// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.

package esign

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"time"

	"go.gearno.de/kit/log"
	"go.gearno.de/kit/pg"
	"go.probo.inc/probo/pkg/coredata"
	"go.probo.inc/probo/pkg/crypto/hash"
	"go.probo.inc/probo/pkg/filemanager"
)

var (
	ErrLoadFile     = errors.New("esign: cannot load file")
	ErrDownloadPDF  = errors.New("esign: cannot download PDF")
	ErrComputeSeal  = errors.New("esign: cannot compute seal")
	ErrTSATimestamp = errors.New("esign: cannot get TSA timestamp")
)

const (
	currentSealVersion = 1
)

type (
	SealingWorker struct {
		pg             *pg.Client
		fileManager    *filemanager.Service
		tsaClient      *TSAClient
		logger         *log.Logger
		interval       time.Duration
		tsaTimeout     time.Duration
		staleAfter     time.Duration
		maxConcurrency int
	}

	SealingWorkerOption func(*SealingWorker)
)

func WithSealingWorkerInterval(d time.Duration) SealingWorkerOption {
	return func(w *SealingWorker) { w.interval = d }
}

func WithSealingWorkerTSATimeout(d time.Duration) SealingWorkerOption {
	return func(w *SealingWorker) { w.tsaTimeout = d }
}

func WithSealingWorkerStaleAfter(d time.Duration) SealingWorkerOption {
	return func(w *SealingWorker) { w.staleAfter = d }
}

func WithSealingWorkerMaxConcurrency(n int) SealingWorkerOption {
	return func(w *SealingWorker) {
		if n > 0 {
			w.maxConcurrency = n
		}
	}
}

func NewSealingWorker(
	pgClient *pg.Client,
	fileManager *filemanager.Service,
	tsaClient *TSAClient,
	logger *log.Logger,
	opts ...SealingWorkerOption,
) *SealingWorker {
	w := &SealingWorker{
		pg:             pgClient,
		fileManager:    fileManager,
		tsaClient:      tsaClient,
		logger:         logger,
		interval:       10 * time.Second,
		tsaTimeout:     10 * time.Second,
		staleAfter:     5 * time.Minute,
		maxConcurrency: 5,
	}

	for _, opt := range opts {
		opt(w)
	}

	return w
}

func (w *SealingWorker) Run(ctx context.Context) error {
	var (
		wg  sync.WaitGroup
		sem = make(chan struct{}, w.maxConcurrency)
	)

	defer wg.Wait()

LOOP:
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-time.After(w.interval):
		// From there we should not accept cancelations anymore.
		nonCancelableCtx := context.WithoutCancel(ctx)
		w.recoverStaleRows(nonCancelableCtx)

		for {
			if err := w.processNext(ctx, sem, &wg); err != nil {
				if !errors.Is(err, coredata.ErrResourceNotFound) {
					w.logger.ErrorCtx(nonCancelableCtx, "cannot claim signature", log.Error(err))
				}
				break
			}
		}

		goto LOOP
	}
}

func (w *SealingWorker) processNext(ctx context.Context, sem chan struct{}, wg *sync.WaitGroup) error {
	select {
	case sem <- struct{}{}:
	case <-ctx.Done():
		return ctx.Err()
	}

	var (
		signature = coredata.ElectronicSignature{}
		now       = time.Now()

		// From there we should not accept cancelations anymore.
		nonCancelableCtx = context.WithoutCancel(ctx)
	)

	if err := w.pg.WithTx(
		nonCancelableCtx,
		func(tx pg.Conn) error {
			if err := signature.LoadNextAcceptedForUpdateSkipLocked(nonCancelableCtx, tx); err != nil {
				return err
			}

			signature.Status = coredata.ElectronicSignatureStatusProcessing
			signature.ProcessingStartedAt = &now
			signature.AttemptCount++
			signature.LastAttemptedAt = &now
			signature.UpdatedAt = now
			if err := signature.Update(nonCancelableCtx, tx, coredata.NewNoScope()); err != nil {
				return fmt.Errorf("cannot update signature: %w", err)
			}

			return nil
		},
	); err != nil {
		<-sem
		return err
	}

	wg.Add(1)
	go func(signature coredata.ElectronicSignature) {
		defer wg.Done()
		defer func() { <-sem }()

		if err := w.sealAndCommit(nonCancelableCtx, &signature); err != nil {
			if err := w.failSignature(nonCancelableCtx, &signature, err); err != nil {
				w.logger.ErrorCtx(nonCancelableCtx, "cannot fail signature", log.Error(err))
			}
		}
	}(signature)

	return nil
}

func (w *SealingWorker) sealAndCommit(
	ctx context.Context,
	signature *coredata.ElectronicSignature,
) error {
	var (
		scope  = coredata.NewScopeFromObjectID(signature.ID)
		file   coredata.File
		events []coredata.ElectronicSignatureEvent
	)

