splice

# Splicing at index 0 should fail.
!splice 0@1=foo
---
Panic: spliced entry has index or term 0

# Splicing at index 2 should fail (creates gap).
!splice 2@1=foo
---
Panic: first index 2 must touch existing log

# Splicing entries at start should work, both with and without commands, and
# starting at a term after 1. They should be written to the engine and flushed
# to durable storage. It should also update the state.
splice 1@2= 2@2=command oplog=true
status
scan
---
engine: set Entry(1) 0x000000000000000001 = 0x010200
engine: set Entry(2) 0x000000000000000002 = 0x02020107636f6d6d616e64
engine: flush
splice → 2@2 command
last=2@2 commit=0@0
1@2 None
2@2 command

# Splicing an empty list should work and be a noop.
splice oplog=true
status
scan
---
splice → 2@2 command
last=2@2 commit=0@0
1@2 None
2@2 command

# Splicing multiple duplicate entries should fail.
!splice 3@2= 3@2=
---
Panic: spliced entries are not contiguous

# Splicing entries with a gap should fail.
!splice 3@2= 5@2=
---
Panic: spliced entries are not contiguous

# Splicing entries with a term regression should fail.
!splice 3@2= 4@1=
---
Panic: spliced entries have term regression

# Splicing entries with a gap from the base should fail.
!splice 4@2=
---
Panic: first index 4 must touch existing log

# Splicing with a term regression from the base should fail.
!splice 3@1=
---
Panic: splice term regression 2 → 1

# Fully overlapping entries is a noop.
splice 1@2= 2@2=command oplog=true
scan
---
splice → 2@2 command
1@2 None
2@2 command

# An overlapping prefix is a noop.
splice 1@2= oplog=true
scan
---
splice → 2@2 command
1@2 None
2@2 command

# An overlapping suffix is a noop.
splice 2@2=command oplog=true
scan
---
splice → 2@2 command
1@2 None
2@2 command

# Changing a command with the same term/index should fail.
!splice 2@2=foo
scan
---
Panic: command mismatch at Entry { index: 2, term: 2, command: Some([99, 111, 109, 109, 97, 110, 100]) }
1@2 None
2@2 command

# Appending a new entry in the same term should work, as should
# appending one in a new term.
splice 3@2=bar
splice 4@3=
scan
---
splice → 3@2 bar
splice → 4@3 None
1@2 None
2@2 command
3@2 bar
4@3 None

# Splicing with suffix overlap should work, and only write the new entries.
splice 3@2=bar 4@3= 5@3=foo 6@3=bar oplog=true
scan
---
engine: set Entry(5) 0x000000000000000005 = 0x05030103666f6f
engine: set Entry(6) 0x000000000000000006 = 0x06030103626172
engine: flush
splice → 6@3 bar
1@2 None
2@2 command
3@2 bar
4@3 None
5@3 foo
6@3 bar

# Splicing at an existing index with a new term should replace the tail.
splice 4@4= oplog=true
status
scan
---
engine: set Entry(4) 0x000000000000000004 = 0x040400
engine: delete Entry(5) 0x000000000000000005
engine: delete Entry(6) 0x000000000000000006
engine: flush
splice → 4@4 None
last=4@4 commit=0@0
1@2 None
2@2 command
3@2 bar
4@4 None

# This also holds at the start of the log.
splice 1@5= 2@5=foo 3@5=bar oplog=true
status
scan
---
engine: set Entry(1) 0x000000000000000001 = 0x010500
engine: set Entry(2) 0x000000000000000002 = 0x02050103666f6f
engine: set Entry(3) 0x000000000000000003 = 0x03050103626172
engine: delete Entry(4) 0x000000000000000004
engine: flush
splice → 3@5 bar
last=3@5 commit=0@0
1@5 None
2@5 foo
3@5 bar

# Splicing across the commit index should work, as long as the entries match.
commit 2
splice 1@5= 2@5=foo 3@5=bar 4@5=
status
scan
---
commit → 2@5 foo
splice → 4@5 None
last=4@5 commit=2@5
1@5 None
2@5 foo
3@5 bar
4@5 None

# Splicing across the commit index can replace a tail after the commit index.
splice 3@6= 4@6=bar
status
scan
---
splice → 4@6 bar
last=4@6 commit=2@5
1@5 None
2@5 foo
3@6 None
4@6 bar

# But replacing a tail at or before the commit index should fail.
!splice 2@7=
!splice 1@7=
---
Panic: spliced entries below commit index
Panic: spliced entries below commit index

# Dump the raw data.
dump
---
Entry(1) 0x000000000000000001 = 0x010500
Entry(2) 0x000000000000000002 = 0x02050103666f6f
Entry(3) 0x000000000000000003 = 0x030600
Entry(4) 0x000000000000000004 = 0x04060103626172
CommitIndex 0x02 = 0x0205