package gitsync

import (
	"context"
	"database/sql"
	"errors"
	"time"

	"github.com/google/uuid"
	"golang.org/x/xerrors"

	"cdr.dev/slog/v3"
	"github.com/coder/coder/v2/coderd/database"
	"github.com/coder/quartz"
)

const (
	// defaultBatchSize is the maximum number of stale rows fetched
	// per tick.
	defaultBatchSize int32 = 50

	// defaultInterval is the polling interval between ticks.
	defaultInterval = 10 * time.Second

	// defaultTickTimeout is the maximum time a single tick may
	// run. Decoupled from the polling interval so that a batch
	// of concurrent HTTP calls has enough headroom to complete.
	defaultTickTimeout = 30 * time.Second

	// NoTokenBackoff is the backoff duration applied to rows
	// whose owner has no linked external-auth token. Much longer
	// than DiffStatusTTL because the user must manually link
	// their account before retrying is useful.
	NoTokenBackoff = 10 * time.Minute

	// NoPRBackoff is the backoff applied when a branch has no
	// associated pull request yet. Kept short so that PRs created
	// shortly after a push (e.g. via `gh pr create`) are
	// discovered quickly instead of waiting for the 5-minute
	// acquisition lock to expire.
	NoPRBackoff = 15 * time.Second

	// NoPRRetryWindow is how long after MarkStale the worker
	// applies the short NoPRBackoff. Outside this window the
	// worker lets the 5-minute acquisition lock serve as the
	// natural retry interval, avoiding indefinite fast-polling
	// for branches that never receive a PR.
	//
	// Together with NoPRBackoff this bounds the number of
	// GitHub API calls to ~NoPRRetryWindow/NoPRBackoff (≈8)
	// per push. Keep both values in sync when adjusting.
	NoPRRetryWindow = 2 * time.Minute
)

// Store is the narrow DB interface the Worker needs.
type Store interface {
	AcquireStaleChatDiffStatuses(
		ctx context.Context, limitVal int32,
	) ([]database.AcquireStaleChatDiffStatusesRow, error)
	BackoffChatDiffStatus(
		ctx context.Context, arg database.BackoffChatDiffStatusParams,
	) error
	UpsertChatDiffStatus(
		ctx context.Context, arg database.UpsertChatDiffStatusParams,
	) (database.ChatDiffStatus, error)
	UpsertChatDiffStatusReference(
		ctx context.Context, arg database.UpsertChatDiffStatusReferenceParams,
	) (database.ChatDiffStatus, error)
	GetChatsByWorkspaceIDs(
		ctx context.Context, ids []uuid.UUID,
	) ([]database.Chat, error)
}

// EventPublisher notifies the frontend of diff status changes.
type PublishDiffStatusChangeFunc func(ctx context.Context, chatID uuid.UUID) error

// Worker is a background loop that periodically refreshes stale
// chat diff statuses by delegating to a Refresher.
type Worker struct {
	store                     Store
	refresher                 *Refresher
	publishDiffStatusChangeFn PublishDiffStatusChangeFunc
	clock                     quartz.Clock
	logger                    slog.Logger
	batchSize                 int32
	interval                  time.Duration
	tickTimeout               time.Duration
	done                      chan struct{}
}

// WorkerOption configures a Worker.
type WorkerOption func(*Worker)

// WithTickTimeout sets the maximum duration for a single tick.
func WithTickTimeout(d time.Duration) WorkerOption {
	return func(w *Worker) {
		if d > 0 {
			w.tickTimeout = d
		}
	}
}

// NewWorker creates a Worker with default batch size and interval.
func NewWorker(
	store Store,
	refresher *Refresher,
	publisher PublishDiffStatusChangeFunc,
	clock quartz.Clock,
	logger slog.Logger,
	opts ...WorkerOption,
) *Worker {
	w := &Worker{
		store:                     store,
		refresher:                 refresher,
		publishDiffStatusChangeFn: publisher,
		clock:                     clock,
		logger:                    logger,
		batchSize:                 defaultBatchSize,
		interval:                  defaultInterval,
		tickTimeout:               defaultTickTimeout,
		done:                      make(chan struct{}),
	}
	for _, o := range opts {
		o(w)
	}
	return w
}

// Start launches the background loop. It blocks until ctx is
// cancelled, then closes w.done.
func (w *Worker) Start(ctx context.Context) {
	defer close(w.done)

	ticker := w.clock.NewTicker(w.interval, "gitsync", "worker")
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			w.tick(ctx)
		}
	}
}

