using System.Text;
using TMPro;
using UnityEngine;
using UnityEngine.UI;

namespace AppUI.Localization
{
    /// <summary>
    /// 按 UI 可用宽度在文案中插入零宽空格 <c>\u200B</c>，配合 TMP / Legacy Text 自动换行。
    /// </summary>
    static class AppUILocalizationTextBreak
    {
        const char ZeroWidthSpace = '\u200B';

        public static float ResolveMaxWidth(RectTransform rect, float maxWidth)
        {
            if (maxWidth > 0f)
                return maxWidth;

            if (rect == null)
                return 0f;

            float width = rect.rect.width;
            if (width > 0f)
                return width;

            return LayoutUtility.GetPreferredWidth(rect);
        }

        public static float ResolveMaxHeight(RectTransform rect, float maxHeight)
        {
            if (maxHeight > 0f)
                return maxHeight;

            if (rect == null)
                return 0f;

            float height = rect.rect.height;
            if (height > 0f)
                return height;

            return LayoutUtility.GetPreferredHeight(rect);
        }

        public static string InsertWidthBreaks(string text, TMP_Text tmpText, float maxWidth, float maxHeight = 0f)
        {
            if (string.IsNullOrEmpty(text) || tmpText == null)
                return text;

            maxWidth = ResolveMaxWidth(tmpText.rectTransform, maxWidth);
            if (maxWidth <= 0f)
                return text;

            if (FitsSingleLine(text, tmpText, maxWidth))
                return text;

            var output = new StringBuilder(text.Length + 16);
            InsertWidthBreaksInto(text, output, maxWidth, line => tmpText.GetPreferredValues(line, 0, 0).x);

            string result = output.ToString();
            maxHeight = ResolveMaxHeight(tmpText.rectTransform, maxHeight);
            if (maxHeight > 0f && tmpText.GetPreferredValues(result, maxWidth, 0).y > maxHeight)
                return result;

            return result;
        }

        public static string InsertWidthBreaks(string text, Text legacyText, float maxWidth, float maxHeight = 0f)
        {
            if (string.IsNullOrEmpty(text) || legacyText == null)
                return text;

            maxWidth = ResolveMaxWidth(legacyText.rectTransform, maxWidth);
            if (maxWidth <= 0f)
                return text;

            float Measure(string line)
            {
                var settings = legacyText.GetGenerationSettings(new Vector2(maxWidth, 0f));
                settings.generateOutOfBounds = true;
                return new TextGenerator().GetPreferredWidth(line, settings) / legacyText.pixelsPerUnit;
            }

            if (Measure(text) <= maxWidth)
                return text;

            var output = new StringBuilder(text.Length + 16);
            InsertWidthBreaksInto(text, output, maxWidth, Measure);

            string result = output.ToString();
            maxHeight = ResolveMaxHeight(legacyText.rectTransform, maxHeight);
            if (maxHeight > 0f)
            {
                var settings = legacyText.GetGenerationSettings(new Vector2(maxWidth, maxHeight));
                settings.generateOutOfBounds = true;
                float height = new TextGenerator().GetPreferredHeight(result, settings) / legacyText.pixelsPerUnit;
                if (height > maxHeight)
                    return result;
            }

            return result;
        }

        static bool FitsSingleLine(string text, TMP_Text tmpText, float maxWidth)
        {
            if (text.IndexOf('\n') >= 0)
                return false;

            Vector2 preferred = tmpText.GetPreferredValues(text, maxWidth, 0);
            if (preferred.x <= maxWidth)
                return true;

            return tmpText.GetPreferredValues(text, 0, 0).x <= maxWidth;
        }

        static void InsertWidthBreaksInto(string source, StringBuilder output, float maxWidth, System.Func<string, float> measureWidth)
        {
            for (int i = 0; i < source.Length; i++)
            {
                char c = source[i];
                if (c == '<')
                {
                    int end = source.IndexOf('>', i);
                    if (end > i)
                    {
                        output.Append(source, i, end - i + 1);
                        i = end;
                        continue;
                    }
                }

                if (c == '\n')
                {
                    output.Append(c);
                    continue;
                }

                output.Append(c);
                while (GetVisibleLineLength(output) > 1 && measureWidth(GetCurrentLine(output)) > maxWidth)
                    output.Insert(FindLastVisibleIndex(output), ZeroWidthSpace);
            }
        }

        static int FindLineStart(StringBuilder sb)
        {
            for (int i = sb.Length - 1; i >= 0; i--)
            {
                if (sb[i] == ZeroWidthSpace || sb[i] == '\n')
                    return i + 1;
            }

            return 0;
        }

        static string GetCurrentLine(StringBuilder sb)
        {
            int start = FindLineStart(sb);
            return sb.ToString(start, sb.Length - start);
        }

        static int GetVisibleLineLength(StringBuilder sb)
        {
            string line = GetCurrentLine(sb);
            int count = 0;
            for (int i = 0; i < line.Length; i++)
            {
                if (line[i] == '<')
                {
                    int end = line.IndexOf('>', i);
                    if (end > i)
                    {
                        i = end;
                        continue;
                    }
                }

                count++;
            }

            return count;
        }

        static int FindLastVisibleIndex(StringBuilder sb)
        {
            int lineStart = FindLineStart(sb);
            for (int i = sb.Length - 1; i >= lineStart; i--)
            {
                if (sb[i] == ZeroWidthSpace || sb[i] == '\n')
                    continue;

                if (sb[i] == '>')
                {
                    int open = i;
                    while (open >= lineStart && sb[open] != '<')
                        open--;
                    if (open >= lineStart)
                    {
                        i = open;
                        continue;
                    }
                }

                if (sb[i] == '<')
                    continue;

                return i;
            }

            return sb.Length - 1;
        }
    }
}