package web

import (
	"net/url"
	"sort"
	"strings"

	"github.com/m/projax/store"
)

// Phase 5i Slice C — kanban view_type. Read-only: groups the filtered item
// set into columns by the chosen group_by dimension. Drag-to-change-group
// is deliberately out of scope (design.md §3 / slice ordering A→B→D→C→E).
//
// m's Q6 pick (2026-05-26): default group_by = status (active/done/archived).
// Other values (area / tag / management) remain selectable via the
// group_by chip strip.

// Kanban group_by values. The DB CHECK constraint on projax.views.group_by
// is open-ended (text); the validation list lives here so the handler can
// reject typos before they round-trip.
const (
	GroupByStatus     = "status"
	GroupByArea       = "area"
	GroupByTag        = "tag"
	GroupByManagement = "management"
)

var allGroupBy = []string{GroupByStatus, GroupByArea, GroupByTag, GroupByManagement}

// ParseGroupBy pulls `group_by` from q. Empty / unknown values fall back to
// the default (status). Lower-cases for case-insensitive matching.
func ParseGroupBy(q url.Values) string {
	raw := strings.ToLower(strings.TrimSpace(q.Get("group_by")))
	for _, g := range allGroupBy {
		if raw == g {
			return g
		}
	}
	return GroupByStatus
}

// KanbanColumn is one column in the rendered board.
type KanbanColumn struct {
	Key   string        // the raw group value (status="active", tag="work", …)
	Label string        // human-readable header
	Items []*store.Item // sorted: pinned-first, then updated_at desc, then title
}

// KanbanBoard is the rendered shape. Columns are ordered by the canonical
// per-dimension order (status: active/done/archived; management: mai/self/
// external/unmanaged; area + tag: alphabetical with the items they hold).
type KanbanBoard struct {
	GroupBy string
	Columns []KanbanColumn
	Total   int // total cards across columns
}

// BuildKanbanBoard groups the matched items by groupBy. Pure: takes whatever
// list of items the handler filtered, returns the column shape.
func BuildKanbanBoard(items []*store.Item, groupBy string) KanbanBoard {
	if groupBy == "" {
		groupBy = GroupByStatus
	}
	keyer := groupByKeyer(groupBy)
	byKey := map[string][]*store.Item{}
	emittedKeys := []string{}
	seen := map[string]bool{}
	for _, it := range items {
		for _, k := range keyer(it) {
			if !seen[k] {
				seen[k] = true
				emittedKeys = append(emittedKeys, k)
			}
			byKey[k] = append(byKey[k], it)
		}
	}
	// Stable column ordering per dimension.
	switch groupBy {
	case GroupByStatus:
		emittedKeys = orderKeyedFirst(emittedKeys, []string{"active", "done", "archived"})
	case GroupByManagement:
		emittedKeys = orderKeyedFirst(emittedKeys, []string{"mai", "self", "external", "unmanaged"})
	default:
		sort.Strings(emittedKeys)
	}
	board := KanbanBoard{GroupBy: groupBy}
	for _, k := range emittedKeys {
		cardItems := byKey[k]
		sort.SliceStable(cardItems, func(i, j int) bool {
			a, b := cardItems[i], cardItems[j]
			if a.Pinned != b.Pinned {
				return a.Pinned
			}
			if !a.UpdatedAt.Equal(b.UpdatedAt) {
				return a.UpdatedAt.After(b.UpdatedAt)
			}
			return a.Title < b.Title
		})
		board.Columns = append(board.Columns, KanbanColumn{
			Key:   k,
			Label: columnLabel(groupBy, k),
			Items: cardItems,
		})
		board.Total += len(cardItems)
	}
	return board
}

// groupByKeyer returns a function that maps an item to its column keys (a
// slice because tags can put one item in multiple columns).
func groupByKeyer(groupBy string) func(*store.Item) []string {
	switch groupBy {
	case GroupByStatus:
		return func(it *store.Item) []string {
			s := it.Status
			if s == "" {
				s = "active"
			}
			return []string{s}
		}
	case GroupByManagement:
		return func(it *store.Item) []string {
			if len(it.Management) == 0 {
				return []string{"unmanaged"}
			}
			out := make([]string, 0, len(it.Management))
			out = append(out, it.Management...)
			return out
		}
	case GroupByArea:
		return func(it *store.Item) []string {
			// First segment of the primary path is the area (dev / work / home …).
			p := it.PrimaryPath()
			if p == "" {
				return []string{"—"}
			}
			if idx := strings.IndexByte(p, '.'); idx > 0 {
				return []string{p[:idx]}
			}
			return []string{p}
		}
	case GroupByTag:
		return func(it *store.Item) []string {
			if len(it.Tags) == 0 {
				return []string{"untagged"}
			}
			return append([]string(nil), it.Tags...)
		}
	}
	return func(it *store.Item) []string { return []string{it.Status} }
}

// columnLabel renders the column header. Status / management get title-case
// for legibility; area and tag stay verbatim.
func columnLabel(groupBy, key string) string {
	switch groupBy {
	case GroupByStatus, GroupByManagement:
		if key == "" {
			return "—"
		}
		return strings.ToUpper(key[:1]) + key[1:]
	}
	return key
}

// orderKeyedFirst returns `actual` with `preferred` entries first (in the
// preferred order, when present in actual), then any remaining actual
// entries appended in input order.
func orderKeyedFirst(actual, preferred []string) []string {
	present := map[string]bool{}
	for _, k := range actual {
		present[k] = true
	}
	out := make([]string, 0, len(actual))
	for _, k := range preferred {
		if present[k] {
			out = append(out, k)
			delete(present, k)
		}
	}
	for _, k := range actual {
		if present[k] {
			out = append(out, k)
			delete(present, k)
		}
	}
	return out
}

// GroupByChip is one entry in the group-by chip strip rendered above the
// kanban board. Active marks the current group_by; URL is the toggle target.
type GroupByChip struct {
	Label  string
	URL    string
	Active bool
}

// GroupByChips builds the group-by chip strip. base must already include the
// `?view_type=kanban` segment; we append `&group_by=<value>` on top.
func GroupByChips(base string, filter TreeFilter, current string) []GroupByChip {
	out := make([]GroupByChip, 0, len(allGroupBy))
	for _, g := range allGroupBy {
		u := filter.URLOn(base)
		if !strings.Contains(u, "?") {
			u += "?view_type=kanban&group_by=" + g
		} else {
			u += "&view_type=kanban&group_by=" + g
		}
		out = append(out, GroupByChip{
			Label:  g,
			URL:    u,
			Active: g == current,
		})
	}
	return out
}