package llm

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"os"
	"os/exec"
	"strings"
	"syscall"
	"time"

	"github.com/enmanuel/agents/internal/config"
	coretypes "github.com/enmanuel/agents/pkg/llm"
)

const (
	defaultClaudeBinary  = "claude"
	defaultClaudeTimeout = 5 * time.Minute
)

// claudeJSONOutput represents the JSON output from `claude -p --output-format json`.
type claudeJSONOutput struct {
	Type         string           `json:"type"`
	Subtype      string           `json:"subtype"`
	CostUSD      float64          `json:"cost_usd"`
	IsError      bool             `json:"is_error"`
	Duration     float64          `json:"duration_api_ms"`
	NumTurns     int              `json:"num_turns"`
	Result       string           `json:"result"`
	SessionID    string           `json:"session_id"`
	TotalCost    float64          `json:"total_cost_usd"`
	Usage        claudeUsage      `json:"usage"`
	ContentBlock []claudeContent  `json:"content"`
}

type claudeUsage struct {
	InputTokens  int `json:"input_tokens"`
	OutputTokens int `json:"output_tokens"`
}

type claudeContent struct {
	Type string `json:"type"`
	Text string `json:"text"`
}

// NewClaudeCodeComplete creates a CompleteFunc that executes `claude -p` as a subprocess.
func NewClaudeCodeComplete(cfg config.ClaudeCodeCfg, log *slog.Logger) coretypes.CompleteFunc {
	binary := cfg.Binary
	if binary == "" {
		binary = defaultClaudeBinary
	}

	timeout := cfg.Timeout
	if timeout <= 0 {
		timeout = defaultClaudeTimeout
	}

	// Resolve working directory once at init time.
	workDir := resolveWorkDir(cfg.WorkingDir, log)

	return func(ctx context.Context, req coretypes.CompletionRequest) (coretypes.CompletionResponse, error) {
		ctx, cancel := context.WithTimeout(ctx, timeout)
		defer cancel()

		args := buildClaudeArgs(cfg, req)

		prompt := flattenMessages(req.Messages)

		log.Debug("claude_code_exec",
			"binary", binary,
			"args", strings.Join(args, " "),
			"prompt_len", len(prompt),
			"working_dir", workDir,
			"streaming", cfg.Streaming,
		)

		cmd := exec.CommandContext(ctx, binary, args...)
		if workDir != "" {
			cmd.Dir = workDir
		}
		// Build clean env: inherit parent but remove ANTHROPIC_API_KEY
		// so claude uses its own OAuth auth instead of a potentially invalid key.
		cmd.Env = filterEnv(os.Environ(), "ANTHROPIC_API_KEY")
		cmd.Stdin = strings.NewReader(prompt)

		// Create a new process group so we can kill claude + all its children.
		cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
		// Override the default cancel behavior: kill the entire process group
		// instead of just the main process, preventing orphaned child processes.
		cmd.Cancel = func() error {
			if cmd.Process != nil {
				pgid := cmd.Process.Pid
				log.Info("killing claude-code process group", "pgid", pgid)
				// Negative PID = kill entire process group
				return syscall.Kill(-pgid, syscall.SIGKILL)
			}
			return nil
		}

		// Choose between streaming and buffered mode
		if cfg.Streaming && req.StreamFunc != nil {
			return executeStreaming(ctx, cmd, req.StreamFunc, log)
		}
		return executeBuffered(ctx, cmd, log)
	}
}

// executeBuffered runs the claude subprocess and collects all output at once.
// This is the original (non-streaming) code path.
func executeBuffered(ctx context.Context, cmd *exec.Cmd, log *slog.Logger) (coretypes.CompletionResponse, error) {
	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr

	start := time.Now()
	err := cmd.Run()
	elapsed := time.Since(start)

	// Ensure the process group is fully dead after Run returns.
	if cmd.Process != nil {
		_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
	}

	log.Debug("claude_code_done",
		"elapsed_ms", elapsed.Milliseconds(),
		"stdout_len", stdout.Len(),
		"stderr_len", stderr.Len(),
		"exit_err", err,
	)

	return parseClaudeOutput(stdout.Bytes(), stderr.Bytes(), err, elapsed, log)
}

// executeStreaming runs the claude subprocess with --output-format stream-json,
// reads stdout line by line, emits StreamEvents via the callback, and accumulates
// the final result.
func executeStreaming(ctx context.Context, cmd *exec.Cmd, streamFn coretypes.StreamFunc, log *slog.Logger) (coretypes.CompletionResponse, error) {
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return coretypes.CompletionResponse{}, fmt.Errorf("claude-code: stdout pipe: %w", err)
	}

	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	start := time.Now()
	if err := cmd.Start(); err != nil {
		return coretypes.CompletionResponse{}, fmt.Errorf("claude-code: start: %w", err)
	}

