diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..b043266
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,39 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        node-version: [16.x, 18.x, 19.x]
+        platform:
+        - os: ubuntu-latest
+          shell: bash
+        - os: macos-latest
+          shell: bash
+        - os: windows-latest
+          shell: bash
+        - os: windows-latest
+          shell: powershell
+      fail-fast: false
+
+    runs-on: ${{ matrix.platform.os }}
+    defaults:
+      run:
+        shell: ${{ matrix.platform.shell }}
+
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v1.1.0
+
+      - name: Use Nodejs ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run Tests
+        run: npm test -- -c -t0
diff --git a/.github/workflows/typedoc.yml b/.github/workflows/typedoc.yml
new file mode 100644
index 0000000..e5bc0ef
--- /dev/null
+++ b/.github/workflows/typedoc.yml
@@ -0,0 +1,50 @@
+# Simple workflow for deploying static content to GitHub Pages
+name: Deploy static content to Pages
+
+on:
+  # Runs on pushes targeting the default branch
+  push:
+    branches: ["main"]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow one concurrent deployment
+concurrency:
+  group: "pages"
+  cancel-in-progress: true
+
+jobs:
+  # Single deploy job since we're just deploying
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Use Nodejs ${{ matrix.node-version }}
+        uses: actions/setup-node@v3
+        with:
+          node-version: 18.x
+      - name: Install dependencies
+        run: npm install
+      - name: Generate typedocs
+        run: npm run typedoc
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v3
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v1
+        with:
+          path: './docs'
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v1
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..42cdaf6
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/.tshy*
+/node_modules
+/dist
diff --git a/LICENSE.md b/LICENSE.md
new file mode 100644
index 0000000..881248b
--- /dev/null
+++ b/LICENSE.md
@@ -0,0 +1,63 @@
+All packages under `src/` are licensed according to the terms in
+their respective `LICENSE` or `LICENSE.md` files.
+
+The remainder of this project is licensed under the Blue Oak
+Model License, as follows:
+
+-----
+
+# Blue Oak Model License
+
+Version 1.0.0
+
+## Purpose
+
+This license gives everyone as much permission to work with
+this software as possible, while protecting contributors
+from liability.
+
+## Acceptance
+
+In order to receive this license, you must agree to its
+rules.  The rules of this license are both obligations
+under that agreement and conditions to your license.
+You must not do anything with this software that triggers
+a rule that you cannot or will not follow.
+
+## Copyright
+
+Each contributor licenses you to do everything with this
+software that would otherwise infringe that contributor's
+copyright in it.
+
+## Notices
+
+You must ensure that everyone who gets a copy of
+any part of this software from you, with or without
+changes, also gets the text of this license or a link to
+<https://blueoakcouncil.org/license/1.0.0>.
+
+## Excuse
+
+If anyone notifies you in writing that you have not
+complied with [Notices](#notices), you can keep your
+license by taking all practical steps to comply within 30
+days after the notice.  If you do not do so, your license
+ends immediately.
+
+## Patent
+
+Each contributor licenses you to do everything with this
+software that would otherwise infringe any patent claims
+they can license or become able to license.
+
+## Reliability
+
+No contributor can revoke this license.
+
+## No Liability
+
+***As far as the law allows, this software comes as is,
+without any warranty or condition, and no contributor
+will be liable to anyone for any damages related to this
+software or this license, under any kind of legal claim.***
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..016e149
--- /dev/null
+++ b/README.md
@@ -0,0 +1,235 @@
+# tshy - TypeScript HYbridizer
+
+Hybrid (CommonJS/ESM) TypeScript node package builder.
+
+This tool manages the `exports` in your package.json file, and
+builds your TypeScript program using `tsc` 5.2 in both ESM and
+CJS modes.
+
+## USAGE
+
+Install tshy:
+
+```
+npm i -D tshy
+```
+
+Put this in your package.json to use it with the default configs:
+
+```json
+{
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "prepare": "tshy"
+  }
+}
+```
+
+Put your source code in `./src`.
+
+The built files will end up in `./dist/esm` (ESM) and
+`./dist/commonjs` (CommonJS).
+
+Your `exports` will be edited to reflect the correct module entry
+points.
+
+## Configuration
+
+Mostly, this is opinionated convention, and so there is very
+little to configure.
+
+Source must be in `./src`. Builds are in `./dist/cjs` for
+CommonJS and `./dist/mjs` for ESM.
+
+There is very little configuration for this. The only thing to
+decide is the exported paths. If you have a `./index.ts` file,
+then that will be listed as the main `"."` export by default.
