package server

import (
	"context"
	"database/sql"
	"encoding/json"
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/jmoiron/sqlx"
	"vdi-cloud/platform/internal/model"
	"vdi-cloud/platform/internal/store"
	"vdi-cloud/platform/pkg/proxmox"
)

// This optional, single-host group is provisioned by the administrator. Device
// requests may select a bound desktop; they cannot choose VMIDs or PCI devices.
const exclusiveGPULock int64 = 7651092039

type gpuPrepareState struct {
	Phase    string `json:"phase"`
	Node     string `json:"node"`
	Members  []int  `json:"members"`
	Terminal string `json:"terminal"`
	VMID     int    `json:"vmid,omitempty"`
	UPID     string `json:"upid,omitempty"`
}

func (s *Server) exclusiveGPU(d model.Desktop) bool {
	if d.Provider != "proxmox" || d.Node != s.Config.ExclusiveGPUNode {
		return false
	}
	for _, id := range s.Config.ExclusiveGPUVMIDs {
		if d.VMID == id {
			return true
		}
	}
	return false
}

// Maintenance submissions take the same group lock as terminal preparations.
// Call inside their existing transaction; the durable reservation also covers
// the interval between enqueueing a preparation and claiming it in the worker.
func (s *Server) exclusiveGPUMaintenance(ctx context.Context, db sqlx.ExtContext, d model.Desktop) error {
	if !s.exclusiveGPU(d) {
		return nil
	}
	locked, err := tryGPULock(ctx, db)
	if err != nil {
		return err
	}
	var busy bool
	if locked {
		err = sqlx.GetContext(ctx, db, &busy, `SELECT EXISTS(SELECT 1 FROM tasks WHERE kind='gpu-prepare' AND status IN ('queued','running','timeout'))`)
	}
	if err != nil {
		return err
	}
	if !locked || busy {
		return errors.New("显卡正在切换或结果未确认，请先核对切换任务")
	}
	return nil
}

func (s *Server) gpuMembers(ctx context.Context, db sqlx.ExtContext) ([]model.Desktop, error) {
	var members []model.Desktop
	err := sqlx.SelectContext(ctx, db, &members, `SELECT * FROM desktops WHERE provider='proxmox' AND node=$1 AND vmid=ANY($2) ORDER BY vmid`, s.Config.ExclusiveGPUNode, s.Config.ExclusiveGPUVMIDs)
	if err == nil && len(members) != len(s.Config.ExclusiveGPUVMIDs) {
		err = errors.New("exclusive GPU group is incomplete")
	}
	return members, err
}

func tryGPULock(ctx context.Context, db sqlx.ExtContext) (bool, error) {
	var locked bool
	err := sqlx.GetContext(ctx, db, &locked, "SELECT pg_try_advisory_xact_lock($1)", exclusiveGPULock)
	return locked, err
}

func (s *Server) gpuAllowsConnection(c *gin.Context, d model.Desktop) bool {
	if !s.exclusiveGPU(d) {
		return true
	}
	locked, err := tryGPULock(c.Request.Context(), deviceTx(c))
	var busy bool
	if err == nil && locked {
		err = deviceTx(c).GetContext(c.Request.Context(), &busy, `SELECT EXISTS(SELECT 1 FROM tasks WHERE kind='gpu-prepare' AND status IN ('queued','running','timeout'))`)
	}
	if err != nil {
		s.dbError(c, err)
		return false
	}
	if !locked || busy {
		s.fail(c, 409, "gpu_switch_busy", "显卡正在切换或上次切换尚未确认，请稍后重试或联系管理员")
		return false
	}
	pve := s.currentPVE()
	if pve == nil {
		s.fail(c, 503, "pve_unavailable", "计算平台不可用")
		return false
	}
	for _, id := range s.Config.ExclusiveGPUVMIDs {
		power, e := pve.Power(c.Request.Context(), d.Node, id)
		expected := "stopped"
		if id == d.VMID {
			expected = "running"
		}
		if e != nil || power != expected {
			s.fail(c, 409, "gpu_owner_not_ready", "桌面电源或显卡归属尚未就绪，请先准备桌面")
			return false
		}
	}
	return true
}

