package config

import (
	"fmt"
	"log/slog"
	"os"
	"strconv"
	"strings"
	"time"

	"git.warky.dev/wdevs/amcs/internal/buildinfo"
	"gopkg.in/yaml.v3"
)

func Load(explicitPath string) (*Config, string, error) {
	return LoadWithLogger(explicitPath, nil)
}

// LoadWithLogger is Load with a logger surface for migration notices. Passing
// nil is fine — migration events will simply not be logged.
func LoadWithLogger(explicitPath string, log *slog.Logger) (*Config, string, error) {
	path := ResolvePath(explicitPath)

	data, err := os.ReadFile(path)
	if err != nil {
		return nil, path, fmt.Errorf("read config %q: %w", path, err)
	}

	raw := map[string]any{}
	if err := yaml.Unmarshal(data, &raw); err != nil {
		return nil, path, fmt.Errorf("decode config %q: %w", path, err)
	}
	if raw == nil {
		raw = map[string]any{}
	}

	applied, err := Migrate(raw)
	if err != nil {
		return nil, path, fmt.Errorf("migrate config %q: %w", path, err)
	}

	if len(applied) > 0 {
		if err := rewriteConfigFile(path, data, raw); err != nil {
			return nil, path, err
		}
		if log != nil {
			for _, step := range applied {
				log.Warn("config migrated",
					slog.String("path", path),
					slog.Int("from_version", step.From),
					slog.Int("to_version", step.To),
					slog.String("describe", step.Describe),
				)
			}
		}
	}

	cfg, err := decodeTyped(raw)
	if err != nil {
		return nil, path, fmt.Errorf("decode migrated config %q: %w", path, err)
	}
	cfg.Version = CurrentConfigVersion

	applyEnvOverrides(&cfg)
	if err := cfg.Validate(); err != nil {
		return nil, path, err
	}

	return &cfg, path, nil
}

func decodeTyped(raw map[string]any) (Config, error) {
	out, err := yaml.Marshal(raw)
	if err != nil {
		return Config{}, fmt.Errorf("re-marshal migrated config: %w", err)
	}
	cfg := defaultConfig()
	if err := yaml.Unmarshal(out, &cfg); err != nil {
		return Config{}, err
	}
	return cfg, nil
}

func rewriteConfigFile(path string, original []byte, migrated map[string]any) error {
	backupPath := fmt.Sprintf("%s.bak.%d", path, time.Now().Unix())
	if err := os.WriteFile(backupPath, original, 0o600); err != nil {
		return fmt.Errorf("write backup %q: %w", backupPath, err)
	}

	out, err := yaml.Marshal(migrated)
	if err != nil {
		return fmt.Errorf("marshal migrated config: %w", err)
	}
	if err := os.WriteFile(path, out, 0o600); err != nil {
		return fmt.Errorf("write migrated config %q: %w", path, err)
	}
	return nil
}

func ResolvePath(explicitPath string) string {
	if path := strings.TrimSpace(explicitPath); path != "" {
		if path != ".yaml" && path != ".yml" {
			return path
		}
	}

	if envPath := strings.TrimSpace(os.Getenv("AMCS_CONFIG")); envPath != "" {
		return envPath
	}

	return DefaultConfigPath
}

func defaultConfig() Config {
	info := buildinfo.Current()
	return Config{
		Version: CurrentConfigVersion,
		Server: ServerConfig{
			Host:         "0.0.0.0",
			Port:         8080,
			ReadTimeout:  10 * time.Minute,
			WriteTimeout: 10 * time.Minute,
			IdleTimeout:  60 * time.Second,
		},
		MCP: MCPConfig{
			Path:           "/mcp",
			SSEPath:        "/sse",
			ServerName:     "amcs",
			Version:        info.Version,
			Transport:      "streamable_http",
			SessionTimeout: 10 * time.Minute,
		},
		Auth: AuthConfig{
			HeaderName: "x-brain-key",
			QueryParam: "key",
		},
		AI: AIConfig{
			Providers: map[string]ProviderConfig{},
			Embeddings: EmbeddingsRoleConfig{
				Dimensions: 1536,
			},
			Metadata: MetadataRoleConfig{
				Temperature: 0.1,
				Timeout:     10 * time.Second,
			},
		},
		Capture: CaptureConfig{
			Source: DefaultSource,
			MetadataDefaults: CaptureMetadataDefault{
				Type:          "observation",
				TopicFallback: "uncategorized",
			},
		},
		Search: SearchConfig{
			DefaultLimit:     10,
			DefaultThreshold: 0.5,
			MaxLimit:         50,
		},
		Logging: LoggingConfig{
			Level:  "info",
			Format: "json",
		},
		Backfill: BackfillConfig{
			Enabled:      false,
			RunOnStartup: false,
			Interval:     15 * time.Minute,
			BatchSize:    20,
			MaxPerRun:    100,
		},
		MetadataRetry: MetadataRetryConfig{
			Enabled:      false,
			RunOnStartup: false,
			Interval:     24 * time.Hour,
			MaxPerRun:    100,
		},
	}
}

func applyEnvOverrides(cfg *Config) {
	overrideString(&cfg.Database.URL, "AMCS_DATABASE_URL")
	overrideString(&cfg.MCP.PublicURL, "AMCS_PUBLIC_URL")

	overrideProviderField(cfg, "AMCS_LITELLM_BASE_URL", "litellm", func(p *ProviderConfig, v string) { p.BaseURL = v })
	overrideProviderField(cfg, "AMCS_LITELLM_API_KEY", "litellm", func(p *ProviderConfig, v string) { p.APIKey = v })
	overrideProviderField(cfg, "AMCS_OLLAMA_BASE_URL", "ollama", func(p *ProviderConfig, v string) { p.BaseURL = v })
	overrideProviderField(cfg, "AMCS_OLLAMA_API_KEY", "ollama", func(p *ProviderConfig, v string) { p.APIKey = v })
	overrideProviderField(cfg, "AMCS_OPENROUTER_API_KEY", "openrouter", func(p *ProviderConfig, v string) { p.APIKey = v })

	if value, ok := os.LookupEnv("AMCS_SERVER_PORT"); ok {
		if port, err := strconv.Atoi(strings.TrimSpace(value)); err == nil {
			cfg.Server.Port = port
		}
	}
}

// overrideProviderField applies an env var to every configured provider of the
// given type. This preserves the v1 behaviour where e.g. AMCS_LITELLM_API_KEY
// rewrote the single litellm block — in v2 it rewrites every litellm provider.
func overrideProviderField(cfg *Config, envKey, providerType string, apply func(*ProviderConfig, string)) {
	value, ok := os.LookupEnv(envKey)
	if !ok {
		return
	}
	value = strings.TrimSpace(value)
	for name, p := range cfg.AI.Providers {
		if p.Type != providerType {
			continue
		}
		apply(&p, value)
		cfg.AI.Providers[name] = p
	}
}

func overrideString(target *string, envKey string) {
	if value, ok := os.LookupEnv(envKey); ok {
		*target = strings.TrimSpace(value)
	}
}