package graph

import (
	"bytes"
	"crypto/ed25519"
	"crypto/rand"
	"encoding/pem"
	"errors"
	"fmt"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"golang.org/x/crypto/ssh"

	"github.com/brasse-b/archivum/internal/auth"
	"github.com/brasse-b/archivum/internal/config"
	"github.com/brasse-b/archivum/internal/git"
)

// The identity used for commits that the sync engine itself creates
// (merge commits, pre-reset snapshots).
const (
	syncAuthor = "Archivum Sync"
	syncEmail  = "sync@archivum.local"
)

// ── SSH key management ────────────────────────────────────────────────────────

// sshDir returns the directory holding the sync keypair and known_hosts,
// next to config.json so it lives on the persistent /config volume.
func (s *Server) sshDir() string {
	return filepath.Join(filepath.Dir(s.configPath), "ssh")
}

// ensureSSHKey generates an ed25519 keypair on first use and returns
// (keyPath, knownHostsPath, publicKey). The private key never leaves
// the server; the public key is what gets registered as a deploy key.
func (s *Server) ensureSSHKey() (string, string, string, error) {
	dir := s.sshDir()
	keyPath := filepath.Join(dir, "id_ed25519")
	pubPath := keyPath + ".pub"
	khPath := filepath.Join(dir, "known_hosts")

	if err := os.MkdirAll(dir, 0700); err != nil {
		return "", "", "", err
	}
	if f, err := os.OpenFile(khPath, os.O_CREATE, 0644); err == nil {
		f.Close()
	}

	if pub, err := os.ReadFile(pubPath); err == nil {
		if _, err := os.Stat(keyPath); err == nil {
			return keyPath, khPath, strings.TrimSpace(string(pub)), nil
		}
	}

	pub, priv, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return "", "", "", err
	}
	block, err := ssh.MarshalPrivateKey(priv, "archivum-git-sync")
	if err != nil {
		return "", "", "", err
	}
	if err := os.WriteFile(keyPath, pem.EncodeToMemory(block), 0600); err != nil {
		return "", "", "", err
	}
	sshPub, err := ssh.NewPublicKey(pub)
	if err != nil {
		return "", "", "", err
	}
	pubLine := bytes.TrimSpace(ssh.MarshalAuthorizedKey(sshPub))
	pubLine = append(pubLine, []byte(" archivum-git-sync\n")...)
	if err := os.WriteFile(pubPath, pubLine, 0644); err != nil {
		return "", "", "", err
	}
	log.Printf("[gitsync] generated new ssh keypair at %s", keyPath)
	return keyPath, khPath, strings.TrimSpace(string(pubLine)), nil
}

// ── Engine wiring ─────────────────────────────────────────────────────────────

// configureGitSync (re)applies git-sync settings: key, remote and the
// background ticker. Called from initRuntime and after updateGitSync.
func (s *Server) configureGitSync(cfg *config.Config) {
	s.syncMu.Lock()
	if s.syncStop != nil {
		close(s.syncStop)
		s.syncStop = nil
	}
	s.syncMu.Unlock()

	if cfg == nil {
		return
	}
	gs := cfg.GitSync
	gs.Normalize()

	s.mu.RLock()
	repo := s.gitRepo
	s.mu.RUnlock()
	if repo == nil || !gs.Enabled || gs.RemoteURL == "" {
		return
	}

	keyPath, khPath, _, err := s.ensureSSHKey()
	if err != nil {
		log.Printf("[gitsync] ssh key setup failed: %v", err)
		return
	}
	repo.SetSSHKey(keyPath, khPath)
	if err := repo.SetRemote(gs.RemoteURL); err != nil {
		log.Printf("[gitsync] setting remote failed: %v", err)
		return
	}
	log.Printf("[gitsync] enabled — remote=%s live=%s readOnly=%v auto=%dmin",
		gs.RemoteURL, gs.LiveBranch, gs.ReadOnly, gs.AutoSyncMinutes)

	stop := make(chan struct{})
	s.syncMu.Lock()
	s.syncStop = stop
	s.syncMu.Unlock()

	go func() {
		// One eager sync shortly after (re)configuration, then on the
		// configured interval. Manual-only mode still gets the eager
		// run so status is populated after a restart.
		timer := time.NewTimer(10 * time.Second)
		defer timer.Stop()
		select {
		case <-stop:
			return
		case <-timer.C:
			s.backgroundSync()
		}
		if gs.AutoSyncMinutes <= 0 {
			return
		}
		ticker := time.NewTicker(time.Duration(gs.AutoSyncMinutes) * time.Minute)
		defer ticker.Stop()
		for {
			select {
			case <-stop:
				return
			case <-ticker.C:
				s.backgroundSync()
			}
		}
	}()
}

