PdfPig/src/UglyToad.PdfPig/Content/Word.cs

namespace UglyToad.PdfPig.Content
{
    using Core;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    /// <summary>
    /// A word.
    /// </summary>
    public class Word
    {
        /// <summary>
        /// The text of the word.
        /// </summary>
        public string Text { get; }

        /// <summary>
        /// The text orientation of the word.
        /// </summary>
        public TextOrientation TextOrientation { get; }

        /// <summary>
        /// The rectangle completely containing the word.
        /// </summary>
        public PdfRectangle BoundingBox { get; }

        /// <summary>
        /// The name of the font for the word.
        /// </summary>
        public string? FontName { get; }

        /// <summary>
        /// The letters contained in the word.
        /// </summary>
        public IReadOnlyList<Letter> Letters { get; }

        /// <summary>
        /// Create a new <see cref="Word"/>.
        /// </summary>
        /// <param name="letters">The letters contained in the word, in the correct order.</param>
        public Word(IReadOnlyList<Letter> letters)
        {
            if (letters is null)
            {
                throw new ArgumentNullException(nameof(letters));
            }

            if (letters.Count == 0)
            {
                throw new ArgumentException("Empty letters provided.", nameof(letters));
            }

            Letters = letters;

            var tempTextOrientation = letters[0].TextOrientation;
            if (tempTextOrientation != TextOrientation.Other)
            {
                foreach (var letter in letters)
                {
                    if (letter.TextOrientation != tempTextOrientation)
                    {
                        tempTextOrientation = TextOrientation.Other;
                        break;
                    }
                }
            }

            Tuple<string, PdfRectangle> data;
            switch (tempTextOrientation)
            {
                case TextOrientation.Horizontal:
                    data = GetBoundingBoxH(letters);
                    break;

                case TextOrientation.Rotate180:
                    data = GetBoundingBox180(letters);
                    break;

                case TextOrientation.Rotate90:
                    data = GetBoundingBox90(letters);
                    break;

                case TextOrientation.Rotate270:
                    data = GetBoundingBox270(letters);
                    break;

                case TextOrientation.Other:
                default:
                    data = GetBoundingBoxOther(letters);
                    break;
            }

            Text = data.Item1;
            BoundingBox = data.Item2;

            FontName = letters[0].FontName;
            TextOrientation = tempTextOrientation;
        }

        #region Bounding box
        private Tuple<string, PdfRectangle> GetBoundingBoxH(IReadOnlyList<Letter> letters)
        {
            var builder = new StringBuilder();

            var blX = double.MaxValue;
            var trX = double.MinValue;
            var blY = double.MaxValue;
            var trY = double.MinValue;

            for (var i = 0; i < letters.Count; i++)
            {
                var letter = letters[i];
                builder.Append(letter.Value);

                if (letter.StartBaseLine.X < blX)
                {
                    blX = letter.StartBaseLine.X;
                }

                if (letter.StartBaseLine.Y < blY)
                {
                    blY = letter.StartBaseLine.Y;
                }

                var right = letter.StartBaseLine.X + Math.Max(letter.Width, letter.GlyphRectangle.Width);
                if (right > trX)
                {
                    trX = right;
                }

                if (letter.GlyphRectangle.TopLeft.Y > trY)
                {
                    trY = letter.GlyphRectangle.TopLeft.Y;
                }
            }

            return new Tuple<string, PdfRectangle>(builder.ToString(), new PdfRectangle(blX, blY, trX, trY));
        }

        private Tuple<string, PdfRectangle> GetBoundingBox180(IReadOnlyList<Letter> letters)
        {
            var builder = new StringBuilder();

            var blX = double.MinValue;
            var blY = double.MinValue;
            var trX = double.MaxValue;
            var trY = double.MaxValue;

            for (var i = 0; i < letters.Count; i++)
            {
                var letter = letters[i];
                builder.Append(letter.Value);

                if (letter.StartBaseLine.X > blX)
                {
                    blX = letter.StartBaseLine.X;
                }

                if (letter.StartBaseLine.Y > blY)
                {
                    blY = letter.StartBaseLine.Y;
                }

                var right = letter.StartBaseLine.X - Math.Max(letter.Width, letter.GlyphRectangle.Width);
                if (right < trX)
                {
                    trX = right;
                }

                if (letter.GlyphRectangle.TopRight.Y < trY)
                {
                    trY = letter.GlyphRectangle.TopRight.Y;
                }
            }

            return new Tuple<string, PdfRectangle>(builder.ToString(), new PdfRectangle(blX, blY, trX, trY));
        }

        private Tuple<string, PdfRectangle> GetBoundingBox90(IReadOnlyList<Letter> letters)
        {
            var builder = new StringBuilder();

            var b = double.MaxValue;
            var r = double.MaxValue;
            var t = double.MinValue;
            var l = double.MinValue;

            for (var i = 0; i < letters.Count; i++)
            {
                var letter = letters[i];
                builder.Append(letter.Value);

                if (letter.StartBaseLine.X < b)
                {
                    b = letter.StartBaseLine.X;
                }

                if (letter.EndBaseLine.Y < r)
                {
                    r = letter.EndBaseLine.Y;
                }

                var right = letter.StartBaseLine.X + letter.GlyphRectangle.Height;
                if (right > t)
                {
                    t = right;
                }

                if (letter.GlyphRectangle.BottomLeft.Y > l)
                {
                    l = letter.GlyphRectangle.BottomLeft.Y;
                }
            }

            return new Tuple<string, PdfRectangle>(builder.ToString(), new PdfRectangle(
                new PdfPoint(t, l), new PdfPoint(t, r),
                new PdfPoint(b, l), new PdfPoint(b, r)));
        }

