package maintenance

import (
	"context"
	"fmt"

	"evobgp/internal/pgmonitor"
)

// TableHints are PostgreSQL statistics hints for UI recommendations.
type TableHints struct {
	TableName       string   `json:"table_name"`
	DeadTuples      int64    `json:"n_dead_tup"`
	BloatRatio      float64  `json:"bloat_ratio,omitempty"`
	LastAutovacuum  string   `json:"last_autovacuum,omitempty"`
	RecommendVacuum bool     `json:"recommend_vacuum"`
	Detail          string   `json:"detail,omitempty"`
	Refs            []string `json:"refs,omitempty"`
}

// DBStatsProvider wraps pgmonitor for maintenance policy hints.
type DBStatsProvider struct {
	pg *pgmonitor.Service
}

// NewDBStatsProvider constructs a stats provider.
func NewDBStatsProvider(pg *pgmonitor.Service) *DBStatsProvider {
	return &DBStatsProvider{pg: pg}
}

// Hints returns table-level vacuum/bloat hints.
func (d *DBStatsProvider) Hints(ctx context.Context, tableName string) (TableHints, error) {
	out := TableHints{TableName: tableName}
	if d == nil || d.pg == nil {
		return out, fmt.Errorf("maintenance: postgres monitoring not configured")
	}
	if err := ValidateTableName(tableName); err != nil {
		return out, err
	}
	tables, err := d.pg.Tables(ctx, 100)
	if err != nil {
		return out, err
	}
	for _, t := range tables {
		if t.Relname != tableName {
			continue
		}
		out.DeadTuples = t.DeadTuples
		out.BloatRatio = t.BloatRatio
		if t.LastAutovacuum != nil {
			out.LastAutovacuum = t.LastAutovacuum.UTC().Format("2006-01-02T15:04:05Z")
		}
		if t.BloatRatio > 0.2 && t.DeadTuples > 5000 {
			out.RecommendVacuum = true
			out.Detail = "Высокая доля n_dead_tup; рекомендуется VACUUM."
			out.Refs = []string{t.Relname}
		}
		return out, nil
	}
	out.Detail = "Таблица не найдена в pg_stat_user_tables (top by size)."
	return out, nil
}