package ads

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

	"github.com/go-jet/jet/v2/postgres"
	"github.com/go-jet/jet/v2/qrm"
	"github.com/google/uuid"

	"scrabble/backend/internal/postgres/jet/backend/model"
	"scrabble/backend/internal/postgres/jet/backend/table"
)

// Store is the Postgres-backed query surface for advertising campaigns, their
// messages and the single global display-settings row.
type Store struct {
	db *sql.DB
}

// NewStore constructs a Store wrapping db.
func NewStore(db *sql.DB) *Store { return &Store{db: db} }

// ListCampaigns returns every campaign with its messages, the default first then
// by creation time, for the admin console.
func (s *Store) ListCampaigns(ctx context.Context) ([]Campaign, error) {
	return s.loadCampaigns(ctx, false)
}

// ActiveCampaigns returns the enabled campaigns with their messages, the default
// first then by creation time. Window filtering and the default-remainder weight
// are applied by the Service (ActiveSet), not here.
func (s *Store) ActiveCampaigns(ctx context.Context) ([]Campaign, error) {
	return s.loadCampaigns(ctx, true)
}

// loadCampaigns reads campaigns (optionally only the enabled ones) and attaches
// each one's messages in display order, with a single messages query (the table
// is small, so this avoids both an N+1 and a join projection).
func (s *Store) loadCampaigns(ctx context.Context, enabledOnly bool) ([]Campaign, error) {
	sel := postgres.SELECT(table.AdCampaigns.AllColumns).FROM(table.AdCampaigns)
	if enabledOnly {
		sel = sel.WHERE(table.AdCampaigns.Enabled.EQ(postgres.Bool(true)))
	}
	sel = sel.ORDER_BY(table.AdCampaigns.IsDefault.DESC(), table.AdCampaigns.CreatedAt.ASC())

	var rows []model.AdCampaigns
	if err := sel.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("ads: list campaigns: %w", err)
	}
	byID, err := s.messagesByCampaign(ctx)
	if err != nil {
		return nil, err
	}
	out := make([]Campaign, 0, len(rows))
	for _, r := range rows {
		c := modelToCampaign(r)
		c.Messages = byID[r.CampaignID]
		out = append(out, c)
	}
	return out, nil
}

// Campaign returns one campaign with its messages, or ErrNotFound.
func (s *Store) Campaign(ctx context.Context, id uuid.UUID) (Campaign, error) {
	sel := postgres.SELECT(table.AdCampaigns.AllColumns).
		FROM(table.AdCampaigns).
		WHERE(table.AdCampaigns.CampaignID.EQ(postgres.UUID(id))).
		LIMIT(1)
	var row model.AdCampaigns
	if err := sel.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Campaign{}, ErrNotFound
		}
		return Campaign{}, fmt.Errorf("ads: get campaign %s: %w", id, err)
	}
	c := modelToCampaign(row)
	msgs, err := s.messagesFor(ctx, id)
	if err != nil {
		return Campaign{}, err
	}
	c.Messages = msgs
	return c, nil
}

// CreateCampaign inserts a campaign (always non-default) and returns its new id.
func (s *Store) CreateCampaign(ctx context.Context, c Campaign) (uuid.UUID, error) {
	id := uuid.New()
	now := time.Now().UTC()
	stmt := table.AdCampaigns.INSERT(
		table.AdCampaigns.CampaignID, table.AdCampaigns.Name, table.AdCampaigns.Weight,
		table.AdCampaigns.IsDefault, table.AdCampaigns.Enabled,
		table.AdCampaigns.StartsAt, table.AdCampaigns.EndsAt,
		table.AdCampaigns.CreatedAt, table.AdCampaigns.UpdatedAt,
	).VALUES(
		postgres.UUID(id), postgres.String(c.Name), postgres.Int(int64(c.Weight)),
		postgres.Bool(false), postgres.Bool(c.Enabled),
		tsOrNull(c.StartsAt), tsOrNull(c.EndsAt),
		postgres.TimestampzT(now), postgres.TimestampzT(now),
	)
	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
		return uuid.Nil, fmt.Errorf("ads: create campaign: %w", err)
	}
	return id, nil
}

