package agent

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"os/exec"
	"strings"
	"sync"
	"time"
)

// hermesBlockedArgs are flags hardcoded by the daemon that must not be
// overridden by user-configured custom_args. `acp` is the protocol
// subcommand that drives the ACP JSON-RPC transport; overriding it
// would break the daemon↔Hermes communication contract.
var hermesBlockedArgs = map[string]blockedArgMode{
	"acp": blockedStandalone,
}

// hermesBackend implements Backend by spawning `hermes acp` and communicating
// via the ACP (Agent Communication Protocol) JSON-RPC 2.0 over stdin/stdout.
// This is the same pattern as Codex but with the ACP protocol instead of
// the Codex-specific JSON-RPC methods.
type hermesBackend struct {
	cfg Config
}

func (b *hermesBackend) Execute(ctx context.Context, prompt string, opts ExecOptions) (*Session, error) {
	execPath := b.cfg.ExecutablePath
	if execPath == "" {
		execPath = "hermes"
	}
	if _, err := exec.LookPath(execPath); err != nil {
		return nil, fmt.Errorf("hermes executable not found at %q: %w", execPath, err)
	}

	timeout := opts.Timeout
	if timeout == 0 {
		timeout = 20 * time.Minute
	}
	runCtx, cancel := context.WithTimeout(ctx, timeout)

	hermesArgs := append([]string{"acp"}, filterCustomArgs(opts.CustomArgs, hermesBlockedArgs, b.cfg.Logger)...)
	cmd := exec.CommandContext(runCtx, execPath, hermesArgs...)
	b.cfg.Logger.Debug("agent command", "exec", execPath, "args", hermesArgs)
	if opts.Cwd != "" {
		cmd.Dir = opts.Cwd
	}

	env := buildEnv(b.cfg.Env)
	// Enable yolo mode so Hermes auto-approves all tool executions.
	env = append(env, "HERMES_YOLO_MODE=1")
	cmd.Env = env

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("hermes stdout pipe: %w", err)
	}
	stdin, err := cmd.StdinPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("hermes stdin pipe: %w", err)
	}
	cmd.Stderr = newLogWriter(b.cfg.Logger, "[hermes:stderr] ")

	if err := cmd.Start(); err != nil {
		cancel()
		return nil, fmt.Errorf("start hermes: %w", err)
	}

	b.cfg.Logger.Info("hermes acp started", "pid", cmd.Process.Pid, "cwd", opts.Cwd)

	msgCh := make(chan Message, 256)
	resCh := make(chan Result, 1)

	var outputMu sync.Mutex
	var output strings.Builder

	promptDone := make(chan hermesPromptResult, 1)

	c := &hermesClient{
		cfg:   b.cfg,
		stdin: stdin,
		pending: make(map[int]*pendingRPC),
		onMessage: func(msg Message) {
			if msg.Type == MessageText {
				outputMu.Lock()
				output.WriteString(msg.Content)
				outputMu.Unlock()
			}
			trySend(msgCh, msg)
		},
		onPromptDone: func(result hermesPromptResult) {
			select {
			case promptDone <- result:
			default:
			}
		},
	}

	// Start reading stdout in background.
	readerDone := make(chan struct{})
	go func() {
		defer close(readerDone)
		scanner := bufio.NewScanner(stdout)
		scanner.Buffer(make([]byte, 0, 1024*1024), 10*1024*1024)
		for scanner.Scan() {
			line := strings.TrimSpace(scanner.Text())
			if line == "" {
				continue
			}
			c.handleLine(line)
		}
		c.closeAllPending(fmt.Errorf("hermes process exited"))
	}()

	// Drive the ACP session lifecycle in a goroutine.
	go func() {
		defer cancel()
		defer close(msgCh)
		defer close(resCh)
		defer func() {
			stdin.Close()
			_ = cmd.Wait()
		}()

		startTime := time.Now()
		finalStatus := "completed"
		var finalError string
		var sessionID string

		// 1. Initialize handshake.
		_, err := c.request(runCtx, "initialize", map[string]any{
			"protocolVersion": 1,
			"clientInfo": map[string]any{
				"name":    "multica-agent-sdk",
				"version": "0.2.0",
			},
			"clientCapabilities": map[string]any{},
		})
		if err != nil {
			finalStatus = "failed"
			finalError = fmt.Sprintf("hermes initialize failed: %v", err)
			resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
			return
		}

