// Package store is crossbar's durable state: the lease table and the
// accounting log (requests, lease events, host-health polls) with rollup
// queries that answer per-route / per-model / per-host usage. All times are
// stored as Unix milliseconds (INTEGER) and returned as time.Time in UTC.
package store

import (
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"time"

	_ "modernc.org/sqlite"
)

// State is the lease's placement state.
type State string

const (
	Active State = "active"
	Pinned State = "pinned"
)

// Reasons a lease event carries.
const (
	ReasonNew       = "new"
	ReasonUnhealthy = "unhealthy"
	ReasonIdle      = "idle"
	ReasonPin       = "pin"
	ReasonRelease   = "release"
	ReasonDrain     = "drain"
)

// By selects the grouping column of a Usage query.
type By string

const (
	ByRoute By = "route"
	ByModel By = "model"
	ByHost  By = "host"
)

// Lease is one routed model on one host.
type Lease struct {
	Route, FP, Model, Host string
	State                  State
	Created, LastUsed      time.Time
}

// LeaseEvent records a change to a lease.
type LeaseEvent struct {
	TS                             time.Time
	Route, Model, FromHost, ToHost string
	Reason                         string
}

// Request is one proxied request, for the accounting log.
type Request struct {
	Route, FP, Model, Host                       string
	Started                                      time.Time
	QueuedMs, TTFBMs, TotalMs                    int64
	Status                                       int
	Streamed                                     bool
	PromptTokens, CachedTokens, CompletionTokens int64
	Err                                          string
}

// HostHealth is one poller observation of a host.
type HostHealth struct {
	TS      time.Time
	Host    string
	Healthy bool
	Loaded  []string
}

// UsageRow is one group of a Usage query.
type UsageRow struct {
	Key              string `json:"key"`
	Requests         int64  `json:"requests"`
	Errors           int64  `json:"errors"`
	BusyMs           int64  `json:"busy_ms"`
	QueuedMs         int64  `json:"queued_ms"`
	PromptTokens     int64  `json:"prompt_tokens"`
	CachedTokens     int64  `json:"cached_tokens"`
	CompletionTokens int64  `json:"completion_tokens"`
}

// CacheHitRatio is CachedTokens / PromptTokens, or 0 when there were no prompt
// tokens to spend.
func (u UsageRow) CacheHitRatio() float64 {
	if u.PromptTokens == 0 {
		return 0
	}
	return float64(u.CachedTokens) / float64(u.PromptTokens)
}

// Store holds the SQLite connection to crossbar's durable state.
type Store struct {
	db *sql.DB
}

// Open connects to path in WAL mode and creates the tables if they are missing.
// It fails if the directory that holds the file does not exist.
func Open(path string) (*Store, error) {
	if dir := filepath.Dir(path); dir != "" {
		if _, err := os.Stat(dir); err != nil {
			return nil, fmt.Errorf("store: %s: %w", dir, err)
		}
	}
	db, err := sql.Open("sqlite", "file:"+path+"?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)")
	if err != nil {
		return nil, wrap(err)
	}
	if _, err := db.Exec(schema); err != nil {
		_ = db.Close()
		return nil, wrap(err)
	}
	return &Store{db: db}, nil
}

// Close releases the connection.
func (s *Store) Close() error {
	return wrap(s.db.Close())
}

// JournalMode reports the active journal mode ("wal").
func (s *Store) JournalMode() string {
	var mode string
	_ = s.db.QueryRow(`PRAGMA journal_mode`).Scan(&mode)
	return mode
}

// SaveLease inserts or replaces a lease on (route, fp, model).
func (s *Store) SaveLease(l Lease) error {
	_, err := s.db.Exec(`
		INSERT OR REPLACE INTO leases (route, fp, model, host, state, created, last_used)
		VALUES (?, ?, ?, ?, ?, ?, ?)`,
		l.Route, l.FP, l.Model, l.Host, string(l.State),
		l.Created.UnixMilli(), l.LastUsed.UnixMilli())
	return wrap(err)
}

