// Package netbox resolves a PXE-booting machine (by MAC or hostname) into the
// normalized model.Host that bootapi renders templates against. It talks to the
// NetBox REST API (v4.x) behind the Resolver interface so the server can be
// tested with an httptest fake.
package netbox

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

	"git.unkin.net/unkin/bootapi/internal/model"
)

// ErrNotFound is returned when NetBox has no device matching the query. The
// server maps it to an HTTP 404 (and, for iPXE, a safe fallback boot script).
var ErrNotFound = errors.New("netbox: device not found")

// Resolver turns a MAC or hostname into a fully-resolved Host.
type Resolver interface {
	HostByMAC(ctx context.Context, mac string) (*model.Host, error)
	HostByName(ctx context.Context, name string) (*model.Host, error)
}

// Writer mutates NetBox. Today it only flips the pxe_enabled gate (the
// end-of-kickstart callback). Kept separate from Resolver so read-only callers
// need not depend on write scope.
type Writer interface {
	SetPXEEnabled(ctx context.Context, deviceID int, enabled bool) error
}

// API is the full NetBox surface bootapi uses (reads + the pxe_enabled write).
type API interface {
	Resolver
	Writer
}

// Client is the HTTP-backed Resolver.
type Client struct {
	baseURL string
	token   string
	http    *http.Client
}

// Options configures a Client.
type Options struct {
	BaseURL  string
	Token    string
	Timeout  time.Duration
	Insecure bool
	// HTTPClient overrides the constructed client (used by tests).
	HTTPClient *http.Client
}

// New builds a NetBox Client.
func New(o Options) *Client {
	hc := o.HTTPClient
	if hc == nil {
		tr := &http.Transport{}
		if o.Insecure {
			tr.TLSClientConfig = &tls.Config{InsecureSkipVerify: true} //nolint:gosec // opt-in dev flag
		}
		timeout := o.Timeout
		if timeout == 0 {
			timeout = 5 * time.Second
		}
		hc = &http.Client{Timeout: timeout, Transport: tr}
	}
	return &Client{
		baseURL: strings.TrimRight(o.BaseURL, "/"),
		token:   o.Token,
		http:    hc,
	}
}

// --- NetBox API JSON shapes (only the fields bootapi consumes) ---

type nbList[T any] struct {
	Count   int `json:"count"`
	Results []T `json:"results"`
}

type nbRef struct {
	ID   int    `json:"id"`
	Name string `json:"name"`
	Slug string `json:"slug"`
}

type nbVLAN struct {
	VID  int    `json:"vid"`
	Name string `json:"name"`
}

type nbMAC struct {
	MACAddress string `json:"mac_address"`
}

type nbDevice struct {
	ID           int            `json:"id"`
	Name         string         `json:"name"`
	Platform     *nbRef         `json:"platform"`
	Role         *nbRef         `json:"role"`
	Site         *nbRef         `json:"site"`
	PrimaryIP    *nbIPRef       `json:"primary_ip"`
	CustomFields map[string]any `json:"custom_fields"`
}

type nbIPRef struct {
	Address string `json:"address"`
}

type nbInterface struct {
	ID                int     `json:"id"`
	Name              string  `json:"name"`
	MACAddress        string  `json:"mac_address"`
	PrimaryMACAddress *nbMAC  `json:"primary_mac_address"`
	UntaggedVLAN      *nbVLAN `json:"untagged_vlan"`
	Device            *nbRef  `json:"device"`
}

func (i nbInterface) mac() string {
	if i.MACAddress != "" {
		return normalizeMAC(i.MACAddress)
	}
	if i.PrimaryMACAddress != nil {
		return normalizeMAC(i.PrimaryMACAddress.MACAddress)
	}
	return ""
}

type nbIPAddress struct {
	Address          string         `json:"address"`
	AssignedObjectID int            `json:"assigned_object_id"`
	CustomFields     map[string]any `json:"custom_fields"`
}

// --- Resolver implementation ---

// HostByMAC finds the device owning an interface with the given MAC and
// resolves it to a Host.
func (c *Client) HostByMAC(ctx context.Context, mac string) (*model.Host, error) {
	mac = normalizeMAC(mac)
	if mac == "" {
		return nil, fmt.Errorf("netbox: empty MAC")
	}
	var list nbList[nbInterface]
	if err := c.get(ctx, "/api/dcim/interfaces/", url.Values{"mac_address": {mac}}, &list); err != nil {
		return nil, err
	}
	var dev *nbRef
	for _, i := range list.Results {
		if i.mac() == mac && i.Device != nil {
			dev = i.Device
			break
		}
	}
	if dev == nil {
		return nil, ErrNotFound
	}
	return c.resolveDevice(ctx, dev.ID)
}