// backgroundSync fetches and, when the live branch is checked out,
// fast-forwards it and pushes local commits. It never merges: anything
// that needs a real merge raises the attention flag for an admin.
func (s *Server) backgroundSync() {
	s.mu.RLock()
	repo := s.gitRepo
	cfg := s.cfg
	s.mu.RUnlock()
	if repo == nil || cfg == nil || !cfg.GitSync.Enabled {
		return
	}
	gs := cfg.GitSync

	record := func(err error, attention bool) {
		s.syncMu.Lock()
		s.lastSyncAt = time.Now().Format(time.RFC3339)
		if err != nil {
			s.lastSyncErr = err.Error()
		} else {
			s.lastSyncErr = ""
		}
		s.syncAttention = attention
		s.syncMu.Unlock()
	}

	if repo.MergeInProgress() {
		record(errors.New("merge väntar på att lösas i admin-panelen"), true)
		return
	}
	if err := repo.Fetch(); err != nil {
		record(fmt.Errorf("fetch: %w", err), false)
		return
	}
	// Bootstrap: an empty wiki (no commits yet) adopts the remote live
	// branch automatically, so a fresh instance needs no manual reset.
	if !repo.HasCommits() {
		if repo.RemoteBranchExists(gs.LiveBranch) {
			_, err := repo.ResetToRemote(gs.LiveBranch, syncAuthor, syncEmail)
			if err != nil {
				record(fmt.Errorf("bootstrap från remote: %w", err), true)
			} else {
				log.Printf("[gitsync] empty wiki bootstrapped from origin/%s", gs.LiveBranch)
				record(nil, false)
			}
			return
		}
	}
	current, err := repo.CurrentBranch()
	if err != nil || current != gs.LiveBranch {
		// Someone is working on another branch; leave it alone.
		record(nil, false)
		return
	}

	ahead, behind, hasUpstream := repo.AheadBehind(gs.LiveBranch)
	if !hasUpstream {
		if gs.ReadOnly {
			record(nil, false)
			return
		}
		record(repo.Push(gs.LiveBranch), false)
		return
	}
	if behind > 0 {
		if err := repo.Pull(gs.LiveBranch, syncAuthor, syncEmail, true); err != nil {
			// Not fast-forwardable (or unrelated histories): an admin
			// must pull/merge or reset from the UI.
			record(fmt.Errorf("kan inte snabbspola — manuell merge eller reset krävs (%w)", err), true)
			return
		}
	}
	if ahead > 0 && !gs.ReadOnly {
		if err := repo.Push(gs.LiveBranch); err != nil {
			record(fmt.Errorf("push: %w", err), false)
			return
		}
	}
	record(nil, false)
}

// gitSyncState returns the shared handles used by every handler below.
func (s *Server) gitSyncState() (*git.Repo, *config.Config) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.gitRepo, s.cfg
}

// ── GraphQL handlers (admin only) ─────────────────────────────────────────────

func (s *Server) handleGitSyncSettings(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	_, cfg := s.gitSyncState()
	if cfg == nil {
		writeGQLError(w, "server not initialised")
		return
	}
	gs := cfg.GitSync
	gs.Normalize()
	publicKey := ""
	if pub, err := os.ReadFile(filepath.Join(s.sshDir(), "id_ed25519.pub")); err == nil {
		publicKey = strings.TrimSpace(string(pub))
	}
	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitSyncSettings": map[string]interface{}{
				"enabled":         gs.Enabled,
				"remoteUrl":       gs.RemoteURL,
				"liveBranch":      gs.LiveBranch,
				"readOnly":        gs.ReadOnly,
				"autoSyncMinutes": gs.AutoSyncMinutes,
				"publicKey":       publicKey,
				"keySet":          publicKey != "",
			},
		},
	})
}

func (s *Server) handleUpdateGitSync(w http.ResponseWriter, req gqlRequest, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	input, ok := req.Variables["input"].(map[string]interface{})
	if !ok {
		input, _ = req.Variables["i"].(map[string]interface{})
	}
	if input == nil {
		writeGQLError(w, "missing input")
		return
	}
	s.mu.RLock()
	cfg := s.cfg
	s.mu.RUnlock()
	if cfg == nil {
		writeGQLError(w, "server not initialised")
		return
	}

