package main

import (
	"fmt"
	"log/slog"
	"os"
	"strings"

	"reasonix/internal/agent"
	"reasonix/internal/control"
	"reasonix/internal/provider"
	"reasonix/internal/store"
)

func systemPromptFrom(messages []provider.Message) string {
	for _, m := range messages {
		if m.Role == provider.RoleSystem {
			return m.Content
		}
	}
	return ""
}

// logSystemPromptSwap leaves a trace whenever a resume/rebind replaces a
// conversation's persisted system prompt with different bytes: that swap
// invalidates the whole conversation's provider prefix cache (misses bill at
// 10x hits) and persists the rewrite. With probe snapshots keeping composition
// deterministic, this should fire only on genuine config changes — if it shows
// up in field logs without one, a new nondeterminism source crept into the
// prompt assembly.
func logSystemPromptSwap(persisted, fresh, path string) {
	if persisted == "" || fresh == "" || persisted == fresh {
		return
	}
	slog.Warn("desktop: resume swapped a differing system prompt; conversation prefix cache will miss",
		"path", path, "persisted_len", len(persisted), "fresh_len", len(fresh))
}

func withFreshSystemPrompt(messages []provider.Message, system string) []provider.Message {
	if strings.TrimSpace(system) == "" {
		return messages
	}
	out := append([]provider.Message(nil), messages...)
	for i := range out {
		if out[i].Role == provider.RoleSystem {
			out[i].Content = system
			out[i].ReasoningContent = ""
			out[i].ReasoningSignature = ""
			out[i].ToolCalls = nil
			out[i].ToolCallID = ""
			out[i].Name = ""
			return out
		}
	}
	return append([]provider.Message{{Role: provider.RoleSystem, Content: system}}, out...)
}

func sessionWithFreshSystemPrompt(session *agent.Session, system string) *agent.Session {
	if session == nil {
		return nil
	}
	messages := session.Snapshot()
	persisted := systemPromptFrom(messages)
	if persisted == "" && strings.TrimSpace(system) == "" {
		return session
	}
	logSystemPromptSwap(persisted, system, "")
	return session.CloneWithMessages(withFreshSystemPrompt(messages, system))
}

func resumeWithFreshSystemPrompt(ctrl interface {
	History() []provider.Message
	Resume(*agent.Session, string)
	SetSessionPath(string)
}, messages []provider.Message, path string) {
	if ctrl == nil {
		return
	}
	if len(messages) > 0 {
		fresh := systemPromptFrom(ctrl.History())
		logSystemPromptSwap(systemPromptFrom(messages), fresh, path)
		next := withFreshSystemPrompt(messages, fresh)
		if path != "" {
			if loaded, err := agent.LoadSession(path); err == nil && loaded != nil {
				if resumed, ok := loaded.CloneWithMessagesIfCompatible(next); ok {
					ctrl.Resume(resumed, path)
					return
				}
			}
		}
		ctrl.Resume(agent.NewSession("").CloneWithMessages(next), path)
		return
	}
	if path != "" {
		ctrl.SetSessionPath(path)
	}
}

// resumeWithFreshSystemPromptAndGoal resumes an existing session without
// seeding Goal state before Resume. A goal-state sidecar is authoritative;
// only legacy sessions that predate the sidecar fall back to the tab profile.
func resumeWithFreshSystemPromptAndGoal(ctrl control.SessionAPI, messages []provider.Message, path, legacyGoal string) {
	if ctrl == nil {
		return
	}
	_, sidecarErr := os.Stat(store.SessionGoalState(path))
	resumeWithFreshSystemPrompt(ctrl, messages, path)
	if os.IsNotExist(sidecarErr) && strings.TrimSpace(legacyGoal) != "" {
		ctrl.SetGoal(strings.TrimSpace(legacyGoal))
	}
}

func resumeLoadedSessionAndGoal(ctrl control.SessionAPI, session *agent.Session, path, legacyGoal string) {
	if ctrl == nil || session == nil {
		return
	}
	_, sidecarErr := os.Stat(store.SessionGoalState(path))
	ctrl.Resume(sessionWithFreshSystemPrompt(session, systemPromptFrom(ctrl.History())), path)
	if os.IsNotExist(sidecarErr) && strings.TrimSpace(legacyGoal) != "" {
		ctrl.SetGoal(strings.TrimSpace(legacyGoal))
	}
}