// HostByName finds a device by its NetBox name and resolves it to a Host.
func (c *Client) HostByName(ctx context.Context, name string) (*model.Host, error) {
	// Strip any domain suffix: NetBox device names are short hostnames.
	short := name
	if i := strings.IndexByte(short, '.'); i >= 0 {
		short = short[:i]
	}
	var list nbList[nbDevice]
	if err := c.get(ctx, "/api/dcim/devices/", url.Values{"name": {short}}, &list); err != nil {
		return nil, err
	}
	if len(list.Results) == 0 {
		return nil, ErrNotFound
	}
	return c.resolveDevice(ctx, list.Results[0].ID)
}

// resolveDevice fetches the device, its interfaces and IP addresses, and
// assembles a Host. It performs three bounded API calls.
func (c *Client) resolveDevice(ctx context.Context, id int) (*model.Host, error) {
	var dev nbDevice
	if err := c.get(ctx, fmt.Sprintf("/api/dcim/devices/%d/", id), nil, &dev); err != nil {
		return nil, err
	}

	devID := url.Values{"device_id": {fmt.Sprint(id)}}
	var ifaces nbList[nbInterface]
	if err := c.get(ctx, "/api/dcim/interfaces/", devID, &ifaces); err != nil {
		return nil, err
	}
	var ips nbList[nbIPAddress]
	if err := c.get(ctx, "/api/ipam/ip-addresses/", devID, &ips); err != nil {
		return nil, err
	}

	return buildHost(&dev, ifaces.Results, ips.Results), nil
}

// buildHost assembles the normalized Host from raw NetBox objects. It is pure
// (no I/O) so it can be unit-tested directly against fixture structs.
func buildHost(dev *nbDevice, ifaces []nbInterface, ips []nbIPAddress) *model.Host {
	cf := dev.CustomFields
	domain := cfString(cf, "domain")

	h := &model.Host{
		DeviceID:         dev.ID,
		Hostname:         dev.Name,
		Domain:           domain,
		Custom:           cf,
		Nameservers:      cfStringList(cf, "nameservers"),
		TemplateOverride: cfString(cf, "provision_template"),
		PXEEnabled:       cfBool(cf, "pxe_enabled"),
		Arch:             "x86_64",
	}
	if dev.Platform != nil {
		h.Platform = dev.Platform.Slug
		h.OSFamily, h.OSVersion = splitPlatform(dev.Platform.Slug)
	}
	if dev.Role != nil {
		h.Role = dev.Role.Slug
	}

	// Index IP addresses by the interface they are assigned to.
	ipByIface := map[int]nbIPAddress{}
	for _, ip := range ips {
		if _, seen := ipByIface[ip.AssignedObjectID]; !seen {
			ipByIface[ip.AssignedObjectID] = ip
		}
	}

	primaryAddr := ""
	if dev.PrimaryIP != nil {
		primaryAddr = dev.PrimaryIP.Address
		h.PrimaryIP = addrOnly(primaryAddr)
	}

	deviceGateway := cfString(cf, "gateway")

	for _, in := range ifaces {
		iface := model.Interface{
			Name: in.Name,
			MAC:  in.mac(),
		}
		if in.UntaggedVLAN != nil {
			iface.VLAN = in.UntaggedVLAN.VID
		}
		if ip, ok := ipByIface[in.ID]; ok {
			iface.IP = addrOnly(ip.Address)
			iface.PrefixLen = prefixLen(ip.Address)
			iface.Netmask = netmaskFor(iface.PrefixLen)
			if g := cfString(ip.CustomFields, "gateway"); g != "" {
				iface.Gateway = g
			}
			if iface.IP != "" && iface.IP == h.PrimaryIP {
				iface.Primary = true
			}
		}
		if iface.Gateway == "" {
			iface.Gateway = deviceGateway
		}
		h.Interfaces = append(h.Interfaces, iface)
	}

	sortPrimaryFirst(h.Interfaces)

	if h.Domain != "" {
		h.FQDN = h.Hostname + "." + h.Domain
	} else {
		h.FQDN = h.Hostname
	}
	return h
}

// sortPrimaryFirst moves the primary interface to the front, preserving the
// relative order of the rest.
func sortPrimaryFirst(ifaces []model.Interface) {
	for i := range ifaces {
		if ifaces[i].Primary && i != 0 {
			p := ifaces[i]
			copy(ifaces[1:i+1], ifaces[0:i])
			ifaces[0] = p
			return
		}
	}
}

// SetPXEEnabled PATCHes the device's pxe_enabled custom field. This is the only
// write bootapi performs; the NetBox token therefore needs write scope on the
// device custom field (see docs/security.md).
func (c *Client) SetPXEEnabled(ctx context.Context, deviceID int, enabled bool) error {
	body := map[string]any{"custom_fields": map[string]any{"pxe_enabled": enabled}}
	b, err := json.Marshal(body)
	if err != nil {
		return err
	}
	path := fmt.Sprintf("/api/dcim/devices/%d/", deviceID)
	req, err := http.NewRequestWithContext(ctx, http.MethodPatch, c.baseURL+path, bytes.NewReader(b))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")
	if c.token != "" {
		req.Header.Set("Authorization", "Token "+c.token)
	}
	resp, err := c.http.Do(req)
	if err != nil {
		return fmt.Errorf("netbox patch device %d: %w", deviceID, err)
	}
	defer func() { _ = resp.Body.Close() }()
	if resp.StatusCode == http.StatusNotFound {
		return ErrNotFound
	}
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("netbox patch device %d: HTTP %d", deviceID, resp.StatusCode)
	}
	return nil
}

