package localapi

import (
	"context"
	"net/http"
	"path"
	"regexp"
	"strings"

	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
	"gitea.dooplex.hu/admin/felhom-agent/internal/storage"
)

// POST /disks/same-disk (v0.157.0) — felhom.eu architecture/16-storage-physical-identity.md §4.
//
// The controller asks whether two of ITS paths sit on the same physical disk; the agent answers from its
// own /sys + udev read, never from the caller's claim (`16` §10). A guest path is mapped only to a place
// the agent itself made:
//   - /mnt/felhom-drives/<name>[/…] → the host mount at exactly /mnt/felhom-drives/<name> (the drive's
//     felhom-data bind, or a network share's mount). A path whose <name> is not mounted there (an absent
//     drive: the bare directory on the root disk) is UNMAPPED — never "the system disk".
//   - /mnt/sys_drive, /var/lib/felhom, /var/lib/docker [/…] → the guest's data volume (mp0, mp=/var/lib/felhom;
//     or a legacy mp at that exact path) → the PVE storage holding it → that storage's identity.
//   - anything else → unmapped.
// Answer: {different, proven, reason, a, b}. Act on `proven` first: different+proven = a counted second
// copy; same_disk+proven = not a second copy; proven=false = unknown (reason vm|network|usb_bridge|
// weak_wwn|no_serial|unmapped). Pinned by samedisk_test.go.

type sameDiskRequest struct {
	VMID int    `json:"vmid,omitempty"`
	A    string `json:"a"`
	B    string `json:"b"`
}

// SamePlace is one side of the answer.
type SamePlace struct {
	Path          string   `json:"path"`
	Mapped        bool     `json:"mapped"`
	Kind          string   `json:"kind,omitempty"`
	PhysicalDisks []string `json:"physical_disks,omitempty"`
	Identity      string   `json:"identity,omitempty"`
	Reason        string   `json:"reason,omitempty"`
}

// SameDiskResponse is the wire answer.
type SameDiskResponse struct {
	Different bool      `json:"different"`
	Proven    bool      `json:"proven"`
	Reason    string    `json:"reason,omitempty"`
	A         SamePlace `json:"a"`
	B         SamePlace `json:"b"`
}

// sysDataPaths are the guest paths that live on the guest's one data volume (golden v3: mp0 at
// /var/lib/felhom, its docker/ and sys_drive/ folders bound in the guest — 07 §7.5.1).
var sysDataPaths = []string{"/var/lib/felhom", "/mnt/sys_drive", "/var/lib/docker"}

func (s *Server) handleSameDisk(w http.ResponseWriter, r *http.Request, vmid int) {
	if s.ident == nil {
		writeErr(w, http.StatusServiceUnavailable, "disk identity not configured on this host")
		return
	}
	var req sameDiskRequest
	if !decodeBody(w, r, &req) {
		return
	}
	if !s.scopedFromBody(w, req.VMID, vmid, r.URL.Path) {
		return
	}
	if !path.IsAbs(req.A) || !path.IsAbs(req.B) {
		writeErr(w, http.StatusBadRequest, "a and b must be absolute guest paths")
		return
	}
	a := s.mapGuestPlace(r.Context(), vmid, req.A)
	b := s.mapGuestPlace(r.Context(), vmid, req.B)
	resp := SameDiskResponse{A: a.view, B: b.view}
	resp.Different, resp.Proven, resp.Reason = storage.Relation(a.id, b.id)
	s.logger.Info("local-api: same-disk", "vmid", vmid, "a", req.A, "b", req.B,
		"different", resp.Different, "proven", resp.Proven, "reason", resp.Reason)
	writeOK(w, resp)
}

