package daemon

import (
	"context"
	"errors"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"banger/internal/api"
	"banger/internal/firecracker"
	"banger/internal/model"
	"banger/internal/system"
)

func (d *Daemon) StartVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	return d.withVMLockByRef(ctx, idOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		image, err := d.store.GetImageByID(ctx, vm.ImageID)
		if err != nil {
			return model.VMRecord{}, err
		}
		if vm.State == model.VMStateRunning && system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
			if d.logger != nil {
				d.logger.Info("vm already running", vmLogAttrs(vm)...)
			}
			return vm, nil
		}
		return d.startVMLocked(ctx, vm, image)
	})
}

func (d *Daemon) startVMLocked(ctx context.Context, vm model.VMRecord, image model.Image) (_ model.VMRecord, err error) {
	op := d.beginOperation("vm.start", append(vmLogAttrs(vm), imageLogAttrs(image)...)...)
	defer func() {
		if err != nil {
			err = annotateLogPath(err, vm.Runtime.LogPath)
			op.fail(err, vmLogAttrs(vm)...)
			return
		}
		op.done(vmLogAttrs(vm)...)
	}()
	op.stage("preflight")
	vmCreateStage(ctx, "preflight", "checking host prerequisites")
	if err := d.validateStartPrereqs(ctx, vm, image); err != nil {
		return model.VMRecord{}, err
	}
	if err := os.MkdirAll(vm.Runtime.VMDir, 0o755); err != nil {
		return model.VMRecord{}, err
	}
	op.stage("cleanup_runtime")
	if err := d.cleanupRuntime(ctx, vm, true); err != nil {
		return model.VMRecord{}, err
	}
	clearRuntimeHandles(&vm)
	op.stage("bridge")
	if err := d.ensureBridge(ctx); err != nil {
		return model.VMRecord{}, err
	}
	op.stage("socket_dir")
	if err := d.ensureSocketDir(); err != nil {
		return model.VMRecord{}, err
	}

	shortID := system.ShortID(vm.ID)
	apiSock := filepath.Join(d.layout.RuntimeDir, "fc-"+shortID+".sock")
	dmName := "fc-rootfs-" + shortID
	tapName := "tap-fc-" + shortID
	if strings.TrimSpace(vm.Runtime.VSockPath) == "" {
		vm.Runtime.VSockPath = defaultVSockPath(d.layout.RuntimeDir, vm.ID)
	}
	if vm.Runtime.VSockCID == 0 {
		vm.Runtime.VSockCID, err = defaultVSockCID(vm.Runtime.GuestIP)
		if err != nil {
			return model.VMRecord{}, err
		}
	}
	if err := os.RemoveAll(apiSock); err != nil && !os.IsNotExist(err) {
		return model.VMRecord{}, err
	}
	if err := os.RemoveAll(vm.Runtime.VSockPath); err != nil && !os.IsNotExist(err) {
		return model.VMRecord{}, err
	}

	op.stage("system_overlay", "overlay_path", vm.Runtime.SystemOverlay)
	vmCreateStage(ctx, "prepare_rootfs", "preparing system overlay")
	if err := d.ensureSystemOverlay(ctx, &vm); err != nil {
		return model.VMRecord{}, err
	}

	op.stage("dm_snapshot", "dm_name", dmName)
	vmCreateStage(ctx, "prepare_rootfs", "creating root filesystem snapshot")
	handles, err := d.createDMSnapshot(ctx, image.RootfsPath, vm.Runtime.SystemOverlay, dmName)
	if err != nil {
		return model.VMRecord{}, err
	}
	vm.Runtime.BaseLoop = handles.BaseLoop
	vm.Runtime.COWLoop = handles.COWLoop
	vm.Runtime.DMName = handles.DMName
	vm.Runtime.DMDev = handles.DMDev
	vm.Runtime.APISockPath = apiSock
	vm.Runtime.State = model.VMStateRunning
	vm.State = model.VMStateRunning
	vm.Runtime.LastError = ""

