package chattool

import (
	"context"
	"encoding/json"
	"fmt"
	"regexp"
	"strings"
	"time"

	"charm.land/fantasy"

	"github.com/coder/coder/v2/codersdk/workspacesdk"
)

const (
	// defaultTimeout is the default timeout for command
	// execution.
	defaultTimeout = 10 * time.Second

	// maxOutputToModel is the maximum output sent to the LLM.
	maxOutputToModel = 32 << 10 // 32KB

	// snapshotTimeout is how long a non-blocking fallback
	// request is allowed to take when retrieving a process
	// output snapshot after a blocking wait times out.
	snapshotTimeout = 30 * time.Second
)

// nonInteractiveEnvVars are set on every process to prevent
// interactive prompts that would hang a headless execution.
var nonInteractiveEnvVars = map[string]string{
	"GIT_EDITOR":          "true",
	"GIT_SEQUENCE_EDITOR": "true",
	"EDITOR":              "true",
	"VISUAL":              "true",
	"GIT_TERMINAL_PROMPT": "0",
	"NO_COLOR":            "1",
	"TERM":                "dumb",
	"PAGER":               "cat",
	"GIT_PAGER":           "cat",
}

// fileDumpPatterns detects commands that dump entire files.
// When matched, a note is added suggesting read_file instead.
var fileDumpPatterns = []*regexp.Regexp{
	regexp.MustCompile(`^cat\s+`),
	regexp.MustCompile(`^(rg|grep)\s+.*--include-all`),
	regexp.MustCompile(`^(rg|grep)\s+-l\s+`),
}

// ExecuteResult is the structured response from the execute
// tool.
type ExecuteResult struct {
	Success             bool                            `json:"success"`
	Output              string                          `json:"output,omitempty"`
	ExitCode            int                             `json:"exit_code"`
	WallDurationMs      int64                           `json:"wall_duration_ms"`
	Error               string                          `json:"error,omitempty"`
	Truncated           *workspacesdk.ProcessTruncation `json:"truncated,omitempty"`
	Note                string                          `json:"note,omitempty"`
	BackgroundProcessID string                          `json:"background_process_id,omitempty"`
}

// ExecuteOptions configures the execute tool.
type ExecuteOptions struct {
	GetWorkspaceConn func(context.Context) (workspacesdk.AgentConn, error)
	DefaultTimeout   time.Duration
}

// ProcessToolOptions configures a process management tool
// (process_output, process_list, or process_signal). Each of
// these tools only needs a workspace connection resolver.
type ProcessToolOptions struct {
	GetWorkspaceConn func(context.Context) (workspacesdk.AgentConn, error)
}

// ExecuteArgs are the parameters accepted by the execute tool.
type ExecuteArgs struct {
	Command         string  `json:"command" description:"The shell command to execute."`
	Timeout         *string `json:"timeout,omitempty" description:"Timeout duration (e.g. '30s', '5m'). Default is 10s. Only applies to foreground commands."`
	WorkDir         *string `json:"workdir,omitempty" description:"Working directory for the command."`
	RunInBackground *bool   `json:"run_in_background,omitempty" description:"Run this command in the background without blocking. Use for long-running processes like dev servers, file watchers, or builds that run longer than 5 seconds. Do NOT use shell & to background processes — it will not work correctly. Always use this parameter instead."`
}

// Execute returns an AgentTool that runs a shell command in the
// workspace via the agent HTTP API.
func Execute(options ExecuteOptions) fantasy.AgentTool {
	return fantasy.NewAgentTool(
		"execute",
		"Execute a shell command in the workspace. Use run_in_background=true for long-running processes (dev servers, file watchers, builds). Never use shell '&' for backgrounding. If the command fails or times out, the response may include a background_process_id; use process_output with that ID to retrieve the result.",
		func(ctx context.Context, args ExecuteArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
			if options.GetWorkspaceConn == nil {
				return fantasy.NewTextErrorResponse("workspace connection resolver is not configured"), nil
			}
			conn, err := options.GetWorkspaceConn(ctx)
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}
			return executeTool(ctx, conn, args, options.DefaultTimeout), nil
		},
	)
}

func executeTool(
	ctx context.Context,
	conn workspacesdk.AgentConn,
	args ExecuteArgs,
	optTimeout time.Duration,
) fantasy.ToolResponse {
	if args.Command == "" {
		return fantasy.NewTextErrorResponse("command is required")
	}

