package agent

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"os/exec"
	"strings"
	"sync"
	"sync/atomic"
	"time"
)

// qoderBlockedArgs are flags hardcoded by the daemon that must not be
// overridden by user-configured custom_args. Qoder enters ACP mode via the
// global `--acp` flag; letting users strip or duplicate it would break the
// daemon↔Qoder transport contract. `--yolo` is daemon-owned so headless ACP
// always runs in bypass-permissions mode (see Qoder ACP docs). The legacy `acp`
// subcommand style is blocked so custom_args cannot switch the binary mode.
var qoderBlockedArgs = map[string]blockedArgMode{
	"--acp":  blockedStandalone,
	"acp":    blockedStandalone,
	"--yolo": blockedStandalone,
}

// qoderBackend implements Backend by spawning `qodercli --yolo --acp` and
// communicating via the ACP (Agent Communication Protocol) JSON-RPC 2.0
// transport over stdin/stdout.
//
// Qoder CLI uses global flags (`--yolo`, `--acp`), not an `acp` subcommand. We
// reuse hermesClient like Hermes/Kimi/Kiro and mirror their streaming gate so
// history replay flushed during session/setup does not corrupt the streamed
// output or leave the UI stuck on a stale assistant chunk.
type qoderBackend struct {
	cfg Config
}

var qoderReaderDrainGrace = 2 * time.Second

type qoderMessageStream struct {
	ch     chan Message
	mu     sync.Mutex
	closed bool
}

func newQoderMessageStream(size int) *qoderMessageStream {
	return &qoderMessageStream{ch: make(chan Message, size)}
}

func (s *qoderMessageStream) send(msg Message) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.closed {
		return
	}
	trySend(s.ch, msg)
}

func (s *qoderMessageStream) close() {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.closed {
		return
	}
	s.closed = true
	close(s.ch)
}

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

	// Translate the agent's mcp_config (Claude-style object of objects) into
	// the array shape ACP session/new and session/resume expect. Reuse the
	// shared converter so remote MCP `headers` (e.g. Authorization) survive as
	// [{name, value}] and output is deterministic. Fail closed on malformed
	// JSON so the launch surfaces the real error instead of silently dropping
	// every MCP server.
	mcpServers, err := buildACPMcpServers(opts.McpConfig, b.cfg.Logger)
	if err != nil {
		return nil, fmt.Errorf("qoder: invalid mcp_config: %w", err)
	}

	timeout := opts.Timeout
	runCtx, cancel := runContext(ctx, timeout)

	qoderArgs := append(
		[]string{"--yolo", "--acp"},
		filterCustomArgs(opts.CustomArgs, qoderBlockedArgs, b.cfg.Logger)...,
	)
	cmd := exec.CommandContext(runCtx, execPath, qoderArgs...)
	hideAgentWindow(cmd)
	b.cfg.Logger.Info("agent command", "exec", execPath, "args", qoderArgs)
	if opts.Cwd != "" {
		cmd.Dir = opts.Cwd
	}
	cmd.Env = buildEnv(b.cfg.Env)

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("qoder stdout pipe: %w", err)
	}
	stdin, err := cmd.StdinPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("qoder stdin pipe: %w", err)
	}
	// StderrPipe + an explicit copier give us a join point (`stderrDone`)
	// that fires before the failure-promotion decision; see the matching
	// comment in hermes.go for why the io.MultiWriter form races with
	// stopReason=end_turn under load (a terminal provider error can land
	// after we've already read finalOutput and reported "completed").
	providerErr := newACPProviderErrorSniffer("qoder")
	stderr, err := cmd.StderrPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("qoder stderr pipe: %w", err)
	}

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

	stderrSink := io.MultiWriter(newLogWriter(b.cfg.Logger, "[qoder:stderr] "), providerErr)
	stderrDone := make(chan struct{})
	go func() {
		defer close(stderrDone)
		_, _ = io.Copy(stderrSink, stderr)
	}()

