/**
 * @fileoverview This file contains various utility functions related to
 * character and user statistics, such as creating an HTML stat block,
 * calculating total stats, and creating an HTML report from the provided stats.
 * It also provides methods for handling user stats and character stats,
 * as well as a utility for humanizing generation time from milliseconds.
 */

const fs = require("fs");
const path = require("path");
const util = require("util");
const writeFileAtomic = require("write-file-atomic");
const writeFile = util.promisify(writeFileAtomic);
const readFile = util.promisify(fs.readFile);
const readdir = util.promisify(fs.readdir);
const crypto = require("crypto");

let charStats = {};
let lastSaveTimestamp = 0;
const statsFilePath = "public/stats.json";

/**
 * Convert a timestamp to an integer timestamp.
 * (sorry, it's momentless for now, didn't want to add a package just for this)
 * This function can handle several different timestamp formats:
 * 1. Unix timestamps (the number of seconds since the Unix Epoch)
 * 2. ST "humanized" timestamps, formatted like "YYYY-MM-DD @HHh MMm SSs ms"
 * 3. Date strings in the format "Month DD, YYYY H:MMam/pm"
 *
 * The function returns the timestamp as the number of milliseconds since
 * the Unix Epoch, which can be converted to a JavaScript Date object with new Date().
 *
 * @param {string|number} timestamp - The timestamp to convert.
 * @returns {number|null} The timestamp in milliseconds since the Unix Epoch, or null if the input cannot be parsed.
 *
 * @example
 * // Unix timestamp
 * timestampToMoment(1609459200);
 * // ST humanized timestamp
 * timestampToMoment("2021-01-01 @00h 00m 00s 000ms");
 * // Date string
 * timestampToMoment("January 1, 2021 12:00am");
 */
function timestampToMoment(timestamp) {
    if (!timestamp) {
        return null;
    }

    if (typeof timestamp === "number") {
        return timestamp;
    }

    const pattern1 =
        /(\d{4})-(\d{1,2})-(\d{1,2}) @(\d{1,2})h (\d{1,2})m (\d{1,2})s (\d{1,3})ms/;
    const replacement1 = (
        match,
        year,
        month,
        day,
        hour,
        minute,
        second,
        millisecond
    ) => {
        return `${year}-${month.padStart(2, "0")}-${day.padStart(
            2,
            "0"
        )}T${hour.padStart(2, "0")}:${minute.padStart(
            2,
            "0"
        )}:${second.padStart(2, "0")}.${millisecond.padStart(3, "0")}Z`;
    };
    const isoTimestamp1 = timestamp.replace(pattern1, replacement1);
    if (!isNaN(new Date(isoTimestamp1))) {
        return new Date(isoTimestamp1).getTime();
    }

    const pattern2 = /(\w+)\s(\d{1,2}),\s(\d{4})\s(\d{1,2}):(\d{1,2})(am|pm)/i;
    const replacement2 = (match, month, day, year, hour, minute, meridiem) => {
        const monthNames = [
            "January",
            "February",
            "March",
            "April",
            "May",
            "June",
            "July",
            "August",
            "September",
            "October",
            "November",
            "December",
        ];
        const monthNum = monthNames.indexOf(month) + 1;
        const hour24 =
            meridiem.toLowerCase() === "pm"
                ? (parseInt(hour, 10) % 12) + 12
                : parseInt(hour, 10) % 12;
        return `${year}-${monthNum.toString().padStart(2, "0")}-${day.padStart(
            2,
            "0"
        )}T${hour24.toString().padStart(2, "0")}:${minute.padStart(
            2,
            "0"
        )}:00Z`;
    };
    const isoTimestamp2 = timestamp.replace(pattern2, replacement2);
    if (!isNaN(new Date(isoTimestamp2))) {
        return new Date(isoTimestamp2).getTime();
    }

    return null;
}

/**
 * Collects and aggregates stats for all characters.
 *
 * @param {string} chatsPath - The path to the directory containing the chat files.
 * @param {string} charactersPath - The path to the directory containing the character files.
 * @returns {Object} The aggregated stats object.
 */
async function collectAndCreateStats(chatsPath, charactersPath) {
    console.log("Collecting and creating stats...");
    const files = await readdir(charactersPath);

    const pngFiles = files.filter((file) => file.endsWith(".png"));

    let processingPromises = pngFiles.map((file, index) =>
        calculateStats(chatsPath, file, index)
    );
    const statsArr = await Promise.all(processingPromises);

    let finalStats = {};
    for (let stat of statsArr) {
        finalStats = { ...finalStats, ...stat };
    }
    // tag with timestamp on when stats were generated
    finalStats.timestamp = Date.now();
    return finalStats;
}