        private Tuple<string, PdfRectangle> GetBoundingBox270(IReadOnlyList<Letter> letters)
        {
            var builder = new StringBuilder();

            var t = double.MaxValue;
            var b = double.MinValue;
            var l = double.MaxValue;
            var r = double.MinValue;

            for (var i = 0; i < letters.Count; i++)
            {
                var letter = letters[i];
                builder.Append(letter.Value);

                if (letter.StartBaseLine.X > b)
                {
                    b = letter.StartBaseLine.X;
                }

                if (letter.StartBaseLine.Y < l)
                {
                    l = letter.StartBaseLine.Y;
                }

                var right = letter.StartBaseLine.X - letter.GlyphRectangle.Height;
                if (right < t)
                {
                    t = right;
                }

                if (letter.GlyphRectangle.BottomRight.Y > r)
                {
                    r = letter.GlyphRectangle.BottomRight.Y;
                }
            }

            return new Tuple<string, PdfRectangle>(builder.ToString(), new PdfRectangle(
                new PdfPoint(t, l), new PdfPoint(t, r),
                new PdfPoint(b, l), new PdfPoint(b, r)));
        }

        private Tuple<string, PdfRectangle> GetBoundingBoxOther(IReadOnlyList<Letter> letters)
        {
            var builder = new StringBuilder();
            for (var i = 0; i < letters.Count; i++)
            {
                builder.Append(letters[i].Value);
            }

            if (letters.Count == 1)
            {
                return new Tuple<string, PdfRectangle>(builder.ToString(), letters[0].GlyphRectangle);
            }
            else
            {
                var baseLinePoints = letters.SelectMany(r => new[]
                {
                    r.StartBaseLine,
                    r.EndBaseLine,
                }).ToList();

                // Fitting a line through the base lines points
                // to find the orientation (slope)
                double x0 = baseLinePoints.Average(p => p.X);
                double y0 = baseLinePoints.Average(p => p.Y);
                double sumProduct = 0;
                double sumDiffSquaredX = 0;

                for (int i = 0; i < baseLinePoints.Count; i++)
                {
                    var point = baseLinePoints[i];
                    var x_diff = point.X - x0;
                    var y_diff = point.Y - y0;
                    sumProduct += x_diff * y_diff;
                    sumDiffSquaredX += x_diff * x_diff;
                }

                double cos = 0;
                double sin = 1;
                if (sumDiffSquaredX > 1e-3)
                {
                    // not vertical line
                    double angleRad = Math.Atan(sumProduct / sumDiffSquaredX); // -π/2 ≤ θ ≤ π/2
                    cos = Math.Cos(angleRad);
                    sin = Math.Sin(angleRad);
                }

                // Rotate the points to build the axis-aligned bounding box (AABB)
                var inverseRotation = new TransformationMatrix(
                    cos, -sin, 0,
                    sin, cos, 0,
                    0, 0, 1);

                var transformedPoints = letters.SelectMany(r => new[]
                {
                    r.StartBaseLine,
                    r.EndBaseLine,
                    r.GlyphRectangle.TopLeft,
                    r.GlyphRectangle.TopRight
                }).Distinct().Select(p => inverseRotation.Transform(p));

                var aabb = new PdfRectangle(transformedPoints.Min(p => p.X),
                                            transformedPoints.Min(p => p.Y),
                                            transformedPoints.Max(p => p.X),
                                            transformedPoints.Max(p => p.Y));

                // Rotate back the AABB to obtain to oriented bounding box (OBB)
                var rotateBack = new TransformationMatrix(
                    cos, sin, 0,
                    -sin, cos, 0,
                    0, 0, 1);

                // Candidates bounding boxes
                var obb = rotateBack.Transform(aabb);
                var obb1 = new PdfRectangle(obb.BottomLeft, obb.TopLeft, obb.BottomRight, obb.TopRight);
                var obb2 = new PdfRectangle(obb.BottomRight, obb.BottomLeft, obb.TopRight, obb.TopLeft);
                var obb3 = new PdfRectangle(obb.TopRight, obb.BottomRight, obb.TopLeft, obb.BottomLeft);

                // Find the orientation of the OBB, using the baseline angle
                // Assumes word order is correct
                var firstLetter = letters[0];
                var lastLetter = letters[letters.Count - 1];

                var baseLineAngle = Math.Atan2(
                    lastLetter.EndBaseLine.Y - firstLetter.StartBaseLine.Y,
                    lastLetter.EndBaseLine.X - firstLetter.StartBaseLine.X) * 180 / Math.PI;

                double deltaAngle = Math.Abs(BoundAngle180(obb.Rotation - baseLineAngle));
                double deltaAngle1 = Math.Abs(BoundAngle180(obb1.Rotation - baseLineAngle));
                if (deltaAngle1 < deltaAngle)
                {
                    deltaAngle = deltaAngle1;
                    obb = obb1;
                }

                double deltaAngle2 = Math.Abs(BoundAngle180(obb2.Rotation - baseLineAngle));
                if (deltaAngle2 < deltaAngle)
                {
                    deltaAngle = deltaAngle2;
                    obb = obb2;
                }

                double deltaAngle3 = Math.Abs(BoundAngle180(obb3.Rotation - baseLineAngle));
                if (deltaAngle3 < deltaAngle)
                {
                    obb = obb3;
                }

                return new Tuple<string, PdfRectangle>(builder.ToString(), obb);
            }
        }
        #endregion

        /// <summary>
        /// Bound angle so that -180 ≤ θ ≤ 180.
        /// </summary>
        /// <param name="angle">The angle to bound.</param>
        private static double BoundAngle180(double angle)
        {
            angle = (angle + 180) % 360;
            if (angle < 0) angle += 360;
            return angle - 180;
        }

        /// <inheritdoc />
        public override string ToString()
        {
            return Text;
        }
    }
}