// Package switcher implements the account-switcher state machine.
// It is the only component allowed to flip the active Claude account.
package switcher

import (
	"context"
	"errors"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync/atomic"
	"time"

	"forge.secuaas.ovh/olivier/claude-failover/internal/config"
	"forge.secuaas.ovh/olivier/claude-failover/internal/notify"
	"forge.secuaas.ovh/olivier/claude-failover/internal/quota"
	"forge.secuaas.ovh/olivier/claude-failover/internal/safety"
	"forge.secuaas.ovh/olivier/claude-failover/internal/state"
	"forge.secuaas.ovh/olivier/claude-failover/internal/symlinks"
	"forge.secuaas.ovh/olivier/claude-failover/internal/tmux"
)

// ErrPartialSwap is returned (and wrapped) when the switcher flipped
// ~/.claude to the target home, EnsureForAccount failed on the target,
// and the rollback flip back to the previous home ALSO failed. The daemon
// is in a documented degraded state: the active-account setter was NOT
// called, but the filesystem symlink may point at an account whose shared
// state is inconsistent. Operator intervention is required. Callers can
// interrogate AccountSwitcher.IsPartialSwap() to expose the flag to
// health-checks / watchdogs.
var ErrPartialSwap = errors.New("switcher: partial swap — flip succeeded but ensure + rollback both failed")

// SwitchState represents the current phase of a failover operation.
type SwitchState string

const (
	StateNormal    SwitchState = "normal"
	StateSaving    SwitchState = "saving"
	StateSwitching SwitchState = "switching"
	StateResuming  SwitchState = "resuming"
)

// resumeRe matches `claude --resume <uuid>` in pane capture output.
var resumeRe = regexp.MustCompile(`claude\s+--resume\s+([a-f0-9-]{36})`)

// reMinutes matches "in N minutes" in a reset-time string.
var reMinutes = regexp.MustCompile(`in\s+(\d+)\s+minute`)

// reHours matches "in N hours" in a reset-time string.
var reHours = regexp.MustCompile(`in\s+(\d+)\s+hour`)

// AccountSwitcher consumes SwitchRequests and orchestrates account failover:
// save session context → flip ~/.claude symlink → restart sessions.
type AccountSwitcher struct {
	tmux         tmux.Client
	state        *state.State
	config       *config.Config
	switchCh     <-chan quota.SwitchRequest
	notifier     *notify.Notifier
	currentState SwitchState
	logger       *log.Logger
	// homeDir is the directory containing the .claude symlink. Overridable for tests.
	// When empty, os.UserHomeDir() is used.
	homeDir string
	// sharedSymlinks is the list of shared-state links reconciled on the
	// target account home after every flip. Overridable for tests so the
	// suite never touches the operator's real /home/ubuntu/.claude-*
	// shared directories. When nil, symlinks.RequiredShared is used.
	sharedSymlinks []symlinks.SharedSymlink
	// partialSwap is set to 1 when a flip+ensure+rollback sequence left the
	// daemon in an inconsistent state (symlink possibly flipped, but active
	// account NOT updated, and rollback flip ALSO failed). Health-checks /
	// watchdogs read this flag via IsPartialSwap(). It is sticky: once set,
	// it stays set until the operator restarts the daemon after fixing the
	// filesystem state. We use atomic access so watchdog goroutines can read
	// it without blocking the switcher.
	partialSwap atomic.Bool
}

// New creates an AccountSwitcher.
// notifier may be nil; notifications are skipped when absent.
func New(
	tc tmux.Client,
	s *state.State,
	cfg *config.Config,
	switchCh <-chan quota.SwitchRequest,
	notifier *notify.Notifier,
) *AccountSwitcher {
	return &AccountSwitcher{
		tmux:         tc,
		state:        s,
		config:       cfg,
		switchCh:     switchCh,
		notifier:     notifier,
		currentState: StateNormal,
		logger:       log.Default(),
	}
}

// Run starts the switcher event loop until ctx is cancelled.
func (a *AccountSwitcher) Run(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			return
		case req := <-a.switchCh:
			a.executeSwitch(req)
		}
	}
}

