# Functions for creating samples of datasets
# Copyright (C) 2018  Nathan TeBlunthuis

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

sample.by.wiki <- function(dt,outcome,N.per.wiki=30){
    set.seed(0)
    sample.params <- dt[,.N,by=wiki.name]
    sample.params[,group.sd := dt[,.(group.sd=sd(.SD[[outcome]])),by=wiki.name]$group.sd]

    sample.params[,p.in.group := N / nrow(dt)]

    sample.params[,min.N := min(N)]
    sample.params[,n.from.group := pmin(min.N/(1-group.sd), N)]

    sample.params[,p.sampled := n.from.group/N]

    sample.params[,weight := 1/p.sampled]
    dt[sample.params,":="(prob=p.sampled,weight=weight),on=.(wiki.name)]
    sample.idx <- sample(nrow(dt),size=sum(sample.params$n.from.group,na.rm=TRUE),prob=dt$prob)

    return(dt[sample.idx])
}

sample.newcomers <- function()
{
    wikis.to.remove <- newcomers[,.N,by="wiki.name"][N<30]$wiki.name
    remember(nrow(wikis.to.remove),"n.wikis.insufficient.newcomers")
    newcomers.presample <- newcomers[!(wiki.name  %in% wikis.to.remove)]
    newcomers.sample <- sample.by.wiki(newcomers.presample,"survives")
    return(newcomers.sample)
}

sample.ns4.edits <- function(){
    wikis.to.keep <- ns4.reg.edits[,.(.N,N.reverts=sum(reverted)),by=wiki.name][(N>30)&(N.reverts > 30)]
    ns4.reg.edits.sub <- ns4.reg.edits[wiki.name %in% wikis.to.keep$wiki.name]
    ns4.reg.edits.sample <- sample.by.wiki(ns4.reg.edits.sub,"reverted")
    return(ns4.reg.edits.sample)
}

sample.wiki.data <- function(){
    ## just choose 100 random wikis
    wikis.to.keep <- sample(unique(wiki.data$wiki.name),100)
    wiki.data.sample <- wiki.data[wiki.name %in% wikis.to.keep]
    return(wiki.data.sample)
}