package agent

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"slices"
	"strconv"
	"strings"
)

// HandleCommand processes agent-level slash commands. Returns true if the
// input was recognized as a command, false otherwise.
// The emit function is used to send output events. sessionID and agentsDir
// are passed from the session to avoid the agent needing session-level knowledge.
func (ag *Agent) HandleCommand(ctx context.Context, input string) bool {
	if !strings.HasPrefix(input, "/") {
		return false
	}
	parts := strings.Fields(input)
	if len(parts) == 0 {
		return false
	}
	cmd := parts[0]
	args := parts[1:]

	switch cmd {
	case "/i":
		ag.cmdInject(ctx, args)
	case "/irw":
		ag.cmdInjectRewrite(ctx, args)
	case "/backend":
		ag.cmdBackend(ctx, args)
	case "/models":
		ag.cmdModels(ctx, args)
	case "/model":
		ag.cmdModel(ctx, args)
	case "/maxsteps":
		ag.cmdMaxSteps(ctx, args)
	case "/agents":
		ag.cmdAgents(ctx, args)
	case "/agent":
		ag.cmdAgent(ctx, args)
	case "/compact":
		ag.cmdCompact(ctx, args)
	case "/context":
		ag.cmdContext(ctx, args)
	case "/cost":
		ag.cmdCost(ctx, args)
	case "/usage":
		ag.cmdUsage(ctx, args)
	case "/history":
		ag.cmdHistory(ctx, args)
	case "/clear":
		ag.cmdClear(ctx, args)
	case "/sp":
		ag.cmdSP(ctx, args)
	default:
		return false
	}
	return true
}

func (ag *Agent) cmdBackend(_ context.Context, args []string) {
	if len(args) == 0 {
		ag.emit(infoEvent(ag.runtime.Backend.Name()))
		return
	}
	if ag.IsRunning() {
		ag.emit(infoEvent("error: cannot switch backend while agent is running"))
		return
	}
	be, err := ag.newBackend(args[0])
	if err != nil {
		ag.emit(infoEvent(fmt.Sprintf("error: failed to switch backend: %v", err)))
		return
	}
	ag.runtime.Backend = be
	ag.emit(infoEvent(fmt.Sprintf("switched backend to: %s (model: %s)", be.Name(), be.Model())))
}

func (ag *Agent) cmdModels(ctx context.Context, args []string) {
	models := ag.runtime.Backend.Models(ctx)
	if len(models) == 0 {
		ag.emit(infoEvent("no models available"))
		return
	}
	slices.Sort(models)
	current := ag.runtime.Backend.Model()
	for _, m := range models {
		marker := "  "
		if m == current {
			marker = "* "
		}
		ag.emit(infoEvent(marker + m))
	}
}

func (ag *Agent) cmdModel(_ context.Context, args []string) {
	if len(args) == 0 {
		ag.emit(infoEvent(ag.runtime.Backend.Model()))
		return
	}
	ag.runtime.Backend.SetModel(args[0])
	ag.emit(infoEvent("switched model to: " + args[0]))
}

func (ag *Agent) cmdMaxSteps(_ context.Context, args []string) {
	if len(args) == 0 {
		if ag.runtime.MaxSteps == 0 {
			ag.emit(infoEvent("maxsteps: unlimited"))
		} else {
			ag.emit(infoEvent(fmt.Sprintf("maxsteps: %d", ag.runtime.MaxSteps)))
		}
		return
	}
	n, err := strconv.Atoi(args[0])
	if err != nil || n < 0 {
		ag.emit(infoEvent("error: maxsteps requires a non-negative integer (0 = unlimited)"))
		return
	}
	ag.runtime.MaxSteps = n
	if n == 0 {
		ag.emit(infoEvent("maxsteps: unlimited"))
	} else {
		ag.emit(infoEvent(fmt.Sprintf("maxsteps: %d", n)))
	}
}

func (ag *Agent) cmdAgents(_ context.Context, _ []string) {
	seen := make(map[string]bool)
	found := false
	for _, dir := range AgentsDirs() {
		entries, err := os.ReadDir(dir)
		if err != nil {
			continue
		}
		for _, e := range entries {
			if e.IsDir() || !strings.HasSuffix(e.Name(), ".json") {
				continue
			}
			name := strings.TrimSuffix(e.Name(), ".json")
			if seen[name] {
				continue
			}
			seen[name] = true
			marker := "  "
			if name == ag.agentName {
				marker = "* "
			}
			ag.emit(infoEvent(marker + name))
			found = true
		}
	}
	if !found {
		ag.emit(infoEvent("no agents found"))
	}
}

func (ag *Agent) cmdAgent(_ context.Context, args []string) {
	if len(args) == 0 {
		ag.emit(infoEvent("active agent: " + ag.agentName))
		return
	}
	if ag.IsRunning() {
		ag.emit(infoEvent("error: cannot switch agent while agent is running"))
		return
	}
	name := args[0]
	cfgPath := AgentConfigPath(ag.agentsDir, name)
	f, err := os.Open(cfgPath)
	if err != nil {
		ag.emit(infoEvent(fmt.Sprintf("error: agent %q: %v", name, err)))
		return
	}
	cfg, err := Load(f)
	f.Close()
	if err != nil {
		ag.emit(infoEvent(fmt.Sprintf("error: agent %q: %v", name, err)))
		return
	}
	disp := ag.newToolServer()
	env := []string{"OLLIE_SESSION_ID=" + ag.sessionID, "OLLIE_UNAME=" + ag.id}
	env = append(env, ag.promptEnvExtra...)
	rt := BuildRuntime(cfg, disp, ag.cwd, env, ag.baseLayers...)
	if rt.CfgBackend != "" {
		newBe, err := ag.newBackend(rt.CfgBackend)
		if err != nil {
			ag.emit(infoEvent(fmt.Sprintf("error: backend %q: %v", rt.CfgBackend, err)))
			return
		}
		if rt.CfgModel != "" {
			newBe.SetModel(rt.CfgModel)
		}
		rt.Backend = newBe
	} else {
		rt.Backend = ag.runtime.Backend
		if rt.CfgModel != "" {
			rt.Backend.SetModel(rt.CfgModel)
		}
	}
	ag.runtime = rt
	ag.agentName = name
	ag.history = nil
	ag.wireToolsChanged()
	ag.notifyChange()
	for _, msg := range rt.Messages {
		ag.emit(infoEvent(msg))
	}
	ag.emit(infoEvent("agent: " + name))
}

