package main

import (
	"reasonix/internal/agent"
)

// SessionClearResult is the post-clear session identity the frontend must apply
// atomically so hydrate/mode-switch cannot re-bind to the destroyed transcript.
type SessionClearResult struct {
	SessionPath       string `json:"sessionPath"`
	SessionRevision   int64  `json:"sessionRevision,omitempty"`
	SessionDigest     string `json:"sessionDigest,omitempty"`
	SessionGeneration uint64 `json:"sessionGeneration"`
}

// ClearSession discards the current conversation and rotates to a fresh unsaved one.
func (a *App) ClearSession() (SessionClearResult, error) {
	return a.ClearSessionForTab("")
}

// ClearSessionForTab clears the requested tab regardless of later focus changes.
// On success it returns the replacement session identity (path/revision/digest
// and a tab-local generation) so the frontend can retire the old transcript
// without waiting for a later MetaForTab round trip.
func (a *App) ClearSessionForTab(tabID string) (SessionClearResult, error) {
	tab, ctrl := a.tabAndCtrlByID(tabID)
	if a.tabIsReadOnly(tab) {
		return SessionClearResult{}, readOnlyChannelErr()
	}
	if ctrl == nil {
		return SessionClearResult{}, a.workspaceNotReadyErr(tab)
	}
	if err := a.ensureTabControllerWorkspace(tab); err != nil {
		return SessionClearResult{}, err
	}
	ctrl = a.controllerForTab(tab)
	if ctrl == nil {
		return SessionClearResult{}, a.workspaceNotReadyErr(tab)
	}
	if controllerHasActiveRuntimeWork(ctrl) {
		return a.clearActiveSessionRuntime(tab, ctrl)
	}
	if err := ctrl.ClearSession(); err != nil {
		return SessionClearResult{}, err
	}
	if err := a.ensureTabSessionLeaseForRebuild(tab, ctrl.SessionPath(), ""); err != nil {
		// Wails bridge return: a raw lease error would carry the session path
		// and holder id across to the frontend.
		return SessionClearResult{}, userFacingSessionLeaseError("", err)
	}
	tab.resetTelemetry(ctrl.SessionPath())
	// Mirror the controller: ClearSession cleared the active goal.
	a.clearTabGoal(tab)
	a.persistTabSessionPath(tab, ctrl.SessionPath())
	a.invalidatePromptHistoryCache()
	return a.bumpAndSnapshotSessionClear(tab), nil
}

func (a *App) bumpAndSnapshotSessionClear(tab *WorkspaceTab) SessionClearResult {
	if tab == nil {
		return SessionClearResult{}
	}
	a.mu.Lock()
	tab.SessionGeneration++
	gen := tab.SessionGeneration
	path := tab.currentSessionPath()
	if path == "" && tab.Ctrl != nil {
		path = tab.Ctrl.SessionPath()
	}
	a.mu.Unlock()
	var revision int64
	var digest string
	if meta, ok, err := agent.LoadBranchMeta(path); err == nil && ok {
		revision = meta.Revision
		digest = meta.ContentDigest
	}
	return SessionClearResult{
		SessionPath: path, SessionRevision: revision, SessionDigest: digest, SessionGeneration: gen,
	}
}

// clearTabGoal drops the tab's persisted goal copy so rebuilds and restarts
// cannot re-seed a goal the controller has already cleared on session rotation.
func (a *App) clearTabGoal(tab *WorkspaceTab) {
	if tab == nil {
		return
	}
	a.mu.Lock()
	tab.goal = ""
	if current := a.tabs[tab.ID]; current == tab {
		a.saveTabsLocked()
	}
	a.mu.Unlock()
}