package delivery

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"

	"gorm.io/gorm"
	"sneak.berlin/go/webhooker/internal/database"
)

// archiveNameMaxLen is how many characters of a webhook or target
// name an archive file name keeps.
const archiveNameMaxLen = 40

// databaseTarget is a no-retry target that archives the full
// inbound event into the target's own archive SQLite file, separate
// from the per-webhook event database. The event is already
// persisted in the per-webhook event DB by the time delivery runs;
// the database target additionally writes a durable long-term copy
// into the file ArchiveFileName names and then records a single
// attempt whose outcome reflects whether the archive write
// succeeded. See archiveWriter for the close/reopen, auto-recreate,
// and expiry semantics.
type databaseTarget struct {
	eng *Engine

	// writers holds one archive writer per database target, keyed
	// by target ID.
	mu      sync.Mutex
	writers map[string]*archiveWriter
}

// ArchiveFileName returns the file name of a database target's
// archive: archive-WEBHOOKNAME-TARGETNAME-TARGETID.db, with both
// names passed through archiveNamePart. The target ID keeps the
// name unique when two targets' names come out the same.
func ArchiveFileName(webhookName, targetName, targetID string) string {
	return "archive-" + archiveNamePart(webhookName) + "-" +
		archiveNamePart(targetName) + "-" + targetID + ".db"
}

// archiveNamePart makes a webhook or target name safe to put in a
// file name. It is lowercased; ASCII letters and digits are kept,
// every other run of characters becomes a single "-", and no "-" is
// left at either end. It is cut to archiveNameMaxLen characters, and
// a name with nothing left is "unnamed".
func archiveNamePart(name string) string {
	var b strings.Builder

	dash := false

	for _, r := range strings.ToLower(name) {
		if (r < 'a' || r > 'z') && (r < '0' || r > '9') {
			dash = b.Len() > 0

			continue
		}

		if dash {
			b.WriteByte('-')

			dash = false
		}

		b.WriteRune(r)
	}

	part := b.String()
	if len(part) > archiveNameMaxLen {
		part = strings.TrimRight(part[:archiveNameMaxLen], "-")
	}

	if part == "" {
		return "unnamed"
	}

	return part
}

// Deliver implements Target. It archives the event, then
// records one successful attempt and marks the delivery
// delivered. An archiving error fails the delivery: the
// attempt is recorded as failed with the error and the
// delivery is marked failed, so a target that could not do
// its one job (archiving) never reports success. The target
// does not retry; the event remains durably stored in the
// per-webhook event database.
func (t *databaseTarget) Deliver(
	_ context.Context,
	webhookDB *gorm.DB,
	d *database.Delivery,
	_ *Task,
	_ Scheduler,
) {
	start := time.Now()

	err := t.archive(d)

	elapsed := time.Since(start)

	t.eng.observeAttempt(d.Target.Type, elapsed)

	if err != nil {
		t.eng.log.Error(
			"failed to archive event to database target",
			"delivery_id", d.ID,
			"event_id", d.EventID,
			"error", err,
		)

		recErr := t.eng.recordResult(
			webhookDB, d, 1, false, 0, "",
			err.Error(), elapsed.Milliseconds(),
		)
		if recErr != nil {
			t.eng.bookkeepingFailed(d, recErr)

			return
		}

		t.eng.settleStatus(
			webhookDB, d, d.Target.Type,
			database.DeliveryStatusFailed,
		)

		return
	}

	recErr := t.eng.recordResult(
		webhookDB, d, 1, true, 0, "", "",
		elapsed.Milliseconds(),
	)
	if recErr != nil {
		t.eng.bookkeepingFailed(d, recErr)

		return
	}

	t.eng.settleStatus(
		webhookDB, d, d.Target.Type,
		database.DeliveryStatusDelivered,
	)
}

