// Copyright (C) 2026 Dcntrlized
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package containers

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
	"time"

	"git.dcntrlized.org/Dcntrlized/Maestro/lib/authmgmt"
	"git.dcntrlized.org/Dcntrlized/Maestro/lib/docker"
	"git.dcntrlized.org/Dcntrlized/Maestro/lib/logger"
	"git.dcntrlized.org/Dcntrlized/Maestro/lib/types"
	"github.com/docker/docker/api/types/image"
	registrytypes "github.com/docker/docker/api/types/registry"
)

// InstallContainer downloads the raw docker-compose.yaml and pulls the Docker image.
func InstallContainer(ctx context.Context, item types.RegistryContainer) error {
	// 1. Determine storage path (XDG_DATA_HOME or ~/.dcntrlized/[name]/)
	targetDir, err := getContainerDataDir(item.Name)
	if err != nil {
		return fmt.Errorf("failed to determine data directory: %w", err)
	}

	if err := os.MkdirAll(targetDir, 0755); err != nil {
		return fmt.Errorf("failed to create directory %s: %w", targetDir, err)
	}

	// 2. Fetch raw docker-compose.yaml from the Git URL
	rawURL, err := composeRawURL(item)
	if err != nil {
		return fmt.Errorf("failed to resolve repository URL: %w", err)
	}
	composePath := filepath.Join(targetDir, "docker-compose.yaml")

	logger.Info("Fetching compose file from %s...", rawURL)
	if err := downloadCompose(ctx, rawURL, composePath); err != nil {
		return fmt.Errorf("failed to download docker-compose.yaml: %w", err)
	}

	// 2.5. Persist install metadata so installed-but-not-running state can be tracked without Docker lookups
	// The version is required for update detection; fall back to the image tag when the payload omitted it.
	if item.Version == "" {
		item.Version = imageTag(item.Image)
	}
	metadata := types.InstalledMetadata{
		RegistryContainer: item,
		InstalledAt:       time.Now().UTC().Format(time.RFC3339),
	}

	// 2.6. Pin the auth service's signing key (security theme M2 §5): fetch its
	// attestation over plaintext HTTP and store the fingerprint in the install
	// record so the container gets AUTH_PINNED_FINGERPRINT at start. This is an
	// app-level fingerprint comparison, not a transport identity. Best-effort —
	// when the auth service is not reachable yet the pin stays empty and is
	// retried on start.
	if att, err := fetchAuthAttestation(ctx); err == nil {
		metadata.AuthFingerprint = att.Fingerprint
		metadata.AuthKid = att.Kid
		metadata.AuthAttestedAt = att.IssuedAt
	} else {
		logger.Warn("Install %s: auth attestation not pinned (will retry at start): %v", item.Name, err)
	}

	metadataPath := filepath.Join(targetDir, "metadata.json")
	if err := writeMetadata(metadataPath, metadata); err != nil {
		return fmt.Errorf("failed to write metadata: %w", err)
	}

	// 3. Pull the Docker Image with Registry Authentication
	logger.Info("Pulling docker image %s...", item.Image)
	cli, err := docker.NewDockerClient()
	if err != nil {
		return fmt.Errorf("failed to initialize docker client: %w", err)
	}
	defer cli.Close()

	pullOpts := image.PullOptions{}

	// Build auth payload if git credentials or registry auth env vars exist
	authHeader, err := buildRegistryAuthHeader()
	if err != nil {
		return fmt.Errorf("failed to create registry auth: %w", err)
	}
	if authHeader != "" {
		pullOpts.RegistryAuth = authHeader
	}

	reader, err := cli.ImagePull(ctx, item.Image, pullOpts)
	if err != nil {
		return fmt.Errorf("failed to pull docker image %s: %w", item.Image, err)
	}
	defer reader.Close()

	// Drain reader stream to ensure Docker finishes downloading layers
	_, _ = io.Copy(io.Discard, reader)

	logger.Info("Successfully installed container service: %s", item.Name)
	return nil
}

// buildRegistryAuthHeader builds the base64-encoded auth header required by Docker SDK
func buildRegistryAuthHeader() (string, error) {
	username := os.Getenv("REGISTRY_USER")
	token := os.Getenv("GIT_TOKEN")
	if token == "" {
		token = os.Getenv("GITHUB_TOKEN")
	}

