-- local db = require("solvitdb")
local db = {}
local fs = require("filesystem")
local json = require("json")
local dbpath = "/ag2/testdb.json"
function db.create()
  local handle = fs.open(dbpath,"w")
  handle:write("{}")
  handle:close()
end
function db.readJSON()
  local handle = fs.open(dbpath,"r")
  local content = ""
  while true do
    local s = handle:read(math.huge or math.maxinteger)
    if not s then break end
    content=content..s
  end
  handle:close()
  return content
end
function db.get(pack)
  local dbc = json.decode(db.readJSON())
  return dbc[pack]
end
function db.set(pack,info)
  local dbc = json.decode(db.readJSON())
  dbc[pack]=info
  local handle = fs.open(dbpath,"w")
  handle:write(json.encode(dbc))
  handle:close()
end
function db.remove(pack)
  local dbc = json.decode(db.readJSON())
  dbc[pack]=nil
  local handle = fs.open(dbpath,"w")
  handle:write(json.encode(dbc))
  handle:close()
end

local avs = {}
function avs.splitSingular(s)
  local result = {}
  for str in string.gmatch(s, "([^.]+)") do
    table.insert(result,tonumber(str) or -1)
  end
  return result
end

function avs.parse(pack)
  if not string.find(pack,"=") then
    return {pack}
  end
  local idx=pack:find("=")
  local name=pack:sub(1,idx-1)
  local verstr=pack:sub(idx+1)
  if string.find(verstr,"-") then
    idx=verstr:find("-")
    verstr={verstr:sub(1,idx-1),verstr:sub(idx+1)}
  else
    verstr={verstr}
  end
  for i=1,#verstr do
    verstr[i]=avs.splitSingular(verstr[i])
  end
  if #verstr>1 then
    for i=1,3 do
      verstr[1][i]=math.max(verstr[1][i],0)
    end
  end
  return {name,verstr}
end

function avs.serializeSingle(ver)
  local ver2 = table.copy(ver)
  for i=1,3 do
    if ver2[i]==-1 then
      ver2[i]="*"
    else
      ver2[i]=tostring(ver2[i])
    end
  end
  return ver2[1].."."..ver2[2].."."..ver2[3]
end

function avs.serializeVersion(ver)
  out=""
  for i=1,#ver do
    out=out..avs.serializeSingle(ver[i])
    if i~=#ver then
      out=out.."-"
    end
  end
  return out
end

function avs.serializePack(pack)
  if #pack==1 then
    return pack[1]
  end
  return pack[1].."="..avs.serializeVersion(pack[2])
end

function avs.singleGreater(ver1,ver2)
  for i=1,3 do
    if ver1[i]~=ver2[i] then
      if ver1[i]==-1 or ver1[i]>ver2[i] then
        return true
      end
      if ver2[i]==-1 or ver2[i]>ver1[i] then
        return false
      end
    end
  end
  return false
end

function avs.singleLesser(ver1,ver2)
  return avs.singleGreater(ver2,ver1)
end

function avs.singleMin(ver1,ver2)
  return avs.singleLesser(ver1,ver2) and ver1 or ver2
end

function avs.singleMax(ver1,ver2)
  return avs.singleGreater(ver1,ver2) and ver1 or ver2
end

function avs.compatibleRange(vers)
  for i=1,#vers do
    if type(vers[i])=="string" then vers[i]=avs.parse(vers[i])[2] end
    if #vers[i]==1 then vers[i]={vers[i][1],vers[i][1]} end
  end
  local range = vers[1]
  for i=2,#vers do
    range[1]=avs.singleMax(range[1],vers[i][1])
    range[2]=avs.singleMin(range[2],vers[i][2])
  end
  if avs.singleGreater(range[1],range[2]) then
    return nil
  end
  return range
end

local function packageInArray(pack,arr)
  for i=1,#arr do
    if arr[i][1]==pack[1] then -- TODO: check for compatible package version
      return true
    end
  end
  return false
end

local function startTransaction()
  if not fs.exists(dbpath) then
    db.create()
  end

  local packInfo = {}
  local ins = {}
  local rem = {}
  local transaction = {}
  function transaction.install(name)
    table.insert(ins,avs.parse(name))
  end
  function transaction.remove(name)
  end
  function transaction.addInfo(name,info)
    packInfo[name]=info
    -- print(require("serialize").table(packInfo))
  end
  function transaction.finalize(settings)
    local function getPackInfo(pack)
      return packInfo[avs.serializePack(pack)]
    end

    local foundDeps=false
    repeat
      foundDeps=false
      -- find missing package information
      local missing = {}
      for i=1,#ins do
        if getPackInfo(ins[i])==nil then
          table.insert(missing,avs.serializePack(ins[i]))
        end
      end
      if #missing>0 then
        return false,missing
      end
      -- find dependencies
      local i=1
      while i<=#ins do
        local deps = getPackInfo(ins[i]).dependencies
        if deps and #deps>=1 then
          for j=1,#deps do
            local dep = avs.parse(deps[j])
            if (not packageInArray(dep,ins)) and db.get(dep[1]) then
              foundDeps=true
              table.insert(ins,j,dep)
            end
          end
          i=i+#deps
        end
        i=i+1
      end
    until not foundDeps

    return {install=ins}

    -- return "true, {["install"] = {"dep1", "package1", "package2"}, ["remove"] = {"package3"}}" on success
    -- return "false, {"dep1"}" when not enough data
    -- return "false, "[verbose string]"" when conflict found
    -- TODO: be able to resolve conflicts
    -- TODO: implement removing packages
    -- TODO: handle same constant AVS
    -- TODO: handle different constant AVS conflict
    -- TODO: handle same range AVS
    -- TODO: handle different intercompatible 1.*.* range AVS
    -- TODO: handle different incompatible 1.*.* range AVS
    -- TODO: handle different intercompatible 1.*.*-2.*.* range AVS
    -- TODO: handle different incompatible 1.*.*-2.*.* range AVS
    -- TODO: handle conflicts from package info
    -- TODO: handle reverse conflicts from another package's info
  end
  function transaction.store()
    for i,v in pairs(packInfo) do
      db.set(i,v)
    end
    -- TODO: make and store reverse dependencies
  end
  return transaction
end

return { avs=avs,startTransaction=startTransaction }