#!/usr/bin/env Rscript
library(ggplot2)
library(plyr)

# Process command-line arguments
args <- commandArgs(trailingOnly = TRUE)
if (length(args) != 2)
  stop("usage: tweet-engangement input-file output-base-name")
input.filename <- args[1]
name <- args[2]

t <- read.csv(input.filename, header=TRUE)

# Convert time to POSIX type
t$ptime <- as.POSIXct(strptime(t$time, format="%Y-%m-%d %H:%M %z"))


# Plot tweet impressions by hour
t$hour <- strftime(t$ptime, "%H", tz="Europe/Athens")
s <- ddply(t, ~hour, summarize, mean=mean(impressions))
output.filename <- paste(name, '-hour.png', sep='')
png(filename=output.filename)
ggplot(data=s, aes(x=hour, y=mean)) +
  geom_bar(stat="identity") +
  labs(title=paste('Impressions for', name),
    x='Local hour', y='Mean impressions')
dev.off()

# Plot tweet impressions by day of week
t$dow <- strftime(t$ptime, "%a", tz="Europe/Athens")
s <- ddply(t, ~dow, summarize, mean=mean(impressions))
output.filename <- paste(name, '-dow.png', sep='')
png(filename=output.filename)
ggplot(data=s, aes(x=dow, y=mean)) +
  geom_bar(stat="identity") +
  labs(title=paste('Impressions for', name),
    x='Day of week', y='Mean impressions')
dev.off()