// UpdateCampaign updates a campaign's name, weight, enabled flag and validity
// window. The default flag is never touched here. Returns ErrNotFound when no
// campaign matches.
func (s *Store) UpdateCampaign(ctx context.Context, c Campaign) error {
	stmt := table.AdCampaigns.UPDATE(
		table.AdCampaigns.Name, table.AdCampaigns.Weight, table.AdCampaigns.Enabled,
		table.AdCampaigns.StartsAt, table.AdCampaigns.EndsAt, table.AdCampaigns.UpdatedAt,
	).SET(
		postgres.String(c.Name), postgres.Int(int64(c.Weight)), postgres.Bool(c.Enabled),
		tsOrNull(c.StartsAt), tsOrNull(c.EndsAt), postgres.TimestampzT(time.Now().UTC()),
	).WHERE(table.AdCampaigns.CampaignID.EQ(postgres.UUID(c.ID)))
	return execOne(ctx, s.db, stmt, "update campaign")
}

// DeleteCampaign removes a campaign (its messages cascade). Returns ErrNotFound
// when no campaign matches. The Service refuses to delete the default.
func (s *Store) DeleteCampaign(ctx context.Context, id uuid.UUID) error {
	stmt := table.AdCampaigns.DELETE().WHERE(table.AdCampaigns.CampaignID.EQ(postgres.UUID(id)))
	return execOne(ctx, s.db, stmt, "delete campaign")
}

// AddMessage inserts a message into a campaign and returns its new id.
func (s *Store) AddMessage(ctx context.Context, m Message) (uuid.UUID, error) {
	id := uuid.New()
	now := time.Now().UTC()
	stmt := table.AdMessages.INSERT(
		table.AdMessages.MessageID, table.AdMessages.CampaignID, table.AdMessages.Position,
		table.AdMessages.BodyEn, table.AdMessages.BodyRu,
		table.AdMessages.CreatedAt, table.AdMessages.UpdatedAt,
	).VALUES(
		postgres.UUID(id), postgres.UUID(m.CampaignID), postgres.Int(int64(m.Position)),
		postgres.String(m.BodyEn), postgres.String(m.BodyRu),
		postgres.TimestampzT(now), postgres.TimestampzT(now),
	)
	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
		return uuid.Nil, fmt.Errorf("ads: add message: %w", err)
	}
	return id, nil
}

// UpdateMessageBodies updates a message's bilingual bodies (its position is
// unchanged). Returns ErrNotFound when no message matches.
func (s *Store) UpdateMessageBodies(ctx context.Context, id uuid.UUID, bodyEn, bodyRu string) error {
	stmt := table.AdMessages.UPDATE(
		table.AdMessages.BodyEn, table.AdMessages.BodyRu, table.AdMessages.UpdatedAt,
	).SET(
		postgres.String(bodyEn), postgres.String(bodyRu), postgres.TimestampzT(time.Now().UTC()),
	).WHERE(table.AdMessages.MessageID.EQ(postgres.UUID(id)))
	return execOne(ctx, s.db, stmt, "update message")
}

// SetMessagePosition updates only a message's position (used to reorder).
func (s *Store) SetMessagePosition(ctx context.Context, id uuid.UUID, position int) error {
	stmt := table.AdMessages.UPDATE(table.AdMessages.Position, table.AdMessages.UpdatedAt).
		SET(postgres.Int(int64(position)), postgres.TimestampzT(time.Now().UTC())).
		WHERE(table.AdMessages.MessageID.EQ(postgres.UUID(id)))
	return execOne(ctx, s.db, stmt, "reorder message")
}

// DeleteMessage removes a message. Returns ErrNotFound when no message matches.
func (s *Store) DeleteMessage(ctx context.Context, id uuid.UUID) error {
	stmt := table.AdMessages.DELETE().WHERE(table.AdMessages.MessageID.EQ(postgres.UUID(id)))
	return execOne(ctx, s.db, stmt, "delete message")
}

// Settings returns the global display timings.
func (s *Store) Settings(ctx context.Context) (Timings, error) {
	sel := postgres.SELECT(table.AdSettings.AllColumns).FROM(table.AdSettings).LIMIT(1)
	var row model.AdSettings
	if err := sel.QueryContext(ctx, s.db, &row); err != nil {
		return Timings{}, fmt.Errorf("ads: get settings: %w", err)
	}
	return Timings{
		HoldMs:         int(row.HoldMs),
		EdgePauseMs:    int(row.EdgePauseMs),
		ScrollPxPerSec: int(row.ScrollPxPerSec),
		FadeOutMs:      int(row.FadeOutMs),
		GapMs:          int(row.GapMs),
		FadeInMs:       int(row.FadeInMs),
	}, nil
}

