// Package core wires together the Lua VM, provider registry, scheduler and
// runtime store and exposes management operations (hot reload, adapters,
// sources) for the web UI and gateway.
package core

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"llmsproxy/internal/config"
	"llmsproxy/internal/lua"
	"llmsproxy/internal/provider"
	"llmsproxy/internal/scheduler"
)

// Core owns the running configuration and adapters. mu guards every read and
// write of c.cfg (keys / sources / auto rules) from the management API while
// request paths look keys up concurrently; the AUTO chain itself is swapped
// atomically and needs no lock.
type Core struct {
	mu        sync.Mutex
	cfg       *config.Config
	vm        *lua.VM
	store     *config.Store
	scheduler *scheduler.Scheduler
	registry  *provider.Registry
	autoChain atomic.Pointer[scheduler.Chain]
}

// New builds the core from a config file plus runtime overlay.
func New(cfgPath string) (*Core, error) {
	cfg, err := config.Load(cfgPath)
	if err != nil {
		return nil, err
	}
	return NewFromConfig(cfg)
}

// NewFromConfig builds the core from an already-loaded config.
func NewFromConfig(cfg *config.Config) (*Core, error) {
	c := &Core{cfg: cfg}
	c.vm = lua.NewVM(cfg.AdapterDir)
	if err := c.vm.Start(); err != nil {
		return nil, fmt.Errorf("lua vm: %w", err)
	}
	c.store = config.NewStore(cfg.RuntimeFile)
	if err := c.store.Load(); err != nil {
		return nil, fmt.Errorf("runtime store: %w", err)
	}
	c.scheduler = scheduler.New(buildRetries(cfg))
	// One-time migration: lift auto rules and keys from legacy runtime.json
	// into config.yaml so all configuration lives in one place.
	c.migrateFromRuntime()
	if err := c.seedKeys(); err != nil {
		return nil, err
	}
	if err := c.seedAuto(); err != nil {
		return nil, err
	}
	if err := c.rebuildRegistry(); err != nil {
		return nil, err
	}
	return c, nil
}

// migrateFromRuntime lifts auto rules and keys from legacy runtime.json into
// c.cfg — but only if they are not already present in the YAML config. This
// lets people upgrade without losing their data; once migrated, the YAML file
// is authoritative and runtime.json's auto/keys are ignored.
func (c *Core) migrateFromRuntime() {
	legacy := c.store.LoadLegacy()
	if legacy == nil {
		return
	}
	changed := false
	if len(legacy.Auto) > 0 && len(c.cfg.Auto) == 0 {
		c.cfg.Auto = legacy.Auto
		changed = true
	}
	if len(legacy.Keys) > 0 && len(c.cfg.Keys) == 0 {
		c.cfg.Keys = legacy.Keys
		changed = true
	}
	if changed {
		if err := c.cfg.Save(); err != nil {
			fmt.Printf("[core] migrate to config.yaml: %v\n", err)
		}
	}
}

// seedAuto uses the existing auto rules from config.yaml, or creates an
// initial chain from legacy per-source model priority (first run only).
func (c *Core) seedAuto() error {
	if len(c.cfg.Auto) > 0 {
		return nil
	}
	type item struct {
		model string
		prio  int
	}
	var flat []item
	for _, s := range c.mergedSources() {
		for _, m := range s.Models {
			if m.Kind == "image" {
				continue
			}
			flat = append(flat, item{m.ID, m.Priority})
		}
	}
	sort.SliceStable(flat, func(i, j int) bool {
		if flat[i].prio != flat[j].prio {
			return flat[i].prio > flat[j].prio
		}
		return flat[i].model < flat[j].model
	})
	entries := make([]config.ModelScope, 0, len(flat))
	for _, it := range flat {
		entries = append(entries, config.ModelScope{Model: it.model})
	}
	c.cfg.Auto = entries
	return c.cfg.Save()
}

// seedKeys ensures config.yaml has admin keys for every gateway_keys entry
// from the YAML config (once). After first save they become GWKey records
// in c.cfg.Keys and gateway_keys is no longer read for auth.
func (c *Core) seedKeys() error {
	existing := map[string]bool{}
	for _, k := range c.cfg.Keys {
		existing[k.Key] = true
	}
	changed := false
	for i, raw := range c.cfg.GatewayKeys {
		if raw == "" || existing[raw] {
			continue
		}
		name := "admin"
		if i > 0 {
			name = fmt.Sprintf("admin-%d", i+1)
		}
		c.cfg.Keys = append(c.cfg.Keys, config.GWKey{
			Key:       raw,
			Role:      "admin",
			Name:      name,
			CreatedAt: time.Now().Unix(),
			Seed:      true,
		})
		changed = true
	}
	if changed {
		return c.cfg.Save()
	}
	return nil
}

