package plugins

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/url"
	"os"
	"path/filepath"

	commonv1 "code.icb4dc0.de/buildr/api/generated/common/v1"
	wasiv1 "code.icb4dc0.de/buildr/api/generated/wasi/v1"

	"code.icb4dc0.de/buildr/buildr/internal/config"
	"code.icb4dc0.de/buildr/buildr/internal/slices"

	"github.com/go-git/go-git/v5/plumbing/hash"
	"github.com/google/uuid"
	"golang.org/x/sync/errgroup"

	"code.icb4dc0.de/buildr/buildr/internal/ioutils"
	"code.icb4dc0.de/buildr/buildr/modules"
	"code.icb4dc0.de/buildr/buildr/modules/plugin"

	"code.icb4dc0.de/buildr/buildr/modules/state"
)

type Manager struct {
	Downloader Downloader
	plugins    state.Plugins
	cacheDir   string
}

func (p *Manager) Init(plugins state.Plugins, cacheDir string) {
	p.cacheDir = cacheDir
	p.plugins = plugins
}

func (p *Manager) Register(ctx context.Context, registry *modules.TypeRegistry) error {
	plugins, err := p.plugins.List(ctx)
	if err != nil {
		return err
	}

	grp, grpcCtx := errgroup.WithContext(ctx)
	for _, registeredPlugin := range plugins {
		registeredPlugin := registeredPlugin
		grp.Go(func() error {
			knownModules, err := p.plugins.ModulesForPlugin(grpcCtx, *registeredPlugin.ID)
			if err != nil {
				return err
			}

			for _, module := range knownModules {
				module := module
				registry.RegisterModule(modules.ModuleFactoryFunc(func() modules.ModuleWithMeta {
					var (
						defaultSpec = new(commonv1.ModuleSpec)
						mod         = plugin.Module{
							PluginPayload: &plugin.PayloadFile{
								Path:     registeredPlugin.LocalPath,
								Checksum: registeredPlugin.Hash,
							},
							PluginCategory: module.Category,
							PluginType:     module.Type,
							ModuleSpec:     make(map[string]any),
						}
					)

					if err := defaultSpec.UnmarshalVT(module.DefaultSpec); err == nil {
						mod.SetModuleSpec(defaultSpec)
					}

					return &modules.Metadata[plugin.Module]{
						Module: mod,
					}
				}))
			}

			return nil
		})
	}

	return grp.Wait()
}

func (p *Manager) UpdatePlugins(ctx context.Context, refs ...config.PluginReference) error {
	knownPlugins, err := p.plugins.List(ctx)
	if err != nil {
		return err
	}

	pluginsByName := make(map[string]state.Plugin, len(knownPlugins))
	for _, p := range knownPlugins {
		pluginsByName[p.Name] = p
	}

	for _, pluginReference := range refs {
		var requiredDownload bool
		if knownPlugin, ok := pluginsByName[pluginReference.Name]; !ok {
			requiredDownload = true
		} else {
			delete(pluginsByName, pluginReference.Name)
			if requiredDownload, err = p.validateKnownPlugin(knownPlugin, pluginReference); err != nil {
				return err
			}
		}

		if requiredDownload {
			slog.Info("Downloading plugin", slog.String("plugin", pluginReference.Name))
			if downloadedPlugin, payload, err := p.downloadPlugin(ctx, pluginReference); err != nil {
				return err
			} else if pluginID, err := p.plugins.UpsertPlugin(ctx, *downloadedPlugin); err != nil {
				return err
			} else if inventory, err := plugin.DiscoverInventory(ctx, payload); err != nil {
				return err
			} else {
				pluginModules := slices.Map(inventory.Specs, func(in *wasiv1.PluginInventoryResponse_InventorySpec) state.PluginModule {
					return moduleReferenceToPluginModule(pluginID, in)
				})
				if err := p.plugins.UpsertModules(ctx, pluginModules); err != nil {
					return err
				}
			}
		}
	}

