refactor: share event handling in AST builder

packages/toon/src/decode/decoders.ts

@@ -1,4 +1,4 @@
-import type { ArrayHeaderInfo, DecodeStreamOptions, Depth, JsonStreamEvent, ParsedLine } from '../types'
+import type { ArrayHeaderInfo, DecodeStreamOptions, Depth, JsonPrimitive, JsonStreamEvent, ParsedLine } from '../types'
 import type { StreamingScanState } from './scanner'
 import { COLON, DEFAULT_DELIMITER, LIST_ITEM_MARKER, LIST_ITEM_PREFIX } from '../constants'
 import { findClosingQuote } from '../shared/string-utils'
@@ -320,13 +320,7 @@ function* decodeTabularArraySync(
       assertExpectedCount(values.length, header.fields!.length, 'tabular row values', options)
 
       const primitives = mapRowValuesToPrimitives(values)
-
+      yield* yieldObjectFromFields(header.fields!, primitives)
-      yield { type: 'startObject' }
-      for (let i = 0; i < header.fields!.length; i++) {
-        yield { type: 'key', key: header.fields![i]! }
-        yield { type: 'primitive', value: primitives[i]! }
-      }
-      yield { type: 'endObject' }
 
       rowCount++
     }
@@ -747,13 +741,7 @@ async function* decodeTabularArrayAsync(
       assertExpectedCount(values.length, header.fields!.length, 'tabular row values', options)
 
       const primitives = mapRowValuesToPrimitives(values)
-
+      yield* yieldObjectFromFields(header.fields!, primitives)
-      yield { type: 'startObject' }
-      for (let i = 0; i < header.fields!.length; i++) {
-        yield { type: 'key', key: header.fields![i]! }
-        yield { type: 'primitive', value: primitives[i]! }
-      }
-      yield { type: 'endObject' }
 
       rowCount++
     }
@@ -963,3 +951,19 @@ async function* decodeListItemAsync(
 }
 
 // #endregion
+
+// #region Shared decoder helpers
+
+function* yieldObjectFromFields(
+  fields: string[],
+  primitives: JsonPrimitive[],
+): Generator<JsonStreamEvent> {
+  yield { type: 'startObject' }
+  for (let i = 0; i < fields.length; i++) {
+    yield { type: 'key', key: fields[i]! }
+    yield { type: 'primitive', value: primitives[i]! }
+  }
+  yield { type: 'endObject' }
+}
+
+// #endregion

packages/toon/src/decode/event-builder.ts

@@ -3,22 +3,50 @@ import { QUOTED_KEY_MARKER } from './expand'
 
 // #region Build context types
 
-/**
- * Stack context for building JSON values from events.
- */
 type BuildContext
   = | { type: 'object', obj: JsonObject, currentKey?: string, quotedKeys: Set<string> }
     | { type: 'array', arr: JsonValue[] }
 
+interface BuildState {
+  stack: BuildContext[]
+  root: JsonValue | undefined
+}
+
 // #endregion
 
 // #region Synchronous AST builder
 
 export function buildValueFromEvents(events: Iterable<JsonStreamEvent>): JsonValue {
-  const stack: BuildContext[] = []
+  const state: BuildState = { stack: [], root: undefined }
-  let root: JsonValue | undefined
 
   for (const event of events) {
+    applyEvent(state, event)
+  }
+
+  return finalizeState(state)
+}
+
+// #endregion
+
+// #region Asynchronous AST builder
+
+export async function buildValueFromEventsAsync(events: AsyncIterable<JsonStreamEvent>): Promise<JsonValue> {
+  const state: BuildState = { stack: [], root: undefined }
+
+  for await (const event of events) {
+    applyEvent(state, event)
+  }
+
+  return finalizeState(state)
+}
+
+// #endregion
+
+// #region Shared event handlers
+
+function applyEvent(state: BuildState, event: JsonStreamEvent): void {
+  const { stack } = state
+
   switch (event.type) {
     case 'startObject': {
       const obj: JsonObject = {}
@@ -69,7 +97,7 @@ export function buildValueFromEvents(events: Iterable<JsonStreamEvent>): JsonVal
       }
 
       if (stack.length === 0) {
-          root = context.obj
+        state.root = context.obj
       }
 
       break
@@ -112,7 +140,7 @@ export function buildValueFromEvents(events: Iterable<JsonStreamEvent>): JsonVal
       }
 
       if (stack.length === 0) {
-          root = context.arr
+        state.root = context.arr
       }
 
       break
@@ -141,7 +169,7 @@ export function buildValueFromEvents(events: Iterable<JsonStreamEvent>): JsonVal
     case 'primitive': {
       if (stack.length === 0) {
         // Root primitive
-          root = event.value
+        state.root = event.value
       }
       else {
         const parent = stack[stack.length - 1]!
@@ -160,175 +188,18 @@ export function buildValueFromEvents(events: Iterable<JsonStreamEvent>): JsonVal
       break
     }
   }
-  }
+}
 