	cleanupOnErr := func(err error) (model.VMRecord, error) {
		vm.State = model.VMStateError
		vm.Runtime.State = model.VMStateError
		vm.Runtime.LastError = err.Error()
		op.stage("cleanup_after_failure", "error", err.Error())
		if cleanupErr := d.cleanupRuntime(context.Background(), vm, true); cleanupErr != nil {
			err = errors.Join(err, cleanupErr)
		}
		clearRuntimeHandles(&vm)
		_ = d.store.UpsertVM(context.Background(), vm)
		return model.VMRecord{}, err
	}

	op.stage("patch_root_overlay")
	vmCreateStage(ctx, "prepare_rootfs", "writing guest configuration")
	if err := d.patchRootOverlay(ctx, vm, image); err != nil {
		return cleanupOnErr(err)
	}
	op.stage("prepare_host_features")
	vmCreateStage(ctx, "prepare_host_features", "preparing host-side vm features")
	if err := d.prepareCapabilityHosts(ctx, &vm, image); err != nil {
		return cleanupOnErr(err)
	}
	op.stage("tap")
	tap, err := d.acquireTap(ctx, tapName)
	if err != nil {
		return cleanupOnErr(err)
	}
	vm.Runtime.TapDevice = tap
	op.stage("metrics_file", "metrics_path", vm.Runtime.MetricsPath)
	if err := os.WriteFile(vm.Runtime.MetricsPath, nil, 0o644); err != nil {
		return cleanupOnErr(err)
	}

	op.stage("firecracker_binary")
	fcPath, err := d.firecrackerBinary()
	if err != nil {
		return cleanupOnErr(err)
	}
	op.stage("firecracker_launch", "log_path", vm.Runtime.LogPath, "metrics_path", vm.Runtime.MetricsPath)
	vmCreateStage(ctx, "boot_firecracker", "starting firecracker")
	machineConfig := firecracker.MachineConfig{
		BinaryPath:      fcPath,
		VMID:            vm.ID,
		SocketPath:      apiSock,
		LogPath:         vm.Runtime.LogPath,
		MetricsPath:     vm.Runtime.MetricsPath,
		KernelImagePath: image.KernelPath,
		InitrdPath:      image.InitrdPath,
		KernelArgs:      system.BuildBootArgs(vm.Name),
		Drives: []firecracker.DriveConfig{{
			ID:       "rootfs",
			Path:     vm.Runtime.DMDev,
			ReadOnly: false,
			IsRoot:   true,
		}},
		TapDevice: tap,
		VSockPath: vm.Runtime.VSockPath,
		VSockCID:  vm.Runtime.VSockCID,
		VCPUCount: vm.Spec.VCPUCount,
		MemoryMiB: vm.Spec.MemoryMiB,
		Logger:    d.logger,
	}
	d.contributeMachineConfig(&machineConfig, vm, image)
	machine, err := firecracker.NewMachine(ctx, machineConfig)
	if err != nil {
		return cleanupOnErr(err)
	}
	if err := machine.Start(ctx); err != nil {
		// Use a fresh context: the request ctx may already be cancelled (client
		// disconnect), but we still need the PID so cleanupRuntime can kill the
		// Firecracker process that was spawned before the failure.
		vm.Runtime.PID = d.resolveFirecrackerPID(context.Background(), machine, apiSock)
		return cleanupOnErr(err)
	}
	vm.Runtime.PID = d.resolveFirecrackerPID(context.Background(), machine, apiSock)
	op.debugStage("firecracker_started", "pid", vm.Runtime.PID)
	op.stage("socket_access", "api_socket", apiSock)
	if err := d.ensureSocketAccess(ctx, apiSock, "firecracker api socket"); err != nil {
		return cleanupOnErr(err)
	}
	op.stage("vsock_access", "vsock_path", vm.Runtime.VSockPath, "vsock_cid", vm.Runtime.VSockCID)
	if err := d.ensureSocketAccess(ctx, vm.Runtime.VSockPath, "firecracker vsock socket"); err != nil {
		return cleanupOnErr(err)
	}
	vmCreateStage(ctx, "wait_vsock_agent", "waiting for guest vsock agent")
	if err := waitForGuestVSockAgent(ctx, d.logger, vm.Runtime.VSockPath, vsockReadyWait); err != nil {
		return cleanupOnErr(err)
	}
	op.stage("post_start_features")
	vmCreateStage(ctx, "wait_guest_ready", "waiting for guest services")
	if err := d.postStartCapabilities(ctx, vm, image); err != nil {
		return cleanupOnErr(err)
	}
	system.TouchNow(&vm)
	op.stage("persist")
	vmCreateStage(ctx, "finalize", "saving vm state")
	if err := d.store.UpsertVM(ctx, vm); err != nil {
		return cleanupOnErr(err)
	}
	return vm, nil
}

