local Observable = require "rx.observable"

--- Returns a new Observable that produces values computed by extracting the given keys from the
-- tables produced by the original.
-- @arg {string...} keys - The key to extract from the table. Multiple keys can be specified to
--                         recursively pluck values from nested tables.
-- @returns {Observable}
function Observable:pluck(key, ...)
    if not key then
        return self
    end

    if type(key) ~= "string" and type(key) ~= "number" then
        return Observable.throw("pluck key must be a string")
    end

    return Observable.create(function(observer)
        local function onNext(t)
            return observer:onNext(t[key])
        end

        local function onError(e)
            return observer:onError(e)
        end

        local function onCompleted()
            return observer:onCompleted()
        end

        return self:subscribe(onNext, onError, onCompleted)
    end):pluck(...)
end