// Done returns a channel that is closed when the worker exits.
func (w *Worker) Done() <-chan struct{} {
	return w.done
}

func chatDiffStatusFromRow(row database.AcquireStaleChatDiffStatusesRow) database.ChatDiffStatus {
	return database.ChatDiffStatus{
		ChatID:           row.ChatID,
		Url:              row.Url,
		PullRequestState: row.PullRequestState,
		ChangesRequested: row.ChangesRequested,
		Additions:        row.Additions,
		Deletions:        row.Deletions,
		ChangedFiles:     row.ChangedFiles,
		AuthorLogin:      row.AuthorLogin,
		AuthorAvatarUrl:  row.AuthorAvatarUrl,
		BaseBranch:       row.BaseBranch,
		HeadBranch:       row.HeadBranch,
		PrNumber:         row.PrNumber,
		Commits:          row.Commits,
		Approved:         row.Approved,
		ReviewerCount:    row.ReviewerCount,
		RefreshedAt:      row.RefreshedAt,
		StaleAt:          row.StaleAt,
		CreatedAt:        row.CreatedAt,
		UpdatedAt:        row.UpdatedAt,
		GitBranch:        row.GitBranch,
		GitRemoteOrigin:  row.GitRemoteOrigin,
		PullRequestTitle: row.PullRequestTitle,
		PullRequestDraft: row.PullRequestDraft,
	}
}

func (w *Worker) tick(ctx context.Context) {
	// Use a dedicated tick timeout that is longer than the
	// polling interval. This gives concurrent HTTP calls enough
	// headroom without stalling the next tick excessively.
	ctx, cancel := context.WithTimeout(ctx, w.tickTimeout)
	defer cancel()

	acquiredRows, err := w.store.AcquireStaleChatDiffStatuses(ctx, w.batchSize)
	if err != nil {
		w.logger.Warn(ctx, "acquire stale chat diff statuses",
			slog.Error(err))
		return
	}
	if len(acquiredRows) == 0 {
		return
	}

	// Build refresh requests directly from acquired rows.
	requests := make([]RefreshRequest, 0, len(acquiredRows))
	for _, row := range acquiredRows {
		requests = append(requests, RefreshRequest{
			Row:     chatDiffStatusFromRow(row),
			OwnerID: row.OwnerID,
		})
	}

	results, err := w.refresher.Refresh(ctx, requests)
	if err != nil {
		w.logger.Warn(ctx, "batch refresh chat diff statuses",
			slog.Error(err))
		return
	}

	for _, res := range results {
		if res.Error != nil {
			w.logger.Debug(ctx, "refresh chat diff status",
				slog.F("chat_id", res.Request.Row.ChatID),
				slog.Error(res.Error))
			// Apply a longer backoff for rows whose owner has
			// no linked token — retrying every 2 minutes is
			// pointless until the user links their account.
			backoff := DiffStatusTTL
			if errors.Is(res.Error, ErrNoTokenAvailable) {
				backoff = NoTokenBackoff
			}
			// Back off so the row isn't retried immediately.
			if err := w.store.BackoffChatDiffStatus(ctx,
				database.BackoffChatDiffStatusParams{
					ChatID:  res.Request.Row.ChatID,
					StaleAt: w.clock.Now().UTC().Add(backoff),
				},
			); err != nil {
				w.logger.Warn(ctx, "backoff failed chat diff status",
					slog.F("chat_id", res.Request.Row.ChatID),
					slog.Error(err))
			}
			continue
		}
		if res.Params == nil {
			// No PR exists yet for this branch. If the row was
			// recently marked stale (e.g. a git push just
			// happened), apply a short backoff so the PR is
			// discovered quickly once created. Outside the
			// retry window, do not shorten the backoff; the
			// 5-minute acquisition lock will serve as the retry
			// interval instead.
			age := w.clock.Now().Sub(res.Request.Row.UpdatedAt)
			if age < NoPRRetryWindow {
				if err := w.store.BackoffChatDiffStatus(ctx,
					database.BackoffChatDiffStatusParams{
						ChatID:  res.Request.Row.ChatID,
						StaleAt: w.clock.Now().UTC().Add(NoPRBackoff),
					},
				); err != nil {
					w.logger.Warn(ctx, "backoff no-pr chat diff status",
						slog.F("chat_id", res.Request.Row.ChatID),
						slog.Error(err))
				}
			}
			continue
		}
		if _, err := w.store.UpsertChatDiffStatus(ctx, *res.Params); err != nil {
			w.logger.Warn(ctx, "upsert refreshed chat diff status",
				slog.F("chat_id", res.Request.Row.ChatID),
				slog.Error(err))
			continue
		}
		if w.publishDiffStatusChangeFn != nil {
			if err := w.publishDiffStatusChangeFn(ctx, res.Request.Row.ChatID); err != nil {
				w.logger.Debug(ctx, "publish diff status change",
					slog.F("chat_id", res.Request.Row.ChatID),
					slog.Error(err))
			}
		}
	}
}

