package daemon

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

	"banger/internal/firecracker"
	"banger/internal/imagepull"
	"banger/internal/model"
	"banger/internal/roothelper"
	"banger/internal/system"
)

// buildKernelArgs assembles the kernel command line for a start.
// Direct-boot images (no initrd) get kernel-level IP config so the
// network is up before init, plus init= pointing at the universal
// first-boot wrapper. Anything else uses the plain variant.
func buildKernelArgs(vm model.VMRecord, image model.Image, bridgeIP, defaultDNS string) string {
	if strings.TrimSpace(image.InitrdPath) == "" {
		return system.BuildBootArgsWithKernelIP(
			vm.Name, vm.Runtime.GuestIP, bridgeIP, defaultDNS,
		) + " init=" + imagepull.FirstBootScriptPath
	}
	return system.BuildBootArgs(vm.Name)
}

// startContext is the mutable state threaded through every start
// step. `vm` and `live` are pointers so steps mutate in place —
// dodges returning redundant copies and keeps step bodies readable.
// Values computed by `startVMLocked` before the driver runs
// (apiSock, dmName, tapName) live here too so each step can read
// them without rederiving.
type startContext struct {
	vm      *model.VMRecord
	image   model.Image
	live    *model.VMHandles
	apiSock string
	dmName  string
	tapName string
	fcPath  string

	// systemOverlayCreated records whether the system_overlay step
	// actually created the file (vs. the file existing from a crashed
	// prior attempt). The undo honours it so a leftover-but-valid
	// overlay isn't deleted under us.
	systemOverlayCreated bool
}

// startStep is one phase in the start-VM pipeline. Phases with no
// rollback obligation leave `undo` nil — the driver simply skips
// them on the rollback path. `createStage` / `createDetail` are
// forwarded to `vmCreateStage` so the async-create RPC caller sees
// progress; they're "" for phases that were never part of the
// user-facing progress stream.
type startStep struct {
	name         string
	attrs        []any
	createStage  string
	createDetail string
	run          func(ctx context.Context, sc *startContext) error
	undo         func(ctx context.Context, sc *startContext) error
}

// runStartSteps walks steps in order, logging each via `op.stage`
// (and `vmCreateStage` when the step opted in). On the first
// run-err, it rolls back the prefix (including the failing step, so
// a step that acquired resources before erroring gets its undo
// fired) and returns the original err joined with any rollback err.
//
// Contract: `undo` must be safe to call even when `run` returned
// an error — check zero-value guards rather than assuming success.
// This is cheaper than a two-phase acquire/commit per step and
// matches how `cleanupPreparedCapabilities` in capabilities.go
// treats partial-success rollback.
func (s *VMService) runStartSteps(ctx context.Context, op *operationLog, sc *startContext, steps []startStep) error {
	done := make([]startStep, 0, len(steps))
	for _, step := range steps {
		if step.createStage != "" {
			vmCreateStage(ctx, step.createStage, step.createDetail)
		}
		op.stage(step.name, step.attrs...)
		if err := step.run(ctx, sc); err != nil {
			done = append(done, step) // include the failing step — see contract above
			if rollbackErr := s.rollbackStartSteps(op, sc, done); rollbackErr != nil {
				err = errors.Join(err, rollbackErr)
			}
			return err
		}
		done = append(done, step)
	}
	return nil
}

// rollbackStartSteps iterates completed steps in reverse, calling
// each non-nil `undo` with a detached context — the original ctx
// may already be cancelled (RPC client disconnect), but cleanup
// still needs to run. Undo errors are joined together; one step's
// failure doesn't short-circuit the rest.
func (s *VMService) rollbackStartSteps(op *operationLog, sc *startContext, done []startStep) error {
	var err error
	for i := len(done) - 1; i >= 0; i-- {
		step := done[i]
		if step.undo == nil {
			continue
		}
		op.stage("rollback_" + step.name)
		if undoErr := step.undo(context.Background(), sc); undoErr != nil {
			err = errors.Join(err, fmt.Errorf("rollback %s: %w", step.name, undoErr))
		}
	}
	return err
}