type mappedPlace struct {
	view SamePlace
	id   storage.PlaceIdentity
}

func (s *Server) mapGuestPlace(ctx context.Context, vmid int, guestPath string) mappedPlace {
	p := path.Clean(guestPath)
	out := mappedPlace{view: SamePlace{Path: p}}
	set := func(kind string, id storage.PlaceIdentity) mappedPlace {
		if !id.Computed() {
			return out
		}
		out.id = id
		out.view.Mapped, out.view.Kind = true, kind
		out.view.PhysicalDisks, out.view.Identity, out.view.Reason = id.PhysicalDisks, id.Identity, id.Reason
		return out
	}
	if strings.HasPrefix(p, StableParentDir+"/") {
		name := strings.SplitN(strings.TrimPrefix(p, StableParentDir+"/"), "/", 2)[0]
		if id, kind, ok := s.ownMountIdentity(StableParentDir + "/" + name); ok {
			return set(kind, id)
		}
		return out
	}
	for _, root := range sysDataPaths {
		if p != root && !strings.HasPrefix(p, root+"/") {
			continue
		}
		id := s.guestDataVolumeIdentity(ctx, vmid, root)
		return set(storage.PlaceKindSystem, id)
	}
	return out
}

// ownMountIdentity judges a HOST path only when it is ITSELF a mountpoint (an enrolled drive's raw mount
// or its felhom-data bind, a network share). A path that is not its own mount — an absent drive, whose
// directory now sits on the root disk — is not computed, never root's identity (the R-118 trap).
func (s *Server) ownMountIdentity(hostPath string) (storage.PlaceIdentity, string, bool) {
	if s.ident == nil || hostPath == "" {
		return storage.PlaceIdentity{}, "", false
	}
	mounts, err := s.hostReader().Mounts()
	if err != nil {
		return storage.PlaceIdentity{}, "", false
	}
	m, ok := storage.MountFor(mounts, hostPath)
	if !ok || path.Clean(m.MountPoint) != path.Clean(hostPath) {
		return storage.PlaceIdentity{}, "", false
	}
	id := s.ident.HostPath(hostPath)
	if !id.Computed() {
		return id, "", false
	}
	kind := storage.PlaceKindDisk
	switch {
	case id.Reason == storage.ReasonNetwork:
		kind = storage.PlaceKindNetwork
	case strings.HasPrefix(m.Device, "/dev/") && !strings.HasPrefix(m.Device, "/dev/mapper/") && isPartitionPath(m.Device):
		kind = storage.PlaceKindPartition
	}
	return id, kind, true
}

var rePartitionName = regexp.MustCompile(`^(nvme[0-9]+n[0-9]+p[0-9]+|(sd|vd|hd)[a-z]+[0-9]+)$`)

func isPartitionPath(dev string) bool { return rePartitionName.MatchString(path.Base(dev)) }

// guestDataVolumeIdentity finds the guest mountpoint that holds root (mp=/var/lib/felhom on golden v3, or a
// legacy mp at that exact path) and returns the identity of the PVE storage that holds its volume.
func (s *Server) guestDataVolumeIdentity(ctx context.Context, vmid int, root string) storage.PlaceIdentity {
	if s.guests == nil || s.storage == nil {
		return storage.PlaceIdentity{}
	}
	cfg, err := s.guests.GuestConfig(ctx, vmid)
	if err != nil {
		return storage.PlaceIdentity{}
	}
	storeID, fallback := "", ""
	for _, spec := range cfg.MountPoints() {
		st, mp, _ := parseMount(spec)
		if strings.HasPrefix(st, "/") {
			continue // a host bind (mp8, mp9), not a volume
		}
		switch mp {
		case root:
			storeID = st // a legacy mp at exactly this path wins
		case "/var/lib/felhom":
			fallback = st // golden v3: the one data volume
		}
	}
	if storeID == "" {
		storeID = fallback
	}
	if storeID == "" {
		return storage.PlaceIdentity{}
	}
	targets, err := s.storage.Observe(ctx)
	if err != nil {
		return storage.PlaceIdentity{}
	}
	for _, t := range targets {
		if t.Name == storeID {
			return identityOfTarget(t)
		}
	}
	return storage.PlaceIdentity{}
}

func identityOfTarget(t hub.StorageTarget) storage.PlaceIdentity {
	if t.Identity == "" {
		return storage.PlaceIdentity{}
	}
	disks := t.PhysicalDisks
	if disks == nil {
		disks = []string{}
	}
	return storage.PlaceIdentity{PhysicalDisks: disks, Identity: t.Identity, Reason: t.IdentityReason}
}