// Package agentapi is the in-guest controller's client for the host agent's per-guest local
// API (doc 03 §6, slice 8A). It reaches the agent over the bridge, pinning the agent's
// self-signed leaf by SHA-256 (the same pin convention the agent uses for the Proxmox/PBS host
// certs), and authenticates with the per-guest bearer token. In 8A it exercises GET /storage
// (connectivity + the controller learning its mounts); the full surface (the /backup/due
// quiesce loop) lands in 8B.
package agentapi

import (
	"bytes"
	"context"
	"crypto/sha256"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

// Client talks to one agent local-API endpoint with a pinned leaf + bearer token.
type Client struct {
	baseURL string
	token   string
	hc      *http.Client
}

// MountInfo mirrors the agent's GET /storage mount entry (doc 03 §6).
type MountInfo struct {
	Key        string `json:"key"`
	Storage    string `json:"storage"`
	MountPoint string `json:"mount_point"`
	Class      string `json:"class"` // fast | slow | ""
	Backup     bool   `json:"backup"`
}

// StorageResponse mirrors the agent's GET /storage data payload.
type StorageResponse struct {
	VMID   int         `json:"vmid"`
	Mounts []MountInfo `json:"mounts"`
}

// apiResponse is the agent's {ok,data,error} envelope.
type apiResponse struct {
	OK    bool            `json:"ok"`
	Data  json.RawMessage `json:"data"`
	Error string          `json:"error"`
}

// New builds a pinned client for endpoint ("host:port") with the given per-guest token and the
// agent leaf-cert SHA-256 fingerprint (hex, ':'-separators tolerated). The pin is the trust
// anchor — the agent serves a self-signed cert, so chain verification is replaced by an exact
// leaf-DER SHA-256 match (fails closed on any mismatch).
func New(endpoint, token, fingerprintHex string) (*Client, error) {
	endpoint = strings.TrimSpace(endpoint)
	if endpoint == "" {
		return nil, fmt.Errorf("agentapi: endpoint required")
	}
	if token == "" {
		return nil, fmt.Errorf("agentapi: token required")
	}
	want, err := normalizeFingerprint(fingerprintHex)
	if err != nil {
		return nil, err
	}
	tlsCfg := &tls.Config{
		InsecureSkipVerify: true, // self-signed leaf — the pin below is the real check
		VerifyPeerCertificate: func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
			if len(rawCerts) == 0 {
				return fmt.Errorf("agentapi: TLS pin: peer presented no certificate")
			}
			got := sha256.Sum256(rawCerts[0]) // leaf DER
			if hex.EncodeToString(got[:]) != want {
				return fmt.Errorf("agentapi: TLS pin mismatch: agent leaf SHA-256 does not match the bootstrap fingerprint")
			}
			return nil
		},
		MinVersion: tls.VersionTLS12,
	}
	return &Client{
		baseURL: "https://" + endpoint,
		token:   token,
		hc: &http.Client{
			Timeout:   15 * time.Second,
			Transport: &http.Transport{TLSClientConfig: tlsCfg},
		},
	}, nil
}

// Storage calls GET /storage and returns this guest's mounts (connectivity + placement view).
func (c *Client) Storage(ctx context.Context) (StorageResponse, error) {
	var out StorageResponse
	body, err := c.get(ctx, "/storage")
	if err != nil {
		return out, err
	}
	if err := json.Unmarshal(body, &out); err != nil {
		return out, fmt.Errorf("agentapi: decode /storage: %w", err)
	}
	return out, nil
}

// ---- slice 8B: app-consistent backup (quiesce loop) -------------------------------------

// DueResponse mirrors the agent's GET /backup/due payload.
type DueResponse struct {
	VMID   int    `json:"vmid"`
	Due    bool   `json:"due"`
	Reason string `json:"reason"`
}

// BackupResponse mirrors the agent's POST /backup payload.
type BackupResponse struct {
	VMID  int    `json:"vmid"`
	JobID string `json:"job_id"`
	Phase string `json:"phase"`
}

// StatusResponse mirrors the agent's GET /backup/status payload.
type StatusResponse struct {
	VMID  int    `json:"vmid"`
	Phase string `json:"phase"` // idle | running | done | failed
	JobID string `json:"job_id"`
	Error string `json:"error"`
}

