package store

import (
	"context"
	"encoding/binary"
	"fmt"
	"math"
	"sort"
	"strings"
	"time"
)

// Note — a recall/preference item. No predicate reads it (facts are for that);
// query-answering ranks notes by embedding cosine. Score is set by QueryNotes.
type Note struct {
	ID     int64
	Ts     time.Time
	Text   string
	Source string
	Score  float64
}

// WriteNote appends a note with its embedding (stored as a little-endian
// float32 BLOB). Source is provenance (tap:voice, etc.).
func (s *Store) WriteNote(ctx context.Context, ts time.Time, text string, embedding []float32, source string) (int64, error) {
	res, err := s.db.ExecContext(ctx,
		`INSERT INTO notes (ts, text, embedding, source) VALUES (?,?,?,?)`,
		ts.UnixMilli(), text, floatsToBlob(embedding), source)
	if err != nil {
		return 0, fmt.Errorf("write note: %w", err)
	}
	id, err := res.LastInsertId()
	if err != nil {
		return 0, fmt.Errorf("last insert id: %w", err)
	}
	return id, nil
}

// QueryNotes returns the top-k notes by cosine similarity to embedding, highest
// first (ties broken newest-first). Fewer than k notes ⇒ returns what exists.
//
// ponytail: brute-force O(n) cosine over every note each query. Add sqlite-vec
// or an ANN index only when note count or latency actually bites — at personal
// scale (hundreds–thousands) a full scan is sub-millisecond.
func (s *Store) QueryNotes(ctx context.Context, embedding []float32, k int) ([]Note, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT id, ts, text, embedding, source FROM notes WHERE `+notHisWordsSQL)
	if err != nil {
		return nil, fmt.Errorf("query notes: %w", err)
	}
	defer rows.Close()

	var out []Note
	for rows.Next() {
		var n Note
		var tsMilli int64
		var blob []byte
		if err := rows.Scan(&n.ID, &tsMilli, &n.Text, &blob, &n.Source); err != nil {
			return nil, err
		}
		n.Ts = time.UnixMilli(tsMilli).UTC()
		n.Score = cosine(embedding, blobToFloats(blob))
		out = append(out, n)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	sort.Slice(out, func(i, j int) bool {
		if out[i].Score != out[j].Score {
			return out[i].Score > out[j].Score
		}
		return out[i].Ts.After(out[j].Ts) // newest breaks ties
	})
	if k > 0 && len(out) > k {
		out = out[:k]
	}
	return out, nil
}

// ReadSourcePrefixes — note sources that are text Maven READ somewhere, not
// text he said or wrote: RSS items (internal/rss) and crawled pages
// (internal/crawl).
//
// They are notes because that is where fetched text lands, and they are kept out
// of recall because recall answers questions about HIM. "что я говорил про
// переезд" must not be answered out of a stranger's web page that happened to
// land near in the vector space, and the fallback line for that is "вот что я
// нашла: " followed by the stranger's words. Ask for them by source instead —
// that is what RecentNotesFromSource is for.
var ReadSourcePrefixes = []string{"rss:", "crawl:"}

// notHisWordsSQL — the WHERE clause that drops the read sources. Built from the
// list above so adding a source is one line.
var notHisWordsSQL = buildNotHisWordsSQL()

func buildNotHisWordsSQL() string {
	var b strings.Builder
	b.WriteString("(source IS NULL OR (")
	for i, p := range ReadSourcePrefixes {
		if i > 0 {
			b.WriteString(" AND ")
		}
		fmt.Fprintf(&b, "source NOT LIKE '%s%%'", p)
	}
	b.WriteString("))")
	return b.String()
}

