package orchestrator

import (
	"context"
	"errors"
	"fmt"
	"net/netip"
	"sort"
	"sync"
	"time"

	"cloudipvalidator/internal/db"
	"cloudipvalidator/internal/openstack"
)

// This file implements the background floating-IP scan job. With thousands of
// floating IPs a scan takes tens of seconds (Neutron is read page by page)
// and then enqueues thousands of rows, so it can neither run inside an HTTP
// request nor under the auto-cycle mutex. StartScan launches it on the
// process-lifetime context and returns immediately; the job publishes its
// progress as a ScanStatus that anyone can poll.

// ScanState is the phase of the scan job.
type ScanState string

const (
	ScanIdle      ScanState = "idle" // no scan has run in this process yet
	ScanClearing  ScanState = "clearing"
	ScanListing   ScanState = "listing"
	ScanEnqueuing ScanState = "enqueuing"
	ScanDone      ScanState = "done"
	ScanError     ScanState = "error"
	ScanCancelled ScanState = "cancelled"
)

const (
	// scanChunkSize is how many addresses go into one db.SubmitIPs call, i.e.
	// one short transaction; the single DB connection is released in between
	// so the orchestrator tick and the API stay responsive.
	scanChunkSize = 500
	// defaultScanTimeout is used when Cfg.FIPScanTimeoutSeconds is zero.
	defaultScanTimeout = 1800 * time.Second
	// cancelWait bounds how long CancelScan waits for the job to wind down.
	cancelWait = 5 * time.Second
)

// ScanOptions selects the variant of a scan.
type ScanOptions struct {
	// ClearFirst clears the whole queue before scanning (auto-cycle step 1).
	// Ignored together with DryRun: a dry run never touches the queue.
	ClearFirst bool
	// DryRun only discovers and counts the free floating IPs; the queue is
	// left untouched.
	DryRun bool
}

// ScanStatus is a snapshot of the scan job's progress.
type ScanStatus struct {
	State             ScanState
	Running           bool
	DryRun            bool
	Pages             int // Neutron pages read so far
	Discovered        int // floating IPs seen (free and associated)
	Free              int // of those, free (no port) — the addresses to enqueue
	Added             int
	Requeued          int
	Reordered         int
	SkippedInProgress int
	StartedAt         *time.Time
	FinishedAt        *time.Time
	Error             string
}

// scanResult is what a finished job leaves for the synchronous wrapper.
type scanResult struct {
	submit db.SubmitIPsResult
	free   int
	err    error
}

// scanRun is one execution of the job.
type scanRun struct {
	done   chan struct{} // closed when the job has finished (result is set)
	cancel context.CancelFunc
	result scanResult
}

// scanJob is the zero-value-usable scan state embedded in Orchestrator
// (tests build Orchestrator as a literal, so there is no constructor-only
// initialization).
type scanJob struct {
	mu              sync.Mutex
	lifeCtx         context.Context // process lifetime; nil = context.Background()
	status          ScanStatus      // zero value reads as idle (see snapshot)
	run             *scanRun        // current/last run
	cancelRequested bool
}

// SetContext sets the lifetime context background jobs (the scan) run on.
// Call once at startup; until then context.Background() is used. Cancelling
// it cancels a running scan.
func (o *Orchestrator) SetContext(ctx context.Context) {
	o.scan.mu.Lock()
	defer o.scan.mu.Unlock()
	o.scan.lifeCtx = ctx
}

func (j *scanJob) lifetime() context.Context {
	if j.lifeCtx != nil {
		return j.lifeCtx
	}
	return context.Background()
}

// snapshot returns a copy of the status; caller holds j.mu.
func (j *scanJob) snapshot() ScanStatus {
	st := j.status
	if st.State == "" {
		st.State = ScanIdle
	}
	return st
}

// ScanStatus returns the current scan status (state "idle" if no scan has run
// in this process yet).
func (o *Orchestrator) ScanStatus() ScanStatus {
	o.scan.mu.Lock()
	defer o.scan.mu.Unlock()
	return o.scan.snapshot()
}