	// For Gitea/Forgejo container registries, token auth works using "token" or your username as the user, and GIT_TOKEN as password.
	if username == "" {
		username = "oauth2" // Fallback username when using personal access tokens
	}

	if token == "" {
		return "", nil // No token set; proceed unauthenticated
	}

	authConfig := registrytypes.AuthConfig{
		Username: username,
		Password: token,
	}

	encodedJSON, err := json.Marshal(authConfig)
	if err != nil {
		return "", err
	}

	return base64.URLEncoding.EncodeToString(encodedJSON), nil
}

// getDataRoot resolves the directory that stores installed container metadata,
// using the first variable that is set. DCNTRLIZED_INSTALL_DIR is used as-is;
// the others are base dirs with ".dcntrlized" appended.
func getDataRoot() (string, error) {
	if dir := os.Getenv("DCNTRLIZED_INSTALL_DIR"); dir != "" {
		return dir, nil
	}

	if xdg := os.Getenv("XDG_DATA_HOME"); xdg != "" {
		return filepath.Join(xdg, ".dcntrlized"), nil
	}

	if xdgHome := os.Getenv("XDG_HOME_DIR"); xdgHome != "" {
		return filepath.Join(xdgHome, ".dcntrlized"), nil
	}

	if home := os.Getenv("HOME"); home != "" {
		return filepath.Join(home, ".dcntrlized"), nil
	}

	return filepath.Join("/data", ".dcntrlized"), nil
}

// DataRoot is the exported accessor for the storage root shared by installed
// container metadata and Maestro's private key material (instance identity,
// session/secrets keys, config-signing keypair).
func DataRoot() (string, error) {
	return getDataRoot()
}

// EnsureDataRoot creates the data root directory if it does not exist yet.
// This gives a clear, early error when the install directory is missing or not
// writable (e.g. the container's bind mount source was removed) instead of a
// confusing "no such file or directory" when installing a container.
//
// When started as root inside the container it hands the data root over to the
// host user (discovered at runtime, or overridden via DCNTRLIZED_UID/GID) and
// drops privileges, so every file created afterwards stays user-owned.
func EnsureDataRoot() error {
	root, err := getDataRoot()
	if err != nil {
		return err
	}
	if err := os.MkdirAll(root, 0755); err != nil {
		return fmt.Errorf("failed to create data root %s (is the host directory present and writable?): %w", root, err)
	}
	if os.Geteuid() == 0 {
		identity, err := resolveRuntimeIdentity(root)
		if err != nil {
			return err
		}
		if err := healOwnerState(root, identity); err != nil {
			return fmt.Errorf("failed to hand owner state dir to uid %d: %w", identity.uid, err)
		}
		if err := os.Chown(root, identity.uid, identity.gid); err != nil {
			return fmt.Errorf("failed to chown data root %s to %d:%d: %w", root, identity.uid, identity.gid, err)
		}
		if err := dropPrivileges(identity, root); err != nil {
			return err
		}
	}
	return nil
}

// healOwnerState gives the instance-owner gate's state directory to the
// runtime user. Boots before the privilege drop opened the gate's stores as
// root first, leaving a root-owned <root>/maestro behind; after the handoff
// every write then failed with EACCES (surfacing as a bogus
// ERR_INVALID_CREDENTIALS on /api/auth/setup). Repairs such installs here,
// while the process can still chown. Missing dirs are fine — nothing to heal.
func healOwnerState(root string, id runtimeIdentity) error {
	dir := filepath.Join(root, "maestro")
	entries, err := os.ReadDir(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return fmt.Errorf("read owner state dir: %w", err)
	}
	if err := os.Chown(dir, id.uid, id.gid); err != nil {
		return fmt.Errorf("chown %s: %w", dir, err)
	}
	for _, e := range entries {
		p := filepath.Join(dir, e.Name())
		if err := os.Chown(p, id.uid, id.gid); err != nil && !os.IsNotExist(err) {
			return fmt.Errorf("chown %s: %w", p, err)
		}
	}
	return nil
}

// runtimeIdentity is the user the container should run as, plus any
// supplementary groups needed to keep working (e.g. the docker socket group).
type runtimeIdentity struct {
	username string
	hostDir  string
	uid, gid int
	groups   []int
}

