using System;
using System.IO;
using System.Text;
using WasmBox.Wasm.Binary;

namespace WasmBox.Wasm {
    /// <summary>
    /// A description of the limits of a table or memory.
    /// </summary>
    public struct ResizableLimits {
        /// <summary>
        /// Creates resizable limits with the given initial size and no maximal
        /// size.
        /// </summary>
        /// <param name="initial">The initial size of the resizable limits.</param>
        public ResizableLimits(uint initial) {
            this.Initial = initial;
            this.Maximum = default( uint? );
        }

        /// <summary>
        /// Creates resizable limits with the given initial and maximal sizes.
        /// </summary>
        /// <param name="initial">The initial size of the resizable limits.</param>
        /// <param name="maximum">The maximal size of the resizable limits.</param>
        public ResizableLimits(uint initial, uint maximum) {
            this.Initial = initial;
            this.Maximum = new uint?( maximum);
        }

        /// <summary>
        /// Creates resizable limits with the given initial and maximal sizes.
        /// </summary>
        /// <param name="initial">The initial size of the resizable limits.</param>
        /// <param name="maximum">The optional maximal size of the resizable limits.</param>
        public ResizableLimits(uint initial, uint? maximum ) {
            this.Initial = initial;
            this.Maximum = maximum;
        }

        /// <summary>
        /// Gets a Boolean that tells if these resizable limits have a maximum size.
        /// </summary>
        public bool HasMaximum => Maximum.HasValue;

        /// <summary>
        /// Gets the initial length (in units of table elements or wasm pages).
        /// </summary>
        /// <returns>The initial length of the resizable limits.</returns>
        public uint Initial { get; private set; }

        /// <summary>
        /// Gets the maximal length (in units of table elements or wasm pages).
        /// This value may be <c>null</c> to signify that no maximum is specified.
        /// </summary>
        /// <returns>The maximum length of the resizable limits, if any.</returns>
        public uint? Maximum { get; private set; }

        /// <summary>
        /// Writes these resizable limits to the given WebAssembly file writer.
        /// </summary>
        /// <param name="writer">The WebAssembly file writer.</param>
        public void WriteTo(BinaryWasmWriter writer) {
            writer.WriteVarUInt1(HasMaximum);
            writer.WriteVarUInt32(Initial);
            if (HasMaximum) {
                writer.WriteVarUInt32(Maximum.Value);
            }
        }

        /// <summary>
        /// Writes a textual representation of these resizable limits to the given writer.
        /// </summary>
        /// <param name="writer">The writer to which text is written.</param>
        public void Dump(TextWriter writer) {
            writer.Write("{initial: ");
            writer.Write(Initial);
            if (HasMaximum) {
                writer.Write(", max: ");
                writer.Write(Maximum.Value);
            }
            writer.Write("}");
        }

        /// <inheritdoc/>
        public override string ToString() {
            var builder = new StringBuilder();
            Dump(new StringWriter(builder));
            return builder.ToString();
        }
    }
}