func (d *Daemon) StopVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	return d.withVMLockByRef(ctx, idOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		return d.stopVMLocked(ctx, vm)
	})
}

func (d *Daemon) stopVMLocked(ctx context.Context, current model.VMRecord) (vm model.VMRecord, err error) {
	vm = current
	op := d.beginOperation("vm.stop", "vm_ref", vm.ID)
	defer func() {
		if err != nil {
			op.fail(err, vmLogAttrs(vm)...)
			return
		}
		op.done(vmLogAttrs(vm)...)
	}()
	if vm.State != model.VMStateRunning || !system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
		op.stage("cleanup_stale_runtime")
		if err := d.cleanupRuntime(ctx, vm, true); err != nil {
			return model.VMRecord{}, err
		}
		vm.State = model.VMStateStopped
		vm.Runtime.State = model.VMStateStopped
		clearRuntimeHandles(&vm)
		if err := d.store.UpsertVM(ctx, vm); err != nil {
			return model.VMRecord{}, err
		}
		return vm, nil
	}
	op.stage("graceful_shutdown")
	if err := d.sendCtrlAltDel(ctx, vm); err != nil {
		return model.VMRecord{}, err
	}
	op.stage("wait_for_exit", "pid", vm.Runtime.PID)
	if err := d.waitForExit(ctx, vm.Runtime.PID, vm.Runtime.APISockPath, gracefulShutdownWait); err != nil {
		if !errors.Is(err, errWaitForExitTimeout) {
			return model.VMRecord{}, err
		}
		op.stage("graceful_shutdown_timeout", "pid", vm.Runtime.PID)
	}
	op.stage("cleanup_runtime")
	if err := d.cleanupRuntime(ctx, vm, true); err != nil {
		return model.VMRecord{}, err
	}
	vm.State = model.VMStateStopped
	vm.Runtime.State = model.VMStateStopped
	clearRuntimeHandles(&vm)
	system.TouchNow(&vm)
	if err := d.store.UpsertVM(ctx, vm); err != nil {
		return model.VMRecord{}, err
	}
	return vm, nil
}

func (d *Daemon) KillVM(ctx context.Context, params api.VMKillParams) (model.VMRecord, error) {
	return d.withVMLockByRef(ctx, params.IDOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		return d.killVMLocked(ctx, vm, params.Signal)
	})
}

func (d *Daemon) killVMLocked(ctx context.Context, current model.VMRecord, signalValue string) (vm model.VMRecord, err error) {
	vm = current
	op := d.beginOperation("vm.kill", "vm_ref", vm.ID, "signal", signalValue)
	defer func() {
		if err != nil {
			op.fail(err, vmLogAttrs(vm)...)
			return
		}
		op.done(vmLogAttrs(vm)...)
	}()
	if vm.State != model.VMStateRunning || !system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
		op.stage("cleanup_stale_runtime")
		if err := d.cleanupRuntime(ctx, vm, true); err != nil {
			return model.VMRecord{}, err
		}
		vm.State = model.VMStateStopped
		vm.Runtime.State = model.VMStateStopped
		clearRuntimeHandles(&vm)
		if err := d.store.UpsertVM(ctx, vm); err != nil {
			return model.VMRecord{}, err
		}
		return vm, nil
	}

