package web

import (
	"context"
	"net/http"
	"sort"
	"strings"
	"time"

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

// Timeline cache TTL — looser than the dashboard's 60s because /timeline is
// browse-y rather than action-y. Per filter+window key. Phase 5b unified
// onto internal/cache.TTLCache[V].
const timelineCacheTTL = 90 * time.Second

// timelineKindTodo / Event / Doc / Creation are the four filterable row
// kinds. They double as the `?kind=` query values. Re-export the
// aggregate-package constants under the web names callers already use.
const (
	timelineKindTodo     = aggregate.KindTodo
	timelineKindEvent    = aggregate.KindEvent
	timelineKindDoc      = aggregate.KindDoc
	timelineKindCreation = aggregate.KindCreation
)

// timelineDefaultPastDays / FutureDays bound the default window: 30 days back
// and 90 forward, per design.md §12.
const (
	timelineDefaultPastDays   = 30
	timelineDefaultFutureDays = 90
)

// TimelineRow is one entry on the chronological spine. Re-exported from
// internal/aggregate so MCP + web share one row shape. (Pre-Phase-5a
// web/timeline.go defined its own copy; the aggregator package now owns
// the canonical sum-type wrapper.)
type TimelineRow = aggregate.TimelineRow

// TimelineDay groups rows that share a date for the spine header.
type TimelineDay = aggregate.TimelineDay

// TimelinePayload is the rendered shape for /timeline.
type TimelinePayload struct {
	Days        []TimelineDay // outer order respects ?order=
	From        time.Time     // window start (inclusive)
	To          time.Time     // window end (exclusive)
	ToInclusive time.Time     // To - 1 day; used by templates for display
	Order       string        // "desc" (default) or "asc"
	Kinds       []string      // active row kinds (default: all four)
	BuiltAt     time.Time
	Cached      bool
	TotalRows   int // count across all days
}

// TimelineQuery is the parsed user input. Built from URL params; round-trips
// to QueryString for the cache key.
type TimelineQuery struct {
	Filter TreeFilter
	From   time.Time
	To     time.Time
	Order  string   // "asc" | "desc"
	Kinds  []string // sorted, lower-case; empty means "all four"
	// Phase 4f: when true, per-item timeline_exclude arrays are ignored —
	// every source surfaces regardless. Used for the "show me what I'm
	// hiding" peek (URL: ?include_excluded=1, MCP arg: include_excluded).
	IncludeExcluded bool
}

// activeKinds returns the effective kind set for filter math: returns the
// requested subset, or all four when the user did not narrow.
func (q TimelineQuery) activeKinds() []string {
	if len(q.Kinds) == 0 {
		return []string{timelineKindTodo, timelineKindEvent, timelineKindDoc, timelineKindCreation}
	}
	return q.Kinds
}

func (q TimelineQuery) wantKind(k string) bool {
	for _, x := range q.activeKinds() {
		if x == k {
			return true
		}
	}
	return false
}

// cacheKey is filter + window + order + kinds → string. Used both for the
// in-process cache and as the canonical URL state.
func (q TimelineQuery) cacheKey() string {
	parts := []string{
		"f=" + q.Filter.QueryString(),
		"from=" + q.From.Format("2006-01-02"),
		"to=" + q.To.Format("2006-01-02"),
		"order=" + q.Order,
	}
	if len(q.Kinds) > 0 {
		parts = append(parts, "kinds="+strings.Join(q.Kinds, ","))
	}
	if q.IncludeExcluded {
		parts = append(parts, "include_excluded=1")
	}
	return strings.Join(parts, "|")
}

