package store

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/kami/maven/internal/calendar"
)

// WriteFact appends a fact row. confidence must be 1.0 for taps and (0,1) for
// inferences; the caller is responsible for that provenance discipline.
//
// If voidsID is Valid, this row voids (cancels) the referenced fact. The
// caller must have verified voidsID points at an existing fact — we check it
// here too and refuse to write a dangling voids pointer (the audit trail must
// stay coherent).
func (s *Store) WriteFact(ctx context.Context, ts time.Time, kind FactKind, key, value, source string, confidence float64, voidsID sql.NullInt64) (int64, error) {
	if confidence <= 0.0 || confidence > 1.0 {
		return 0, fmt.Errorf("%w: %f", ErrConfidence, confidence)
	}
	if voidsID.Valid {
		var ok int64
		err := s.db.QueryRowContext(ctx, "SELECT 1 FROM facts WHERE id = ?", voidsID.Int64).Scan(&ok)
		if errors.Is(err, sql.ErrNoRows) {
			return 0, fmt.Errorf("%w: id=%d", ErrVoidsMissing, voidsID.Int64)
		}
		if err != nil {
			return 0, fmt.Errorf("voids lookup: %w", err)
		}
	}
	res, err := s.db.ExecContext(ctx,
		`INSERT INTO facts (ts, kind, key, value, source, confidence, voids_id) VALUES (?,?,?,?,?,?,?)`,
		ts.UnixMilli(), string(kind), key, value, source, confidence, voidsID)
	if err != nil {
		return 0, fmt.Errorf("write fact: %w", err)
	}
	id, err := res.LastInsertId()
	if err != nil {
		return 0, fmt.Errorf("last insert id: %w", err)
	}
	return id, nil
}

// LatestFact returns the latest non-voided fact for key, or ErrNoFact.
// "Non-voided" = no later row has voids_id pointing at it. We resolve this by
// taking the newest row whose id is not referenced by any voids_id.
func (s *Store) LatestFact(ctx context.Context, key string) (Fact, error) {
	row := s.db.QueryRowContext(ctx, `
		SELECT id, ts, kind, key, value, source, confidence, voids_id
		  FROM facts
		 WHERE key = ?
		   AND id NOT IN (SELECT voids_id FROM facts WHERE voids_id IS NOT NULL)
		 ORDER BY ts DESC, id DESC
		 LIMIT 1`, key)
	return scanFact(row)
}

// RecentFacts — the newest n facts across all keys, for the monitoring dash.
// Includes voided rows (the audit trail is the point: you want to SEE a
// correction, not have it hidden). Newest first.
func (s *Store) RecentFacts(ctx context.Context, n int) ([]Fact, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT id, ts, kind, key, value, source, confidence, voids_id
		  FROM facts ORDER BY ts DESC, id DESC LIMIT ?`, n)
	if err != nil {
		return nil, fmt.Errorf("recent facts: %w", err)
	}
	defer rows.Close()
	var out []Fact
	for rows.Next() {
		f, err := scanFact(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, f)
	}
	return out, rows.Err()
}

// RecentActiveFactsByKind — the newest n facts of one kind, newest first, with
// the retracted ones left out. "Active" means two exclusions: a row some later
// row voids, and the void marker VoidLatestFact writes to retract it. A
// correction still counts, because a correction is a value he stands behind.
//
// It exists because the facts table is shared and the noisy writers are not the
// interesting ones. A caller that reads n recent rows and then keeps the self
// ones has a window whose real length is set by how often the pollers write:
// one WireGuard peer alone rehandshakes every couple of minutes, which is
// enough env rows to reduce a 2000-row window to under three days. Filtering in
// SQL makes the bound mean what the caller thinks it means.
//
// Voided rows are excluded here and included by RecentFacts on purpose. The
// dash shows the audit trail, because you want to SEE a correction. A reader
// that asks what he usually does must not count something he explicitly took
// back.
func (s *Store) RecentActiveFactsByKind(ctx context.Context, kind FactKind, n int) ([]Fact, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT id, ts, kind, key, value, source, confidence, voids_id
		  FROM facts
		 WHERE kind = ?
		   AND NOT (voids_id IS NOT NULL AND value = '"voided"')
		   AND id NOT IN (SELECT voids_id FROM facts WHERE voids_id IS NOT NULL)
		 ORDER BY ts DESC, id DESC LIMIT ?`, string(kind), n)
	if err != nil {
		return nil, fmt.Errorf("recent facts by kind: %w", err)
	}
	defer rows.Close()
	var out []Fact
	for rows.Next() {
		f, err := scanFact(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, f)
	}
	return out, rows.Err()
}