func (ag *Agent) cmdCompact(ctx context.Context, _ []string) {
	if ag.IsRunning() {
		ag.emit(infoEvent("error: cannot compact while agent is running"))
		return
	}
	if ag.history == nil {
		ag.emit(infoEvent("nothing to compact"))
		return
	}
	ag.SetState("compacting")
	n, err := ag.runCompact(ctx, "manual")
	ag.SetState("idle")
	if err != nil {
		ag.emit(infoEvent("compact error: " + err.Error()))
		return
	}
	if n == 0 {
		ag.emit(infoEvent("nothing to compact"))
		return
	}
	ag.emit(infoEvent(fmt.Sprintf("compacted %d messages", n)))
	ag.saveSession()
}

func (ag *Agent) cmdContext(ctx context.Context, _ []string) {
	if ag.history == nil {
		ag.emit(infoEvent("no active session"))
		return
	}
	ctxLen := ag.runtime.Backend.ContextLength(ctx)
	if ctxLen <= 0 {
		ctxLen = defaultContextLength
	}
	estimated := ag.history.estimateTokens()
	pct := estimated * 100 / ctxLen
	ag.emit(infoEvent(fmt.Sprintf("~%d / %d tokens (%d%%)", estimated, ctxLen, pct)))
	ag.emit(infoEvent(strings.TrimRight(ag.history.contextDebug(), "\n")))
}

func (ag *Agent) cmdCost(_ context.Context, _ []string) {
	if ag.history == nil {
		ag.emit(infoEvent("no active session"))
		return
	}
	ag.emit(infoEvent(fmt.Sprintf("last=$%.4f  session=$%.4f",
		ag.history.LastTurnCostUSD, ag.history.SessionCostUSD)))
}

func (ag *Agent) cmdUsage(ctx context.Context, _ []string) {
	if ag.history == nil {
		ag.emit(infoEvent("no active session"))
		return
	}
	ctxLen := ag.runtime.Backend.ContextLength(ctx)
	if ctxLen <= 0 {
		ctxLen = defaultContextLength
	}
	estimated := ag.history.estimateTokens()
	pct := estimated * 100 / ctxLen
	usageStr := fmt.Sprintf("~%d / %d tokens (%d%%) | %d in, %d out, %d requests",
		estimated, ctxLen, pct,
		ag.history.TotalInputTokens, ag.history.TotalOutputTokens,
		ag.history.TotalRequests)
	if ag.history.Estimated {
		usageStr += " [estimated]"
	}
	ag.emit(infoEvent(usageStr))
}

func (ag *Agent) cmdHistory(_ context.Context, _ []string) {
	if ag.history == nil {
		ag.emit(infoEvent("no active session"))
		return
	}
	for _, msg := range ag.history.history() {
		preview := msg.Content
		if len(preview) > 200 {
			preview = preview[:200] + "..."
		}
		ag.emit(infoEvent(fmt.Sprintf("[%s] %s", msg.Role, preview)))
	}
}

func (ag *Agent) cmdClear(_ context.Context, _ []string) {
	if ag.IsRunning() {
		ag.emit(infoEvent("error: cannot clear while agent is running"))
		return
	}
	ag.history = nil
	ag.emit(infoEvent("cleared"))
}

func (ag *Agent) cmdSP(_ context.Context, _ []string) {
	ag.emit(infoEvent(ag.runtime.Preamble))
}

func (ag *Agent) cmdInject(_ context.Context, args []string) {
	prompt := strings.Join(args, " ")
	if prompt == "" {
		ag.emit(infoEvent("error: /i requires a prompt"))
		return
	}
	if ag.IsRunning() {
		ag.Inject(prompt)
	} else {
		go ag.Submit(context.Background(), prompt)
	}
}

func (ag *Agent) cmdInjectRewrite(_ context.Context, args []string) {
	prompt := strings.Join(args, " ")
	if prompt == "" {
		ag.emit(infoEvent("error: /irw requires a prompt"))
		return
	}
	ag.InjectRewrite(prompt)
}

// Inject queues a prompt for mid-turn injection.
func (ag *Agent) Inject(prompt string) {
	if !ag.pendingInject.CompareAndSwap(nil, &prompt) {
		ag.fifo.Push(prompt)
		return
	}
	ag.emit(Event{Role: "info", Content: "\n"})
	ag.emit(Event{Role: "user", Content: prompt})
}

// InjectRewrite replaces the pending inject.
func (ag *Agent) InjectRewrite(prompt string) {
	ag.pendingInject.Store(&prompt)
	ag.emit(Event{Role: "info", Content: "\n"})
	ag.emit(Event{Role: "user", Content: prompt})
}

// CompactionSnapshot returns the pre-compaction snapshot for external persistence.
// Returns nil if no history exists.
func (ag *Agent) CompactionSnapshot() json.RawMessage {
	if ag.history == nil {
		return nil
	}
	snap := ag.history.PreCompactionSnapshot()
	data, err := json.Marshal(snap)
	if err != nil {
		return nil
	}
	return data
}