using System.Collections.Concurrent;
using System.Diagnostics;
using System.Globalization;
using System.IO.Compression;
using System.Text.Json;
using System.Text.RegularExpressions;
using InnovEnergy.App.Backend.DataTypes;
using InnovEnergy.App.Backend.DataTypes.Methods;
using InnovEnergy.Lib.S3Utils;
using S3Bucket = InnovEnergy.Lib.S3Utils.DataTypes.S3Bucket;
using S3Region = InnovEnergy.Lib.S3Utils.DataTypes.S3Region;

namespace InnovEnergy.App.Backend.Services;

/// <summary>
/// One data point of the dynamic-pricing "Current Price" history (CHF/kWh).
/// </summary>
public class PricePoint
{
    public Int64  Timestamp { get; set; } // unix seconds
    public Double Price     { get; set; } // CHF/kWh
}

/// <summary>
/// Builds the "Current Price" history shown on the Configuration tab for
/// Growatt (device 3) and Sinexcel (device 4) installations.
///
/// CurrentPrice only lives inside the per-10-second chunk files (Config.CurrentPrice);
/// there is no pre-aggregated source. To keep load bounded we sample ONE chunk per
/// 15-minute slot, fetch those in parallel, and cache each fully-past day (immutable).
/// </summary>
public static class CurrentPriceHistoryService
{
    private const Int64  BucketSeconds       = 900; // 15-minute resolution
    private const Int32  MaxParallelFetches  = 24;
    private const Int32  CacheRetentionDays  = 14;  // bound the in-memory day cache
    private const String S3CfgPath           = "/home/ubuntu/.s3cfg";

    private static readonly Regex ChunkFileRegex = new(@"/([0-9]+)\.(csv|json)$", RegexOptions.Compiled);

    // Immutable past days cached as "{installationId}:{yyyyMMdd}".
    private static readonly ConcurrentDictionary<String, List<PricePoint>> DayCache = new();

    public static async Task<List<PricePoint>> GetHistory(Installation installation, Int64 startSec, Int64 endSec)
    {
        var todayUtc = DateTime.UtcNow.Date;
        var firstDay = DateTimeOffset.FromUnixTimeSeconds(startSec).UtcDateTime.Date;
        var lastDay  = DateTimeOffset.FromUnixTimeSeconds(endSec).UtcDateTime.Date;

        var points = new List<PricePoint>();
        for (var day = firstDay; day <= lastDay; day = day.AddDays(1))
            points.AddRange(await GetDay(installation, day, cacheable: day < todayUtc));

        return points
            .Where(p => p.Timestamp >= startSec && p.Timestamp <= endSec)
            .OrderBy(p => p.Timestamp)
            .ToList();
    }

    private static async Task<List<PricePoint>> GetDay(Installation installation, DateTime dayUtc, Boolean cacheable)
    {
        var key = $"{installation.Id}:{dayUtc:yyyyMMdd}";
        if (cacheable && DayCache.TryGetValue(key, out var cached))
            return cached;

        var dayStart = new DateTimeOffset(dayUtc, TimeSpan.Zero).ToUnixTimeSeconds();
        var dayEnd   = dayStart + 86400 - 1;

        var timestamps = SampleByBucket(ListChunkTimestamps(installation, dayStart, dayEnd));
        var points     = await FetchPrices(installation, timestamps);

        // Only cache non-empty past days: an empty result can mean a transient s3cmd/S3
        // failure, and caching that would serve "no data" forever until restart.
        if (cacheable && points.Count > 0)
            CacheDay(key, points);

        return points;
    }

    private static void CacheDay(String key, List<PricePoint> points)
    {
        DayCache[key] = points;

        // Prune entries older than the retention window to bound memory growth.
        var cutoff = DateTime.UtcNow.Date.AddDays(-CacheRetentionDays);
        foreach (var existingKey in DayCache.Keys)
        {
            var datePart = existingKey.Substring(existingKey.IndexOf(':') + 1);
            if (DateTime.TryParseExact(datePart, "yyyyMMdd", CultureInfo.InvariantCulture,
                    DateTimeStyles.None, out var day) && day < cutoff)
                DayCache.TryRemove(existingKey, out _);
        }
    }

    // Keep the first chunk in each 15-minute slot.
    private static List<Int64> SampleByBucket(List<Int64> timestamps)
    {
        var seenBuckets = new HashSet<Int64>();
        var picked      = new List<Int64>();
        foreach (var t in timestamps.OrderBy(x => x))
            if (seenBuckets.Add(t / BucketSeconds))
                picked.Add(t);
        return picked;
    }