+
+You can set other entry points by putting this in your
+`package.json` file:
+
+```json
+{
+  "tshy": {
+    "exports": {
+      "./foo": "./src/foo.ts",
+      "./bar": "./src/bar.ts",
+      ".": "./src/something-other-than-index.ts",
+      "./package.json": "./package.json"
+    }
+  }
+}
+```
+
+Any exports pointing to files in `./src` will be updated to their
+appropriate build target locations, like:
+
+```json
+{
+  "exports": {
+    "./foo": {
+      "import": {
+        "types": "./dist/mjs/foo.d.ts",
+        "default": "./dist/mjs/foo.js"
+      },
+      "require": {
+        "types": "./dist/cjs/foo.d.ts",
+        "default": "./dist/cjs/foo.js"
+      }
+    }
+  }
+}
+```
+
+Any exports that are not within `./src` will not be built, and
+can be either a string, or a `{ import, require, types }` object:
+
+```json
+{
+  "exports": {
+    "./package.json": "./package.json"
+    "./thing": {
+      "import": "./lib/thing.mjs",
+      "require": "./lib/thing.cjs",
+      "types": "./lib/thing.d.ts"
+    }
+  }
+}
+```
+
+## Selecting Dialects
+
+You can tell tshy which dialect you're building for by setting
+the `dialects` config to an array of strings:
+
+```json
+{
+  "tshy": {
+    "dialects": [
+      "esm",
+      "commonjs"
+    ]
+  }
+}
+```
+
+The default is `["esm", "commonjs"]` (ie, both of them). If you
+set it to just one, then only that dialect will be built and
+exported.
+
+## CommonJS Dialect Polyfills
+
+Sometimes you have to do something in different ways depending on
+the JS dialect in use. For example, maybe you have to use
+`import.meta.url` in ESM, but polyfill with
+`pathToFileURL(__filename)` in CommonJS.
+
+To do this, create a polyfill file with the CommonJS code in
+`<name>-cjs.cts`. (The `cts` extension matters.)
+
+```js
+// src/source-dir-cjs.cts
+//     ^^^^^^^^^^--------- matching name
+//               ^^^^----- "-cts" tag
+//                   ^^^^- ".cts" filename suffix
+// this one has a -cjs.cts suffix, so it will override the
+// module at src/source-dir.ts in the CJS build,
+// and be excluded from the esm build.
+import { pathToFileURL } from 'node:url'
+//@ts-ignore - Have to ignore because TSC thinks this is ESM
+export const sourceDir = pathToFileURL(__dirname)
+```
+
+Then put the "real" ESM code in `<name>.ts` (not `.mts`!)
+
+```js
+// src/source-dir.ts
+// This is the ESM version of the module
+export const sourceDir = new URL('.', import.meta.url)
+```
+
+Then in your code, you can just `import { sourceDir } from
+'./source-dir.js'` and it'll work in both dialects.
+
+## `.cts` and `.mts` files
+
+Files named `*.mts` will be excluded from the CommonJS build.
+
+Files named `*.cts` will be excluded from the ESM build.
+
+If you need to do something one way for CJS and another way for
+ESM, use the "Dialect Switching" trick, with the ESM code living
+in `src/<whatever>.ts` and the CommonJS polyfill living in
+`src/<whatever>-cjs.cts`.
+
+## Atomic Builds
+
+Code is built in `./.tshy-build-tmp` and then copied over only if
+the build succeeds. This makes it work in monorepo cases where
+you may have packages that depend on one another and are all
+being built in parallel (as long as they've been built one time,
+of course).
+
+## Exports Management
+
+The `exports` field in your package.json file will be updated
+based on the `tshy.exports` configuration, as described above.
+
+If you don't provide that config, then the default is:
+
+```json
+{
+  "tshy": {
+    "exports": {
+      ".": "./src/index.ts",
+      "./package.json": "./package.json"
+    }
+  }
+}
+```
+
+## Package `#imports`
+
+Using the `imports` field in `package.json` is not currently
+supported, because this looks at the nearest `package.json` to
+get local imports, and the package.json files placed in
+`dist/{cjs,mjs}` can't have local imports outside of their
+folders.
+
+There's a way it could theoretically be done, but it's a bit
+complicated. A future version may support this.
+
+## TSConfigs
+
+Put whatever configuration you want in `tsconfig.json`, with the
+following caveats:
+
+* `include` - will be overridden based on build, best omitted
+* `exclude` - will be overridden based on build, best omitted
+* compilerOptions:
+    * `outDir` - will be overridden based on build, best omitted
+    * `rootDir` - will be set to `./src` in the build, can only
+      cause annoying errors otherwise.
+    * `target` - will be set to `es2022`
+    * `module` - will be set to `NodeNext`
+    * `moduleResolution` - will be set to `NodeNext`
+
+If you don't have a `tsconfig.json` file, then one will be
+provided for you.
+
+Then the `tsconfig.json` file will be used as the default project
+for code hints in VSCode/nvim, your tests, etc.
+
+## `src/package.json`
+
+As of TypeScript 5.2, the only way to emit JavaScript to ESM or
+CJS, and also import packages using node-style `"exports"`-aware
+module resolution, is to set the `type` field in the
+`package.json` file closest to the TypeScript source code.
+
+During the build, `tshy` will create a file at `src/package.json`
+for this purpose, and then delete it afterwards. If that file
+exists and _wasn't_ put there by `tshy`, then it will be
+destroyed.
