<?php
require_once __DIR__ . "/../db/config.php";
require_once __DIR__ . "/../includes/lang.php";
session_start();

header("Content-Type: application/json");

$db = db();
$user_id = $_SESSION["user_id"] ?? null;

if (!$user_id) {
    echo json_encode(["success" => false, "error" => __("unauthorized")]);
    exit;
}

$from_coin = $_POST["from_coin"] ?? "";
$to_coin = $_POST["to_coin"] ?? "";
$amount = (float)($_POST["amount"] ?? 0);

if ($amount <= 0 || !$from_coin || !$to_coin || $from_coin === $to_coin) {
    echo json_encode(["success" => false, "error" => __("invalid_amount")]);
    exit;
}

/**
 * Robust price fetching using OKX as primary and CoinCap as fallback
 */
function getPrice($symbol) {
    if ($symbol === "USDT") return 1.0;
    
    // Primary: OKX
    $pair = strtoupper($symbol) . "-USDT";
    $url = "https://www.okx.com/api/v5/market/ticker?instId=" . $pair;
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_TIMEOUT, 5);
    curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/5.0"); // OKX might require UA
    $response = curl_exec($ch);
    curl_close($ch);
    
    if ($response) {
        $data = json_decode($response, true);
        if (isset($data["data"][0]["last"])) {
            return (float)$data["data"][0]["last"];
        }
    }
    
    // Fallback: CoinCap
    $slugMap = [
        "BTC" => "bitcoin", "ETH" => "ethereum", "BNB" => "binance-coin",
        "SOL" => "solana", "XRP" => "ripple", "ADA" => "cardano",
        "DOGE" => "dogecoin", "DOT" => "polkadot", "MATIC" => "polygon",
        "AVAX" => "avalanche", "LINK" => "chainlink", "SHIB" => "shiba-inu",
        "TRX" => "tron", "BCH" => "bitcoin-cash", "LTC" => "litecoin",
        "UNI" => "uniswap"
    ];
    $slug = $slugMap[strtoupper($symbol)] ?? strtolower($symbol);
    $url = "https://api.coincap.io/v2/assets/" . $slug;
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_TIMEOUT, 5);
    $response = curl_exec($ch);
    curl_close($ch);
    
    if ($response) {
        $data = json_decode($response, true);
        if (isset($data["data"]["priceUsd"])) {
            return (float)$data["data"]["priceUsd"];
        }
    }
    
    return null;
}

$from_price = getPrice($from_coin);
$to_price = getPrice($to_coin);

if ($from_price === null || $to_price === null) {
    echo json_encode(["success" => false, "error" => __("rate_fetch_failed")]);
    exit;
}

$rate = $from_price / $to_price;
$target_amount = $amount * $rate;

$db->beginTransaction();
try {
    // Check balance of from_coin
    $stmt = $db->prepare("SELECT available FROM user_balances WHERE user_id = ? AND symbol = ?");
    $stmt->execute([$user_id, $from_coin]);
    $from_balance = $stmt->fetchColumn() ?: 0;

    if ($from_balance < $amount) {
        throw new Exception(__("insufficient_balance"));
    }

    // Deduct from_coin
    $db->prepare("UPDATE user_balances SET available = available - ? WHERE user_id = ? AND symbol = ?")
       ->execute([$amount, $user_id, $from_coin]);

    // Add to_coin
    $stmt = $db->prepare("SELECT id FROM user_balances WHERE user_id = ? AND symbol = ?");
    $stmt->execute([$user_id, $to_coin]);
    if (!$stmt->fetch()) {
        $db->prepare("INSERT INTO user_balances (user_id, symbol, available) VALUES (?, ?, 0)")
           ->execute([$user_id, $to_coin]);
    }
    $db->prepare("UPDATE user_balances SET available = available + ? WHERE user_id = ? AND symbol = ?")
       ->execute([$target_amount, $user_id, $to_coin]);

    // Record exchange
    $stmt = $db->prepare("INSERT INTO exchange_records (user_id, from_symbol, to_symbol, from_amount, to_amount, rate, ip_address) VALUES (?, ?, ?, ?, ?, ?, ?)");
    $stmt->execute([$user_id, $from_coin, $to_coin, $amount, $target_amount, $rate, getRealIP()]);

    // Record transaction
    $db->prepare("INSERT INTO transactions (user_id, type, amount, symbol, status, ip_address) VALUES (?, 'swap', ?, ?, 'completed', ?)")
       ->execute([$user_id, $amount, $from_coin, getRealIP()]);

    $db->commit();
    echo json_encode(["success" => true, "target_amount" => $target_amount]);
} catch (Exception $e) {
    $db->rollBack();
    echo json_encode(["success" => false, "error" => $e->getMessage()]);
}