// Package config loads localchat settings from the environment and an
// optional .env file.
package config

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

// DefaultSystemPrompt is used when SYSTEM_PROMPT is not set.
const DefaultSystemPrompt = "You are a friendly, concise assistant running fully offline on the user's own machine. Answer clearly. Use Markdown when it helps."

// Config holds all runtime settings.
type Config struct {
	Addr         string        // LOCALCHAT_ADDR: where the web UI listens
	BaseURL      string        // LLM_BASE_URL: OpenAI-compatible API root, e.g. http://127.0.0.1:8000/v1
	APIKey       string        // LLM_API_KEY: optional bearer token for the model server
	Model        string        // LLM_MODEL: model id; empty means "first model the server lists"
	SystemPrompt string        // SYSTEM_PROMPT
	Title        string        // LOCALCHAT_TITLE: name shown in the UI
	MaxHistory   int           // MAX_HISTORY: messages sent back to the model as context
	Timeout      time.Duration // LLM_TIMEOUT: upper bound for a single reply
}

// Load reads the configuration from environment variables, applying defaults.
func Load() (Config, error) {
	c := Config{
		Addr:         env("LOCALCHAT_ADDR", "127.0.0.1:3000"),
		BaseURL:      strings.TrimRight(env("LLM_BASE_URL", "http://127.0.0.1:8000/v1"), "/"),
		APIKey:       os.Getenv("LLM_API_KEY"),
		Model:        os.Getenv("LLM_MODEL"),
		SystemPrompt: env("SYSTEM_PROMPT", DefaultSystemPrompt),
		Title:        env("LOCALCHAT_TITLE", "localchat"),
		MaxHistory:   20,
		Timeout:      5 * time.Minute,
	}
	if v := os.Getenv("MAX_HISTORY"); v != "" {
		n, err := strconv.Atoi(v)
		if err != nil || n < 1 {
			return c, fmt.Errorf("MAX_HISTORY must be a positive integer, got %q", v)
		}
		c.MaxHistory = n
	}
	if v := os.Getenv("LLM_TIMEOUT"); v != "" {
		d, err := time.ParseDuration(v)
		if err != nil {
			return c, fmt.Errorf("LLM_TIMEOUT: %w", err)
		}
		c.Timeout = d
	}
	return c, nil
}

func env(key, fallback string) string {
	if v, ok := os.LookupEnv(key); ok && v != "" {
		return v
	}
	return fallback
}

// LoadEnvFile sets variables from a KEY=VALUE file. Variables that are
// already set in the environment win, so the real environment can override
// the file. Blank lines and lines starting with # are ignored; values may be
// wrapped in single or double quotes.
func LoadEnvFile(path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for n := 1; sc.Scan(); n++ {
		line := strings.TrimSpace(sc.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		key, val, ok := strings.Cut(strings.TrimPrefix(line, "export "), "=")
		if !ok {
			return fmt.Errorf("%s:%d: expected KEY=VALUE", path, n)
		}
		key, val = strings.TrimSpace(key), strings.TrimSpace(val)
		if len(val) >= 2 && (val[0] == '"' || val[0] == '\'') && val[len(val)-1] == val[0] {
			val = val[1 : len(val)-1]
		}
		if _, set := os.LookupEnv(key); !set {
			os.Setenv(key, val)
		}
	}
	return sc.Err()
}