// Package requests owns the lifecycle of what users ask to have added. The
// synchronous Service handles Create/List/Approve/Reject/Cancel; approving
// records the request on the wanted list (M502 #5520): an album or a track
// wants its album's release group, an artist is followed. The async
// Reconciler (separate file) completes approved requests once the library
// holds what they asked for.
package requests

import (
	"context"
	"errors"
	"fmt"

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

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

// Public errors. Handlers map these to API error codes.
var (
	ErrInvalidKindFields = errors.New("requests: missing required fields for kind")
	ErrNotPending        = errors.New("requests: request is not pending")
	// ErrNotFound aliases apierror.ErrNotFound so handlers can errors.Is
	// against the shared sentinel.
	ErrNotFound = apierror.ErrNotFound
)

// CreateParams is the input for a new request from a user. AlbumMBID is the
// album's MusicBrainz release group.
type CreateParams struct {
	Kind       string // "artist", "album", or "track"
	ArtistMBID string
	AlbumMBID  string // required for kind=album/track
	TrackMBID  string // required for kind=track
	ArtistName string
	AlbumTitle string // required for kind=album/track
	TrackTitle string // required for kind=track
}

// Service owns the request lifecycle.
type Service struct {
	pool *pgxpool.Pool
}

// NewService constructs a Service.
func NewService(pool *pgxpool.Pool) *Service {
	return &Service{pool: pool}
}

// Create validates the kind→required-fields invariant and inserts a
// pending row.
func (s *Service) Create(ctx context.Context, userID pgtype.UUID, p CreateParams) (dbq.Request, error) {
	row, _, err := s.CreateTracked(ctx, userID, p)
	return row, err
}

// CreateTracked is Create, also reporting whether a row was inserted. A
// request that dedupes into one already in flight is not new, so callers
// that announce new requests (M489) say nothing for it.
func (s *Service) CreateTracked(ctx context.Context, userID pgtype.UUID, p CreateParams) (dbq.Request, bool, error) {
	if err := validateKindFields(p); err != nil {
		return dbq.Request{}, false, err
	}
	q := dbq.New(s.pool)
	// Dedup: if a non-terminal request for this MBID already exists,
	// return it instead of inserting a duplicate. The Discover/search UI
	// already hides requested candidates; this backstops races and direct
	// API callers. Match on the new request's own-kind MBID.
	dedupMBID := p.ArtistMBID
	switch p.Kind {
	case "album":
		dedupMBID = p.AlbumMBID
	case "track":
		dedupMBID = p.TrackMBID
	}
	if existing, derr := q.GetNonTerminalRequestForMBID(ctx, dedupMBID); derr == nil {
		return existing, false, nil
	} else if !errors.Is(derr, pgx.ErrNoRows) {
		return dbq.Request{}, false, fmt.Errorf("create: dedup check: %w", derr)
	}
	row, err := q.CreateRequest(ctx, dbq.CreateRequestParams{
		UserID:     userID,
		Kind:       dbq.RequestKind(p.Kind),
		ArtistMbid: p.ArtistMBID,
		AlbumMbid:  strPtr(p.AlbumMBID),
		TrackMbid:  strPtr(p.TrackMBID),
		ArtistName: p.ArtistName,
		AlbumTitle: strPtr(p.AlbumTitle),
		TrackTitle: strPtr(p.TrackTitle),
	})
	if err != nil {
		return dbq.Request{}, false, fmt.Errorf("create: %w", err)
	}
	return row, true, nil
}

// DisplayName is a request as a person would say it: "Moe Shop" for an
// artist, "Moe Shop – WWW" for an album or a track.
func DisplayName(row dbq.Request) string {
	if t := requestedTitle(row); t != "" {
		return row.ArtistName + " – " + t
	}
	return row.ArtistName
}

// requestedTitle is the album or track a request names, or "" for an
// artist request. DisplayName is the artist and this, joined.
func requestedTitle(row dbq.Request) string {
	switch {
	case row.Kind == dbq.RequestKindTrack && row.TrackTitle != nil:
		return *row.TrackTitle
	case row.Kind == dbq.RequestKindAlbum && row.AlbumTitle != nil:
		return *row.AlbumTitle
	}
	return ""
}

func validateKindFields(p CreateParams) error {
	if p.ArtistMBID == "" || p.ArtistName == "" {
		return fmt.Errorf("%w: artist_mbid and artist_name are always required", ErrInvalidKindFields)
	}
	switch p.Kind {
	case "artist":
		// fine
	case "album":
		if p.AlbumMBID == "" || p.AlbumTitle == "" {
			return fmt.Errorf("%w: album kind requires album_mbid and album_title", ErrInvalidKindFields)
		}
	case "track":
		if p.AlbumMBID == "" || p.AlbumTitle == "" {
			return fmt.Errorf("%w: track kind requires album_mbid and album_title (its album is what is wanted)", ErrInvalidKindFields)
		}
		if p.TrackMBID == "" || p.TrackTitle == "" {
			return fmt.Errorf("%w: track kind requires track_mbid and track_title", ErrInvalidKindFields)
		}
	default:
		return fmt.Errorf("%w: unknown kind %q", ErrInvalidKindFields, p.Kind)
	}
	return nil
}

