package reconcile

import (
	"context"
	"encoding/json"
	"sync"

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

// RunState is a guest's desired/actual power state. The empty value means
// "unmanaged" on the desired side (the reconciler leaves run-state alone).
type RunState string

const (
	// RunUnspecified (the zero value) — on a DesiredGuest it means run-state is not
	// managed; the reconciler never starts/stops the guest for run-state reasons.
	RunUnspecified RunState = ""
	// RunRunning maps to proxmox status "running".
	RunRunning RunState = "running"
	// RunStopped maps to proxmox status "stopped".
	RunStopped RunState = "stopped"
)

// normRun maps a raw proxmox status string to a RunState, collapsing anything
// unrecognized (e.g. "") to RunUnspecified so actual-state comparison is well-defined.
func normRun(status string) RunState {
	switch status {
	case "running":
		return RunRunning
	case "stopped":
		return RunStopped
	default:
		return RunUnspecified
	}
}

// DesiredGuest is the target state for one existing guest. Every field is
// individually optional ("unmanaged") so a desired-state source can pin only what it
// cares about — slice 4's planner only acts on the fields that are set.
type DesiredGuest struct {
	VMID int
	// Run is the target power state; RunUnspecified leaves it alone.
	Run RunState
	// Spec, when non-nil, manages sizing. Reuses hub.GuestSpec (cores/memory/disk).
	// Phase A reconciles Cores and Memory via SetConfig; DiskBytes is reported but
	// NOT reconciled here (a rootfs grow is `pct resize`, grow-only and separate —
	// deferred to a later slice). Nil = sizing unmanaged.
	Spec *hub.GuestSpec
	// Description, when non-nil, manages the cosmetic `description` field (the first
	// proven SetConfig round-trip, slice-4 pre-check). Nil = unmanaged.
	Description *string
	// Decommission, when true, is an EXPLICIT destructive intent to tear the guest down
	// (slice 10A). It is the canonical destructive desired-state delta: the planner emits an
	// ActionDecommission, which classifies ClassDecommission → Destructive → the gate refuses it
	// `pending_signature` unless a verified operator signature is present. 10A never has a signer,
	// so a decommission is always gated (never executed); the signed execution path is 10B. An
	// explicit flag (not "absent from the desired list") is the safe design — a partial/empty hub
	// list can never silently mass-destroy guests.
	Decommission bool
}

// DesiredState is the vmid-keyed target for this host. At slice 4 the only live
// source is the empty provider, so Guests is empty in production; fixtures inject it
// in tests. Host-level desired state (storage manifest, etc.) arrives in later slices.
type DesiredState struct {
	Guests map[int]DesiredGuest
}

// ActualGuest is one guest's observed state, read from Proxmox.
type ActualGuest struct {
	VMID int
	Run  RunState
	// SpecKnown is false when GuestConfig could not be read (the run-state from the
	// list is still trusted; spec/description comparisons are skipped). Mirrors the
	// collector's "keep run-status, omit spec" degradation.
	SpecKnown   bool
	Cores       int
	MemoryMiB   int64  // proxmox LXC `memory` is MiB
	DiskBytes   int64  // rootfs size in bytes (from the LXC list MaxDisk; for grow planning)
	Description string // raw (may carry PVE's trailing newline; compared via normalizers)
}

// ActualState is the vmid-keyed observed state for this host.
type ActualState struct {
	Guests map[int]ActualGuest
}

// DesiredProvider is the seam the desired-state source plugs into. At slice 4 the
// only implementation is EmptyProvider (no live source); slice 10's hub-serving path
// is the real implementation. Do NOT invent a hub/local-file source here.
type DesiredProvider interface {
	Desired(ctx context.Context) (DesiredState, error)
}

// EmptyProvider is the slice-4 production provider: no desired state, so reconcile is
// a live no-op (the engine computes an empty action set).
type EmptyProvider struct{}

// Desired returns an empty desired state.
func (EmptyProvider) Desired(context.Context) (DesiredState, error) {
	return DesiredState{Guests: map[int]DesiredGuest{}}, nil
}

// StaticProvider serves a fixed DesiredState — used by fixtures (and usable as a
// local override later). It never mutates the value it was given.
type StaticProvider struct{ State DesiredState }

// Desired returns the static state.
func (p StaticProvider) Desired(context.Context) (DesiredState, error) { return p.State, nil }