    // List every chunk filename in range via `s3cmd ls` over the 5-digit timestamp prefixes
    // (same listing approach as Controller.GetCsvTimestampsForInstallation).
    private static List<Int64> ListChunkTimestamps(Installation installation, Int64 start, Int64 end)
    {
        var all         = new List<Int64>();
        var startPrefix = Int64.Parse(start.ToString().Substring(0, 5));
        var endPrefix   = Int64.Parse(end.ToString().Substring(0, 5));

        for (var prefix = startPrefix; prefix <= endPrefix; prefix++)
        {
            var output = RunS3cmdLs("s3://" + installation.BucketName() + "/" + prefix);
            foreach (var line in output.Split('\n'))
            {
                var match = ChunkFileRegex.Match(line);
                if (match.Success && Int64.TryParse(match.Groups[1].Value, out var t) && t >= start && t <= end)
                    all.Add(t);
            }
        }
        return all;
    }

    private static String RunS3cmdLs(String bucketPath)
    {
        try
        {
            var startInfo = new ProcessStartInfo
            {
                FileName               = "s3cmd",
                Arguments              = $"--config {S3CfgPath} ls {bucketPath}",
                RedirectStandardOutput = true,
                RedirectStandardError  = true,
                UseShellExecute        = false,
                CreateNoWindow         = true
            };
            using var process = new Process { StartInfo = startInfo };
            process.Start();
            var output = process.StandardOutput.ReadToEnd();
            process.StandardError.ReadToEnd();
            process.WaitForExit();
            return process.ExitCode == 0 ? output : "";
        }
        catch (Exception e)
        {
            Console.WriteLine($"[CurrentPriceHistory] s3cmd ls failed for {bucketPath}: {e.Message}");
            return "";
        }
    }

    private static async Task<List<PricePoint>> FetchPrices(Installation installation, List<Int64> timestamps)
    {
        var region = new S3Region($"https://{installation.S3Region}.{installation.S3Provider}", ExoCmd.S3Credentials!);
        var bucket = region.Bucket(installation.BucketName());

        using var gate = new SemaphoreSlim(MaxParallelFetches);

        var tasks = timestamps.Select(async ts =>
        {
            await gate.WaitAsync();
            try
            {
                var price = await FetchPriceAt(bucket, ts);
                return price.HasValue ? new PricePoint { Timestamp = ts, Price = price.Value } : null;
            }
            finally
            {
                gate.Release();
            }
        });

        var results = await Task.WhenAll(tasks);
        return results.Where(p => p != null).Select(p => p!).OrderBy(p => p.Timestamp).ToList();
    }

    private static async Task<Double?> FetchPriceAt(S3Bucket bucket, Int64 ts)
    {
        try
        {
            var raw  = await bucket.Path($"{ts}.json").GetObjectAsString();
            var json = DecodeChunk(raw);
            return json == null ? null : ExtractCurrentPrice(json);
        }
        catch
        {
            return null; // missing chunk / decode error -> just skip this slot
        }
    }

    // Chunk objects are Base64-encoded ZIP archives whose inner "data.json" holds the record.
    private static String? DecodeChunk(String raw)
    {
        try
        {
            var trimmed = raw.Trim();
            if (trimmed.StartsWith('{'))
                return raw; // defensive: already plain JSON

            var bytes = Convert.FromBase64String(trimmed);
            using var zip = new ZipArchive(new MemoryStream(bytes), ZipArchiveMode.Read);
            var entry = zip.GetEntry("data.json");
            if (entry == null)
                return null;

            using var reader = new StreamReader(entry.Open());
            return reader.ReadToEnd();
        }
        catch
        {
            return null;
        }
    }

    // data.json is an object keyed by timestamp(s); read Config.CurrentPrice of the last record.
    private static Double? ExtractCurrentPrice(String json)
    {
        using var doc = JsonDocument.Parse(json);
        if (doc.RootElement.ValueKind != JsonValueKind.Object)
            return null;

        var found  = false;
        var record = default(JsonElement);
        foreach (var prop in doc.RootElement.EnumerateObject())
        {
            record = prop.Value;
            found  = true;
        }

        if (!found
            || !record.TryGetProperty("Config", out var config)
            || !config.TryGetProperty("CurrentPrice", out var currentPrice))
            return null;

        return currentPrice.ValueKind switch
        {
            JsonValueKind.Number => currentPrice.GetDouble(),
            JsonValueKind.String when Double.TryParse(currentPrice.GetString(),
                NumberStyles.Any, CultureInfo.InvariantCulture, out var parsed) => parsed,
            _ => null
        };
    }
}