// buildStartSteps returns the ordered list of phases startVMLocked
// drives. Keeping the list as data (vs. a long linear method body)
// makes the phase inventory diff-readable and lets a test driver
// substitute its own step slice.
//
// Phase names MUST stay 1:1 with the prior inline version — they
// appear in daemon logs, smoke-log greps, and the async-create
// progress stream that clients read.
func (s *VMService) buildStartSteps(op *operationLog, sc *startContext) []startStep {
	return []startStep{
		{
			name:         "preflight",
			createStage:  "preflight",
			createDetail: "checking host prerequisites",
			run: func(ctx context.Context, sc *startContext) error {
				if err := s.validateStartPrereqs(ctx, *sc.vm, sc.image); err != nil {
					return err
				}
				return os.MkdirAll(sc.vm.Runtime.VMDir, 0o755)
			},
		},
		{
			name: "cleanup_runtime",
			run: func(ctx context.Context, sc *startContext) error {
				if err := s.cleanupRuntime(ctx, *sc.vm, true); err != nil {
					return err
				}
				s.clearVMHandles(*sc.vm)
				return nil
			},
		},
		{
			name: "bridge",
			run: func(ctx context.Context, _ *startContext) error {
				return s.net.ensureBridge(ctx)
			},
		},
		{
			name: "socket_dir",
			run: func(_ context.Context, _ *startContext) error {
				return s.net.ensureSocketDir()
			},
		},
		{
			// prepare_sockets is a new op.stage label — the prior
			// inline code ran these `os.RemoveAll` calls before the
			// system_overlay stage without a stage marker. Keeping a
			// distinct name makes the log trace and rollback (if any
			// later step fails) unambiguous.
			name: "prepare_sockets",
			run: func(_ context.Context, sc *startContext) error {
				if err := os.RemoveAll(sc.apiSock); err != nil && !os.IsNotExist(err) {
					return err
				}
				if err := os.RemoveAll(sc.vm.Runtime.VSockPath); err != nil && !os.IsNotExist(err) {
					return err
				}
				return nil
			},
		},
		{
			name:         "system_overlay",
			attrs:        []any{"overlay_path", sc.vm.Runtime.SystemOverlay},
			createStage:  "prepare_rootfs",
			createDetail: "preparing system overlay",
			run: func(ctx context.Context, sc *startContext) error {
				// Record ownership BEFORE the call so a partial-truncate
				// failure still triggers cleanup of the half-created file.
				if !exists(sc.vm.Runtime.SystemOverlay) {
					sc.systemOverlayCreated = true
				}
				return s.ensureSystemOverlay(ctx, sc.vm)
			},
			undo: func(_ context.Context, sc *startContext) error {
				if !sc.systemOverlayCreated {
					return nil
				}
				if err := os.Remove(sc.vm.Runtime.SystemOverlay); err != nil && !os.IsNotExist(err) {
					return err
				}
				return nil
			},
		},
		{
			name:         "dm_snapshot",
			attrs:        []any{"dm_name", sc.dmName},
			createStage:  "prepare_rootfs",
			createDetail: "creating root filesystem snapshot",
			run: func(ctx context.Context, sc *startContext) error {
				snapHandles, err := s.net.createDMSnapshot(ctx, sc.image.RootfsPath, sc.vm.Runtime.SystemOverlay, sc.dmName)
				if err != nil {
					// createDMSnapshot cleans up its own partial state on
					// err; leave sc.live zero so the undo is a no-op.
					return err
				}
				sc.live.BaseLoop = snapHandles.BaseLoop
				sc.live.COWLoop = snapHandles.COWLoop
				sc.live.DMName = snapHandles.DMName
				sc.live.DMDev = snapHandles.DMDev
				s.setVMHandles(sc.vm, *sc.live)