// configureControllerRuntime applies the non-persisted runtime posture before
// Resume. Session grants are copied before a lease is acquired so a replacement
// is fully configured but cannot run against the session until ownership is
// established.
func configureControllerRuntime(ctrl, oldCtrl control.SessionAPI, runtime normalizedTabRuntime) {
	if ctrl == nil {
		return
	}
	ctrl.EnableInteractiveApproval()
	applyTabModeToController(ctrl, runtime.tabMode())
	applyTabToolApprovalModeToController(ctrl, runtime.toolApprovalMode)
	applyTabQualityFloorToController(ctrl, runtime.qualityFloor)
	if next, ok := ctrl.(*control.Controller); ok {
		if prev, ok := oldCtrl.(*control.Controller); ok {
			next.RestoreSessionAuthorizations(prev.SessionAuthorizations())
		}
	}
}

func normalizeRestoredControllerRuntime(ctrl control.SessionAPI, requested normalizedTabRuntime) (normalizedTabRuntime, error) {
	if ctrl == nil {
		return normalizedTabRuntime{}, fmt.Errorf("replacement controller is nil")
	}
	plan := requested.collaborationMode == "plan"
	ctrl.SetPlanMode(plan)
	applyTabToolApprovalModeToController(ctrl, requested.toolApprovalMode)
	if plan && ctrl.GoalStatus() == control.GoalStatusRunning {
		// Explicit Plan wins over inconsistent legacy data. Clearing the running
		// Goal also prevents a stale scope from being executed after approval.
		ctrl.ClearGoal()
	}

	actual := requested
	actual.collaborationMode = "normal"
	actual.legacyGoal = ""
	switch {
	case ctrl.PlanMode():
		actual.collaborationMode = "plan"
	case ctrl.GoalStatus() == control.GoalStatusRunning && strings.TrimSpace(ctrl.Goal()) != "":
		actual.collaborationMode = "goal"
		actual.legacyGoal = strings.TrimSpace(ctrl.Goal())
	}
	actual.toolApprovalMode = normalizeToolApprovalMode(ctrl.ToolApprovalMode())
	if ctrl.PlanMode() != (actual.collaborationMode == "plan") {
		return normalizedTabRuntime{}, fmt.Errorf("replacement collaboration mode validation failed")
	}
	if actual.toolApprovalMode != normalizeToolApprovalMode(requested.toolApprovalMode) {
		return normalizedTabRuntime{}, fmt.Errorf("replacement tool approval mode = %q, want %q", actual.toolApprovalMode, requested.toolApprovalMode)
	}
	return actual, nil
}

func resumeControllerRuntimeWithMessages(ctrl control.SessionAPI, messages []provider.Message, path string, requested normalizedTabRuntime) (normalizedTabRuntime, error) {
	resumeWithFreshSystemPromptAndGoal(ctrl, messages, path, requested.legacyGoal)
	return normalizeRestoredControllerRuntime(ctrl, requested)
}

func resumeControllerRuntimeWithSession(ctrl control.SessionAPI, session *agent.Session, path string, requested normalizedTabRuntime) (normalizedTabRuntime, error) {
	if session != nil {
		resumeLoadedSessionAndGoal(ctrl, session, path, requested.legacyGoal)
	} else {
		resumeWithFreshSystemPromptAndGoal(ctrl, nil, path, requested.legacyGoal)
	}
	return normalizeRestoredControllerRuntime(ctrl, requested)
}