package osupdate

import (
	"context"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"time"

	"gitea.dooplex.hu/admin/felhom-agent/internal/signedjobs"
)

// OpConfigUpdate is the signed op that brings a box's ROOT-OWNED files (sudoers, wrappers, units) to a release's config
// bundle (R-840, `11` §5.4.2). The params pin the agent version and the bundle's sha256; the root wrapper re-verifies
// the signature, the host binding, the nonce and the sha ITSELF — this executor is only the courier.
const OpConfigUpdate = "agent_config_update"

// BundleFileName is the bundle's name beside the binary in the Gitea generic package felhom-agent/<version>/.
const BundleFileName = "felhom-config-bundle.json"

var (
	bundleVersionRe = regexp.MustCompile(`^[0-9]+\.[0-9]+\.[0-9]+(-[0-9A-Za-z.]+)?$`)
	bundleSHARe     = regexp.MustCompile(`^[0-9a-f]{64}$`)
)

// ConfigUpdateParams are the signed params (the wrapper reads the same two names out of the signed blob).
type ConfigUpdateParams struct {
	AgentVersion string `json:"agent_version"`
	BundleSHA256 string `json:"bundle_sha256"`
}

// BundleURL derives the bundle's URL from the agent binary's URL template (".../felhom-agent/{version}/felhom-agent").
func BundleURL(binaryTemplate, version string) (string, error) {
	if !strings.HasSuffix(binaryTemplate, "/felhom-agent") || !strings.Contains(binaryTemplate, "{version}") {
		return "", fmt.Errorf("cannot derive the bundle URL from %q (want …/{version}/felhom-agent)", binaryTemplate)
	}
	t := strings.TrimSuffix(binaryTemplate, "felhom-agent") + BundleFileName
	return strings.ReplaceAll(t, "{version}", version), nil
}

// ConfigUpdateExecutor runs a verified agent_config_update (signedjobs.Executor).
type ConfigUpdateExecutor struct {
	Leg         *Leg
	URLTemplate string // the agent binary's template (config.SelfUpdate.URLTemplate)
	Username    string
	Token       string
	HTTPClient  *http.Client
	// AfterInstall runs after a bundle installed (the capability re-probe; nil = none).
	AfterInstall func(ctx context.Context)
}

// Execute implements signedjobs.Executor.
func (e ConfigUpdateExecutor) Execute(ctx context.Context, op string, params json.RawMessage) error {
	if op != OpConfigUpdate {
		return signedjobs.ErrNoExecutor
	}
	so, ok := signedjobs.SignedOpFrom(ctx)
	if !ok {
		return fmt.Errorf("agent_config_update: no signed envelope in the context — the wrapper could not verify it")
	}
	var p ConfigUpdateParams
	if err := json.Unmarshal(params, &p); err != nil {
		return fmt.Errorf("agent_config_update: bad params: %w", err)
	}
	if !bundleVersionRe.MatchString(p.AgentVersion) || !bundleSHARe.MatchString(p.BundleSHA256) {
		return fmt.Errorf("agent_config_update: params must pin agent_version (semver) and bundle_sha256 (64 hex)")
	}
	lg := e.Leg.log().With("op", OpConfigUpdate, "agent_version", p.AgentVersion)
	url, err := BundleURL(e.URLTemplate, p.AgentVersion)
	if err != nil {
		return fmt.Errorf("agent_config_update: %w", err)
	}
	dir := e.Leg.PlanDir
	if dir == "" {
		dir = DefaultPlanDir
	}
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return fmt.Errorf("agent_config_update: plan dir: %w", err)
	}
	path := filepath.Join(dir, "bundle-"+p.AgentVersion+".json")
	start := time.Now()
	got, err := e.download(ctx, url, path)
	if err != nil {
		_ = os.Remove(path)
		return fmt.Errorf("agent_config_update: download %s: %w", url, err)
	}
	defer os.Remove(path)
	// The agent's own check is a courtesy (an early, clear error); the wrapper's is the gate.
	if got != p.BundleSHA256 {
		return fmt.Errorf("agent_config_update: the downloaded bundle's sha256 is %s, the signed job pins %s — nothing installed", got, p.BundleSHA256)
	}
	lg.Info("osupdate: config bundle downloaded; handing it to the root wrapper", "sha256", got[:16], "duration_ms", time.Since(start).Milliseconds())
	runID := "bundle-" + e.Leg.now().UTC().Format("20060102T150405Z")
	wr, err := e.Leg.call(ctx, runID, map[string]any{"release_id": "bundle-" + p.AgentVersion, "layer": LayerHost,
		"mode": "bundle", "bundle": path,
		"signed": map[string]string{"blob_b64": base64.StdEncoding.EncodeToString(so.Blob), "sig": string(so.Sig)}})
	if err != nil {
		return fmt.Errorf("agent_config_update: %w", err)
	}
	if wr.refused() {
		lg.Warn("osupdate: config bundle REFUSED by the wrapper — nothing changed", "refused", string(wr.Refused))
		return fmt.Errorf("agent_config_update: refused: %s", wr.Refused)
	}
	if wr.failed() {
		lg.Error("osupdate: config bundle FAILED — the wrapper put the previous files back", "failed", string(wr.Failed), "bundle", string(wr.Bundle))
		return fmt.Errorf("agent_config_update: failed (previous files restored): %s", wr.Failed)
	}
	lg.Warn("osupdate: config bundle INSTALLED", "bundle", string(wr.Bundle), "pass_seconds", wr.PassSeconds)
	if e.AfterInstall != nil {
		e.AfterInstall(ctx)
	}
	return nil
}

func (e ConfigUpdateExecutor) download(ctx context.Context, url, dest string) (string, error) {
	hc := e.HTTPClient
	if hc == nil {
		hc = &http.Client{Timeout: 2 * time.Minute}
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return "", err
	}
	if e.Username != "" || e.Token != "" {
		req.SetBasicAuth(e.Username, e.Token)
	}
	resp, err := hc.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return "", fmt.Errorf("HTTP %d", resp.StatusCode)
	}
	f, err := os.OpenFile(dest, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o600)
	if err != nil {
		return "", err
	}
	h := sha256.New()
	// 4 MB is the wrapper's own limit; read one byte more so an oversized bundle fails there, visibly.
	if _, err := io.Copy(io.MultiWriter(f, h), io.LimitReader(resp.Body, 4*1024*1024+1)); err != nil {
		f.Close()
		return "", err
	}
	if err := f.Close(); err != nil {
		return "", err
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}