// executeSwitch performs the full failover sequence.
func (a *AccountSwitcher) executeSwitch(req quota.SwitchRequest) {
	if err := a.executeSwitchE(req); err != nil {
		// executeSwitchE already logs the detail; we swallow the error here
		// because the public Run loop has no return channel. The partialSwap
		// flag (if set) remains visible via IsPartialSwap().
		a.logger.Printf("[switcher] SWAP aborted: %v", err)
	}
}

// executeSwitchE runs the swap and returns an error describing any abort or
// partial-swap condition. Split out from executeSwitch so tests can assert
// on the error value without routing through a channel.
func (a *AccountSwitcher) executeSwitchE(req quota.SwitchRequest) error {
	a.logger.Printf("[switcher] SWAP initiated from=%q reset=%q", req.From, req.ResetTime)

	// Refuse to proceed if a previous swap left the daemon in an
	// inconsistent state. The operator must intervene (fix the filesystem,
	// restart the daemon) before any further failover can be attempted —
	// otherwise we'd stack symlink flips on top of a broken state.
	if a.partialSwap.Load() {
		err := fmt.Errorf("refusing swap: daemon is in partial-swap degraded state (operator intervention required)")
		a.logger.Printf("[switcher] %v", err)
		return err
	}

	// 1. SAVING — capture resume UUIDs from all working sessions plus
	// every dedicated session unconditionally (dedicated sessions are
	// user-driven and may not be tracked as "working" in state, but their
	// UUIDs are the most valuable to preserve across a swap).
	a.currentState = StateSaving
	a.saveAllSessions()
	a.saveDedicatedUUIDs()

	// 2. SWITCHING — find target, flip symlink, restart sessions.
	a.currentState = StateSwitching
	target := a.findTargetAccount(req.From)
	if target == nil {
		a.logger.Printf("[switcher] no alternate account found for %q — aborting swap", req.From)
		a.currentState = StateNormal
		return nil
	}
	previous := a.findAccountByName(req.From)

	if err := a.flipSymlink(target.Home); err != nil {
		a.logger.Printf("[switcher] flipSymlink error: %v", err)
	}
	// Ensure the target account home exposes the three shared-state
	// symlinks (session-env, file-history, projects). If this fails we
	// MUST NOT proceed with SetActiveAccount — the daemon would otherwise
	// declare the target "active" while its shared state is divergent,
	// silently writing transcripts into private /projects directories and
	// breaking `claude --resume` across sessions. Instead we attempt to
	// roll back the ~/.claude flip to the previous account. If the
	// rollback also fails, the daemon is in a documented degraded state
	// (ErrPartialSwap) and the operator must intervene.
	if err := symlinks.EnsureForAccount(target.Home, a.requiredShared()); err != nil {
		a.logger.Printf("[switcher] ensure shared symlinks for %q failed: %v — attempting rollback", target.Home, err)
		if previous == nil || previous.Home == "" {
			// No known previous home to roll back to — set the degraded
			// flag and bail out. This is equivalent to a rollback failure
			// because the filesystem is pointed at a broken target.
			a.partialSwap.Store(true)
			a.currentState = StateNormal
			return fmt.Errorf("%w: ensure failed (%v) and no previous account home is known for rollback", ErrPartialSwap, err)
		}
		if rbErr := a.flipSymlink(previous.Home); rbErr != nil {
			// Both the ensure AND the rollback failed. The daemon is now
			// in a documented inconsistent state: ~/.claude may point at
			// target whose shared-state is divergent, but SetActiveAccount
			// has NOT been called so state.ActiveAccount is still the
			// previous account. No further failover can be attempted
			// until the operator intervenes.
			a.partialSwap.Store(true)
			a.logger.Printf("[switcher] CRITICAL partial swap: ensure=%v rollback=%v — daemon in degraded state, operator intervention required", err, rbErr)
			a.currentState = StateNormal
			return fmt.Errorf("%w: ensure=%v rollback=%v", ErrPartialSwap, err, rbErr)
		}
		// Rollback succeeded — symlink is back on the previous account,
		// SetActiveAccount was NEVER called, state is consistent with
		// "no swap happened". Return an explicit error so the caller
		// knows the swap was cancelled.
		a.logger.Printf("[switcher] rollback successful: ~/.claude → %s (swap cancelled)", previous.Home)
		a.currentState = StateNormal
		return fmt.Errorf("swap cancelled: ensure shared symlinks failed on target %q: %w", target.Home, err)
	}
	a.killAllPoolSessions()
	a.recreatePoolSessions()
	a.relaunchDedicatedSessions(target.Home)