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000..0c7a490
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,620 @@
+{
+  "name": "tshy",
+  "version": "0.0.0-0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "tshy",
+      "version": "0.0.0-0",
+      "license": "BlueOak-1.0.0",
+      "dependencies": {
+        "chalk": "^5.3.0",
+        "foreground-child": "^3.1.1",
+        "mkdirp": "^3.0.1",
+        "rimraf": "^5.0.1",
+        "sync-content": "^1.0.2",
+        "typescript": "5.2"
+      },
+      "bin": {
+        "tshy": "dist/esm/index.js"
+      },
+      "devDependencies": {
+        "@types/node": "^20.6.0",
+        "typedoc": "^0.25.1"
+      },
+      "engines": {
+        "node": "16 >=16.17 || 18 >=18.16.0 || >=20.6.1"
+      }
+    },
+    "node_modules/@isaacs/cliui": {
+      "version": "8.0.2",
+      "resolved": "https://registry.npmjs.org/@isaacs/cliui/-/cliui-8.0.2.tgz",
+      "integrity": "sha512-O8jcjabXaleOG9DQ0+ARXWZBTfnP4WNAqzuiJK7ll44AmxGKv/J2M4TPjxjY3znBCfvBXFzucm1twdyFybFqEA==",
+      "dependencies": {
+        "string-width": "^5.1.2",
+        "string-width-cjs": "npm:string-width@^4.2.0",
+        "strip-ansi": "^7.0.1",
+        "strip-ansi-cjs": "npm:strip-ansi@^6.0.1",
+        "wrap-ansi": "^8.1.0",
+        "wrap-ansi-cjs": "npm:wrap-ansi@^7.0.0"
+      },
+      "engines": {
+        "node": ">=12"
+      }
+    },
+    "node_modules/@pkgjs/parseargs": {
+      "version": "0.11.0",
+      "resolved": "https://registry.npmjs.org/@pkgjs/parseargs/-/parseargs-0.11.0.tgz",
+      "integrity": "sha512-+1VkjdD0QBLPodGrJUeqarH8VAIvQODIbwh9XpP5Syisf7YoQgsJKPNFoqqLQlu+VQ/tVSshMR6loPMn8U+dPg==",
+      "optional": true,
+      "engines": {
+        "node": ">=14"
+      }
+    },
+    "node_modules/@types/node": {
+      "version": "20.6.0",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-20.6.0.tgz",
+      "integrity": "sha512-najjVq5KN2vsH2U/xyh2opaSEz6cZMR2SetLIlxlj08nOcmPOemJmUK2o4kUzfLqfrWE0PIrNeE16XhYDd3nqg==",
+      "dev": true
+    },
+    "node_modules/ansi-regex": {
+      "version": "6.0.1",
+      "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-6.0.1.tgz",
+      "integrity": "sha512-n5M855fKb2SsfMIiFFoVrABHJC8QtHwVx+mHWP3QcEqBHYienj5dHSgjbxtC0WEZXYt4wcD6zrQElDPhFuZgfA==",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/ansi-regex?sponsor=1"
+      }
+    },
+    "node_modules/ansi-sequence-parser": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/ansi-sequence-parser/-/ansi-sequence-parser-1.1.1.tgz",
+      "integrity": "sha512-vJXt3yiaUL4UU546s3rPXlsry/RnM730G1+HkpKE012AN0sx1eOrxSu95oKDIonskeLTijMgqWZ3uDEe3NFvyg==",
+      "dev": true
+    },
+    "node_modules/ansi-styles": {
+      "version": "6.2.1",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-6.2.1.tgz",
+      "integrity": "sha512-bN798gFfQX+viw3R7yrGWRqnrN2oRkEkUjjl4JNn4E8GxxbjtG3FbrEIIY3l8/hrwUwIeCZvi4QuOTP4MErVug==",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/ansi-styles?sponsor=1"
+      }
+    },
+    "node_modules/balanced-match": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.2.tgz",
+      "integrity": "sha512-3oSeUO0TMV67hN1AmbXsK4yaqU7tjiHlbxRDZOpH0KW9+CeX4bRAaX0Anxt0tx2MrpRpWwQaPwIlISEJhYU5Pw=="
+    },
+    "node_modules/brace-expansion": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-2.0.1.tgz",
+      "integrity": "sha512-XnAIvQ8eM+kC6aULx6wuQiwVsnzsi9d3WxzV3FpWTGA19F621kwdbsAcFKXgKUHZWsy+mY6iL1sHTxWEFCytDA==",
+      "dependencies": {
+        "balanced-match": "^1.0.0"
+      }
+    },
+    "node_modules/chalk": {
+      "version": "5.3.0",
+      "resolved": "https://registry.npmjs.org/chalk/-/chalk-5.3.0.tgz",
+      "integrity": "sha512-dLitG79d+GV1Nb/VYcCDFivJeK1hiukt9QjRNVOsUtTy1rR1YJsmpGGTZ3qJos+uw7WmWF4wUwBd9jxjocFC2w==",
+      "engines": {
+        "node": "^12.17.0 || ^14.13 || >=16.0.0"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/chalk?sponsor=1"
+      }
+    },
+    "node_modules/color-convert": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-2.0.1.tgz",
+      "integrity": "sha512-RRECPsj7iu/xb5oKYcsFHSppFNnsj/52OVTRKb4zP5onXwVF3zVmmToNcOfGC+CRDpfK/U584fMg38ZHCaElKQ==",
+      "dependencies": {
+        "color-name": "~1.1.4"
+      },
+      "engines": {
+        "node": ">=7.0.0"
+      }
+    },
