package repository

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/google/uuid"
	"gorm.io/gorm"

	"apskel-pos-be/internal/constants"
	"apskel-pos-be/internal/entities"
)

var (
	// ErrGameBudgetNotFound means no budget with that id in the organization, or no
	// global budget covering the day asked for.
	ErrGameBudgetNotFound = errors.New("enakgame: budget not found")
	// ErrGameBudgetPeriodTaken means a global budget of the organization already
	// starts on that day.
	ErrGameBudgetPeriodTaken = errors.New("enakgame: a global budget already starts on that day")
	// ErrGameBudgetInUse means rewards or events point at the budget, so it stays.
	ErrGameBudgetInUse = errors.New("enakgame: budget is in use")
	// ErrGameBudgetTxRequired is returned by LockGlobalBudgets outside a transaction,
	// where the lock would be released at once.
	ErrGameBudgetTxRequired = errors.New("enakgame: budget lock must run inside a transaction")
)

// GameBudgetFilter selects an organization's budgets.
type GameBudgetFilter struct {
	OrganizationID uuid.UUID
	// Empty for both scopes.
	Scope  string
	Offset int
	Limit  int
}

// GameBudgetRepository stores EnakGame budgets (docs/rfc-enakgame.md §5.6), always
// scoped to an organization.
//
// Period dates are written and compared as dates (YYYY-MM-DD of the time given), so
// the database session's time zone cannot move them to another day.
type GameBudgetRepository interface {
	CreateBudget(ctx context.Context, budget *entities.GameBudget) error
	GetBudget(ctx context.Context, organizationID, id uuid.UUID) (*entities.GameBudget, error)
	// UpdateBudget stores the name, period, amount, thresholds and exhaustion policy.
	UpdateBudget(ctx context.Context, budget *entities.GameBudget) error
	// ListBudgets returns a page of budgets, latest period first, and the total.
	ListBudgets(ctx context.Context, filter GameBudgetFilter) ([]entities.GameBudget, int64, error)
	// GetGlobalBudgetOn returns the organization's global budget whose period holds
	// day, a date in Asia/Jakarta.
	GetGlobalBudgetOn(ctx context.Context, organizationID uuid.UUID, day time.Time) (*entities.GameBudget, error)
	// DeleteBudget removes a budget nothing points at; otherwise ErrGameBudgetInUse.
	DeleteBudget(ctx context.Context, organizationID, id uuid.UUID) error

	// LockGlobalBudgets serializes the writers of an organization's global budgets
	// until the transaction ends, so two of them cannot both find a period free.
	LockGlobalBudgets(ctx context.Context, organizationID uuid.UUID) error
	// GlobalBudgetOverlaps reports whether another global budget of the organization
	// shares a day with start..end. except is the budget being changed, if any.
	GlobalBudgetOverlaps(ctx context.Context, organizationID uuid.UUID, start, end time.Time, except *uuid.UUID) (bool, error)
	// CreateNextGlobalBudgets gives every global budget holding today, whose next day
	// no global budget holds yet, a successor: from that next day to the end of its
	// month, with the same amount, thresholds and policy (§12). It returns what it
	// made.
	CreateNextGlobalBudgets(ctx context.Context, today time.Time) ([]entities.GameBudget, error)
}

type gameBudgetRepository struct {
	db *gorm.DB
}

func NewGameBudgetRepository(db *gorm.DB) GameBudgetRepository {
	return &gameBudgetRepository{db: db}
}

func budgetDate(t time.Time) string { return t.Format("2006-01-02") }

func (r *gameBudgetRepository) CreateBudget(ctx context.Context, budget *entities.GameBudget) error {
	if budget.ID == uuid.Nil {
		budget.ID = uuid.New()
	}
	thresholds := budget.Thresholds
	if len(thresholds) == 0 {
		thresholds = entities.JSONDocument(`{}`)
	}
	var rows []struct{ CreatedAt, UpdatedAt time.Time }
	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
		INSERT INTO game_budgets (id, organization_id, scope, name, period_start, period_end, amount,
			thresholds, exhaustion_policy, created_by)
		VALUES (?, ?, ?, ?, ?::date, ?::date, ?, ?::jsonb, ?, ?)
		RETURNING created_at, updated_at`,
		budget.ID, budget.OrganizationID, budget.Scope, budget.Name, budgetDate(budget.PeriodStart), budgetDate(budget.PeriodEnd),
		budget.Amount, thresholds, budget.ExhaustionPolicy, budget.CreatedBy).Scan(&rows).Error
	if err != nil {
		if isUniqueViolation(err, "uq_game_budgets_global_period") {
			return ErrGameBudgetPeriodTaken
		}
		return fmt.Errorf("failed to create game budget: %w", err)
	}
	budget.Thresholds = thresholds
	budget.CreatedAt, budget.UpdatedAt = rows[0].CreatedAt, rows[0].UpdatedAt
	return nil
}

func (r *gameBudgetRepository) first(q *gorm.DB) (*entities.GameBudget, error) {
	var budget entities.GameBudget
	if err := q.First(&budget).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrGameBudgetNotFound
		}
		return nil, fmt.Errorf("failed to read game budget: %w", err)
	}
	return &budget, nil
}

func (r *gameBudgetRepository) GetBudget(ctx context.Context, organizationID, id uuid.UUID) (*entities.GameBudget, error) {
	return r.first(DBFromContext(ctx, r.db).WithContext(ctx).Where("organization_id = ? AND id = ?", organizationID, id))
}

