package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"os"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"

	"mgit.msbls.de/m/ImaGen/internal/backend"
	"mgit.msbls.de/m/ImaGen/internal/config"
	"mgit.msbls.de/m/ImaGen/internal/output"
	"mgit.msbls.de/m/ImaGen/internal/prompt"
	"mgit.msbls.de/m/ImaGen/internal/worker"
)

// runWorker is the `imagen worker` subcommand: a long-running daemon that
// consumes the imagen.jobs queue and writes results into imagen.images via
// the same cloud-sync path generate uses.
func runWorker(ctx context.Context, args []string) error {
	fs := flag.NewFlagSet("worker", flag.ContinueOnError)
	var (
		configPath   string
		pollInterval time.Duration
		jobTimeout   time.Duration
	)
	fs.StringVar(&configPath, "config", "", "config file path (default: ~/.config/imagen.yaml)")
	fs.DurationVar(&pollInterval, "poll-interval", 5*time.Second, "safety-poll cadence between LISTEN wakeups")
	fs.DurationVar(&jobTimeout, "job-timeout", 5*time.Minute, "max wall-time per job before the worker marks it failed")
	fs.Usage = func() {
		fmt.Fprintln(fs.Output(), `Usage: imagen worker [flags]

Long-running daemon. LISTENs on the Postgres 'imagen_jobs' channel and polls
imagen.jobs every --poll-interval as a safety net, claims pending rows, runs
the generation pipeline, then updates the row with status + image_id.

Env:
  IMAGEN_WORKER_DATABASE_URL   Postgres DSN for direct LISTEN + UPDATE.
                               Required (PostgREST cannot LISTEN).
  SUPABASE_URL, SUPABASE_SERVICE_KEY, IMAGEN_OWNER_USER_ID
                               Reused from generate's cloud-sync path; the
                               worker writes imagen.images rows through the
                               same code path. Per-job owner_user_id from the
                               job row overrides IMAGEN_OWNER_USER_ID.`)
		fs.PrintDefaults()
	}
	if err := fs.Parse(args); err != nil {
		return err
	}

	cfg, cfgErr := config.Load(configPath)
	if cfgErr != nil && !os.IsNotExist(cfgErr) {
		return cfgErr
	}

	dsn := os.Getenv("IMAGEN_WORKER_DATABASE_URL")
	if dsn == "" {
		return userErr("IMAGEN_WORKER_DATABASE_URL not set; the worker needs a direct Postgres DSN for LISTEN/NOTIFY")
	}

	q, err := dialQueue(ctx, dsn)
	if err != nil {
		return fmt.Errorf("queue: %w", err)
	}
	defer q.Close()

	p := &workerPipeline{cfg: cfg}
	w := worker.New(q, p, worker.Config{
		PollInterval: pollInterval,
		JobTimeout:   jobTimeout,
		Logger:       func(format string, a ...any) { fmt.Fprintf(os.Stderr, format+"\n", a...) },
	})
	fmt.Fprintln(os.Stderr, "imagen worker: ready (poll-interval", pollInterval, "job-timeout", jobTimeout, ")")
	return w.Run(ctx)
}

// pgxQueue is the production Queue. It opens one dedicated connection used
// for both LISTEN (long-lived) and UPDATE operations. A second connection
// would split state needlessly — a single worker process processes one job
// at a time so the connection is never contended.
type pgxQueue struct {
	conn *pgx.Conn
}

func dialQueue(ctx context.Context, dsn string) (*pgxQueue, error) {
	conn, err := pgx.Connect(ctx, dsn)
	if err != nil {
		return nil, fmt.Errorf("pgx.Connect: %w", err)
	}
	if _, err := conn.Exec(ctx, "LISTEN imagen_jobs"); err != nil {
		conn.Close(ctx)
		return nil, fmt.Errorf("LISTEN imagen_jobs: %w", err)
	}
	return &pgxQueue{conn: conn}, nil
}

func (q *pgxQueue) Close() {
	if q == nil || q.conn == nil {
		return
	}
	// Best-effort: a 5s budget is enough to send a polite TerminateMessage.
	shutdown, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	_ = q.conn.Close(shutdown)
}

// ClaimNextPending atomically marks the oldest pending row 'running' and
// returns it. FOR UPDATE SKIP LOCKED is belt + braces against a second worker
// process — out of scope for v1 but cheap insurance.
func (q *pgxQueue) ClaimNextPending(ctx context.Context) (*worker.Job, error) {
	const stmt = `
		UPDATE imagen.jobs
		SET status='running', started_at=now()
		WHERE id = (
			SELECT id FROM imagen.jobs
			WHERE status='pending'
			ORDER BY created_at
			LIMIT 1
			FOR UPDATE SKIP LOCKED
		)
		RETURNING id, owner_user_id, prompt, backend,
		          COALESCE(model,''),
		          COALESCE(width, 0), COALESCE(height, 0),
		          COALESCE(steps, 0), COALESCE(seed, 0),
		          COALESCE(style,'')`
	var j worker.Job
	err := q.conn.QueryRow(ctx, stmt).Scan(
		&j.ID, &j.OwnerUserID, &j.Prompt, &j.Backend,
		&j.Model, &j.Width, &j.Height, &j.Steps, &j.Seed, &j.Style,
	)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &j, nil
}

func (q *pgxQueue) MarkDone(ctx context.Context, jobID, imageID string) error {
	_, err := q.conn.Exec(ctx,
		`UPDATE imagen.jobs SET status='done', image_id=$2, completed_at=now() WHERE id=$1`,
		jobID, imageID)
	return err
}

func (q *pgxQueue) MarkFailed(ctx context.Context, jobID, msg string) error {
	// Trim outrageously long error text so a 10MB stack-trace doesn't end up
	// in the row (callers see a summary, full text goes to stderr / logs).
	const maxLen = 2000
	if len(msg) > maxLen {
		msg = msg[:maxLen] + "... [truncated]"
	}
	_, err := q.conn.Exec(ctx,
		`UPDATE imagen.jobs SET status='failed', error=$2, completed_at=now() WHERE id=$1`,
		jobID, msg)
	return err
}

