package mysql

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

// RetentionInventory 是指定截止时间前的只读保留清单。
// 它只提供核对数量，不代表记录已经满足归档条件，也不执行删除或搬迁。
type RetentionInventory struct {
	// Cutoff 是清单使用的 UTC 截止时间，严格早于该时间的记录才会计入。
	Cutoff time.Time `json:"cutoff"`
	// ExpiredIdempotency 是已过幂等保留期的请求记录数量。
	ExpiredIdempotency uint64 `json:"expired_idempotency"`
	// TerminalTasks 是已进入确定终态且已完成的任务数量。
	TerminalTasks uint64 `json:"terminal_tasks"`
	// UncertainTasks 是仍带未知效果的任务数量，必须人工核对后才能处理。
	UncertainTasks uint64 `json:"uncertain_tasks"`
	// ActiveTasks 是尚未终结的任务数量，不能进入普通历史归档。
	ActiveTasks uint64 `json:"active_tasks"`
	// TerminalWorkflows 是已进入确定终态且已完成的流程数量。
	TerminalWorkflows uint64 `json:"terminal_workflows"`
	// ActiveWorkflows 是尚未终结的流程数量，不能进入普通历史归档。
	ActiveWorkflows uint64 `json:"active_workflows"`
	// AcknowledgedDeliveries 是已经确认的结果交付数量。
	AcknowledgedDeliveries uint64 `json:"acknowledged_deliveries"`
	// UnconfirmedDeliveries 是仍未确认的结果交付数量，不能无声清理。
	UnconfirmedDeliveries uint64 `json:"unconfirmed_deliveries"`
	// ProcessedInbox 是已经完成内部消费的流程事件数量。
	ProcessedInbox uint64 `json:"processed_inbox"`
	// UnprocessedInbox 是尚未完成内部消费的流程事件数量，不能清理。
	UnprocessedInbox uint64 `json:"unprocessed_inbox"`
	// Events 是截止时间前追加的不可变事件数量。
	Events uint64 `json:"events"`
	// AuditEvents 是截止时间前追加的管理审计数量，默认应单独保留。
	AuditEvents uint64 `json:"audit_events"`
}

// ReadRetentionInventory performs bounded-by-time, read-only count queries.
// It deliberately does not decide policy or mutate any table; callers must
// review retention windows, backups, outstanding effects and audit rules first.
func ReadRetentionInventory(ctx context.Context, db *sql.DB, cutoff time.Time) (RetentionInventory, error) {
	if db == nil {
		return RetentionInventory{}, errors.New("database is required")
	}
	if cutoff.IsZero() {
		return RetentionInventory{}, errors.New("cutoff is required")
	}
	cutoff = cutoff.UTC()
	var now time.Time
	if err := db.QueryRowContext(ctx, "SELECT UTC_TIMESTAMP(6)").Scan(&now); err != nil {
		return RetentionInventory{}, errors.New("database time unavailable")
	}
	if cutoff.After(now.UTC()) {
		return RetentionInventory{}, errors.New("cutoff cannot be in the future")
	}
	result := RetentionInventory{Cutoff: cutoff}
	queries := []struct {
		destination *uint64
		query       string
	}{
		{&result.ExpiredIdempotency, "SELECT COUNT(*) FROM orbit_idempotency_keys WHERE expires_at<?"},
		{&result.TerminalTasks, "SELECT COUNT(*) FROM pulse_tasks WHERE state IN ('SUCCEEDED','FAILED','CANCELLED') AND completed_at IS NOT NULL AND completed_at<? AND effect_uncertain=FALSE"},
		{&result.UncertainTasks, "SELECT COUNT(*) FROM pulse_tasks WHERE effect_uncertain=TRUE AND created_at<?"},
		{&result.ActiveTasks, "SELECT COUNT(*) FROM pulse_tasks WHERE state NOT IN ('SUCCEEDED','FAILED','CANCELLED') AND created_at<?"},
		{&result.TerminalWorkflows, "SELECT COUNT(*) FROM weave_instances WHERE state IN ('SUCCEEDED','FAILED','CANCELLED') AND completed_at IS NOT NULL AND completed_at<?"},
		{&result.ActiveWorkflows, "SELECT COUNT(*) FROM weave_instances WHERE state NOT IN ('SUCCEEDED','FAILED','CANCELLED') AND created_at<?"},
		{&result.AcknowledgedDeliveries, "SELECT COUNT(*) FROM orbit_deliveries WHERE state='ACKED' AND acknowledged_at IS NOT NULL AND acknowledged_at<?"},
		{&result.UnconfirmedDeliveries, "SELECT COUNT(*) FROM orbit_deliveries WHERE state<>'ACKED' AND created_at<?"},
		{&result.ProcessedInbox, "SELECT COUNT(*) FROM weave_inbox WHERE state='PROCESSED' AND processed_at IS NOT NULL AND processed_at<?"},
		{&result.UnprocessedInbox, "SELECT COUNT(*) FROM weave_inbox WHERE state<>'PROCESSED' AND created_at<?"},
		{&result.Events, "SELECT COUNT(*) FROM orbit_events WHERE occurred_at<?"},
		{&result.AuditEvents, "SELECT COUNT(*) FROM orbit_audit_events WHERE created_at<?"},
	}
	for _, item := range queries {
		if err := db.QueryRowContext(ctx, item.query, cutoff).Scan(item.destination); err != nil {
			return RetentionInventory{}, errors.New("retention inventory unavailable")
		}
	}
	return result, nil
}