// 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 (
	"fmt"
	"os"
	"path/filepath"

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

// Core owns the running configuration and adapters.
type Core struct {
	cfg       *config.Config
	vm        *lua.VM
	store     *config.Store
	scheduler *scheduler.Scheduler
	registry  *provider.Registry
}

// 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))
	if err := c.rebuildRegistry(); err != nil {
		return nil, err
	}
	return c, nil
}

func buildRetries(cfg *config.Config) int {
	return len(cfg.Sources) // allow fallback across all 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 }

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 }

// Config exposes the underlying configuration (read-only usage).
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
			out = append(out, byName[n])
		}
	}
	return out
}

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)
	}
	return nil
}

// Reload re-reads the runtime store and rebuilds sources (adapter reload is not
// strictly needed since adapters are loaded into the VM at startup; uploaded
// adapters are placed in the adapter dir and loaded by the web UI).
func (c *Core) Reload() error {
	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() }

// UploadAdapter saves a new Lua adapter script to the adapter dir and loads it.
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
	}
	if err := c.vm.LoadAdapter(path); err != nil {
		return fmt.Errorf("load adapter: %w", err)
	}
	return nil
}

// RemoveAdapter deletes an adapter script and evicts it from the VM.
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 {
	if err := normalizeSource(&src); err != nil {
		return err
	}
	if err := c.store.Upsert(src); err != nil {
		return err
	}
	return c.rebuildRegistry()
}

func (c *Core) RemoveSource(name string) error {
	if _, err := c.store.Remove(name); err != nil {
		return err
	}
	return c.rebuildRegistry()
}

func (c *Core) Sources() []config.Source { 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()
	}
}