Json path

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
class val JsonPath
  """
  Compiled JSONPath query for extracting values from JSON documents.

  JSONPath queries navigate JSON structures using string path expressions
  (RFC 9535). Compile a path with `JsonPathParser.parse()`, then apply
  it to any number of documents with `query()`:

  ```pony
  match JsonPathParser.parse("$.store.book[*].author")
  | let path: JsonPath =>
    let authors = path.query(doc)
  | let err: JsonPathParseError =>
    env.err.print(err.string())
  end
  ```

  Evaluation follows RFC 9535 semantics: missing keys, out-of-bounds
  indices, and type mismatches produce empty results, never errors.
  Only malformed path strings produce errors (at parse time). Filter
  expressions support function extensions (`length`, `count`, `match`,
  `search`, `value`) per RFC 9535 Section 2.4.

  For simple single-value extraction, `query_one()` returns the first
  match or JsonNotFound.
  """

  let _segments: Array[_Segment] val

  new val _create(segments': Array[_Segment] val) =>
    _segments = segments'

  fun query(root: JsonValue): Array[JsonValue] val =>
    """
    Execute this query against a JSON document.

    Returns all matching values. Returns an empty array if no values
    match. Evaluation never errors.
    """
    _JsonPathEval(root, root, _segments)

  fun query_one(root: JsonValue): (JsonValue | JsonNotFound) =>
    """
    Execute this query and return the first matching value, or
    JsonNotFound if no values match.

    Convenience for paths known to select at most one value.
    """
    let results = query(root)
    if results.size() > 0 then
      try results(0)? else JsonNotFound end
    else
      JsonNotFound
    end


primitive JsonPathParser
  """
  Parser for JSONPath expressions.

  Provides two entry points:
  - `parse()` returns errors as data (consistent with `JsonParser.parse()`)
  - `compile()` raises on invalid input (convenience for known-valid paths)
  """

  fun parse(path: String): (JsonPath | JsonPathParseError) =>
    """
    Parse a JSONPath expression. Returns a compiled query on success
    or a structured error on failure.
    """
    let parser = _JsonPathParser(path)
    try
      let segments = parser.parse()?
      JsonPath._create(segments)
    else
      parser.error_result()
    end

  fun compile(path: String): JsonPath ? =>
    """
    Parse a JSONPath expression, raising on invalid input.

    Use this when the path string is known to be valid (e.g., a string
    literal). For user-provided paths, prefer `parse()` which returns
    errors as data.
    """
    match JsonPathParser.parse(path)
    | let jp: JsonPath => jp
    | let _: JsonPathParseError => error
    end


class val JsonPathParseError is Stringable
  """Structured parse error for JSONPath expressions."""

  let message: String
  let offset: USize

  new val create(message': String, offset': USize) =>
    message = message'
    offset = offset'

  fun string(): String iso^ =>
    let s = recover iso String(64) end
    s.append("JSONPath parse error at offset ")
    s.append(offset.string())
    s.append(": ")
    s.append(message)
    consume s