package pier

import (
	"fmt"
	"net/url"
	"strconv"
	"strings"
	"time"

	"git.golem15.com/golem15/summercms/modules/compass"
)

// Configuration keys of the MCP module, all under mcp.* (config/mcp.yaml or
// SUMMER_MCP__* environment variables).
const (
	// EnabledKey mounts the endpoint when true; false (the default) mounts
	// nothing. surf reads it to call the mount hook.
	EnabledKey = "mcp.enabled"
	// PathKey is the endpoint path (POST, GET and DELETE), default /mcp.
	PathKey = "mcp.path"
	// AllowPersonalTokensKey lets personal API tokens (a frontend user token
	// through the published resolver, an admin g15_ token through cabana)
	// open sessions; false (the default) accepts OAuth access tokens only.
	AllowPersonalTokensKey = "mcp.allow_personal_tokens"
	// SessionStoreKey selects where session records live: memory (the
	// default, one instance) or redis (shared through redis.url).
	SessionStoreKey = "mcp.sessions.store"
	// SessionIdleTTLKey is the sliding idle TTL of a session, default 30m.
	SessionIdleTTLKey = "mcp.sessions.idle_ttl"
	// SessionMaxPerBindingKey caps the open sessions of one binding (one
	// client and user, or one personal token), default 20.
	SessionMaxPerBindingKey = "mcp.sessions.max_per_binding"
	// ResourceKey is the resource indicator the endpoint identifies itself
	// by in the protected resource metadata; default app.url plus mcp.path.
	ResourceKey = "mcp.resource"
	// ThrottleKey is the inline throttle of the endpoint, surf's
	// <max>,<minutes> spelling, default 120,1.
	ThrottleKey = "mcp.throttle"
	// AllowedOriginsKey lists the browser origins allowed to call the
	// endpoint; default the origin of app.url. A request without an Origin
	// header is never refused by it.
	AllowedOriginsKey = "mcp.allowed_origins"
	// CallTimeoutKey bounds one in-process tool call, and the guard checks
	// run while a session or stateless server is re-filtered, default 30s.
	CallTimeoutKey = "mcp.call_timeout"
	// MaxResultBytesKey caps the route answer captured for a tool result,
	// default 1048576 (1 MiB); a larger answer is a tool error.
	MaxResultBytesKey = "mcp.max_result_bytes"
)

// Defaults of the mcp.* keys.
const (
	DefaultPath           = "/mcp"
	DefaultSessionStore   = "memory"
	DefaultIdleTTL        = 30 * time.Minute
	DefaultMaxPerBinding  = 20
	DefaultThrottle       = "120,1"
	DefaultCallTimeout    = 30 * time.Second
	DefaultMaxResultBytes = int64(1 << 20)
)

// Session store names.
const (
	StoreMemory = "memory"
	StoreRedis  = "redis"
)

// Config is the MCP module's configuration as LoadConfig reads it from the
// mcp.* keys, with defaults applied and every value validated.
type Config struct {
	Enabled             bool
	Path                string
	AllowPersonalTokens bool
	SessionStore        string
	IdleTTL             time.Duration
	MaxPerBinding       int
	Resource            string
	Throttle            string
	AllowedOrigins      []string
	CallTimeout         time.Duration
	MaxResultBytes      int64
	// AppURL is app.url trimmed of its trailing slash, the base of the
	// default Resource and of the protected resource metadata URL.
	AppURL string
}

// LoadConfig reads the mcp.* keys. A nil config is every default with the
// endpoint disabled. An invalid value fails with an error naming the key.
func LoadConfig(cfg *compass.Config) (Config, error) {
	out := Config{
		Path:           DefaultPath,
		SessionStore:   DefaultSessionStore,
		IdleTTL:        DefaultIdleTTL,
		MaxPerBinding:  DefaultMaxPerBinding,
		Throttle:       DefaultThrottle,
		CallTimeout:    DefaultCallTimeout,
		MaxResultBytes: DefaultMaxResultBytes,
	}
	if cfg == nil {
		return out, nil
	}
	out.Enabled = cfg.Bool(EnabledKey)
	out.AllowPersonalTokens = cfg.Bool(AllowPersonalTokensKey)
	out.AppURL = strings.TrimRight(strings.TrimSpace(cfg.String("app.url")), "/")

	path, err := endpointPath(cfg.String(PathKey))
	if err != nil {
		return out, err
	}
	out.Path = path

	store := strings.ToLower(strings.TrimSpace(cfg.String(SessionStoreKey)))
	switch store {
	case "":
	case StoreMemory, StoreRedis:
		out.SessionStore = store
	default:
		return out, fmt.Errorf("pier: %s must be %s or %s, got %q", SessionStoreKey, StoreMemory, StoreRedis, store)
	}