+    "node_modules/color-name": {
+      "version": "1.1.4",
+      "resolved": "https://registry.npmjs.org/color-name/-/color-name-1.1.4.tgz",
+      "integrity": "sha512-dOy+3AuW3a2wNbZHIuMZpTcgjGuLU/uBL/ubcZF9OXbDo8ff4O8yVp5Bf0efS8uEoYo5q4Fx7dY9OgQGXgAsQA=="
+    },
+    "node_modules/cross-spawn": {
+      "version": "7.0.3",
+      "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.3.tgz",
+      "integrity": "sha512-iRDPJKUPVEND7dHPO8rkbOnPpyDygcDFtWjpeWNCgy8WP2rXcxXL8TskReQl6OrB2G7+UJrags1q15Fudc7G6w==",
+      "dependencies": {
+        "path-key": "^3.1.0",
+        "shebang-command": "^2.0.0",
+        "which": "^2.0.1"
+      },
+      "engines": {
+        "node": ">= 8"
+      }
+    },
+    "node_modules/eastasianwidth": {
+      "version": "0.2.0",
+      "resolved": "https://registry.npmjs.org/eastasianwidth/-/eastasianwidth-0.2.0.tgz",
+      "integrity": "sha512-I88TYZWc9XiYHRQ4/3c5rjjfgkjhLyW2luGIheGERbNQ6OY7yTybanSpDXZa8y7VUP9YmDcYa+eyq4ca7iLqWA=="
+    },
+    "node_modules/emoji-regex": {
+      "version": "9.2.2",
+      "resolved": "https://registry.npmjs.org/emoji-regex/-/emoji-regex-9.2.2.tgz",
+      "integrity": "sha512-L18DaJsXSUk2+42pv8mLs5jJT2hqFkFE4j21wOmgbUqsZ2hL72NsUU785g9RXgo3s0ZNgVl42TiHp3ZtOv/Vyg=="
+    },
+    "node_modules/foreground-child": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/foreground-child/-/foreground-child-3.1.1.tgz",
+      "integrity": "sha512-TMKDUnIte6bfb5nWv7V/caI169OHgvwjb7V4WkeUvbQQdjr5rWKqHFiKWb/fcOwB+CzBT+qbWjvj+DVwRskpIg==",
+      "dependencies": {
+        "cross-spawn": "^7.0.0",
+        "signal-exit": "^4.0.1"
+      },
+      "engines": {
+        "node": ">=14"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/isaacs"
+      }
+    },
+    "node_modules/glob": {
+      "version": "10.3.4",
+      "resolved": "https://registry.npmjs.org/glob/-/glob-10.3.4.tgz",
+      "integrity": "sha512-6LFElP3A+i/Q8XQKEvZjkEWEOTgAIALR9AO2rwT8bgPhDd1anmqDJDZ6lLddI4ehxxxR1S5RIqKe1uapMQfYaQ==",
+      "dependencies": {
+        "foreground-child": "^3.1.0",
+        "jackspeak": "^2.0.3",
+        "minimatch": "^9.0.1",
+        "minipass": "^5.0.0 || ^6.0.2 || ^7.0.0",
+        "path-scurry": "^1.10.1"
+      },
+      "bin": {
+        "glob": "dist/cjs/src/bin.js"
+      },
+      "engines": {
+        "node": ">=16 || 14 >=14.17"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/isaacs"
+      }
+    },
+    "node_modules/is-fullwidth-code-point": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/is-fullwidth-code-point/-/is-fullwidth-code-point-3.0.0.tgz",
+      "integrity": "sha512-zymm5+u+sCsSWyD9qNaejV3DFvhCKclKdizYaJUuHA83RLjb7nSuGnddCHGv0hk+KY7BMAlsWeK4Ueg6EV6XQg==",
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/isexe": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/isexe/-/isexe-2.0.0.tgz",
+      "integrity": "sha512-RHxMLp9lnKHGHRng9QFhRCMbYAcVpn69smSGcq3f36xjgVVWThj4qqLbTLlq7Ssj8B+fIQ1EuCEGI2lKsyQeIw=="
+    },
+    "node_modules/jackspeak": {
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diff --git a/package.json b/package.json
new file mode 100644
index 0000000..7486897
--- /dev/null
+++ b/package.json
@@ -0,0 +1,71 @@
+{
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+  "type": "module",
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+  "scripts": {
+    "postversion": "npm publish",
+    "prepublishOnly": "git push origin --follow-tags",
+    "prepare": "tsc -p tsconfig/esm.json && bash scripts/fixup.sh",
+    "pretest": "npm run prepare",
+    "presnap": "npm run prepare",
+    "format": "prettier --write . --loglevel warn --ignore-path ../../.prettierignore --cache",
+    "typedoc": "typedoc"
+  },
+  "engines": {
+    "node": "16 >=16.17 || 18 >=18.16.0 || >=20.6.1"
+  },
+  "repository": "https://github.com/isaacs/tshy",
+  "keywords": [
+    "typescript",
+    "tsc",
+    "hybrid",
+    "esm",
+    "commonjs",
+    "build"
+  ],
+  "devDependencies": {
+    "@types/node": "^20.6.0",
+    "typedoc": "^0.25.1"
+  },
+  "prettier": {
+    "semi": false,
+    "printWidth": 70,
+    "tabWidth": 2,
+    "useTabs": false,
+    "singleQuote": true,
+    "jsxSingleQuote": false,
+    "bracketSameLine": true,
+    "arrowParens": "avoid",
+    "endOfLine": "lf"
+  },
+  "tshy": {
+    "dialects": [
+      "esm"