// resolveRuntimeIdentity determines the user to hand the data root to.
// An explicit DCNTRLIZED_UID/GID wins; otherwise the host user is discovered
// from the bind-mounted home directory, falling back to the data root's owner
// (self-heals upgrades) and finally to uid 1000.
func resolveRuntimeIdentity(dataRoot string) (runtimeIdentity, error) {
	username := filepath.Base(hostPath(mountSource("/host-home")))
	if username == "" || username == "." || username == "/" {
		username = "user"
	}
	hostDir := hostPath(mountSource(dataRoot))
	if hostDir == "" {
		hostDir = "(unknown)"
	}

	var id runtimeIdentity
	if uidStr := os.Getenv("DCNTRLIZED_UID"); uidStr != "" {
		uid, err := strconv.Atoi(uidStr)
		if err != nil {
			return runtimeIdentity{}, fmt.Errorf("invalid DCNTRLIZED_UID %q: %w", uidStr, err)
		}
		gid, err := strconv.Atoi(os.Getenv("DCNTRLIZED_GID"))
		if err != nil {
			gid = uid
		}
		id = runtimeIdentity{uid: uid, gid: gid, groups: dockerSocketGroups(uid)}
	} else {
		uid, gid, err := discoverHostUser(dataRoot)
		if err != nil {
			return runtimeIdentity{}, err
		}
		id = runtimeIdentity{uid: uid, gid: gid, groups: dockerSocketGroups(uid)}
	}

	id.username, id.hostDir = username, hostDir
	logger.Info("User: %s (%d, %d)", id.username, id.uid, id.gid)
	return id, nil
}

// discoverHostUser finds the host user's uid/gid, preferring the read-only
// bind mount of the host home directory, then the data root's owner.
func discoverHostUser(dataRoot string) (uid, gid int, err error) {
	if uid, gid, ok := statOwner("/host-home"); ok && uid != 0 {
		logger.Debug("Host user resolved from /host-home")
		return uid, gid, nil
	}
	if uid, gid, ok := statOwner(dataRoot); ok && uid != 0 {
		logger.Debug("Host user resolved from data root owner")
		return uid, gid, nil
	}
	logger.Warn("Could not determine host user (no /host-home or owned data root); defaulting to uid 1000")
	return 1000, 1000, nil
}

// statOwner returns the numeric uid/gid owning the given path.
func statOwner(path string) (uid, gid int, ok bool) {
	st, err := os.Stat(path)
	if err != nil {
		return 0, 0, false
	}
	sys, ok := st.Sys().(*syscall.Stat_t)
	if !ok {
		return 0, 0, false
	}
	return int(sys.Uid), int(sys.Gid), true
}

// mountSource returns the host source path of the bind mount at mountPoint by
// parsing /proc/self/mountinfo, or "" when the mount does not exist.
func mountSource(mountPoint string) string {
	data, err := os.ReadFile("/proc/self/mountinfo")
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(data), "\n") {
		fields := strings.Fields(line)
		if len(fields) < 5 {
			continue
		}
		// Format: <id> <parent> <major:minor> <root> <mountpoint> <opts> ...
		// For bind mounts, <root> is the source path on the host.
		if fields[4] == mountPoint {
			return unescapeMountPath(fields[3])
		}
	}
	return ""
}

// unescapeMountPath decodes the octal escapes used in mountinfo paths (e.g. \040).
func unescapeMountPath(s string) string {
	if !strings.Contains(s, `\`) {
		return s
	}
	var b strings.Builder
	for i := 0; i < len(s); i++ {
		if s[i] == '\\' && i+3 < len(s) {
			if v, err := strconv.ParseUint(s[i+1:i+4], 8, 8); err == nil {
				b.WriteByte(byte(v))
				i += 3
				continue
			}
		}
		b.WriteByte(s[i])
	}
	return b.String()
}

// hostPath converts a mount source into a host-visible path. Btrfs encodes
// subvolumes as "@name/..." (e.g. "@home/franciscofadigas" mounted at
// "/home/franciscofadigas"); ordinary sources already start with "/".
func hostPath(source string) string {
	if source == "" {
		return ""
	}
	if strings.HasPrefix(source, "/@") {
		return "/" + strings.TrimPrefix(source, "/@")
	}
	if strings.HasPrefix(source, "@") {
		return "/" + strings.TrimPrefix(source, "@")
	}
	return source
}

// dockerSocketPath is where the host's docker socket is mounted into the container.
const dockerSocketPath = "/var/run/docker.sock"