// CalendarEvents returns calendar facts whose key date falls within [from, to).
// Calendar event keys have the format calendar_event_YYYYMMDD_<summary>.
//
// Every calendar source is included, not just the personal CalDAV poll: the work
// calendar arrives as ambient:notif notifications (Vikunja #126) and belongs in
// the same answer. The source stays on each Fact, along with its confidence, so
// the caller can hedge a reading it did not get from a calendar server —
// filtering by source here would have thrown that judgement away.
//
// One row per event, not one per write. The facts table is append-only, so a
// standup moved from 14:00 to 16:00 leaves two rows under the same key, and the
// day plan used to recite both as if the owner had two meetings. Voided rows
// are excluded, the latest row wins within a source, and the best-evidenced
// source wins across them — a calendar read beats the notification relay that
// guessed at the same meeting.
func (s *Store) CalendarEvents(ctx context.Context, from, to time.Time) ([]Fact, error) {
	prefixFrom := calendar.KeyPrefixForDay(from)
	prefixTo := calendar.KeyPrefixForDay(to)
	sources := calendar.Sources()
	args := make([]any, 0, len(sources)+2)
	for _, src := range sources {
		args = append(args, src)
	}
	args = append(args, prefixFrom, prefixTo)
	rows, err := s.db.QueryContext(ctx, `
        SELECT id, ts, kind, key, value, source, confidence, voids_id
          FROM facts
         WHERE source IN (`+placeholders(len(sources))+`)
           AND key >= ? AND key < ?
           AND id NOT IN (SELECT voids_id FROM facts WHERE voids_id IS NOT NULL)
         ORDER BY key, ts, id`, args...)
	if err != nil {
		return nil, fmt.Errorf("calendar events: %w", err)
	}
	defer rows.Close()
	var out []Fact
	for rows.Next() {
		f, err := scanFact(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, f)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return latestPerCalendarKey(out), nil
}

// latestPerCalendarKey reduces the append-only rows for one day to one row per
// event key. Input must be ordered by key then oldest-first, so the last row
// seen for a key and source is that source's current value.
func latestPerCalendarKey(in []Fact) []Fact {
	type slot struct {
		bySource map[string]Fact
		order    []string
	}
	var keys []string
	byKey := map[string]*slot{}
	for _, f := range in {
		s, ok := byKey[f.Key]
		if !ok {
			s = &slot{bySource: map[string]Fact{}}
			byKey[f.Key] = s
			keys = append(keys, f.Key)
		}
		if _, seen := s.bySource[f.Source]; !seen {
			s.order = append(s.order, f.Source)
		}
		s.bySource[f.Source] = f
	}
	out := make([]Fact, 0, len(keys))
	for _, k := range keys {
		s := byKey[k]
		best := s.bySource[s.order[0]]
		for _, src := range s.order[1:] {
			if s.bySource[src].Confidence > best.Confidence {
				best = s.bySource[src]
			}
		}
		out = append(out, best)
	}
	return out
}

// LatestFactBySource — provenance-scoped. A rule on `service_down` trusts only
// source=poll:healthcheck; a compromised poller can't forge a trigger. Use this
// from rules, not LatestFact, whenever the rule's source contract matters.
func (s *Store) LatestFactBySource(ctx context.Context, key, source string) (Fact, error) {
	row := s.db.QueryRowContext(ctx, `
		SELECT id, ts, kind, key, value, source, confidence, voids_id
		  FROM facts
		 WHERE key = ? AND source = ?
		   AND id NOT IN (SELECT voids_id FROM facts WHERE voids_id IS NOT NULL)
		 ORDER BY ts DESC, id DESC
		 LIMIT 1`, key, source)
	return scanFact(row)
}

// Since returns how long ago the latest non-voided fact for key landed, or
// (0, ErrNoFact). Implements the `since(key)==null → don't fire` guard from
// the spec — silence on no-data is "shuts up when uncertain".
func (s *Store) Since(ctx context.Context, key string, now time.Time) (time.Duration, error) {
	f, err := s.LatestFact(ctx, key)
	if err != nil {
		return 0, err
	}
	if now.Before(f.Ts) {
		return 0, nil
	}
	return now.Sub(f.Ts), nil
}