// DeleteLease removes the lease identified by (route, fp, model).
func (s *Store) DeleteLease(route, fp, model string) error {
	_, err := s.db.Exec(`DELETE FROM leases WHERE route = ? AND fp = ? AND model = ?`, route, fp, model)
	return wrap(err)
}

// ListLeases returns every lease, ordered by (route, fp, model).
func (s *Store) ListLeases() ([]Lease, error) {
	rows, err := s.db.Query(`
		SELECT route, fp, model, host, state, created, last_used
		FROM leases ORDER BY route, fp, model`)
	if err != nil {
		return nil, wrap(err)
	}
	defer rows.Close()
	return scanLeases(rows)
}

// RecordEvent appends a lease event.
func (s *Store) RecordEvent(e LeaseEvent) error {
	_, err := s.db.Exec(`
		INSERT INTO lease_events (ts, route, model, from_host, to_host, reason)
		VALUES (?, ?, ?, ?, ?, ?)`,
		e.TS.UnixMilli(), e.Route, e.Model, e.FromHost, e.ToHost, e.Reason)
	return wrap(err)
}

// RecordRequest appends one request to the accounting log.
func (s *Store) RecordRequest(r Request) error {
	_, err := s.db.Exec(`
		INSERT INTO requests (route, fp, model, host, started, queued_ms, ttfb_ms, total_ms, status, streamed, prompt_tokens, cached_tokens, completion_tokens, err)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
		r.Route, r.FP, r.Model, r.Host,
		r.Started.UnixMilli(), r.QueuedMs, r.TTFBMs, r.TotalMs,
		r.Status, btoi(r.Streamed),
		r.PromptTokens, r.CachedTokens, r.CompletionTokens, r.Err)
	return wrap(err)
}

// RecordHostHealth appends one host-health observation.
func (s *Store) RecordHostHealth(h HostHealth) error {
	b, err := encodeLoaded(h.Loaded)
	if err != nil {
		return wrap(err)
	}
	_, err = s.db.Exec(`
		INSERT INTO host_health (ts, host, healthy, loaded_models)
		VALUES (?, ?, ?, ?)`,
		h.TS.UnixMilli(), h.Host, btoi(h.Healthy), string(b))
	return wrap(err)
}

// Usage sums requests at or after since, grouped by by. A zero since means all
// time. It counts the live requests table plus the requests_daily rollup whose
// day is at or after since. Results are ordered by Key.
func (s *Store) Usage(since time.Time, by By) ([]UsageRow, error) {
	col, err := byColumn(by)
	if err != nil {
		return nil, err
	}
	sinceMs := since.UnixMilli()
	query := `
	SELECT key,
	       SUM(requests)  AS requests,
	       SUM(errors)    AS errors,
	       SUM(busy_ms)   AS busy_ms,
	       SUM(queued_ms) AS queued_ms,
	       SUM(prompt_tokens)     AS prompt_tokens,
	       SUM(cached_tokens)     AS cached_tokens,
	       SUM(completion_tokens) AS completion_tokens
	FROM (
		SELECT ` + col + ` AS key, 1 AS requests,
		       CASE WHEN status >= 400 THEN 1 ELSE 0 END AS errors,
		       total_ms AS busy_ms, queued_ms,
		       prompt_tokens, cached_tokens, completion_tokens
		FROM requests WHERE started >= ?
		UNION ALL
		SELECT ` + col + ` AS key, requests, errors, busy_ms, queued_ms,
		       prompt_tokens, cached_tokens, completion_tokens
		FROM requests_daily WHERE day >= ?
	)
	GROUP BY key
	ORDER BY key`
	rows, err := s.db.Query(query, sinceMs, sinceMs)
	if err != nil {
		return nil, wrap(err)
	}
	defer rows.Close()
	return scanUsage(rows)
}

