module DatePicker exposing (Model, Msg, view, init, initWithConfig, update, getNow)

{-| A date range picker.

# View
@docs view

# Update
@docs init, initWithConfig, getNow, update

# State
@docs Model

# Definitions
@docs Msg

-}

import Platform.Cmd as Cmd
import Html exposing (Html, Attribute, text, div, span, input, label)
import Html.Events exposing (onClick)
import Html.Attributes exposing (classList, style, type_, value, maxlength)
import Date exposing (Date, toTime, fromTime, now, year, month, day)
import Task exposing (perform)
import Array exposing (initialize)
import DatePicker.Helpers as Helpers
import DatePicker.Style as Style
import DatePicker.Config as Config


-- MODEL


type Choice
    = Start
    | End
    | None


{-| A model to track the state of the date picker.

An instance of this should appear somewhere in your applications model.
-}
type alias Model =
    { focused : Date
    , choice : Choice
    , selected : Maybe Date
    , selectedEnd : Maybe Date
    , config : Config.Config
    }


{-| Set the focus to the current date.

This can be used to initialize the date picker.

    init : Config -> ( Model, Cmd Msg )
    init config =
        ( (DatePicker.initWithConfig config), DatePicker.getNow Msg )
-}
getNow : (Msg -> msg) -> Cmd msg
getNow tagger =
    perform (tagger << SetFocused) Date.now


{-| An initial state with nothing selected and a default configuration.
-}
init : Model
init =
    { focused = Helpers.defaultDate
    , choice = Start
    , selected = Nothing
    , selectedEnd = Nothing
    , config = Config.defaultConfig
    }


{-| Initialize the data picker with nothing selected and a custom configuration.

Custom configurations can be used to override the styling, placeholder strings,
and whether the picker selects a single date or a range.
-}
initWithConfig : Config.Config -> Model
initWithConfig config =
    { focused = config.defaultDate
    , choice = Start
    , selected = Nothing
    , selectedEnd = Nothing
    , config = config
    }



-- UPDATE


{-| A message type for the date picker.
-}
type Msg
    = SetFocused Date
    | SetSelecting Choice
    | SetSelected Choice (Maybe Date)


{-| Update the date picker.
-}
update : Msg -> Model -> Model
update msg model =
    case msg of
        SetFocused date ->
            { model | focused = date }

        SetSelecting choice ->
            { model | choice = choice }

        SetSelected choice result ->
            case choice of
                Start ->
                    case model.selectedEnd of
                        Just selectedEnd ->
                            case result of
                                Just date ->
                                    if Helpers.isBefore selectedEnd date then
                                        { model | selected = Just date }
                                    else
                                        { model | selected = Just date, selectedEnd = Nothing }

                                Nothing ->
                                    { model | selected = Nothing }

                        Nothing ->
                            { model | selected = result, choice = End }

                End ->
                    case model.selected of
                        Just selected ->
                            case result of
                                Just date ->
                                    if Helpers.isBefore selected date then
                                        { model | selected = Just date, selectedEnd = Nothing }
                                    else
                                        { model | selectedEnd = Just date }

                                Nothing ->
                                    { model | selectedEnd = Nothing }

                        Nothing ->
                            { model | selectedEnd = result, choice = Start }

                None ->
                    model



-- VIEW


{-| Render a date picker.
-}
view : Model -> Html Msg
view model =
    div [ styling model Style.Container ]
        [ viewInputs model, viewDatepicker model ]


viewInputs : Model -> Html Msg
viewInputs model =
    let
        inputs =
            if model.config.useRange then
                [ viewInput model Start, viewInput model End ]
            else
                [ viewInput model Start ]
    in
        div [ styling model Style.InputsContainer ] inputs


viewInput : Model -> Choice -> Html Msg
viewInput model choice =
    let
        value_ =
            case choice of
                Start ->
                    model.selected

                End ->
                    model.selectedEnd

                None ->
                    Just Helpers.defaultDate

        placeholder =
            case choice of
                Start ->
                    model.config.placeholderFrom

                End ->
                    model.config.placeholderTo

                None ->
                    ""
    in
        div [ styling model Style.InputContainer, onClick (SetSelecting choice) ]
            [ label [ styling model Style.InputLabel ]
                [ span [] []
                , input [ styling model Style.Input, type_ "text", maxlength 10 ] []
                ]
            , div [ styling model Style.InputDisplayTextContainer ]
                [ span [ styling model Style.InputDisplayText ] [ text (Helpers.dateAsString placeholder value_) ] ]
            ]


viewDatepicker : Model -> Html Msg
viewDatepicker model =
    div
        [ styling model Style.DatepickerContainer ]
        [ viewMonth model
        , viewWeekdays model
        , viewDays model
        ]


viewMonth : Model -> Html Msg
viewMonth model =
    let
        prevMonth =
            Helpers.addMonth -1 model.focused

        nextMonth =
            Helpers.addMonth 1 model.focused

        monthString =
            toString (month model.focused)
    in
        div [ styling model Style.MonthMenu ]
            [ div [ styling model Style.ArrowLeft, onClick (SetFocused prevMonth) ]
                [ span [ styling model Style.ArrowLeftInner ] [] ]
            , span [ styling model Style.MonthContainer ]
                [ span [ styling model Style.Month ] [ text monthString ]
                , span [ styling model Style.Year ] [ text <| toString <| year model.focused ]
                ]
            , div [ styling model Style.ArrowRight, onClick (SetFocused nextMonth) ]
                [ span [ styling model Style.ArrowRightInner ] [] ]
            ]


viewWeekdays : Model -> Html Msg
viewWeekdays model =
    let
        days =
            [ "Mo", "Tu", "We", "Th", "Fr", "Sa", "Su" ]

        createDay day =
            div [ styling model Style.WeekDay ] [ text day ]
    in
        div [ styling model Style.WeekDays ]
            (List.map createDay days)


viewDays : Model -> Html Msg
viewDays model =
    let
        createDay =
            viewDay model (Helpers.firstOfSlide model.focused)

        days =
            Array.toList (Array.initialize 42 createDay)
    in
        div [ styling model Style.Days ]
            days


viewDay : Model -> Date -> Int -> Html Msg
viewDay model init diff =
    let
        date =
            Helpers.addDay diff init

        highlighted =
            case model.selected of
                Just selected ->
                    case model.selectedEnd of
                        Just selectedEnd ->
                            Helpers.isBetween selected selectedEnd date

                        Nothing ->
                            Helpers.equals selected date

                Nothing ->
                    False

        isNotCurrentMonth =
            month date /= month model.focused

        styling =
            if model.config.useDefaultStyles then
                Style.getDefaultStyle Style.Day
                    |> (++) ((?) highlighted (Style.getDefaultStyle Style.DayHighlight))
                    |> (++) ((?) isNotCurrentMonth (Style.getDefaultStyle Style.DayNotCurrentMonth))
                    |> style
            else
                model.config.getClasses Style.Day
                    |> (++) ((?) highlighted (model.config.getClasses Style.DayHighlight))
                    |> (++) ((?) isNotCurrentMonth (model.config.getClasses Style.DayNotCurrentMonth))
                    |> classList
    in
        div [ styling, onClick (SetSelected model.choice <| Just date) ]
            [ text (toString (day date)) ]



-- styling helpers + more


(?) : Bool -> List a -> List a
(?) condition ifTrue =
    if condition then
        ifTrue
    else
        []


styling : Model -> Style.View -> Attribute a
styling model view =
    if model.config.useDefaultStyles then
        style (Style.getDefaultStyle view)
    else
        classList (model.config.getClasses view)