/**
 * Loads the stats file into memory. If the file doesn't exist or is invalid,
 * initializes stats by collecting and creating them for each character.
 *
 * @param {string} chatsPath - The path to the directory containing the chat files.
 * @param {string} charactersPath - The path to the directory containing the character files.
 */
async function loadStatsFile(chatsPath, charactersPath) {
    try {
        const statsFileContent = await readFile(statsFilePath, "utf-8");
        charStats = JSON.parse(statsFileContent);
    } catch (err) {
        // If the file doesn't exist or is invalid, initialize stats
        if (err.code === "ENOENT" || err instanceof SyntaxError) {
            charStats = await collectAndCreateStats(chatsPath, charactersPath); // Call your function to collect and create stats
            await saveStatsToFile();
        } else {
            throw err; // Rethrow the error if it's something we didn't expect
        }
    }
    console.debug("Stats loaded from files.");
}
/**
 * Saves the current state of charStats to a file, only if the data has changed since the last save.
 */
async function saveStatsToFile() {
    if (charStats.timestamp > lastSaveTimestamp) {
        //console.debug("Saving stats to file...");
        await writeFile(statsFilePath, JSON.stringify(charStats));
        lastSaveTimestamp = Date.now();
    } else {
        //console.debug('Stats have not changed since last save. Skipping file write.');
    }
}

/**
 * Attempts to save charStats to a file and then terminates the process.
 * If an error occurs during the file write, it logs the error before exiting.
 */
async function writeStatsToFileAndExit(charStats) {
    try {
        await saveStatsToFile(charStats);
    } catch (err) {
        console.error("Failed to write stats to file:", err);
    } finally {
        process.exit();
    }
}

/**
 * Reads the contents of a file and returns the lines in the file as an array.
 *
 * @param {string} filepath - The path of the file to be read.
 * @returns {Array<string>} - The lines in the file.
 * @throws Will throw an error if the file cannot be read.
 */
function readAndParseFile(filepath) {
    try {
        let file = fs.readFileSync(filepath, "utf8");
        let lines = file.split("\n");
        return lines;
    } catch (error) {
        console.error(`Error reading file at ${filepath}: ${error}`);
        return [];
    }
}

/**
 * Calculates the time difference between two dates.
 *
 * @param {string} gen_started - The start time in ISO 8601 format.
 * @param {string} gen_finished - The finish time in ISO 8601 format.
 * @returns {number} - The difference in time in milliseconds.
 */
function calculateGenTime(gen_started, gen_finished) {
    let startDate = new Date(gen_started);
    let endDate = new Date(gen_finished);
    return endDate - startDate;
}

/**
 * Counts the number of words in a string.
 *
 * @param {string} str - The string to count words in.
 * @returns {number} - The number of words in the string.
 */
function countWordsInString(str) {
    const match = str.match(/\b\w+\b/g);
    return match ? match.length : 0;
}

/**
 * calculateStats - Calculate statistics for a given character chat directory.
 *
 * @param  {string} char_dir The directory containing the chat files.
 * @param  {string} item     The name of the character.
 * @return {object}          An object containing the calculated statistics.
 */
const calculateStats = (chatsPath, item, index) => {
    const char_dir = path.join(chatsPath, item.replace(".png", ""));
    let chat_size = 0;
    let date_last_chat = 0;
    const stats = {
        total_gen_time: 0,
        user_word_count: 0,
        non_user_word_count: 0,
        user_msg_count: 0,
        non_user_msg_count: 0,
        total_swipe_count: 0,
        chat_size: 0,
        date_last_chat: 0,
        date_first_chat: new Date("9999-12-31T23:59:59.999Z").getTime(),
    };
    let uniqueGenStartTimes = new Set();

    if (fs.existsSync(char_dir)) {
        const chats = fs.readdirSync(char_dir);
        if (Array.isArray(chats) && chats.length) {
            for (const chat of chats) {
                const result = calculateTotalGenTimeAndWordCount(
                    char_dir,
                    chat,
                    uniqueGenStartTimes
                );
                stats.total_gen_time += result.totalGenTime || 0;
                stats.user_word_count += result.userWordCount || 0;
                stats.non_user_word_count += result.nonUserWordCount || 0;
                stats.user_msg_count += result.userMsgCount || 0;
                stats.non_user_msg_count += result.nonUserMsgCount || 0;
                stats.total_swipe_count += result.totalSwipeCount || 0;

                const chatStat = fs.statSync(path.join(char_dir, chat));
                stats.chat_size += chatStat.size;
                stats.date_last_chat = Math.max(
                    stats.date_last_chat,
                    Math.floor(chatStat.mtimeMs)
                );
                stats.date_first_chat = Math.min(
                    stats.date_first_chat,
                    result.firstChatTime
                );
            }
        }
    }

    return { [item]: stats };
};