		// 2. Create or resume a session.
		cwd := opts.Cwd
		if cwd == "" {
			cwd = "."
		}

		if opts.ResumeSessionID != "" {
			result, err := c.request(runCtx, "session/resume", map[string]any{
				"cwd":       cwd,
				"sessionId": opts.ResumeSessionID,
			})
			if err != nil {
				finalStatus = "failed"
				finalError = fmt.Sprintf("hermes session/resume failed: %v", err)
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			sessionID = opts.ResumeSessionID
			_ = result
		} else {
			result, err := c.request(runCtx, "session/new", map[string]any{
				"cwd":        cwd,
				"mcpServers": []any{},
			})
			if err != nil {
				finalStatus = "failed"
				finalError = fmt.Sprintf("hermes session/new failed: %v", err)
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			sessionID = extractHermesSessionID(result)
			if sessionID == "" {
				finalStatus = "failed"
				finalError = "hermes session/new returned no session ID"
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
		}

		c.sessionID = sessionID
		b.cfg.Logger.Info("hermes session created", "session_id", sessionID)

		// 3. Build the prompt content. If we have a system prompt, prepend it.
		userText := prompt
		if opts.SystemPrompt != "" {
			userText = opts.SystemPrompt + "\n\n---\n\n" + prompt
		}

		// 4. Send the prompt and wait for PromptResponse.
		_, err = c.request(runCtx, "session/prompt", map[string]any{
			"sessionId": sessionID,
			"prompt": []map[string]any{
				{"type": "text", "text": userText},
			},
		})
		if err != nil {
			// If the request itself failed (not just context cancelled),
			// check if the context was cancelled/timed out.
			if runCtx.Err() == context.DeadlineExceeded {
				finalStatus = "timeout"
				finalError = fmt.Sprintf("hermes timed out after %s", timeout)
			} else if runCtx.Err() == context.Canceled {
				finalStatus = "aborted"
				finalError = "execution cancelled"
			} else {
				finalStatus = "failed"
				finalError = fmt.Sprintf("hermes session/prompt failed: %v", err)
			}
		} else {
			// The prompt completed. Check if we got a promptDone result
			// from the response parsing.
			select {
			case pr := <-promptDone:
				if pr.stopReason == "cancelled" {
					finalStatus = "aborted"
					finalError = "hermes cancelled the prompt"
				}
				// Merge usage from the PromptResponse.
				c.usageMu.Lock()
				c.usage.InputTokens += pr.usage.InputTokens
				c.usage.OutputTokens += pr.usage.OutputTokens
				c.usageMu.Unlock()
			default:
			}
		}

		duration := time.Since(startTime)
		b.cfg.Logger.Info("hermes finished", "pid", cmd.Process.Pid, "status", finalStatus, "duration", duration.Round(time.Millisecond).String())

		// Close stdin and cancel context to signal hermes acp to exit.
		stdin.Close()
		cancel()

		// Wait for the reader goroutine to finish so all output is accumulated.
		<-readerDone

		outputMu.Lock()
		finalOutput := output.String()
		outputMu.Unlock()

		// Build usage map.
		c.usageMu.Lock()
		u := c.usage
		c.usageMu.Unlock()

		var usageMap map[string]TokenUsage
		if u.InputTokens > 0 || u.OutputTokens > 0 || u.CacheReadTokens > 0 {
			model := opts.Model
			if model == "" {
				model = "unknown"
			}
			usageMap = map[string]TokenUsage{model: u}
		}

		resCh <- Result{
			Status:     finalStatus,
			Output:     finalOutput,
			Error:      finalError,
			DurationMs: duration.Milliseconds(),
			SessionID:  sessionID,
			Usage:      usageMap,
		}
	}()

	return &Session{Messages: msgCh, Result: resCh}, nil
}

// ── hermesClient: ACP JSON-RPC 2.0 transport ──

type hermesPromptResult struct {
	stopReason string
	usage      TokenUsage
}

type hermesClient struct {
	cfg       Config
	stdin     interface{ Write([]byte) (int, error) }
	mu        sync.Mutex
	nextID    int
	pending   map[int]*pendingRPC
	sessionID string
	onMessage func(Message)
	onPromptDone func(hermesPromptResult)

	usageMu sync.Mutex
	usage   TokenUsage
}

func (c *hermesClient) request(ctx context.Context, method string, params any) (json.RawMessage, error) {
	c.mu.Lock()
	id := c.nextID
	c.nextID++
	pr := &pendingRPC{ch: make(chan rpcResult, 1), method: method}
	c.pending[id] = pr
	c.mu.Unlock()

	msg := map[string]any{
		"jsonrpc": "2.0",
		"id":      id,
		"method":  method,
		"params":  params,
	}
	data, err := json.Marshal(msg)
	if err != nil {
		c.mu.Lock()
		delete(c.pending, id)
		c.mu.Unlock()
		return nil, err
	}
	data = append(data, '\n')
	if _, err := c.stdin.Write(data); err != nil {
		c.mu.Lock()
		delete(c.pending, id)
		c.mu.Unlock()
		return nil, fmt.Errorf("write %s: %w", method, err)
	}

