// Package reacquisition turns a missing file back into a Lidarr request
// without anyone pressing anything (milestone #290).
//
// The unit of work is the ALBUM, not the track. Lidarr acquires releases;
// there is no meaningful "fetch me one track", and a track-kind request needs
// a recording MBID plenty of files lack. Grouping also does most of the
// safety work: the loss that produced #2523 — three reorganised albums, ~40
// missing files — becomes three requests rather than forty.
package reacquisition

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"sync"
	"time"

	"github.com/jackc/pgx/v5/pgxpool"

	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

// Settings is the operator-tunable policy, mirroring the columns and CHECK
// ranges in migration 0056.
type Settings struct {
	Enabled          bool
	GraceHours       int32
	BackoffBaseHours int32
	BackoffMaxHours  int32
	MaxAttempts      int32
	MaxPerPass       int32
	AutoApprove      bool
}

// Defaults mirror migration 0056's column defaults. Duplicated here so a
// database that cannot be read still yields a sane policy rather than a
// zero-valued one — a zero grace window would fire on every transient
// unmount, which is the exact failure the grace period exists to prevent.
var Defaults = Settings{
	Enabled:          true,
	GraceHours:       24,
	BackoffBaseHours: 6,
	BackoffMaxHours:  168,
	MaxAttempts:      3,
	MaxPerPass:       20,
	AutoApprove:      true,
}

// ErrOutOfRange is returned by Set for values migration 0056's CHECKs would
// reject, so the API layer answers 400 instead of surfacing a constraint
// violation.
var ErrOutOfRange = errors.New("reacquisition setting out of range")

// SettingsService caches the settings and owns their persistence. Cached
// because the sweeper reads them every pass and the admin card reads them on
// every render; neither needs a round-trip.
type SettingsService struct {
	pool   *pgxpool.Pool
	logger *slog.Logger

	mu  sync.RWMutex
	cur Settings
}

// NewSettingsService loads once and caches.
//
// Always returns a usable service, even alongside a non-nil error: a
// boot-time database hiccup should leave the sweeper running on defaults
// rather than take it out entirely. The error is returned so the caller can
// log that the cache holds defaults rather than stored state.
func NewSettingsService(ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger) (*SettingsService, error) {
	s := &SettingsService{pool: pool, logger: logger, cur: Defaults}
	row, err := dbq.New(pool).GetReacquisitionSettings(ctx)
	if err != nil {
		return s, fmt.Errorf("reacquisition: load settings: %w", err)
	}
	s.cur = fromRow(row)
	return s, nil
}

// Get returns the cached settings.
func (s *SettingsService) Get() Settings {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.cur
}

// Set validates, persists and re-caches.
func (s *SettingsService) Set(ctx context.Context, in Settings) (Settings, error) {
	if err := validate(in); err != nil {
		return Settings{}, err
	}
	row, err := dbq.New(s.pool).UpdateReacquisitionSettings(ctx, dbq.UpdateReacquisitionSettingsParams{
		Enabled:          in.Enabled,
		GraceHours:       in.GraceHours,
		BackoffBaseHours: in.BackoffBaseHours,
		BackoffMaxHours:  in.BackoffMaxHours,
		MaxAttempts:      in.MaxAttempts,
		MaxPerPass:       in.MaxPerPass,
		AutoApprove:      in.AutoApprove,
	})
	if err != nil {
		return Settings{}, fmt.Errorf("reacquisition: save settings: %w", err)
	}
	out := fromRow(row)
	s.mu.Lock()
	s.cur = out
	s.mu.Unlock()
	return out, nil
}

// Backoff is how long to wait before the next attempt on an album that has
// already been tried [attempts] times: base * 2^(attempts-1), clamped to the
// configured maximum. Zero attempts means "never tried", which is always due.
//
// Exported and pure so the schedule is testable without a database, and so
// the admin surface can show the same number the sweeper will act on.
func (s Settings) Backoff(attempts int32) time.Duration {
	if attempts <= 0 {
		return 0
	}
	hours := s.BackoffBaseHours
	for i := int32(1); i < attempts; i++ {
		hours *= 2
		// Clamp inside the loop as well as after: doubling from a large base
		// enough times would overflow int32 before the comparison ran.
		if hours >= s.BackoffMaxHours {
			return time.Duration(s.BackoffMaxHours) * time.Hour
		}
	}
	if hours > s.BackoffMaxHours {
		hours = s.BackoffMaxHours
	}
	return time.Duration(hours) * time.Hour
}

func validate(in Settings) error {
	switch {
	case in.GraceHours < 1 || in.GraceHours > 720:
		return fmt.Errorf("%w: grace_hours must be 1-720", ErrOutOfRange)
	case in.BackoffBaseHours < 1 || in.BackoffBaseHours > 168:
		return fmt.Errorf("%w: backoff_base_hours must be 1-168", ErrOutOfRange)
	case in.BackoffMaxHours < 1 || in.BackoffMaxHours > 720:
		return fmt.Errorf("%w: backoff_max_hours must be 1-720", ErrOutOfRange)
	case in.BackoffMaxHours < in.BackoffBaseHours:
		return fmt.Errorf("%w: backoff_max_hours must be >= backoff_base_hours", ErrOutOfRange)
	case in.MaxAttempts < 1 || in.MaxAttempts > 10:
		return fmt.Errorf("%w: max_attempts must be 1-10", ErrOutOfRange)
	case in.MaxPerPass < 1 || in.MaxPerPass > 200:
		return fmt.Errorf("%w: max_per_pass must be 1-200", ErrOutOfRange)
	}
	return nil
}

func fromRow(row dbq.ReacquisitionSetting) Settings {
	return Settings{
		Enabled:          row.Enabled,
		GraceHours:       row.GraceHours,
		BackoffBaseHours: row.BackoffBaseHours,
		BackoffMaxHours:  row.BackoffMaxHours,
		MaxAttempts:      row.MaxAttempts,
		MaxPerPass:       row.MaxPerPass,
		AutoApprove:      row.AutoApprove,
	}
}