// Events returns lease events at or after since, oldest first, at most limit.
func (s *Store) Events(since time.Time, limit int) ([]LeaseEvent, error) {
	rows, err := s.db.Query(`
		SELECT ts, route, model, from_host, to_host, reason
		FROM lease_events WHERE ts >= ?
		ORDER BY ts ASC LIMIT ?`, since.UnixMilli(), limit)
	if err != nil {
		return nil, wrap(err)
	}
	defer rows.Close()
	return scanEvents(rows)
}

// Prune moves every request older than now-retention into requests_daily (adding
// into the existing daily row for that day/route/model/host), deletes the live
// rows, and returns how many were removed. All in one transaction.
func (s *Store) Prune(now time.Time, retention time.Duration) (int64, error) {
	threshold := now.Add(-retention).UnixMilli()
	tx, err := s.db.Begin()
	if err != nil {
		return 0, wrap(err)
	}
	defer func() { _ = tx.Rollback() }()

	rows, err := tx.Query(`
		SELECT route, model, host, started, total_ms, queued_ms,
		       status, prompt_tokens, cached_tokens, completion_tokens
		FROM requests WHERE started < ?`, threshold)
	if err != nil {
		_ = tx.Rollback()
		return 0, wrap(err)
	}

	type bucket struct {
		day   int64
		route string
		model string
		host  string
	}
	type agg struct {
		requests int64
		errors   int64
		busyMs   int64
		queuedMs int64
		prompt   int64
		cached   int64
		done     int64
	}
	aggs := map[bucket]*agg{}
	count := int64(0)
	for rows.Next() {
		var (
			route, model, host   string
			started              int64
			totalMs, queuedMs    int64
			status               int
			prompt, cached, done int64
		)
		if err := rows.Scan(&route, &model, &host, &started, &totalMs, &queuedMs, &status, &prompt, &cached, &done); err != nil {
			_ = rows.Close()
			_ = tx.Rollback()
			return 0, wrap(err)
		}
		count++
		k := bucket{day: midnight(started), route: route, model: model, host: host}
		a := aggs[k]
		if a == nil {
			a = &agg{}
			aggs[k] = a
		}
		a.requests++
		if status >= 400 {
			a.errors++
		}
		a.busyMs += totalMs
		a.queuedMs += queuedMs
		a.prompt += prompt
		a.cached += cached
		a.done += done
	}
	if err := rows.Err(); err != nil {
		_ = rows.Close()
		_ = tx.Rollback()
		return 0, wrap(err)
	}
	_ = rows.Close()

	upsert := `
		INSERT INTO requests_daily (day, route, model, host, requests, errors, busy_ms, queued_ms, prompt_tokens, cached_tokens, completion_tokens)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
		ON CONFLICT (day, route, model, host) DO UPDATE SET
			requests          = requests          + excluded.requests,
			errors            = errors            + excluded.errors,
			busy_ms           = busy_ms           + excluded.busy_ms,
			queued_ms         = queued_ms         + excluded.queued_ms,
			prompt_tokens     = prompt_tokens     + excluded.prompt_tokens,
			cached_tokens     = cached_tokens     + excluded.cached_tokens,
			completion_tokens = completion_tokens + excluded.completion_tokens`
	for k, a := range aggs {
		if _, err := tx.Exec(upsert, k.day, k.route, k.model, k.host,
			a.requests, a.errors, a.busyMs, a.queuedMs, a.prompt, a.cached, a.done); err != nil {
			_ = tx.Rollback()
			return 0, wrap(err)
		}
	}
	if _, err := tx.Exec(`DELETE FROM requests WHERE started < ?`, threshold); err != nil {
		_ = tx.Rollback()
		return 0, wrap(err)
	}
	if err := tx.Commit(); err != nil {
		return 0, wrap(err)
	}
	return count, nil
}