package appservice

import (
	"errors"
	"fmt"
	"net/url"
	"os"
	"regexp"
	"strings"

	"gopkg.in/yaml.v3"

	"github.com/dariuszjaniak/warp/server/internal/userapi"
)

// Registration is one application service's registration file, the YAML
// document the Application Service API defines and every bridge writes.
//
// Unknown keys are ignored rather than refused, unlike Warp's own config
// file: registration files are written by the bridges, which add their own
// and unstable keys freely (push_ephemeral, the MSC3202 ones), and a bridge
// upgrade that adds one must not stop the homeserver from starting.
type Registration struct {
	// ID names the application service. It is what the ping endpoint is
	// addressed by and what its delivery cursor is stored under, so
	// changing it starts the service over from the top of the stream.
	ID string `yaml:"id"`

	// URL is where transactions and queries are sent. Empty (or null in
	// the file) is a service that receives nothing, and only uses the
	// Client-Server API.
	URL string `yaml:"url"`

	// ASToken is what the service authenticates to this server with;
	// HSToken is what this server authenticates to the service with.
	ASToken string `yaml:"as_token"`
	HSToken string `yaml:"hs_token"`

	// SenderLocalpart is the localpart of the service's own user, which it
	// acts as when it does not ask to act as somebody else.
	SenderLocalpart string `yaml:"sender_localpart"`

	Namespaces Namespaces `yaml:"namespaces"`

	// RateLimited is whether the users the service acts as are rate
	// limited. Absent is true, as the spec has it. The sender itself never
	// is.
	RateLimited *bool `yaml:"rate_limited"`

	// Protocols are the third-party protocols the service provides.
	Protocols []string `yaml:"protocols"`

	// path is the file the registration was read from, for messages.
	path string
}

// Namespaces are the users, aliases and rooms a service is interested in.
type Namespaces struct {
	Users   []Namespace `yaml:"users"`
	Aliases []Namespace `yaml:"aliases"`
	Rooms   []Namespace `yaml:"rooms"`
}

// Namespace is one regular expression and whether the service claims what
// it matches for itself alone.
type Namespace struct {
	Exclusive bool   `yaml:"exclusive"`
	Regex     string `yaml:"regex"`

	re *regexp.Regexp
}

// Matches reports whether an ID is in the namespace.
func (n Namespace) Matches(id string) bool { return n.re != nil && n.re.MatchString(id) }

// LoadRegistration reads and validates a registration file.
func LoadRegistration(path, serverName string) (*Registration, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read application service registration: %w", err)
	}
	reg, err := ParseRegistration(data, serverName)
	if err != nil {
		return nil, fmt.Errorf("%s: %w", path, err)
	}
	reg.path = path
	return reg, nil
}

// ParseRegistration parses and validates a registration document.
func ParseRegistration(data []byte, serverName string) (*Registration, error) {
	var reg Registration
	if err := yaml.Unmarshal(data, &reg); err != nil {
		return nil, fmt.Errorf("parse application service registration: %w", err)
	}
	if err := reg.validate(serverName); err != nil {
		return nil, err
	}
	return &reg, nil
}

// validate checks a registration and compiles its namespaces, reporting
// every problem rather than the first.
func (r *Registration) validate(serverName string) error {
	var errs []error
	bad := func(format string, args ...any) { errs = append(errs, fmt.Errorf(format, args...)) }

	if strings.TrimSpace(r.ID) == "" {
		bad("id: must not be empty")
	}
	if r.ASToken == "" {
		bad("as_token: must not be empty")
	}
	if r.HSToken == "" {
		bad("hs_token: must not be empty")
	}
	if r.ASToken != "" && r.ASToken == r.HSToken {
		// Either side could then impersonate the other.
		bad("as_token and hs_token must differ")
	}
	if r.URL != "" {
		u, err := url.Parse(r.URL)
		switch {
		case err != nil:
			bad("url: %v", err)
		case u.Scheme != "http" && u.Scheme != "https":
			bad("url: must be an http(s) URL, got %q", r.URL)
		case u.Host == "":
			bad("url: has no host")
		}
	}
	r.SenderLocalpart = userapi.NormaliseLocalpart(r.SenderLocalpart)
	if err := userapi.ValidateLocalpart(r.SenderLocalpart, serverName); err != nil {
		bad("sender_localpart: %v", err)
	}
	for _, group := range []struct {
		name string
		list []Namespace
	}{
		{"users", r.Namespaces.Users},
		{"aliases", r.Namespaces.Aliases},
		{"rooms", r.Namespaces.Rooms},
	} {
		for i := range group.list {
			ns := &group.list[i]
			if ns.Regex == "" {
				bad("namespaces.%s[%d].regex: must not be empty", group.name, i)
				continue
			}
			re, err := compileNamespace(ns.Regex)
			if err != nil {
				bad("namespaces.%s[%d].regex: %v", group.name, i, err)
				continue
			}
			ns.re = re
		}
	}
	return errors.Join(errs...)
}

// compileNamespace compiles a namespace regular expression, anchored at
// the start.
//
// The spec does not say how a namespace matches, and the registration
// files in the wild are written against Synapse, which anchors at the
// start and not at the end — so "@_irc_" matches every user whose ID
// begins with it. Anchoring both ends would quietly match nothing for
// those files; anchoring neither would let "@bot" match "@notabot".
func compileNamespace(expr string) (*regexp.Regexp, error) {
	return regexp.Compile(`^(?:` + expr + `)`)
}

// RateLimitedUsers reports whether the users the service acts as are rate
// limited.
func (r *Registration) RateLimitedUsers() bool { return r.RateLimited == nil || *r.RateLimited }

// Path is the file the registration came from, or "".
func (r *Registration) Path() string { return r.path }