package store

import (
	"database/sql"
	"errors"
	"fmt"
	"time"
)

// ledger.go: reserve-before-call / settle-after money discipline (порт
// семантики vojo Reserve/Settle/ReleaseReservation на SQLite). Потолки — на
// книгу (суммарно) и на день (Р7); проверяются по committed + reserved под
// immediate-транзакцией write-пула, так что конкурентные вызовы не
// проскакивают потолок больше чем на одну максимальную резервацию.

// ReserveResult is the outcome of a pre-call admission check.
type ReserveResult int

const (
	ReserveOK ReserveResult = iota
	ReserveDeniedBook // per-book USD ceiling hit
	ReserveDeniedDay  // daily USD ceiling hit
)

// Reservation is the handle Settle/Release need to undo the admission.
type Reservation struct {
	BookID   string
	Date     string // UTC day the reservation was booked under
	Estimate float64
}

// Ceilings are the admission limits. Zero means "no limit" for that axis —
// fail-fast in config forbids an all-zero pair for real runs.
type Ceilings struct {
	BookUSD float64
	DayUSD  float64
}

func todayUTC() string { return time.Now().UTC().Format("2006-01-02") }

// Reserve books estimate USD against the ceilings BEFORE the call. On success
// the estimate is added to reserved_usd; Settle converts it to committed
// spend, Release returns it. Denials are results, not errors.
func (s *Store) Reserve(bookID string, estimate float64, c Ceilings) (Reservation, ReserveResult, error) {
	ctx, cancel := opContext()
	defer cancel()
	day := todayUTC()
	res := Reservation{BookID: bookID, Date: day, Estimate: estimate}

	tx, err := s.w.BeginTx(ctx, nil) // write pool: immediate tx, serialized
	if err != nil {
		return res, ReserveOK, err
	}
	defer tx.Rollback()

	var bookTotal, dayTotal float64
	if err := tx.QueryRowContext(ctx,
		`SELECT COALESCE(SUM(committed_usd + reserved_usd), 0) FROM spend WHERE book_id = ?`, bookID,
	).Scan(&bookTotal); err != nil {
		return res, ReserveOK, err
	}
	if err := tx.QueryRowContext(ctx,
		`SELECT COALESCE(SUM(committed_usd + reserved_usd), 0) FROM spend WHERE date = ?`, day,
	).Scan(&dayTotal); err != nil {
		return res, ReserveOK, err
	}
	if c.BookUSD > 0 && bookTotal+estimate > c.BookUSD {
		return res, ReserveDeniedBook, nil
	}
	if c.DayUSD > 0 && dayTotal+estimate > c.DayUSD {
		return res, ReserveDeniedDay, nil
	}

	if _, err := tx.ExecContext(ctx,
		`INSERT INTO spend (book_id, date, reserved_usd) VALUES (?, ?, ?)
		 ON CONFLICT (book_id, date) DO UPDATE SET reserved_usd = reserved_usd + excluded.reserved_usd`,
		bookID, day, estimate); err != nil {
		return res, ReserveOK, err
	}
	if err := tx.Commit(); err != nil {
		return res, ReserveOK, err
	}
	return res, ReserveOK, nil
}

// Release frees a reservation whose call produced no billable spend (transport
// exhaustion, terminal 4xx before a 2xx). MAX(0, …) guards a double-release.
func (s *Store) Release(res Reservation) error {
	ctx, cancel := opContext()
	defer cancel()
	_, err := s.w.ExecContext(ctx,
		`UPDATE spend SET reserved_usd = MAX(0, reserved_usd - ?) WHERE book_id = ? AND date = ?`,
		res.Estimate, res.BookID, res.Date)
	return err
}

// Checkpoint is one persisted raw LLM response (см. migrate.go v1).
type Checkpoint struct {
	RequestHash       string
	JobID             int64
	ChunkIdx          int
	Attempt           int
	Stage             string
	Role              string
	ModelRequested    string
	ModelActual       string
	ResponseText      string
	UsageJSON         string
	CostUSD           float64
	FinishReason      string
	ProviderRequestID string
}

