local db = {}
local file = fs.open("data.db","r+")
if not file then error("failed to open db file") end

local function readTable()
    file.seek("set")
    return textutils.unserialise(file.readAll() or "{}") or {}
end

local function writeTable(t)
    file.seek("set")
    file.write(textutils.serialise(t))
    file.flush()
end

---returns a list of all materials
---@return string[]
function db.getMaterials()
    local table = readTable()
    local materials = {}
    for k,_ in pairs(table.materials or {}) do
        materials[#materials+1] = k
    end
    return materials
end

---gets the price of a material
---@param mat string
---@return number
function db.getPrice(mat)
    return (readTable().materials or {})[mat]
end

---returns a list of all currencies
---@return string[]
function db.getCurrencies()
    local table = readTable()
    local currencies = {}
    for k,_ in pairs(table.currencies or {}) do
        currencies[#currencies+1] = k
    end
    return currencies
end

---gets the worth of a currency
---@param cur string
---@return number
function db.getCurrencyWorth(cur)
    return (readTable().currencies or {})[cur]
end

---sets the price of a material
---@param mat string
---@param price number
function db.setPrice(mat,price)
    local table = readTable()
    if not table.materials then table.materials = {} end
    table.materials[mat] = price
    writeTable(table)
end

---sets the worth of a currency
---@param cur string
---@param worth number
function db.setWorth(cur,worth)
    local table = readTable()
    if not table.currencies then table.currencies = {} end
    table.currencies[cur] = worth
    writeTable(table)
end

---gets the currency unit string
---@return string
function db.getCurrencyUnit()
    return readTable().currency_unit or "cr"
end

---sets the currency unit string
---@param unit string
function db.setCurrencyUnit(unit)
    local table = readTable()
    table.currency_unit = unit
    writeTable(table)
end

return db