				// Fields that used to land next to the (now-deleted)
				// cleanupOnErr closure. They belong with the DM
				// snapshot because that's the first step producing
				// runtime identity the downstream code reads back.
				sc.vm.Runtime.APISockPath = sc.apiSock
				sc.vm.Runtime.State = model.VMStateRunning
				sc.vm.State = model.VMStateRunning
				sc.vm.Runtime.LastError = ""
				return nil
			},
			undo: func(ctx context.Context, sc *startContext) error {
				if sc.live.DMName == "" && sc.live.BaseLoop == "" && sc.live.COWLoop == "" {
					return nil
				}
				return s.net.cleanupDMSnapshot(ctx, dmSnapshotHandles{
					BaseLoop: sc.live.BaseLoop,
					COWLoop:  sc.live.COWLoop,
					DMName:   sc.live.DMName,
					DMDev:    sc.live.DMDev,
				})
			},
		},
		{
			// See the comment in the prior inline version: stale
			// bitmaps from a reused COW make e2cp/e2rm refuse to
			// touch the snapshot. e2fsck -fy is a no-op on a fresh
			// snapshot. Exit codes 0 + 1 are both "ok" here.
			name: "fsck_snapshot",
			run: func(ctx context.Context, sc *startContext) error {
				return s.privOps().FsckSnapshot(ctx, sc.live.DMDev)
			},
		},
		{
			name:         "patch_root_overlay",
			createStage:  "prepare_rootfs",
			createDetail: "writing guest configuration",
			run: func(ctx context.Context, sc *startContext) error {
				return s.patchRootOverlay(ctx, *sc.vm, sc.image, sc.live.DMDev)
			},
		},
		{
			name:         "prepare_host_features",
			createStage:  "prepare_host_features",
			createDetail: "preparing host-side vm features",
			run: func(ctx context.Context, sc *startContext) error {
				return s.capHooks.prepareHosts(ctx, sc.vm, sc.image)
			},
			// On err, prepareHosts already cleaned up the prefix that
			// succeeded before the failing capability. On success, any
			// LATER step failure triggers this undo, which tears down
			// ALL prepared caps via their Cleanup hooks.
			undo: func(ctx context.Context, sc *startContext) error {
				return s.capHooks.cleanupState(ctx, *sc.vm)
			},
		},
		{
			name: "tap",
			run: func(ctx context.Context, sc *startContext) error {
				tap, err := s.net.acquireTap(ctx, sc.tapName)
				if err != nil {
					return err
				}
				sc.live.TapDevice = tap
				s.setVMHandles(sc.vm, *sc.live)
				return nil
			},
			undo: func(ctx context.Context, sc *startContext) error {
				if sc.live.TapDevice == "" {
					return nil
				}
				return s.net.releaseTap(ctx, sc.live.TapDevice)
			},
		},
		{
			name:  "metrics_file",
			attrs: []any{"metrics_path", sc.vm.Runtime.MetricsPath},
			run: func(_ context.Context, sc *startContext) error {
				return os.WriteFile(sc.vm.Runtime.MetricsPath, nil, 0o644)
			},
			undo: func(_ context.Context, sc *startContext) error {
				if err := os.Remove(sc.vm.Runtime.MetricsPath); err != nil && !os.IsNotExist(err) {
					return err
				}
				return nil
			},
		},
		{
			name: "firecracker_binary",
			run: func(ctx context.Context, sc *startContext) error {
				fcPath, err := s.net.firecrackerBinary(ctx)
				if err != nil {
					return err
				}
				sc.fcPath = fcPath
				return nil
			},
		},
		{
			name:         "firecracker_launch",
			attrs:        []any{"log_path", sc.vm.Runtime.LogPath, "metrics_path", sc.vm.Runtime.MetricsPath},
			createStage:  "boot_firecracker",
			createDetail: "starting firecracker",
			run: func(ctx context.Context, sc *startContext) error {
