package todo

import "strconv"

// filter is which slice of the list a page shows. Its name is what forms
// post back as `filter`; its path is where the 303 goes.
type filter string

const (
	filterAll       filter = "all"
	filterActive    filter = "active"
	filterCompleted filter = "completed"
)

// parseFilter reads a posted filter. Missing or unknown is "all".
func parseFilter(s string) filter {
	switch f := filter(s); f {
	case filterActive, filterCompleted:
		return f
	}
	return filterAll
}

func (f filter) path() string {
	if f == filterAll {
		return "/"
	}
	return "/" + string(f)
}

func (f filter) shows(t Todo) bool {
	switch f {
	case filterActive:
		return !t.Completed
	case filterCompleted:
		return t.Completed
	}
	return true
}

// view is everything the page template draws.
type view struct {
	Filter    filter
	Items     []item
	Total     int
	Left      int
	Completed int
	Editing   bool
}

type item struct {
	ID        int64
	Title     string
	Completed bool
	Editing   bool
	EditHref  string
}

// newView sorts the list into what the page shows. Counts cover the
// whole list whichever filter is on; editing is the item whose editor is
// open, or 0.
func newView(todos []Todo, f filter, editing int64) view {
	v := view{Filter: f, Total: len(todos)}
	for _, t := range todos {
		if t.Completed {
			v.Completed++
		} else {
			v.Left++
		}
		if !f.shows(t) {
			continue
		}
		it := item{ID: t.ID, Title: t.Title, Completed: t.Completed,
			Editing:  t.ID == editing,
			EditHref: f.path() + "?edit=" + strconv.FormatInt(t.ID, 10)}
		v.Editing = v.Editing || it.Editing
		v.Items = append(v.Items, it)
	}
	return v
}

// Class is the li's class attribute: completed, editing, both or none.
func (it item) Class() string {
	switch {
	case it.Completed && it.Editing:
		return "completed editing"
	case it.Completed:
		return "completed"
	case it.Editing:
		return "editing"
	}
	return ""
}

// AllCompleted is toggle-all's checked state.
func (v view) AllCompleted() bool { return v.Total > 0 && v.Left == 0 }