func gpuGroupBusy(ctx context.Context, db sqlx.ExtContext, members []model.Desktop, taskID string) (bool, error) {
	ids := make([]string, 0, len(members))
	for _, d := range members {
		ids = append(ids, d.ID)
	}
	var busy bool
	err := sqlx.GetContext(ctx, db, &busy, `SELECT EXISTS(SELECT 1 FROM terminals WHERE session_desktop_id=ANY($1) AND last_seen>now()-interval '90 seconds') OR EXISTS(SELECT 1 FROM tasks WHERE target_id=ANY($1) AND id!=$2 AND kind!='terminal' AND status IN ('queued','running','timeout'))`, ids, taskID)
	return busy, err
}

func (s *Server) prepareGPUDesktop(c *gin.Context) {
	var in struct {
		DesktopID string `json:"desktopId" binding:"required,max=100"`
	}
	if !s.decode(c, &in) {
		return
	}
	tx := deviceTx(c)
	ctx := c.Request.Context()
	terminal := c.GetString("terminalId")
	var d model.Desktop
	err := tx.GetContext(ctx, &d, `SELECT d.* FROM desktops d JOIN bindings b ON b.desktop_id=d.id JOIN users u ON u.id=b.user_id JOIN terminals t ON t.id=u.terminal_id WHERE d.id=$1 AND t.id=$2 AND u.enabled AND t.enabled`, in.DesktopID, terminal)
	if err == sql.ErrNoRows {
		s.fail(c, 403, "desktop_forbidden", "该终端没有桌面使用权限")
		return
	}
	if err != nil {
		s.dbError(c, err)
		return
	}
	if !s.exclusiveGPU(d) || d.SetupRequired || d.Endpoint == "" {
		s.fail(c, 409, "desktop_not_preparable", "该桌面未启用显卡切换或连接配置尚未完成")
		return
	}
	locked, err := tryGPULock(ctx, tx)
	if err != nil {
		s.dbError(c, err)
		return
	}
	if !locked {
		s.fail(c, 409, "gpu_switch_busy", "显卡正在切换，请稍后重试")
		return
	}
	var previous model.Task
	err = tx.GetContext(ctx, &previous, `SELECT * FROM tasks WHERE kind='gpu-prepare' AND status IN ('queued','running','timeout') ORDER BY created_at DESC LIMIT 1`)
	if err == nil {
		if previous.Actor == "device:"+terminal && previous.TargetID == d.ID && previous.Status != "timeout" {
			s.deviceJSON(c, 202, gin.H{"taskId": previous.ID, "status": previous.Status, "message": previous.Message})
			return
		}
		s.fail(c, 409, "gpu_switch_busy", "已有显卡切换任务或未确认结果，请稍后重试或联系管理员")
		return
	}
	if err != sql.ErrNoRows {
		s.dbError(c, err)
		return
	}
	members, err := s.gpuMembers(ctx, tx)
	if err != nil {
		s.dbError(c, err)
		return
	}
	for _, member := range members {
		if !s.hardwareAllowsConnection(c, member.ID) {
			return
		}
	}
	busy, err := gpuGroupBusy(ctx, tx, members, "")
	if err != nil {
		s.dbError(c, err)
		return
	}
	if busy {
		s.fail(c, 409, "gpu_group_in_use", "请先退出正在使用的云桌面；其他终端使用中或管理任务未结束时无法切换")
		return
	}
	state := gpuPrepareState{Phase: "queued", Node: d.Node, Members: s.Config.ExclusiveGPUVMIDs, Terminal: terminal}
	encoded, _ := json.Marshal(state)
	id := store.ID("task_")
	_, err = tx.ExecContext(ctx, `INSERT INTO tasks(id,kind,action,target_id,target_name,actor,status,message,provider_ref,idempotency_key) VALUES($1,'gpu-prepare','prepare-desktop',$2,$3,$4,'queued','正在准备桌面，等待显卡切换',$5,$1)`, id, d.ID, d.Name, "device:"+terminal, string(encoded))
	if err != nil {
		s.dbError(c, err)
		return
	}
	s.deviceJSON(c, 202, gin.H{"taskId": id, "status": "queued", "message": "正在准备桌面，首次启动可能需要两分钟"})
}

