opus/sys/apis/history.lua

local Util = require('util')

local History    = { }
local History_mt = { __index = History }

function History.load(filename, limit)

  local self = setmetatable({
    limit = limit,
    filename = filename,
  }, History_mt)

  self.entries = Util.readLines(filename) or { }
  self.pos = #self.entries + 1

  return self
end

function History:add(line)
  if line ~= self.entries[#self.entries] then
    table.insert(self.entries, line)
    if self.limit then
      while #self.entries > self.limit do
        table.remove(self.entries, 1)
      end
    end
    Util.writeLines(self.filename, self.entries)
    self.pos = #self.entries + 1
  end
end

function History:reset()
  self.pos = #self.entries + 1
end

function History:back()
  if self.pos > 1 then
    self.pos = self.pos - 1
    return self.entries[self.pos]
  end
end

function History:forward()
  if self.pos <= #self.entries then
    self.pos = self.pos + 1
    return self.entries[self.pos]
  end
end

return History