1 files changed, 105 insertions, 0 deletions
diff --git a/src/gleam_json_ffi.mjs b/src/gleam_json_ffi.mjs
new file mode 100644
index 0000000..e7cdecd
--- /dev/null
+++ b/src/gleam_json_ffi.mjs
@@ -0,0 +1,105 @@
+import { Ok, Error, CustomType } from './gleam.mjs'
+import { bit_string_to_string } from '../../gleam_stdlib/dist/gleam_stdlib.mjs'
+
+export class DecodeError extends CustomType {
+  get __gleam_prelude_variant__() {
+    return "DecodeError";
+  }
+}
+
+export class UnexpectedEndOfInput extends CustomType {
+  static isInstance(err) {
+    return err.message === 'Unexpected end of JSON input'
+  }
+
+  get __gleam_prelude_variant__() {
+    return "UnexpectedEndOfInput"
+  }
+}
+
+export class UnexpectedByte extends CustomType {
+  static regex = /Unexpected token (.) in JSON at position (\d+)/
+
+  static isInstance(err) {
+    return this.regex.test(err)
+  }
+
+  constructor(err) {
+    super()
+    const match = UnexpectedByte.regex.exec(err.message)
+    this.byte = "0x" + match[1].charCodeAt(0).toString(16).toUpperCase()
+    this.position = Number(match[2])
+  }
+
+  get __gleam_prelude_variant__() {
+    return `UnexpectedByte`;
+  }
+}
+
+export class UnexpectedSequence extends CustomType {
+  static isInstance(err) {
+    return false
+  }
+
+  get __gleam_prelude_variant__() {
+    return "UnexpectedSequence";
+  }
+}
+
+export class UnexpectedFormat extends CustomType {
+  static isInstance(err) {
+    return false
+  }
+
+  constructor(decodeErrs) {
+    super()
+    this[0] = decodeErrs
+  }
+
+  get __gleam_prelude_variant__() {
+    return "UnexpectedFormat";
+  }
+}
+
+export function json_to_string(json) {
+  return JSON.stringify(json)
+}
+
+export function object_from(entries) {
+  return Object.fromEntries(entries)
+}
+
+export function array(list) {
+  return list.toArray()
+}
+
+export function do_null() {
+  return null
+}
+
+export function identity(x) {
+  return x
+}
+
+export function decode(bit_string) {
+  const stringResult = bit_string_to_string(bit_string)
+  if (!stringResult.isOk()) return stringResult
+  try {
+    const result = JSON.parse(stringResult[0])
+    return new Ok(result)
+  } catch (err) {
+    return getJsonDecodeError(err)
+  }
+}
+
+function getJsonDecodeError(stdErr) {
+  const ErrClass = [
+    UnexpectedByte,
+    UnexpectedEndOfInput,
+    UnexpectedFormat,
+    UnexpectedSequence,
+  ].find((klass) => klass.isInstance(stdErr))
+
+  if (ErrClass) return new Error(new ErrClass(stdErr))
+  else return new Error()
+}