	select {
	case res := <-pr.ch:
		return res.result, res.err
	case <-ctx.Done():
		c.mu.Lock()
		delete(c.pending, id)
		c.mu.Unlock()
		return nil, ctx.Err()
	}
}

func (c *hermesClient) closeAllPending(err error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for id, pr := range c.pending {
		pr.ch <- rpcResult{err: err}
		delete(c.pending, id)
	}
}

func (c *hermesClient) handleLine(line string) {
	var raw map[string]json.RawMessage
	if err := json.Unmarshal([]byte(line), &raw); err != nil {
		return
	}

	// Check if it's a response to our request (has id + result or error).
	if _, hasID := raw["id"]; hasID {
		if _, hasResult := raw["result"]; hasResult {
			c.handleResponse(raw)
			return
		}
		if _, hasError := raw["error"]; hasError {
			c.handleResponse(raw)
			return
		}
	}

	// Notification (no id, has method) — session updates from Hermes.
	if _, hasMethod := raw["method"]; hasMethod {
		c.handleNotification(raw)
	}
}

func (c *hermesClient) handleResponse(raw map[string]json.RawMessage) {
	var id int
	if err := json.Unmarshal(raw["id"], &id); err != nil {
		// Try float (JSON numbers are floats by default).
		var fid float64
		if err := json.Unmarshal(raw["id"], &fid); err != nil {
			return
		}
		id = int(fid)
	}

	c.mu.Lock()
	pr, ok := c.pending[id]
	if ok {
		delete(c.pending, id)
	}
	c.mu.Unlock()

	if !ok {
		return
	}

	if errData, hasErr := raw["error"]; hasErr {
		var rpcErr struct {
			Code    int    `json:"code"`
			Message string `json:"message"`
		}
		_ = json.Unmarshal(errData, &rpcErr)
		pr.ch <- rpcResult{err: fmt.Errorf("%s: %s (code=%d)", pr.method, rpcErr.Message, rpcErr.Code)}
	} else {
		// If this is a prompt response, extract usage and stop reason.
		if pr.method == "session/prompt" {
			c.extractPromptResult(raw["result"])
		}
		pr.ch <- rpcResult{result: raw["result"]}
	}
}

func (c *hermesClient) extractPromptResult(data json.RawMessage) {
	var resp struct {
		StopReason string `json:"stopReason"`
		Usage      *struct {
			InputTokens      int64 `json:"inputTokens"`
			OutputTokens     int64 `json:"outputTokens"`
			TotalTokens      int64 `json:"totalTokens"`
			ThoughtTokens    int64 `json:"thoughtTokens"`
			CachedReadTokens int64 `json:"cachedReadTokens"`
		} `json:"usage"`
	}
	if err := json.Unmarshal(data, &resp); err != nil {
		return
	}

	pr := hermesPromptResult{
		stopReason: resp.StopReason,
	}
	if resp.Usage != nil {
		pr.usage = TokenUsage{
			InputTokens:  resp.Usage.InputTokens,
			OutputTokens: resp.Usage.OutputTokens,
			CacheReadTokens: resp.Usage.CachedReadTokens,
		}
	}

	if c.onPromptDone != nil {
		c.onPromptDone(pr)
	}
}

func (c *hermesClient) handleNotification(raw map[string]json.RawMessage) {
	var method string
	_ = json.Unmarshal(raw["method"], &method)

	if method != "session/update" {
		return
	}

	var params struct {
		SessionID string          `json:"sessionId"`
		Update    json.RawMessage `json:"update"`
	}
	if p, ok := raw["params"]; ok {
		_ = json.Unmarshal(p, &params)
	}
	if len(params.Update) == 0 {
		return
	}

	// Parse the update discriminator.
	var updateType struct {
		SessionUpdate string `json:"sessionUpdate"`
	}
	_ = json.Unmarshal(params.Update, &updateType)

	switch updateType.SessionUpdate {
	case "agent_message_chunk":
		c.handleAgentMessage(params.Update)
	case "agent_thought_chunk":
		c.handleAgentThought(params.Update)
	case "tool_call":
		c.handleToolCallStart(params.Update)
	case "tool_call_update":
		c.handleToolCallUpdate(params.Update)
	case "usage_update":
		c.handleUsageUpdate(params.Update)
	}
}

func (c *hermesClient) handleAgentMessage(data json.RawMessage) {
	var msg struct {
		Content struct {
			Type string `json:"type"`
			Text string `json:"text"`
		} `json:"content"`
	}
	if err := json.Unmarshal(data, &msg); err != nil || msg.Content.Text == "" {
		return
	}
	if c.onMessage != nil {
		c.onMessage(Message{Type: MessageText, Content: msg.Content.Text})
	}
}

