package httpapi

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net/http"
	"strings"
	"time"

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

	"knowledge-governance/internal/governance"
	"knowledge-governance/internal/jobs"
	"knowledge-governance/internal/librarydiff"
	"knowledge-governance/internal/librarysnapshot"
	postgresstore "knowledge-governance/internal/platform/postgres"
)

// 整库版本/状态/差异读取契约 + 生产同步的 fail-closed 入口。
//
// 三类版本严格分开，不能互相顶替：
//   - 测试封存（archive 里的 sealed 产物）——只证明测试库有一份完整版本；
//   - 生产当前生效（library_versions.kind=production_effective）——必须有生产验证证据；
//   - 生产预备份（kind=production_prebackup）——每次生产写入前的独立备份。
// 生产未建立权威版本时返回 unknown，不拿最新测试快照冒充。

type libraryVersionView struct {
	ID           string         `json:"id"`
	Kind         string         `json:"kind"`
	SnapshotID   string         `json:"snapshot_id"`
	VersionLabel string         `json:"version_label"`
	SourceJobID  string         `json:"source_job_id"`
	Evidence     map[string]any `json:"evidence"`
	CreatedBy    string         `json:"created_by"`
	CreatedAt    time.Time      `json:"created_at"`
	SupersededAt *time.Time     `json:"superseded_at,omitempty"`
}

// librarySyncJobType 与 worker 的处理器类型一致；单独定义避免 API 依赖 worker 包。
const librarySyncJobType = "library.sync"

// libraryRecoverJobType 是"按预备份恢复并校验"的队列类型（同一份定义也在 worker 里）。
const libraryRecoverJobType = "library.recover"

type libraryKnownView struct {
	State   string              `json:"state"` // known | unknown
	Version *libraryVersionView `json:"version,omitempty"`
	Reason  string              `json:"reason,omitempty"`
	// EmptyBaseline 表示"没有生效版本记录，但生产目标可读且确实是空的"：
	// 这是首次发布的合法起点，和"生产非空却没有权威版本"必须区分。
	EmptyBaseline bool `json:"empty_baseline,omitempty"`
}

// productionScopeEmpty 只读探测生产目标：真正连库数一遍，不用缓存或推断。
func productionScopeEmpty(ctx context.Context, config Config, scope string) (bool, error) {
	if strings.TrimSpace(config.LibraryProductionDatabaseURL) == "" {
		return false, errors.New("生产整库目标未配置")
	}
	kb := config.LibraryProductionInternalKB
	if scope == "external" {
		kb = config.LibraryProductionExternalKB
	}
	if kb == "" {
		return false, errors.New("生产知识库未配置")
	}
	pool, err := pgxpool.New(ctx, config.LibraryProductionDatabaseURL)
	if err != nil {
		return false, err
	}
	defer pool.Close()
	var count int64
	err = pool.QueryRow(ctx, `SELECT count(*) FROM knowledges WHERE tenant_id=$1 AND knowledge_base_id=$2 AND deleted_at IS NULL`,
		config.LibraryProductionTenantID, kb).Scan(&count)
	if err != nil {
		return false, err
	}
	return count == 0, nil
}

type libraryDiffView struct {
	State   string `json:"state"` // unknown | computed
	Reason  string `json:"reason,omitempty"`
	Added   []any  `json:"added"`
	Updated []any  `json:"updated"`
	Removed []any  `json:"removed"`
	// BaseSnapshot/TargetSnapshot 标明这次比对用的是哪两个整库版本，
	// 避免把某次历史差异当成"当前拟发布"。
	BaseSnapshot   string `json:"base_snapshot,omitempty"`
	TargetSnapshot string `json:"target_snapshot,omitempty"`
	// Wiki 是**页面级**差异：只能证明页面被增/改/撤，不能证明共享正文、实体、
	// 概念或边被重新计算——后者需要 WeKnora 内部语义，本平台不做也不声称。
	Wiki *libraryWikiDiffView `json:"wiki,omitempty"`
}

type libraryWikiDiffView struct {
	State   string `json:"state"` // computed | unknown
	Reason  string `json:"reason,omitempty"`
	Added   int    `json:"added"`
	Updated int    `json:"updated"`
	Removed int    `json:"removed"`
	// Sample 只列前若干页，避免把整库 Wiki 列表塞进接口。
	Sample []string `json:"sample"`
	Note   string   `json:"note"`
	// Pages 是逐页的**贡献级**明细：哪一页、变了哪几类语义、掉/加了哪些来源文档。
	// 页面级计数只看增删改；撤销一份共享贡献时页面通常仍是"更新"，
	// 只有这里的 sources_removed / changed 才能证明那份贡献确实被摘掉了。
	Pages          []libraryWikiPageView `json:"pages,omitempty"`
	PagesTruncated bool                  `json:"pages_truncated,omitempty"`
	SourcesAdded   int                   `json:"sources_added"`
	SourcesRemoved int                   `json:"sources_removed"`
	BaseCount      int                   `json:"base_count"`
	TargetCount    int                   `json:"target_count"`
}