-  if (stack.length !== 0) {
+function finalizeState(state: BuildState): JsonValue {
+  if (state.stack.length !== 0) {
     throw new Error('Incomplete event stream: stack not empty at end')
   }
 
-  if (root === undefined) {
+  if (state.root === undefined) {
     throw new Error('No root value built from events')
   }
 
-  return root
+  return state.root
-}
-
-// #endregion
-
-// #region Asynchronous AST builder
-
-export async function buildValueFromEventsAsync(events: AsyncIterable<JsonStreamEvent>): Promise<JsonValue> {
-  const stack: BuildContext[] = []
-  let root: JsonValue | undefined
-
-  for await (const event of events) {
-    switch (event.type) {
-      case 'startObject': {
-        const obj: JsonObject = {}
-        const quotedKeys = new Set<string>()
-
-        if (stack.length === 0) {
-          stack.push({ type: 'object', obj, quotedKeys })
-        }
-        else {
-          const parent = stack[stack.length - 1]!
-          if (parent.type === 'object') {
-            if (parent.currentKey === undefined) {
-              throw new Error('Object startObject event without preceding key')
-            }
-            parent.obj[parent.currentKey] = obj
-            parent.currentKey = undefined
-          }
-          else if (parent.type === 'array') {
-            parent.arr.push(obj)
-          }
-
-          stack.push({ type: 'object', obj, quotedKeys })
-        }
-
-        break
-      }
-
-      case 'endObject': {
-        if (stack.length === 0) {
-          throw new Error('Unexpected endObject event')
-        }
-
-        const context = stack.pop()!
-        if (context.type !== 'object') {
-          throw new Error('Mismatched endObject event')
-        }
-
-        // Attach quoted keys metadata if any keys were quoted
-        if (context.quotedKeys.size > 0) {
-          Object.defineProperty(context.obj, QUOTED_KEY_MARKER, {
-            value: context.quotedKeys,
-            enumerable: false,
-            writable: false,
-            configurable: false,
-          })
-        }
-
-        if (stack.length === 0) {
-          root = context.obj
-        }
-
-        break
-      }
-
-      case 'startArray': {
-        const arr: JsonValue[] = []
-        if (stack.length === 0) {
-          stack.push({ type: 'array', arr })
-        }
-        else {
-          const parent = stack[stack.length - 1]!
-          if (parent.type === 'object') {
-            if (parent.currentKey === undefined) {
-              throw new Error('Array startArray event without preceding key')
-            }
-            parent.obj[parent.currentKey] = arr
-            parent.currentKey = undefined
-          }
-          else if (parent.type === 'array') {
-            parent.arr.push(arr)
-          }
-
-          stack.push({ type: 'array', arr })
-        }
-
-        break
-      }
-
-      case 'endArray': {
-        if (stack.length === 0) {
-          throw new Error('Unexpected endArray event')
-        }
-
-        const context = stack.pop()!
-        if (context.type !== 'array') {
-          throw new Error('Mismatched endArray event')
-        }
-
-        if (stack.length === 0) {
-          root = context.arr
-        }
-
-        break
-      }
-
-      case 'key': {
-        if (stack.length === 0) {
-          throw new Error('Key event outside of object context')
-        }
-
-        const parent = stack[stack.length - 1]!
-        if (parent.type !== 'object') {
-          throw new Error('Key event in non-object context')
-        }
-
-        parent.currentKey = event.key
-
-        // Track quoted keys for path expansion
-        if (event.wasQuoted) {
-          parent.quotedKeys.add(event.key)
-        }
-
-        break
-      }
-
-      case 'primitive': {
-        if (stack.length === 0) {
-          root = event.value
-        }
-        else {
-          const parent = stack[stack.length - 1]!
-          if (parent.type === 'object') {
-            if (parent.currentKey === undefined) {
-              throw new Error('Primitive event without preceding key in object')
-            }
-            parent.obj[parent.currentKey] = event.value
-            parent.currentKey = undefined
-          }
-          else if (parent.type === 'array') {
-            parent.arr.push(event.value)
-          }
-        }
-
-        break
-      }
-    }
-  }
-
-  if (stack.length !== 0) {
-    throw new Error('Incomplete event stream: stack not empty at end')
-  }
-
-  if (root === undefined) {
-    throw new Error('No root value built from events')
-  }
-
-  return root
 }
 
 // #endregion