	if out.IdleTTL, err = durationKey(cfg, SessionIdleTTLKey, DefaultIdleTTL); err != nil {
		return out, err
	}
	if out.CallTimeout, err = durationKey(cfg, CallTimeoutKey, DefaultCallTimeout); err != nil {
		return out, err
	}
	if cfg.Has(SessionMaxPerBindingKey) {
		n := cfg.Int(SessionMaxPerBindingKey)
		if n < 1 {
			return out, fmt.Errorf("pier: %s must be a whole number of at least 1", SessionMaxPerBindingKey)
		}
		out.MaxPerBinding = n
	}
	if cfg.Has(MaxResultBytesKey) {
		n := cfg.Int(MaxResultBytesKey)
		if n < 1 {
			return out, fmt.Errorf("pier: %s must be a whole number of bytes of at least 1", MaxResultBytesKey)
		}
		out.MaxResultBytes = int64(n)
	}
	if raw := strings.TrimSpace(cfg.String(ThrottleKey)); raw != "" {
		if err := validateThrottle(raw); err != nil {
			return out, fmt.Errorf("pier: %s must be <max>,<minutes> with both at least 1 (for example 120,1), got %q", ThrottleKey, raw)
		}
		out.Throttle = raw
	}

	if raw := strings.TrimSpace(cfg.String(ResourceKey)); raw != "" {
		u, err := url.Parse(raw)
		if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" || u.Fragment != "" || u.RawQuery != "" {
			return out, fmt.Errorf("pier: %s must be an http or https URL without query or fragment, got %q", ResourceKey, raw)
		}
		out.Resource = strings.TrimRight(raw, "/")
	} else if out.AppURL != "" {
		out.Resource = out.AppURL + out.Path
	} else if out.Enabled {
		return out, fmt.Errorf("pier: %s or app.url is required when %s is true", ResourceKey, EnabledKey)
	}

	origins, err := originsKey(cfg, AllowedOriginsKey)
	if err != nil {
		return out, err
	}
	if origins == nil && out.AppURL != "" {
		if u, err := url.Parse(out.AppURL); err == nil && u.Scheme != "" && u.Host != "" {
			origins = []string{u.Scheme + "://" + u.Host}
		}
	}
	out.AllowedOrigins = origins
	return out, nil
}

// endpointPath validates mcp.path: an absolute URL path without scheme,
// host, query, wildcard or dot segments, with no trailing slash.
func endpointPath(raw string) (string, error) {
	value := strings.TrimSpace(raw)
	if value == "" {
		return DefaultPath, nil
	}
	path := strings.TrimSuffix(value, "/")
	bad := !strings.HasPrefix(path, "/") || strings.ContainsAny(path, "{}?# \t\r\n\\") || path == ""
	if !bad {
		for _, seg := range strings.Split(path[1:], "/") {
			if seg == "" || seg == "." || seg == ".." {
				bad = true
				break
			}
		}
	}
	if bad {
		return "", fmt.Errorf("pier: %s must be an absolute URL path such as /mcp (no scheme, host, query or wildcard), got %q", PathKey, raw)
	}
	return path, nil
}

// durationKey reads a Go duration (30m, 45s) or a whole number of seconds.
func durationKey(cfg *compass.Config, key string, fallback time.Duration) (time.Duration, error) {
	raw := strings.TrimSpace(cfg.String(key))
	if raw == "" {
		return fallback, nil
	}
	d, err := time.ParseDuration(raw)
	if err != nil {
		n, nerr := strconv.Atoi(raw)
		if nerr != nil {
			return 0, fmt.Errorf("pier: %s must be a duration such as 30m or 45s, got %q", key, raw)
		}
		d = time.Duration(n) * time.Second
	}
	if d <= 0 {
		return 0, fmt.Errorf("pier: %s must be a positive duration, got %q", key, raw)
	}
	return d, nil
}

// validateThrottle checks surf's inline throttle spelling <max>,<minutes>.
func validateThrottle(raw string) error {
	nStr, mStr, ok := strings.Cut(raw, ",")
	if !ok {
		return fmt.Errorf("not <max>,<minutes>")
	}
	n, errN := strconv.Atoi(strings.TrimSpace(nStr))
	m, errM := strconv.Atoi(strings.TrimSpace(mStr))
	if errN != nil || errM != nil || n < 1 || m < 1 {
		return fmt.Errorf("not <max>,<minutes>")
	}
	return nil
}

// originsKey reads a YAML list or a comma-separated string of origins
// (scheme://host[:port]); nil when the key is absent or empty.
func originsKey(cfg *compass.Config, key string) ([]string, error) {
	raw, ok := cfg.Lookup(key)
	if !ok || raw == nil {
		return nil, nil
	}
	var items []string
	switch v := raw.(type) {
	case []any:
		for _, item := range v {
			items = append(items, fmt.Sprint(item))
		}
	case []string:
		items = append(items, v...)
	case string:
		items = strings.Split(v, ",")
	default:
		return nil, fmt.Errorf("pier: %s must be a list of origins such as https://example.com", key)
	}
	var out []string
	for _, item := range items {
		item = strings.TrimSpace(item)
		if item == "" {
			continue
		}
		u, err := url.Parse(item)
		if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" || u.Path != "" || u.RawQuery != "" || u.Fragment != "" {
			return nil, fmt.Errorf("pier: %s entries must be origins such as https://example.com, got %q", key, item)
		}
		out = append(out, strings.ToLower(u.Scheme+"://"+u.Host))
	}
	return out, nil
}