type libraryWikiPageView struct {
	Slug            string   `json:"slug"`
	Title           string   `json:"title"`
	PageType        string   `json:"page_type,omitempty"`
	Status          string   `json:"status"` // added | updated | removed
	Changed         []string `json:"changed"`
	SourcesAdded    []string `json:"sources_added,omitempty"`
	SourcesRemoved  []string `json:"sources_removed,omitempty"`
	CitationsBefore int      `json:"citations_before"`
	CitationsAfter  int      `json:"citations_after"`
}

// wikiPageLimit 是接口一次最多返回的页数；超出部分只给计数，不给半截明细。
const wikiPageLimit = 50

func wikiViewFrom(result librarydiff.WikiResult, limit int) *libraryWikiDiffView {
	if limit <= 0 {
		limit = wikiPageLimit
	}
	view := &libraryWikiDiffView{State: result.State, Added: result.Added, Updated: result.Updated,
		Removed: result.Removed, Sample: []string{}, SourcesAdded: result.SourcesAdded,
		SourcesRemoved: result.SourcesRemoved, BaseCount: result.BaseCount, TargetCount: result.TargetCount,
		Note: "逐页比对正文、来源文档、引用分块、出入边与目录；语义重算发生在源侧，本平台只如实比对与保留结果"}
	for index, page := range result.Pages {
		if index >= limit {
			view.PagesTruncated = true
			break
		}
		view.Pages = append(view.Pages, libraryWikiPageView{Slug: page.Slug, Title: page.Title,
			PageType: page.PageType, Status: page.Status, Changed: librarydiff.ChangedLabels(page.Changed),
			SourcesAdded: page.SourcesAdded, SourcesRemoved: page.SourcesRemoved,
			CitationsBefore: page.CitationsBefore, CitationsAfter: page.CitationsAfter})
	}
	for _, page := range view.Pages {
		if len(view.Sample) >= 20 {
			break
		}
		label := map[string]string{"added": "新增", "updated": "更新", "removed": "撤销"}[page.Status]
		view.Sample = append(view.Sample, label+" "+page.Title)
	}
	return view
}

// wikiDiffOf 比较两份快照的 wiki_pages 行数组（页面级）。
// 它不能替代"删除文档后共享正文/实体/边/引用如何变化"的语义证据。
func wikiDiffOf(archive *librarysnapshot.Archive, baseID, targetID string) *libraryWikiDiffView {
	unknown := func(reason string) *libraryWikiDiffView {
		return &libraryWikiDiffView{State: "unknown", Reason: reason, Sample: []string{},
			Note: "页面级比对缺失时不能声称 Wiki 已同步"}
	}
	rows := func(id string) ([]map[string]any, string) {
		// 只读清单定位 wiki_pages 部件：整版 Load 会把"比两页 Wiki"变成
		// 逐部件校验整库字节（79 版归档上单版就 252ms）。被读取的那一个部件
		// 由 OpenPart 自己复核摘要，所以正文仍然是验过的字节。
		manifest, err := archive.LoadManifest(id)
		if err != nil {
			return nil, "快照不可读"
		}
		for _, part := range manifest.Parts {
			if part.Kind != "wiki" || part.Name != "wiki_pages" {
				continue
			}
			reader, err := archive.OpenPart(part)
			if err != nil {
				return nil, "Wiki 正文不可读"
			}
			defer reader.Close()
			parsed, err := librarydiff.ReadDocuments(reader)
			if err != nil {
				return nil, "Wiki 行格式不符"
			}
			return parsed, ""
		}
		return nil, "快照里没有 wiki_pages 部件"
	}
	base, reason := rows(baseID)
	if reason != "" {
		return unknown("生产版本：" + reason)
	}
	target, reason := rows(targetID)
	if reason != "" {
		return unknown("测试版本：" + reason)
	}
	result, err := librarydiff.CompareWiki(base, target)
	if err != nil {
		return unknown("Wiki 逐页比对失败：" + err.Error())
	}
	return wikiViewFrom(result, wikiPageLimit)
}