	// Update active account and record the swap timestamp so the quota
	// monitor can enforce a cooldown before requesting another one.
	a.state.SetActiveAccount(target.Name)
	a.state.RecordSwap(req.From, target.Name)

	// 3. RESUMING — sessions are alive, dispatcher will fill them.
	a.currentState = StateResuming

	// 4. Notify.
	msg := fmt.Sprintf("Switch %s → %s (reset: %s)", req.From, target.Name, req.ResetTime)
	a.logger.Printf("[switcher] SWAP complete: %s", msg)
	if a.notifier != nil {
		a.notifier.Telegram("🔄 " + msg) //nolint:errcheck
	}

	// 5. Schedule return to primary account if reset time is known.
	if req.ResetTime != "" {
		go a.scheduleReturn(req.From, req.ResetTime)
	}

	a.currentState = StateNormal
	return nil
}

// IsPartialSwap reports whether the switcher is in a degraded state after a
// flip+ensure+rollback sequence all failed. Health-checks and watchdogs use
// this signal to surface an operator-actionable alert. The flag is sticky
// for the lifetime of the process: once set, it remains set until the daemon
// is restarted (after the operator has fixed the filesystem).
func (a *AccountSwitcher) IsPartialSwap() bool {
	return a.partialSwap.Load()
}

// findAccountByName returns the account config entry matching name, or nil.
// Unlike findTargetAccount (which returns the first NON-matching account),
// this is used by the rollback path to recover the previous home.
func (a *AccountSwitcher) findAccountByName(name string) *config.AccountConfig {
	if name == "" {
		return nil
	}
	for i := range a.config.Accounts {
		if a.config.Accounts[i].Name == name {
			return &a.config.Accounts[i]
		}
	}
	return nil
}

// saveDedicatedUUIDs captures the resume UUID for every configured dedicated
// session, regardless of its tracked state. Dedicated sessions are typically
// user-driven and not in state="working", but their UUIDs are the most
// valuable to preserve across a swap so the user's work is not lost.
func (a *AccountSwitcher) saveDedicatedUUIDs() {
	for _, ds := range a.config.Pool.Dedicated {
		if !a.tmux.HasSession(ds.Name) {
			continue
		}
		tail, err := a.tmux.CapturePaneTail(ds.Name, 200)
		if err != nil {
			continue
		}
		uuid := extractResumeUUID(tail)
		if uuid == "" {
			continue
		}
		dir := a.resumeContextDir()
		if err := os.MkdirAll(dir, 0700); err != nil {
			a.logger.Printf("[switcher] mkdir %s: %v", dir, err)
			continue
		}
		path := filepath.Join(dir, ds.Name+"-resume-id.txt")
		if err := os.WriteFile(path, []byte(uuid), 0600); err != nil {
			a.logger.Printf("[switcher] write %s: %v", path, err)
			continue
		}
		a.logger.Printf("[switcher] saved dedicated resume UUID for %q: %s", ds.Name, uuid)
	}
}

