package model

import (
	"errors"
	"fmt"
	"log/slog"
	"strings"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/config"
)

// Provider names accepted by the provider-aware factory. These are the only two
// protocols the factory understands today; adding a vendor means adding a case
// here plus a matching adapter, not touching the rest of the package.
const (
	// ProviderOpenAI selects the OpenAI-compatible /chat/completions protocol.
	ProviderOpenAI = "openai"
	// ProviderAnthropic selects the Anthropic Messages /v1/messages protocol.
	ProviderAnthropic = "anthropic"
)

// ErrUnknownProvider is returned by the provider-aware factory when the
// configured provider name is not recognized.
var ErrUnknownProvider = errors.New("model: unknown provider")

// NewChatAdapter builds a single provider adapter selected by cfg.Provider. The
// empty provider defaults to openai for backward compatibility. An unrecognized
// provider returns ErrUnknownProvider.
func NewChatAdapter(cfg config.LLMConfig) (Adapter, error) {
	switch cfg.Provider {
	case ProviderOpenAI, "":
		return NewOpenAIChat(cfg), nil
	case ProviderAnthropic:
		return NewAnthropicChat(cfg), nil
	default:
		return nil, fmt.Errorf("model: %w: provider %q", ErrUnknownProvider, cfg.Provider)
	}
}

// NewChatChain builds a fallback Chain for the configured provider: the primary
// model first, then the provider's fallback model when set and distinct. Each
// step is served by an adapter of the selected protocol. The empty provider
// defaults to openai. An unrecognized provider returns ErrUnknownProvider.
func NewChatChain(cfg config.LLMConfig) (*Chain, error) {
	return NewChatChainWithLog(cfg, nil)
}

// NewChatChainWithLog is NewChatChain with a logger attached to every adapter it
// builds, so a provider-level reasoning decision (a thinking budget raised to fit
// max_tokens, a reasoning_effort value downgraded or ignored) is reported with
// its module source. A nil logger leaves the adapters' discard default in place.
//
// It is also the only builder that appends the optional local third rung
// (裁决 03.4.3, primary → fallback → local), because that rung may speak a
// different protocol than the active group and therefore needs the raw logger to
// build its own adapter. It is appended only when the local rung is enabled AND
// fully configured; otherwise the chain keeps its two-level shape and the reason
// is reported.
func NewChatChainWithLog(cfg config.LLMConfig, log *slog.Logger) (*Chain, error) {
	var chain *Chain
	var err error
	switch cfg.Provider {
	case ProviderOpenAI, "":
		chain, err = newOpenAIChain(cfg, WithOpenAILogger(log))
	case ProviderAnthropic:
		chain, err = newAnthropicChain(cfg, WithAnthropicLogger(log))
	default:
		return nil, fmt.Errorf("model: %w: provider %q", ErrUnknownProvider, cfg.Provider)
	}
	if err != nil {
		return nil, err
	}
	if step, ok := localChainStep(cfg, log); ok {
		chain.steps = append(chain.steps, step)
	}
	return chain, nil
}

// localChainStep builds the local third degradation rung as a chain step. It
// returns ok=false (and, when the rung was asked for but is incomplete, a WARN
// naming the missing field) when the rung is off, unconfigured or its provider is
// unknown — a half-configured step would only ever fail, which is worse than not
// having it.
func localChainStep(cfg config.LLMConfig, log *slog.Logger) (Step, bool) {
	local := cfg.Local
	// Configured() already requires Enabled, so the rung is off by default and a
	// disabled rung can never become a chain step. The warning is emitted only
	// when the rung was actually asked for but is incomplete.
	if !local.Configured() {
		if local.Enabled {
			warn(log, "local model rung enabled but not configured; skipping it",
				"base_url_set", strings.TrimSpace(local.BaseURL) != "",
				"model_set", strings.TrimSpace(local.Model) != "")
		}
		return Step{}, false
	}
	localCfg := config.LLMConfig{
		Provider: local.Provider,
		BaseURL:  local.BaseURL,
		APIKey:   local.APIKey,
		Model:    local.Model,
	}
	switch local.Provider {
	case ProviderAnthropic:
		return Step{Model: local.Model, Adapter: NewAnthropicChat(localCfg, WithAnthropicLogger(log))}, true
	case ProviderOpenAI, "":
		return Step{Model: local.Model, Adapter: NewOpenAIChat(localCfg, WithOpenAILogger(log))}, true
	default:
		warn(log, "local model rung skipped: unknown provider",
			"provider", local.Provider, "field", "LLM_LOCAL_PROVIDER")
		return Step{}, false
	}
}

// newOpenAIChain builds a fallback chain from the OpenAI-compatible config block.
// Each step is an OpenAIChatAdapter against the configured endpoint.
func newOpenAIChain(cfg config.LLMConfig, opts ...OpenAIOption) (*Chain, error) {
	if cfg.BaseURL == "" || cfg.Model == "" {
		return nil, ErrNoModel
	}
	steps := []Step{{Model: cfg.Model, Adapter: NewOpenAIChat(cfg, opts...)}}
	if cfg.Fallback != "" && cfg.Fallback != cfg.Model {
		steps = append(steps, Step{Model: cfg.Fallback, Adapter: NewOpenAIChat(cfg, opts...)})
	}
	return NewChain(steps...), nil
}

// newAnthropicChain builds a fallback chain from the Anthropic config block. Each
// step is an AnthropicChatAdapter against the configured /v1/messages endpoint.
func newAnthropicChain(cfg config.LLMConfig, opts ...AnthropicOption) (*Chain, error) {
	if cfg.AnthropicBaseURL == "" || cfg.AnthropicModel == "" {
		return nil, ErrNoModel
	}
	steps := []Step{{Model: cfg.AnthropicModel, Adapter: NewAnthropicChat(cfg, opts...)}}
	if cfg.AnthropicFallback != "" && cfg.AnthropicFallback != cfg.AnthropicModel {
		steps = append(steps, Step{Model: cfg.AnthropicFallback, Adapter: NewAnthropicChat(cfg, opts...)})
	}
	return NewChain(steps...), nil
}

// DefaultModelForProvider returns the primary model name for the configured
// provider: the flat OpenAI Model for "openai", the Anthropic model for
// "anthropic". Used by callers (e.g. cmd/cyrene) to seed a Router's default.
func DefaultModelForProvider(cfg config.LLMConfig) string {
	if cfg.Provider == ProviderAnthropic {
		return cfg.AnthropicModel
	}
	return cfg.Model
}

// warn reports through the injected logger, falling back to a discard logger that
// still carries the module source so an unsourced record can never be emitted
// (project rule §10). It exists because a chain may be built without a logger
// (NewChatChain) while a skipped rung must still be reported.
func warn(log *slog.Logger, msg string, args ...any) {
	if log == nil {
		log = discardLogger("model")
	}
	log.Warn(msg, args...)
}