// computeLibraryDiff 用归档里的 knowledges 行数组比较两个快照：
// 身份是文档 ID，内容是排除易变列后的整行摘要；任一侧读不到就返回 false，
// 由调用方保持 unknown 并写明原因，而不是给出空差异冒充"无变化"。
func computeLibraryDiff(root, baseID, targetID string) (libraryDiffView, bool) {
	unknown := libraryDiffView{State: "unknown", Added: []any{}, Updated: []any{}, Removed: []any{},
		BaseSnapshot: baseID, TargetSnapshot: targetID}
	if root == "" {
		unknown.Reason = "整库归档未配置，无法比较生产与测试版本"
		return unknown, false
	}
	if baseID == "" || targetID == "" {
		unknown.Reason = "生产当前版本或测试封存缺失，没有可比的两份整库版本"
		return unknown, false
	}
	archive, err := librarysnapshot.Open(root, 256*1024*1024)
	if err != nil {
		unknown.Reason = "归档根不可用，无法比较"
		return unknown, false
	}
	defer archive.Close()
	read := func(id string) ([]map[string]any, string) {
		// 清单级定位 + OpenPart 复核被读取部件：差异只需要 knowledges 一列部件，
		// 没有理由为它重算整版所有 blob。
		manifest, loadErr := archive.LoadManifest(id)
		if loadErr != nil {
			return nil, "快照不在本地归档或校验失败"
		}
		for _, part := range manifest.Parts {
			if part.Kind != "database" || part.Name != "knowledges" {
				continue
			}
			reader, openErr := archive.OpenPart(part)
			if openErr != nil {
				return nil, "归档正文不可读"
			}
			defer reader.Close()
			rows, readErr := librarydiff.ReadDocuments(reader)
			if readErr != nil {
				return nil, "归档正文格式不符"
			}
			return rows, ""
		}
		return nil, "快照里没有 knowledges 部件"
	}
	base, reason := read(baseID)
	if reason != "" {
		unknown.Reason = "生产版本：" + reason
		return unknown, false
	}
	target, reason := read(targetID)
	if reason != "" {
		unknown.Reason = "测试版本：" + reason
		return unknown, false
	}
	result, err := librarydiff.Compare(base, target)
	if err != nil {
		unknown.Reason = "差异计算失败：" + err.Error()
		return unknown, false
	}
	view := libraryDiffView{State: "computed", Added: []any{}, Updated: []any{}, Removed: []any{},
		BaseSnapshot: baseID, TargetSnapshot: targetID}
	view.Wiki = wikiDiffOf(archive, baseID, targetID)
	for _, item := range result.Added {
		view.Added = append(view.Added, item)
	}
	for _, item := range result.Updated {
		view.Updated = append(view.Updated, item)
	}
	for _, item := range result.Removed {
		view.Removed = append(view.Removed, item)
	}
	return view, true
}

// libraryAuthorizationView 让页面能直说"有没有授权、有效期到什么时候"。
type libraryAuthorizationView struct {
	State        string     `json:"state"` // active | none
	AuthorizedBy string     `json:"authorized_by,omitempty"`
	ExpiresAt    *time.Time `json:"expires_at,omitempty"`
	Reason       string     `json:"reason,omitempty"`
}

type libraryGateView struct {
	SyncAllowed bool     `json:"sync_allowed"`
	Reasons     []string `json:"reasons"`
}

type libraryOverview struct {
	Scope            string                   `json:"scope"`
	TestSealed       *librarySnapshotView     `json:"test_sealed,omitempty"`
	TestSealedReason string                   `json:"test_sealed_reason,omitempty"`
	Production       libraryKnownView         `json:"production"`
	Prebackup        libraryKnownView         `json:"prebackup"`
	Diff             libraryDiffView          `json:"diff"`
	Job              *governance.LibraryJob   `json:"job,omitempty"`
	Jobs             []governance.LibraryJob  `json:"jobs"`
	Gate             libraryGateView          `json:"gate"`
	Authorization    libraryAuthorizationView `json:"authorization"`
	CaptureAvailable bool                     `json:"capture_available"`
	CaptureReason    string                   `json:"capture_reason,omitempty"`
	Now              time.Time                `json:"now"`
}

type libraryJobStore interface {
	CreateLibraryJob(ctx context.Context, job governance.LibraryJob, stages []string, now time.Time) (governance.LibraryJob, bool, error)
	LibraryJob(ctx context.Context, id string) (governance.LibraryJob, error)
	ListLibraryJobs(ctx context.Context, scope string, limit int) ([]governance.LibraryJob, error)
	RecordLibraryVersion(ctx context.Context, version governance.LibraryVersion) error
	LibraryVersions(ctx context.Context, scope string, limit int) ([]governance.LibraryVersion, error)
	UpdateLibraryStage(ctx context.Context, jobID, stage, state string, total, completed, bytesTotal, bytesDone *int64, detail string, now time.Time) error
	AdvanceLibraryJob(ctx context.Context, jobID string, state governance.LibraryJobState, stage, message, recovery, snapshotID, targetSnapshotID string, now time.Time) error
	AttachLibraryQueueJob(ctx context.Context, jobID, queueJobID string, now time.Time) error
	CancelLibraryJob(ctx context.Context, jobID, reason string, now time.Time) error
}

func libraryStore(config Config) (libraryJobStore, bool) {
	store, ok := config.Store.(libraryJobStore)
	return store, ok
}

