// Package housecarl is Guard's client for Housecarl's API: ban lists and
// their bans, and the log of dropped packets (Housecarl's docs/bans.md
// and docs/api.md).
package housecarl

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"guard/internal/version"
)

// Prefix starts every API path.
const Prefix = "/api/v1"

// Client talks to one Housecarl.
type Client struct {
	base  string
	token string
	http  *http.Client
}

// Options say how to reach Housecarl.
type Options struct {
	URL, Socket string
	Token       string
	CACert      string
	Insecure    bool
	Timeout     time.Duration
}

// New makes a client.
func New(o Options) (*Client, error) {
	timeout := o.Timeout
	if timeout == 0 {
		timeout = 15 * time.Second
	}
	tr := http.DefaultTransport.(*http.Transport).Clone()
	base := strings.TrimRight(o.URL, "/")
	if o.Socket != "" {
		sock := o.Socket
		tr.DialContext = func(ctx context.Context, _, _ string) (net.Conn, error) {
			var d net.Dialer
			return d.DialContext(ctx, "unix", sock)
		}
		base = "http://housecarl"
	}
	if o.CACert != "" || o.Insecure {
		cfg := &tls.Config{InsecureSkipVerify: o.Insecure}
		if o.CACert != "" {
			pem, err := os.ReadFile(o.CACert)
			if err != nil {
				return nil, err
			}
			pool := x509.NewCertPool()
			if !pool.AppendCertsFromPEM(pem) {
				return nil, fmt.Errorf("%s holds no PEM certificate", o.CACert)
			}
			cfg.RootCAs = pool
		}
		tr.TLSClientConfig = cfg
	}
	return &Client{base: base, token: strings.TrimSpace(o.Token), http: &http.Client{Transport: tr, Timeout: timeout}}, nil
}

// Error is an error answer from Housecarl.
type Error struct {
	Status  int
	Code    string
	Message string
}

func (e *Error) Error() string {
	if e.Message == "" {
		return fmt.Sprintf("Housecarl answered %d", e.Status)
	}
	return e.Message
}

// Refused reports whether Housecarl refused a request for good: asking
// again won't help (a bad request, no permission, an address never
// banned). Anything else (no answer, a server error) is worth retrying.
func Refused(err error) bool {
	var he *Error
	return errors.As(err, &he) && he.Status >= 400 && he.Status < 500 && he.Status != http.StatusTooManyRequests
}

func (c *Client) do(ctx context.Context, method, path string, query url.Values, body, out any) error {
	var rd io.Reader
	if body != nil {
		b, err := json.Marshal(body)
		if err != nil {
			return err
		}
		rd = bytes.NewReader(b)
	}
	u := c.base + Prefix + path
	if len(query) > 0 {
		u += "?" + query.Encode()
	}
	req, err := http.NewRequestWithContext(ctx, method, u, rd)
	if err != nil {
		return err
	}
	req.Header.Set("User-Agent", "guard/"+version.Short())
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}
	if c.token != "" {
		req.Header.Set("Authorization", "Bearer "+c.token)
	}
	resp, err := c.http.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	data, _ := io.ReadAll(io.LimitReader(resp.Body, 16<<20))
	if resp.StatusCode >= 300 {
		var eb struct {
			Error struct {
				Code    string `json:"code"`
				Message string `json:"message"`
			} `json:"error"`
		}
		json.Unmarshal(data, &eb)
		return &Error{Status: resp.StatusCode, Code: eb.Error.Code, Message: eb.Error.Message}
	}
	if out != nil && len(data) > 0 {
		return json.Unmarshal(data, out)
	}
	return nil
}

// BanList is a Housecarl ban list (the fields Guard uses).
type BanList struct {
	ID          int64  `json:"id"`
	Name        string `json:"name"`
	Scope       string `json:"scope"`
	DefaultTime int    `json:"default_time"`
	MaxTime     int    `json:"max_time"`
	GroupV6     int    `json:"group_v6"`
	Disabled    bool   `json:"disabled"`
}

// V6Group is the IPv6 prefix length the list bans by.
func (b *BanList) V6Group() int {
	if b.GroupV6 > 0 {
		return b.GroupV6
	}
	return 64
}

// Ban is an active ban.
type Ban struct {
	ID       int64      `json:"id"`
	List     string     `json:"list"`
	Address  string     `json:"address"`
	Protocol string     `json:"protocol"`
	Port     int        `json:"port"`
	Expires  *time.Time `json:"expires"`
	Timeout  int        `json:"timeout"`
	Created  time.Time  `json:"created"`
	Who      string     `json:"who"`
	Source   string     `json:"source"`
	Reason   string     `json:"reason"`
	Existing bool       `json:"existing"`
}

// BanInput asks for a ban.
type BanInput struct {
	Address  string `json:"address"`
	Protocol string `json:"protocol,omitempty"`
	Ports    string `json:"ports,omitempty"`
	Time     int    `json:"time,omitempty"`
	Source   string `json:"source,omitempty"`
	Reason   string `json:"reason,omitempty"`
}

// BanResult is what a ban made.
type BanResult struct {
	Bans   []Ban `json:"bans"`
	Closed int   `json:"closed"`
}

// LogEntry is a packet in Housecarl's log.
type LogEntry struct {
	Time     time.Time `json:"time"`
	Prefix   string    `json:"prefix"`
	Protocol string    `json:"protocol"`
	Source   string    `json:"source"`
	Dest     string    `json:"destination"`
	SrcPort  int       `json:"source_port"`
	DestPort int       `json:"destination_port"`
	Verdict  string    `json:"verdict"`
	Shadow   bool      `json:"shadow"`
}

func listPath(list string) string { return "/banlists/" + url.PathEscape(list) }

// BanList reads a ban list.
func (c *Client) BanList(ctx context.Context, list string) (*BanList, error) {
	var b BanList
	if err := c.do(ctx, "GET", listPath(list), nil, nil, &b); err != nil {
		return nil, err
	}
	return &b, nil
}

// Ban bans an address.
func (c *Client) Ban(ctx context.Context, list string, in BanInput) (*BanResult, error) {
	var out BanResult
	if err := c.do(ctx, "POST", listPath(list)+"/bans", nil, in, &out); err != nil {
		return nil, err
	}
	return &out, nil
}

// Unban lifts every ban of an address in a list.
func (c *Client) Unban(ctx context.Context, list, addr string) (int, error) {
	var out map[string]int
	err := c.do(ctx, "DELETE", listPath(list)+"/bans", url.Values{"address": {addr}}, nil, &out)
	return out["removed"], err
}

// Bans lists a list's active bans ("" for every list the token may read).
func (c *Client) Bans(ctx context.Context, list string) ([]Ban, error) {
	path := "/bans"
	if list != "" {
		path = listPath(list) + "/bans"
	}
	var out []Ban
	err := c.do(ctx, "GET", path, nil, nil, &out)
	return out, err
}

// Log reads Housecarl's log of packets after a time, newest first.
func (c *Client) Log(ctx context.Context, after time.Time) ([]LogEntry, error) {
	var out []LogEntry
	err := c.do(ctx, "GET", "/log", url.Values{"after": {after.UTC().Format(time.RFC3339Nano)}, "limit": {"2000"}}, nil, &out)
	return out, err
}