	newCfg := *cfg
	gs := config.GitSyncConfig{
		Enabled:         boolVal(input, "enabled"),
		RemoteURL:       strings.TrimSpace(strVal(input, "remoteUrl")),
		LiveBranch:      strings.TrimSpace(strVal(input, "liveBranch")),
		ReadOnly:        boolVal(input, "readOnly"),
		AutoSyncMinutes: intVal(input, "autoSyncMinutes"),
	}
	gs.Normalize()
	newCfg.GitSync = gs

	if err := config.Save(s.configPath, &newCfg); err != nil {
		writeGQLError(w, fmt.Sprintf("failed to save config: %v", err))
		return
	}
	s.mu.Lock()
	s.cfg = &newCfg
	s.mu.Unlock()
	s.configureGitSync(&newCfg)

	log.Printf("[admin] git sync updated by %s (enabled=%v remote=%s)",
		sess.Username, gs.Enabled, gs.RemoteURL)
	writeJSON(w, `{"data":{"updateGitSync":true}}`)
}

func (s *Server) handleGitRegenerateKey(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	dir := s.sshDir()
	os.Remove(filepath.Join(dir, "id_ed25519"))
	os.Remove(filepath.Join(dir, "id_ed25519.pub"))
	_, _, publicKey, err := s.ensureSSHKey()
	if err != nil {
		writeGQLError(w, fmt.Sprintf("key generation failed: %v", err))
		return
	}
	s.mu.RLock()
	cfg := s.cfg
	s.mu.RUnlock()
	if cfg != nil {
		s.configureGitSync(cfg)
	}
	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitRegenerateKey": map[string]interface{}{"publicKey": publicKey},
		},
	})
}

func (s *Server) handleGitSyncStatus(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, cfg := s.gitSyncState()
	if repo == nil || cfg == nil {
		writeGQLError(w, "server not initialised")
		return
	}
	gs := cfg.GitSync
	gs.Normalize()

	current, _ := repo.CurrentBranch()
	ahead, behind, hasUpstream := 0, 0, false
	if gs.Enabled {
		ahead, behind, hasUpstream = repo.AheadBehind(current)
	}
	conflicts := repo.ConflictFiles()
	s.syncMu.Lock()
	lastAt, lastErr, attention := s.lastSyncAt, s.lastSyncErr, s.syncAttention
	s.syncMu.Unlock()

	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitSyncStatus": map[string]interface{}{
				"enabled":         gs.Enabled,
				"currentBranch":   current,
				"liveBranch":      gs.LiveBranch,
				"readOnly":        gs.ReadOnly,
				"ahead":           ahead,
				"behind":          behind,
				"hasUpstream":     hasUpstream,
				"dirty":           repo.HasUncommitted(),
				"mergeInProgress": repo.MergeInProgress(),
				"conflicts":       conflicts,
				"lastSyncAt":      lastAt,
				"lastSyncError":   lastErr,
				"attention":       attention || repo.MergeInProgress(),
			},
		},
	})
}

func (s *Server) handleGitBranches(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, _ := s.gitSyncState()
	if repo == nil {
		writeGQLError(w, "server not initialised")
		return
	}
	local, remote, err := repo.Branches()
	if err != nil {
		writeGQLError(w, err.Error())
		return
	}
	current, _ := repo.CurrentBranch()
	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitBranches": map[string]interface{}{
				"current": current,
				"local":   local,
				"remote":  remote,
			},
		},
	})
}

func (s *Server) handleGitCreateBranch(w http.ResponseWriter, req gqlRequest, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, _ := s.gitSyncState()
	name := strings.TrimSpace(strVal(req.Variables, "name"))
	if repo == nil || name == "" {
		writeGQLError(w, "missing branch name")
		return
	}
	if err := repo.CreateBranch(name); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	log.Printf("[gitsync] %s created branch %s", sess.Username, name)
	writeJSON(w, `{"data":{"gitCreateBranch":true}}`)
}

func (s *Server) handleGitSwitchBranch(w http.ResponseWriter, req gqlRequest, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, _ := s.gitSyncState()
	name := strings.TrimSpace(strVal(req.Variables, "name"))
	if repo == nil || name == "" {
		writeGQLError(w, "missing branch name")
		return
	}
	if repo.MergeInProgress() {
		writeGQLError(w, "merge in progress — resolve or abort it first")
		return
	}
	if err := repo.SwitchBranch(name); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	log.Printf("[gitsync] %s switched to branch %s", sess.Username, name)
	writeJSON(w, `{"data":{"gitSwitchBranch":true}}`)
}

