document.addEventListener("DOMContentLoaded", () => {
    // DOM Elements
    const passwordOutput = document.getElementById("password-output");
    const btnRegenerate = document.getElementById("btn-regenerate");
    const btnCopy = document.getElementById("btn-copy");
    const copyTooltip = document.getElementById("copy-tooltip");
    const lengthSlider = document.getElementById("length-slider");
    const lengthVal = document.getElementById("length-val");
    const chkUpper = document.getElementById("chk-upper");
    const chkLower = document.getElementById("chk-lower");
    const chkNumbers = document.getElementById("chk-numbers");
    const chkSymbols = document.getElementById("chk-symbols");
    const chkExcludeAmbiguous = document.getElementById("chk-exclude-ambiguous");
    const entropyVal = document.getElementById("entropy-val");
    const strengthLabel = document.getElementById("strength-label");
    const strengthMeter = document.getElementById("strength-meter");
    const crackTime = document.getElementById("crack-time");

    // Cryptographically secure random integer generation [0, max - 1]
    function getRandomInt(max) {
        const array = new Uint32Array(1);
        const maxVal = 4294967296; // 2^32
        const limit = maxVal - (maxVal % max);
        
        do {
            window.crypto.getRandomValues(array);
        } while (array[0] >= limit);
        
        return array[0] % max;
    }

    // Cryptographically secure Fisher-Yates shuffle
    function secureShuffle(array) {
        for (let i = array.length - 1; i > 0; i--) {
            const j = getRandomInt(i + 1);
            const temp = array[i];
            array[i] = array[j];
            array[j] = temp;
        }
        return array;
    }

    // Core Password Generation Logic
    function generatePassword(length, useUpper, useLower, useNumbers, useSymbols, excludeAmbiguous) {
        let upperPool = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        let lowerPool = "abcdefghijklmnopqrstuvwxyz";
        let numberPool = "0123456789";
        let symbolPool = "!@#$%^&*()_+-=[]{}|;':\",./<>?~`";

        if (excludeAmbiguous) {
            upperPool = upperPool.replace(/[IO]/g, "");
            lowerPool = lowerPool.replace(/[lo]/g, "");
            numberPool = numberPool.replace(/[01]/g, "");
            symbolPool = symbolPool.replace(/[|]/g, ""); // Exclude vertical bar as it looks like I/l/1
        }

        const pools = [];
        if (useUpper) pools.push(upperPool);
        if (useLower) pools.push(lowerPool);
        if (useNumbers) pools.push(numberPool);
        if (useSymbols) pools.push(symbolPool);

        if (pools.length === 0) return { password: "", poolSize: 0 };

        const combinedPool = pools.join("");
        const passwordChars = [];

        // 1. Guarantee at least one character from each selected class to satisfy constraints
        pools.forEach(pool => {
            const randIdx = getRandomInt(pool.length);
            passwordChars.push(pool[randIdx]);
        });

        // 2. Fill the remaining spots up to target length
        while (passwordChars.length < length) {
            const randIdx = getRandomInt(combinedPool.length);
            passwordChars.push(combinedPool[randIdx]);
        }

        // 3. Shuffle array elements securely to remove sequential pattern
        secureShuffle(passwordChars);

        return {
            password: passwordChars.join(""),
            poolSize: combinedPool.length
        };
    }

    // Determine Strength and Crack Time Estimates
    function getStrengthMetrics(entropy) {
        if (entropy === 0) {
            return {
                rating: 0,
                label: "Rating: -",
                crackTime: "Select at least one character class",
                colorClass: ""
            };
        }
        if (entropy < 28) {
            return {
                rating: 0,
                label: "Rating: 0/5 (Very Weak)",
                crackTime: "Can be broken in seconds/minutes",
                colorClass: "strength-label-0"
            };
        } else if (entropy < 40) {
            return {
                rating: 1,
                label: "Rating: 1/5 (Weak)",
                crackTime: "Can be broken in hours",
                colorClass: "strength-label-1"
            };
        } else if (entropy < 60) {
            return {
                rating: 2,
                label: "Rating: 2/5 (Fair)",
                crackTime: "Can be broken in days or months",
                colorClass: "strength-label-2"
            };
        } else if (entropy < 80) {
            return {
                rating: 3,
                label: "Rating: 3/5 (Good)",
                crackTime: "Can be broken in years",
                colorClass: "strength-label-3"
            };
        } else if (entropy < 100) {
            return {
                rating: 4,
                label: "Rating: 4/5 (Strong)",
                crackTime: "Takes decades to break",
                colorClass: "strength-label-4"
            };
        } else {
            return {
                rating: 5,
                label: "Rating: 5/5 (Centurial)",
                crackTime: "Takes centuries or millennia to break",
                colorClass: "strength-label-5"
            };
        }
    }