// RecentNotesFromSource returns the newest n notes whose source starts with
// prefix, newest first. The answer path for feeds and watches uses it: scanning
// the last 200 notes of ANY source meant a busy day of voice notes pushed the
// newest headline out of the window, and she said "в лентах пока ничего нового"
// while the poller was working fine.
func (s *Store) RecentNotesFromSource(ctx context.Context, prefix string, n int) ([]Note, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT id, ts, text, source FROM notes WHERE source LIKE ? ORDER BY ts DESC LIMIT ?`,
		prefix+"%", n)
	if err != nil {
		return nil, fmt.Errorf("recent notes by source: %w", err)
	}
	defer rows.Close()
	var out []Note
	for rows.Next() {
		var nt Note
		var tsMilli int64
		if err := rows.Scan(&nt.ID, &tsMilli, &nt.Text, &nt.Source); err != nil {
			return nil, err
		}
		nt.Ts = time.UnixMilli(tsMilli).UTC()
		out = append(out, nt)
	}
	return out, rows.Err()
}

// RecentNotes returns the newest n notes, newest first — a browse view (no
// embedding math; Score stays 0). This is the read surface for /dash: notes
// captured by voice are otherwise only reachable through semantic query.
func (s *Store) RecentNotes(ctx context.Context, n int) ([]Note, error) {
	return s.recentNotesWhere(ctx, "", n)
}

// RecentNotesBySource returns the newest n notes written by one source, newest
// first. The filter is in SQL, not in the caller, because a caller that reads n
// rows and then keeps the ones it wants has a window measured in OTHER writers'
// traffic: once n newer notes from anywhere have landed, the rows it was
// looking for are gone. Anything that needs "the last n of mine" wants this.
func (s *Store) RecentNotesBySource(ctx context.Context, source string, n int) ([]Note, error) {
	return s.recentNotesWhere(ctx, "WHERE source = ?", n, source)
}

// RecentNotesExcludingSource returns the newest n notes NOT written by source.
// Same reasoning inverted: a reader that wants n notes he wrote must not have
// its budget eaten by rows it is about to discard.
func (s *Store) RecentNotesExcludingSource(ctx context.Context, source string, n int) ([]Note, error) {
	return s.recentNotesWhere(ctx, "WHERE source <> ?", n, source)
}

func (s *Store) recentNotesWhere(ctx context.Context, where string, n int, args ...any) ([]Note, error) {
	args = append(args, n)
	rows, err := s.db.QueryContext(ctx,
		`SELECT id, ts, text, source FROM notes `+where+` ORDER BY ts DESC LIMIT ?`, args...)
	if err != nil {
		return nil, fmt.Errorf("recent notes: %w", err)
	}
	defer rows.Close()
	var out []Note
	for rows.Next() {
		var nt Note
		var tsMilli int64
		if err := rows.Scan(&nt.ID, &tsMilli, &nt.Text, &nt.Source); err != nil {
			return nil, err
		}
		nt.Ts = time.UnixMilli(tsMilli).UTC()
		out = append(out, nt)
	}
	return out, rows.Err()
}

// cosine similarity. Embedder vectors are L2-normalized, so this is just the
// dot product — but normalize defensively in case a caller passes a raw vector.
func cosine(a, b []float32) float64 {
	if len(a) != len(b) || len(a) == 0 {
		return 0
	}
	var dot, na, nb float64
	for i := range a {
		dot += float64(a[i]) * float64(b[i])
		na += float64(a[i]) * float64(a[i])
		nb += float64(b[i]) * float64(b[i])
	}
	if na == 0 || nb == 0 {
		return 0
	}
	return dot / (math.Sqrt(na) * math.Sqrt(nb))
}

func floatsToBlob(v []float32) []byte {
	b := make([]byte, 4*len(v))
	for i, f := range v {
		binary.LittleEndian.PutUint32(b[4*i:], math.Float32bits(f))
	}
	return b
}

func blobToFloats(b []byte) []float32 {
	v := make([]float32, len(b)/4)
	for i := range v {
		v[i] = math.Float32frombits(binary.LittleEndian.Uint32(b[4*i:]))
	}
	return v
}