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import { resolve } from "node:path";
import type { ExecBackend, ExecBackendResolver } from "@dispatch/exec-backend";
import type { ToolContract, ToolResult } from "@dispatch/kernel";
interface ValidatedArgs {
readonly path: string;
readonly content: string;
readonly overwrite: boolean;
}
export type OverwriteDecision = "create" | "overwrite" | { readonly error: string };
/** Pure: decide the action based on file existence and the overwrite flag. */
export function decideOverwrite(fileExists: boolean, overwrite: boolean): OverwriteDecision {
if (!fileExists && !overwrite) return "create";
if (fileExists && !overwrite) {
return { error: "Error: File already exists; set overwrite: true to replace it." };
}
if (fileExists && overwrite) return "overwrite";
return { error: "Error: overwrite: true but the file does not exist." };
}
/** Pure: validate and coerce args from the model. */
export function validateArgs(args: unknown): ValidatedArgs | { readonly error: string } {
if (args === null || args === undefined || typeof args !== "object") {
return { error: "Error: Arguments must be an object." };
}
const obj = args as Record<string, unknown>;
const rawPath = obj.path;
if (typeof rawPath !== "string" || rawPath.length === 0) {
return { error: 'Error: Missing or invalid "path" parameter (must be a non-empty string).' };
}
const rawContent = obj.content;
if (typeof rawContent !== "string") {
return {
error: 'Error: Missing or invalid "content" parameter (must be a string).',
};
}
let overwrite = false;
if (obj.overwrite !== undefined) {
if (typeof obj.overwrite !== "boolean") {
return { error: 'Error: Invalid "overwrite" parameter (must be a boolean).' };
}
overwrite = obj.overwrite;
}
return { path: rawPath, content: rawContent, overwrite };
}
/**
* Factory: create a write_file ToolContract.
*
* `resolveBackend` is the injected seam: each `execute` resolves an
* `ExecBackend` from `ctx.computerId` (undefined → local `node:fs`; a set
* id → a remote SSH backend in a later wave). The tool programs against the
* `ExecBackend` surface, never `node:fs` directly, so it is transport-agnostic.
*
* `workdir` is the fallback base directory when `ctx.cwd` is omitted. It is
* injected so the tool is testable; `execute` prefers `ctx.cwd` when present.
*/
export function createWriteFileTool(deps: {
readonly resolveBackend: ExecBackendResolver;
readonly workdir?: string;
}): ToolContract {
const workdir = deps.workdir !== undefined ? resolve(deps.workdir) : undefined;
return {
name: "write_file",
description:
"Write a whole file to disk. " +
"By default, creates a new file; errors if it already exists. " +
"Set overwrite: true to replace an existing file (errors if the file does not exist). " +
"Parent directories are NOT auto-created — the parent must already exist.",
parameters: {
type: "object",
properties: {
path: {
type: "string",
description: "Path to the file, relative to the working directory.",
},
content: {
type: "string",
description: "The full content to write to the file.",
},
overwrite: {
type: "boolean",
description:
"When false/unset: creates a new file (errors if it already exists). " +
"When true: replaces an existing file (errors if it does not exist).",
default: false,
},
},
required: ["path", "content"],
},
concurrencySafe: false,
async execute(args: unknown, ctx): Promise<ToolResult> {
const validated = validateArgs(args);
if ("error" in validated) {
return { content: validated.error, isError: true };
}
const { path: relPath, content, overwrite } = validated;
const effectiveBase = ctx.cwd ? resolve(ctx.cwd) : workdir;
if (effectiveBase === undefined) {
return {
content:
"Error: No working directory (neither ctx.cwd nor a baked workdir was provided).",
isError: true,
};
}
const resolvedPath = resolve(effectiveBase, relPath);
const backend: ExecBackend = deps.resolveBackend(ctx.computerId);
// Check existence. `backend.exists` never throws — it returns false
// when the path is missing — so the old try/catch around `access`
// collapses to a single boolean read.
const fileExists = await backend.exists(resolvedPath);
// Pure decision.
const decision = decideOverwrite(fileExists, overwrite);
if (typeof decision === "object") {
return { content: decision.error, isError: true };
}
// Verify it's not a directory. `backend.stat` returns a
// `{ isFile, isDirectory }` result; only reached when the file
// exists, so an ENOENT here is a lost race left to propagate
// (same as the prior uncaught `stat` call).
if (fileExists) {
const pathStat = await backend.stat(resolvedPath);
if (pathStat.isDirectory) {
return {
content: `Error: "${relPath}" is a directory, not a file.`,
isError: true,
};
}
}
// Write the file. LocalExecBackend throws node:fs-style errors
// carrying a `.code` (e.g. ENOENT when the parent dir is missing);
// the catch surfaces the message verbatim.
try {
await backend.writeFile(resolvedPath, content);
} catch (err: unknown) {
return {
content: `Error writing file: ${err instanceof Error ? err.message : String(err)}`,
isError: true,
};
}
const action = decision === "create" ? "Created" : "Overwrote";
return { content: `${action} "${relPath}" (${content.length} bytes).` };
},
};
}
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