feat(cli): add JSONL and directory input readers

Add TextPair dataclass and read_jsonl/read_paired_jsonl functions
for parsing candidate-reference pairs from JSONL files.

src/veritext/cli/readers.py

@@ -0,0 +1,120 @@
+"""Input readers for CLI operations."""
+
+import json
+from dataclasses import dataclass
+from pathlib import Path
+
+
+@dataclass
+class TextPair:
+    """A candidate-reference text pair for validation."""
+
+    candidate: str
+    reference: str
+
+
+def read_jsonl(path: Path) -> list[TextPair]:
+    """
+    Read text pairs from a JSONL file.
+
+    Each line must be a JSON object with 'candidate' and 'reference' keys.
+
+    Args:
+        path: Path to the JSONL file.
+
+    Returns:
+        List of TextPair objects.
+
+    Raises:
+        FileNotFoundError: If the file does not exist.
+        ValueError: If any line is malformed or missing required keys.
+    """
+    if not path.exists():
+        raise FileNotFoundError(f"File not found: {path}")
+
+    pairs: list[TextPair] = []
+    with path.open() as f:
+        for line_num, line in enumerate(f, start=1):
+            line = line.strip()
+            if not line:
+                continue
+
+            try:
+                data = json.loads(line)
+            except json.JSONDecodeError as e:
+                raise ValueError(f"Invalid JSON on line {line_num}: {e}") from e
+
+            if "candidate" not in data:
+                raise ValueError(f"Missing 'candidate' key on line {line_num}")
+            if "reference" not in data:
+                raise ValueError(f"Missing 'reference' key on line {line_num}")
+
+            pairs.append(
+                TextPair(
+                    candidate=str(data["candidate"]),
+                    reference=str(data["reference"]),
+                )
+            )
+
+    return pairs
+
+
+def read_paired_jsonl(candidates_path: Path, references_path: Path) -> list[TextPair]:
+    """
+    Read text pairs from separate candidate and reference JSONL files.
+
+    Each file should contain one JSON object per line with a 'text' key.
+
+    Args:
+        candidates_path: Path to the candidates JSONL file.
+        references_path: Path to the references JSONL file.
+
+    Returns:
+        List of TextPair objects.
+
+    Raises:
+        FileNotFoundError: If either file does not exist.
+        ValueError: If files have different lengths or are malformed.
+    """
+    candidates = _read_text_jsonl(candidates_path, "candidates")
+    references = _read_text_jsonl(references_path, "references")
+
+    if len(candidates) != len(references):
+        raise ValueError(
+            f"Number of candidates ({len(candidates)}) does not match "
+            f"number of references ({len(references)})"
+        )
+
+    return [
+        TextPair(candidate=c, reference=r)
+        for c, r in zip(candidates, references, strict=True)
+    ]
+
+
+def _read_text_jsonl(path: Path, label: str) -> list[str]:
+    """Read text values from a JSONL file with 'text' key per line."""
+    if not path.exists():
+        raise FileNotFoundError(f"{label.capitalize()} file not found: {path}")
+
+    texts: list[str] = []
+    with path.open() as f:
+        for line_num, line in enumerate(f, start=1):
+            line = line.strip()
+            if not line:
+                continue
+
+            try:
+                data = json.loads(line)
+            except json.JSONDecodeError as e:
+                raise ValueError(
+                    f"Invalid JSON in {label} file on line {line_num}: {e}"
+                ) from e
+
+            if "text" not in data:
+                raise ValueError(
+                    f"Missing 'text' key in {label} file on line {line_num}"
+                )
+
+            texts.append(str(data["text"]))
+
+    return texts