func (s *Server) gpuPrepareStatus(c *gin.Context) {
	var task model.Task
	err := deviceTx(c).GetContext(c.Request.Context(), &task, `SELECT * FROM tasks WHERE id=$1 AND kind='gpu-prepare' AND actor=$2`, c.Param("id"), "device:"+c.GetString("terminalId"))
	if err == sql.ErrNoRows {
		s.fail(c, 404, "task_not_found", "切换任务不存在")
		return
	}
	if err != nil {
		s.dbError(c, err)
		return
	}
	s.deviceJSON(c, 200, gin.H{"taskId": task.ID, "status": task.Status, "message": task.Message})
}

func (s *Server) saveGPUStage(ctx context.Context, t model.Task, state gpuPrepareState, message string) error {
	data, _ := json.Marshal(state)
	result, err := s.DB.ExecContext(ctx, `UPDATE tasks SET provider_ref=$1,message=$2,updated_at=now() WHERE id=$3 AND status='running'`, string(data), message, t.ID)
	if err == nil {
		n, _ := result.RowsAffected()
		if n != 1 {
			err = errors.New("GPU task reservation lost")
		}
	}
	return err
}

func sunshineReady(ctx context.Context, endpoint string) bool {
	host := endpoint
	if parsed, _, err := net.SplitHostPort(endpoint); err == nil {
		host = parsed
	}
	// Platform endpoints are hostnames/IPs, never arbitrary URLs or paths.
	if strings.ContainsAny(host, "/\\@?#") || host == "" {
		return false
	}
	req, err := http.NewRequestWithContext(ctx, "GET", "http://"+net.JoinHostPort(host, "47989")+"/serverinfo", nil)
	if err != nil {
		return false
	}
	client := http.Client{Timeout: 2 * time.Second, Transport: &http.Transport{Proxy: nil}, CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }}
	defer client.CloseIdleConnections()
	response, err := client.Do(req)
	if err != nil {
		return false
	}
	defer response.Body.Close()
	var info struct {
		XMLName  xml.Name `xml:"root"`
		Status   string   `xml:"status_code,attr"`
		Hostname string   `xml:"hostname"`
	}
	return response.StatusCode == 200 && xml.NewDecoder(io.LimitReader(response.Body, 65536)).Decode(&info) == nil && info.Status == "200" && info.Hostname != ""
}