// get performs a GET against the NetBox API and decodes the JSON body into out.
func (c *Client) get(ctx context.Context, path string, q url.Values, out any) error {
	u := c.baseURL + path
	if len(q) > 0 {
		u += "?" + q.Encode()
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
	if err != nil {
		return err
	}
	req.Header.Set("Accept", "application/json")
	if c.token != "" {
		req.Header.Set("Authorization", "Token "+c.token)
	}
	resp, err := c.http.Do(req)
	if err != nil {
		return fmt.Errorf("netbox request %s: %w", path, err)
	}
	defer func() { _ = resp.Body.Close() }()
	if resp.StatusCode == http.StatusNotFound {
		return ErrNotFound
	}
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("netbox %s: HTTP %d", path, resp.StatusCode)
	}
	if err := json.NewDecoder(resp.Body).Decode(out); err != nil {
		return fmt.Errorf("netbox decode %s: %w", path, err)
	}
	return nil
}

// --- helpers ---

func normalizeMAC(s string) string {
	s = strings.TrimSpace(s)
	if s == "" {
		return ""
	}
	// Drop common separators then re-insert colons every 2 hex chars.
	var hex strings.Builder
	for _, r := range strings.ToLower(s) {
		if (r >= '0' && r <= '9') || (r >= 'a' && r <= 'f') {
			hex.WriteRune(r)
		}
	}
	h := hex.String()
	if len(h) != 12 {
		// Not a canonical 48-bit MAC; return lower-cased trimmed input.
		return strings.ToLower(s)
	}
	var b strings.Builder
	for i := 0; i < 12; i += 2 {
		if i > 0 {
			b.WriteByte(':')
		}
		b.WriteString(h[i : i+2])
	}
	return b.String()
}

func addrOnly(cidr string) string {
	if i := strings.IndexByte(cidr, '/'); i >= 0 {
		return cidr[:i]
	}
	return cidr
}

func prefixLen(cidr string) int {
	_, ipnet, err := net.ParseCIDR(cidr)
	if err != nil {
		return 0
	}
	ones, _ := ipnet.Mask.Size()
	return ones
}

func netmaskFor(prefix int) string {
	if prefix <= 0 || prefix > 32 {
		return ""
	}
	mask := net.CIDRMask(prefix, 32)
	return fmt.Sprintf("%d.%d.%d.%d", mask[0], mask[1], mask[2], mask[3])
}

// splitPlatform derives (family, majorVersion) from a NetBox platform slug such
// as "almalinux9" -> ("almalinux","9") or "fedora42" -> ("fedora","42").
func splitPlatform(slug string) (family, version string) {
	slug = strings.ToLower(slug)
	i := strings.IndexFunc(slug, func(r rune) bool { return r >= '0' && r <= '9' })
	if i < 0 {
		return slug, ""
	}
	family = strings.Trim(slug[:i], "-_")
	version = slug[i:]
	if d := strings.IndexByte(version, '.'); d >= 0 {
		version = version[:d]
	}
	return family, version
}

func cfString(cf map[string]any, key string) string {
	if cf == nil {
		return ""
	}
	switch v := cf[key].(type) {
	case string:
		return v
	case map[string]any: // NetBox object custom fields serialize as {value,label}
		if s, ok := v["value"].(string); ok {
			return s
		}
	}
	return ""
}

// cfBool reads a boolean custom field. Returns nil when the field is absent or
// null so callers can distinguish "unset" from "false".
func cfBool(cf map[string]any, key string) *bool {
	if cf == nil {
		return nil
	}
	switch v := cf[key].(type) {
	case bool:
		return &v
	case string: // tolerate "true"/"false" string encodings
		switch strings.ToLower(v) {
		case "true", "1", "yes":
			b := true
			return &b
		case "false", "0", "no":
			b := false
			return &b
		}
	}
	return nil
}

func cfStringList(cf map[string]any, key string) []string {
	if cf == nil {
		return nil
	}
	switch v := cf[key].(type) {
	case string:
		return splitComma(v)
	case []any:
		var out []string
		for _, e := range v {
			if s, ok := e.(string); ok && s != "" {
				out = append(out, s)
			}
		}
		return out
	}
	return nil
}

func splitComma(v string) []string {
	var out []string
	for _, p := range strings.Split(v, ",") {
		if p = strings.TrimSpace(p); p != "" {
			out = append(out, p)
		}
	}
	return out
}