// instanceMaintenanceGuard 在"实例级维护"被别的作业持有时拒绝新的写入请求。
// 只看 scope 行是不够的：internal 与 external 动的是同一批容器。
func instanceMaintenanceGuard(ctx context.Context, config Config, scope string) (map[string]any, bool) {
	instance := config.LibraryTargetInstance
	if instance == "" {
		return nil, false
	}
	store, ok := config.Store.(interface {
		InstanceMaintenanceOf(ctx context.Context, instance string) (*postgresstore.LibraryInstanceMaintenance, error)
	})
	if !ok {
		return nil, false
	}
	held, err := store.InstanceMaintenanceOf(ctx, instance)
	if err != nil || held == nil || held.ReleasedAt != nil {
		return nil, false
	}
	return map[string]any{"code": "library_target_in_maintenance",
		"error":    "目标实例正在维护中，验证完成前不接受新的写入请求",
		"instance": held.Instance, "owner_job": held.OwnerJobID, "owner_scope": held.OwnerScope,
		"state": held.State, "ingress_state": held.IngressState}, true
}

// libraryMaintenanceRecoverHandler 是"按预备份恢复并校验"的唯一入口：
// 它只建一个恢复作业，真正的恢复与校验由 worker 在维护关闭状态下执行。
func libraryMaintenanceRecoverHandler(w http.ResponseWriter, r *http.Request, config Config) {
	if r.Method != http.MethodPost {
		writeJSON(w, http.StatusMethodNotAllowed, map[string]string{"error": "method not allowed"})
		return
	}
	var request struct {
		Scope       string `json:"scope"`
		WindowJobID string `json:"window_job_id"`
	}
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&request); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid request body"})
		return
	}
	if request.Scope != "internal" && request.Scope != "external" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "scope must be internal or external"})
		return
	}
	instance := config.LibraryTargetInstance
	if instance == "" {
		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"code": "library_recovery_unavailable",
			"error": "目标维护未接线：无法执行按预备份恢复"})
		return
	}
	store, ok := config.Store.(interface {
		InstanceMaintenanceOf(ctx context.Context, instance string) (*postgresstore.LibraryInstanceMaintenance, error)
	})
	if !ok {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "维护记录存储不可用"})
		return
	}
	held, err := store.InstanceMaintenanceOf(r.Context(), instance)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "无法读取维护记录"})
		return
	}
	if held == nil || held.ReleasedAt != nil {
		writeJSON(w, http.StatusConflict, map[string]any{"code": "library_no_held_window",
			"error": "目标实例当前没有未释放的维护窗口，不需要恢复"})
		return
	}
	if held.OwnerScope != request.Scope {
		writeJSON(w, http.StatusConflict, map[string]any{"code": "library_window_scope_mismatch",
			"error": "维护窗口属于另一个 scope", "owner_scope": held.OwnerScope})
		return
	}
	if request.WindowJobID != "" && request.WindowJobID != held.OwnerJobID {
		writeJSON(w, http.StatusConflict, map[string]any{"code": "library_window_mismatch",
			"error": "维护窗口属于另一个作业", "owner_job": held.OwnerJobID})
		return
	}
	now := time.Now().UTC()
	payload, err := json.Marshal(map[string]string{"scope": held.OwnerScope, "window_job_id": held.OwnerJobID})
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot build recovery payload"})
		return
	}
	// 队列作业 id 与幂等键都按窗口固定：重复点击只会得到同一个恢复作业。
	// 队列 id 有长度上限（36），窗口作业 id 比它还长，所以按窗口摘要取短 id。
	sum := sha256.Sum256([]byte(held.OwnerJobID))
	queueID := "lrec-" + hex.EncodeToString(sum[:14])
	queueJob, err := config.Store.Enqueue(r.Context(), jobs.EnqueueRequest{
		ID: queueID, Type: libraryRecoverJobType, Payload: payload,
		AvailableAt: now, MaxAttempts: 1, IdempotencyKey: "library.recover:" + held.OwnerJobID,
	}, now)
	if err != nil || queueJob == nil {
		writeJSON(w, http.StatusConflict, map[string]any{"code": "library_recovery_enqueue_failed",
			"error": "恢复作业投递失败（或已有同窗口的恢复作业）", "detail": errString(err)})
		return
	}
	// 上一次恢复失败（比如故障还没修完）不该让这个窗口永久卡死：
	// 运维修好之后可以再点一次，作业会被重新排队；但同一窗口不许并发两份。
	if queueJob.State == jobs.StateFailed || queueJob.State == jobs.StateCancelled {
		retrier, ok := config.Store.(interface {
			RetryLibraryRecovery(ctx context.Context, id, windowJobID string, now time.Time) (bool, error)
		})
		if !ok {
			writeJSON(w, http.StatusConflict, map[string]any{"code": "library_recovery_stuck",
				"error": "上一次恢复失败，且当前存储不支持重新排队"})
			return
		}
		retried, retryErr := retrier.RetryLibraryRecovery(r.Context(), queueJob.ID, held.OwnerJobID, now)
		if retryErr != nil {
			writeJSON(w, http.StatusInternalServerError, map[string]any{"code": "library_recovery_retry_failed",
				"error": "重新排队恢复作业失败", "detail": errString(retryErr)})
			return
		}
		if !retried {
			writeJSON(w, http.StatusConflict, map[string]any{"code": "library_recovery_busy",
				"error": "同一窗口已有恢复作业在跑", "job": queueJob})
			return
		}
		queueJob.State = jobs.StatePending
		queueJob.Attempt = 0
		queueJob.LastError = ""
	}
	writeJSON(w, http.StatusAccepted, map[string]any{"job": queueJob, "window_job_id": held.OwnerJobID,
		"scope": held.OwnerScope, "instance": held.Instance})
}

