package ollama

import (
	"context"
	"log/slog"
	"sync"
	"time"
)

// ModelInventory maintains an in-memory cache of the Ollama target's installed
// and running models, refreshed by a background poller.
//
// Why: foreman needs a reasonably fresh view of installed models for validation,
// passthrough, and scheduling without hitting the target on every request.
// What: wraps a mutex-protected model list updated by a polling goroutine.
// Test: create with a stub client, poll, verify Models()/HasModel()/Degraded().
type ModelInventory struct {
	client Client
	logger *slog.Logger

	mu             sync.RWMutex
	models         []ModelInfo
	runningModels  []RunningModel
	lastPoll       time.Time
	degraded       bool
}

// NewModelInventory creates a new ModelInventory backed by the given client.
//
// Why: separates construction from the poll loop so callers can control lifecycle.
// What: returns an inventory ready for polling; call Start to begin the background loop.
// Test: create, call Refresh manually, assert Models() is populated.
func NewModelInventory(client Client, logger *slog.Logger) *ModelInventory {
	return &ModelInventory{
		client: client,
		logger: logger,
	}
}

// Models returns the current known model list.
//
// Why: the /api/tags handler and model validation need the cached list.
// What: returns a copy of the model slice under a read lock.
// Test: Refresh, call Models(), verify the returned slice matches.
func (inv *ModelInventory) Models() []ModelInfo {
	inv.mu.RLock()
	defer inv.mu.RUnlock()
	out := make([]ModelInfo, len(inv.models))
	copy(out, inv.models)
	return out
}

// HasModel checks whether a model name is in the current inventory.
//
// Why: job submission validates the model name before queuing.
// What: scans the model list for an exact name match.
// Test: Refresh with known models, assert HasModel returns true/false correctly.
func (inv *ModelInventory) HasModel(name string) bool {
	inv.mu.RLock()
	defer inv.mu.RUnlock()
	for _, m := range inv.models {
		if m.Name == name {
			return true
		}
	}
	return false
}

// ResidentModels returns the list of currently-loaded models from the last /api/ps poll.
//
// Why: the scheduler (Phase 3) uses this to decide if a model swap is needed.
// What: returns a copy of the running model slice under a read lock.
// Test: Refresh, call ResidentModels(), verify it matches /api/ps output.
func (inv *ModelInventory) ResidentModels() []RunningModel {
	inv.mu.RLock()
	defer inv.mu.RUnlock()
	out := make([]RunningModel, len(inv.runningModels))
	copy(out, inv.runningModels)
	return out
}

// LastPoll returns the timestamp of the most recent successful poll.
//
// Why: health/diagnostics use this to judge staleness.
// What: returns the lastPoll time under a read lock.
// Test: Refresh, assert LastPoll is non-zero and recent.
func (inv *ModelInventory) LastPoll() time.Time {
	inv.mu.RLock()
	defer inv.mu.RUnlock()
	return inv.lastPoll
}

// Degraded reports whether the target was unreachable on the last poll attempt.
//
// Why: the /healthz endpoint surfaces this to operators and probes.
// What: returns the degraded flag under a read lock.
// Test: Refresh with an unreachable stub, assert Degraded() is true; then with a
// reachable stub, assert it clears.
func (inv *ModelInventory) Degraded() bool {
	inv.mu.RLock()
	defer inv.mu.RUnlock()
	return inv.degraded
}

// Refresh performs an immediate poll of /api/tags and /api/ps on the target.
//
// Why: called by the poller goroutine and on-demand (e.g., model-miss re-check).
// What: fetches tags and ps, updates the cached lists, clears or sets the degraded
// flag based on success/failure.
// Test: stub both endpoints, call Refresh, verify Models() and ResidentModels() match.
func (inv *ModelInventory) Refresh(ctx context.Context) error {
	tags, tagsErr := inv.client.Tags(ctx)
	ps, psErr := inv.client.Ps(ctx)

	inv.mu.Lock()
	defer inv.mu.Unlock()

	if tagsErr != nil {
		inv.degraded = true
		inv.logger.Warn("model poll failed: tags",
			"error", tagsErr,
			"retained_models", len(inv.models),
		)
		return tagsErr
	}

	// Tags succeeded — update model list and clear degraded.
	inv.models = tags.Models
	inv.lastPoll = time.Now()
	inv.degraded = false

	if psErr != nil {
		// Tags worked but ps failed — log but don't mark degraded for ps alone.
		inv.logger.Warn("model poll partial: ps failed", "error", psErr)
	} else {
		inv.runningModels = ps.Models
	}

	return nil
}

// Start begins the background polling loop. It blocks until ctx is cancelled.
// Call this in a goroutine.
//
// Why: continuous polling keeps the model inventory fresh for validation and scheduling.
// What: polls at the given interval, respecting context cancellation for clean shutdown.
// Test: start with a short interval and cancelled context, verify it exits cleanly.
func (inv *ModelInventory) Start(ctx context.Context, interval time.Duration) {
	// Do an initial poll immediately.
	if err := inv.Refresh(ctx); err != nil {
		inv.logger.Warn("initial model poll failed", "error", err)
	}

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			if err := inv.Refresh(ctx); err != nil {
				inv.logger.Warn("periodic model poll failed", "error", err)
			}
		}
	}
}