using System;
using System.Collections.Generic;

namespace Neatly.UI
{
    public static class ImageHeader
    {
        delegate Size DelegateVector(byte[] bytes);

        public struct Size
        {
            public static readonly Size zero = new Size(0,0);
            public int width;
            public int height;

            public Size(int width, int height)
            {
                this.width = width;
                this.height = height;
            }
            
        }
        private struct ParseItem
        {
            private byte[] m_Head;
            private DelegateVector m_Action;

            public ParseItem(byte[] bytes, DelegateVector action)
            {
                this.m_Head = bytes;
                this.m_Action = action;
            }

            public bool IsRightTexture(byte[] sourceByte)
            {
                if (sourceByte.Length < m_Head.Length)
                {
                    return false;
                }
                for (int i = 0; i < m_Head.Length; i++)
                {
                    if (sourceByte[i] != m_Head[i])
                    {
                        return false;
                    }
                }
                return true;
            }

            public Size GetSize(byte[] sourceByte)
            {
                return m_Action(sourceByte);
            }
        }

        public static Size GetSize(byte[] sourceByte)
        {
            try
            {
                for (int i = 0; i < m_ParseList.Count; i++)
                {
                    return m_ParseList[i].IsRightTexture(sourceByte) ? m_ParseList[i].GetSize(sourceByte) : Size.zero;
                }
            }
            catch (Exception e)
            {
                return Size.zero;
            }
            return Size.zero;
        }

        private static List<ParseItem> m_ParseList = new List<ParseItem>
        {
            new ParseItem(new byte[] {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A}, GetPngSize), //Png
        };

        //Png 尺寸解析
        private static Size GetPngSize(byte[] bytes)
        {
            int sizeIndex = 16;
            int width = bytes[sizeIndex] << 24 | bytes[sizeIndex + 1] << 16 | bytes[sizeIndex + 2] << 8 | bytes[sizeIndex + 3];
            int height = bytes[sizeIndex + 4] << 24 | bytes[sizeIndex + 5] << 16 | bytes[sizeIndex + 6] << 8 | bytes[sizeIndex + 7];
            return new Size(width, height);
        }
    }
}