func (s *Server) executeGPUPrepare(parent context.Context, t model.Task) {
	ctx, cancel := context.WithTimeout(parent, 180*time.Second)
	defer cancel()
	state := gpuPrepareState{}
	err := json.Unmarshal([]byte(t.ProviderRef), &state)
	uncertain := false
	if err == nil && state.Phase != "queued" && state.Phase != "" {
		uncertain = true
	}
	if err == nil && (state.Phase != "queued" || state.Node != s.Config.ExclusiveGPUNode || fmt.Sprint(state.Members) != fmt.Sprint(s.Config.ExclusiveGPUVMIDs)) {
		err = errors.New("GPU group changed or task already submitted")
	}
	var tx *sqlx.Tx
	if err == nil {
		tx, err = s.DB.BeginTxx(ctx, nil)
	}
	if tx != nil {
		defer tx.Rollback()
	}
	// Hold this lock on a dedicated transaction throughout the switch. Tickets
	// fail promptly instead of waiting behind a VM boot; no root credential leaves
	// the platform. An API restart never automatically replays an uncertain POST.
	if err == nil {
		var locked bool
		locked, err = tryGPULock(ctx, tx)
		if err == nil && !locked {
			err = errors.New("GPU group locked")
		}
	}
	var members []model.Desktop
	if err == nil {
		members, err = s.gpuMembers(ctx, tx)
	}
	var target model.Desktop
	if err == nil {
		for _, d := range members {
			if d.ID == t.TargetID {
				target = d
			}
		}
		var allowed bool
		err = tx.GetContext(ctx, &allowed, `SELECT EXISTS(SELECT 1 FROM bindings b JOIN users u ON u.id=b.user_id JOIN terminals term ON term.id=u.terminal_id WHERE b.desktop_id=$1 AND u.terminal_id=$2 AND u.enabled AND term.enabled)`, t.TargetID, state.Terminal)
		if err == nil && (!allowed || target.ID == "" || target.SetupRequired || target.Endpoint == "") {
			err = errors.New("desktop authorization/configuration changed")
		}
	}
	if err == nil {
		var busy bool
		busy, err = gpuGroupBusy(ctx, tx, members, t.ID)
		if err == nil && busy {
			err = errors.New("GPU group is in use")
		}
	}
	if err == nil {
		err = s.RefreshCompute(ctx)
	}
	pve := s.currentPVE()
	if err == nil && pve == nil {
		err = errors.New("PVE unavailable")
	}
	action := func(d model.Desktop, operation string) error {
		state.Phase = operation + "-submitting"
		state.VMID = d.VMID
		state.UPID = ""
		if err := s.saveGPUStage(ctx, t, state, "正在"+map[string]string{"start": "启动所选桌面", "shutdown": "正常关闭上一台桌面"}[operation]); err != nil {
			return err
		}
		uncertain = true
		upid, err := pve.Action(ctx, d.Node, d.VMID, operation)
		if err != nil {
			var rejected *proxmox.HTTPError
			if errors.As(err, &rejected) && rejected.Status >= 400 && rejected.Status < 500 {
				uncertain = false
			}
			return err
		}
		state.Phase = operation + "-waiting"
		state.UPID = upid
		if err = s.saveGPUStage(ctx, t, state, "正在等待虚拟机电源操作完成"); err != nil {
			return err
		}
		if err = pve.Wait(ctx, d.Node, upid, time.Second); err != nil {
			return err
		}
		power, err := pve.Power(ctx, d.Node, d.VMID)
		expected := "running"
		if operation == "shutdown" {
			expected = "stopped"
		}
		if err == nil && power != expected {
			err = errors.New("VM power transition not confirmed")
		}
		if err == nil {
			uncertain = false
		}
		return err
	}
	if err == nil {
		for _, d := range members {
			if d.ID == target.ID {
				continue
			}
			power, e := pve.Power(ctx, d.Node, d.VMID)
			if e != nil {
				err = e
				break
			}
			if power == "running" {
				err = action(d, "shutdown")
			} else if power != "stopped" {
				err = errors.New("unexpected VM power state")
			}
			if err != nil {
				break
			}
		}
	}
	if err == nil {
		power, e := pve.Power(ctx, target.Node, target.VMID)
		err = e
		if err == nil && power == "stopped" {
			err = action(target, "start")
		} else if err == nil && power != "running" {
			err = errors.New("unexpected target state")
		}
	}
	if err == nil {
		state.Phase = "service-waiting"
		err = s.saveGPUStage(ctx, t, state, "桌面已开机，正在等待连接服务")
		for err == nil && !sunshineReady(ctx, target.Endpoint) {
			select {
			case <-ctx.Done():
				err = ctx.Err()
			case <-time.After(time.Second):
			}
		}
	}
	if err == nil {
		// Recheck all owners immediately before releasing the reservation.
		for _, d := range members {
			power, e := pve.Power(ctx, d.Node, d.VMID)
			expected := "stopped"
			if d.ID == target.ID {
				expected = "running"
			}
			if e != nil || power != expected {
				err = errors.New("final GPU ownership check failed")
				break
			}
			if _, e = s.DB.ExecContext(ctx, `UPDATE desktops SET power_state=$1,service_state='unknown',updated_at=now() WHERE id=$2`, power, d.ID); e != nil {
				err = e
				break
			}
		}
	}
	status, message := "success", "桌面已启动，连接服务已响应"
	if err != nil {
		log.Printf("GPU prepare task=%s phase=%s error=%v", t.ID, state.Phase, err)
		status = "failed"
		message = "桌面准备失败，请检查桌面授权、占用状态及 PVE"
		if uncertain {
			status = "timeout"
			message = "电源操作或服务状态尚未确认，已阻止再次切换；请管理员核对 PVE 原任务"
		}
	}
	finalCtx, finish := context.WithTimeout(context.Background(), 5*time.Second)
	defer finish()
	if err == nil {
		state.Phase = "completed"
		_ = s.saveGPUStage(finalCtx, t, state, message)
	}
	_ = s.complete(finalCtx, t, status, message)
}

