// Package worker implements the single-worker loop that pulls jobs from the
// SQLite queue, executes them against the Ollama target, and records results.
//
// Why: foreman serializes all chat work through one worker to avoid swap thrash
// on the target (ADR-0009). The worker is the only writer of job state transitions.
// What: runs a goroutine that picks the next job (drain-by-model), calls Ollama,
// stores the result, fires webhooks, and notifies waiting sync handlers.
// Test: create with a stub client, enqueue jobs, verify serial execution,
// drain-by-model ordering, retry on connection error, and completion notification.
package worker

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"strconv"
	"sync"
	"time"

	"gitea.stevedudenhoeffer.com/steve/foreman/internal/ollama"
	"gitea.stevedudenhoeffer.com/steve/foreman/internal/store"
	"gitea.stevedudenhoeffer.com/steve/foreman/internal/webhook"
)

// Notifier manages channels that sync HTTP handlers use to wait for job completion.
//
// Why: the /api/chat handler blocks until its job finishes; a notification map
// avoids polling the DB.
// What: maps job IDs to channels; the worker signals completion by closing the channel.
// Test: register a waiter, complete the job, verify the channel unblocks.
type Notifier struct {
	mu       sync.Mutex
	waiters  map[string]chan struct{}
	// results stores the terminal job state so the waiter can read it after notification.
	results  map[string]jobResult
}

type jobResult struct {
	State  store.JobState
	Result json.RawMessage
	Error  *string
}

// NewNotifier creates a new Notifier.
func NewNotifier() *Notifier {
	return &Notifier{
		waiters: make(map[string]chan struct{}),
		results: make(map[string]jobResult),
	}
}

// Register creates a wait channel for the given job ID. The caller should select
// on the returned channel and their context.
//
// Why: each sync chat handler needs its own completion signal.
// What: allocates a buffered channel keyed by job ID.
// Test: register, verify channel is open, complete, verify it closes.
func (n *Notifier) Register(jobID string) <-chan struct{} {
	n.mu.Lock()
	defer n.mu.Unlock()
	ch := make(chan struct{})
	n.waiters[jobID] = ch
	return ch
}

// Complete signals that the job has reached a terminal state and stores the result.
//
// Why: the worker calls this when a job is done or failed; the HTTP handler unblocks.
// What: closes the wait channel and stores the result for retrieval.
// Test: register, complete, verify the channel is closed and result is available.
func (n *Notifier) Complete(jobID string, state store.JobState, result json.RawMessage, errMsg *string) {
	n.mu.Lock()
	defer n.mu.Unlock()
	n.results[jobID] = jobResult{State: state, Result: result, Error: errMsg}
	if ch, ok := n.waiters[jobID]; ok {
		close(ch)
		delete(n.waiters, jobID)
	}
}

// Result returns the stored result for a completed job, if any.
//
// Why: after the wait channel closes, the HTTP handler needs the result data.
// What: returns the cached result and cleans up.
// Test: complete a job, call Result, verify data, call again, verify cleaned up.
func (n *Notifier) Result(jobID string) (store.JobState, json.RawMessage, *string, bool) {
	n.mu.Lock()
	defer n.mu.Unlock()
	r, ok := n.results[jobID]
	if ok {
		delete(n.results, jobID)
	}
	return r.State, r.Result, r.Error, ok
}

// Worker is the single-threaded job execution loop.
type Worker struct {
	store      *store.Store
	client     ollama.Client
	inventory  *ollama.ModelInventory
	notifier   *Notifier
	dispatcher *webhook.Dispatcher
	logger     *slog.Logger

	// keepAlive is the JSON-encoded keep_alive value sent in outbound chat requests
	// to control how long the worker model stays resident on the target. Derived from
	// FOREMAN_KEEP_ALIVE config; does not affect the embedder.
	keepAlive json.RawMessage

	// wake is signaled when a new job is enqueued.
	wake chan struct{}
}

// New creates a new Worker.
//
// Why: dependency injection makes the worker testable with stub clients and stores.
// What: wires all dependencies and creates the wake channel.
// Test: create with stubs, call Run in a goroutine, enqueue a job, verify execution.
func New(
	st *store.Store,
	client ollama.Client,
	inv *ollama.ModelInventory,
	notifier *Notifier,
	dispatcher *webhook.Dispatcher,
	logger *slog.Logger,
	keepAlive string,
) *Worker {
	return &Worker{
		store:      st,
		client:     client,
		inventory:  inv,
		notifier:   notifier,
		dispatcher: dispatcher,
		logger:     logger,
		keepAlive:  encodeKeepAlive(keepAlive),
		wake:       make(chan struct{}, 1),
	}
}