	signal := strings.TrimSpace(signalValue)
	if signal == "" {
		signal = "TERM"
	}
	op.stage("send_signal", "pid", vm.Runtime.PID, "signal", signal)
	if _, err := d.runner.RunSudo(ctx, "kill", "-"+signal, strconv.Itoa(vm.Runtime.PID)); err != nil {
		return model.VMRecord{}, err
	}
	op.stage("wait_for_exit", "pid", vm.Runtime.PID)
	if err := d.waitForExit(ctx, vm.Runtime.PID, vm.Runtime.APISockPath, 30*time.Second); err != nil {
		if !errors.Is(err, errWaitForExitTimeout) {
			return model.VMRecord{}, err
		}
		op.stage("signal_timeout", "pid", vm.Runtime.PID, "signal", signal)
	}
	op.stage("cleanup_runtime")
	if err := d.cleanupRuntime(ctx, vm, true); err != nil {
		return model.VMRecord{}, err
	}
	vm.State = model.VMStateStopped
	vm.Runtime.State = model.VMStateStopped
	clearRuntimeHandles(&vm)
	system.TouchNow(&vm)
	if err := d.store.UpsertVM(ctx, vm); err != nil {
		return model.VMRecord{}, err
	}
	return vm, nil
}

func (d *Daemon) RestartVM(ctx context.Context, idOrName string) (vm model.VMRecord, err error) {
	op := d.beginOperation("vm.restart", "vm_ref", idOrName)
	defer func() {
		if err != nil {
			op.fail(err, vmLogAttrs(vm)...)
			return
		}
		op.done(vmLogAttrs(vm)...)
	}()
	resolved, err := d.FindVM(ctx, idOrName)
	if err != nil {
		return model.VMRecord{}, err
	}
	return d.withVMLockByID(ctx, resolved.ID, func(vm model.VMRecord) (model.VMRecord, error) {
		op.stage("stop")
		vm, err = d.stopVMLocked(ctx, vm)
		if err != nil {
			return model.VMRecord{}, err
		}
		image, err := d.store.GetImageByID(ctx, vm.ImageID)
		if err != nil {
			return model.VMRecord{}, err
		}
		op.stage("start", vmLogAttrs(vm)...)
		return d.startVMLocked(ctx, vm, image)
	})
}

func (d *Daemon) DeleteVM(ctx context.Context, idOrName string) (model.VMRecord, error) {
	return d.withVMLockByRef(ctx, idOrName, func(vm model.VMRecord) (model.VMRecord, error) {
		return d.deleteVMLocked(ctx, vm)
	})
}

func (d *Daemon) deleteVMLocked(ctx context.Context, current model.VMRecord) (vm model.VMRecord, err error) {
	vm = current
	op := d.beginOperation("vm.delete", "vm_ref", vm.ID)
	defer func() {
		if err != nil {
			op.fail(err, vmLogAttrs(vm)...)
			return
		}
		op.done(vmLogAttrs(vm)...)
	}()
	if vm.State == model.VMStateRunning && system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
		op.stage("kill_running_vm", "pid", vm.Runtime.PID)
		_ = d.killVMProcess(ctx, vm.Runtime.PID)
	}
	op.stage("cleanup_runtime")
	if err := d.cleanupRuntime(ctx, vm, false); err != nil {
		return model.VMRecord{}, err
	}
	op.stage("delete_store_record")
	if err := d.store.DeleteVM(ctx, vm.ID); err != nil {
		return model.VMRecord{}, err
	}
	if vm.Runtime.VMDir != "" {
		op.stage("delete_vm_dir", "vm_dir", vm.Runtime.VMDir)
		if err := os.RemoveAll(vm.Runtime.VMDir); err != nil {
			return model.VMRecord{}, err
		}
	}
	return vm, nil
}