// activeGrantFor 只查"目标+快照+同一参数摘要"的未过期未撤销授权。
func activeGrantFor(ctx context.Context, config Config, scope, snapshotID string) (governance.LibraryReleaseAuthorization, bool) {
	if snapshotID == "" {
		return governance.LibraryReleaseAuthorization{}, false
	}
	store, ok := config.Store.(interface {
		ActiveLibraryAuthorization(ctx context.Context, scope, snapshotID, paramsDigest string, now time.Time) (governance.LibraryReleaseAuthorization, bool, error)
	})
	if !ok {
		return governance.LibraryReleaseAuthorization{}, false
	}
	digest, err := librarySyncParamsDigest(scope, snapshotID)
	if err != nil {
		return governance.LibraryReleaseAuthorization{}, false
	}
	grant, found, err := store.ActiveLibraryAuthorization(ctx, scope, snapshotID, digest, time.Now().UTC())
	if err != nil || !found {
		return governance.LibraryReleaseAuthorization{}, false
	}
	return grant, true
}

func authorizationViewOf(grant governance.LibraryReleaseAuthorization, found bool) libraryAuthorizationView {
	if !found {
		return libraryAuthorizationView{State: "none", Reason: "没有与目标快照匹配的有效发布授权"}
	}
	expires := grant.ExpiresAt
	return libraryAuthorizationView{State: "active", AuthorizedBy: grant.AuthorizedBy, ExpiresAt: &expires}
}

func scopeFromQuery(r *http.Request) (string, error) {
	scope := strings.TrimSpace(r.URL.Query().Get("scope"))
	if scope == "" {
		scope = "internal"
	}
	if scope != "internal" && scope != "external" {
		return "", errors.New("scope must be internal or external")
	}
	return scope, nil
}

func libraryVersionViewOf(item governance.LibraryVersion) libraryVersionView {
	return libraryVersionView{ID: item.ID, Kind: string(item.Kind), SnapshotID: item.SnapshotID,
		VersionLabel: item.VersionLabel, SourceJobID: item.SourceJobID, Evidence: item.Evidence,
		CreatedBy: item.CreatedBy, CreatedAt: item.CreatedAt, SupersededAt: item.SupersededAt}
}

// librarySyncGate 只依据真实存在的证据判断能不能写生产：闸口、生产端点、
// 生产权威版本、目标快照的预备份。任何一项缺失都给出具体原因，不默认放行。
func errString(err error) string {
	if err == nil {
		return ""
	}
	return err.Error()
}

func librarySyncGate(config Config, production libraryKnownView, prebackup libraryKnownView, target string) libraryGateView {
	return librarySyncGateWithGrant(config, production, prebackup, target, false)
}

