# install.packages(c("dodgr", "igraph", "ggraph", "ggplot2"))  # run once if needed

library(dodgr)
library(igraph)
library(ggraph)
library(ggplot2)

## 1. Define the tree as a directed graph (X upstream of A)
#              X
#              |
#              A
#            /   \
#           B     C
#          / \   / \
#         D   E F   G

graph <- data.frame(
  edge_id  = 1:7,
  from     = c("X", "A","A",  "B","B",  "C","C"),
  to       = c("A", "B","C",  "D","E",  "F","G"),
  weight   = rep(1, 7),   # used by dodgr for routing
  distance = rep(1, 7)    # distance-like metric
)

## 2. Define OD flows at the leaf nodes (demands at D, E, F, G)
from  <- "X"                            # origin (root)
to    <- c("D", "E", "F", "G")          # leaves
flows <- matrix(c(5, 5, 10, 10),        # X->D, X->E, X->F, X->G
                nrow = length(from))

## 3. Use dodgr to aggregate flows on each edge
agg <- dodgr_flows_aggregate(
  graph     = graph,
  from      = from,
  to        = to,
  flows     = flows,
  contract  = FALSE,
  norm_sums = FALSE      # keep raw flow sums (not normalised)
)

## 4. Compute pressure drop per edge from the flows
# Simple model: ΔP_e = R_e * Q_e^2
# Here we just set R_e = 1 Pa / (flow_unit^2) for all edges
# (You’d normally use real R values from duct calcs)

agg$R_coeff    <- 1
agg$dp_edge_Pa <- agg$R_coeff * agg$flow^2

# Quick check in console
print(agg[, c("edge_id", "from", "to", "flow", "dp_edge_Pa")])

## 5. Build an igraph object with attributes for plotting
g <- graph_from_data_frame(
  d = agg[, c("from", "to", "flow", "dp_edge_Pa")],
  directed = TRUE
)

## 6. Plot the tree with edge labels (flow + ΔP) and save as PDF

# Create the plot object
p <- ggraph(g, layout = "tree") +
  # edges with labels: show flow and ΔP on each edge
  geom_edge_link(aes(
      label = paste0("Q=", flow, "\nΔP=", round(dp_edge_Pa, 2), " Pa")
    ),
    angle_calc  = "along",
    label_dodge = unit(2, "mm"),
    label_size  = 3
  ) +
  geom_node_point(size = 4) +
  geom_node_text(aes(label = name), vjust = -1, size = 4) +
  theme_void() +
  ggtitle("Tree with Flows and Pressure Drops")

# Save to PDF in your working directory
ggsave("tree_flows.pdf", p, width = 6, height = 8)

# After running this script, check your working directory for "tree_flows.pdf"