	// Build the environment map for the process request.
	env := make(map[string]string, len(nonInteractiveEnvVars)+1)
	env["CODER_CHAT_AGENT"] = "true"
	for k, v := range nonInteractiveEnvVars {
		env[k] = v
	}

	background := args.RunInBackground != nil && *args.RunInBackground

	// Detect shell-style backgrounding (trailing &) and promote to
	// background mode. Models sometimes use "cmd &" instead of the
	// run_in_background parameter, which causes the shell to fork
	// and exit immediately, leaving an untracked orphan process.
	trimmed := strings.TrimSpace(args.Command)
	if !background && strings.HasSuffix(trimmed, "&") && !strings.HasSuffix(trimmed, "&&") && !strings.HasSuffix(trimmed, "|&") {
		background = true
		args.Command = strings.TrimSpace(strings.TrimSuffix(trimmed, "&"))
	}

	var workDir string
	if args.WorkDir != nil {
		workDir = *args.WorkDir
	}

	if background {
		return executeBackground(ctx, conn, args.Command, workDir, env)
	}
	return executeForeground(ctx, conn, args, optTimeout, workDir, env)
}

// executeBackground starts a process in the background and
// returns immediately with the process ID.
func executeBackground(
	ctx context.Context,
	conn workspacesdk.AgentConn,
	command string,
	workDir string,
	env map[string]string,
) fantasy.ToolResponse {
	resp, err := conn.StartProcess(ctx, workspacesdk.StartProcessRequest{
		Command:    command,
		WorkDir:    workDir,
		Env:        env,
		Background: true,
	})
	if err != nil {
		return errorResult(fmt.Sprintf("start background process: %v", err))
	}

	result := ExecuteResult{
		Success:             true,
		BackgroundProcessID: resp.ID,
	}
	data, err := json.Marshal(result)
	if err != nil {
		return fantasy.NewTextErrorResponse(err.Error())
	}
	return fantasy.NewTextResponse(string(data))
}

// executeForeground starts a process and waits for its
// completion, enforcing the configured timeout.
func executeForeground(
	ctx context.Context,
	conn workspacesdk.AgentConn,
	args ExecuteArgs,
	optTimeout time.Duration,
	workDir string,
	env map[string]string,
) fantasy.ToolResponse {
	timeout := optTimeout
	if timeout <= 0 {
		timeout = defaultTimeout
	}
	if args.Timeout != nil {
		parsed, err := time.ParseDuration(*args.Timeout)
		if err != nil {
			return fantasy.NewTextErrorResponse(
				fmt.Sprintf("invalid timeout %q: %v", *args.Timeout, err),
			)
		}
		timeout = parsed
	}

	cmdCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()

	start := time.Now()

	resp, err := conn.StartProcess(cmdCtx, workspacesdk.StartProcessRequest{
		Command:    args.Command,
		WorkDir:    workDir,
		Env:        env,
		Background: false,
	})
	if err != nil {
		return errorResult(fmt.Sprintf("start process: %v", err))
	}

	result := waitForProcess(cmdCtx, ctx, conn, resp.ID, timeout)
	result.WallDurationMs = time.Since(start).Milliseconds()

	// Add an advisory note for file-dump commands.
	if note := detectFileDump(args.Command); note != "" {
		result.Note = note
	}

	data, err := json.Marshal(result)
	if err != nil {
		return fantasy.NewTextErrorResponse(err.Error())
	}
	return fantasy.NewTextResponse(string(data))
}

// truncateOutput safely truncates output to maxOutputToModel,
// ensuring the result is valid UTF-8 even if the cut falls in
// the middle of a multi-byte character.
func truncateOutput(output string) string {
	if len(output) > maxOutputToModel {
		output = strings.ToValidUTF8(output[:maxOutputToModel], "")
	}
	return output
}

// waitForProcess waits for process completion using the
// blocking process output API instead of polling.
// waitForProcess blocks until the process exits or the context
// expires. On any error (timeout or transport), it tries a
// non-blocking snapshot to recover. Total wall time may exceed
// timeout by up to snapshotTimeout if recovery is needed.
func waitForProcess(
	ctx context.Context,
	parentCtx context.Context,
	conn workspacesdk.AgentConn,
	processID string,
	timeout time.Duration,
) ExecuteResult {
	// Block until the process exits or the context is
	// canceled.
	resp, err := conn.ProcessOutput(ctx, processID, &workspacesdk.ProcessOutputOptions{
		Wait: true,
	})
	if err != nil {
		origErr := err
		timedOut := ctx.Err() != nil

		// Fetch a snapshot with a fresh context. The blocking
		// request may have failed due to a context timeout or
		// a transport error (e.g. the server's WriteTimeout
		// killed the connection). Either way, the process may
		// still have output available.
		bgCtx, bgCancel := context.WithTimeout(
			parentCtx,
			snapshotTimeout,
		)
		defer bgCancel()
		resp, err = conn.ProcessOutput(bgCtx, processID, nil)
		if err != nil {
			errMsg := fmt.Sprintf("get process output: %v; use process_output with ID %s to retry", origErr, processID)
			if timedOut {
				errMsg = fmt.Sprintf("command timed out after %s; failed to get output: %v", timeout, err)
			}
			return ExecuteResult{
				Success:             false,
				ExitCode:            -1,
				Error:               errMsg,
				BackgroundProcessID: processID,
			}
		}