	// Scan stdout line by line, parsing each JSON event
	var lastResult *claudeJSONOutput
	scanner := bufio.NewScanner(stdout)
	scanner.Buffer(make([]byte, 0, 256*1024), 1024*1024) // allow up to 1MB lines

	for scanner.Scan() {
		line := scanner.Bytes()
		if len(line) == 0 {
			continue
		}

		evt, parsed, parseErr := parseStreamLine(line)
		if parseErr != nil {
			log.Debug("stream_line_parse_error", "err", parseErr, "line_len", len(line))
			continue
		}

		// Emit the event to the callback
		streamFn(evt)

		// Keep track of the final result event
		if parsed != nil && parsed.Type == "result" {
			lastResult = parsed
		}
	}

	// Wait for the process to finish
	waitErr := cmd.Wait()
	elapsed := time.Since(start)

	// Ensure the process group is fully dead after Run returns.
	if cmd.Process != nil {
		_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
	}

	if scanErr := scanner.Err(); scanErr != nil {
		log.Warn("stream_scanner_error", "err", scanErr)
	}

	log.Debug("claude_code_stream_done",
		"elapsed_ms", elapsed.Milliseconds(),
		"stderr_len", stderr.Len(),
		"exit_err", waitErr,
	)

	// Build response from the last result event
	if lastResult != nil {
		return buildResponseFromResult(lastResult, waitErr, elapsed, log)
	}

	// Fallback: if no result event was captured, treat stderr/waitErr as error
	if waitErr != nil {
		errMsg := stderr.String()
		if errMsg == "" {
			errMsg = waitErr.Error()
		}
		return coretypes.CompletionResponse{}, fmt.Errorf("claude-code stream process failed: %s", errMsg)
	}

	return coretypes.CompletionResponse{
		Content:      "",
		FinishReason: "stop",
	}, nil
}

// buildResponseFromResult converts a parsed result event into a CompletionResponse.
func buildResponseFromResult(output *claudeJSONOutput, execErr error, elapsed time.Duration, log *slog.Logger) (coretypes.CompletionResponse, error) {
	if output.IsError {
		return coretypes.CompletionResponse{}, fmt.Errorf("claude-code error: %s", output.Result)
	}

	content := output.Result
	if content == "" && len(output.ContentBlock) > 0 {
		var parts []string
		for _, block := range output.ContentBlock {
			if block.Type == "text" && block.Text != "" {
				parts = append(parts, block.Text)
			}
		}
		content = strings.Join(parts, "\n")
	}

	finishReason := "stop"
	if execErr != nil {
		finishReason = "error"
	}

	log.Info("claude_code_response",
		"content_len", len(content),
		"input_tokens", output.Usage.InputTokens,
		"output_tokens", output.Usage.OutputTokens,
		"num_turns", output.NumTurns,
		"cost_usd", output.TotalCost,
		"elapsed_ms", elapsed.Milliseconds(),
	)

	return coretypes.CompletionResponse{
		Content: content,
		Usage: coretypes.TokenUsage{
			InputTokens:  output.Usage.InputTokens,
			OutputTokens: output.Usage.OutputTokens,
			TotalTokens:  output.Usage.InputTokens + output.Usage.OutputTokens,
		},
		FinishReason: finishReason,
	}, nil
}

// ── Stream event parsing ────────────────────────────────────────────────

// claudeStreamEvent is the raw JSON shape from `claude -p --output-format stream-json`.
// Each line of stdout is one JSON object with at least a "type" field.
type claudeStreamEvent struct {
	Type    string `json:"type"`
	Subtype string `json:"subtype"`

	// For type=assistant, the message contains content blocks
	Message *claudeStreamMessage `json:"message"`

	// For type=result — reuse claudeJSONOutput fields
	IsError   bool             `json:"is_error"`
	Result    string           `json:"result"`
	NumTurns  int              `json:"num_turns"`
	TotalCost float64          `json:"total_cost_usd"`
	Usage     claudeUsage      `json:"usage"`
	Content   []claudeContent  `json:"content"`
}

// claudeStreamMessage represents the assistant message in a stream event.
type claudeStreamMessage struct {
	Content []claudeStreamContentBlock `json:"content"`
}

// claudeStreamContentBlock represents a content block within an assistant message.
type claudeStreamContentBlock struct {
	Type  string `json:"type"`
	Text  string `json:"text"`
	Name  string `json:"name"`  // tool_use: tool name
	ID    string `json:"id"`    // tool_use: call ID
	Input any    `json:"input"` // tool_use: tool input (object or string)
}

