// Package config loads runtime configuration for the CarrotAssistant backend.
//
// Configuration can be supplied via environment variables (preferred for
// containers) and falls back to sensible defaults suitable for local
// development. Secrets such as the master key MUST be provided in
// production through the environment.
package config

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// Config holds all runtime configuration values.
type Config struct {
	// HTTPAddr is the address the API server listens on.
	HTTPAddr string
	// DataDir is the root directory for persistent files (sqlite db,
	// generated skill markdown, etc.).
	DataDir string
	// DBPath is the resolved SQLite database file path.
	DBPath string
	// SkillsDir is the root directory where skill markdown files live,
	// organised as <SkillsDir>/<app_slug>/<skill_slug>.md.
	SkillsDir string
	// MasterKey is used to encrypt secrets at rest (model api keys). It
	// must be 32 bytes; if a shorter value is supplied it is padded, if a
	// longer one is supplied it is truncated. Provide a strong value in
	// production via the MASTER_KEY env var.
	MasterKey string
	// JWTSecret signs admin session tokens.
	JWTSecret string
	// AdminBootstrapUser, if set and no admin user exists, is created on
	// first run. Useful for fresh deployments.
	AdminBootstrapUser     string
	AdminBootstrapPassword string
	// DefaultAdminUser / DefaultAdminPassword are used when bootstrapping
	// is requested and no explicit credentials are configured.
	DefaultAdminUser     string
	DefaultAdminPassword string
}

// Load reads configuration from environment variables with defaults.
func Load() (*Config, error) {
	c := &Config{
		HTTPAddr:               env("HTTP_ADDR", ":8080"),
		DataDir:                env("DATA_DIR", "./data"),
		MasterKey:              env("MASTER_KEY", ""),
		JWTSecret:              env("JWT_SECRET", ""),
		AdminBootstrapUser:     env("ADMIN_BOOTSTRAP_USER", ""),
		AdminBootstrapPassword: env("ADMIN_BOOTSTRAP_PASSWORD", ""),
		DefaultAdminUser:       env("DEFAULT_ADMIN_USER", "admin"),
		DefaultAdminPassword:   env("DEFAULT_ADMIN_PASSWORD", "changeme"),
	}

	// Resolve derived paths to absolute form for stable behaviour in the
	// file loader and the HTTP handler layer.
	dataDir, err := filepath.Abs(c.DataDir)
	if err != nil {
		return nil, fmt.Errorf("resolve data dir: %w", err)
	}
	c.DataDir = dataDir
	c.DBPath = filepath.Join(dataDir, "carrot.db")
	c.SkillsDir = filepath.Join(dataDir, "skills")

	for _, dir := range []string{c.DataDir, c.SkillsDir} {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return nil, fmt.Errorf("mkdir %s: %w", dir, err)
		}
	}

	// In development we allow empty secrets and substitute a deterministic
	// value so the server still runs. A warning is printed to make the
	// insecure state obvious; production should always set these.
	if c.MasterKey == "" {
		c.MasterKey = "carrot-dev-master-key-please-change"
	}
	if c.JWTSecret == "" {
		c.JWTSecret = "carrot-dev-jwt-secret-please-change"
	}
	if len(c.MasterKey) > 32 {
		c.MasterKey = c.MasterKey[:32]
	}
	if len(c.MasterKey) < 32 {
		c.MasterKey = padKey(c.MasterKey, 32)
	}

	return c, nil
}

// env returns the value of the named env var, or fallback when unset/empty.
func env(key, fallback string) string {
	if v := strings.TrimSpace(os.Getenv(key)); v != "" {
		return v
	}
	return fallback
}

// padKey right-pads a short master key to the requested length. This only
// exists so the dev defaults work; production must supply a real 32-byte key.
func padKey(k string, n int) string {
	if len(k) >= n {
		return k[:n]
	}
	return k + strings.Repeat("0", n-len(k))
}