	if err := w.pg.WithConn(
		ctx,
		func(conn pg.Conn) error {
			if err := file.LoadByID(ctx, conn, scope, signature.FileID); err != nil {
				return fmt.Errorf("cannot load file: %w", err)
			}

			return nil
		},
	); err != nil {
		return fmt.Errorf("%w: %w", ErrLoadFile, err)
	}

	pdfBytes, err := w.fileManager.GetFileBytes(ctx, &file)
	if err != nil {
		return fmt.Errorf("%w: %w", ErrDownloadPDF, err)
	}

	fileHash := hash.SHA256Hex(pdfBytes)
	signature.FileHash = &fileHash

	seal, err := signature.ComputeSeal(currentSealVersion)
	if err != nil {
		return fmt.Errorf("%w: %w", ErrComputeSeal, err)
	}
	signature.Seal = &seal
	signature.SealVersion = currentSealVersion
	events = append(
		events,
		signature.NewEvent(
			coredata.ElectronicSignatureEventTypeSealComputed,
			coredata.ElectronicSignatureEventSourceServer,
		),
	)

	tsaCtx, cancel := context.WithTimeout(ctx, w.tsaTimeout)
	defer cancel()
	tsaToken, err := w.tsaClient.Timestamp(tsaCtx, []byte(seal))
	if err != nil {
		return fmt.Errorf("%w: %w", ErrTSATimestamp, err)
	}
	signature.TSAToken = tsaToken
	events = append(
		events,
		signature.NewEvent(
			coredata.ElectronicSignatureEventTypeTimestampRequested,
			coredata.ElectronicSignatureEventSourceServer,
		),
	)

	if err := w.pg.WithTx(
		ctx,
		func(tx pg.Conn) error {
			var current coredata.ElectronicSignature
			if err := current.LoadByID(ctx, tx, scope, signature.ID); err != nil {
				return fmt.Errorf("cannot load signature: %w", err)
			}

			if current.Status != coredata.ElectronicSignatureStatusProcessing {
				return fmt.Errorf("esign: unexpected status %s, expected PROCESSING", current.Status)
			}

			signature.Status = coredata.ElectronicSignatureStatusCompleted
			signature.UpdatedAt = time.Now()
			if err := signature.Update(ctx, tx, scope); err != nil {
				return fmt.Errorf("cannot update signature: %w", err)
			}
			events = append(
				events,
				signature.NewEvent(
					coredata.ElectronicSignatureEventTypeSignatureCompleted,
					coredata.ElectronicSignatureEventSourceServer,
				),
			)

			for i := range events {
				if err := events[i].Insert(ctx, tx, scope); err != nil {
					return fmt.Errorf("cannot insert %s event: %w", events[i].EventType, err)
				}
			}

			return nil
		},
	); err != nil {
		return fmt.Errorf("cannot commit signing results: %w", err)
	}

	return nil
}

func (w *SealingWorker) failSignature(
	ctx context.Context,
	signature *coredata.ElectronicSignature,
	processingError error,
) error {
	scope := coredata.NewScopeFromObjectID(signature.ID)

	w.logger.ErrorCtx(
		ctx,
		"sealing worker failure",
		log.Error(processingError),
		log.String("signature_id", signature.ID.String()),
	)

	return w.pg.WithTx(
		ctx,
		func(tx pg.Conn) error {
			errStr := userFacingError(processingError)
			signature.LastError = &errStr
			signature.ProcessingStartedAt = nil
			signature.UpdatedAt = time.Now()
			if signature.AttemptCount >= signature.MaxAttempts {
				signature.Status = coredata.ElectronicSignatureStatusFailed
			} else {
				signature.Status = coredata.ElectronicSignatureStatusAccepted
			}
			if err := signature.Update(ctx, tx, scope); err != nil {
				return fmt.Errorf("cannot update signature: %w", err)
			}

			event := signature.NewEvent(coredata.ElectronicSignatureEventTypeProcessingError, coredata.ElectronicSignatureEventSourceServer)
			if err := event.Insert(ctx, tx, scope); err != nil {
				return fmt.Errorf("cannot insert PROCESSING_ERROR event: %w", err)
			}

			return nil
		},
	)
}

func userFacingError(err error) string {
	switch {
	case errors.Is(err, ErrTSATimestamp):
		return "The timestamp authority is temporarily unavailable."
	case errors.Is(err, ErrLoadFile):
		return "Unable to load the document for signing."
	case errors.Is(err, ErrDownloadPDF):
		return "Unable to retrieve the document."
	case errors.Is(err, ErrComputeSeal):
		return "Unable to generate the cryptographic seal."
	default:
		return "An unexpected error occurred while processing your signature."
	}
}

func (w *SealingWorker) recoverStaleRows(ctx context.Context) {
	if err := w.pg.WithConn(
		ctx,
		func(conn pg.Conn) error {
			return coredata.ResetStaleProcessingSignatures(ctx, conn, w.staleAfter)
		},
	); err != nil {
		w.logger.ErrorCtx(ctx, "cannot recover stale signatures", log.Error(err))
	}
}