// Package config loads ByteClaw configuration from YAML/JSON files and env vars.
package config

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"gopkg.in/yaml.v3"
)

type LLM struct {
	// Provider selects a preset: openai, openrouter, ollama, dahl, gonkarouter or custom.
	Provider    string  `yaml:"provider" json:"provider"`
	BaseURL     string  `yaml:"base_url" json:"base_url"`
	APIKey      string  `yaml:"api_key" json:"api_key"`
	Model       string  `yaml:"model" json:"model"`
	TimeoutSec  int     `yaml:"timeout_sec" json:"timeout_sec"`
	Temperature float64 `yaml:"temperature" json:"temperature"`
	// Providers holds optional per-preset settings (keys stay server-side) so the
	// active provider can be switched at runtime, e.g. providers: {dahl: {api_key: ...}}.
	Providers map[string]ProviderOverride `yaml:"providers" json:"providers"`
}

type ProviderOverride struct {
	BaseURL string `yaml:"base_url" json:"base_url"`
	APIKey  string `yaml:"api_key" json:"api_key"`
	Model   string `yaml:"model" json:"model"`
}

type Agent struct {
	SystemPrompt  string    `yaml:"system_prompt" json:"system_prompt"`
	MaxIterations int       `yaml:"max_iterations" json:"max_iterations"`
	HistoryLimit  int       `yaml:"history_limit" json:"history_limit"`
	Summarize     Summarize `yaml:"summarize" json:"summarize"`
}

// Summarize controls automatic summarisation of long sessions.
type Summarize struct {
	Enabled bool `yaml:"enabled" json:"enabled"`
	// Summarise when unsummarised messages exceed MaxMessages or ~MaxTokens (chars/4).
	MaxMessages int `yaml:"max_messages" json:"max_messages"`
	MaxTokens   int `yaml:"max_tokens" json:"max_tokens"`
	// KeepRecent newest messages always stay verbatim.
	KeepRecent int `yaml:"keep_recent" json:"keep_recent"`
}

type WebFetch struct {
	Enabled bool `yaml:"enabled" json:"enabled"`
	// MaxBytes caps the response body read from remote servers.
	MaxBytes   int64 `yaml:"max_bytes" json:"max_bytes"`
	TimeoutSec int   `yaml:"timeout_sec" json:"timeout_sec"`
	// AllowPrivate permits fetching loopback/private/link-local addresses (SSRF risk). Default false.
	AllowPrivate bool `yaml:"allow_private" json:"allow_private"`
}

// Shell configures the opt-in shell tool (default off).
type Shell struct {
	Enabled         bool     `yaml:"enabled" json:"enabled"`
	AllowedCommands []string `yaml:"allowed_commands" json:"allowed_commands"`
	TimeoutSec      int      `yaml:"timeout_sec" json:"timeout_sec"`
	MaxOutputBytes  int      `yaml:"max_output_bytes" json:"max_output_bytes"`
}

type Tools struct {
	Shell    Shell    `yaml:"shell" json:"shell"`
	WebFetch WebFetch `yaml:"web_fetch" json:"web_fetch"`
	// FilesEnabled enables read/write/list tools confined to the workspace directory.
	FilesEnabled bool `yaml:"files_enabled" json:"files_enabled"`
	// FileMaxBytes caps file reads/writes.
	FileMaxBytes int64 `yaml:"file_max_bytes" json:"file_max_bytes"`
}

type Config struct {
	Listen    string `yaml:"listen" json:"listen"`
	AuthToken string `yaml:"auth_token" json:"auth_token"`
	// AllowedOrigins for browser WebSocket/CORS. Empty = same host only. "*" must be set explicitly.
	AllowedOrigins []string `yaml:"allowed_origins" json:"allowed_origins"`
	DataDir        string   `yaml:"data_dir" json:"data_dir"`
	Workspace      string   `yaml:"workspace" json:"workspace"`
	LLM            LLM      `yaml:"llm" json:"llm"`
	Agent          Agent    `yaml:"agent" json:"agent"`
	Tools          Tools    `yaml:"tools" json:"tools"`
}

// Default returns a config with secure defaults.
func Default() Config {
	return Config{
		Listen:  "127.0.0.1:8787",
		DataDir: "./data",
		LLM: LLM{
			Provider:    "openai",
			TimeoutSec:  120,
			Temperature: 0.7,
		},
		Agent: Agent{
			SystemPrompt:  "You are ByteClaw, a concise and helpful self-hosted assistant. Use tools when they help.",
			MaxIterations: 8,
			HistoryLimit:  50,
			Summarize:     Summarize{Enabled: true, MaxMessages: 40, MaxTokens: 12000, KeepRecent: 10},
		},
		Tools: Tools{
			WebFetch:     WebFetch{Enabled: true, MaxBytes: 512 * 1024, TimeoutSec: 15},
			FilesEnabled: true,
			Shell:        Shell{Enabled: false, TimeoutSec: 30, MaxOutputBytes: 64 * 1024},
			FileMaxBytes: 1 << 20,
		},
	}
}

// Load reads path (optional; .json or .yaml/.yml) on top of defaults, then applies env overrides.
func Load(path string) (Config, error) {
	cfg := Default()
	if path != "" {
		b, err := os.ReadFile(path)
		if err != nil {
			return cfg, fmt.Errorf("read config: %w", err)
		}
		switch strings.ToLower(filepath.Ext(path)) {
		case ".json":
			err = json.Unmarshal(b, &cfg)
		default:
			err = yaml.Unmarshal(b, &cfg)
		}
		if err != nil {
			return cfg, fmt.Errorf("parse config: %w", err)
		}
	}
	applyEnv(&cfg, os.Getenv)
	if err := applyPreset(&cfg.LLM, os.Getenv); err != nil {
		return cfg, err
	}
	if cfg.Workspace == "" {
		cfg.Workspace = filepath.Join(cfg.DataDir, "workspace")
	}
	return cfg, cfg.Validate()
}

func applyEnv(c *Config, get func(string) string) {
	set := func(key string, dst *string) {
		if v := get(key); v != "" {
			*dst = v
		}
	}
	set("BYTECLAW_LISTEN", &c.Listen)
	set("BYTECLAW_AUTH_TOKEN", &c.AuthToken)
	set("BYTECLAW_DATA_DIR", &c.DataDir)
	set("BYTECLAW_WORKSPACE", &c.Workspace)
	set("BYTECLAW_LLM_PROVIDER", &c.LLM.Provider)
	set("BYTECLAW_LLM_BASE_URL", &c.LLM.BaseURL)
	set("BYTECLAW_LLM_API_KEY", &c.LLM.APIKey)
	set("BYTECLAW_LLM_MODEL", &c.LLM.Model)
	if v := get("BYTECLAW_ALLOWED_ORIGINS"); v != "" {
		c.AllowedOrigins = nil
		for _, o := range strings.Split(v, ",") {
			if o = strings.TrimSpace(o); o != "" {
				c.AllowedOrigins = append(c.AllowedOrigins, o)
			}
		}
	}
}

// Validate enforces required fields and secure settings.
func (c Config) Validate() error {
	var errs []error
	if len(c.AuthToken) < 16 {
		errs = append(errs, errors.New("auth_token must be set and at least 16 characters (BYTECLAW_AUTH_TOKEN)"))
	}
	if c.LLM.BaseURL == "" || c.LLM.Model == "" {
		errs = append(errs, errors.New("llm.base_url and llm.model are required"))
	}
	if c.Agent.MaxIterations <= 0 {
		errs = append(errs, errors.New("agent.max_iterations must be > 0"))
	}
	return errors.Join(errs...)
}