+    ],
+    "exports": {
+      "./package.json": "./package.json",
+      ".": "./src/index.ts"
+    }
+  },
+  "exports": {
+    "./package.json": "./package.json",
+    ".": {
+      "import": {
+        "types": "./dist/esm/index.d.ts",
+        "default": "./dist/esm/index.js"
+      }
+    }
+  }
+}
diff --git a/scripts/fixup.sh b/scripts/fixup.sh
new file mode 100644
index 0000000..58590f3
--- /dev/null
+++ b/scripts/fixup.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+chmod 0755 .tshy-build-tmp/esm/index.js
+sync-content .tshy-build-tmp dist
+rm -rf .tshy-build-tmp
diff --git a/src/bins.ts b/src/bins.ts
new file mode 100644
index 0000000..202c6d3
--- /dev/null
+++ b/src/bins.ts
@@ -0,0 +1,15 @@
+// chmod bins after build
+import { chmodSync } from 'fs'
+import { resolve } from 'path'
+import pkg from './package.js'
+export default () => {
+  const { bin } = pkg
+  if (!bin) return
+  if (typeof bin === 'string') {
+    chmodSync(resolve(bin), 0o755)
+  } else {
+    for (const v of Object.values(bin)) {
+      chmodSync(resolve(v), 0o755)
+    }
+  }
+}
diff --git a/src/build.ts b/src/build.ts
new file mode 100644
index 0000000..e175a97
--- /dev/null
+++ b/src/build.ts
@@ -0,0 +1,64 @@
+import chalk from 'chalk'
+import { spawnSync, SpawnSyncReturns } from 'node:child_process'
+import { renameSync } from 'node:fs'
+import { relative, resolve } from 'node:path/posix'
+import { rimrafSync } from 'rimraf'
+import { syncContentSync } from 'sync-content'
+import bins from './bins.js'
+import dialects from './dialects.js'
+import { fail } from './fail.js'
+import polyfills from './polyfills.js'
+import setFolderDialect from './set-folder-dialect.js'
+import './tsconfig.js'
+import writePackage from './write-package.js'
+
+const buildFail = (res: SpawnSyncReturns<Buffer>) => {
+  setFolderDialect('src')
+  fail('build failed')
+  console.error(res)
+  process.exit(1)
+}
+
+rimrafSync('.tshy-build-tmp')
+
+if (dialects.includes('esm')) {
+  setFolderDialect('src', 'esm')
+  const res = spawnSync('tsc -p .tshy/esm.json', {
+    shell: true,
+    stdio: 'inherit',
+  })
+  setFolderDialect('src')
+  if (res.status || res.signal) buildFail(res)
+  setFolderDialect('.tshy-build-tmp/esm', 'esm')
+  console.error(chalk.cyan.bold('built esm'))
+}
+
+if (dialects.includes('commonjs')) {
+  setFolderDialect('src', 'commonjs')
+  const res = spawnSync('tsc -p .tshy/commonjs.json', {
+    shell: true,
+    stdio: 'inherit',
+  })
+  setFolderDialect('src')
+  if (res.status || res.signal) buildFail(res)
+  setFolderDialect('.tshy-build-tmp/commonjs', 'commonjs')
+  console.error(chalk.cyan.bold('built commonjs'), res)
+  // apply polyfills
+  for (const [f, t] of polyfills.entries()) {
+    const stemFrom = resolve(
+      '.tshy-build-tmp/commonjs',
+      relative(resolve('src'), resolve(f))
+    ).replace(/\.cts$/, '')
+    const stemTo = resolve(
+      '.tshy-build-tmp/commonjs',
+      relative(resolve('src'), resolve(t))
+    ).replace(/\.ts$/, '')
+    renameSync(`${stemFrom}.cjs`, `${stemTo}.js`)
+    renameSync(`${stemFrom}.d.cts`, `${stemTo}.d.ts`)
+  }
+}
+
+syncContentSync('.tshy-build-tmp', 'dist')
+rimrafSync('.tshy-build-tmp')
+bins()
+writePackage()
diff --git a/src/config.ts b/src/config.ts
new file mode 100644
index 0000000..414c528
--- /dev/null
+++ b/src/config.ts
@@ -0,0 +1,117 @@
+// get the config and package and stuff
+
+import { fail } from './fail.js'
+import { Dialect, Package, TshyConfig, TshyExport } from './types.js'
+
+const validConfig = (e: any): e is TshyConfig =>
+  !!e &&
+  typeof e === 'object' &&
+  (e.exports === undefined || validExports(e['exports'])) &&
+  (e.dialects === undefined || validDialects(e['dialects']))
+
+const isDialect = (d: any): d is Dialect =>
+  d === 'commonjs' || d === 'esm'
+
+const validDialects = (
+  d: any
+): d is Exclude<TshyConfig['dialects'], undefined> =>
+  !!d && Array.isArray(d) && !d.some(d => !isDialect(d))
+
+const validExports = (
+  e: any
+): e is Exclude<TshyConfig['exports'], undefined> => {
+  if (!e) return false
+  if (typeof e !== 'object') return false
+  for (const [sub, exp] of Object.entries(e)) {
+    if (sub !== '.' && !sub.startsWith('./')) {
+      fail(
+        `tshy.exports key must be "." or start with "./", got: ${sub}`