// parseTimelineQuery folds URL params into a TimelineQuery. Defaults: past 30
// days through future 90 days; order=desc; kinds=all.
func parseTimelineQuery(r *http.Request, now time.Time) TimelineQuery {
	q := TimelineQuery{
		Filter: ParseTreeFilter(r.URL.Query()),
		From:   startOfDay(now.AddDate(0, 0, -timelineDefaultPastDays)),
		To:     startOfDay(now.AddDate(0, 0, timelineDefaultFutureDays)),
		Order:  "desc",
	}
	if v := strings.TrimSpace(r.URL.Query().Get("from")); v != "" {
		if t, err := time.Parse("2006-01-02", v); err == nil {
			q.From = startOfDay(t)
		}
	}
	if v := strings.TrimSpace(r.URL.Query().Get("to")); v != "" {
		if t, err := time.Parse("2006-01-02", v); err == nil {
			// `to` is inclusive in URL terms; convert to exclusive bound by adding a day.
			q.To = startOfDay(t).AddDate(0, 0, 1)
		}
	}
	// `before` advances the window into the past for "older" pagination.
	if v := strings.TrimSpace(r.URL.Query().Get("before")); v != "" {
		if t, err := time.Parse("2006-01-02", v); err == nil {
			q.To = startOfDay(t)
			q.From = q.To.AddDate(0, 0, -timelineDefaultPastDays-timelineDefaultFutureDays)
		}
	}
	if v := strings.TrimSpace(r.URL.Query().Get("order")); v == "asc" {
		q.Order = "asc"
	}
	if r.URL.Query().Get("include_excluded") == "1" {
		q.IncludeExcluded = true
	}
	// Past-only / future-only narrowing.
	switch strings.TrimSpace(r.URL.Query().Get("when")) {
	case "past":
		if q.To.After(startOfDay(now)) {
			q.To = startOfDay(now)
		}
	case "future":
		if q.From.Before(startOfDay(now)) {
			q.From = startOfDay(now)
		}
	}
	// Accept both `?kind=event,doc` (comma-joined) and
	// `?kind=event&kind=doc` (HTMX multi-select submission). The earlier
	// q.Get + comma-split flavour dropped everything past the first value
	// when the chip strip's <select multiple> submitted — same pre-5d
	// shape calendar's parser carried before commit 6f0a318. parseValues
	// (web/server.go) merges both URL styles into a single slice.
	for _, k := range parseValues(r.URL.Query(), "kind") {
		switch k {
		case timelineKindTodo, timelineKindEvent, timelineKindDoc, timelineKindCreation:
			q.Kinds = append(q.Kinds, k)
		}
	}
	sort.Strings(q.Kinds)
	return q
}

// handleTimeline renders the chronological spine at /timeline.
func (s *Server) handleTimeline(w http.ResponseWriter, r *http.Request) {
	now := time.Now()
	q := parseTimelineQuery(r, now)

	key := q.cacheKey()
	if r.URL.Query().Get("refresh") == "1" {
		s.timeline.InvalidateAll()
	}
	payload, hit := s.timeline.Get(key)
	if !hit {
		built, err := s.buildTimeline(r.Context(), q, now)
		if err != nil {
			s.fail(w, r, err)
			return
		}
		s.timeline.Set(key, built)
		payload = built
	}
	display := *payload
	display.Cached = hit

	projects, err := s.parentOptions(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	data := map[string]any{
		"Title":             "timeline",
		"P":                 display,
		"Filter":            q.Filter,
		"Query":             q,
		"Now":               now,
		"Projects":          projects,
		"BasePath":          "/views/timeline",
		"ProjectChipTarget": "#timeline-section",
	}
	if r.Header.Get("HX-Request") == "true" {
		s.render(w, r, "timeline_section", data)
		return
	}
	s.render(w, r, "timeline", data)
}

// buildTimeline gathers every dated source, applies the kind/filter narrowing,
// and groups rows by day in the requested order.
func (s *Server) buildTimeline(ctx context.Context, q TimelineQuery, now time.Time) (*TimelinePayload, error) {
	items, err := s.Store.ListAll(ctx)
	if err != nil {
		return nil, err
	}
	linkKinds, err := s.linkKindsByItem(ctx)
	if err != nil {
		return nil, err
	}

	byID := map[string]*store.Item{}
	matched := []*store.Item{}
	for _, it := range items {
		// Always index every live item by ID so `event_date` rows can look up
		// their owning item even if the filter would otherwise hide it. We do
		// the filter check at row-emit time (per source).
		byID[it.ID] = it
		if !q.Filter.Active() || q.Filter.Matches(it, linkKinds[it.ID]) {
			matched = append(matched, it)
		}
	}
	matchedSet := map[string]struct{}{}
	for _, it := range matched {
		matchedSet[it.ID] = struct{}{}
	}

