How to plot horizontal lines based on Parabolic SAR swing points?

Question

I recently added the SAR to a particular trading strategy. Even more recently I had the idea to plot horizontal lines every time the SAR changes direction because I noticed when it does change direction the very first plot is based on the low or high between the bar that changes direction and the previous bar that changed direction. At first I thought this shouldn't be too difficult for myself to implement, but reading through the SAR code I was only sort of able to understand it and had no idea how and what to reference, especially as the variables and such are not global but are inside the function itself. I thought to see if ChatGPT could help me. After much frustrations this is what I got:

indicator("Parabolic SAR Levels with Horizontal Change Lines", overlay=true)

// Define the input parameters for the Parabolic SAR
start = input.float(0.02, title="Start", step=0.01)
increment = input.float(0.02, title="Increment", step=0.01)
maximum = input.float(0.2, title="Maximum", step=0.01)

// Pine Script implementation of Parabolic SAR
pine_sar(start, inc, max) =>
    var float result = na
    var float maxMin = na
    var float acceleration = na
    var bool isBelow = na
    bool isFirstTrendBar = false

    if bar_index == 1
        if close > close[1]
            isBelow := true
            maxMin := high
            result := low[1]
        else
            isBelow := false
            maxMin := low
            result := high[1]
        isFirstTrendBar := true
        acceleration := start

    result := result + acceleration * (maxMin - result)

    if isBelow
        if result > low
            isFirstTrendBar := true
            isBelow := false
            result := math.max(high, maxMin)
            maxMin := low
            acceleration := start
    else
        if result < high
            isFirstTrendBar := true
            isBelow := true
            result := math.min(low, maxMin)
            maxMin := high
            acceleration := start

    if not isFirstTrendBar
        if isBelow
            if high > maxMin
                maxMin := high
                acceleration := math.min(acceleration + inc, max)
        else
            if low < maxMin
                maxMin := low
                acceleration := math.min(acceleration + inc, max)

    if isBelow
        result := math.min(result, low[1])
        if bar_index > 1
            result := math.min(result, low[2])
    else
        result := math.max(result, high[1])
        if bar_index > 1
            result := math.max(result, high[2])

    result

// Calculate the Parabolic SAR
psar = pine_sar(start, increment, maximum)

// Plot the Parabolic SAR
plot(psar, title="Parabolic SAR", color=#000000, linewidth=1, style=plot.style_cross)

// Variables to store line information
var line currentLine = na
var float lastHighLow = na
var bool lastIsBelow = na

// Check for change in SAR direction
isBelow = psar < close

// Update the highest high or lowest low between changes
if na(lastIsBelow) or isBelow != lastIsBelow
    if not na(currentLine)
        line.set_x2(currentLine, bar_index - 1) // Extend the line to the previous bar

    // Create a new horizontal line from the high/low of the identified bar
    float highLow = na
    if isBelow
        highLow := high
    else
        highLow := low

    currentLine := line.new(x1=bar_index, y1=highLow, x2=bar_index, y2=highLow, color=#000000, width=1)

    // Update the last high/low price and SAR direction
    lastHighLow := highLow
    lastIsBelow := isBelow
else
    if isBelow
        if high > lastHighLow
            lastHighLow := high
    else
        if low < lastHighLow
            lastHighLow := low

    // Extend the current line to the current bar
    line.set_x2(currentLine, bar_index)
    line.set_y1(currentLine, lastHighLow)
    line.set_y2(currentLine, lastHighLow)

Well, ChatGPT has done reasonably well after much time spent prompting poorly by me, but I/it's run into a wall. It is correctly identifying those swing highs and lows between changes in direction of the SAR, but the line beginnings and ends are wrong; I can't seem to get it to plot the x1 and x2 coordinates properly. As you can see in the image the lines appear to extend backward in time (in reality I think the code is plotting the x1 at the bar that caused the previous SAR change and the x2 at the bar that caused the most recent SAR change). I used these two points of reference for ChatGPT in order to identify the swing prices (y coordinates) between them, but it seems to want to use those two points of reference for the x coordinates as well, and I have no idea why, and I can't seem to get ChatGPT to understand what I want. Now I am here asking for help.

The absolute best outcome would be for the x1 to be the same bar that the y coordinates are based on, and have its terminus be at the next SAR direction change (on chart it would look like a line drawn from a swing price point forward until there is a SAR direction change), but I'd be happy just to have each x coordinate be at a SAR direction change; in other words the line would plot from one bar that caused the SAR change to the next bar that causes a SAR change.

And the one other request/question I have is that it also be possible to use a lowest or highest close for the y coordinates, and then the option for the user to select either closes or highs/lows to use for y coordinates?

update

My preference would be for the line to start at the high price. So, when you look at the very first star or circle plot for the SAR every time it changes trend you'll see that it aligns with the highest high or lowest low from the previous SAR trend. I would really like for the line to start at that high or low. Your end point is correct: the last bar in that SAR trend. All that said, I would be happy with the line starting from where you have it drawn in that pic. Basically in this case the line would be drawn for the total extent that the SAR is plotted

Red lines are what I would like. Vertical lines just show where a new SAR starts and emphasizes my point about how the current lines look as though they're plotted in reverse or backward

Huge huge thanks to anyone who might be able to help me out with any part of this.

How to plot horizontal lines based on Parabolic SAR swing points?

Answers (1)

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