// parseStreamLine parses a single JSON line from the stream-json output.
// Returns the StreamEvent, optionally the raw parsed result (if type=result),
// and any parse error.
func parseStreamLine(line []byte) (coretypes.StreamEvent, *claudeJSONOutput, error) {
	var raw claudeStreamEvent
	if err := json.Unmarshal(line, &raw); err != nil {
		return coretypes.StreamEvent{}, nil, fmt.Errorf("parse stream line: %w", err)
	}

	switch raw.Type {
	case "system":
		// Init event — emit as init
		return coretypes.StreamEvent{
			Kind: coretypes.StreamInit,
		}, nil, nil

	case "assistant":
		// Assistant message with content blocks — extract tool_use and text events
		if raw.Message != nil && len(raw.Message.Content) > 0 {
			// Look for the most interesting content block
			for _, block := range raw.Message.Content {
				switch block.Type {
				case "tool_use":
					inputStr := truncateToolInput(block.Input)
					return coretypes.StreamEvent{
						Kind:      coretypes.StreamToolUse,
						ToolName:  block.Name,
						ToolInput: inputStr,
					}, nil, nil
				case "tool_result":
					return coretypes.StreamEvent{
						Kind: coretypes.StreamToolResult,
					}, nil, nil
				case "text":
					return coretypes.StreamEvent{
						Kind:    coretypes.StreamText,
						Content: block.Text,
					}, nil, nil
				}
			}
		}
		// Assistant message without interesting content blocks
		return coretypes.StreamEvent{
			Kind: coretypes.StreamText,
		}, nil, nil

	case "result":
		// Final result event
		result := &claudeJSONOutput{
			Type:      raw.Type,
			Subtype:   raw.Subtype,
			IsError:   raw.IsError,
			Result:    raw.Result,
			NumTurns:  raw.NumTurns,
			TotalCost: raw.TotalCost,
			Usage:     raw.Usage,
		}
		evt := coretypes.StreamEvent{
			Kind:    coretypes.StreamResult,
			Content: raw.Result,
			IsError: raw.IsError,
		}
		return evt, result, nil

	default:
		// Unknown event type — emit as text with raw type info
		return coretypes.StreamEvent{
			Kind:    coretypes.StreamText,
			Content: raw.Type,
		}, nil, nil
	}
}

// truncateToolInput converts tool input to a short description string.
func truncateToolInput(input any) string {
	if input == nil {
		return ""
	}

	switch v := input.(type) {
	case string:
		return truncateStr(v, 100)
	case map[string]any:
		// For tool inputs like {"command": "ls -la"}, extract the most useful field
		if cmd, ok := v["command"]; ok {
			return truncateStr(fmt.Sprintf("%v", cmd), 100)
		}
		if file, ok := v["file_path"]; ok {
			return truncateStr(fmt.Sprintf("%v", file), 100)
		}
		// Fallback: serialize the whole thing
		b, err := json.Marshal(v)
		if err != nil {
			return ""
		}
		return truncateStr(string(b), 100)
	default:
		b, err := json.Marshal(v)
		if err != nil {
			return ""
		}
		return truncateStr(string(b), 100)
	}
}

// truncateStr shortens a string to maxLen, appending "..." if truncated.
func truncateStr(s string, maxLen int) string {
	if len(s) <= maxLen {
		return s
	}
	return s[:maxLen-3] + "..."
}

// ── Shared helpers ──────────────────────────────────────────────────────

// resolveWorkDir determines the working directory for the claude subprocess.
// If configured is empty, it creates a temporary directory to avoid inheriting the launcher's CWD.
// If configured is non-empty, it ensures the directory exists.
func resolveWorkDir(configured string, log *slog.Logger) string {
	if configured == "" {
		tmp, err := os.MkdirTemp("", "claude-agent-*")
		if err != nil {
			log.Error("claude-code: failed to create temp working dir", "err", err)
			return "" // Fall through — cmd.Dir will remain empty (inherits CWD).
		}
		log.Warn("claude-code working_dir is empty, using temporary directory",
			"dir", tmp,
		)
		return tmp
	}

	// Ensure configured directory exists.
	if err := os.MkdirAll(configured, 0o755); err != nil {
		log.Error("claude-code: failed to create working dir", "dir", configured, "err", err)
	}
	return configured
}

// buildClaudeArgs constructs the CLI arguments for claude -p.
func buildClaudeArgs(cfg config.ClaudeCodeCfg, req coretypes.CompletionRequest) []string {
	outputFormat := "json"
	if cfg.Streaming && req.StreamFunc != nil {
		outputFormat = "stream-json"
	}

	args := []string{"--print", "--output-format", outputFormat}

	// stream-json requires --verbose
	if outputFormat == "stream-json" {
		args = append(args, "--verbose")
	}

	if req.SystemPrompt != "" {
		args = append(args, "--system-prompt", req.SystemPrompt)
	}