// Reconcile only a known original PVE task. An unknown submission requires
// manual operator investigation; this endpoint never resubmits a power action.
func (s *Server) reconcileGPUPrepare(c *gin.Context) {
	var task model.Task
	if err := s.DB.GetContext(c.Request.Context(), &task, `SELECT * FROM tasks WHERE id=$1 AND kind='gpu-prepare' AND status='timeout'`, c.Param("id")); err != nil {
		s.fail(c, 409, "not_uncertain", "该任务无需核对或不存在")
		return
	}
	var state gpuPrepareState
	if json.Unmarshal([]byte(task.ProviderRef), &state) != nil || state.UPID == "" {
		s.fail(c, 409, "unknown_submission", "未记录原 PVE 任务编号，需要在 PVE 手工核对，不能自动重发")
		return
	}
	tx, err := s.DB.BeginTxx(c.Request.Context(), nil)
	if err != nil {
		s.dbError(c, err)
		return
	}
	defer tx.Rollback()
	locked, err := tryGPULock(c.Request.Context(), tx)
	if err != nil || !locked {
		s.fail(c, 409, "gpu_switch_busy", "显卡正在切换")
		return
	}
	pve := s.currentPVE()
	if pve == nil {
		s.fail(c, 503, "pve_unavailable", "计算平台不可用")
		return
	}
	original, err := pve.Task(c.Request.Context(), state.Node, state.UPID)
	if err != nil || original.Status != "stopped" {
		s.fail(c, 409, "pve_task_pending", "原 PVE 任务未结束或无法核对")
		return
	}
	for _, id := range state.Members {
		power, e := pve.Power(c.Request.Context(), state.Node, id)
		if e != nil || (power != "running" && power != "stopped") {
			s.fail(c, 409, "power_unknown", "虚拟机实际电源状态未确认")
			return
		}
	}
	_, err = tx.ExecContext(c.Request.Context(), `UPDATE tasks SET status='failed',message='管理员已核对原 PVE 任务及实际电源状态，可重新准备桌面',updated_at=now() WHERE id=$1 AND status='timeout'`, task.ID)
	if err == nil {
		_, err = tx.ExecContext(c.Request.Context(), `INSERT INTO audit_logs VALUES($1,$2,'reconcile-gpu-switch',$3,'success',$4,now())`, store.ID("audit_"), c.MustGet("admin").(model.Administrator).Username, task.TargetName, task.ID)
	}
	if err == nil {
		err = tx.Commit()
	}
	if err != nil {
		s.dbError(c, err)
		return
	}
	c.JSON(200, gin.H{"reconciled": true, "vmid": strconv.Itoa(state.VMID)})
}