// saveConfig writes the current config (including auto rules and keys) back
// to config.yaml.
func (c *Core) saveConfig() error {
	return c.cfg.Save()
}

func buildRetries(cfg *config.Config) int {
	return len(cfg.Sources)
}

// VM exposes the Lua adapter runtime.
func (c *Core) VM() *lua.VM { return c.vm }

func (c *Core) Scheduler() *scheduler.Scheduler { return c.scheduler }

func (c *Core) Registry() *provider.Registry { return c.registry }

// AutoChain returns the current AUTO scheduling chain.
func (c *Core) AutoChain() *scheduler.Chain { return c.autoChain.Load() }

func (c *Core) DefaultModel() string { return c.cfg.DefaultModel }

func (c *Core) GatewayKeys() []string { return c.cfg.GatewayKeys }

func (c *Core) Listen() string { return c.cfg.Listen }

func (c *Core) TLS() (cert, key string) {
	return c.cfg.TLSCertFile, c.cfg.TLSKeyFile
}

func (c *Core) PublicBaseURL() string { return c.cfg.PublicBaseURL }

// ---- gateway key management (web UI) ----

// ListKeys returns all gateway keys (admin view).
func (c *Core) ListKeys() []config.GWKey {
	c.mu.Lock()
	defer c.mu.Unlock()
	out := make([]config.GWKey, len(c.cfg.Keys))
	copy(out, c.cfg.Keys)
	return out
}

// FindKey looks up a gateway key record by its secret value.
func (c *Core) FindKey(key string) (config.GWKey, bool) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for _, k := range c.cfg.Keys {
		if k.Key == key {
			return k, true
		}
	}
	return config.GWKey{}, false
}

// CreateKey builds a new random gateway key and persists it to config.yaml.
func (c *Core) CreateKey(name, role string, models []config.ModelScope, note string) (config.GWKey, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	models = cleanScopes(models)
	key := make([]byte, 16)
	if _, err := rand.Read(key); err != nil {
		return config.GWKey{}, err
	}
	rec := config.GWKey{
		Key:       "sk-gw-" + hex.EncodeToString(key),
		Role:      role,
		Name:      name,
		Models:    models,
		Note:      note,
		CreatedAt: time.Now().Unix(),
	}
	if rec.Role == "" {
		rec.Role = "user"
	}
	c.cfg.Keys = append(c.cfg.Keys, rec)
	if err := c.saveConfig(); err != nil {
		return config.GWKey{}, err
	}
	return rec, nil
}

// UpdateKey mutates a key's name/role/model scope and persists it.
func (c *Core) UpdateKey(key, name, role string, models []config.ModelScope, note string) (config.GWKey, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for i, k := range c.cfg.Keys {
		if k.Key == key {
			if name != "" {
				c.cfg.Keys[i].Name = name
			}
			if role == "admin" || role == "user" {
				c.cfg.Keys[i].Role = role
			}
			// models == nil means the caller did not provide a scope (leave
			// the existing one untouched); an explicit [] clears it.
			if models != nil {
				c.cfg.Keys[i].Models = cleanScopes(models)
			}
			c.cfg.Keys[i].Note = note
			if err := c.saveConfig(); err != nil {
				return config.GWKey{}, err
			}
			return c.cfg.Keys[i], nil
		}
	}
	return config.GWKey{}, fmt.Errorf("key not found")
}

// DeleteKey removes a key record; returns false if it did not exist.
func (c *Core) DeleteKey(key string) (bool, error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for i, k := range c.cfg.Keys {
		if k.Key == key {
			c.cfg.Keys = append(c.cfg.Keys[:i], c.cfg.Keys[i+1:]...)
			return true, c.saveConfig()
		}
	}
	return false, nil
}

// ---- AUTO scheduling slots (web UI) ----

// AutoRules returns the AUTO scheduling slots in priority order.
func (c *Core) AutoRules() []config.ModelScope {
	c.mu.Lock()
	defer c.mu.Unlock()
	out := make([]config.ModelScope, len(c.cfg.Auto))
	copy(out, c.cfg.Auto)
	return out
}

// cleanScopes drops empty model entries and normalizes placeholder source
// names; it returns nil when no entries survive so an empty scope means
// "unrestricted" (nil) instead of a restrictive-but-empty list — a non-nil
// empty slice would 403 every model in-process yet become unrestricted again
// after a restart (config omits empty models with omitempty).
func cleanScopes(entries []config.ModelScope) []config.ModelScope {
	var clean []config.ModelScope
	for _, e := range entries {
		if e.Model == "" {
			continue
		}
		if e.Source == "undefined" || e.Source == "null" {
			e.Source = ""
		}
		clean = append(clean, e)
	}
	return clean
}

