5 files changed, 132 insertions, 0 deletions
diff --git a/extension/src/languages/index.d.ts b/extension/src/languages/index.d.ts
new file mode 100644
index 00000000..be7ddfbc
--- /dev/null
+++ b/extension/src/languages/index.d.ts
@@ -0,0 +1,13 @@
+export interface LanguageLibrary {
+  language: string;
+  fileExtensions: string[];
+  parseFirstStacktrace: (stdout: string) => string | undefined;
+  lineIsFunctionDef: (line: string) => boolean;
+  parseFunctionDefForName: (line: string) => string;
+  lineIsComment: (line: string) => boolean;
+  writeImport: (
+    sourcePath: string,
+    pathToImport: string,
+    namesToImport?: string[] | undefined
+  ) => string;
+}
diff --git a/extension/src/languages/index.ts b/extension/src/languages/index.ts
new file mode 100644
index 00000000..31d73a0b
--- /dev/null
+++ b/extension/src/languages/index.ts
@@ -0,0 +1,19 @@
+import pythonLanguageLibrary from "./python";
+import javascriptLanguageLibrary from "./javascript";
+import { LanguageLibrary } from "./index.d";
+
+export const languageLibraries: LanguageLibrary[] = [
+  pythonLanguageLibrary,
+  javascriptLanguageLibrary,
+];
+
+export function getLanguageLibrary(filepath: string): LanguageLibrary {
+  for (let languageLibrary of languageLibraries) {
+    for (let fileExtension of languageLibrary.fileExtensions) {
+      if (filepath.endsWith(fileExtension)) {
+        return languageLibrary;
+      }
+    }
+  }
+  throw new Error(`No language library found for file ${filepath}`);
+}
diff --git a/extension/src/languages/javascript/index.ts b/extension/src/languages/javascript/index.ts
new file mode 100644
index 00000000..1c21a2fc
--- /dev/null
+++ b/extension/src/languages/javascript/index.ts
@@ -0,0 +1,16 @@
+import { LanguageLibrary } from "../index.d";
+import { notImplemented } from "../notImplemented";
+
+const NI = (propertyName: string) => notImplemented(propertyName, "javascript");
+
+const javascriptLangaugeLibrary: LanguageLibrary = {
+  language: "javascript",
+  fileExtensions: [".js", ".jsx", ".ts", ".tsx"],
+  parseFirstStacktrace: NI("parseFirstStacktrace"),
+  lineIsFunctionDef: NI("lineIsFunctionDef"),
+  parseFunctionDefForName: NI("parseFunctionDefForName"),
+  lineIsComment: NI("lineIsComment"),
+  writeImport: NI("writeImport"),
+};
+
+export default javascriptLangaugeLibrary;
diff --git a/extension/src/languages/notImplemented.ts b/extension/src/languages/notImplemented.ts
new file mode 100644
index 00000000..bbba2382
--- /dev/null
+++ b/extension/src/languages/notImplemented.ts
@@ -0,0 +1,10 @@
+export function notImplemented(
+  propertyName: string,
+  langauge: string
+): (...args: any[]) => never {
+  return (...args: any[]) => {
+    throw new Error(
+      `Property ${propertyName} not implemented for language ${langauge}.`
+    );
+  };
+}
diff --git a/extension/src/languages/python/index.ts b/extension/src/languages/python/index.ts
new file mode 100644
index 00000000..50282b45
--- /dev/null
+++ b/extension/src/languages/python/index.ts
@@ -0,0 +1,74 @@
+import path = require("path");
+import { LanguageLibrary } from "../index.d";
+
+const tracebackStart = "Traceback (most recent call last):";
+const tracebackEnd = (buf: string): string | undefined => {
+  let lines = buf
+    .split("\n")
+    .filter((line: string) => line.trim() !== "~~^~~")
+    .filter((line: string) => line.trim() !== "");
+  for (let i = 0; i < lines.length; i++) {
+    if (
+      lines[i].startsWith("  File") &&
+      i + 2 < lines.length &&
+      lines[i + 2][0] !== " "
+    ) {
+      return lines.slice(0, i + 3).join("\n");
+    }
+  }
+  return undefined;
+};
+
+function parseFirstStacktrace(stdout: string): string | undefined {
+  let startIdx = stdout.indexOf(tracebackStart);
+  if (startIdx < 0) return undefined;
+  stdout = stdout.substring(startIdx);
+  return tracebackEnd(stdout);
+}
+
+function lineIsFunctionDef(line: string): boolean {
+  return line.startsWith("def ");
+}
+
+function parseFunctionDefForName(line: string): string {
+  return line.split("def ")[1].split("(")[0];
+}
+
+function lineIsComment(line: string): boolean {
+  return line.trim().startsWith("#");
+}
+
+function writeImport(
+  sourcePath: string,
+  pathToImport: string,
+  namesToImport: string[] | undefined = undefined
+): string {
+  let segs = path.relative(sourcePath, pathToImport).split(path.sep);
+  let importFrom = "";
+  for (let seg of segs) {
+    if (seg === "..") {
+      importFrom = "." + importFrom;
+    } else {
+      if (!importFrom.endsWith(".")) {
+        importFrom += ".";
+      }
+      importFrom += seg.split(".").slice(0, -1).join(".");
+    }
+  }
+
+  return `from ${importFrom} import ${
+    namesToImport ? namesToImport.join(", ") : "*"
+  }`;
+}
+
+const pythonLangaugeLibrary: LanguageLibrary = {
+  language: "python",
+  fileExtensions: [".py"],
+  parseFirstStacktrace,
+  lineIsFunctionDef,
+  parseFunctionDefForName,
+  lineIsComment,
+  writeImport,
+};
+
+export default pythonLangaugeLibrary;