	for _, obsoletePlugin := range pluginsByName {
		slog.Info("Removing obsolete plugin", slog.String("plugin", obsoletePlugin.Name))
		if err := os.Remove(obsoletePlugin.LocalPath); err != nil {
			if !errors.Is(err, os.ErrNotExist) {
				return err
			}
		}

		if err := p.plugins.Remove(ctx, *obsoletePlugin.ID); err != nil {
			return err
		}
	}

	return nil
}

func (p *Manager) downloadPlugin(ctx context.Context, ref config.PluginReference) (pl *state.Plugin, payload []byte, err error) {
	pluginURL, err := url.Parse(ref.URL)
	if err != nil {
		return nil, nil, err
	}

	targetPath := filepath.Join(p.cacheDir, ref.Name)
	if err := p.Downloader.Download(ctx, targetPath, pluginURL); err != nil {
		return nil, nil, err
	}

	computedHash, payload, err := hashFile(targetPath, sha256.New())
	if err != nil {
		return nil, nil, err
	}

	if ref.Checksum != nil {
		expectedHash, err := hex.DecodeString(*ref.Checksum)
		if err != nil {
			return nil, nil, err
		}

		if !bytes.Equal(expectedHash, computedHash) {
			return nil, nil, fmt.Errorf("plugin checksum mismatch - expected %s, got %s", *ref.Checksum, hex.EncodeToString(computedHash))
		}
	}

	return &state.Plugin{
		Name:      ref.Name,
		URL:       pluginURL,
		LocalPath: targetPath,
		Hash:      computedHash,
	}, payload, nil
}

func (p *Manager) validateKnownPlugin(knownPlugin state.Plugin, ref config.PluginReference) (requireUpdate bool, err error) {
	// check if URL is valid
	_, err = url.Parse(ref.URL)
	if err != nil {
		return false, err
	}

	// expected file does not exist
	if _, err := os.Stat(knownPlugin.LocalPath); err != nil {
		return true, nil
	}

	// by default require update if URL was changed
	if ref.URL != knownPlugin.URL.String() {
		return true, nil
	}

	// check if SHA256 is valid
	computedHash, equal, err := validateHashForFile(knownPlugin.LocalPath, knownPlugin.Hash)
	if err != nil {
		return false, err
	} else if !equal {
		return true, nil
	}

	// if checksum differs from expected, require update
	if ref.Checksum != nil {
		expectedChecksum, err := hex.DecodeString(*ref.Checksum)
		if err != nil {
			return false, err
		}

		if !bytes.Equal(computedHash, expectedChecksum) {
			return true, nil
		}
	}

	return false, nil
}

func validateHashForFile(filePath string, expectedHash []byte) (computedHash []byte, equal bool, err error) {
	computedHash, _, err = hashFile(filePath, sha256.New())
	if err != nil {
		return nil, false, err
	}

	if !bytes.Equal(expectedHash, computedHash) {
		return nil, false, nil
	}

	return computedHash, true, nil
}

func hashFile(filePath string, h hash.Hash) (computedHash, payload []byte, err error) {
	f, err := os.Open(filePath)
	if err != nil {
		return nil, nil, err
	}

	defer func() {
		_ = f.Close()
	}()

	buf := bytes.NewBuffer(nil)
	w := io.MultiWriter(h, buf)

	if _, err := ioutils.CopyWithPooledBuffer(w, f); err != nil {
		return nil, nil, err
	}

	return h.Sum(nil), buf.Bytes(), nil
}

func moduleReferenceToPluginModule(pluginID uuid.UUID, in *wasiv1.PluginInventoryResponse_InventorySpec) state.PluginModule {
	return state.PluginModule{
		PluginID:    pluginID,
		Type:        in.ModuleRef.ModuleType,
		Category:    in.ModuleRef.ModuleCategory,
		DefaultSpec: in.EmptySpec,
	}
}