// Backup status phases (mirror the agent's vocabulary).
const (
	PhaseIdle    = "idle"
	PhaseRunning = "running"
	PhaseDone    = "done"
	PhaseFailed  = "failed"
)

// BackupDue reports whether a policy-scheduled backup is due for this guest (the quiesce trigger).
func (c *Client) BackupDue(ctx context.Context) (DueResponse, error) {
	var out DueResponse
	body, err := c.get(ctx, "/backup/due")
	if err != nil {
		return out, err
	}
	if err := json.Unmarshal(body, &out); err != nil {
		return out, fmt.Errorf("agentapi: decode /backup/due: %w", err)
	}
	return out, nil
}

// StartBackup enqueues a backup of this guest (the agent vzdump) and returns the job to poll.
func (c *Client) StartBackup(ctx context.Context) (BackupResponse, error) {
	var out BackupResponse
	body, err := c.post(ctx, "/backup", struct{}{})
	if err != nil {
		return out, err
	}
	if err := json.Unmarshal(body, &out); err != nil {
		return out, fmt.Errorf("agentapi: decode POST /backup: %w", err)
	}
	return out, nil
}

// BackupStatus reports the current/last backup job phase for this guest.
func (c *Client) BackupStatus(ctx context.Context) (StatusResponse, error) {
	var out StatusResponse
	body, err := c.get(ctx, "/backup/status")
	if err != nil {
		return out, err
	}
	if err := json.Unmarshal(body, &out); err != nil {
		return out, fmt.Errorf("agentapi: decode /backup/status: %w", err)
	}
	return out, nil
}

// get issues an authenticated GET and unwraps the {ok,data,error} envelope.
func (c *Client) get(ctx context.Context, path string) (json.RawMessage, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+path, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Authorization", "Bearer "+c.token)
	resp, err := c.hc.Do(req)
	if err != nil {
		return nil, fmt.Errorf("agentapi: GET %s: %w", path, err)
	}
	defer resp.Body.Close()
	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("agentapi: GET %s: HTTP %d", path, resp.StatusCode)
	}
	var env apiResponse
	if err := json.Unmarshal(raw, &env); err != nil {
		return nil, fmt.Errorf("agentapi: GET %s: bad envelope: %w", path, err)
	}
	if !env.OK {
		return nil, fmt.Errorf("agentapi: GET %s: %s", path, env.Error)
	}
	return env.Data, nil
}

// post issues an authenticated JSON POST and unwraps the {ok,data,error} envelope. The agent
// returns 200 or 202 for accepted requests.
func (c *Client) post(ctx context.Context, path string, body any) (json.RawMessage, error) {
	buf, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+path, bytes.NewReader(buf))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Authorization", "Bearer "+c.token)
	req.Header.Set("Content-Type", "application/json")
	resp, err := c.hc.Do(req)
	if err != nil {
		return nil, fmt.Errorf("agentapi: POST %s: %w", path, err)
	}
	defer resp.Body.Close()
	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusAccepted {
		return nil, fmt.Errorf("agentapi: POST %s: HTTP %d", path, resp.StatusCode)
	}
	var env apiResponse
	if err := json.Unmarshal(raw, &env); err != nil {
		return nil, fmt.Errorf("agentapi: POST %s: bad envelope: %w", path, err)
	}
	if !env.OK {
		return nil, fmt.Errorf("agentapi: POST %s: %s", path, env.Error)
	}
	return env.Data, nil
}

// normalizeFingerprint lowercases and strips ':'/' ' separators, requiring a 64-hex SHA-256.
func normalizeFingerprint(fp string) (string, error) {
	s := strings.ToLower(strings.NewReplacer(":", "", " ", "", "\t", "").Replace(strings.TrimSpace(fp)))
	if len(s) != 64 {
		return "", fmt.Errorf("agentapi: fingerprint must be a SHA-256 (64 hex chars), got %d", len(s))
	}
	if _, err := hex.DecodeString(s); err != nil {
		return "", fmt.Errorf("agentapi: fingerprint is not valid hex: %w", err)
	}
	return s, nil
}