		// Snapshot succeeded. If the process finished, return
		// its real result (transparent recovery).
		if !resp.Running {
			exitCode := 0
			if resp.ExitCode != nil {
				exitCode = *resp.ExitCode
			}
			output := truncateOutput(resp.Output)
			return ExecuteResult{
				Success:   exitCode == 0,
				Output:    output,
				ExitCode:  exitCode,
				Truncated: resp.Truncated,
			}
		}

		// Process still running, return partial output.
		output := truncateOutput(resp.Output)
		errMsg := fmt.Sprintf("command timed out after %s", timeout)
		if !timedOut {
			errMsg = fmt.Sprintf("get process output: %v (process still running, use process_output to check later)", origErr)
		}
		return ExecuteResult{
			Success:             false,
			Output:              output,
			ExitCode:            -1,
			Error:               errMsg,
			Truncated:           resp.Truncated,
			BackgroundProcessID: processID,
		}
	}

	// The server-side wait may return before the
	// process exits if maxWaitDuration is shorter than
	// the client's timeout. Retry if our context still
	// has time left.
	if resp.Running {
		if ctx.Err() == nil {
			// Still within the caller's timeout, retry.
			return waitForProcess(ctx, parentCtx, conn, processID, timeout)
		}
		output := truncateOutput(resp.Output)
		return ExecuteResult{
			Success:             false,
			Output:              output,
			ExitCode:            -1,
			Error:               fmt.Sprintf("command timed out after %s", timeout),
			Truncated:           resp.Truncated,
			BackgroundProcessID: processID,
		}
	}

	exitCode := 0
	if resp.ExitCode != nil {
		exitCode = *resp.ExitCode
	}
	output := truncateOutput(resp.Output)
	return ExecuteResult{
		Success:   exitCode == 0,
		Output:    output,
		ExitCode:  exitCode,
		Truncated: resp.Truncated,
	}
}

// errorResult builds a ToolResponse from an ExecuteResult with
// an error message.
func errorResult(msg string) fantasy.ToolResponse {
	data, err := json.Marshal(ExecuteResult{
		Success: false,
		Error:   msg,
	})
	if err != nil {
		return fantasy.NewTextErrorResponse(msg)
	}
	return fantasy.NewTextResponse(string(data))
}

// detectFileDump checks whether the command matches a file-dump
// pattern and returns an advisory note, or empty string if no
// match.
func detectFileDump(command string) string {
	for _, pat := range fileDumpPatterns {
		if pat.MatchString(command) {
			return "Consider using read_file instead of " +
				"dumping file contents with shell commands."
		}
	}
	return ""
}

const (
	// defaultProcessOutputTimeout is the default time the
	// process_output tool blocks waiting for new output or
	// process exit before returning. This avoids polling
	// loops that waste tokens and HTTP round-trips.
	defaultProcessOutputTimeout = 10 * time.Second
)

// ProcessOutputArgs are the parameters accepted by the
// process_output tool.
type ProcessOutputArgs struct {
	ProcessID   string  `json:"process_id"`
	WaitTimeout *string `json:"wait_timeout,omitempty" description:"Override the default 10s block duration. The call blocks until the process exits or this timeout is reached. Set to '0s' for an immediate snapshot without waiting."`
}

// ProcessOutput returns an AgentTool that retrieves the output
// of a background process by its ID.
func ProcessOutput(options ProcessToolOptions) fantasy.AgentTool {
	return fantasy.NewAgentTool(
		"process_output",
		"Retrieve output from a background process. "+
			"Use the process_id returned by execute with "+
			"run_in_background=true or from a timed-out "+
			"execute's background_process_id. Blocks up to "+
			"10s for the process to exit, then returns the "+
			"output and exit_code. If still running after "+
			"the timeout, returns the output so far. Use "+
			"wait_timeout to override the default 10s wait "+
			"(e.g. '30s', or '0s' for an immediate snapshot).",
		func(ctx context.Context, args ProcessOutputArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
			if options.GetWorkspaceConn == nil {
				return fantasy.NewTextErrorResponse("workspace connection resolver is not configured"), nil
			}
			if args.ProcessID == "" {
				return fantasy.NewTextErrorResponse("process_id is required"), nil
			}
			conn, err := options.GetWorkspaceConn(ctx)
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}