// archive writes the full event as a row into the target's
// archive database, honouring the optional per-target expiry
// parsed from the target config JSON.
func (t *databaseTarget) archive(d *database.Delivery) error {
	webhookID := d.Event.WebhookID
	if webhookID == "" {
		return errArchiveMissingWebhookID
	}

	expiry, err := parseArchiveExpiry(d.Target.Config)
	if err != nil {
		return err
	}

	w, err := t.writerFor(d.TargetID)
	if err != nil {
		return err
	}

	row := archivedEvent{
		EventID:      d.Event.ID,
		WebhookID:    webhookID,
		EntrypointID: d.Event.EntrypointID,
		Method:       d.Event.Method,
		Headers:      d.Event.Headers,
		Body:         d.Event.Body,
		ContentType:  d.Event.ContentType,
	}

	return w.write(row, expiry)
}

// writerFor returns the archive writer for a database target,
// creating and caching it on first use. Each target has one writer
// so its close/reopen debounce state is shared across concurrent
// deliveries, and so a rename and the idle sweep take the same lock
// as its writes.
func (t *databaseTarget) writerFor(
	targetID string,
) (*archiveWriter, error) {
	t.mu.Lock()
	defer t.mu.Unlock()

	w, ok := t.writers[targetID]
	if !ok {
		var err error

		w, err = t.newWriter(targetID)
		if err != nil {
			return nil, err
		}

		if t.writers == nil {
			t.writers = make(map[string]*archiveWriter)
		}

		t.writers[targetID] = w
	}

	// A delivery claims the entry: even if the idle sweep created
	// it moments ago, it now belongs to the registry proper and
	// the sweep must leave it in place when it finishes.
	w.sweepOwned = false

	return w, nil
}

// sweepWriterFor returns the archive writer the idle sweep should
// prune a target's archive through, together with whether the sweep
// itself created the registry entry.
//
// The sweep must route its prune through the registered writer so
// the writer's mutex orders it against concurrent writes, but it
// must never leave a registry entry behind: a sweep that ran
// concurrently with the target's deletion would otherwise
// re-create an entry that nothing will ever evict again, which is
// exactly the leak eviction exists to prevent. An entry the sweep
// creates is therefore marked sweep-owned and handed back to
// releaseSweepWriter when the sweep is done.
func (t *databaseTarget) sweepWriterFor(
	targetID string,
) (*archiveWriter, bool, error) {
	t.mu.Lock()
	defer t.mu.Unlock()

	w, ok := t.writers[targetID]
	if ok {
		return w, false, nil
	}

	w, err := t.newWriter(targetID)
	if err != nil {
		return nil, false, err
	}

	if t.writers == nil {
		t.writers = make(map[string]*archiveWriter)
	}

	w.sweepOwned = true
	t.writers[targetID] = w

	return w, true, nil
}

// releaseSweepWriter drops a registry entry that the idle sweep
// created, so a sweep leaves the registry exactly as it found it.
//
// The entry is removed only if it is still the very writer the
// sweep installed and no delivery has claimed it in the meantime
// (writerFor clears sweepOwned when it hands a writer to the
// write path). Both conditions are evaluated under the registry
// lock, so an eviction that raced the sweep — which removes the
// entry outright — simply finds nothing left to do here, and a
// delivery that adopted the writer keeps a registered, evictable
// one.
func (t *databaseTarget) releaseSweepWriter(
	targetID string, w *archiveWriter,
) {
	t.mu.Lock()
	defer t.mu.Unlock()

	cur, ok := t.writers[targetID]
	if !ok || cur != w || !cur.sweepOwned {
		return
	}

	delete(t.writers, targetID)
}

// newWriter builds the writer for a database target's archive. The
// file is the one ArchivePath gives for the webhook and the target as
// the main database names them now; from then on only rename changes
// the name the writer uses. It does not touch the archive file.
func (t *databaseTarget) newWriter(
	targetID string,
) (*archiveWriter, error) {
	if t.eng.dbManager == nil {
		return nil, errArchiveNoDataDir
	}