// dockerSocketGroups returns the group of the mounted docker socket when it is
// group-accessible, so the container can keep talking to it after dropping
// privileges without hardcoding the host's docker group id.
func dockerSocketGroups(runAsUID int) []int {
	st, err := os.Stat(dockerSocketPath)
	if err != nil {
		return nil
	}
	if st.Mode()&0o020 == 0 {
		return nil
	}
	sys, ok := st.Sys().(*syscall.Stat_t)
	if !ok || sys.Gid == 0 || int(sys.Gid) == runAsUID {
		return nil
	}
	return []int{int(sys.Gid)}
}

// dropPrivileges switches the process to the given uid/gid, keeping the
// supplementary groups needed for the docker socket.
func dropPrivileges(id runtimeIdentity, guestDir string) error {
	if err := syscall.Setgroups(id.groups); err != nil {
		return fmt.Errorf("failed to set supplementary groups %v: %w", id.groups, err)
	}
	if err := syscall.Setgid(id.gid); err != nil {
		return fmt.Errorf("failed to set gid to %d: %w", id.gid, err)
	}
	if err := syscall.Setuid(id.uid); err != nil {
		return fmt.Errorf("failed to set uid to %d: %w", id.uid, err)
	}
	if os.Geteuid() != id.uid {
		return fmt.Errorf("failed to drop privileges: still running as euid %d (want %d)", os.Geteuid(), id.uid)
	}
	logger.Info("Handoff %s (%s) %d:%d", guestDir, id.hostDir, id.uid, id.gid)
	return nil
}

func getContainerDataDir(serviceName string) (string, error) {
	root, err := getDataRoot()
	if err != nil {
		return "", err
	}
	return filepath.Join(root, serviceName), nil
}

// composeRawURL resolves the raw docker-compose.yaml URL for a container,
// preferring the repository URL in item.URL (falling back to item.Source) and
// rejecting URLs without an http/https scheme.
func composeRawURL(item types.RegistryContainer) (string, error) {
	base := strings.TrimRight(item.URL, "/")
	if base == "" {
		base = strings.TrimRight(item.Source, "/")
	}
	u, err := url.Parse(base)
	if err != nil || (u.Scheme != "http" && u.Scheme != "https") {
		return "", fmt.Errorf("invalid repository URL %q", base)
	}
	return fmt.Sprintf("%s/raw/branch/master/docker-compose.yaml", base), nil
}

// downloadCompose fetches the compose file, retrying on the main branch when
// the repository's default branch is not master.
func downloadCompose(ctx context.Context, url, destPath string) error {
	err := downloadFile(ctx, url, destPath)
	if err != nil {
		mainURL := strings.Replace(url, "/raw/branch/master/", "/raw/branch/main/", 1)
		if mainURL != url {
			if retryErr := downloadFile(ctx, mainURL, destPath); retryErr == nil {
				return nil
			}
		}
		return err
	}
	return nil
}

func downloadFile(ctx context.Context, url string, destPath string) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}

	token := os.Getenv("GIT_TOKEN")
	if token == "" {
		token = os.Getenv("GITHUB_TOKEN")
	}

	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode == http.StatusUnauthorized || resp.StatusCode == http.StatusForbidden {
		return fmt.Errorf("authentication failed (HTTP %d): ensure GIT_TOKEN is set and has access to the repository", resp.StatusCode)
	}

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("unexpected HTTP status fetching compose file: %s", resp.Status)
	}

	out, err := os.Create(destPath)
	if err != nil {
		return err
	}
	defer out.Close()

	_, err = io.Copy(out, resp.Body)
	return err
}

func writeMetadata(path string, metadata types.InstalledMetadata) error {
	data, err := json.MarshalIndent(metadata, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, 0644)
}

// fetchAuthAttestation fetches the auth service's public key statement over
// plaintext HTTP (rev 9 removed the mTLS identity layer). It backs the M2 §5
// app-level pin: the returned fingerprint is what consumer containers are
// pinned to.
func fetchAuthAttestation(ctx context.Context) (*authmgmt.Attestation, error) {
	client, err := authmgmt.New()
	if err != nil {
		return nil, fmt.Errorf("auth management client: %w", err)
	}
	fetchCtx, cancel := context.WithTimeout(ctx, 8*time.Second)
	defer cancel()
	att, err := client.Attestation(fetchCtx)
	if err != nil {
		return nil, err
	}
	if att.Fingerprint == "" {
		return nil, fmt.Errorf("attestation carried an empty fingerprint")
	}
	return att, nil
}