// encodeKeepAlive converts a FOREMAN_KEEP_ALIVE config string to a json.RawMessage
// suitable for the Ollama ChatRequest KeepAlive field.
//
// Why: Ollama's keep_alive field accepts either a JSON number (seconds, or -1 for
// forever) or a JSON string duration ("15m", "1h"). Pure-numeric values and "-1"
// are encoded as JSON numbers; everything else is encoded as a JSON string.
// What: returns a json.RawMessage containing the appropriate JSON representation.
// Test: assert "-1" -> `-1`, "0" -> `0`, "15m" -> `"15m"`, "3600" -> `3600`.
func encodeKeepAlive(val string) json.RawMessage {
	if val == "" {
		val = "-1"
	}

	// If the value parses as an integer, emit it as a JSON number.
	// This covers "-1", "0", "3600", etc.
	if _, err := strconv.Atoi(val); err == nil {
		return json.RawMessage(val)
	}

	// Otherwise, emit it as a JSON string (e.g. "15m", "1h").
	b, _ := json.Marshal(val)
	return json.RawMessage(b)
}

// Wake signals the worker that a new job may be available. Non-blocking.
//
// Why: the HTTP handlers signal the worker to check for new work immediately
// instead of waiting for the next poll cycle.
// What: sends on the wake channel (drops if already pending).
// Test: call Wake multiple times, verify no blocking.
func (w *Worker) Wake() {
	select {
	case w.wake <- struct{}{}:
	default:
	}
}

// Run starts the worker loop. It blocks until ctx is cancelled. On startup it
// resets any interrupted jobs back to queued.
//
// Why: the main loop is the core of foreman's job execution (ADR-0009).
// What: resets interrupted jobs, then loops: pick next job, execute, record result.
// Test: enqueue jobs, run worker with a cancellable context, verify all execute.
func (w *Worker) Run(ctx context.Context) {
	// Reset any jobs stuck in loading/working from a previous crash.
	if n, err := w.store.ResetInterruptedJobs(); err != nil {
		w.logger.Error("failed to reset interrupted jobs", "error", err)
	} else if n > 0 {
		w.logger.Info("reset interrupted jobs", "count", n)
	}

	for {
		if ctx.Err() != nil {
			return
		}

		currentModel := w.currentWorkerModel()
		job, err := w.store.NextJob(currentModel)
		if err != nil {
			if errors.Is(err, sql.ErrNoRows) {
				// No jobs available — wait for a wake signal or context cancel.
				select {
				case <-w.wake:
					continue
				case <-ctx.Done():
					return
				}
			}
			w.logger.Error("failed to fetch next job", "error", err)
			select {
			case <-time.After(1 * time.Second):
				continue
			case <-ctx.Done():
				return
			}
		}

		w.executeJob(ctx, job)
	}
}

// currentWorkerModel returns the model name currently in the worker slot (slot 2).
// The embedder is in slot 1; any other model is the worker model.
func (w *Worker) currentWorkerModel() string {
	residents := w.inventory.ResidentModels()
	embedModel := w.getEmbedModel()
	for _, r := range residents {
		if r.Name != embedModel {
			return r.Name
		}
	}
	return ""
}

// getEmbedModel returns the embedder model name from the first resident model
// that looks like an embedder slot. This is a heuristic — in practice the embed
// model is the one that stays loaded with keep_alive=-1.
func (w *Worker) getEmbedModel() string {
	// We check inventory for a model that matches common embed model patterns.
	// The simplest approach: the embedder is usually the first (smallest) resident.
	// However, we can't easily know which is which without config.
	// For now, return empty — drain-by-model still works because we prefer
	// whatever model is resident.
	return ""
}

// executeJob runs a single job through its lifecycle.
func (w *Worker) executeJob(ctx context.Context, job store.Job) {
	w.logger.Info("executing job", "job_id", job.ID, "model", job.Model, "attempt", job.Attempt)

	// Determine if we need to load a new model.
	needsLoad := !w.isModelResident(job.Model)

	if needsLoad {
		w.transitionState(job, store.JobStateLoading)
	}
	w.transitionState(job, store.JobStateWorking)

	// Parse the payload into a ChatRequest.
	var chatReq ollama.ChatRequest
	if err := json.Unmarshal(job.Payload, &chatReq); err != nil {
		errMsg := fmt.Sprintf("invalid chat request payload: %v", err)
		w.failJob(job, &errMsg)
		return
	}

	// Ensure model is set.
	chatReq.Model = job.Model

	// Set stream to false for worker execution — we collect the full response.
	streamFalse := false
	chatReq.Stream = &streamFalse

	// Override keep_alive with the configured value so the worker model stays
	// resident for the desired duration. The embedder is pinned separately.
	chatReq.KeepAlive = w.keepAlive

	// Execute the chat request.
	resp, _, err := w.client.Chat(ctx, chatReq, false)
	if err != nil {
		w.handleExecutionError(job, err)
		return
	}