// SaveAutoRules persists the AUTO scheduling slots to config.yaml, rebuilds
// the chain and clears the cooldown of every slot — preference scores are
// kept, so a reliably good model keeps its edge while an edited chain applies
// immediately.
func (c *Core) SaveAutoRules(entries []config.ModelScope) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.cfg.Auto = cleanScopes(entries)
	if err := c.saveConfig(); err != nil {
		return err
	}
	c.buildAutoChain()
	if ch := c.autoChain.Load(); ch != nil {
		for _, tn := range ch.Tiers {
			for _, sl := range tn.Slots {
				if p := c.registry.ProviderForSlot(sl.Model, sl.Source); p != nil {
					p.ResetModelCooldown(sl.Model)
				}
			}
		}
	}
	return nil
}

// ResetHealth clears the scheduling backoff state of every provider.
func (c *Core) ResetHealth() {
	for _, p := range c.registry.Providers() {
		p.ResetHealth()
	}
}

func (c *Core) ProviderForModel(model string) *provider.Provider {
	return c.registry.ProviderForModel(model)
}

func (c *Core) ProviderForSlot(model, source string) *provider.Provider {
	return c.registry.ProviderForSlot(model, source)
}

func (c *Core) Config() *config.Config { return c.cfg }

// mergedSources = base YAML sources + runtime sources (runtime wins by name).
func (c *Core) mergedSources() []config.Source {
	byName := map[string]config.Source{}
	order := []string{}
	for _, s := range c.cfg.Sources {
		byName[s.Name] = s
		order = append(order, s.Name)
	}
	for _, s := range c.store.List() {
		if _, ok := byName[s.Name]; !ok {
			order = append(order, s.Name)
		}
		byName[s.Name] = s
	}
	out := make([]config.Source, 0, len(order))
	seen := map[string]bool{}
	for _, n := range order {
		if !seen[n] {
			seen[n] = true
			s := c.resolveSourceKey(byName[n])
			if s.Timeout == 0 {
				s.Timeout = config.DefaultSourceTimeout
			}
			if s.QueueTimeout == 0 {
				s.QueueTimeout = config.DefaultSourceQueueTimeout
			}
			if s.MaxConcurrent == 0 {
				s.MaxConcurrent = config.DefaultSourceConcurrency
			}
			out = append(out, s)
		}
	}
	return out
}

// resolveSourceKey applies api_key_env and decrypts enc:v1: ciphertext.
func (c *Core) resolveSourceKey(s config.Source) config.Source {
	if s.APIKeyEnv != "" {
		if v := os.Getenv(s.APIKeyEnv); v != "" {
			s.APIKey = v
		}
		return s
	}
	if box := c.store.SecretBox(); box != nil && strings.HasPrefix(s.APIKey, "enc:v1:") {
		s.APIKey = box.MustDecrypt(s.APIKey)
	}
	return s
}

func (c *Core) rebuildRegistry() error {
	srcs := c.mergedSources()
	providers := make([]*provider.Provider, 0, len(srcs))
	adapterConcurrency := map[string]int{}
	for _, s := range srcs {
		providers = append(providers, provider.New(s, c.vm))
		if s.Adapter != "" {
			adapterConcurrency[s.Adapter] += s.MaxConcurrent
		}
	}
	c.vm.ConfigureConcurrency(adapterConcurrency)
	if c.registry == nil {
		c.registry = provider.NewRegistry(providers, c.cfg.DefaultModel)
	} else {
		c.registry.Replace(providers)
	}
	c.buildAutoChain()
	return nil
}

// buildAutoChain rebuilds the AUTO chain snapshot from config.yaml rules
// against the current providers. Slot model ids are normalized to the exact
// configured spelling (case-insensitive match), otherwise ModelFor would fall
// back to the source's best chat model and cooldown/quota bookkeeping would
// key on a name that never matches.
func (c *Core) buildAutoChain() {
	prov := func(model, source string) scheduler.Provider {
		p := c.registry.ProviderForSlot(model, source)
		if p == nil {
			return nil
		}
		if m := p.ModelByID(model); m != nil && m.Kind == "image" {
			return nil
		}
		return p
	}
	rules := c.cfg.Auto
	sr := make([]scheduler.Rule, 0, len(rules))
	for _, e := range rules {
		model, source := e.Model, e.Source
		if p := c.registry.ProviderForSlot(e.Model, e.Source); p != nil {
			if exact := p.ModelIDFold(e.Model); exact != "" {
				model = exact
			}
			if m := p.ModelByID(model); m != nil && m.Kind == "image" {
				continue // image-kind models never join the chat AUTO chain
			}
			if source == "" {
				source = p.Name()
			}
		}
		sr = append(sr, scheduler.Rule{
			Model:  model,
			Source: source,
			Tier:   e.Tier,
			Quota:  e.TokenQuota,
			Period: e.Period,
			Hours:  e.Hours,
		})
	}
	c.autoChain.Store(scheduler.BuildChain(sr, prov))
}