			timeout := defaultProcessOutputTimeout
			if args.WaitTimeout != nil {
				parsed, err := time.ParseDuration(*args.WaitTimeout)
				if err != nil {
					return fantasy.NewTextErrorResponse(
						fmt.Sprintf("invalid wait_timeout %q: %v", *args.WaitTimeout, err),
					), nil
				}
				timeout = parsed
			}
			var opts *workspacesdk.ProcessOutputOptions
			// Save parent context before applying timeout.
			parentCtx := ctx
			if timeout > 0 {
				opts = &workspacesdk.ProcessOutputOptions{
					Wait: true,
				}
				var cancel context.CancelFunc
				ctx, cancel = context.WithTimeout(ctx, timeout)
				defer cancel()
			}
			resp, err := conn.ProcessOutput(ctx, args.ProcessID, opts)
			if err != nil {
				// The blocking request may have failed due to a
				// context timeout or a transport error (e.g.
				// server WriteTimeout). Try a non-blocking
				// snapshot if the parent context is still alive.
				if parentCtx.Err() != nil {
					return errorResult(fmt.Sprintf("get process output: %v", err)), nil
				}
				bgCtx, bgCancel := context.WithTimeout(parentCtx, snapshotTimeout)
				defer bgCancel()
				resp, err = conn.ProcessOutput(bgCtx, args.ProcessID, nil)
				if err != nil {
					return errorResult(fmt.Sprintf("get process output: %v", err)), nil
				}
				// Fall through to normal response handling below.
			}
			output := truncateOutput(resp.Output)
			exitCode := 0
			if resp.ExitCode != nil {
				exitCode = *resp.ExitCode
			}
			result := ExecuteResult{
				Success:   !resp.Running && exitCode == 0,
				Output:    output,
				ExitCode:  exitCode,
				Truncated: resp.Truncated,
			}
			if resp.Running {
				// Process is still running, success is not
				// yet determined.
				result.Success = true
				result.Note = "process is still running"
			}
			data, err := json.Marshal(result)
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}
			return fantasy.NewTextResponse(string(data)), nil
		},
	)
}

// ProcessList returns an AgentTool that lists all tracked
// processes on the workspace agent.
func ProcessList(options ProcessToolOptions) fantasy.AgentTool {
	return fantasy.NewAgentTool(
		"process_list",
		"List all tracked processes in the workspace. "+
			"Returns process IDs, commands, status (running or "+
			"exited), and exit codes. Use this to discover "+
			"background processes or check which processes are "+
			"still running.",
		func(ctx context.Context, _ struct{}, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
			if options.GetWorkspaceConn == nil {
				return fantasy.NewTextErrorResponse("workspace connection resolver is not configured"), nil
			}
			conn, err := options.GetWorkspaceConn(ctx)
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}
			resp, err := conn.ListProcesses(ctx)
			if err != nil {
				return errorResult(fmt.Sprintf("list processes: %v", err)), nil
			}
			data, err := json.Marshal(resp)
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}
			return fantasy.NewTextResponse(string(data)), nil
		},
	)
}

// ProcessSignalArgs are the parameters accepted by the
// process_signal tool.
type ProcessSignalArgs struct {
	ProcessID string `json:"process_id"`
	Signal    string `json:"signal"`
}

// ProcessSignal returns an AgentTool that sends a signal to a
// tracked process on the workspace agent.
func ProcessSignal(options ProcessToolOptions) fantasy.AgentTool {
	return fantasy.NewAgentTool(
		"process_signal",
		"Send a signal to a background process. "+
			"Use \"terminate\" (SIGTERM) for graceful shutdown "+
			"or \"kill\" (SIGKILL) to force stop. Use the "+
			"process_id returned by execute with "+
			"run_in_background=true or from process_list.",
		func(ctx context.Context, args ProcessSignalArgs, _ fantasy.ToolCall) (fantasy.ToolResponse, error) {
			if options.GetWorkspaceConn == nil {
				return fantasy.NewTextErrorResponse("workspace connection resolver is not configured"), nil
			}
			if args.ProcessID == "" {
				return fantasy.NewTextErrorResponse("process_id is required"), nil
			}
			if args.Signal != "terminate" && args.Signal != "kill" {
				return fantasy.NewTextErrorResponse(
					"signal must be \"terminate\" or \"kill\"",
				), nil
			}
			conn, err := options.GetWorkspaceConn(ctx)
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}
			if err := conn.SignalProcess(ctx, args.ProcessID, args.Signal); err != nil {
				return errorResult(fmt.Sprintf("signal process: %v", err)), nil
			}
			data, err := json.Marshal(map[string]any{
				"success": true,
				"message": fmt.Sprintf(
					"signal %q sent to process %s",
					args.Signal, args.ProcessID,
				),
			})
			if err != nil {
				return fantasy.NewTextErrorResponse(err.Error()), nil
			}
			return fantasy.NewTextResponse(string(data)), nil
		},
	)
}