func (r *gameBudgetRepository) UpdateBudget(ctx context.Context, budget *entities.GameBudget) error {
	thresholds := budget.Thresholds
	if len(thresholds) == 0 {
		thresholds = entities.JSONDocument(`{}`)
	}
	result := DBFromContext(ctx, r.db).WithContext(ctx).Exec(`
		UPDATE game_budgets SET name = ?, period_start = ?::date, period_end = ?::date, amount = ?,
			thresholds = ?::jsonb, exhaustion_policy = ?, updated_at = NOW()
		WHERE organization_id = ? AND id = ?`,
		budget.Name, budgetDate(budget.PeriodStart), budgetDate(budget.PeriodEnd), budget.Amount,
		thresholds, budget.ExhaustionPolicy, budget.OrganizationID, budget.ID)
	if result.Error != nil {
		if isUniqueViolation(result.Error, "uq_game_budgets_global_period") {
			return ErrGameBudgetPeriodTaken
		}
		return fmt.Errorf("failed to update game budget: %w", result.Error)
	}
	if result.RowsAffected == 0 {
		return ErrGameBudgetNotFound
	}
	budget.Thresholds = thresholds
	return nil
}

func (r *gameBudgetRepository) ListBudgets(ctx context.Context, filter GameBudgetFilter) ([]entities.GameBudget, int64, error) {
	q := DBFromContext(ctx, r.db).WithContext(ctx).Model(&entities.GameBudget{}).Where("organization_id = ?", filter.OrganizationID)
	if filter.Scope != "" {
		q = q.Where("scope = ?", filter.Scope)
	}
	var total int64
	if err := q.Count(&total).Error; err != nil {
		return nil, 0, fmt.Errorf("failed to count game budgets: %w", err)
	}
	var budgets []entities.GameBudget
	if err := q.Order("period_start DESC, created_at DESC, id").Offset(filter.Offset).Limit(filter.Limit).Find(&budgets).Error; err != nil {
		return nil, 0, fmt.Errorf("failed to list game budgets: %w", err)
	}
	return budgets, total, nil
}

func (r *gameBudgetRepository) GetGlobalBudgetOn(ctx context.Context, organizationID uuid.UUID, day time.Time) (*entities.GameBudget, error) {
	d := budgetDate(day)
	return r.first(DBFromContext(ctx, r.db).WithContext(ctx).
		Where("organization_id = ? AND scope = ? AND period_start <= ?::date AND period_end >= ?::date",
			organizationID, constants.GameBudgetScopeGlobal, d, d).
		Order("period_start DESC"))
}

func (r *gameBudgetRepository) DeleteBudget(ctx context.Context, organizationID, id uuid.UUID) error {
	result := DBFromContext(ctx, r.db).WithContext(ctx).Exec(`DELETE FROM game_budgets WHERE organization_id = ? AND id = ?`, organizationID, id)
	if result.Error != nil {
		if isForeignKeyViolation(result.Error) {
			return ErrGameBudgetInUse
		}
		return fmt.Errorf("failed to delete game budget: %w", result.Error)
	}
	if result.RowsAffected == 0 {
		return ErrGameBudgetNotFound
	}
	return nil
}

func (r *gameBudgetRepository) LockGlobalBudgets(ctx context.Context, organizationID uuid.UUID) error {
	tx, ok := ctx.Value(txKey).(*gorm.DB)
	if !ok || tx == nil {
		return ErrGameBudgetTxRequired
	}
	err := tx.WithContext(ctx).Exec(`SELECT pg_advisory_xact_lock(hashtextextended(?, 0))`, "game_budgets:global:"+organizationID.String()).Error
	if err != nil {
		return fmt.Errorf("failed to lock game budgets: %w", err)
	}
	return nil
}

func (r *gameBudgetRepository) GlobalBudgetOverlaps(ctx context.Context, organizationID uuid.UUID, start, end time.Time, except *uuid.UUID) (bool, error) {
	q := DBFromContext(ctx, r.db).WithContext(ctx).Model(&entities.GameBudget{}).
		Where("organization_id = ? AND scope = ? AND period_start <= ?::date AND period_end >= ?::date",
			organizationID, constants.GameBudgetScopeGlobal, budgetDate(end), budgetDate(start))
	if except != nil {
		q = q.Where("id <> ?", *except)
	}
	var count int64
	if err := q.Count(&count).Error; err != nil {
		return false, fmt.Errorf("failed to check game budget periods: %w", err)
	}
	return count > 0, nil
}

func (r *gameBudgetRepository) CreateNextGlobalBudgets(ctx context.Context, today time.Time) ([]entities.GameBudget, error) {
	d := budgetDate(today)
	var created []entities.GameBudget
	// ON CONFLICT covers another instance creating the same successor at once.
	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
		INSERT INTO game_budgets (organization_id, scope, name, period_start, period_end, amount,
			thresholds, exhaustion_policy, created_by)
		SELECT b.organization_id, b.scope, 'Budget global ' || to_char(b.period_end + 1, 'YYYY-MM'),
			b.period_end + 1,
			(date_trunc('month', b.period_end + 1) + INTERVAL '1 month - 1 day')::date,
			b.amount, b.thresholds, b.exhaustion_policy, b.created_by
		FROM game_budgets b
		WHERE b.scope = ? AND b.period_start <= ?::date AND b.period_end >= ?::date
			AND NOT EXISTS (
				SELECT 1 FROM game_budgets n
				WHERE n.organization_id = b.organization_id AND n.scope = b.scope
					AND n.period_start <= b.period_end + 1 AND n.period_end >= b.period_end + 1)
		ON CONFLICT DO NOTHING
		RETURNING *`, constants.GameBudgetScopeGlobal, d, d).Scan(&created).Error
	if err != nil {
		return nil, fmt.Errorf("failed to create next game budgets: %w", err)
	}
	return created, nil
}