using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Text;
using System.Text.Encodings.Web;
using Microsoft.Extensions.Primitives;

namespace Iceshrimp.Frontend.Core.Miscellaneous;

// Adapted under MIT from https://raw.githubusercontent.com/dotnet/aspnetcore/3f1acb59718cadf111a0a796681e3d3509bb3381/src/Http/Http.Abstractions/src/QueryString.cs

/// <summary>
///     Provides correct handling for QueryString value when needed to reconstruct a request or redirect URI string
/// </summary>
[DebuggerDisplay("{Value}")]
public readonly struct QueryString : IEquatable<QueryString>
{
	/// <summary>
	///     Represents the empty query string. This field is read-only.
	/// </summary>
	public static readonly QueryString Empty = new(string.Empty);

	/// <summary>
	///     Initialize the query string with a given value. This value must be in escaped and delimited format with
	///     a leading '?' character.
	/// </summary>
	/// <param name="value">The query string to be assigned to the Value property.</param>
	public QueryString(string? value)
	{
		if (!string.IsNullOrEmpty(value) && value[0] != '?')
		{
			throw new ArgumentException(@"The leading '?' must be included for a non-empty query.", nameof(value));
		}

		Value = value;
	}

	/// <summary>
	///     The escaped query string with the leading '?' character
	/// </summary>
	public string? Value { get; }

	/// <summary>
	///     True if the query string is not empty
	/// </summary>
	[MemberNotNullWhen(true, nameof(Value))]
	public bool HasValue => !string.IsNullOrEmpty(Value);

	/// <summary>
	///     Provides the query string escaped in a way which is correct for combining into the URI representation.
	///     A leading '?' character will be included unless the Value is null or empty. Characters which are potentially
	///     dangerous are escaped.
	/// </summary>
	/// <returns>The query string value</returns>
	public override string ToString()
	{
		return ToUriComponent();
	}

	/// <summary>
	///     Provides the query string escaped in a way which is correct for combining into the URI representation.
	///     A leading '?' character will be included unless the Value is null or empty. Characters which are potentially
	///     dangerous are escaped.
	/// </summary>
	/// <returns>The query string value</returns>
	public string ToUriComponent()
	{
		// Escape things properly so System.Uri doesn't mis-interpret the data.
		return HasValue ? Value.Replace("#", "%23") : string.Empty;
	}

	/// <summary>
	///     Returns an QueryString given the query as it is escaped in the URI format. The string MUST NOT contain any
	///     value that is not a query.
	/// </summary>
	/// <param name="uriComponent">The escaped query as it appears in the URI format.</param>
	/// <returns>The resulting QueryString</returns>
	public static QueryString FromUriComponent(string uriComponent)
	{
		if (string.IsNullOrEmpty(uriComponent))
		{
			return new QueryString(string.Empty);
		}

		return new QueryString(uriComponent);
	}

	/// <summary>
	///     Returns an QueryString given the query as from a Uri object. Relative Uri objects are not supported.
	/// </summary>
	/// <param name="uri">The Uri object</param>
	/// <returns>The resulting QueryString</returns>
	public static QueryString FromUriComponent(Uri uri)
	{
		ArgumentNullException.ThrowIfNull(uri);

		var queryValue = uri.GetComponents(UriComponents.Query, UriFormat.UriEscaped);
		if (!string.IsNullOrEmpty(queryValue))
		{
			queryValue = "?" + queryValue;
		}

		return new QueryString(queryValue);
	}

	/// <summary>
	///     Create a query string with a single given parameter name and value.
	/// </summary>
	/// <param name="name">The un-encoded parameter name</param>
	/// <param name="value">The un-encoded parameter value</param>
	/// <returns>The resulting QueryString</returns>
	public static QueryString Create(string name, string value)
	{
		ArgumentNullException.ThrowIfNull(name);

		if (!string.IsNullOrEmpty(value))
		{
			value = UrlEncoder.Default.Encode(value);
		}

		return new QueryString($"?{UrlEncoder.Default.Encode(name)}={value}");
	}

	/// <summary>
	///     Creates a query string composed from the given name value pairs.
	/// </summary>
	/// <param name="parameters"></param>
	/// <returns>The resulting QueryString</returns>
	public static QueryString Create(IEnumerable<KeyValuePair<string, string?>> parameters)
	{
		var builder = new StringBuilder();
		var first   = true;
		foreach (var pair in parameters)
		{
			AppendKeyValuePair(builder, pair.Key, pair.Value, first);
			first = false;
		}

		return new QueryString(builder.ToString());
	}

	/// <summary>
	///     Creates a query string composed from the given name value pairs.
	/// </summary>
	/// <param name="parameters"></param>
	/// <returns>The resulting QueryString</returns>
	public static QueryString Create(IEnumerable<KeyValuePair<string, StringValues>> parameters)
	{
		var builder = new StringBuilder();
		var first   = true;

		foreach (var pair in parameters)
		{
			// If nothing in this pair.Values, append null value and continue
			if (StringValues.IsNullOrEmpty(pair.Value))
			{
				AppendKeyValuePair(builder, pair.Key, null, first);
				first = false;
				continue;
			}

