r - Remove Default Background Color and Make Title in Plot Zone

Question

I have this ggplot2 plot which I want to modify to fit the following conditions:

1. Remove default background that is hash colour to be plain.
2. Make (a) to be the plot title located within the plot area that is not close to the line (automatically).
3. Make $phi = .8$ to be automatically at the head of the line (still within the plot area).
4. And sd = 1 to be automatically at the tail of the line.

EDIT

5. The four(4) Border lines to be present.
6. Gridlines to be grey colour.

.

## simulate ARIMA(1, 0, 0)
set.seed(799837)
ts <- arima.sim(n = 10, model = list(ar = 0.95, order = c(1, 0, 0)), sd = 10)

gplot <- ggplot(NULL, aes(y = ts, x = seq_along(ts))) + scale_x_continuous(breaks = seq(1,10,2)) +
  geom_line(color = "#F2AA4CFF") + geom_point(color = "#101820FF") + xlab('Time') + ylab('Series') + ggtitle(expression("(a)
sd = 1
"~phi~"=.8")) + 
  theme(axis.text = element_text(size = 10, angle = 0, vjust = 0.0, hjust = 0.0), axis.title = element_text(size = 10), axis.title.x = element_text(angle = 0, hjust = 0.5, vjust = 0.5, size = 10), axis.title.y = element_text(angle = 90, hjust = 0.5, vjust = 0.5, size = 14), plot.title = element_text(size = 14, margin = margin(t = 25, b = -20, l = 0, r = 0))) + 
scale_y_continuous(expand = c(0.0, 0.00))

gplot

Answer 1

Here is an example how of this might look semi automatic. The specifics depend on how different your actual time series data is, but this might help as inspiration. Exact positions and text styling can of course be tweaked to your liking.

set.seed(799837)
ts <- arima.sim(n = 10, model = list(ar = 0.95, order = c(1, 0, 0)), sd = 10)    

gplot <- ggplot(NULL, aes(y = ts, x = seq_along(ts))) + 
      geom_line(color = "#F2AA4CFF") + 
      geom_point(color = "#101820FF") + 
      annotate("text", x = mean(seq_along(ts)), y = max(ts) * 1.1, label = "(a)")+
      annotate("text", x = min(seq_along(ts)), y = max(ts) * 1.1, label = 'paste(~phi~"=.8")', parse = TRUE )+ 
      annotate("text", x= max(seq_along(ts)), y = ts[[max(seq_along(ts))]] * 1.1, label = "sd=1") +
      xlab('Time') + 
      ylab('Series') + 
      theme(axis.text = element_text(size = 10, angle = 0, vjust = 0.0, hjust = 0.0), 
            axis.title = element_text(size = 10), 
            axis.title.x = element_text(angle = 0, hjust = 0.5, vjust = 0.5, size = 10), 
            axis.title.y = element_text(angle = 90, hjust = 0.5, vjust = 0.5, size = 14), 
            plot.title = element_text(size = 14, margin = margin(t = 25, b = -20, l = 0, r = 0)),
            panel.background = element_blank()) + 
      scale_x_continuous(breaks = seq(1,10,2)) +
      scale_y_continuous(expand = c(0.0, 0.00))