package rest

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

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

type explorerStats struct {
	TotalBlocks       int64 `json:"total_blocks"`
	TotalTransactions int64 `json:"total_transactions"`
	TotalAddresses    int64 `json:"total_addresses"`
	LatestBlock       int64 `json:"latest_block"`
}

type statsQueryFunc func(ctx context.Context, sql string, args ...any) pgx.Row

func loadExplorerStats(ctx context.Context, chainID int, queryRow statsQueryFunc) (explorerStats, error) {
	var stats explorerStats

	if err := queryRow(ctx,
		`SELECT COUNT(*) FROM blocks WHERE chain_id = $1`,
		chainID,
	).Scan(&stats.TotalBlocks); err != nil {
		return explorerStats{}, fmt.Errorf("query total blocks: %w", err)
	}

	if err := queryRow(ctx,
		`SELECT COUNT(*) FROM transactions WHERE chain_id = $1`,
		chainID,
	).Scan(&stats.TotalTransactions); err != nil {
		return explorerStats{}, fmt.Errorf("query total transactions: %w", err)
	}

	if err := queryRow(ctx,
		`SELECT COUNT(*) FROM (
			SELECT from_address AS address
			FROM transactions
			WHERE chain_id = $1 AND from_address IS NOT NULL AND from_address <> ''
			UNION
			SELECT to_address AS address
			FROM transactions
			WHERE chain_id = $1 AND to_address IS NOT NULL AND to_address <> ''
		) unique_addresses`,
		chainID,
	).Scan(&stats.TotalAddresses); err != nil {
		return explorerStats{}, fmt.Errorf("query total addresses: %w", err)
	}

	if err := queryRow(ctx,
		`SELECT COALESCE(MAX(number), 0) FROM blocks WHERE chain_id = $1`,
		chainID,
	).Scan(&stats.LatestBlock); err != nil {
		return explorerStats{}, fmt.Errorf("query latest block: %w", err)
	}

	return stats, nil
}

// handleStats handles GET /api/v2/stats
func (s *Server) handleStats(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		writeMethodNotAllowed(w)
		return
	}
	if !s.requireDB(w) {
		return
	}

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	stats, err := loadExplorerStats(ctx, s.chainID, s.db.QueryRow)
	if err != nil {
		writeError(w, http.StatusServiceUnavailable, "service_unavailable", "explorer stats are temporarily unavailable")
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(stats)
}