using System;
using Unity.Collections.LowLevel.Unsafe;

namespace Unity.Collections
{
    /// <summary>
    /// Provides extension methods for FixedString*N*.
    /// </summary>
    [BurstCompatible]
    public unsafe static partial class FixedStringMethods
    {
        /// <summary>
        /// Returns the index of the first occurrence of a byte sequence in this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="bytes">A byte sequence to search for within this string.</param>
        /// <param name="bytesLen">The number of bytes in the byte sequence.</param>
        /// <returns>The index of the first occurrence of the byte sequence in this string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int IndexOf<T>(ref this T fs, byte* bytes, int bytesLen)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var dst = fs.GetUnsafePtr();
            var dstLen = fs.Length;
            for (var i = 0; i <= dstLen - bytesLen; ++i)
            {
                for (var j = 0; j < bytesLen; ++j)
                    if (dst[i + j] != bytes[j])
                        goto end_of_loop;
                return i;
                end_of_loop : {}
            }
            return -1;
        }

        /// <summary>
        /// Returns the index of the first occurrence of a byte sequence within a subrange of this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="bytes">A byte sequence to search for within this string.</param>
        /// <param name="bytesLen">The number of bytes in the byte sequence.</param>
        /// <param name="startIndex">The first index in this string to consider as the first byte of the byte sequence.</param>
        /// <param name="distance">The last index in this string to consider as the first byte of the byte sequence.</param>
        /// <returns>The index of the first occurrence of the byte sequence in this string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int IndexOf<T>(ref this T fs, byte* bytes, int bytesLen, int startIndex, int distance = Int32.MaxValue)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var dst = fs.GetUnsafePtr();
            var dstLen = fs.Length;
            var searchrange = Math.Min(distance - 1, dstLen - bytesLen);
            for (var i = startIndex; i <= searchrange; ++i)
            {
                for (var j = 0; j < bytesLen; ++j)
                    if (dst[i + j] != bytes[j])
                        goto end_of_loop;
                return i;
                end_of_loop : {}
            }
            return -1;
        }

        /// <summary>
        /// Returns the index of the first occurrence of a substring within this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="other">A substring to search for within this string.</param>
        /// <returns>The index of the first occurrence of the second string within this string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static int IndexOf<T,T2>(ref this T fs, in T2 other)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            ref var oref = ref UnsafeUtilityExtensions.AsRef(in other);
            return fs.IndexOf(oref.GetUnsafePtr(), oref.Length);
        }

        /// <summary>
        /// Returns the index of the first occurrence of a substring within a subrange of this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="other">A substring to search for within this string.</param>
        /// <param name="startIndex">The first index in this string to consider as an occurrence of the second string.</param>
        /// <param name="distance">The last index in this string to consider as an occurrence of the second string.</param>
        /// <returns>The index of the first occurrence of the substring within this string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static int IndexOf<T,T2>(ref this T fs, in T2 other, int startIndex, int distance = Int32.MaxValue)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            ref var oref = ref UnsafeUtilityExtensions.AsRef(in other);
            return fs.IndexOf(oref.GetUnsafePtr(), oref.Length, startIndex, distance);
        }

        /// <summary>
        /// Returns true if a given substring occurs within this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="other">A substring to search for within this string.</param>
        /// <returns>True if the substring occurs within this string.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static bool Contains<T,T2>(ref this T fs, in T2 other)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            return fs.IndexOf(in other) != -1;
        }

        /// <summary>
        /// Returns the index of the last occurrence of a byte sequence within this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="bytes">A byte sequence to search for within this string.</param>
        /// <param name="bytesLen">The number of bytes in the byte sequence.</param>
        /// <returns>The index of the last occurrence of the byte sequence within this string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int LastIndexOf<T>(ref this T fs, byte* bytes, int bytesLen)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var dst = fs.GetUnsafePtr();
            var dstLen = fs.Length;
            for (var i = dstLen - bytesLen; i >= 0; --i)
            {
                for (var j = 0; j < bytesLen; ++j)
                    if (dst[i + j] != bytes[j])
                        goto end_of_loop;
                return i;
                end_of_loop : {}
            }
            return -1;
        }

