package backendstatus

import (
	"context"
	"errors"
	"fmt"
	"os"

	"yms-daemon/internal/daemonapi"
	"yms-daemon/internal/deploymentconfig"
	"yms-daemon/internal/systemd"
)

// 诊断项稳定标识，供测试与 reconcile 识别，不参与展示。
const (
	codeNativeActivePortOK    = "native_nginx_active_port"
	codeNativeActiveUnitOK    = "native_active_unit_running"
	codeNativeActiveUnitDown  = "native_active_unit_not_running"
	codeNativeInactiveUnitOK  = "native_inactive_unit_stopped"
	codeNativeInactiveRunning = "native_inactive_unit_running"
	codeNativeSlotJAROK       = "native_slot_jar_link"
	codeNativeSlotJARDrift    = "native_slot_jar_link_drift"
)

// diagnoseNative 对 native 后端做只读诊断。
// native 没有部署单例记录，事实来源是宿主 Nginx 活动端口与 systemd 单元现场状态。
func (d *Diagnoser) diagnoseNative(ctx context.Context) (daemonapi.Diagnosis, error) {
	findings, err := d.nativeGather(ctx)
	if err != nil {
		return daemonapi.Diagnosis{}, err
	}
	return toDiagnosis("backend", deploymentconfig.BackendTypeNative, findings), nil
}

// nativeGather 生成 native 后端的全部诊断项。
func (d *Diagnoser) nativeGather(ctx context.Context) ([]finding, error) {
	before, err := d.gateway.Read()
	if err != nil {
		return nil, fmt.Errorf("read host Nginx configuration: %w", err)
	}
	activePort := before.ActivePort
	findings := make([]finding, 0, 6)
	findings = append(findings, finding{
		level:   daemonapi.DiagnosisLevelOK,
		code:    codeNativeActivePortOK,
		message: fmt.Sprintf("宿主 Nginx 指向后端端口 %d", activePort),
	})

	activeSlot, err := d.config.Backend.SlotForPort(activePort)
	if err != nil {
		return nil, err
	}
	inactiveSlot, err := d.config.Backend.SlotForPort(otherPort(activePort))
	if err != nil {
		return nil, err
	}

	activeUnit, err := d.units.Inspect(ctx, activeSlot.Unit)
	if err != nil {
		return nil, fmt.Errorf("inspect native active unit %s: %w", activeSlot.Unit, err)
	}
	if unitRunning(activeUnit) {
		findings = append(findings, finding{
			level:   daemonapi.DiagnosisLevelOK,
			code:    codeNativeActiveUnitOK,
			message: "活动单元 " + activeSlot.Unit + " 正在运行",
		})
	} else {
		findings = append(findings, finding{
			level:   daemonapi.DiagnosisLevelDrift,
			code:    codeNativeActiveUnitDown,
			message: "活动单元 " + activeSlot.Unit + " 未运行（ActiveState=" + activeUnit.ActiveState + "）",
		})
	}

	inactiveUnit, err := d.units.Inspect(ctx, inactiveSlot.Unit)
	if err != nil {
		return nil, fmt.Errorf("inspect native inactive unit %s: %w", inactiveSlot.Unit, err)
	}
	if unitRunning(inactiveUnit) {
		findings = append(findings, finding{
			level:   daemonapi.DiagnosisLevelDrift,
			code:    codeNativeInactiveRunning,
			message: "非活动单元 " + inactiveSlot.Unit + " 意外运行，两个槽位同时在线",
		})
	} else {
		findings = append(findings, finding{
			level:   daemonapi.DiagnosisLevelOK,
			code:    codeNativeInactiveUnitOK,
			message: "非活动单元 " + inactiveSlot.Unit + " 已停止",
		})
	}

	if ok, detail := jarLinkStatus(activeSlot.JAR); ok {
		findings = append(findings, finding{
			level:   daemonapi.DiagnosisLevelOK,
			code:    codeNativeSlotJAROK,
			message: "活动槽位 JAR 链接有效：" + detail,
		})
	} else {
		findings = append(findings, finding{
			level:   daemonapi.DiagnosisLevelDrift,
			code:    codeNativeSlotJARDrift,
			message: "活动槽位 JAR 链接异常：" + detail,
		})
	}

	return findings, nil
}

// unitRunning 判断 systemd 单元是否处于运行状态。
func unitRunning(unit systemd.Unit) bool {
	return unit.ActiveState != "inactive" && unit.ActiveState != "failed"
}

// jarLinkStatus 检查槽位 JAR 路径是否为指向现存文件的符号链接。
// 返回 ok 与人类可读的详情；JAR 缺失、不是符号链接或目标不存在时返回 ok=false。
func jarLinkStatus(path string) (bool, string) {
	info, err := os.Lstat(path)
	if errors.Is(err, os.ErrNotExist) {
		return false, "路径不存在"
	}
	if err != nil {
		return false, "检查失败：" + err.Error()
	}
	if info.Mode()&os.ModeSymlink == 0 {
		return false, "不是符号链接"
	}
	target, err := os.Readlink(path)
	if err != nil {
		return false, "读取链接目标失败：" + err.Error()
	}
	if _, err := os.Stat(path); err != nil {
		return false, "链接目标不存在：" + target
	}
	return true, "指向 " + target
}