// StartScan starts the background scan job, or — single-flight — joins the one
// already running: then started is false and the returned status is the
// running job's. It never blocks on OpenStack or the database.
func (o *Orchestrator) StartScan(opts ScanOptions) (ScanStatus, bool) {
	st, _, started := o.startScan(opts)
	return st, started
}

func (o *Orchestrator) startScan(opts ScanOptions) (ScanStatus, *scanRun, bool) {
	j := &o.scan
	j.mu.Lock()
	defer j.mu.Unlock()
	if j.status.Running && j.run != nil {
		return j.snapshot(), j.run, false
	}

	timeout := time.Duration(o.Cfg.FIPScanTimeoutSeconds) * time.Second
	if timeout <= 0 {
		timeout = defaultScanTimeout
	}
	ctx, cancel := context.WithTimeout(j.lifetime(), timeout)
	run := &scanRun{done: make(chan struct{}), cancel: cancel}
	if opts.DryRun {
		opts.ClearFirst = false
	}
	now := db.Now()
	state := ScanListing
	if opts.ClearFirst {
		state = ScanClearing
	}
	j.run = run
	j.cancelRequested = false
	j.status = ScanStatus{State: state, Running: true, DryRun: opts.DryRun, StartedAt: &now}
	go o.runScan(ctx, run, opts)
	return j.snapshot(), run, true
}

// CancelScan cancels a running scan and waits (briefly) for it to wind down.
// It reports whether a running scan was cancelled. Already-enqueued chunks
// stay in the queue.
func (o *Orchestrator) CancelScan() bool {
	j := &o.scan
	j.mu.Lock()
	run := j.run
	if !j.status.Running || run == nil {
		j.mu.Unlock()
		return false
	}
	j.cancelRequested = true
	j.mu.Unlock()

	run.cancel()
	select {
	case <-run.done:
	case <-time.After(cancelWait):
	}
	return true
}

// update mutates the status under the lock.
func (j *scanJob) update(f func(*ScanStatus)) {
	j.mu.Lock()
	defer j.mu.Unlock()
	f(&j.status)
}

func (o *Orchestrator) runScan(ctx context.Context, run *scanRun, opts ScanOptions) {
	j := &o.scan
	defer run.cancel()

	res, err := o.doScan(ctx, opts)
	run.result = res

	j.mu.Lock()
	finished := db.Now()
	switch {
	case err == nil:
		j.status.State = ScanDone
	case j.cancelRequested || errors.Is(j.lifetime().Err(), context.Canceled):
		j.status.State = ScanCancelled
		err = fmt.Errorf("scan cancelled: %w", context.Canceled)
		j.status.Error = "cancelled"
	case errors.Is(err, context.DeadlineExceeded):
		j.status.State = ScanError
		err = fmt.Errorf("scan timed out: %w", err)
		j.status.Error = err.Error()
	default:
		j.status.State = ScanError
		j.status.Error = err.Error()
	}
	j.status.Running = false
	j.status.FinishedAt = &finished
	state := j.status.State
	j.mu.Unlock()
	run.result.err = err

	if state == ScanError || state == ScanCancelled {
		o.Log.Warn("floating ip scan did not complete", "state", state, "err", err)
	}
	close(run.done)
}

// doScan is the scan algorithm: optional clear -> read every page into memory
// -> sort -> (unless dry run) enqueue in chunks -> one fip_scan event.
func (o *Orchestrator) doScan(ctx context.Context, opts ScanOptions) (scanResult, error) {
	j := &o.scan
	var res scanResult

	if opts.ClearFirst {
		if _, err := o.ClearQueue(ctx); err != nil {
			return res, fmt.Errorf("clear queue: %w", err)
		}
		j.update(func(s *ScanStatus) { s.State = ScanListing })
	}

	// Read everything first: a read error after retries must leave the queue
	// untouched, so nothing is enqueued until discovery is complete.
	var free []string
	seen := map[string]struct{}{}
	pages, err := o.OS.ListFreeFloatingIPs(ctx, o.ScanPageSize, func(page []openstack.FloatingIP) error {
		nFree := 0
		for _, f := range page {
			if f.PortID != "" || f.Address == "" {
				continue
			}
			if _, dup := seen[f.Address]; dup {
				continue
			}
			seen[f.Address] = struct{}{}
			free = append(free, f.Address)
			nFree++
		}
		j.update(func(s *ScanStatus) {
			s.Pages++
			s.Discovered += len(page)
			s.Free += nFree
		})
		return ctx.Err()
	})
	if err != nil {
		return res, fmt.Errorf("list floating ips: %w", err)
	}
	j.update(func(s *ScanStatus) { s.Pages = pages })
	res.free = len(free)
	sortAddressesAscending(free)