// librarySyncGateWithGrant 在原有证据之外再要求一份有效授权：
// 授权绑定了目标、快照、参数与有效期，缺它就不能写生产。
func librarySyncGateWithGrant(config Config, production libraryKnownView, prebackup libraryKnownView, target string, hasGrant bool) libraryGateView {
	gate := libraryGateView{SyncAllowed: false, Reasons: []string{}}
	if !hasGrant {
		gate.Reasons = append(gate.Reasons, "没有与目标快照匹配的有效发布授权")
	}
	if !config.ProductionReleaseRequestsEnabled {
		gate.Reasons = append(gate.Reasons, "生产写入闸口关闭（PRODUCTION_RELEASE_REQUESTS_ENABLED=false）")
	}
	if !config.ProductionBackupRestoreVerified {
		gate.Reasons = append(gate.Reasons, "没有已核验的生产恢复演练证据（PRODUCTION_BACKUP_RESTORE_VERIFIED=false）")
	}
	// 生产端点以"整库目标是否配置"为准：整库同步直接写 PG/ES/对象，
	// 不依赖 WeKnora 的 HTTP 端，所以不能拿它是否配置当门禁。
	if strings.TrimSpace(config.LibraryProductionDatabaseURL) == "" {
		gate.Reasons = append(gate.Reasons, "生产整库目标未配置（LIBRARY_PRODUCTION_DATABASE_URL），无法核验生产当前状态")
	}
	// 首次发布：生产还没有"生效版本"记录，但只要生产目标可读且是空的，
	// 这就是一个合法的"空基线"，不应该被永久挡住。非空但无权威版本仍然阻断。
	if production.State != "known" && !production.EmptyBaseline {
		gate.Reasons = append(gate.Reasons, "生产当前权威版本未知，不能启动写入")
	}
	if target == "" {
		gate.Reasons = append(gate.Reasons, "还没有可同步的测试封存版本")
	}
	// 预备份是作业内第一步生成的：启动前要求它已存在会造成死循环。
	// 这里只在作业已经被判定失败或回滚失败时提示，不作为启动前的硬门禁。
	if prebackup.State == "failed" {
		gate.Reasons = append(gate.Reasons, "上一次预备份失败，先处理后才能重试")
	}
	if config.LibraryCapacityBudgetBytes <= 0 {
		gate.Reasons = append(gate.Reasons, "容量预算未设置（LIBRARY_CAPACITY_BUDGET_BYTES），无法证明装得下")
	}
	gate.SyncAllowed = len(gate.Reasons) == 0
	return gate
}

func libraryOverviewHandler(w http.ResponseWriter, r *http.Request, config Config) {
	scope, err := scopeFromQuery(r)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": err.Error()})
		return
	}
	store, ok := libraryStore(config)
	if !ok {
		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"available": false,
			"reason": "版本登记存储不可用"})
		return
	}
	now := time.Now().UTC()
	overview := libraryOverview{Scope: scope, Jobs: []governance.LibraryJob{}, Now: now,
		CaptureAvailable: strings.TrimSpace(config.LibraryAgentSocket) != "",
		Gate:             libraryGateView{Reasons: []string{}},
		Diff:             libraryDiffView{State: "unknown", Reason: "生产与测试的文档级差异读取未接线", Added: []any{}, Updated: []any{}, Removed: []any{}}}
	if !overview.CaptureAvailable {
		overview.CaptureReason = "主机侧封存 agent 未接线"
	}

	// 测试封存来自归档：它只是测试侧事实。
	snapshots, snapErr := readLibrarySnapshots(r.Context(), config.LibraryArchiveRoot)
	if snapErr != nil {
		_, overview.TestSealedReason = libraryArchiveErrorStatus(snapErr, "归档不可读")
	} else if !snapshots.Available {
		overview.TestSealedReason = snapshots.Reason
	} else {
		for index := range snapshots.Snapshots {
			if snapshots.Snapshots[index].Scope == scope {
				overview.TestSealed = &snapshots.Snapshots[index]
				break
			}
		}
		if overview.TestSealed == nil {
			overview.TestSealedReason = "还没有该目标的测试封存"
		}
	}

	// 生产生效 / 预备份 / 作业来自持久登记。
	versions, err := store.LibraryVersions(r.Context(), scope, 50)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot read library versions"})
		return
	}
	overview.Production = libraryKnownView{State: "unknown", Reason: "还没有生产验证通过的生效版本记录"}
	overview.Prebackup = libraryKnownView{State: "unknown", Reason: "本次目标快照还没有生产预备份"}
	target := ""
	if overview.TestSealed != nil {
		target = overview.TestSealed.SnapshotID
	}
	for index := range versions {
		item := versions[index]
		view := libraryVersionViewOf(item)
		switch item.Kind {
		case governance.LibraryVersionProductionEffective:
			if item.SupersededAt == nil {
				overview.Production = libraryKnownView{State: "known", Version: &view}
			}
		case governance.LibraryVersionProductionPrebackup:
			// 只有与目标快照绑定的预备份才算"这次同步前的备份"。
			if target != "" && item.SnapshotID == target {
				overview.Prebackup = libraryKnownView{State: "known", Version: &view}
			}
		}
	}

	recent, err := store.ListLibraryJobs(r.Context(), scope, 20)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot read library jobs"})
		return
	}
	overview.Jobs = recent
	for index := range recent {
		if recent[index].State == governance.LibraryJobPending || recent[index].State == governance.LibraryJobRunning {
			overview.Job = &recent[index]
			break
		}
	}
	if overview.Job == nil && len(recent) > 0 {
		overview.Job = &recent[0]
	}

