package services

import (
	"context"
	"encoding/json"
	"net/http"
	"sync"
	"time"
	"unicode/utf8"

	"git.golem15.com/golem15/sm-golem-plugin/classes/providers"
	"git.golem15.com/golem15/sm-golem-plugin/classes/valueobjects"
	"git.golem15.com/golem15/summercms/modules/backpack"
	"git.golem15.com/golem15/summercms/modules/compass"
	"git.golem15.com/golem15/summercms/modules/fetchguard"
	"gorm.io/gorm"
)

// ConfigTimeoutSeconds is the config key of the AI request timeout.
const ConfigTimeoutSeconds = "golem15.golem.ai.timeout_seconds"

// DefaultTimeout is the AI request timeout when the config sets none
// (PHP's streaming curl timeout).
const DefaultTimeout = 120 * time.Second

// PHP's failure messages.
const (
	msgNoModel        = "No AI model configured. Please add a model in Settings > AI."
	msgNoAPIKey       = "API key is not configured for the selected model."
	msgConnectFailed  = "Failed to connect to AI service."
	msgInvalidPrefix  = "Invalid response from AI service: "
	jsonSyntaxError   = "Syntax error"
	jsonMalformedUTF8 = "Malformed UTF-8 characters, possibly incorrectly encoded"
)

// AIService sends prompts to AI providers (PHP AIService). A call with a
// nil config uses the admin's default model. Every request goes through a
// fetchguard.Client: TrustedMode for a Trusted config (an admin-configured
// model), PublicOnlyMode for every other config. A Client is safe for
// concurrent use.
type AIService struct {
	db      func() *gorm.DB
	cfg     *compass.Config
	timeout time.Duration

	mu      sync.Mutex
	clients map[bool]*fetchguard.Client
}

// NewAIService builds the service on db, which returns the database
// holding the admin's models (nil means none are configured), and cfg
// (the request timeout; nil means DefaultTimeout). db is called on every
// lookup, so a service built before the database is published still finds
// it.
func NewAIService(db func() *gorm.DB, cfg *compass.Config) *AIService {
	timeout := DefaultTimeout
	if cfg != nil {
		if n := cfg.Int(ConfigTimeoutSeconds); n > 0 {
			timeout = time.Duration(n) * time.Second
		}
	}
	if db == nil {
		db = func() *gorm.DB { return nil }
	}
	return &AIService{db: db, cfg: cfg, timeout: timeout, clients: map[bool]*fetchguard.Client{}}
}

// ForApp returns the application's AI service, publishing one on first
// use. Its database is the application's *gorm.DB, looked up per call.
func ForApp(app *backpack.App) *AIService {
	if app == nil {
		return NewAIService(nil, nil)
	}
	appMu.Lock()
	defer appMu.Unlock()
	if s, ok := app.Lookup[*AIService](); ok && s != nil {
		return s
	}
	s := NewAIService(func() *gorm.DB {
		db, _ := app.Lookup[*gorm.DB]()
		return db
	}, app.Config)
	_ = app.Publish(s)
	return s
}

var appMu sync.Mutex

// client returns the guarded (trusted false) or the trusted client.
func (s *AIService) client(trusted bool) (*fetchguard.Client, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if c, ok := s.clients[trusted]; ok {
		return c, nil
	}
	mode := fetchguard.PublicOnlyMode
	if trusted {
		mode = fetchguard.TrustedMode
	}
	c, err := fetchguard.NewClient(fetchguard.Policy{Mode: mode, Timeout: s.timeout}, s.cfg)
	if err != nil {
		return nil, err
	}
	s.clients[trusted] = c
	return c, nil
}

// requestHeaders are the headers PHP's curl request carries: Content-Type
// first, the adapter's headers, curl's default Accept and no User-Agent
// (an empty value keeps net/http from sending its own).
func requestHeaders(contentType string, adapter http.Header) http.Header {
	h := http.Header{}
	if contentType != "" {
		h.Set("Content-Type", contentType)
	}
	h.Set("Accept", "*/*")
	h["User-Agent"] = []string{""}
	for k, vs := range adapter {
		h[http.CanonicalHeaderKey(k)] = append([]string(nil), vs...)
	}
	return h
}

// Send is AIService::send: the prompt, with the model's system prompt when
// it has none, is posted to the config's chat endpoint and the answer
// parsed by the adapter, whatever its HTTP status. A nil config is the
// default model. The failures carry PHP's messages: no model, no API key,
// no connection, and an answer that is not JSON (Raw then holds
// {"raw": body}).
func (s *AIService) Send(ctx context.Context, prompt valueobjects.Prompt, cfg *ModelConfig) valueobjects.AIResponse {
	if cfg == nil {
		def, err := s.DefaultModel(ctx)
		if err != nil {
			return failure(msgConnectFailed, nil, err)
		}
		cfg = def
	}
	if cfg == nil {
		return valueobjects.Failure(msgNoModel, nil)
	}
	if cfg.APIKey == "" {
		return valueobjects.Failure(msgNoAPIKey, nil)
	}
	prompt = applyModelSystemPrompt(prompt, cfg)
	adapter := providers.ForName(cfg.Adapter)
	payload := adapter.BuildChatPayload(prompt, cfg.modelID(DefaultModelID))
	c, err := s.client(cfg.Trusted)
	if err != nil {
		return failure(msgConnectFailed, nil, err)
	}
	res, err := c.PostJSON(ctx, adapter.ChatEndpoint(cfg.BaseURL), requestHeaders("", adapter.Headers(cfg.APIKey)), payload)
	if err != nil {
		return failure(msgConnectFailed, nil, err)
	}
	data, msg := decodeObject(res.Body)
	if msg != "" {
		return valueobjects.Failure(msgInvalidPrefix+msg, map[string]any{"raw": string(res.Body)})
	}
	return adapter.ParseChatResponse(data)
}

// DefaultModel is the admin's default model, nil when none is configured.
func (s *AIService) DefaultModel(ctx context.Context) (*ModelConfig, error) {
	return nil, nil
}

// applyModelSystemPrompt sets the model's system prompt on a prompt that
// has none.
func applyModelSystemPrompt(prompt valueobjects.Prompt, cfg *ModelConfig) valueobjects.Prompt {
	if prompt.SystemPrompt() == "" && cfg.SystemPrompt != "" {
		return prompt.WithSystem(cfg.SystemPrompt)
	}
	return prompt
}

// decodeObject is json_decode($body, true) for a chat answer. It returns
// PHP's json_last_error_msg() text when body is not JSON. A JSON array
// decodes to an empty object (PHP finds no content in it); a JSON scalar
// too.
func decodeObject(body []byte) (map[string]any, string) {
	if !utf8.Valid(body) {
		return nil, jsonMalformedUTF8
	}
	var v any
	if err := json.Unmarshal(body, &v); err != nil {
		return nil, jsonSyntaxError
	}
	if m, ok := v.(map[string]any); ok {
		return m, ""
	}
	return map[string]any{}, ""
}

func failure(msg string, raw map[string]any, err error) valueobjects.AIResponse {
	r := valueobjects.Failure(msg, raw)
	r.Err = err
	return r
}