    // Update UI Elements
    function updateApp() {
        const length = parseInt(lengthSlider.value, 10);
        lengthVal.textContent = length;

        const useUpper = chkUpper.checked;
        const useLower = chkLower.checked;
        const useNumbers = chkNumbers.checked;
        const useSymbols = chkSymbols.checked;
        const excludeAmbiguous = chkExcludeAmbiguous.checked;

        const result = generatePassword(length, useUpper, useLower, useNumbers, useSymbols, excludeAmbiguous);
        
        passwordOutput.value = result.password;

        // Entropy: L * log2(R)
        let entropy = 0;
        if (result.poolSize > 0 && result.password.length > 0) {
            entropy = result.password.length * Math.log2(result.poolSize);
        }
        entropyVal.textContent = entropy.toFixed(1);

        // Strength metrics
        const metrics = getStrengthMetrics(entropy);
        strengthLabel.textContent = metrics.label;
        strengthLabel.className = "metric-label " + metrics.colorClass;
        crackTime.textContent = metrics.crackTime;

        // Visual Strength Meter Bars Update
        const segments = strengthMeter.querySelectorAll(".meter-segment");
        segments.forEach(segment => {
            segment.className = "meter-segment";
        });

        if (result.poolSize > 0) {
            const activeCount = Math.max(1, metrics.rating); // light up at least 1 bar if pool is selected
            for (let i = 0; i < activeCount; i++) {
                segments[i].classList.add(`active-${metrics.rating}`);
            }
        }
    }

    // Clipboard Copy Action
    function copyToClipboard(text) {
        if (navigator.clipboard && navigator.clipboard.writeText) {
            return navigator.clipboard.writeText(text);
        } else {
            const textArea = document.createElement("textarea");
            textArea.value = text;
            textArea.style.position = "fixed";
            document.body.appendChild(textArea);
            textArea.focus();
            textArea.select();
            try {
                document.execCommand("copy");
                document.body.removeChild(textArea);
                return Promise.resolve();
            } catch (err) {
                document.body.removeChild(textArea);
                return Promise.reject(err);
            }
        }
    }

    // Event Handlers
    lengthSlider.addEventListener("input", updateApp);
    [chkUpper, chkLower, chkNumbers, chkSymbols, chkExcludeAmbiguous].forEach(el => {
        el.addEventListener("change", updateApp);
    });

    btnRegenerate.addEventListener("click", () => {
        // Trigger subtle spin animation on click
        const icon = btnRegenerate.querySelector(".icon-refresh");
        icon.classList.add("spinning");
        setTimeout(() => {
            icon.classList.remove("spinning");
        }, 500);

        updateApp();
    });

    btnCopy.addEventListener("click", () => {
        if (!passwordOutput.value) return;

        copyToClipboard(passwordOutput.value)
            .then(() => {
                btnCopy.classList.add("copied");
                copyTooltip.textContent = "Copied!";
                
                setTimeout(() => {
                    btnCopy.classList.remove("copied");
                    copyTooltip.textContent = "Copy";
                }, 2000);
            })
            .catch(err => {
                console.error("Copy failed:", err);
                copyTooltip.textContent = "Failed!";
                setTimeout(() => {
                    copyTooltip.textContent = "Copy";
                }, 2000);
            });
    });

    // Initialize state
    updateApp();
});