	// Phase 4f: per-item exclude filter. Pre-compute the subset of `matched`
	// items that retain each source kind. Skipped here = the aggregator never
	// fans out to CalDAV for that item; saves a network call for each
	// excluded link too.
	keepFor := func(kind string) []*store.Item {
		if q.IncludeExcluded {
			return matched
		}
		out := matched[:0:0]
		for _, it := range matched {
			if it.ExcludesTimelineKind(kind) {
				continue
			}
			out = append(out, it)
		}
		return out
	}

	agg := s.Aggregator()
	window := aggregate.Window{From: q.From, To: q.To}
	rows := []TimelineRow{}

	// --- VTODOs (DUE within window for open; LastModified within for done/cancelled). ---
	if q.wantKind(timelineKindTodo) && s.CalDAV != nil {
		for _, tr := range agg.Todos(ctx, keepFor(timelineKindTodo), window) {
			open := tr.Todo.Status != "COMPLETED" && tr.Todo.Status != "CANCELLED"
			var anchor *time.Time
			if open {
				anchor = tr.Todo.Due
			} else if tr.Todo.LastModified != nil {
				anchor = tr.Todo.LastModified
			} else if tr.Todo.Due != nil {
				anchor = tr.Todo.Due
			}
			if anchor == nil {
				continue
			}
			row := tr // copy so the &row below doesn't alias the loop var
			rows = append(rows, TimelineRow{
				Date:        startOfDay(anchor.Local()),
				Kind:        timelineKindTodo,
				Item:        tr.Item,
				ItemPath:    tr.Item.PrimaryPath(),
				Todo:        &row,
				CalendarURL: tr.CalendarURL,
			})
		}
	}

	// --- VEVENTs (DTSTART within window). ---
	if q.wantKind(timelineKindEvent) && s.CalDAV != nil {
		for _, ev := range agg.Events(ctx, keepFor(timelineKindEvent), window) {
			day := startOfDay(ev.Event.Start.Local())
			if day.Before(q.From) || !day.Before(q.To) {
				continue
			}
			row := ev
			rows = append(rows, TimelineRow{
				Date:         day,
				Kind:         timelineKindEvent,
				Item:         ev.Item,
				ItemPath:     ev.Item.PrimaryPath(),
				Event:        &row,
				StartLabel:   aggregate.EventStartLabel(ev.Event),
				DurationHint: aggregate.EventDurationHint(ev.Event),
			})
		}
	}

	// --- Dated item_links (event_date within window). ---
	if q.wantKind(timelineKindDoc) {
		for _, d := range agg.Docs(ctx, matched, window) {
			it := d.Item
			if _, in := matchedSet[it.ID]; q.Filter.Active() && !in {
				continue
			}
			if !q.IncludeExcluded && it.ExcludesTimelineKind(timelineKindDoc) {
				continue
			}
			base := it.PrimaryPath()
			per := base + "." + formatPERDate(*d.Link.EventDate)
			row := d
			rows = append(rows, TimelineRow{
				Date:     startOfDay(*d.Link.EventDate),
				Kind:     timelineKindDoc,
				Item:     it,
				ItemPath: base,
				Doc:      &row,
				Link:     d.Link,
				PER:      per,
			})
		}
	}

	// --- Item-creation events (created_at within window). ---
	if q.wantKind(timelineKindCreation) {
		for _, c := range agg.Creations(ctx, matched, window) {
			it := c.Item
			if _, in := matchedSet[it.ID]; q.Filter.Active() && !in {
				continue
			}
			if !q.IncludeExcluded && it.ExcludesTimelineKind(timelineKindCreation) {
				continue
			}
			row := c
			rows = append(rows, TimelineRow{
				Date:     startOfDay(it.CreatedAt),
				Kind:     timelineKindCreation,
				Item:     it,
				ItemPath: it.PrimaryPath(),
				Creation: &row,
			})
		}
	}

	days := aggregate.BuildTimelineDays(rows, aggregate.BuildOpts{
		Now:       now,
		Order:     q.Order,
		FadeAfter: 30 * 24 * time.Hour,
	})
	totalRows := 0
	for _, d := range days {
		totalRows += len(d.Rows)
	}

	return &TimelinePayload{
		Days:        days,
		From:        q.From,
		To:          q.To,
		ToInclusive: q.To.AddDate(0, 0, -1),
		Order:       q.Order,
		Kinds:       q.activeKinds(),
		BuiltAt:     time.Now(),
		TotalRows:   totalRows,
	}, nil
}