package postgres

import (
	"context"
	"fmt"
	"sort"
)

const LoadRuntimeSettingsSQL = `
SELECT setting_key, setting_value
FROM platform_runtime_settings
WHERE setting_key = ANY($1::text[])
ORDER BY setting_key
`

const UpsertRuntimeSettingSQL = `
INSERT INTO platform_runtime_settings (setting_key, setting_value)
VALUES ($1, $2)
ON CONFLICT (setting_key) DO UPDATE SET
  setting_value = EXCLUDED.setting_value,
  revision = platform_runtime_settings.revision + 1,
  updated_at = now()
`

// LoadRuntimeSettings returns only the requested runtime setting keys. The
// caller owns the editable-key whitelist; the database adapter owns storage.
func (db *Database) LoadRuntimeSettings(ctx context.Context, keys []string) (map[string]string, error) {
	if db.config.Backend != BackendPostgres || db.querier == nil {
		return nil, fmt.Errorf("PostgreSQL is unavailable when ZHINIAN_DATA_BACKEND=%s", db.config.Backend)
	}
	if len(keys) == 0 {
		return map[string]string{}, nil
	}
	rows, err := db.querier.Query(ctx, LoadRuntimeSettingsSQL, keys)
	if err != nil {
		return nil, fmt.Errorf("load runtime settings: %w", err)
	}
	defer rows.Close()
	values := make(map[string]string, len(keys))
	for rows.Next() {
		var key, value string
		if err := rows.Scan(&key, &value); err != nil {
			return nil, fmt.Errorf("scan runtime setting: %w", err)
		}
		values[key] = value
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("read runtime settings: %w", err)
	}
	return values, nil
}

// SaveRuntimeSettings atomically upserts a partial set of settings. Sorting
// makes lock acquisition deterministic when concurrent requests touch several
// keys at once.
func (db *Database) SaveRuntimeSettings(ctx context.Context, values map[string]string) error {
	if db.config.Backend != BackendPostgres || db.transactions == nil {
		return fmt.Errorf("PostgreSQL is unavailable when ZHINIAN_DATA_BACKEND=%s", db.config.Backend)
	}
	if len(values) == 0 {
		return nil
	}
	keys := make([]string, 0, len(values))
	for key := range values {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	tx, err := db.transactions.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin runtime settings update: %w", err)
	}
	finished := false
	defer func() {
		if !finished {
			_ = tx.Rollback(ctx)
		}
	}()
	for _, key := range keys {
		if err := tx.Exec(ctx, UpsertRuntimeSettingSQL, key, values[key]); err != nil {
			return fmt.Errorf("save runtime setting %s: %w", key, err)
		}
	}
	if err := tx.Commit(ctx); err != nil {
		return fmt.Errorf("commit runtime settings update: %w", err)
	}
	finished = true
	return nil
}