// UpdateSettings overwrites the single global display-settings row.
func (s *Store) UpdateSettings(ctx context.Context, t Timings) error {
	stmt := table.AdSettings.UPDATE(
		table.AdSettings.HoldMs, table.AdSettings.EdgePauseMs, table.AdSettings.ScrollPxPerSec,
		table.AdSettings.FadeOutMs, table.AdSettings.GapMs, table.AdSettings.FadeInMs, table.AdSettings.UpdatedAt,
	).SET(
		postgres.Int(int64(t.HoldMs)), postgres.Int(int64(t.EdgePauseMs)), postgres.Int(int64(t.ScrollPxPerSec)),
		postgres.Int(int64(t.FadeOutMs)), postgres.Int(int64(t.GapMs)), postgres.Int(int64(t.FadeInMs)),
		postgres.TimestampzT(time.Now().UTC()),
	).WHERE(table.AdSettings.ID.EQ(postgres.Bool(true)))
	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
		return fmt.Errorf("ads: update settings: %w", err)
	}
	return nil
}

// messagesByCampaign loads every message grouped by campaign id, in display order.
func (s *Store) messagesByCampaign(ctx context.Context) (map[uuid.UUID][]Message, error) {
	sel := postgres.SELECT(table.AdMessages.AllColumns).
		FROM(table.AdMessages).
		ORDER_BY(table.AdMessages.CampaignID.ASC(), table.AdMessages.Position.ASC(), table.AdMessages.CreatedAt.ASC())
	var rows []model.AdMessages
	if err := sel.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("ads: list messages: %w", err)
	}
	out := make(map[uuid.UUID][]Message, len(rows))
	for _, r := range rows {
		out[r.CampaignID] = append(out[r.CampaignID], modelToMessage(r))
	}
	return out, nil
}

// messagesFor loads one campaign's messages in display order.
func (s *Store) messagesFor(ctx context.Context, campaignID uuid.UUID) ([]Message, error) {
	sel := postgres.SELECT(table.AdMessages.AllColumns).
		FROM(table.AdMessages).
		WHERE(table.AdMessages.CampaignID.EQ(postgres.UUID(campaignID))).
		ORDER_BY(table.AdMessages.Position.ASC(), table.AdMessages.CreatedAt.ASC())
	var rows []model.AdMessages
	if err := sel.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("ads: list messages for %s: %w", campaignID, err)
	}
	out := make([]Message, 0, len(rows))
	for _, r := range rows {
		out = append(out, modelToMessage(r))
	}
	return out, nil
}

// execOne runs a statement expected to touch exactly one row, mapping a zero
// row-count to ErrNotFound.
func execOne(ctx context.Context, db qrm.Executable, stmt postgres.Statement, what string) error {
	res, err := stmt.ExecContext(ctx, db)
	if err != nil {
		return fmt.Errorf("ads: %s: %w", what, err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("ads: %s rows: %w", what, err)
	}
	if n == 0 {
		return ErrNotFound
	}
	return nil
}

func modelToCampaign(r model.AdCampaigns) Campaign {
	return Campaign{
		ID:        r.CampaignID,
		Name:      r.Name,
		Weight:    int(r.Weight),
		IsDefault: r.IsDefault,
		Enabled:   r.Enabled,
		StartsAt:  r.StartsAt,
		EndsAt:    r.EndsAt,
		CreatedAt: r.CreatedAt,
		UpdatedAt: r.UpdatedAt,
	}
}

func modelToMessage(r model.AdMessages) Message {
	return Message{
		ID:         r.MessageID,
		CampaignID: r.CampaignID,
		Position:   int(r.Position),
		BodyEn:     r.BodyEn,
		BodyRu:     r.BodyRu,
	}
}

// tsOrNull renders a nullable validity-window bound: NULL for a nil pointer,
// otherwise the UTC timestamp.
func tsOrNull(t *time.Time) postgres.Expression {
	if t == nil {
		return postgres.NULL
	}
	return postgres.TimestampzT(t.UTC())
}