// WaitForJob blocks until a NOTIFY arrives on imagen_jobs, the timeout fires,
// or ctx is cancelled. Notifications during a previous processJob are queued
// by pgx and delivered on the next call — we don't lose wake-ups even when
// processing took longer than poll-interval.
func (q *pgxQueue) WaitForJob(ctx context.Context, timeout time.Duration) error {
	waitCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	_, err := q.conn.WaitForNotification(waitCtx)
	if err != nil {
		if errors.Is(err, context.DeadlineExceeded) {
			return nil // poll cadence fired
		}
		if errors.Is(err, context.Canceled) {
			return context.Canceled
		}
		return err
	}
	return nil
}

// ResetStaleRunning bumps any rows stuck in 'running' back to 'pending' so
// they get re-claimed. Called once at startup. A row stuck in 'running' came
// from a previous worker crash; without this, flexsiebels would poll
// forever on a job nobody is processing.
func (q *pgxQueue) ResetStaleRunning(ctx context.Context) error {
	_, err := q.conn.Exec(ctx,
		`UPDATE imagen.jobs SET status='pending', started_at=NULL WHERE status='running'`)
	return err
}

// workerPipeline is the Pipeline implementation that drives a single job
// through buildBackend → prompt enrichment → generate → write disk →
// cloud-sync, then returns the imagen.images.id back to the worker so it
// can link the row.
type workerPipeline struct {
	cfg *config.Config
}

func (p *workerPipeline) Run(ctx context.Context, job worker.Job) worker.Outcome {
	if job.OwnerUserID == "" {
		return worker.Outcome{Err: fmt.Errorf("job %s: missing owner_user_id", job.ID)}
	}
	if job.Prompt == "" {
		return worker.Outcome{Err: fmt.Errorf("job %s: empty prompt", job.ID)}
	}
	if job.Backend == "" {
		return worker.Outcome{Err: fmt.Errorf("job %s: missing backend", job.ID)}
	}

	be, err := buildBackend(p.cfg, job.Backend)
	if err != nil {
		return worker.Outcome{Err: fmt.Errorf("backend %q: %w", job.Backend, err)}
	}
	attachUsageSink(be)

	finalPrompt, err := prompt.Apply(job.Prompt, job.Style)
	if err != nil {
		return worker.Outcome{Err: fmt.Errorf("style: %w", err)}
	}

	req := backend.Request{
		Prompt: finalPrompt,
		Width:  job.Width,
		Height: job.Height,
		Steps:  job.Steps,
		Seed:   job.Seed,
		Style:  job.Style,
	}
	res, err := be.Generate(ctx, req)
	if err != nil {
		return worker.Outcome{Err: fmt.Errorf("generate: %w", err)}
	}
	defer res.ImageReader.Close()

	writer := buildWriter(p.cfg, false)
	in := output.Inputs{
		Prompt:   job.Prompt,
		Backend:  be.Name(),
		Seed:     seedFromMetadata(res.Metadata, job.Seed),
		Ext:      extFromMime(res.MimeType),
		Metadata: res.Metadata,
	}
	paths, err := writer.Write(res.ImageReader, in)
	if err != nil {
		return worker.Outcome{Err: fmt.Errorf("write disk: %w", err)}
	}

	// Worker is queue-driven: cloud-sync is mandatory because flexsiebels
	// needs imagen.images.id to render the result. Pass cloud_sync=on via
	// the override path (third arg = ownerUserID); we set the mode by
	// disallowing the 'off' branch through the cfg later if the user
	// explicitly turned it off in config.
	if cloudModeOff(p.cfg) {
		// We refuse to silently drop a queued job. If cloud sync is off in
		// config, the worker can't serve flexsiebels at all.
		return worker.Outcome{Err: fmt.Errorf("output.cloud_sync=off in config; the worker requires cloud_sync=on or auto")}
	}
	syncRes, syncErr := maybeCloudSync(ctx, p.cfg, false, job.OwnerUserID, paths, in, res, dimOrFallback(job.Width, res, "width"), dimOrFallback(job.Height, res, "height"))
	if syncErr != nil {
		return worker.Outcome{Err: fmt.Errorf("cloud sync: %w", syncErr)}
	}
	if syncRes == nil || syncRes.ImageID == "" {
		return worker.Outcome{Err: fmt.Errorf("cloud sync returned no imagen.images id (check SUPABASE_URL + SUPABASE_SERVICE_KEY)")}
	}
	return worker.Outcome{ImageID: syncRes.ImageID}
}

func cloudModeOff(cfg *config.Config) bool {
	if cfg == nil {
		return false
	}
	return strings.EqualFold(cfg.Output.CloudSync, "off")
}

// dimOrFallback returns job.<dim> when the job specified one, otherwise the
// dimension reported by the backend's metadata. Some backends (Replicate
// when given an aspect ratio) round the requested size to their nearest
// supported value; this keeps the row honest about what was actually generated.
func dimOrFallback(jobDim int, res *backend.Result, key string) int {
	if jobDim > 0 {
		return jobDim
	}
	return metaInt(res.Metadata, key)
}