// MarkStaleParams holds the arguments for Worker.MarkStale.
type MarkStaleParams struct {
	WorkspaceID uuid.UUID
	Branch      string
	Origin      string
	// ChatID, when set, targets a single chat instead of
	// broadcasting to every chat on the workspace.
	ChatID uuid.UUID
}

// MarkStale persists the git ref for a chat (or all chats on a
// workspace when no ChatID is provided), setting stale_at to the
// past so the next tick picks them up. Publishes a diff status
// event for each affected chat.
// Called from workspaceagents handlers. No goroutines spawned.
func (w *Worker) MarkStale(ctx context.Context, p MarkStaleParams) {
	if p.Branch == "" || p.Origin == "" {
		return
	}

	// When a specific chat is identified, target it directly
	// instead of broadcasting to every chat on the workspace.
	// Note: this path does not verify that the chat belongs to
	// WorkspaceID. This is safe because ChatID originates from
	// chatd via the agent (trusted data flow), but differs from
	// the broadcast path which filters by workspace.
	if p.ChatID != uuid.Nil {
		w.markStaleSingle(ctx, p.ChatID, p.Branch, p.Origin)
		return
	}

	// Broadcast path: scope by workspace. GetChatsByWorkspaceIDs
	// filters archived=false, which is intentional: archived
	// chats aren't in the active sidebar and don't need refreshed
	// git refs.
	chats, err := w.store.GetChatsByWorkspaceIDs(ctx, []uuid.UUID{p.WorkspaceID})
	if err != nil {
		w.logger.Warn(ctx, "list chats for git ref storage",
			slog.F("workspace_id", p.WorkspaceID),
			slog.Error(err))
		return
	}

	for _, chat := range chats {
		w.markStaleSingle(ctx, chat.ID, p.Branch, p.Origin)
	}
}

// markStaleSingle upserts the git ref for a single chat and
// publishes a diff-status change event.
func (w *Worker) markStaleSingle(
	ctx context.Context,
	chatID uuid.UUID,
	branch, origin string,
) {
	_, err := w.store.UpsertChatDiffStatusReference(ctx,
		database.UpsertChatDiffStatusReferenceParams{
			ChatID:          chatID,
			GitBranch:       branch,
			GitRemoteOrigin: origin,
			StaleAt:         w.clock.Now().Add(-time.Second),
			Url:             sql.NullString{},
		},
	)
	if err != nil {
		w.logger.Warn(ctx, "store git ref on chat diff status",
			slog.F("chat_id", chatID),
			slog.Error(err))
		return
	}
	// Notify the frontend immediately so the UI shows the
	// branch info even before the worker refreshes PR data.
	if w.publishDiffStatusChangeFn != nil {
		if pubErr := w.publishDiffStatusChangeFn(ctx, chatID); pubErr != nil {
			w.logger.Debug(ctx, "publish diff status after mark stale",
				slog.F("chat_id", chatID), slog.Error(pubErr))
		}
	}
}

// RefreshChat synchronously refreshes a single chat's diff
// status using the same Refresher pipeline as the background
// worker. Returns nil, nil when no PR exists yet for the
// branch. Called from HTTP handlers for instant feedback.
func (w *Worker) RefreshChat(
	ctx context.Context,
	row database.ChatDiffStatus,
	ownerID uuid.UUID,
) (*database.ChatDiffStatus, error) {
	requests := []RefreshRequest{{
		Row:     row,
		OwnerID: ownerID,
	}}

	results, err := w.refresher.Refresh(ctx, requests)
	if err != nil {
		return nil, xerrors.Errorf("refresh chat diff status: %w", err)
	}

	if len(results) == 0 {
		return nil, nil
	}
	res := results[0]
	if res.Error != nil {
		return nil, xerrors.Errorf("refresh chat diff status: %w", res.Error)
	}
	if res.Params == nil {
		return nil, nil
	}

	upserted, err := w.store.UpsertChatDiffStatus(ctx, *res.Params)
	if err != nil {
		return nil, xerrors.Errorf("upsert chat diff status: %w", err)
	}

	if w.publishDiffStatusChangeFn != nil {
		if err := w.publishDiffStatusChangeFn(ctx, row.ChatID); err != nil {
			w.logger.Debug(ctx, "publish diff status change",
				slog.F("chat_id", row.ChatID),
				slog.Error(err))
		}
	}

	return &upserted, nil
}