1 files changed, 61 insertions, 0 deletions
diff --git a/api/v1/util.py b/api/v1/util.py
new file mode 100644
index 0000000..f2dddad
--- /dev/null
+++ b/api/v1/util.py
@@ -0,0 +1,61 @@
+import typing
+
+from flask import jsonify, request
+from peewee import Model, ModelSelect
+
+_V = typing.TypeVar('_V', bound=Model)
+
+
+def model_paginator(model: typing.Type[_V], mapping: typing.Callable[[_V], dict]):
+    return query_paginator(model.select(), mapping)
+
+
+class ConstrainFailed(Exception):
+    def __init__(self, description: str, parameter: str, reason: str):
+        self.reason = reason
+        self.parameter = parameter
+        self.description = description
+
+
+def try_or_fail_contrain(func: typing.Callable, parameter: str, value=None, default=None):
+    if value is None:
+        value = request.args.get(parameter, default)
+    try:
+        return func(value)
+    except BaseException as e:
+        func = func.__name__
+        raise ConstrainFailed(f"{func}({parameter}) failed with an exception", parameter,
+                              f"{func} raised {type(e).__name__}")
+
+
+def max_constrain(max: int, parameter: str, value=None, default=None):
+    value = try_or_fail_contrain(int, parameter, value, default)
+    if value > max:
+        raise ConstrainFailed(f"requested {parameter} too big", parameter, f'> {max}')
+    return value
+
+
+def min_constrain(min: int, parameter: str, value=None, default=None):
+    value = try_or_fail_contrain(int, parameter, value, default)
+    if value < min:
+        raise ConstrainFailed(f"requested {parameter} too big", parameter, f'< {min}')
+    return value
+
+
+def query_paginator(query: ModelSelect, mapping: typing.Callable[[_V], dict]):
+    size = try_or_fail_contrain(int, 'size', default='50')
+    max_constrain(50, 'size', size)
+    min_constrain(2, 'size', size)
+    offset = try_or_fail_contrain(int, 'offset', default='0')
+    min_constrain(0, 'offset', offset)
+    res = []
+    for obj in query.limit(size + 1).offset(offset):
+        res.append(mapping(obj))
+    more = len(res) > size
+    if more:
+        res[-1:] = []
+    return jsonify({
+        'more': more,
+        'next': offset + size if more else None,
+        'results': res,
+    })