// relaunchDedicatedSessions sends a `claude --resume <uuid>` command to each
// dedicated session after recreation, using the target account's home via
// CLAUDE_CONFIG_DIR so the session follows the active account. If no UUID was
// captured for a session, it is left at the bash prompt for manual restart.
func (a *AccountSwitcher) relaunchDedicatedSessions(targetHome string) {
	for _, ds := range a.config.Pool.Dedicated {
		path := filepath.Join(a.resumeContextDir(), ds.Name+"-resume-id.txt")
		data, err := os.ReadFile(path)
		if err != nil {
			a.logger.Printf("[switcher] no saved resume UUID for %q (%v) — leaving at shell", ds.Name, err)
			continue
		}
		uuid := strings.TrimSpace(string(data))
		if !isValidResumeUUID(uuid) {
			a.logger.Printf("[switcher] invalid UUID for %q: %q", ds.Name, uuid)
			continue
		}
		// FNDG-04b: redeploy the PreToolUse safety hook into the dedicated
		// session's project before --resume. Failure is logged, not fatal:
		// we'd rather relaunch the session without a refreshed hook than
		// leave the user stuck after a quota failover. The existing hook
		// (deployed at initial launch) remains in place.
		if ds.Project != "" {
			if err := safety.EnsureHookDeployed(ds.Project); err != nil {
				a.logger.Printf("[switcher] safety hook redeploy %q: %v (continuing)", ds.Name, err)
			}
		}
		// targetHome is operator-controlled (config file); uuid is regex-validated.
		// Neither is user-supplied runtime input, so shell interpolation is safe.
		cmd := fmt.Sprintf("CLAUDE_CONFIG_DIR=%s claude --dangerously-skip-permissions --resume %s",
			targetHome, uuid)
		if err := a.tmux.SendKeys(ds.Name, cmd); err != nil {
			a.logger.Printf("[switcher] relaunch %q: %v", ds.Name, err)
			continue
		}
		a.logger.Printf("[switcher] relaunched %q on %s (resume=%s)", ds.Name, targetHome, uuid)
	}
}

// isValidResumeUUID defends against corrupted resume-id files by requiring
// the canonical 36-char lowercase hex+dash UUID format.
func isValidResumeUUID(s string) bool {
	if len(s) != 36 {
		return false
	}
	return resumeRe.MatchString("claude --resume " + s)
}

// saveAllSessions captures the resume UUID for every working session.
func (a *AccountSwitcher) saveAllSessions() {
	a.state.ForEachWorking(func(name string, _ *state.SessionState) {
		tail, err := a.tmux.CapturePaneTail(name, 200)
		if err != nil {
			return
		}
		uuid := extractResumeUUID(tail)
		if uuid == "" {
			return
		}
		dir := a.resumeContextDir()
		os.MkdirAll(dir, 0700)
		path := filepath.Join(dir, name+"-resume-id.txt")
		os.WriteFile(path, []byte(uuid), 0600)
		a.logger.Printf("[switcher] saved resume UUID for %q", name)
	})
}

// requiredShared returns the shared-symlink list used when reconciling the
// target account home after a flip. Tests may set a.sharedSymlinks to a
// tmpdir-scoped list so they never touch /home/ubuntu/.claude-*-shared.
func (a *AccountSwitcher) requiredShared() []symlinks.SharedSymlink {
	if a.sharedSymlinks != nil {
		return a.sharedSymlinks
	}
	return symlinks.RequiredShared
}

// resolveHomeDir returns the configured homeDir (test override) or the real
// user home. Tests MUST set a.homeDir to a tmpdir to avoid clobbering the
// production ~/.claude symlink.
func (a *AccountSwitcher) resolveHomeDir() (string, error) {
	if a.homeDir != "" {
		return a.homeDir, nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("UserHomeDir: %w", err)
	}
	return home, nil
}

// flipSymlink replaces ~/.claude with a symlink to targetHome.
// All paths come from config — no hardcoded values.
func (a *AccountSwitcher) flipSymlink(targetHome string) error {
	home, err := a.resolveHomeDir()
	if err != nil {
		return err
	}
	claudeLink := filepath.Join(home, ".claude")
	os.Remove(claudeLink)
	if err := os.Symlink(targetHome, claudeLink); err != nil {
		return fmt.Errorf("symlink %s → %s: %w", claudeLink, targetHome, err)
	}
	a.logger.Printf("[switcher] ~/.claude → %s", targetHome)
	return nil
}