+      )
+      process.exit(1)
+    }
+    if (typeof exp === 'string') {
+      e[sub] = addDot(exp)
+      continue
+    }
+    if (typeof exp !== 'object' || !exp || Array.isArray(exp)) {
+      fail(
+        `tshy.exports ${sub} value must be string or import/require object, ` +
+          `got: ${JSON.stringify(exp)}`
+      )
+      process.exit(1)
+    }
+    const { import: i, require: r } = exp as Exclude<
+      TshyExport,
+      string
+    >
+    if (!i && !e) {
+      fail(
+        `tshy.exports ${sub} needs require or import, ` +
+          `got: ${JSON.stringify(exp)}`
+      )
+      process.exit(1)
+    }
+    if (
+      (i !== undefined && typeof i !== 'string') ||
+      (r !== undefined && typeof r !== 'string')
+    ) {
+      fail(
+        `tshy.exports ${sub} import/require must be strings, ` +
+          `got: ${JSON.stringify(exp)}`
+      )
+      process.exit(1)
+    }
+    if (
+      (i !== undefined && join(i).startsWith('src/')) ||
+      (r !== undefined && join(r).startsWith('src/'))
+    ) {
+      fail(
+        `tshy.exports ${sub} in src/ must be string paths, ` +
+          `got: ${JSON.stringify(exp)}`
+      )
+      process.exit(1)
+    }
+    e[sub] = {}
+    if (e[sub].types) e[sub].types = addDot(e[sub].types)
+    if (e[sub].import) e[sub].types = addDot(e[sub].import)
+    if (e[sub].require) e[sub].types = addDot(e[sub].require)
+  }
+  if (e.dialects) {
+    if (!validDialects(e.dialects)) {
+      fail(
+        `tshy.dialects must be array containing 'esm' and/or 'commonjs', ` +
+          `got: ${JSON.stringify(e.dialects)}`
+      )
+    }
+  }
+  return true
+}
+
+const addDot = (s: string) => `./${join(s)}`
+
+const getConfig = (
+  pkg: Package,
+  sources: Set<string>
+): TshyConfig => {
+  const tshy: TshyConfig = validConfig(pkg.tshy) ? pkg.tshy : {}
+  if (tshy.exports) return tshy
+  const e: Exclude<TshyConfig['exports'], undefined> = {
+    './package.json': './package.json',
+  }
+  for (const i of sources) {
+    if (/^\.\/src\/index\.[^\.]+$/.test(i)) {
+      e['.'] = i
+      break
+    }
+  }
+  pkg.tshy = tshy
+  tshy.exports = e
+  return tshy
+}
+
+import { join } from 'path/posix'
+import pkg from './package.js'
+import sources from './sources.js'
+
+const config: TshyConfig = getConfig(pkg, sources)
+export default config
diff --git a/src/dialects.ts b/src/dialects.ts
new file mode 100644
index 0000000..0b2beb4
--- /dev/null
+++ b/src/dialects.ts
@@ -0,0 +1,2 @@
+import config from './config.js'
+export default config.dialects || ['esm', 'commonjs']
diff --git a/src/exports.ts b/src/exports.ts
new file mode 100644
index 0000000..d566d64
--- /dev/null
+++ b/src/exports.ts
@@ -0,0 +1,105 @@
+import { relative, resolve } from 'node:path/posix'
+import config from './config.js'
+import dialects from './dialects.js'
+import polyfills from './polyfills.js'
+import { Export, TshyConfig, TshyExport } from './types.js'
+
+const getImpTarget = (
+  s: string | TshyExport | undefined
+): string | undefined => {
+  if (s === undefined) return undefined
+  if (typeof s === 'string') {
+    const imp = s.endsWith('.cts') ? undefined : s
+    return !imp || !imp.startsWith('./src/')
+      ? imp
+      : dialects.includes('esm')
+      ? `./dist/esm/${relative(
+          resolve('./src'),
+          resolve(imp)
+        ).replace(/\.(m?)tsx?$/, '.$1js')}`
+      : undefined
+  }
+  if (s && typeof s === 'object') {
+    return getImpTarget(s.import)
+  }
+}
+
+const getReqTarget = (
+  s: string | TshyExport | undefined,
+  polyfills: Map<string, string>
+): string | undefined => {
+  if (s === undefined) return undefined
+  if (typeof s === 'string') {
+    const req = s.endsWith('.mts') ? undefined : s
+    return !req || !req.startsWith('./src/')
+      ? req
+      : dialects.includes('commonjs')
+      ? `./dist/commonjs/${relative(
+          resolve('./src'),
+          resolve(polyfills.get(req) || req)
+        ).replace(/\.(m?)tsx?$/, '.$1js')}`
+      : undefined
+  }
+  if (s && typeof s === 'object') {
+    return getReqTarget(s.require, polyfills)
+  }
+}
+
+const getExports = (
+  c: TshyConfig,
+  polyfills: Map<string, string>
+): Record<string, Export> => {
+  if (!c.exports) {
+    fail('no exports on tshy config (is there code in ./src?)')
