Script to Generate Line Segments but Needs to Avoid Curved Lines and Multiple Line Segments.

updated code, 

// LINE SEGMENTS//
var doc = app.activeDocument;
//REMOVE THIS AFTER FIXED//

// Set stroke properties for the line segments
function setStrokeProperties(item) {
    item.stroked = true; // Ensure it's stroked
    item.strokeWidth = 2; // Set the stroke width

    var newColor;
    
    // Set the stroke color based on the document's color space
    if (doc.documentColorSpace == DocumentColorSpace.RGB) {
        newColor = new RGBColor();
        newColor.red = 0;
        newColor.green = 0;
        newColor.blue = 0;
    } else if (doc.documentColorSpace == DocumentColorSpace.CMYK) {
        newColor = new CMYKColor();
        newColor.cyan = 0;
        newColor.magenta = 0;
        newColor.yellow = 0;
        newColor.black = 100;
    }

    item.strokeColor = newColor;
}

// Function to set the bezier handle properties
function BEZIER(point, pathPoints, index) {
    // Check if the segment is a curve and avoid generating lines
    if (
        (point.leftDirection[0] !== point.anchor[0] || point.leftDirection[1] !== point.anchor[1]) &&
        (point.rightDirection[0] !== point.anchor[0] || point.rightDirection[1] !== point.anchor[1])
    ) {
        return true;
    }

    // Skip line segment creation of open paths
    if (
        (pathPoints.parent.closed === false) &&
        (index === 0 || index === pathPoints.length - 1)
    ) {
        return true;
    }

    // If none of the above conditions are met, generate lines
    return false;
}

// Function to create line segments with a stable stroke color
function createLineSegment(startPoint, endPoint) {
    var newLine = doc.pathItems.add();
    newLine.setEntirePath([startPoint, endPoint]);
    setStrokeProperties(newLine); // Set stroke properties and color

    // Place the line segment in the "LINE SEGMENTS" layer
    newLine.layer = lineLayer;
}

// Create a new layer for line segments
var lineLayer = doc.layers.add();
lineLayer.name = "LINE SEGMENTS";

// Function to process different item types
function processItem(item) {
    if (item.typename === "GroupItem") {
        var groupItems = item.pageItems;
        for (var j = 0; j < groupItems.length; j++) {
            processItem(groupItems[j]);
        }
    } else if (item.typename === "PathItem") {
        var pathPoints = item.pathPoints;
        if (pathPoints.length === 2) {
            if (
                (pathPoints[0].leftDirection[0] !== pathPoints[0].anchor[0] || pathPoints[0].leftDirection[1] !== pathPoints[0].anchor[1]) &&
                (pathPoints[1].rightDirection[0] !== pathPoints[1].anchor[0] || pathPoints[1].rightDirection[1] !== pathPoints[1].anchor[1])
            ) {
                return; // Skip line segment creation
            }
            createLineSegment(pathPoints[0].anchor, pathPoints[1].anchor);
        } else {
            for (var k = 0; k < pathPoints.length; k++) {
                var startPoint = pathPoints[k];
                var endPoint = pathPoints[(k + 1) % pathPoints.length];
                if (BEZIER(startPoint, pathPoints, k) && BEZIER(endPoint, pathPoints, (k + 1) % pathPoints.length)) {
                    continue; // Skip line segment creation
                }
                createLineSegment(startPoint.anchor, endPoint.anchor);
            }
        }
    } else if (item.typename === "CompoundPathItem") {
        // Recursively process each path item within the compound path
        for (var i = 0; i < item.pathItems.length; i++) {
            processItem(item.pathItems[i]);
        }
    }
}

// Now, process the selected items to generate lines
var selectedItems = doc.selection;
for (var i = 0; i < selectedItems.length; i++) {
  var currentItem = selectedItems[i];

  if (currentItem.layer.name === "DUP") {
      continue;
  }

  processItem(currentItem);
}

 
The last thing I want to remove is in red :

What is the purpose of the script? Can you give the simplest example of what you are using it for? 

Ok, I managed to get it right for the first issue.

if (app.documents.length > 0) {
  var doc = app.activeDocument;

  var strokeColor = new RGBColor();
  strokeColor.red = 0;
  strokeColor.green = 0;
  strokeColor.blue = 0;
  var strokeWidth = 0.5;

  function hasHandles(point) {
    return (
      point.leftDirection[0] !== point.anchor[0] || point.leftDirection[1] !== point.anchor[1] ||
      point.rightDirection[0] !== point.anchor[0] || point.rightDirection[1] !== point.anchor[1]
    );
  }

  var selectedItems = doc.selection;
  for (var i = 0; i < selectedItems.length; i++) {
    var currentItem = selectedItems[i];

    if (currentItem.typename === "GroupItem") {
      // If the selected item is a group, iterate through its pageItems
      for (var k = 0; k < currentItem.pageItems.length; k++) {
        var groupItem = currentItem.pageItems[k];
        processItem(groupItem);
      }
    } else {
      processItem(currentItem);
    }
  }

  function processItem(item) {
    if (item.typename === "PathItem") {
      var pathPoints = item.pathPoints;

      for (var j = 0; j < pathPoints.length; j++) {
        var startPoint = pathPoints[j];
        var endPoint = pathPoints[(j + 1) % pathPoints.length];

        // Check if both anchor points have handles
        if (hasHandles(startPoint) && hasHandles(endPoint)) {
          continue; // Skip line segment creation
        }

        var newLine = doc.pathItems.add();
        newLine.setEntirePath([startPoint.anchor, endPoint.anchor]);
        newLine.strokeColor = strokeColor;
        newLine.strokeWidth = strokeWidth;
      }
    } else if (item.typename === "CompoundPathItem") {
      var compoundPathItems = item.pathItems;
      for (var l = 0; l < compoundPathItems.length; l++) {
        var pathItem = compoundPathItems[l];
        var pathPoints = pathItem.pathPoints;

        for (var j = 0; j < pathPoints.length; j++) {
          var startPoint = pathPoints[j];
          var endPoint = pathPoints[(j + 1) % pathPoints.length];

          // Check if both anchor points have handles
          if (hasHandles(startPoint) && hasHandles(endPoint)) {
            continue; // Skip line segment creation
          }

          var newLine = doc.pathItems.add();
          newLine.setEntirePath([startPoint.anchor, endPoint.anchor]);
          newLine.strokeColor = strokeColor;
          newLine.strokeWidth = strokeWidth;
        }
      }
    }
  }
}

 
one problem to go!