        /// <summary>
        /// Returns the index of the last occurrence of a byte sequence within a subrange of this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="bytes">A byte sequence to search for within this string.</param>
        /// <param name="bytesLen">The number of bytes in the byte sequence.</param>
        /// <param name="startIndex">The smallest index in this string to consider as the first byte of the byte sequence.</param>
        /// <param name="distance">The greatest index in this string to consider as the first byte of the byte sequence.</param>
        /// <returns>The index of the last occurrence of the byte sequence within this string. Returns -1 if no occurrences found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int LastIndexOf<T>(ref this T fs, byte* bytes, int bytesLen, int startIndex, int distance = int.MaxValue)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var dst = fs.GetUnsafePtr();
            var dstLen = fs.Length;
            startIndex = Math.Min(dstLen - bytesLen, startIndex);
            var searchrange = Math.Max(0, startIndex - distance);
            for (var i = startIndex; i >= searchrange; --i)
            {
                for (var j = 0; j < bytesLen; ++j)
                    if (dst[i + j] != bytes[j])
                        goto end_of_loop;
                return i;
                end_of_loop : {}
            }
            return -1;
        }

        /// <summary>
        /// Returns the index of the last occurrence of a substring within this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="other">A substring to search for in the this string.</param>
        /// <returns>The index of the last occurrence of the substring within this string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static int LastIndexOf<T,T2>(ref this T fs, in T2 other)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            ref var oref = ref UnsafeUtilityExtensions.AsRef(in other);
            return fs.LastIndexOf(oref.GetUnsafePtr(), oref.Length);
        }

        /// <summary>
        /// Returns the index of the last occurrence of a substring within a subrange of this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to search.</param>
        /// <param name="other">A substring to search for within this string.</param>
        /// <param name="startIndex">The greatest index in this string to consider as an occurrence of the substring.</param>
        /// <param name="distance">The smallest index in this string to consider as an occurrence of the substring.</param>
        /// <returns>the index of the last occurrence of the substring within the first string. Returns -1 if no occurrence is found.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static int LastIndexOf<T,T2>(ref this T fs, in T2 other, int startIndex, int distance = Int32.MaxValue)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            ref var oref = ref UnsafeUtilityExtensions.AsRef(in other);
            return fs.LastIndexOf(oref.GetUnsafePtr(), oref.Length, startIndex, distance);
        }

        /// <summary>
        /// Returns the sort position of this string relative to a byte sequence.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to compare.</param>
        /// <param name="bytes">A byte sequence to compare.</param>
        /// <param name="bytesLen">The number of bytes in the byte sequence.</param>
        /// <returns>A number denoting the sort position of this string relative to the byte sequence:
        ///
        /// 0 denotes that this string and byte sequence have the same sort position.<br/>
        /// -1 denotes that this string should be sorted to precede the byte sequence.<br/>
        /// +1 denotes that this string should be sorted to follow the byte sequence.<br/>
        /// </returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int CompareTo<T>(ref this T fs, byte* bytes, int bytesLen)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var a = fs.GetUnsafePtr();
            var aa = fs.Length;
            int chars = aa < bytesLen ? aa : bytesLen;
            for (var i = 0; i < chars; ++i)
            {
                if (a[i] < bytes[i])
                    return -1;
                if (a[i] > bytes[i])
                    return 1;
            }
            if (aa < bytesLen)
                return -1;
            if (aa > bytesLen)
                return 1;
            return 0;
        }

        /// <summary>
        /// Returns the sort position of this string relative to another.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to compare.</param>
        /// <param name="other">Another string to compare.</param>
        /// <returns>A number denoting the relative sort position of the strings:
        ///
        /// 0 denotes that the strings have the same sort position.<br/>
        /// -1 denotes that this string should be sorted to precede the other.<br/>
        /// +1 denotes that this first string should be sorted to follow the other.<br/>
        /// </returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static int CompareTo<T,T2>(ref this T fs, in T2 other)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            ref var oref = ref UnsafeUtilityExtensions.AsRef(in other);
            return fs.CompareTo(oref.GetUnsafePtr(), oref.Length);
        }

        /// <summary>
        /// Returns true if this string and a byte sequence are equal (meaning they have the same length and content).
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to compare for equality.</param>
        /// <param name="bytes">A sequence of bytes to compare for equality.</param>
        /// <param name="bytesLen">The number of bytes in the byte sequence.</param>
        /// <returns>True if this string and the byte sequence have the same length and if this string's character bytes match the byte sequence.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static bool Equals<T>(ref this T fs, byte* bytes, int bytesLen)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var a = fs.GetUnsafePtr();
            var aa = fs.Length;
            if (aa != bytesLen)
                return false;
            if (a == bytes)
                return true;
            return fs.CompareTo(bytes, bytesLen) == 0;
        }