// ListByStatus returns requests with the given status, ordered by requested_at DESC.
func (s *Service) ListByStatus(ctx context.Context, status string, limit int32) ([]dbq.Request, error) {
	return dbq.New(s.pool).ListRequestsByStatus(ctx, dbq.ListRequestsByStatusParams{
		Status: dbq.RequestStatus(status), Limit: limit,
	})
}

// ListForUser returns all requests by a user, ordered by requested_at DESC.
func (s *Service) ListForUser(ctx context.Context, userID pgtype.UUID, limit int32) ([]dbq.Request, error) {
	return dbq.New(s.pool).ListRequestsForUser(ctx, dbq.ListRequestsForUserParams{
		UserID: userID, Limit: limit,
	})
}

// Approve puts a pending request on the wanted list and marks it approved,
// in one transaction. An album or track request wants the album's release
// group, recorded as the requester's. An artist request follows the artist
// on profileID (the zero id means the default profile) and also wants what
// they have already released that the profile passes: someone asking for an
// artist wants their music, not only what comes next.
func (s *Service) Approve(ctx context.Context, requestID, approverID, profileID pgtype.UUID) (dbq.Request, error) {
	var approved dbq.Request
	err := pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
		q := dbq.New(tx)
		row, err := q.GetRequestByID(ctx, requestID)
		if errors.Is(err, pgx.ErrNoRows) {
			return ErrNotFound
		}
		if err != nil {
			return fmt.Errorf("approve: get: %w", err)
		}
		if row.Status != dbq.RequestStatusPending {
			return ErrNotPending
		}
		switch row.Kind {
		case dbq.RequestKindArtist:
			if _, err := wanted.FollowWith(ctx, q, wanted.FollowParams{
				ArtistMBID: row.ArtistMbid, ArtistName: row.ArtistName,
				ProfileID: profileID, By: approverID, WantExisting: true,
			}); err != nil {
				return err
			}
		default:
			if _, err := wanted.WantWith(ctx, q, wantFor(row)); err != nil {
				return err
			}
		}
		approved, err = q.ApproveRequest(ctx, dbq.ApproveRequestParams{ID: requestID, DecidedBy: approverID})
		if err != nil {
			return fmt.Errorf("approve: persist: %w", err)
		}
		return nil
	})
	return approved, err
}

// wantFor is the want an approved album or track request records.
func wantFor(row dbq.Request) wanted.WantParams {
	p := wanted.WantParams{
		ArtistMBID: row.ArtistMbid, ArtistName: row.ArtistName,
		Reason: wanted.ReasonRequest, CreatedBy: row.UserID,
	}
	if row.AlbumMbid != nil {
		p.GroupMBID = *row.AlbumMbid
	}
	if row.AlbumTitle != nil {
		p.Title = *row.AlbumTitle
	}
	return p
}

// Reject transitions a pending request to rejected, recording notes and
// who decided. Returns ErrNotPending if the request is not pending,
// ErrNotFound if no such request exists.
func (s *Service) Reject(ctx context.Context, requestID pgtype.UUID, adminID pgtype.UUID, notes string) (dbq.Request, error) {
	row, err := dbq.New(s.pool).RejectRequest(ctx, dbq.RejectRequestParams{
		ID: requestID, Notes: strPtr(notes), DecidedBy: adminID,
	})
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			// Either not found OR not pending — check which.
			cur, gerr := dbq.New(s.pool).GetRequestByID(ctx, requestID)
			if gerr != nil {
				return dbq.Request{}, ErrNotFound
			}
			if cur.Status != dbq.RequestStatusPending {
				return dbq.Request{}, ErrNotPending
			}
			return dbq.Request{}, ErrNotFound
		}
		return dbq.Request{}, fmt.Errorf("reject: %w", err)
	}
	return row, nil
}

// Cancel lets a user withdraw their own pending request. The SQL WHERE
// clause enforces both ownership (user_id = $2) and pending status
// (status = 'pending'). A zero-rows result always means ErrNotPending
// from the caller's perspective.
func (s *Service) Cancel(ctx context.Context, requestID pgtype.UUID, userID pgtype.UUID) (dbq.Request, error) {
	row, err := dbq.New(s.pool).CancelRequest(ctx, dbq.CancelRequestParams{
		ID: requestID, DecidedBy: userID,
	})
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return dbq.Request{}, ErrNotPending
		}
		return dbq.Request{}, fmt.Errorf("cancel: %w", err)
	}
	return row, nil
}

func strPtr(s string) *string {
	if s == "" {
		return nil
	}
	return &s
}