func (c *hermesClient) handleAgentThought(data json.RawMessage) {
	var msg struct {
		Content struct {
			Type string `json:"type"`
			Text string `json:"text"`
		} `json:"content"`
	}
	if err := json.Unmarshal(data, &msg); err != nil || msg.Content.Text == "" {
		return
	}
	if c.onMessage != nil {
		c.onMessage(Message{Type: MessageThinking, Content: msg.Content.Text})
	}
}

func (c *hermesClient) handleToolCallStart(data json.RawMessage) {
	var msg struct {
		ToolCallID string `json:"toolCallId"`
		Title      string `json:"title"`
		Kind       string `json:"kind"`
		RawInput   map[string]any `json:"rawInput"`
	}
	if err := json.Unmarshal(data, &msg); err != nil {
		return
	}

	toolName := hermesToolNameFromTitle(msg.Title, msg.Kind)
	if c.onMessage != nil {
		c.onMessage(Message{
			Type:   MessageToolUse,
			Tool:   toolName,
			CallID: msg.ToolCallID,
			Input:  msg.RawInput,
		})
	}
}

func (c *hermesClient) handleToolCallUpdate(data json.RawMessage) {
	var msg struct {
		ToolCallID string `json:"toolCallId"`
		Status     string `json:"status"`
		Kind       string `json:"kind"`
		RawOutput  string `json:"rawOutput"`
	}
	if err := json.Unmarshal(data, &msg); err != nil {
		return
	}

	// Only emit tool result when the call is completed.
	if msg.Status != "completed" && msg.Status != "failed" {
		return
	}

	if c.onMessage != nil {
		c.onMessage(Message{
			Type:   MessageToolResult,
			CallID: msg.ToolCallID,
			Output: msg.RawOutput,
		})
	}
}

func (c *hermesClient) handleUsageUpdate(data json.RawMessage) {
	var msg struct {
		Usage struct {
			InputTokens      int64 `json:"inputTokens"`
			OutputTokens     int64 `json:"outputTokens"`
			TotalTokens      int64 `json:"totalTokens"`
			CachedReadTokens int64 `json:"cachedReadTokens"`
		} `json:"usage"`
	}
	if err := json.Unmarshal(data, &msg); err != nil {
		return
	}

	c.usageMu.Lock()
	// Usage updates from ACP are cumulative snapshots, so take the latest.
	if msg.Usage.InputTokens > c.usage.InputTokens {
		c.usage.InputTokens = msg.Usage.InputTokens
	}
	if msg.Usage.OutputTokens > c.usage.OutputTokens {
		c.usage.OutputTokens = msg.Usage.OutputTokens
	}
	if msg.Usage.CachedReadTokens > c.usage.CacheReadTokens {
		c.usage.CacheReadTokens = msg.Usage.CachedReadTokens
	}
	c.usageMu.Unlock()
}

// ── Helpers ──

func extractHermesSessionID(result json.RawMessage) string {
	var r struct {
		SessionID string `json:"sessionId"`
	}
	if err := json.Unmarshal(result, &r); err != nil {
		return ""
	}
	return r.SessionID
}

// hermesToolNameFromTitle extracts a tool name from the ACP tool call title.
// Hermes ACP titles look like "terminal: ls -la", "read: /path/to/file", etc.
// Some titles have no colon (e.g. "execute code").
func hermesToolNameFromTitle(title string, kind string) string {
	// Check exact-match titles first (no colon).
	switch title {
	case "execute code":
		return "execute_code"
	}

	// Try to extract the tool name from before the first colon.
	if idx := strings.Index(title, ":"); idx > 0 {
		name := strings.TrimSpace(title[:idx])
		// Map common ACP title prefixes back to tool names.
		// Some titles include mode info like "patch (replace)", so check prefix.
		switch {
		case name == "terminal":
			return "terminal"
		case name == "read":
			return "read_file"
		case name == "write":
			return "write_file"
		case strings.HasPrefix(name, "patch"):
			return "patch"
		case name == "search":
			return "search_files"
		case name == "web search":
			return "web_search"
		case name == "extract":
			return "web_extract"
		case name == "delegate":
			return "delegate_task"
		case name == "analyze image":
			return "vision_analyze"
		}
		return name
	}

	// Fall back to kind.
	switch kind {
	case "read":
		return "read_file"
	case "edit":
		return "write_file"
	case "execute":
		return "terminal"
	case "search":
		return "search_files"
	case "fetch":
		return "web_search"
	case "think":
		return "thinking"
	default:
		return kind
	}
}