			// Otherwise, loop through values in pair.Value
			foreach (var value in pair.Value)
			{
				AppendKeyValuePair(builder, pair.Key, value, first);
				first = false;
			}
		}

		return new QueryString(builder.ToString());
	}

	/// <summary>
	///     Concatenates <paramref name="other" /> to the current query string.
	/// </summary>
	/// <param name="other">The <see cref="QueryString" /> to concatenate.</param>
	/// <returns>The concatenated <see cref="QueryString" />.</returns>
	public QueryString Add(QueryString other)
	{
		if (!HasValue || Value.Equals("?", StringComparison.Ordinal))
		{
			return other;
		}

		if (!other.HasValue || other.Value.Equals("?", StringComparison.Ordinal))
		{
			return this;
		}

		// ?name1=value1 Add ?name2=value2 returns ?name1=value1&name2=value2
		return new QueryString(string.Concat(Value, "&", other.Value.AsSpan(1)));
	}

	/// <summary>
	///     Concatenates a query string with <paramref name="name" /> and <paramref name="value" />
	///     to the current query string.
	/// </summary>
	/// <param name="name">The name of the query string to concatenate.</param>
	/// <param name="value">The value of the query string to concatenate.</param>
	/// <returns>The concatenated <see cref="QueryString" />.</returns>
	public QueryString Add(string name, string value)
	{
		ArgumentNullException.ThrowIfNull(name);

		if (!HasValue || Value.Equals("?", StringComparison.Ordinal))
		{
			return Create(name, value);
		}

		var builder = new StringBuilder(Value);
		AppendKeyValuePair(builder, name, value, first: false);
		return new QueryString(builder.ToString());
	}

	/// <summary>
	///     Evalutes if the current query string is equal to <paramref name="other" />.
	/// </summary>
	/// <param name="other">The <see cref="QueryString" /> to compare.</param>
	/// <returns><see langword="true" /> if the query strings are equal.</returns>
	public bool Equals(QueryString other)
	{
		if (!HasValue && !other.HasValue)
		{
			return true;
		}

		return string.Equals(Value, other.Value, StringComparison.Ordinal);
	}

	/// <summary>
	///     Evaluates if the current query string is equal to an object <paramref name="obj" />.
	/// </summary>
	/// <param name="obj">An object to compare.</param>
	/// <returns><see langword="true" /> if the query strings are equal.</returns>
	public override bool Equals(object? obj)
	{
		if (ReferenceEquals(null, obj))
		{
			return !HasValue;
		}

		return obj is QueryString && Equals((QueryString)obj);
	}

	/// <summary>
	///     Gets a hash code for the value.
	/// </summary>
	/// <returns>The hash code as an <see cref="int" />.</returns>
	public override int GetHashCode()
	{
		return HasValue ? Value.GetHashCode() : 0;
	}

	/// <summary>
	///     Evaluates if one query string is equal to another.
	/// </summary>
	/// <param name="left">A <see cref="QueryString" /> instance.</param>
	/// <param name="right">A <see cref="QueryString" /> instance.</param>
	/// <returns><see langword="true" /> if the query strings are equal.</returns>
	public static bool operator ==(QueryString left, QueryString right)
	{
		return left.Equals(right);
	}

	/// <summary>
	///     Evaluates if one query string is not equal to another.
	/// </summary>
	/// <param name="left">A <see cref="QueryString" /> instance.</param>
	/// <param name="right">A <see cref="QueryString" /> instance.</param>
	/// <returns><see langword="true" /> if the query strings are not equal.</returns>
	public static bool operator !=(QueryString left, QueryString right)
	{
		return !left.Equals(right);
	}

	/// <summary>
	///     Concatenates <paramref name="left" /> and <paramref name="right" /> into a single query string.
	/// </summary>
	/// <param name="left">A <see cref="QueryString" /> instance.</param>
	/// <param name="right">A <see cref="QueryString" /> instance.</param>
	/// <returns>The concatenated <see cref="QueryString" />.</returns>
	public static QueryString operator +(QueryString left, QueryString right)
	{
		return left.Add(right);
	}

	private static void AppendKeyValuePair(StringBuilder builder, string key, string? value, bool first)
	{
		builder.Append(first ? '?' : '&');
		builder.Append(UrlEncoder.Default.Encode(key));
		builder.Append('=');
		if (!string.IsNullOrEmpty(value))
		{
			builder.Append(UrlEncoder.Default.Encode(value));
		}
	}
}