package store

import (
	"context"
	"fmt"
	"time"
)

// Search history is the record of what a household looks for, and it has two readers with
// quite different appetites: a television asking for one viewer's last few queries, and
// the console asking what the house as a whole has been searching. Both read the one
// table, which is why the writer's rules live here beside them.

// SearchDedupeWindow is how long an identical query counts as the same search.
//
// Two things write this table for one search — the gateway's own /v1/search handler and
// the client's POST to /v1/search/history — and a television that repeats a query while
// somebody re-reads the results is not a second search either. The window is short enough
// that a query typed again a minute later is its own row, which is what makes the table a
// record of what a household looks for rather than of how its remote behaves.
const SearchDedupeWindow = 30 * time.Second

// SearchRetention is how far back the table goes. RecordSearch prunes to it on every
// write, so it is also the honest ceiling on any window the console offers: a page
// promising 90 days would draw a flat line for two thirds of it.
const SearchRetention = 30 * 24 * time.Hour

// RecordSearch stores a normalized query for future per-user ranking analysis.
//
// Case-insensitive within the dedupe window, matching RecentSearches, which collapses
// case-only duplicates when it reads them back.
func (s *Store) RecordSearch(ctx context.Context, userID, query string) error {
	_, err := s.pool.Exec(ctx,
		`WITH inserted AS (
			INSERT INTO search_history (emby_user_id, query)
			SELECT $1, $2
			WHERE NOT EXISTS (
				SELECT 1 FROM search_history
				WHERE emby_user_id = $1
				  AND lower(query) = lower($2)
				  AND occurred_at > now() - $3::interval
			)
			RETURNING id
		)
		DELETE FROM search_history
		WHERE emby_user_id = $1
		  AND occurred_at < now() - $4::interval`,
		userID, query, SearchDedupeWindow.String(), SearchRetention.String())
	return err
}

// RecentSearches returns a user's distinct queries in most-recently-used order.
// Case-only duplicates collapse to the spelling used most recently.
func (s *Store) RecentSearches(
	ctx context.Context,
	userID string,
	since time.Time,
	limit int,
) ([]string, error) {
	rows, err := s.pool.Query(ctx, `
		SELECT query
		FROM (
			SELECT DISTINCT ON (lower(query)) query, occurred_at
			FROM search_history
			WHERE emby_user_id = $1 AND occurred_at >= $2
			ORDER BY lower(query), occurred_at DESC
		) AS latest
		ORDER BY occurred_at DESC
		LIMIT $3`,
		userID, since, limit)
	if err != nil {
		return nil, fmt.Errorf("store: recent searches: %w", err)
	}
	defer rows.Close()

	queries := make([]string, 0, limit)
	for rows.Next() {
		var query string
		if err := rows.Scan(&query); err != nil {
			return nil, fmt.Errorf("store: scan recent search: %w", err)
		}
		queries = append(queries, query)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("store: read recent searches: %w", err)
	}
	return queries, nil
}

// SearchTerm is one query the household searched for, aggregated across everyone.
type SearchTerm struct {
	Query    string    `json:"query"`
	Searches int       `json:"searches"`
	Viewers  int       `json:"viewers"`
	LastAt   time.Time `json:"lastAt"`
}

// SearchEvent is one search as it happened: the log rather than the summary.
type SearchEvent struct {
	Query      string    `json:"query"`
	UserID     string    `json:"userId"`
	Username   string    `json:"username"`
	OccurredAt time.Time `json:"occurredAt"`
}

// SearchTotals describes a window as a whole. Counted separately from SearchTerms because
// that list is capped — summing a top-twenty would report the top twenty's total as the
// household's, which is wrong by however long the tail is.
type SearchTotals struct {
	Searches int `json:"searches"`
	Queries  int `json:"queries"`
	Viewers  int `json:"viewers"`
}

// SearchTerms aggregates the household's queries since a point in time, most-searched
// first. Grouped case-insensitively and labelled with the spelling used most recently,
// the same rule RecentSearches applies, so one query cannot appear as two rows because
// somebody's on-screen keyboard capitalised it.
func (s *Store) SearchTerms(ctx context.Context, since time.Time, limit int) ([]SearchTerm, error) {
	rows, err := s.pool.Query(ctx, `
		SELECT (array_agg(query ORDER BY occurred_at DESC))[1] AS query,
		       count(*)                     AS searches,
		       count(DISTINCT emby_user_id) AS viewers,
		       max(occurred_at)             AS last_at
		FROM search_history
		WHERE occurred_at >= $1
		GROUP BY lower(query)
		ORDER BY searches DESC, last_at DESC
		LIMIT $2`, since, limit)
	if err != nil {
		return nil, fmt.Errorf("store: search terms: %w", err)
	}
	defer rows.Close()

	terms := []SearchTerm{}
	for rows.Next() {
		var term SearchTerm
		if err := rows.Scan(&term.Query, &term.Searches, &term.Viewers, &term.LastAt); err != nil {
			return nil, fmt.Errorf("store: scan search term: %w", err)
		}
		terms = append(terms, term)
	}
	return terms, rows.Err()
}

// SearchEvents returns the raw log, newest first.
//
// Deliberately not collapsed: the summary above answers "what does this house look for",
// and this answers "what happened just now" — which is the one an operator needs when
// somebody says search is not finding something, because it shows the query exactly as it
// was typed, by whom, and at what time. Usernames are resolved by the caller from
// KnownUsers: they live in sessions and joining a log to them per row would make the
// query's cost depend on how many televisions the household has ever signed in.
func (s *Store) SearchEvents(ctx context.Context, since time.Time, limit int) ([]SearchEvent, error) {
	rows, err := s.pool.Query(ctx, `
		SELECT query, emby_user_id, occurred_at
		FROM search_history
		WHERE occurred_at >= $1
		ORDER BY occurred_at DESC
		LIMIT $2`, since, limit)
	if err != nil {
		return nil, fmt.Errorf("store: search events: %w", err)
	}
	defer rows.Close()

	events := []SearchEvent{}
	for rows.Next() {
		var event SearchEvent
		if err := rows.Scan(&event.Query, &event.UserID, &event.OccurredAt); err != nil {
			return nil, fmt.Errorf("store: scan search event: %w", err)
		}
		events = append(events, event)
	}
	return events, rows.Err()
}

// SearchTotals counts a window: searches made, distinct queries behind them, and how many
// of the household did the searching.
func (s *Store) SearchTotals(ctx context.Context, since time.Time) (SearchTotals, error) {
	var totals SearchTotals
	err := s.pool.QueryRow(ctx, `
		SELECT count(*), count(DISTINCT lower(query)), count(DISTINCT emby_user_id)
		FROM search_history
		WHERE occurred_at >= $1`, since).
		Scan(&totals.Searches, &totals.Queries, &totals.Viewers)
	if err != nil {
		return SearchTotals{}, fmt.Errorf("store: search totals: %w", err)
	}
	return totals, nil
}