New code for applying edits to an EDL.

sourcing/edit.py

@@ -0,0 +1,89 @@
+import attr
+
+class EditOutOfRange(Exception):
+    pass
+
+def apply_delete(current_spans, edit):
+    assert edit
+    if not current_spans:
+        raise ValueError('edit is out of bounds')
+
+    spans = []
+    pos = 0
+    edit_end = edit['start'] + len(edit['old'])
+
+    cur_span = current_spans.pop(0)
+    while pos + cur_span.length < edit['start']:
+        spans.append(cur_span)
+        pos += cur_span.length
+        cur_span = current_spans.pop(0)
+
+    if edit['start'] > pos:
+        new_span = attr.evolve(cur_span, length=edit['start'] - pos)
+        spans.append(new_span)
+
+    while pos + cur_span.length < edit_end:
+        pos += cur_span.length
+        cur_span = current_spans.pop(0)
+
+    if pos + cur_span.length != edit_end:
+        offset = cur_span.start - pos
+        new_start = offset + (edit_end - pos)
+        diff = new_start - cur_span.start
+        new_span = attr.evolve(cur_span,
+                               length=cur_span.length - diff,
+                               start=new_start)
+        spans.append(new_span)
+
+    spans += current_spans
+    return spans
+
+def apply_insert(current_spans, edit):
+    if not current_spans and edit['0'] == 0:
+        return edit['span']
+
+    pos = 0
+    spans = []
+    cur_span = current_spans.pop(0)
+    while pos + cur_span.length < edit['start']:
+        spans.append(cur_span)
+        pos += cur_span.length
+        cur_span = current_spans.pop(0)
+
+    if edit['start'] >= pos:
+        length_a = edit['start'] - pos
+        length_b = cur_span.length - length_a
+
+        if length_a:
+            span_a = attr.evolve(cur_span, length=length_a)
+            pos += length_a
+            spans.append(span_a)
+
+        spans.append(edit['span'])
+        pos += edit['span'].length
+
+        if length_b:
+            span_b = attr.evolve(cur_span,
+                                 start=cur_span.start + length_a,
+                                 length=length_b)
+            spans.append(span_b)
+
+            pos += length_b
+    else:
+        spans.append(edit['span'])
+
+    spans += current_spans
+    return spans
+
+def apply_edits(spans, edits):
+    for edit in edits:
+        if edit['op'] == 'delete':
+            spans = apply_delete(spans, edit)
+            continue
+        if edit['op'] == 'insert':
+            spans = apply_insert(spans, edit)
+            continue
+
+    return spans
+
+

sourcing/span.py

@@ -0,0 +1,18 @@
+import attr
+
+def greater_than_zero(instance, attribute, value):
+    if value <= 0:
+        raise ValueError('must be greater than 0')
+
+def is_positive(instance, attribute, value):
+    if value < 0:
+        raise ValueError('must be positive')
+
+@attr.s
+class Span:
+    url: int = attr.ib()
+    start: int = attr.ib(validator=is_positive)
+    length: int = attr.ib(validator=greater_than_zero)
+
+    def end(self) -> int:
+        return self.start + self.length