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

	msgStream := newQoderMessageStream(256)
	resCh := make(chan Result, 1)

	var outputMu sync.Mutex
	var output strings.Builder
	var streamingCurrentTurn atomic.Bool

	promptDone := make(chan hermesPromptResult, 1)

	c := &hermesClient{
		cfg:          b.cfg,
		stdin:        stdin,
		pending:      make(map[int]*pendingRPC),
		pendingTools: make(map[string]*pendingToolCall),
		acceptNotification: func(string) bool {
			return streamingCurrentTurn.Load()
		},
		onMessage: func(msg Message) {
			if !streamingCurrentTurn.Load() {
				return
			}
			if msg.Type == MessageToolUse {
				msg.Tool = kimiToolNameFromTitle(msg.Tool)
			}
			if msg.Type == MessageText {
				outputMu.Lock()
				output.WriteString(msg.Content)
				outputMu.Unlock()
			}
			msgStream.send(msg)
		},
		onPromptDone: func(result hermesPromptResult) {
			if !streamingCurrentTurn.Load() {
				return
			}
			select {
			case promptDone <- result:
			default:
			}
		},
	}

	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("qoder process exited"))
	}()

	go func() {
		defer cancel()
		defer msgStream.close()
		defer close(resCh)
		defer func() {
			stdin.Close()
			_ = cmd.Wait()
		}()

		startTime := time.Now()
		finalStatus := "completed"
		var finalError string
		var sessionID string
		effectiveModel := strings.TrimSpace(opts.Model)

		initResult, 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("qoder initialize failed: %v", err)
			resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
			return
		}

		// Drop MCP entries whose remote transport the runtime didn't
		// advertise. See the matching comment in hermes.go for why
		// unconditionally sending http/sse to a stdio-only ACP runtime
		// tanks the whole session/new.
		mcpServers = filterACPMcpServersByCapability(mcpServers, extractACPMcpCapabilities(initResult), "qoder", b.cfg.Logger)

		cwd := opts.Cwd
		if cwd == "" {
			cwd = "."
		}

		if opts.ResumeSessionID != "" {
			result, err := c.request(runCtx, "session/resume", map[string]any{
				"cwd":        cwd,
				"sessionId":  opts.ResumeSessionID,
				"mcpServers": mcpServers,
			})
			if err != nil {
				finalStatus = "failed"
				finalError = fmt.Sprintf("qoder session/resume failed: %v", err)
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			var changed bool
			sessionID, changed = resolveResumedSessionID(opts.ResumeSessionID, result)
			if changed {
				b.cfg.Logger.Warn("agent returned a different session id on resume — original was likely lost; continuing with the new id",
					"backend", "qoder",
					"requested", opts.ResumeSessionID,
					"actual", sessionID,
				)
			}
			if effectiveModel == "" {
				effectiveModel = extractACPCurrentModelID(result)
			}
		} else {
			result, err := c.request(runCtx, "session/new", map[string]any{
				"cwd":        cwd,
				"mcpServers": mcpServers,
			})
			if err != nil {
				finalStatus = "failed"
				finalError = fmt.Sprintf("qoder session/new failed: %v", err)
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			sessionID = extractACPSessionID(result)
			if sessionID == "" {
				finalStatus = "failed"
				finalError = "qoder session/new returned no session ID"
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			if effectiveModel == "" {
				effectiveModel = extractACPCurrentModelID(result)
			}
		}

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

		if opts.Model != "" {
			if _, err := c.request(runCtx, "session/set_model", map[string]any{
				"sessionId": sessionID,
				"modelId":   opts.Model,
			}); err != nil {
				b.cfg.Logger.Warn("qoder set_session_model failed", "error", err, "requested_model", opts.Model)
				finalStatus = "failed"
				finalError = fmt.Sprintf("qoder could not switch to model %q: %v", opts.Model, err)
				if opts.ResumeSessionID != "" && isACPSessionNotFound(err) {
					// On a resumed session with a model override, the dead
					// session surfaces here instead of at session/prompt.
					// Clear the id so the daemon's resume-failure fallback
					// retries fresh and stores the replacement session.
					b.cfg.Logger.Warn("resumed session not found at set_model time; clearing session id so the daemon retries fresh",
						"backend", "qoder",
						"session_id", sessionID,
					)
					sessionID = ""
				}
				resCh <- Result{
					Status:     finalStatus,
					Error:      finalError,
					DurationMs: time.Since(startTime).Milliseconds(),
					SessionID:  sessionID,
				}
				return
			}
			b.cfg.Logger.Info("qoder session model set", "model", opts.Model)
		}