// CachingProvider is the slice-10A production provider: a thread-safe cache of the hub-served
// DesiredState plus the generation it corresponds to. The hub-sync layer (internal/desired) calls
// Update when the heartbeat envelope's generation advances and a fresh fetch arrives; the engine
// reads the cache via Desired each reconcile tick. Until the first Update it returns an empty
// state (generation 0) — so reconcile is a live no-op exactly like EmptyProvider, with zero
// mutations, which is the correct cold-start behaviour.
type CachingProvider struct {
	mu    sync.RWMutex
	state DesiredState
	gen   int64
}

// NewCachingProvider builds an empty provider (generation 0, no guests).
func NewCachingProvider() *CachingProvider {
	return &CachingProvider{state: DesiredState{Guests: map[int]DesiredGuest{}}}
}

// Desired returns the cached state (a shallow copy of the guest map so a caller can't mutate the
// cache, and a concurrent Update can't race the read).
func (p *CachingProvider) Desired(context.Context) (DesiredState, error) {
	p.mu.RLock()
	defer p.mu.RUnlock()
	out := DesiredState{Guests: make(map[int]DesiredGuest, len(p.state.Guests))}
	for k, v := range p.state.Guests {
		out.Guests[k] = v
	}
	return out, nil
}

// Update replaces the cached state + generation (called by the sync layer on a generation advance).
func (p *CachingProvider) Update(generation int64, state DesiredState) {
	p.mu.Lock()
	defer p.mu.Unlock()
	if state.Guests == nil {
		state.Guests = map[int]DesiredGuest{}
	}
	p.state = state
	p.gen = generation
}

// Generation returns the cached generation (the agent's view of "what I have applied from").
func (p *CachingProvider) Generation() int64 {
	p.mu.RLock()
	defer p.mu.RUnlock()
	return p.gen
}

// GuestAPI is the narrow Proxmox surface the engine needs: read actual state and
// dispatch the benign-on-existing-guest mutations. *proxmox.Client satisfies it; a
// fake satisfies it in tests. Every mutating call returns a UPID (or "" for the
// synchronous path) per the proxmox/mutate.go contract — the engine WaitTasks a
// non-empty UPID and treats "" as a clean synchronous success.
type GuestAPI interface {
	ListLXC(ctx context.Context) ([]proxmox.Guest, error)
	GuestConfig(ctx context.Context, vmid int) (proxmox.GuestConfig, error)
	Start(ctx context.Context, vmid int) (string, error)
	Stop(ctx context.Context, vmid int) (string, error)
	SetConfig(ctx context.Context, vmid int, params map[string]string) (string, error)
	// ResizeLXC grows a volume (grow-only; the planner never emits a shrink). Async → UPID.
	ResizeLXC(ctx context.Context, vmid int, disk, size string) (string, error)
	// RestoreLXC restores an archive into a (fresh) vmid — the create path (slice 6). Async → UPID.
	RestoreLXC(ctx context.Context, opts proxmox.RestoreLXCOptions) (string, error)
	// DestroyLXC destroys a guest — the scratch-teardown primitive (slice 6). Async → UPID.
	// Destructive-class; the engine only ever issues it for an agent-tagged scratch guest
	// (benign by provenance) via the gate.
	DestroyLXC(ctx context.Context, vmid int) (string, error)
	// GuestStatus reads a single guest's current status (run-state poll during a restore-test).
	GuestStatus(ctx context.Context, vmid int) (proxmox.Guest, error)
	WaitTask(ctx context.Context, upid string, opts proxmox.WaitOptions) (proxmox.TaskStatus, error)
	// TaskStatusOnce is a single non-blocking task-status read — used by crash
	// recovery to learn the outcome of an op that was in flight when the agent died.
	TaskStatusOnce(ctx context.Context, upid string) (proxmox.TaskStatus, error)
	// TaskLogTail fetches up to limit trailing task-log lines — used to surface a guest-start
	// task's warning text (the restore-test fetches it when the start exits "WARNINGS: N", so
	// the advisory is reported without failing a guest that actually boots).
	TaskLogTail(ctx context.Context, upid string, limit int) ([]string, error)
}

// guestDescription decodes the (string-valued) `description` key from a GuestConfig's
// raw Extra map, returning "" when absent. The value is returned raw — PVE appends a
// trailing newline on read, which the normalization layer strips at comparison time.
func guestDescription(cfg proxmox.GuestConfig) string {
	raw, ok := cfg.Extra["description"]
	if !ok || len(raw) == 0 {
		return ""
	}
	var s string
	if err := json.Unmarshal(raw, &s); err != nil {
		return ""
	}
	return s
}