// SettleWithCheckpoint atomically (ONE transaction, one file) converts the
// reservation into committed spend AND persists the raw response. Это
// закрытие дыры «settle прошёл — kill -9 — чекпоинт не записан = двойная
// оплата» (implementation-notes §3.3): после рестарта либо есть и списание, и
// чекпоинт (вызов не повторится), либо нет ни того ни другого (recovery
// снимет резерв, вызов повторится и оплатится один раз). Неустранимая потеря
// — только in-flight вызов, что и есть честные «≤1 вызов» приёмки.
//
// Idempotent per request_hash: a duplicate settle for the same hash books
// nothing and keeps the original checkpoint.
func (s *Store) SettleWithCheckpoint(res Reservation, cost float64, cp Checkpoint) error {
	ctx, cancel := opContext()
	defer cancel()

	tx, err := s.w.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer tx.Rollback()

	ins, err := tx.ExecContext(ctx, `
		INSERT INTO checkpoints (
			request_hash, job_id, chunk_idx, attempt, stage, role,
			model_requested, model_actual, response_text, usage_json,
			cost_usd, finish_reason, provider_request_id
		) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
		ON CONFLICT (request_hash) DO NOTHING`,
		cp.RequestHash, cp.JobID, cp.ChunkIdx, cp.Attempt, cp.Stage, cp.Role,
		cp.ModelRequested, cp.ModelActual, cp.ResponseText, cp.UsageJSON,
		cp.CostUSD, cp.FinishReason, cp.ProviderRequestID)
	if err != nil {
		return fmt.Errorf("store: checkpoint insert: %w", err)
	}
	inserted, _ := ins.RowsAffected()
	if inserted == 0 {
		// Duplicate settle (retried caller): release the reservation, book no
		// new spend — the original settle already did.
		if _, err := tx.ExecContext(ctx,
			`UPDATE spend SET reserved_usd = MAX(0, reserved_usd - ?) WHERE book_id = ? AND date = ?`,
			res.Estimate, res.BookID, res.Date); err != nil {
			return err
		}
		return tx.Commit()
	}

	if _, err := tx.ExecContext(ctx, `
		INSERT INTO spend (book_id, date, committed_usd, reserved_usd) VALUES (?, ?, ?, 0)
		ON CONFLICT (book_id, date) DO UPDATE SET
			committed_usd = committed_usd + excluded.committed_usd,
			reserved_usd  = MAX(0, reserved_usd - ?)`,
		res.BookID, res.Date, cost, res.Estimate); err != nil {
		return fmt.Errorf("store: settle spend: %w", err)
	}
	return tx.Commit()
}

// GetCheckpoint returns the persisted response for a request hash, if any —
// the resume path: a hit means the call is NOT repeated or re-billed.
func (s *Store) GetCheckpoint(requestHash string) (*Checkpoint, error) {
	ctx, cancel := opContext()
	defer cancel()
	cp := Checkpoint{RequestHash: requestHash}
	err := s.r.QueryRowContext(ctx, `
		SELECT job_id, chunk_idx, attempt, stage, role, model_requested, model_actual,
		       response_text, usage_json, cost_usd, finish_reason, provider_request_id
		FROM checkpoints WHERE request_hash = ?`, requestHash).Scan(
		&cp.JobID, &cp.ChunkIdx, &cp.Attempt, &cp.Stage, &cp.Role, &cp.ModelRequested, &cp.ModelActual,
		&cp.ResponseText, &cp.UsageJSON, &cp.CostUSD, &cp.FinishReason, &cp.ProviderRequestID)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &cp, nil
}

// SpentUSD reports (committed, reserved) for a book across all days.
func (s *Store) SpentUSD(bookID string) (committed, reserved float64, err error) {
	ctx, cancel := opContext()
	defer cancel()
	err = s.r.QueryRowContext(ctx,
		`SELECT COALESCE(SUM(committed_usd),0), COALESCE(SUM(reserved_usd),0) FROM spend WHERE book_id = ?`,
		bookID).Scan(&committed, &reserved)
	return
}