	// Marshal the result.
	resultBytes, err := json.Marshal(resp)
	if err != nil {
		errMsg := fmt.Sprintf("marshal result: %v", err)
		w.failJob(job, &errMsg)
		return
	}
	result := json.RawMessage(resultBytes)

	// Store the completion artifact.
	_, artifactErr := w.store.CreateArtifact(store.Artifact{
		JobID:       job.ID,
		Name:        "completion",
		ContentType: "application/json",
		Data:        resultBytes,
	})
	if artifactErr != nil {
		w.logger.Error("failed to store artifact", "error", artifactErr, "job_id", job.ID)
	}

	// Transition to done.
	if err := w.store.UpdateJobState(job.ID, store.JobStateDone, result, nil); err != nil {
		w.logger.Error("failed to update job to done", "error", err, "job_id", job.ID)
	}

	// Notify waiting sync handlers.
	w.notifier.Complete(job.ID, store.JobStateDone, result, nil)

	// Fire webhook if configured.
	w.fireWebhook(job, store.JobStateDone, store.JobStateWorking, result, nil)

	w.logger.Info("job completed", "job_id", job.ID, "model", job.Model)
}

// transitionState updates a job's state and fires a webhook.
func (w *Worker) transitionState(job store.Job, newState store.JobState) {
	prevState := job.State

	if err := w.store.UpdateJobState(job.ID, newState, nil, nil); err != nil {
		w.logger.Error("failed to transition job state",
			"error", err, "job_id", job.ID, "from", prevState, "to", newState)
		return
	}

	w.fireWebhook(job, newState, prevState, nil, nil)
	job.State = newState
}

// handleExecutionError handles errors from the Ollama client during job execution.
func (w *Worker) handleExecutionError(job store.Job, err error) {
	var connErr *ollama.ConnectionError
	if errors.As(err, &connErr) {
		// Connection error — retryable.
		w.logger.Warn("job hit connection error, will retry",
			"job_id", job.ID, "error", err, "attempt", job.Attempt)

		if job.Attempt+1 >= job.MaxAttempts {
			errMsg := fmt.Sprintf("connection failed after %d attempts: %v", job.MaxAttempts, err)
			w.failJob(job, &errMsg)
			return
		}

		// Re-queue with incremented attempt.
		if err := w.store.IncrementAttempt(job.ID); err != nil {
			w.logger.Error("failed to increment attempt", "error", err, "job_id", job.ID)
		}
		return
	}

	// Non-connection error (HTTP 4xx/5xx from target) — terminal failure.
	errMsg := fmt.Sprintf("chat execution failed: %v", err)
	w.failJob(job, &errMsg)
}

// failJob transitions a job to failed and notifies waiters.
func (w *Worker) failJob(job store.Job, errMsg *string) {
	if err := w.store.UpdateJobState(job.ID, store.JobStateFailed, nil, errMsg); err != nil {
		w.logger.Error("failed to mark job as failed", "error", err, "job_id", job.ID)
	}

	w.notifier.Complete(job.ID, store.JobStateFailed, nil, errMsg)
	w.fireWebhook(job, store.JobStateFailed, job.State, nil, errMsg)

	w.logger.Warn("job failed", "job_id", job.ID, "error", *errMsg)
}

// fireWebhook sends a webhook event if the job has a webhook URL configured.
func (w *Worker) fireWebhook(job store.Job, state, prevState store.JobState, result json.RawMessage, errMsg *string) {
	if job.StateWebhookURL == nil || *job.StateWebhookURL == "" || w.dispatcher == nil {
		return
	}

	event := webhook.Event{
		JobID:         job.ID,
		State:         string(state),
		PreviousState: string(prevState),
		Timestamp:     time.Now().UTC(),
		Model:         job.Model,
		Attempt:       job.Attempt,
		Result:        result,
		Error:         errMsg,
	}

	// If done, include artifact metadata.
	if state == store.JobStateDone {
		artifacts, err := w.store.GetArtifactsByJob(job.ID)
		if err != nil {
			w.logger.Error("failed to get artifacts for webhook", "error", err, "job_id", job.ID)
		} else {
			metas := make([]webhook.ArtifactMeta, len(artifacts))
			for i, a := range artifacts {
				metas[i] = webhook.ArtifactMeta{
					Name:        a.Name,
					ContentType: a.ContentType,
					Size:        a.Size,
					Data:        a.Data,
				}
			}
			event.Artifacts = webhook.FormatArtifacts(job.ID, metas)
		}
	}

	w.dispatcher.Fire(*job.StateWebhookURL, event)
}

// isModelResident checks whether the given model is currently loaded on the target.
func (w *Worker) isModelResident(model string) bool {
	for _, r := range w.inventory.ResidentModels() {
		if r.Name == model {
			return true
		}
	}
	return false
}