	if !opts.DryRun && len(free) > 0 {
		j.update(func(s *ScanStatus) { s.State = ScanEnqueuing })
		for off := 0; off < len(free); off += scanChunkSize {
			if err := ctx.Err(); err != nil {
				return res, err
			}
			chunk := free[off:min(off+scanChunkSize, len(free))]
			kind := db.RunManual
			if opts.ClearFirst {
				kind = db.RunAuto // the auto-cycle's scan; a manual scan never clears first
			}
			r, err := o.DB.SubmitIPsAs(ctx, chunk, kind)
			res.submit.Added = append(res.submit.Added, r.Added...)
			res.submit.Requeued = append(res.submit.Requeued, r.Requeued...)
			res.submit.Reordered = append(res.submit.Reordered, r.Reordered...)
			res.submit.SkippedInProgress = append(res.submit.SkippedInProgress, r.SkippedInProgress...)
			j.update(func(s *ScanStatus) {
				s.Added += len(r.Added)
				s.Requeued += len(r.Requeued)
				s.Reordered += len(r.Reordered)
				s.SkippedInProgress += len(r.SkippedInProgress)
			})
			if err != nil {
				return res, fmt.Errorf("submit scanned ips: %w", err)
			}
		}
	}

	if !opts.DryRun {
		o.event(ctx, "control-api", "", nil, "fip_scan", fmt.Sprintf(
			`{"scanned_free":%d,"pages":%d,"added":%d,"requeued":%d,"reordered":%d,"skipped_in_progress":%d}`,
			len(free), pages, len(res.submit.Added), len(res.submit.Requeued),
			len(res.submit.Reordered), len(res.submit.SkippedInProgress)))
	}
	return res, nil
}

// sortAddressesAscending orders addresses numerically (10.0.0.2 before
// 10.0.0.10) so the queue order is deterministic; anything that does not parse
// as an IP goes last, in string order.
func sortAddressesAscending(addrs []string) {
	type keyed struct {
		s  string
		ip netip.Addr
		ok bool
	}
	ks := make([]keyed, len(addrs))
	for i, a := range addrs {
		ip, err := netip.ParseAddr(a)
		ks[i] = keyed{s: a, ip: ip, ok: err == nil}
	}
	sort.SliceStable(ks, func(i, j int) bool {
		a, b := ks[i], ks[j]
		switch {
		case a.ok && b.ok:
			return a.ip.Compare(b.ip) < 0
		case a.ok != b.ok:
			return a.ok
		default:
			return a.s < b.s
		}
	})
	for i := range ks {
		addrs[i] = ks[i].s
	}
}

// ScanFloatingIPs lists every floating IP in the OpenStack project, filters
// to the ones not currently associated to any port (the free pool awaiting
// validation before reissue), and submits that address list to the check
// queue via db.SubmitIPs — the same entry point the admin API's "add
// addresses" call uses, so add/requeue/reorder semantics are identical
// whether the address list came from an operator or from this scan. It is the
// synchronous "start (or join) the background scan and wait for it" wrapper:
// returns the aggregated SubmitIPs outcome plus how many free floating IPs
// were found in total (which can be larger than the sum of the
// SubmitIPsResult slices, since addresses already mid-check are silently
// skipped — see db.SubmitIPs). If ctx is cancelled first it returns
// ctx.Err(); the background job keeps running.
func (o *Orchestrator) ScanFloatingIPs(ctx context.Context) (db.SubmitIPsResult, int, error) {
	return o.ScanAndWait(ctx, ScanOptions{})
}

// ScanAndWait starts (or joins) the background scan with opts and waits for it
// to finish, returning the aggregated SubmitIPs outcome and the number of free
// floating IPs found. Joining a scan that is already running returns that
// scan's result regardless of opts. If ctx ends first it returns ctx.Err()
// and the job keeps running.
func (o *Orchestrator) ScanAndWait(ctx context.Context, opts ScanOptions) (db.SubmitIPsResult, int, error) {
	_, run, _ := o.startScan(opts)
	select {
	case <-run.done:
	case <-ctx.Done():
		return db.SubmitIPsResult{}, 0, ctx.Err()
	}
	return run.result.submit, run.result.free, run.result.err
}