// AutoSlotState is the UI-facing health snapshot of one AUTO chain slot.
type AutoSlotState struct {
	Model         string `json:"model"`
	Source        string `json:"source"`
	Pref          int64  `json:"pref"`
	FailCount     int64  `json:"fail_count"`
	CooldownUntil int64  `json:"cooldown_until"`
	Cooling       bool   `json:"cooling"`
}

// AutoSlotStates returns per-slot health for every slot of the current chain.
func (c *Core) AutoSlotStates() []AutoSlotState {
	ch := c.autoChain.Load()
	if ch == nil {
		return nil
	}
	now := time.Now().Unix()
	var out []AutoSlotState
	for _, tn := range ch.Tiers {
		for _, sl := range tn.Slots {
			pp, ok := sl.Prov.(*provider.Provider)
			if !ok {
				continue
			}
			pref, fail, until := pp.ModelHealthInfo(sl.Model)
			out = append(out, AutoSlotState{
				Model:         sl.Model,
				Source:        sl.Source,
				Pref:          pref,
				FailCount:     fail,
				CooldownUntil: until,
				Cooling:       until > now,
			})
		}
	}
	return out
}

// Reload re-reads the runtime store and rebuilds sources.
func (c *Core) Reload() error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if err := c.store.Load(); err != nil {
		return err
	}
	return c.rebuildRegistry()
}

// ---- adapter management (web UI) ----

func (c *Core) ListAdapters() []lua.APIAdapter {
	return c.vm.ListAdapters()
}

func (c *Core) UploadAdapter(name, code string) error {
	if name == "" {
		return fmt.Errorf("adapter name required")
	}
	if err := os.MkdirAll(c.cfg.AdapterDir, 0755); err != nil {
		return err
	}
	path := filepath.Join(c.cfg.AdapterDir, name+".lua")
	if err := os.WriteFile(path, []byte(code), 0644); err != nil {
		return err
	}
	return c.vm.LoadAdapter(path)
}

func (c *Core) RemoveAdapter(name string) error {
	path := filepath.Join(c.cfg.AdapterDir, name+".lua")
	_ = os.Remove(path)
	c.vm.RemoveAdapter(name)
	return nil
}

// ---- source management (web UI) ----

func (c *Core) AddSource(src config.Source) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if err := normalizeSource(&src); err != nil {
		return err
	}
	if err := config.UpsertSourceInYAML(c.cfg.Path, src.Name, src); err != nil {
		return err
	}
	// Update in-memory Sources so mergedSources() finds the entry.
	replaced := false
	for i, s := range c.cfg.Sources {
		if s.Name == src.Name {
			c.cfg.Sources[i] = src
			replaced = true
			break
		}
	}
	if !replaced {
		c.cfg.Sources = append(c.cfg.Sources, src)
	}
	return c.rebuildRegistry()
}

func (c *Core) RemoveSource(name string) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	for _, s := range c.cfg.Sources {
		if s.Name == name {
			if err := config.RemoveSourceFromYAML(c.cfg.Path, name); err != nil {
				return err
			}
			c.cfg.Sources = c.removeCfgSource(name)
			break
		}
	}
	if _, err := c.store.Remove(name); err != nil {
		return err
	}
	return c.rebuildRegistry()
}

func (c *Core) removeCfgSource(name string) []config.Source {
	out := c.cfg.Sources[:0]
	for _, s := range c.cfg.Sources {
		if s.Name != name {
			out = append(out, s)
		}
	}
	return out
}

func (c *Core) Sources() []config.Source {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.mergedSources()
}

func normalizeSource(s *config.Source) error {
	if s.Name == "" || s.BaseURL == "" {
		return fmt.Errorf("source requires name and base_url")
	}
	if len(s.Models) == 0 {
		return fmt.Errorf("source requires at least one model")
	}
	if s.Adapter == "" {
		s.Adapter = "openai"
	}
	if s.MaxConcurrent == 0 {
		s.MaxConcurrent = 8
	}
	return nil
}

// Close releases resources.
func (c *Core) Close() {
	if c.vm != nil {
		c.vm.Stop()
	}
}