+    process.exit(1)
+  }
+  const e: Record<string, Export> = {}
+  for (const [sub, s] of Object.entries(c.exports)) {
+    const impTarget = getImpTarget(s)
+    const reqTarget = getReqTarget(s, polyfills)
+
+    // only possible for exports outside of ./src
+    const types = typeof s !== 'string' && s.types
+
+    if (typeof s !== 'string' || !s.startsWith('./src/')) {
+      if (impTarget === reqTarget) {
+        if (impTarget === undefined) continue
+        if (types) {
+          e[sub] = {
+            import: impTarget,
+            require: reqTarget,
+            types,
+          }
+        } else if (impTarget !== undefined) e[sub] = impTarget
+        continue
+      }
+      if (types) {
+        e[sub] = {
+          types,
+          import: impTarget,
+          require: reqTarget,
+        }
+        continue
+      }
+    }
+
+    const exp: Export = (e[sub] = {})
+    if (impTarget) {
+      exp.import = {
+        types: impTarget.replace(/\.(m?)js$/, '.d.$1ts'),
+        default: impTarget,
+      }
+    }
+    if (reqTarget) {
+      exp.require = {
+        types: reqTarget.replace(/\.(c?)js$/, '.d.$1ts'),
+        default: reqTarget,
+      }
+    }
+  }
+  return e
+}
+
+import { fail } from './fail.js'
+import pkg from './package.js'
+export default pkg.exports = getExports(config, polyfills)
diff --git a/src/fail.ts b/src/fail.ts
new file mode 100644
index 0000000..174d350
--- /dev/null
+++ b/src/fail.ts
@@ -0,0 +1,5 @@
+import chalk from 'chalk'
+export const fail = (message: string, er?: Error) => {
+  console.error(chalk.red.bold(message))
+  if (er) console.error(er.message)
+}
diff --git a/src/index.ts b/src/index.ts
new file mode 100644
index 0000000..c6c4cf1
--- /dev/null
+++ b/src/index.ts
@@ -0,0 +1,17 @@
+#!/usr/bin/env node
+
+import chalk from 'chalk'
+
+import './exports.js'
+import pkg from './package.js'
+
+const { exports: exp, tshy } = pkg
+
+console.error(chalk.yellow.bold('building'))
+console.error(chalk.cyan.dim('tshy config'), tshy)
+console.error(chalk.cyan.dim('exports'), exp)
+
+// have our config, time to build
+await import('./build.js')
+
+console.log(chalk.bold.green('success!'))
diff --git a/src/package.ts b/src/package.ts
new file mode 100644
index 0000000..3156d5f
--- /dev/null
+++ b/src/package.ts
@@ -0,0 +1,18 @@
+// get the package.json data for the cwd
+
+import { readFileSync } from 'fs'
+import { fail } from './fail.js'
+import { Package } from './types.js'
+
+const readPkg = (): Package => {
+  try {
+    return JSON.parse(readFileSync('package.json', 'utf8'))
+  } catch (er) {
+    fail('failed to read package.json', er as Error)
+    process.exit(1)
+  }
+}
+
+const pkg = readPkg()
+pkg.type = 'module'
+export default pkg
diff --git a/src/polyfills.ts b/src/polyfills.ts
new file mode 100644
index 0000000..97d37b2
--- /dev/null
+++ b/src/polyfills.ts
@@ -0,0 +1,21 @@
+// the modules like -cjs.cts that override a module at .ts
+import sources from './sources.js'
+import chalk from 'chalk'
+
+const getPolyfills = (sources: Set<string>): Map<string, string> =>
+  new Map(
+    [...sources]
+      .filter(
+        f =>
+          f.endsWith('-cjs.cts') &&
+          sources.has(f.replace(/-cjs\.cts$/, '.ts'))
+      )
+      .map(f => [f, f.replace(/-cjs\.cts$/, '.ts')])
+  )
+
+const polyfills = getPolyfills(sources)
+if (polyfills.size) {
+  console.error(chalk.cyan.dim('polyfills detected'), polyfills)
+}
+
+export default getPolyfills(sources)
diff --git a/src/set-folder-dialect.ts b/src/set-folder-dialect.ts
new file mode 100644
index 0000000..74fa3dc
--- /dev/null
+++ b/src/set-folder-dialect.ts
@@ -0,0 +1,16 @@
+import { writeFileSync } from 'fs'
+import { rimrafSync } from 'rimraf'
+import { Dialect } from './types.js'
+
+const writeDialectPJ = (f: string, mode?: Dialect) =>
+  mode
+    ? writeFileSync(
+        f,
+        JSON.stringify({
+          type: mode === 'commonjs' ? 'commonjs' : 'module',
+        })
+      )
+    : rimrafSync(f)
+
+export default (where: string, mode?: Dialect) =>
+  writeDialectPJ(`${where}/package.json`, mode)
diff --git a/src/sources.ts b/src/sources.ts
new file mode 100644
index 0000000..d1d7dfa
--- /dev/null
+++ b/src/sources.ts
@@ -0,0 +1,20 @@
+// get the list of sources in ./src
+
+import { readdirSync } from 'fs'
+import { join } from 'path/posix'
+
+const getSources = (dir = 'src'): string[] => {
+  const sources: string[] = []
+  const entries = readdirSync(dir, { withFileTypes: true })
+  for (const e of entries) {
+    const j = `./${join(dir, e.name)}`
+    if (e.isFile()) sources.push(j)