	// Issue 0145: --mcp-config tells claude where to find external MCP
	// servers (per-agent devicemesh bridge). Must come BEFORE --allowedTools
	// because the allowed list usually references `mcp__<server>__<tool>`
	// names that only exist once the MCP config is loaded.
	if cfg.MCPConfigPath != "" {
		args = append(args, "--mcp-config", cfg.MCPConfigPath)
	}

	// Defensive: DisableTools=true plus a non-empty AllowedTools is a
	// contradiction. The launcher's ApplyMCPBridge already forces
	// DisableTools=false in that case, but this guard keeps direct callers
	// safe too.
	effectiveDisableTools := cfg.DisableTools && len(cfg.AllowedTools) == 0

	if effectiveDisableTools {
		args = append(args, "--tools", "")
	} else {
		if len(cfg.AllowedTools) > 0 {
			args = append(args, "--allowedTools")
			args = append(args, cfg.AllowedTools...)
		}

		if len(cfg.DisallowedTools) > 0 {
			args = append(args, "--disallowedTools")
			args = append(args, cfg.DisallowedTools...)
		}
	}

	if cfg.PermissionMode != "" {
		args = append(args, "--permission-mode", cfg.PermissionMode)
	}

	if cfg.Model != "" {
		args = append(args, "--model", cfg.Model)
	}

	if cfg.FallbackModel != "" {
		args = append(args, "--fallback-model", cfg.FallbackModel)
	}

	if cfg.SessionID != "" {
		args = append(args, "--session-id", cfg.SessionID)
	}

	for _, dir := range cfg.AddDirs {
		args = append(args, "--add-dir", dir)
	}

	return args
}

// flattenMessages converts a conversation history into a single text prompt for stdin.
func flattenMessages(msgs []coretypes.Message) string {
	var b strings.Builder
	for _, m := range msgs {
		switch m.Role {
		case coretypes.RoleUser:
			fmt.Fprintf(&b, "User: %s\n\n", m.Content)
		case coretypes.RoleAssistant:
			fmt.Fprintf(&b, "Assistant: %s\n\n", m.Content)
		case coretypes.RoleTool:
			fmt.Fprintf(&b, "Tool result: %s\n\n", m.Content)
		}
	}
	return b.String()
}

// parseClaudeOutput parses the JSON output from `claude -p --output-format json`.
func parseClaudeOutput(
	stdout, stderr []byte,
	execErr error,
	elapsed time.Duration,
	log *slog.Logger,
) (coretypes.CompletionResponse, error) {
	// If the process failed and there's no stdout, report the error
	if execErr != nil && len(stdout) == 0 {
		errMsg := string(stderr)
		if errMsg == "" {
			errMsg = execErr.Error()
		}
		return coretypes.CompletionResponse{}, fmt.Errorf("claude-code process failed: %s", errMsg)
	}

	// Parse JSON output
	var output claudeJSONOutput
	if err := json.Unmarshal(stdout, &output); err != nil {
		// Fall back to treating stdout as plain text
		log.Warn("claude_code_json_parse_failed", "err", err, "stdout_len", len(stdout))
		return coretypes.CompletionResponse{
			Content:      strings.TrimSpace(string(stdout)),
			FinishReason: "stop",
		}, nil
	}

	if output.IsError {
		return coretypes.CompletionResponse{}, fmt.Errorf("claude-code error: %s", output.Result)
	}

	// Extract text from result field or content blocks
	content := output.Result
	if content == "" && len(output.ContentBlock) > 0 {
		var parts []string
		for _, block := range output.ContentBlock {
			if block.Type == "text" && block.Text != "" {
				parts = append(parts, block.Text)
			}
		}
		content = strings.Join(parts, "\n")
	}

	finishReason := "stop"
	if execErr != nil {
		finishReason = "error"
	}

	log.Info("claude_code_response",
		"content_len", len(content),
		"input_tokens", output.Usage.InputTokens,
		"output_tokens", output.Usage.OutputTokens,
		"num_turns", output.NumTurns,
		"cost_usd", output.TotalCost,
		"elapsed_ms", elapsed.Milliseconds(),
	)

	return coretypes.CompletionResponse{
		Content: content,
		Usage: coretypes.TokenUsage{
			InputTokens:  output.Usage.InputTokens,
			OutputTokens: output.Usage.OutputTokens,
			TotalTokens:  output.Usage.InputTokens + output.Usage.OutputTokens,
		},
		FinishReason: finishReason,
	}, nil
}

// filterEnv returns a copy of environ with the named keys removed.
func filterEnv(environ []string, keys ...string) []string {
	out := make([]string, 0, len(environ))
	for _, e := range environ {
		skip := false
		for _, k := range keys {
			if strings.HasPrefix(e, k+"=") {
				skip = true
				break
			}
		}
		if !skip {
			out = append(out, e)
		}
	}
	return out
}