#' Network Plot
#'
#' Draw an undirected graph from a square matrix
#' where each variable is a node and the pairwise
#' entries are the strength of the relationship
#' (ex: correlation, partial correlation)
#'
#' @param R A square numeric matrix with names columns and rows
#' @param title Optional plot title
#'
#' @return A ggraph object
#'
#' @examples
#' X <- matrix(data = rnorm(100), nrow = 10)
#' R <- cor(X)
#' networkplot(R, title = 'Example Correlation Plot')
#'
#' @import ggraph
#' @import igraph
#'
#' @export
networkplot <- function(R, title = NULL){
	Rm <- tryCatch({
		if(is.matrix(R)){
			if(nrow(R) != ncol(R)) stop('R must be square')
			Rm <- R
		}else if(is.vector(R)){
			m <- length(R)
			n <- (1 + sqrt(1 + 8 * m)) / 2
			if(n != floor(n)) stop('Vector length not compatible with upper triangle')
			n <- as.integer(n)
			Rm <- matrix(0, n, n)
			Rm[upper.tri(Rm)] <- R
			Rm <- Rm + t(Rm)
			diag(Rm) <- 1
		}else{
			Rm <- as.matrix(R)
			if(nrow(Rm) != ncol(Rm)) stop('R must be square')
		}

		if(is.null(rownames(Rm))){
			rownames(Rm) <- as.character(seq_len(nrow(Rm)))
		}

		if(is.null(colnames(Rm))){
			colnames(Rm) <- as.character(seq_len(ncol(Rm)))
		}

		Rm
	}, error = function(e){
		stop(paste('Invalid input for networkplot:', e$message))
	})

	idx <- which(upper.tri(Rm), arr.ind = TRUE)
	edges <- data.frame(
		from = rownames(Rm)[idx[,1]],
		to = colnames(Rm)[idx[,2]],
		r = Rm[idx]
	)
	g <- igraph::graph_from_data_frame(
		edges,
		directed = FALSE
	)

	p <- ggraph::ggraph(graph = g, layout = 'circle') +
	ggraph::geom_edge_arc(
		ggplot2::aes(
			edge_alpha = abs(.data$r),
			edge_color = .data$r
		),
		strength = 0.5
	) +
	ggraph::scale_edge_color_gradient2(
		low = 'red',
		mid = 'white',
		high = 'blue',
		midpoint = 0,
		limits = c(-1, 1),
		guide = 'none'
	) +
	ggraph::geom_node_point(size = 3) +
	ggraph::geom_node_text(
		ggplot2::aes(label = .data$name),
		repel = TRUE,
		size = 3
	) +
	ggplot2::theme_void() +
	ggplot2::theme(legend.position = 'none')

	if(!is.null(title)){
		p <- p +
		ggplot2::ggtitle(title) +
		ggplot2::theme(
			plot.title = ggplot2::element_text(hjust = 0.5)
		)
	}

	return(p)
}