        /// <summary>
        /// Returns true if this string is equal to another.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <typeparam name="T2">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to compare for equality.</param>
        /// <param name="other">Another string to compare for equality.</param>
        /// <returns>true if the two strings have the same length and matching content.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes), typeof(FixedString128Bytes) })]
        public static bool Equals<T,T2>(ref this T fs, in T2 other)
            where T : struct, INativeList<byte>, IUTF8Bytes
            where T2 : struct, INativeList<byte>, IUTF8Bytes
        {
            ref var oref = ref UnsafeUtilityExtensions.AsRef(in other);
            return fs.Equals(oref.GetUnsafePtr(), oref.Length);
        }

        /// <summary>
        /// Returns the Unicode.Rune at an index of this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to read.</param>
        /// <param name="index">A reference to an index in bytes (not characters).</param>
        /// <returns>The Unicode.Rune (character) which starts at the byte index. Returns Unicode.BadRune
        /// if the byte(s) at the index do not form a valid UTF-8 encoded character.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static Unicode.Rune Peek<T>(ref this T fs, int index)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            if (index >= fs.Length)
                return Unicode.BadRune;
            Unicode.Utf8ToUcs(out var rune, fs.GetUnsafePtr(), ref index, fs.Capacity);
            return rune;
        }

        /// <summary>
        /// Returns the Unicode.Rune at an index of this string. Increments the index to the position of the next character.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to read.</param>
        /// <param name="index">A reference to an index in bytes (not characters). Incremented by 1 to 4 depending upon the UTF-8 encoded size of the character read.</param>
        /// <returns>The character (as a `Unicode.Rune`) which starts at the byte index. Returns `Unicode.BadRune`
        /// if the byte(s) at the index do not form a valid UTF-8 encoded character.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static Unicode.Rune Read<T>(ref this T fs, ref int index)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            if (index >= fs.Length)
                return Unicode.BadRune;
            Unicode.Utf8ToUcs(out var rune, fs.GetUnsafePtr(), ref index, fs.Capacity);
            return rune;
        }

        /// <summary>
        /// Writes a Unicode.Rune at an index of this string. Increments the index to the position of the next character.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to modify.</param>
        /// <param name="index">A reference to an index in bytes (not characters). Incremented by 1 to 4 depending upon the UTF-8 encoded size of the character written.</param>
        /// <param name="rune">A rune to write to the string, encoded as UTF-8.</param>
        /// <returns>FormatError.None if successful. Returns FormatError.Overflow if the index is invalid or if there is not enough space to store the encoded rune.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static FormatError Write<T>(ref this T fs, ref int index, Unicode.Rune rune)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var err = Unicode.UcsToUtf8(fs.GetUnsafePtr(), ref index, fs.Capacity, rune);
            if (err != ConversionError.None)
                return FormatError.Overflow;
            return FormatError.None;
        }

        /// <summary>
        /// Returns a copy of this string as a managed string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to copy.</param>
        /// <returns>A copy of this string as a managed string.</returns>
        [NotBurstCompatible]
        public static String ConvertToString<T>(ref this T fs)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            var c = stackalloc char[fs.Length * 2];
            int length = 0;
            Unicode.Utf8ToUtf16(fs.GetUnsafePtr(), fs.Length, c, out length, fs.Length * 2);
            return new String(c, 0, length);
        }

        /// <summary>
        /// Returns a hash code of this string.
        /// </summary>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to get a hash code of.</param>
        /// <returns>A hash code of this string.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int ComputeHashCode<T>(ref this T fs)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            return (int)CollectionHelper.Hash(fs.GetUnsafePtr(), fs.Length);
        }

        /// <summary>
        /// Returns the effective size in bytes of this string.
        /// </summary>
        /// <remarks>
        /// "Effective size" is `Length + 3`, the number of bytes you need to copy when serializing the string.
        /// (The plus 3 accounts for the null-terminator byte and the 2 bytes that store the Length).
        ///
        /// Useful for checking whether this string will fit in the space of a smaller FixedString*N*.
        /// </remarks>
        /// <typeparam name="T">A FixedString*N* type.</typeparam>
        /// <param name="fs">A string to get the effective size of.</param>
        /// <returns>The effective size in bytes of this string.</returns>
        [BurstCompatible(GenericTypeArguments = new[] { typeof(FixedString128Bytes) })]
        public static int EffectiveSizeOf<T>(ref this T fs)
            where T : struct, INativeList<byte>, IUTF8Bytes
        {
            return sizeof(ushort) + fs.Length + 1;
        }
    }
}