	// 差异是真实计算：生产权威版本 + 测试封存都在本地归档时给出逐篇增改撤销，
	// 否则保持 unknown 并说明缺哪一侧，不用空数组冒充"无变化"。
	baseSnapshot := ""
	if overview.Production.State == "known" && overview.Production.Version != nil {
		baseSnapshot = overview.Production.Version.SnapshotID
	}
	// 归档可能很大：差异计算放进看门狗，超时就保持 unknown，别让页面请求挂死。
	diffResult := make(chan struct {
		view libraryDiffView
		ok   bool
	}, 1)
	go func() {
		view, ok := computeLibraryDiff(config.LibraryArchiveRoot, baseSnapshot, target)
		diffResult <- struct {
			view libraryDiffView
			ok   bool
		}{view, ok}
	}()
	var view libraryDiffView
	var diffOK bool
	select {
	case outcome := <-diffResult:
		view, diffOK = outcome.view, outcome.ok
	case <-time.After(8 * time.Second):
		view = libraryDiffView{State: "unknown", Reason: "差异计算超时（归档较大），本次保持不变更结论",
			Added: []any{}, Updated: []any{}, Removed: []any{}, BaseSnapshot: baseSnapshot, TargetSnapshot: target}
		diffOK = false
	}
	if diffOK || view.Reason != "" {
		overview.Diff = view
	}

	grant, hasGrant := activeGrantFor(r.Context(), config, scope, target)
	overview.Authorization = authorizationViewOf(grant, hasGrant)
	overview.Gate = librarySyncGateWithGrant(config, overview.Production, overview.Prebackup, target, hasGrant)
	writeJSON(w, http.StatusOK, overview)
}

func libraryJobsHandler(w http.ResponseWriter, r *http.Request, config Config) {
	scope, err := scopeFromQuery(r)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": err.Error()})
		return
	}
	store, ok := libraryStore(config)
	if !ok {
		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"available": false, "reason": "版本登记存储不可用", "jobs": []any{}})
		return
	}
	items, err := store.ListLibraryJobs(r.Context(), scope, 20)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot read library jobs"})
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"available": true, "jobs": items})
}

func libraryJobDetailHandler(w http.ResponseWriter, r *http.Request, config Config) {
	store, ok := libraryStore(config)
	if !ok {
		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"available": false, "reason": "版本登记存储不可用"})
		return
	}
	id := strings.TrimSpace(r.PathValue("id"))
	if id == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "job id required"})
		return
	}
	job, err := store.LibraryJob(r.Context(), id)
	if err != nil {
		writeJSON(w, http.StatusNotFound, map[string]any{"available": false, "reason": "作业不存在"})
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"available": true, "job": job})
}

// librarySyncEnqueue 是生产同步的唯一入口：闸口未齐时**不建作业**，直接说明缺项。
// 这样按钮永远不会假接通，也不会留下一个永远失败的空作业。
func librarySyncEnqueue(w http.ResponseWriter, r *http.Request, config Config) {
	if r.Method != http.MethodPost {
		writeJSON(w, http.StatusMethodNotAllowed, map[string]string{"error": "method not allowed"})
		return
	}
	store, ok := libraryStore(config)
	if !ok {
		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"code": "library_sync_unavailable", "reasons": []string{"版本登记存储不可用"}})
		return
	}
	var request struct {
		Scope  string `json:"scope"`
		Target string `json:"target_snapshot_id"`
	}
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&request); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid request body"})
		return
	}
	if request.Scope != "internal" && request.Scope != "external" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "scope must be internal or external"})
		return
	}
	overview := libraryOverview{Scope: request.Scope}
	versions, err := store.LibraryVersions(r.Context(), request.Scope, 50)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot read library versions"})
		return
	}
	overview.Production = libraryKnownView{State: "unknown"}
	overview.Prebackup = libraryKnownView{State: "unknown"}
	if empty, probeErr := productionScopeEmpty(r.Context(), config, request.Scope); probeErr == nil && empty {
		overview.Production = libraryKnownView{State: "unknown", EmptyBaseline: true,
			Reason: "生产目标可读且为空：本次是首次发布，写入前仍会生成完整预备份"}
	}
	for index := range versions {
		item := versions[index]
		if item.Kind == governance.LibraryVersionProductionEffective && item.SupersededAt == nil {
			view := libraryVersionViewOf(item)
			overview.Production = libraryKnownView{State: "known", Version: &view}
		}
		if item.Kind == governance.LibraryVersionProductionPrebackup && request.Target != "" && item.SnapshotID == request.Target {
			view := libraryVersionViewOf(item)
			overview.Prebackup = libraryKnownView{State: "known", Version: &view}
		}
	}
	grantFound, hasGrant := activeGrantFor(r.Context(), config, request.Scope, request.Target)
	_ = grantFound
	// 目标实例正在维护（跨对内/对外互斥）：直接拒绝，不等到 worker 里才发现。
	if body, held := instanceMaintenanceGuard(r.Context(), config, request.Scope); held {
		writeJSON(w, http.StatusConflict, body)
		return
	}
	// 目标正在维护（被别的作业持有）：直接拒绝新写入，不等到 worker 里才发现。
	if maintenanceStore, ok := config.Store.(interface {
		LibraryMaintenanceOf(ctx context.Context, scope string) (*postgresstore.LibraryMaintenance, error)
	}); ok {
		if held, err := maintenanceStore.LibraryMaintenanceOf(r.Context(), request.Scope); err == nil && held != nil && held.ReleasedAt == nil {
			writeJSON(w, http.StatusConflict, map[string]any{"code": "library_target_in_maintenance",
				"error":     "目标正在维护中，验证完成前不接受新的写入请求",
				"owner_job": held.OwnerJobID, "state": held.State})
			return
		}
	}
	gate := librarySyncGateWithGrant(config, overview.Production, overview.Prebackup, request.Target, hasGrant)
	if !gate.SyncAllowed {
		writeJSON(w, http.StatusServiceUnavailable, map[string]any{
			"code": "library_sync_blocked", "reasons": gate.Reasons,
			"production": overview.Production, "prebackup": overview.Prebackup,
		})
		return
	}