// killAllPoolSessions kills all autonomous and dedicated pool sessions
// managed by this daemon. Sessions outside the configured
// StartIndex..StartIndex+Max range (e.g. manual operator sessions
// `ccl-0..ccl-9`) are left untouched.
func (a *AccountSwitcher) killAllPoolSessions() {
	prefix := a.config.Pool.Autonomous.Prefix
	if prefix == "" {
		prefix = "ccl-auto-"
	}
	start := a.config.Pool.Autonomous.StartIndex
	for i := start; i < start+a.config.Pool.Autonomous.Max; i++ {
		a.tmux.KillSession(sessionName(prefix, i)) //nolint:errcheck
	}
	for _, ds := range a.config.Pool.Dedicated {
		a.tmux.KillSession(ds.Name) //nolint:errcheck
	}
}

// recreatePoolSessions creates fresh pool sessions after a switch,
// respecting StartIndex so the pool stays within its configured range.
func (a *AccountSwitcher) recreatePoolSessions() {
	prefix := a.config.Pool.Autonomous.Prefix
	if prefix == "" {
		prefix = "ccl-auto-"
	}
	start := a.config.Pool.Autonomous.StartIndex
	for i := start; i < start+a.config.Pool.Autonomous.Min; i++ {
		name := sessionName(prefix, i)
		if err := a.tmux.CreateSession(name, ""); err != nil {
			a.logger.Printf("[switcher] recreate autonomous %q: %v", name, err)
		}
	}
	for _, ds := range a.config.Pool.Dedicated {
		if err := a.tmux.CreateSession(ds.Name, ds.Project); err != nil {
			a.logger.Printf("[switcher] recreate dedicated %q: %v", ds.Name, err)
		}
	}
}

// findTargetAccount returns the first account that is not currentAccount.
func (a *AccountSwitcher) findTargetAccount(currentAccount string) *config.AccountConfig {
	for i := range a.config.Accounts {
		if a.config.Accounts[i].Name != currentAccount {
			return &a.config.Accounts[i]
		}
	}
	return nil
}

// scheduleReturn waits for the quota to reset then switches back to primaryAccount.
func (a *AccountSwitcher) scheduleReturn(primaryAccount, resetTime string) {
	dur := timeUntilReset(resetTime) + 5*time.Minute
	a.logger.Printf("[switcher] return to %q scheduled in %v", primaryAccount, dur.Round(time.Minute))
	time.Sleep(dur)
	a.executeSwitch(quota.SwitchRequest{
		From: a.state.ActiveAccount(),
		To:   primaryAccount,
	})
}

// extractResumeUUID finds a Claude resume UUID in pane output.
func extractResumeUUID(content string) string {
	m := resumeRe.FindStringSubmatch(content)
	if len(m) >= 2 {
		return m[1]
	}
	return ""
}

// resumeContextDir returns the directory for per-session resume UUIDs.
// Honours a.homeDir override so tests never write to the real ~/.claude-context.
func (a *AccountSwitcher) resumeContextDir() string {
	home, _ := a.resolveHomeDir()
	return filepath.Join(home, ".claude-context")
}

// timeUntilReset parses a reset-time string and returns the duration.
// Returns a 2-hour fallback when parsing fails.
func timeUntilReset(resetTime string) time.Duration {
	lower := strings.ToLower(strings.TrimSpace(resetTime))
	if m := reMinutes.FindStringSubmatch(lower); len(m) >= 2 {
		n, _ := strconv.Atoi(m[1])
		return time.Duration(n) * time.Minute
	}
	if m := reHours.FindStringSubmatch(lower); len(m) >= 2 {
		n, _ := strconv.Atoi(m[1])
		return time.Duration(n) * time.Hour
	}
	return 2 * time.Hour
}

func sessionName(prefix string, i int) string {
	return prefix + itoa(i)
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	b := make([]byte, 0, 10)
	for n > 0 {
		b = append([]byte{byte('0' + n%10)}, b...)
		n /= 10
	}
	return string(b)
}