		userText := prompt
		if opts.SystemPrompt != "" {
			userText = opts.SystemPrompt + "\n\n---\n\n" + prompt
		}

		// Flip just before session/prompt so history replay flushed during setup
		// is dropped; every notification for this turn is processed afterward.
		streamingCurrentTurn.Store(true)
		_, err = c.request(runCtx, "session/prompt", map[string]any{
			"sessionId": sessionID,
			"prompt": []map[string]any{
				{"type": "text", "text": userText},
			},
		})
		if err != nil {
			if runCtx.Err() == context.DeadlineExceeded {
				finalStatus = "timeout"
				finalError = fmt.Sprintf("qoder timed out after %s", timeout)
			} else if runCtx.Err() == context.Canceled {
				finalStatus = "aborted"
				finalError = "execution cancelled"
			} else {
				finalStatus = "failed"
				finalError = fmt.Sprintf("qoder session/prompt failed: %v", err)
				if opts.ResumeSessionID != "" && isACPSessionNotFound(err) {
					// The runtime may echo the requested id from
					// session/resume and only reject it at prompt time.
					// Empty SessionID lets the daemon retry with a fresh
					// session instead of pinning future runs to the stale id.
					b.cfg.Logger.Warn("resumed session not found at prompt time; clearing session id so the daemon retries fresh",
						"backend", "qoder",
						"session_id", sessionID,
					)
					sessionID = ""
				}
			}
		} else {
			select {
			case pr := <-promptDone:
				if pr.stopReason == "cancelled" {
					finalStatus = "aborted"
					finalError = "qoder cancelled the prompt"
				}
				c.usageMu.Lock()
				c.usage.InputTokens += pr.usage.InputTokens
				c.usage.OutputTokens += pr.usage.OutputTokens
				c.usage.CacheReadTokens += pr.usage.CacheReadTokens
				c.usageMu.Unlock()
			default:
			}
		}

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

		stdin.Close()
		cancel()

		// Qoder ACP may keep the process — and the stdout/stderr pipes — open
		// after session/prompt returns (it can leave a child holding the
		// inherited fds). The prompt response is already terminal, so bound the
		// drain: wait for both the stdout reader and the stderr copier, but no
		// longer than the grace window. CommandContext cancellation above is
		// what actually tears the process down. Draining stderr here is what
		// makes the provider-error promotion below see a terminal marker before
		// we decide the final status.
		drainCtx, drainCancel := context.WithTimeout(context.Background(), qoderReaderDrainGrace)
		select {
		case <-readerDone:
		case <-drainCtx.Done():
		}
		select {
		case <-stderrDone:
		case <-drainCtx.Done():
		}
		drainCancel()
		// The stdout reader may still run after the grace window. Flip the
		// stream gate before this goroutine's defer closes msgStream; if a
		// late reader already passed the gate, qoderMessageStream serializes
		// send and close so the late send is dropped instead of panicking.
		streamingCurrentTurn.Store(false)

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

		// Promote completed→failed when stderr or the agent text stream show a
		// terminal upstream-LLM failure (HTTP 4xx / rate-limit / expired token).
		// Mirrors hermes/kimi/kiro; without it a run that exhausts retries still
		// reports "completed" because session/prompt ends with stopReason=end_turn
		// even though qodercli wrote a terminal error to stderr.
		finalStatus, finalError = promoteACPResultOnProviderError(finalStatus, finalError, finalOutput, providerErr)

		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 := effectiveModel
			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: msgStream.ch, Result: resCh}, nil
}