+    else if (e.isDirectory()) {
+      sources.push(...getSources(j))
+    }
+  }
+  return sources
+}
+
+const sources = new Set(getSources())
+export default sources
diff --git a/src/tsconfig.ts b/src/tsconfig.ts
new file mode 100644
index 0000000..f2caed5
--- /dev/null
+++ b/src/tsconfig.ts
@@ -0,0 +1,65 @@
+import chalk from 'chalk'
+import { existsSync, writeFileSync } from 'fs'
+import { mkdirpSync } from 'mkdirp'
+
+// the commonjs build needs to exclude anything that will be polyfilled
+import polyfills from './polyfills.js'
+
+const recommended: Record<string, any> = {
+  compilerOptions: {
+    jsx: 'react',
+    declaration: true,
+    declarationMap: true,
+    inlineSources: true,
+    esModuleInterop: true,
+    forceConsistentCasingInFileNames: true,
+    moduleResolution: 'nodenext',
+    resolveJsonModule: true,
+    skipLibCheck: true,
+    sourceMap: true,
+    strict: true,
+    target: 'es2022',
+    module: 'nodenext',
+  },
+}
+
+const build: Record<string, any> = {
+  extends: '../tsconfig.json',
+  compilerOptions: {
+    rootDir: '../src',
+    target: 'es2022',
+    module: 'nodenext',
+    moduleResolution: 'nodenext',
+  },
+}
+
+const commonjs: Record<string, any> = {
+  extends: './build.json',
+  include: ['../src/**/*.ts', '../src/**/*.cts', '../src/**/*.tsx'],
+  exclude: [...polyfills.values()].map(f => `.${f}`),
+  compilerOptions: {
+    outDir: '../.tshy-build-tmp/commonjs',
+  },
+}
+
+const esm: Record<string, any> = {
+  extends: './build.json',
+  include: ['../src/**/*.ts', '../src/**/*.cts', '../src/**/*.tsx'],
+  compilerOptions: {
+    outDir: '../.tshy-build-tmp/esm',
+  },
+}
+
+mkdirpSync('.tshy')
+const writeConfig = (name: string, data: Record<string, any>) =>
+  writeFileSync(
+    `.tshy/${name}.json`,
+    JSON.stringify(data, null, 2) + '\n'
+  )
+
+console.error(chalk.cyan.dim('writing tsconfig files...'))
+if (!existsSync('tsconfig.json'))
+  writeConfig('../tsconfig', recommended)
+writeConfig('build', build)
+writeConfig('commonjs', commonjs)
+writeConfig('esm', esm)
diff --git a/src/types.ts b/src/types.ts
new file mode 100644
index 0000000..9e398e1
--- /dev/null
+++ b/src/types.ts
@@ -0,0 +1,43 @@
+export type TshyConfig = {
+  exports?: Record<string, TshyExport>
+  dialects?: Dialect[]
+}
+
+export type Dialect = 'commonjs' | 'esm'
+
+export type TshyExport =
+  | string
+  | ({ types?: string; import?: string; require?: string } & (
+      | { import: string }
+      | { require: string }
+    ))
+
+export type Package = {
+  name: string
+  version: string
+  type?: 'module'
+  bin?: string | Record<string, string>
+  exports: Record<string, Export>
+  tshy?: TshyConfig
+  [k: string]: any
+}
+
+// VERY limited subset of the datatypes "exports" can be
+// but we're only writing our flavor, so it's fine.
+export type Export =
+  | string
+  | { import?: string; require?: string; types?: string }
+  | {
+      import?:
+        | string
+        | {
+            types: string
+            default: string
+          }
+      require?:
+        | string
+        | {
+            types: string
+            default: string
+          }
+    }
diff --git a/src/write-package.ts b/src/write-package.ts
new file mode 100644
index 0000000..192e13b
--- /dev/null
+++ b/src/write-package.ts
@@ -0,0 +1,6 @@
+import { writeFileSync } from 'fs'
+import pkg from './package.js'
+
+export default () => {
+  writeFileSync('package.json', JSON.stringify(pkg, null, 2) + '\n')
+}
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..42776f8
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,17 @@
+{
+  "compilerOptions": {
+    "jsx": "react",
+    "declaration": true,
+    "declarationMap": true,
+    "inlineSources": true,
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "moduleResolution": "nodenext",
+    "resolveJsonModule": true,
+    "skipLibCheck": true,
+    "sourceMap": true,
+    "strict": true,
+    "target": "es2022",
+    "module": "nodenext"
+  }
+}
diff --git a/tsconfig/esm.json b/tsconfig/esm.json
new file mode 100644
index 0000000..3b94cde
--- /dev/null
+++ b/tsconfig/esm.json
@@ -0,0 +1,7 @@
+{
+  "extends": "../tsconfig.json",
+  "include": ["../src/**/*.ts"],
+  "compilerOptions": {
+    "outDir": "../.tshy-build-tmp/esm"
+  }
+}
diff --git a/typedoc.json b/typedoc.json
new file mode 100644
index 0000000..d56e2a4
--- /dev/null
+++ b/typedoc.json
@@ -0,0 +1,7 @@
+{
+  "tsconfig": "./tsconfig/esm.json",
+  "entryPoints": ["./src/**/*.+(ts|tsx|mts|cts)"],
+  "navigationLinks": {
+    "isaacs projects": "https://isaacs.github.io/"
+  }
+}