupItem();
  }, [scannedData]);

  const handleUpdate = async () => {
    if (!item) return;
    setUpdating(true);
    try {
      const updatedQuantity = item.quantity + quantityAdjust;
      const res = await fetch("/api/inventory", {
        method: "PUT",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({
          id: item.id,
          quantity: updatedQuantity
        })
      });

      if (!res.ok) throw new Error("Failed to update quantity");
      
      const updated = await res.json();
      setItem(updated);
      setQuantityAdjust(0);
      alert(`Updated successfully. New quantity: ${updated.quantity}`);
      
      // Optionally continue scanning
      resetScanner();
    } catch (err) {
      alert("Error: " + err.message);
    } finally {
      setUpdating(false);
    }
  };

  const resetScanner = () => {
    setScannedData(null);
    setItem(null);
    setError(null);
  };

  return (
    <div style={{ maxWidth: "600px", margin: "0 auto" }}>
      <div className="flex justify-between items-center mb-6">
        <div>
          <h2 className="flex items-center gap-2 mb-2">
            <ScanIcon size={28} className="text-primary" />
            Scan QR
          </h2>
          <p className="text-muted">Use your camera scanner to locate and update items.</p>
        </div>
      </div>

      {!scannedData ? (
        <div className="glass overflow-hidden">
          <div id="reader" style={{ width: "100%", border: "none" }}></div>
        </div>
      ) : (
        <div className="glass" style={{ padding: "2rem" }}>
          {loading ? (
            <div className="text-center p-8">Loading inventory details...</div>
          ) : error ? (
            <div className="text-center p-8">
              <AlertTriangle size={48} className="text-danger m-auto mb-4" />
              <h3 className="text-danger mb-2">Item not found</h3>
              <p className="text-muted mb-6">{error}</p>
              <button className="btn btn-secondary w-full" onClick={resetScanner}>
                Scan Again
              </button>
            </div>
          ) : item && (
            <div>
              <div className="flex justify-between items-start mb-6">
                <div>
                  <h3 style={{ fontSize: "1.5rem", marginBottom: "0.25rem" }}>{item.name}</h3>
                  <code className="text-muted" style={{ background: "rgba(255,255,255,0.05)", padding: "2px 6px", borderRadius: "4px" }}>
                    ID: {item.qrCodeId}
                  </code>
                </div>
                <button className="btn btn-danger" onClick={resetScanner} style={{ padding: "0.5rem" }} title="Cancel">
                  <X size={20} />
                </button>
              </div>

              <div style={{ display: "grid", gridTemplateColumns: "1fr 1fr", gap: "1rem", marginBottom: "2rem" }}>
                <div style={{ padding: "1rem", backgroundColor: "rgba(255,255,255,0.05)", borderRadius: "8px" }}>
                  <div className="text-muted" style={{ fontSize: "0.85rem", textTransform: "uppercase" }}>Current Quant.</div>
                  <div style={{ fontSize: "2rem", fontWeight: "bold", color: "var(--text-main)" }}>{item.quantity}</div>
                </div>
                <div style={{ padding: "1rem", backgroundColor: "rgba(255,255,255,0.05)", borderRadius: "8px" }}>
                  <div className="text-muted" style={{ fontSize: "0.85rem", textTransform: "uppercase" }}>Location</div>
                  <div style={{ fontSize: "1.4rem", fontWeight: "600", color: "var(--text-main)", marginTop: "0.3rem" }}>
                    {item.location || "-"}
                  </div>
                </div>
                <div style={{ padding: "1rem", backgroundColor: "rgba(255,255,255,0.05)", borderRadius: "8px", gridColumn: "1 / -1" }}>
                  <div className="text-muted" style={{ fontSize: "0.85rem", textTransform: "uppercase", marginBottom: "0.5rem" }}>Last Updated</div>
                  <div style={{ fontSize: "1.1rem", color: "var(--text-main)" }}>
                    {item.updatedAt ? new Date(item.updatedAt).toLocaleString() : "Never"}
                  </div>
                </div>
              </div>

              <div className="mb-6">
                <label className="text-muted mb-2 block text-center">Adjust Quantity</label>
                <div className="flex justify-center items-center gap-4">
                  <button 
                    className="btn btn-danger"
                    style={{ padding: "1rem", borderRadius: "50%" }}
                    onClick={() => setQuantityAdjust(q => q - 1)}
                  >
                    <Minus size={24} />
                  </button>
                  <div style={{ fontSize: "2.5rem", width: "80px", textAlign: "center", fontWeight: "bold" }}>
                    {quantityAdjust > 0 ? `+${quantityAdjust}` : quantityAdjust}
                  </div>
                  <button 
                    className="btn btn-success"
                    style={{ padding: "1rem", borderRadius: "50%", backgroundColor: "var(--success)", color: "white", border: "none" }}
                    onClick={() => setQuantityAdjust(q => q + 1)}
                  >
                    <Plus size={24} />
                  </button>
                </div>
                
                <div className="text-center mt-4">
                  <span className="text-muted">New Quantity will be: </span>
                  <strong style={{ fontSize: "1.2rem", color: (item.quantity + quantityAdjust) < 0 ? "var(--danger)" : "var(--text-main)" }}>
                    {item.quantity + quantityAdjust}
                  </strong>
                </div>
              </div>

              <button 
                className="btn btn-primary" 
                style={{ width: "100%", justifyContent: "center", padding: "1rem" }}
                onClick={handleUpdate}
                disabled={updating || quantityAdjust === 0 || (item.quantity + quantityAdjust) < 0}
              >
                {updating ? "Saving..." : <><Check size={20} /> Confirm Update</>}
              </button>
            </div>
          )}
        </div>
      )}

      <style>{`
        /* Scanner UI Overrides */
        #reader__dashboard_section_csr span { color: var(--text-main) !important; }
        #reader__dashboard_section_swaplink { color: var(--primary) !important; }
        #reader button {
          background-color: var(--primary);
          color: white;
          border: none;
          padding: 0.5rem 1rem;
          border-radius: 8px;
          cursor: pointer;
          margin-top: 1rem;
        }
        #reader {
          background-color: var(--bg-secondary);
          color: var(--text-main);
        }
      `}</style>
    </div>
  );
}