/**
 * Returns the current charStats object.
 * @returns {Object} The current charStats object.
 **/
function getCharStats() {
    return charStats;
}

/**
 * Sets the current charStats object.
 * @param {Object} stats - The new charStats object.
 **/
function setCharStats(stats) {
    charStats = stats;
    charStats.timestamp = Date.now();
}

/**
 * Calculates the total generation time and word count for a chat with a character.
 *
 * @param {string} char_dir - The directory path where character chat files are stored.
 * @param {string} chat - The name of the chat file.
 * @returns {Object} - An object containing the total generation time, user word count, and non-user word count.
 * @throws Will throw an error if the file cannot be read or parsed.
 */
function calculateTotalGenTimeAndWordCount(
    char_dir,
    chat,
    uniqueGenStartTimes
) {
    let filepath = path.join(char_dir, chat);
    let lines = readAndParseFile(filepath);

    let totalGenTime = 0;
    let userWordCount = 0;
    let nonUserWordCount = 0;
    let nonUserMsgCount = 0;
    let userMsgCount = 0;
    let totalSwipeCount = 0;
    let firstChatTime = new Date("9999-12-31T23:59:59.999Z").getTime();

    for (let [index, line] of lines.entries()) {
        if (line.length) {
            try {
                let json = JSON.parse(line);
                if (json.mes) {
                    let hash = crypto
                        .createHash("sha256")
                        .update(json.mes)
                        .digest("hex");
                    if (uniqueGenStartTimes.has(hash)) {
                        continue;
                    }
                    if (hash) {
                        uniqueGenStartTimes.add(hash);
                    }
                }

                if (json.gen_started && json.gen_finished) {
                    let genTime = calculateGenTime(
                        json.gen_started,
                        json.gen_finished
                    );
                    totalGenTime += genTime;

                    if (json.swipes && !json.swipe_info) {
                        // If there are swipes but no swipe_info, estimate the genTime
                        totalGenTime += genTime * json.swipes.length;
                    }
                }

                if (json.mes) {
                    let wordCount = countWordsInString(json.mes);
                    json.is_user
                        ? (userWordCount += wordCount)
                        : (nonUserWordCount += wordCount);
                    json.is_user ? userMsgCount++ : nonUserMsgCount++;
                }

                if (json.swipes && json.swipes.length > 1) {
                    totalSwipeCount += json.swipes.length - 1; // Subtract 1 to not count the first swipe
                    for (let i = 1; i < json.swipes.length; i++) {
                        // Start from the second swipe
                        let swipeText = json.swipes[i];

                        let wordCount = countWordsInString(swipeText);
                        json.is_user
                            ? (userWordCount += wordCount)
                            : (nonUserWordCount += wordCount);
                        json.is_user ? userMsgCount++ : nonUserMsgCount++;
                    }
                }

                if (json.swipe_info && json.swipe_info.length > 1) {
                    for (let i = 1; i < json.swipe_info.length; i++) {
                        // Start from the second swipe
                        let swipe = json.swipe_info[i];
                        if (swipe.gen_started && swipe.gen_finished) {
                            totalGenTime += calculateGenTime(
                                swipe.gen_started,
                                swipe.gen_finished
                            );
                        }
                    }
                }

                // If this is the first user message, set the first chat time
                if (json.is_user) {
                    //get min between firstChatTime and timestampToMoment(json.send_date)
                    firstChatTime = Math.min(timestampToMoment(json.send_date), firstChatTime);
                }
            } catch (error) {
                console.error(`Error parsing line ${line}: ${error}`);
            }
        }
    }
    return {
        totalGenTime,
        userWordCount,
        nonUserWordCount,
        userMsgCount,
        nonUserMsgCount,
        totalSwipeCount,
        firstChatTime,
    };
}

module.exports = {
    saveStatsToFile,
    loadStatsFile,
    writeStatsToFileAndExit,
    getCharStats,
    setCharStats,
};