	var target database.Target

	err := t.eng.database.DB().
		Preload("Webhook").
		First(&target, "id = ?", targetID).Error
	if err != nil {
		return nil, fmt.Errorf(
			"loading database target %s: %w", targetID, err,
		)
	}

	w := newArchiveWriter(
		ArchivePath(t.eng.dbManager, &target.Webhook, &target),
		t.eng.log,
	)
	w.webhookID = target.WebhookID

	return w, nil
}

// rename moves a database target's archive file to the name for
// webhookName and targetName. It goes through the target's writer,
// so the move holds the lock that writes and the idle sweep take,
// and later writes use the new name.
//
// The writer is created if there is none, and it stays cached. The
// handlers rename before they save the new name, so until the save
// the main database still has the old one; a delivery in that window
// must find this writer rather than build one from the old name.
func (t *databaseTarget) rename(
	targetID, webhookName, targetName string,
) error {
	w, err := t.writerFor(targetID)
	if err != nil {
		return err
	}

	return w.rename(ArchiveFileName(webhookName, targetName, targetID))
}

// evict drops a database target's archive writer from the registry
// and closes its handle, so a deleted target does not leave a
// writer (and an open archive handle within its debounce window)
// alive for the process lifetime.
//
// The map entry is removed under the registry lock, which is
// then released before the handle is closed under the writer's
// own lock: that ordering keeps the registry available to other
// targets while an in-flight write on this one drains, and
// closing under the writer's lock means eviction can never race
// a write.
//
// Eviction is idempotent and silent for a target with no writer,
// which is the common case: only a database target that has
// received an event or been renamed has one. It never deletes the
// archive file.
func (t *databaseTarget) evict(targetID string) {
	t.mu.Lock()

	w, ok := t.writers[targetID]
	if ok {
		delete(t.writers, targetID)
	}

	t.mu.Unlock()

	if !ok {
		return
	}

	w.evict()

	t.eng.log.Info(
		"evicted archive writer",
		"target_id", targetID,
		"path", w.path,
	)
}

// evictWebhook evicts, exactly as evict does, the writer of every
// database target of a webhook.
func (t *databaseTarget) evictWebhook(webhookID string) {
	t.mu.Lock()

	var gone []*archiveWriter

	for targetID, w := range t.writers {
		if w.webhookID == webhookID {
			delete(t.writers, targetID)

			gone = append(gone, w)
		}
	}

	t.mu.Unlock()

	for _, w := range gone {
		w.evict()

		t.eng.log.Info(
			"evicted archive writer",
			"webhook_id", webhookID,
			"path", w.path,
		)
	}
}

// evictAll evicts every cached archive writer, exactly as evict
// does for one target. The engine calls it at shutdown, once its
// workers have returned. Closing the last handle on an archive
// moves the contents of its -wal into the .db and removes the
// -wal, so a clean stop leaves each archive as a single file.
func (t *databaseTarget) evictAll() {
	t.mu.Lock()

	writers := t.writers
	t.writers = nil

	t.mu.Unlock()

	for _, w := range writers {
		w.evict()
	}
}

// sweepArchive prunes one database target's archive of rows older
// than expiry, without requiring a write. A missing archive file is
// left missing (see sweepExpired), so a sweep never creates an
// archive for a target that has never received an event.
//
// It also never leaves a registry entry behind: an entry it had
// to create to reach the writer's mutex is released again once
// the prune is done, so a sweep racing a target deletion cannot
// resurrect the writer the eviction just dropped.
func (t *databaseTarget) sweepArchive(
	targetID string, expiry time.Duration,
) error {
	w, created, err := t.sweepWriterFor(targetID)
	if err != nil {
		return err
	}

	if created {
		defer t.releaseSweepWriter(targetID, w)
	}

	return w.sweepExpired(expiry)
}