package majordomo

import (
	"fmt"
	"os"
	"strings"
	"sync"
	"time"

	"gitea.stevedudenhoeffer.com/steve/majordomo/health"
	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
)

// Registry owns providers, aliases/tiers, env-DSN scheme factories, the
// model health tracker, and Parse. It is safe for concurrent use.
type Registry struct {
	mu        sync.RWMutex
	providers map[string]llm.Provider
	aliases   map[string]string
	schemes   map[string]SchemeFactory
	// envErrs records LLM_* entries that failed to load so the failure
	// surfaces when (and only when) that provider name is actually used.
	envErrs map[string]error

	tracker   *health.Tracker
	chainCfg  ChainConfig
	envLookup func(string) string
}

// SchemeFactory builds a provider instance from an env DSN. name is the
// registry name the provider will be registered under (e.g. "m1" for
// LLM_M1); dsn carries the scheme, credential, and host.
type SchemeFactory func(name string, dsn DSN) (llm.Provider, error)

// ChainConfig tunes failover-chain execution.
type ChainConfig struct {
	// TransientRetries is the number of immediate same-target retries after
	// a transient error. 0 selects the default (1); negative disables
	// retries.
	TransientRetries int

	// AdvanceOnPermanent, when true, makes the chain advance to the next
	// element on permanent errors other than model-not-found instead of
	// returning immediately. Model-not-found always advances (without
	// penalizing health); auth/malformed errors default to fail-fast
	// because failing over cannot help a bad request.
	AdvanceOnPermanent bool

	// Classify overrides the default error classifier (llm.Classify).
	Classify func(error) llm.ErrorClass
}

// DefaultTransientRetries is the default number of same-target retries
// after a single transient error.
const DefaultTransientRetries = 1

func (c ChainConfig) retries() int {
	switch {
	case c.TransientRetries < 0:
		return 0
	case c.TransientRetries == 0:
		return DefaultTransientRetries
	default:
		return c.TransientRetries
	}
}

func (c ChainConfig) classify(err error) llm.ErrorClass {
	if c.Classify != nil {
		return c.Classify(err)
	}
	return llm.Classify(err)
}

type registryConfig struct {
	health    health.Config
	chain     ChainConfig
	envLookup func(string) string
	environ   func() []string
	skipEnv   bool
}

// RegistryOption configures New.
type RegistryOption func(*registryConfig)

// WithHealthConfig overrides the health tracker configuration
// (thresholds, cooldowns, clock).
func WithHealthConfig(cfg health.Config) RegistryOption {
	return func(rc *registryConfig) { rc.health = cfg }
}

// WithChainConfig overrides failover-chain behavior (retry count,
// permanent-error policy, classifier).
func WithChainConfig(cfg ChainConfig) RegistryOption {
	return func(rc *registryConfig) { rc.chain = cfg }
}

// WithClock injects a clock for the health tracker; tests use a fake clock
// to step through backoff windows deterministically.
func WithClock(clock func() time.Time) RegistryOption {
	return func(rc *registryConfig) { rc.health.Clock = clock }
}

// WithEnvLookup injects the env-var lookup used for lazy LLM_* resolution
// during Parse (defaults to os.Getenv). Tests use this to avoid touching
// the process environment.
func WithEnvLookup(lookup func(string) string) RegistryOption {
	return func(rc *registryConfig) { rc.envLookup = lookup }
}

// WithoutEnvProviders disables the eager LLM_* scan at construction time.
// Lazy per-name resolution during Parse still works (use WithEnvLookup to
// control it in tests).
func WithoutEnvProviders() RegistryOption {
	return func(rc *registryConfig) { rc.skipEnv = true }
}

// New creates a Registry with all built-in providers and scheme factories
// registered, then loads LLM_* env-DSN providers from the process
// environment (unless WithoutEnvProviders is given). Malformed LLM_* entries
// do not fail construction; the error surfaces if that provider name is
// referenced in Parse.
func New(opts ...RegistryOption) *Registry {
	cfg := registryConfig{
		envLookup: os.Getenv,
		environ:   os.Environ,
	}
	for _, opt := range opts {
		opt(&cfg)
	}

	r := &Registry{
		providers: make(map[string]llm.Provider),
		aliases:   make(map[string]string),
		schemes:   make(map[string]SchemeFactory),
		envErrs:   make(map[string]error),
		tracker:   health.NewTracker(cfg.health),
		chainCfg:  cfg.chain,
		envLookup: cfg.envLookup,
	}

	registerBuiltins(r)

	if !cfg.skipEnv {
		env := make(map[string]string)
		for _, kv := range cfg.environ() {
			if k, v, ok := strings.Cut(kv, "="); ok {
				env[k] = v
			}
		}
		// Errors are recorded per-name and surfaced on use; see envErrs.
		_ = r.LoadEnv(env)
	}
	return r
}

// RegisterProvider adds or replaces a provider under its Name().
func (r *Registry) RegisterProvider(p llm.Provider) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.providers[p.Name()] = p
}

// RegisterAlias maps a bare name (no slash) to a spec. The spec may be a
// single target, another alias, or a comma-separated chain; Parse expands
// aliases inline and recursively, with cycle detection.
func (r *Registry) RegisterAlias(name, spec string) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.aliases[name] = spec
}

// RegisterScheme adds or replaces an env-DSN scheme factory, letting
// consumers wire custom provider kinds into LLM_* definitions.
func (r *Registry) RegisterScheme(scheme string, factory SchemeFactory) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.schemes[scheme] = factory
}

// Provider returns the registered provider with the given name, if any.
func (r *Registry) Provider(name string) (llm.Provider, bool) {
	r.mu.RLock()
	defer r.mu.RUnlock()
	p, ok := r.providers[name]
	return p, ok
}

// Health exposes the registry's health tracker (read-mostly; useful for
// diagnostics and tests).
func (r *Registry) Health() *health.Tracker { return r.tracker }

// providerFor resolves a provider name: registered providers first, then a
// recorded env-load error for that name, then lazy LLM_* env resolution
// (go-llm parity: "m5" → env LLM_M5, "my-prov" → LLM_MY_PROV). Providers
// resolved lazily are cached in the registry.
func (r *Registry) providerFor(name string) (llm.Provider, error) {
	r.mu.RLock()
	p, ok := r.providers[name]
	envErr := r.envErrs[name]
	r.mu.RUnlock()
	if ok {
		return p, nil
	}
	if envErr != nil {
		return nil, envErr
	}

	envKey := "LLM_" + strings.ToUpper(strings.ReplaceAll(name, "-", "_"))
	envVal := r.envLookup(envKey)
	if envVal == "" {
		return nil, fmt.Errorf("%w: %q (checked registry and %s env var)", ErrUnknownProvider, name, envKey)
	}
	p, err := r.providerFromDSN(name, envVal)
	if err != nil {
		return nil, fmt.Errorf("parse %s: %w", envKey, err)
	}

	r.mu.Lock()
	defer r.mu.Unlock()
	// Another goroutine may have raced us here; keep the first registration.
	if existing, ok := r.providers[name]; ok {
		return existing, nil
	}
	r.providers[name] = p
	return p, nil
}