// SetValue is a convenience for writing a structured (json) value at confidence 1.0
// from a tap. Self-taps (water, meal, shower) land here. Caller supplies source
// like "tap:water"; we serialize the value.
func (s *Store) SetValue(ctx context.Context, kind FactKind, key, source string, value any, ts time.Time) (int64, error) {
	raw, err := json.Marshal(value)
	if err != nil {
		return 0, fmt.Errorf("marshal value: %w", err)
	}
	return s.WriteFact(ctx, ts, kind, key, string(raw), source, 1.0, sql.NullInt64{})
}

// CorrectValue voids the latest non-voided fact for key and writes a replacement
// in one transaction. Use this for "you corrected a bad fact" feedback — keeps
// the audit trail, supersedes the wrong value.
func (s *Store) CorrectValue(ctx context.Context, key, source string, value any, ts time.Time) (newID int64, err error) {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return 0, err
	}
	defer func() {
		if err != nil {
			_ = tx.Rollback()
		}
	}()
	var oldID int64
	err = tx.QueryRowContext(ctx, `
		SELECT id FROM facts
		 WHERE key = ?
		   AND id NOT IN (SELECT voids_id FROM facts WHERE voids_id IS NOT NULL)
		 ORDER BY ts DESC, id DESC LIMIT 1`, key).Scan(&oldID)
	if errors.Is(err, sql.ErrNoRows) {
		// nothing to correct; write as a plain new fact instead — no voiding needed.
	} else if err != nil {
		return 0, fmt.Errorf("correct: find old: %w", err)
	}
	raw, merr := json.Marshal(value)
	if merr != nil {
		return 0, fmt.Errorf("marshal value: %w", merr)
	}
	var voids sql.NullInt64
	if oldID != 0 {
		voids = sql.NullInt64{Int64: oldID, Valid: true}
	}
	res, err := tx.ExecContext(ctx,
		`INSERT INTO facts (ts, kind, key, value, source, confidence, voids_id) VALUES (?,?,?,?,?,?,?)`,
		ts.UnixMilli(), string(KindSelf), key, string(raw), source, 1.0, voids)
	if err != nil {
		return 0, fmt.Errorf("write corrected: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return 0, err
	}
	newID, err = res.LastInsertId()
	if err != nil {
		return 0, fmt.Errorf("last insert id: %w", err)
	}
	return newID, nil
}

// VoidLatestFact voids the latest non-voided fact for key. It writes a new
// fact with voids_id pointing at the old one, keeping the audit trail intact.
// Returns the voided fact's ID and the new void-marker fact's ID.
// If no fact exists for the key, returns ErrNoFact.
func (s *Store) VoidLatestFact(ctx context.Context, key, source string, ts time.Time) (oldID, newID int64, err error) {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return 0, 0, err
	}
	defer func() {
		if err != nil {
			_ = tx.Rollback()
		}
	}()
	err = tx.QueryRowContext(ctx, `
        SELECT id FROM facts
         WHERE key = ?
           AND id NOT IN (SELECT voids_id FROM facts WHERE voids_id IS NOT NULL)
         ORDER BY ts DESC, id DESC LIMIT 1`, key).Scan(&oldID)
	if errors.Is(err, sql.ErrNoRows) {
		return 0, 0, ErrNoFact
	}
	if err != nil {
		return 0, 0, fmt.Errorf("void: find latest: %w", err)
	}
	res, err := tx.ExecContext(ctx,
		`INSERT INTO facts (ts, kind, key, value, source, confidence, voids_id) VALUES (?,?,?,?,?,?,?)`,
		ts.UnixMilli(), string(KindSelf), key, `"voided"`, source, 1.0,
		sql.NullInt64{Int64: oldID, Valid: true})
	if err != nil {
		return 0, 0, fmt.Errorf("void: write void-marker: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return 0, 0, err
	}
	newID, err = res.LastInsertId()
	if err != nil {
		return 0, 0, fmt.Errorf("void: last insert id: %w", err)
	}
	return oldID, newID, nil
}

type rowScanner interface {
	Scan(dest ...any) error
}

func scanFact(r rowScanner) (Fact, error) {
	var f Fact
	var tsMilli int64
	var kind string
	var voids sql.NullInt64
	if err := r.Scan(&f.ID, &tsMilli, &kind, &f.Key, &f.Value, &f.Source, &f.Confidence, &voids); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return Fact{}, ErrNoFact
		}
		return Fact{}, err
	}
	f.Ts = time.UnixMilli(tsMilli).UTC()
	f.Kind = FactKind(kind)
	f.VoidsID = voids
	return f, nil
}

// placeholders renders n comma-separated SQL bind markers.
func placeholders(n int) string {
	return strings.TrimSuffix(strings.Repeat("?,", n), ",")
}