				kernelArgs := buildKernelArgs(*sc.vm, sc.image, s.config.BridgeIP, s.config.DefaultDNS)
				launchReq := roothelper.FirecrackerLaunchRequest{
					BinaryPath:      sc.fcPath,
					VMID:            sc.vm.ID,
					SocketPath:      sc.apiSock,
					LogPath:         sc.vm.Runtime.LogPath,
					MetricsPath:     sc.vm.Runtime.MetricsPath,
					KernelImagePath: sc.image.KernelPath,
					InitrdPath:      sc.image.InitrdPath,
					KernelArgs:      kernelArgs,
					Drives: []firecracker.DriveConfig{{
						ID:       "rootfs",
						Path:     sc.live.DMDev,
						ReadOnly: false,
						IsRoot:   true,
					}},
					TapDevice: sc.live.TapDevice,
					VSockPath: sc.vm.Runtime.VSockPath,
					VSockCID:  sc.vm.Runtime.VSockCID,
					VCPUCount: sc.vm.Spec.VCPUCount,
					MemoryMiB: sc.vm.Spec.MemoryMiB,
				}
				machineConfig := firecracker.MachineConfig{Drives: launchReq.Drives}
				s.capHooks.contributeMachine(&machineConfig, *sc.vm, sc.image)
				launchReq.Drives = machineConfig.Drives
				pid, err := s.privOps().LaunchFirecracker(ctx, launchReq)
				if err != nil {
					return err
				}
				sc.live.PID = pid
				s.setVMHandles(sc.vm, *sc.live)
				op.debugStage("firecracker_started", "pid", sc.live.PID)
				return nil
			},
			undo: func(ctx context.Context, sc *startContext) error {
				var errs []error
				if sc.live.PID > 0 {
					if err := s.net.killVMProcess(ctx, sc.live.PID); err != nil {
						errs = append(errs, err)
					}
				}
				if err := os.Remove(sc.apiSock); err != nil && !os.IsNotExist(err) {
					errs = append(errs, err)
				}
				if err := os.Remove(sc.vm.Runtime.VSockPath); err != nil && !os.IsNotExist(err) {
					errs = append(errs, err)
				}
				return errors.Join(errs...)
			},
		},
		{
			name:  "socket_access",
			attrs: []any{"api_socket", sc.apiSock},
			run: func(ctx context.Context, sc *startContext) error {
				return s.net.ensureSocketAccess(ctx, sc.apiSock, "firecracker api socket")
			},
		},
		{
			name:  "vsock_access",
			attrs: []any{"vsock_path", sc.vm.Runtime.VSockPath, "vsock_cid", sc.vm.Runtime.VSockCID},
			run: func(ctx context.Context, sc *startContext) error {
				return s.net.ensureSocketAccess(ctx, sc.vm.Runtime.VSockPath, "firecracker vsock socket")
			},
		},
		{
			name:         "wait_vsock_agent",
			createStage:  "wait_vsock_agent",
			createDetail: "waiting for guest vsock agent",
			run: func(ctx context.Context, sc *startContext) error {
				return s.net.waitForGuestVSockAgent(ctx, sc.vm.Runtime.VSockPath, vsockReadyWait)
			},
		},
		{
			name:         "post_start_features",
			createStage:  "wait_guest_ready",
			createDetail: "waiting for guest services",
			run: func(ctx context.Context, sc *startContext) error {
				return s.capHooks.postStart(ctx, *sc.vm, sc.image)
			},
			// Capability Cleanup hooks are designed to be idempotent
			// (check feature-enabled flag, no-op if nothing to undo),
			// so calling cleanupState here is safe whether postStart
			// reached every cap or bailed midway.
			undo: func(ctx context.Context, sc *startContext) error {
				return s.capHooks.cleanupState(ctx, *sc.vm)
			},
		},
		{
			name:         "persist",
			createStage:  "finalize",
			createDetail: "saving vm state",
			run: func(ctx context.Context, sc *startContext) error {
				system.TouchNow(sc.vm)
				return s.store.UpsertVM(ctx, *sc.vm)
			},
		},
	}
}