using System;
using System.Collections.Generic;

namespace PKHeX.Core;

public abstract class BlockInfo
{
    // General
    public uint ID { get; protected init; }
    public int Offset { get; protected init; }
    public int Length { get; protected init; }

    public string Summary => $"{ID:00}: {Offset:X5}-{Offset + Length - 1:X5}, {Length:X5}";

    protected abstract bool ChecksumValid(ReadOnlySpan<byte> data);
    protected abstract void SetChecksum(Span<byte> data);

    /// <summary>
    /// Checks if the currently written checksum values are valid.
    /// </summary>
    /// <param name="blocks">Block info objects used for offset/length</param>
    /// <param name="data">Complete data array</param>
    /// <returns>True if checksums are valid, false if anything is invalid.</returns>
    public static bool GetChecksumsValid(IEnumerable<BlockInfo> blocks, ReadOnlySpan<byte> data)
    {
        foreach (var b in blocks)
        {
            if (b.Length + b.Offset > data.Length)
                return false;

            if (!b.ChecksumValid(data))
                return false;
        }
        return true;
    }

    /// <summary>
    /// Applies checksums to the <see cref="data"/> object based on the input blocks.
    /// </summary>
    /// <param name="blocks">Block info objects used for offset/length</param>
    /// <param name="data">Complete data array</param>
    public static void SetChecksums(IEnumerable<BlockInfo> blocks, Span<byte> data)
    {
        foreach (var b in blocks)
            b.SetChecksum(data);
    }

    /// <summary>
    /// Gets information pertaining to the checksum data for diagnostic purposes.
    /// </summary>
    /// <param name="blocks">Block info objects used for offset/length</param>
    /// <param name="data">Complete data array</param>
    /// <returns>Multi-line string with <see cref="Summary"/> data.</returns>
    public static string GetChecksumInfo(IReadOnlyList<BlockInfo> blocks, Span<byte> data)
    {
        var invalid = GetInvalidBlockCount(blocks, data, out var list);
        list.Add($"SAV: {blocks.Count - invalid}/{blocks.Count}");
        return string.Join(Environment.NewLine, list);
    }

    private static int GetInvalidBlockCount(IReadOnlyList<BlockInfo> blocks, Span<byte> data, out List<string> list)
    {
        int invalid = 0;
        list = new List<string>();
        for (int i = 0; i < blocks.Count; i++)
        {
            var block = blocks[i];
            if (block.Length + block.Offset > data.Length)
            {
                list.Add($"Block {i} Invalid Offset/Length.");
                return invalid;
            }

            if (block.ChecksumValid(data))
                continue;

            invalid++;
            list.Add($"Invalid: {i:X2} @ Region {block.Offset:X5}");
        }
        return invalid;
    }
}

public static partial class Extensions
{
    public static bool GetChecksumsValid(this IEnumerable<BlockInfo> blocks, Span<byte> data) => BlockInfo.GetChecksumsValid(blocks, data);
    public static void SetChecksums(this IEnumerable<BlockInfo> blocks, Span<byte> data) => BlockInfo.SetChecksums(blocks, data);
    public static string GetChecksumInfo(this IReadOnlyList<BlockInfo> blocks, Span<byte> data) => BlockInfo.GetChecksumInfo(blocks, data);
}