	// 走到这里说明闸口与证据都齐了才真正建作业；互斥与幂等由数据库索引保证。
	digest, err := governance.LibraryRequestDigest(request.Scope, governance.LibraryJobSync,
		map[string]any{"target_snapshot_id": request.Target})
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot digest request"})
		return
	}
	actor := ""
	if identity, ok := sessionFrom(r.Context()); ok {
		actor = identity.Username
	}
	now := time.Now().UTC()
	jobID := fmt.Sprintf("libsync-%s-%d", request.Scope, now.UnixNano())
	job, reused, err := store.CreateLibraryJob(r.Context(), governance.LibraryJob{
		ID: jobID, Scope: request.Scope, Kind: governance.LibraryJobSync,
		IdempotencyKey: "library.sync:" + request.Scope + ":" + request.Target, RequestDigest: digest,
		TargetSnapshotID: request.Target, Actor: actor,
	}, governance.SyncStages(), now)
	if errors.Is(err, governance.ErrLibraryJobActive) {
		writeJSON(w, http.StatusConflict, map[string]any{"code": "library_sync_active",
			"error": "该目标已有在飞的生产写作业（同步与恢复互斥）"})
		return
	}
	if errors.Is(err, governance.ErrLibraryJobIdempotencyConflict) {
		writeJSON(w, http.StatusConflict, map[string]any{"code": "library_sync_conflict", "error": "同一幂等键对应了不同的请求"})
		return
	}
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot create library sync job"})
		return
	}
	// 上一次同参数请求失败/被取消后，幂等键不能再把新请求塞回那个死作业里：
	// 换一个"重试代次"键重新建作业，旧作业保留为审计记录。
	if reused && (job.State == governance.LibraryJobFailed || job.State == governance.LibraryJobCancelled) {
		job, reused, err = store.CreateLibraryJob(r.Context(), governance.LibraryJob{
			ID: fmt.Sprintf("libsync-%s-%d", request.Scope, now.UnixNano()), Scope: request.Scope,
			Kind:           governance.LibraryJobSync,
			IdempotencyKey: "library.sync:" + request.Scope + ":" + request.Target + ":retry:" + now.Format("20060102T150405.000000000"),
			RequestDigest:  digest, TargetSnapshotID: request.Target, Actor: actor,
		}, governance.SyncStages(), now)
		if err != nil || reused {
			writeJSON(w, http.StatusConflict, map[string]any{"code": "library_sync_retry_conflict",
				"error": "无法为重试创建新作业", "detail": errString(err)})
			return
		}
	}
	if reused {
		writeJSON(w, http.StatusAccepted, map[string]any{"job": job, "reused": true})
		return
	}
	// 业务作业先落库，再投递队列：投递失败就把作业标失败，不留下"看起来在跑"的空作业。
	payload, err := json.Marshal(map[string]string{
		"library_job_id": job.ID, "scope": request.Scope, "target_snapshot_id": request.Target,
	})
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot build sync payload"})
		return
	}
	queueJob, err := config.Store.Enqueue(r.Context(), jobs.EnqueueRequest{
		ID: governance.QueueJobIDFor(job.ID), Type: librarySyncJobType, Payload: payload, AvailableAt: now,
		MaxAttempts: 1, IdempotencyKey: "library.sync.queue:" + job.ID,
	}, now)
	if err != nil || queueJob == nil {
		log.Printf("library sync enqueue failed job=%s: %v", job.ID, err)
		_ = store.CancelLibraryJob(r.Context(), job.ID, "队列投递失败，未开始同步", now)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot enqueue sync job"})
		return
	}
	if attachErr := store.AttachLibraryQueueJob(r.Context(), job.ID, queueJob.ID, now); attachErr != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "cannot attach sync job"})
		return
	}
	writeJSON(w, http.StatusAccepted, map[string]any{"job": job, "reused": false})
}