func (s *Server) handleGitPull(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, cfg := s.gitSyncState()
	if repo == nil || cfg == nil || !cfg.GitSync.Enabled {
		writeGQLError(w, "git sync is not enabled")
		return
	}
	if err := repo.Fetch(); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	current, err := repo.CurrentBranch()
	if err != nil {
		writeGQLError(w, err.Error())
		return
	}
	result := "OK"
	err = repo.Pull(current, sess.Username, sess.Username+"@archivum.local", false)
	switch {
	case errors.Is(err, git.ErrMergeConflict):
		result = "MERGE_CONFLICT"
	case errors.Is(err, git.ErrUnrelatedHistories):
		result = "UNRELATED_HISTORIES"
	case err != nil:
		writeGQLError(w, err.Error())
		return
	}
	s.syncMu.Lock()
	s.lastSyncAt = time.Now().Format(time.RFC3339)
	s.lastSyncErr = ""
	s.syncAttention = result != "OK"
	s.syncMu.Unlock()
	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitPull": map[string]interface{}{
				"result":    result,
				"conflicts": repo.ConflictFiles(),
			},
		},
	})
}

func (s *Server) handleGitPush(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, cfg := s.gitSyncState()
	if repo == nil || cfg == nil || !cfg.GitSync.Enabled {
		writeGQLError(w, "git sync is not enabled")
		return
	}
	if cfg.GitSync.ReadOnly {
		writeGQLError(w, "repository is configured read-only — pushing is disabled")
		return
	}
	current, err := repo.CurrentBranch()
	if err != nil {
		writeGQLError(w, err.Error())
		return
	}
	if err := repo.Push(current); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	log.Printf("[gitsync] %s pushed %s", sess.Username, current)
	writeJSON(w, `{"data":{"gitPush":true}}`)
}

func (s *Server) handleGitResolveMerge(w http.ResponseWriter, req gqlRequest, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, _ := s.gitSyncState()
	if repo == nil {
		writeGQLError(w, "server not initialised")
		return
	}
	strategy := strVal(req.Variables, "strategy")
	paths := strSlice(req.Variables, "paths")
	if err := repo.ResolveConflicts(strategy, paths, sess.Username, sess.Username+"@archivum.local"); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	remaining := repo.ConflictFiles()
	if len(remaining) == 0 {
		s.syncMu.Lock()
		s.syncAttention = false
		s.syncMu.Unlock()
	}
	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitResolveMerge": map[string]interface{}{
				"resolved":  len(remaining) == 0,
				"remaining": remaining,
			},
		},
	})
}

func (s *Server) handleGitAbortMerge(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, _ := s.gitSyncState()
	if repo == nil {
		writeGQLError(w, "server not initialised")
		return
	}
	if err := repo.AbortMerge(); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	s.syncMu.Lock()
	s.syncAttention = false
	s.syncMu.Unlock()
	writeJSON(w, `{"data":{"gitAbortMerge":true}}`)
}

func (s *Server) handleGitResetFromRemote(w http.ResponseWriter, sess *auth.Session) {
	if !s.requireAdmin(w, sess) {
		return
	}
	repo, cfg := s.gitSyncState()
	if repo == nil || cfg == nil || !cfg.GitSync.Enabled {
		writeGQLError(w, "git sync is not enabled")
		return
	}
	if err := repo.Fetch(); err != nil {
		writeGQLError(w, err.Error())
		return
	}
	// Reset the current branch when it exists on the remote; otherwise
	// adopt the live branch (bootstrap case: local repo predates the
	// remote and is on an unrelated branch like master).
	current, err := repo.CurrentBranch()
	if err != nil || current == "" {
		current = cfg.GitSync.LiveBranch
	} else if _, _, hasUpstream := repo.AheadBehind(current); !hasUpstream {
		current = cfg.GitSync.LiveBranch
	}
	backup, err := repo.ResetToRemote(current, syncAuthor, syncEmail)
	if err != nil {
		writeGQLError(w, err.Error())
		return
	}
	s.syncMu.Lock()
	s.syncAttention = false
	s.lastSyncErr = ""
	s.syncMu.Unlock()
	log.Printf("[gitsync] %s reset %s from remote (backup: %s)", sess.Username, current, backup)
	writeJSONObj(w, map[string]interface{}{
		"data": map[string]interface{}{
			"gitResetFromRemote": map[string]interface{}{"backupBranch": backup},
		},
	})
}

func intVal(m map[string]interface{}, key string) int {
	if f, ok := m[key].(float64); ok {
		return int(f)
	}
	return 0
}