Implement LPOS

.gitignore

@@ -2,3 +2,5 @@
 /integration/dump.rdb
 *.swp
 /integration/nodes.conf
+.idea/
+miniredis.iml

cmd_list.go

@@ -23,6 +23,7 @@ func commandsList(m *Miniredis) {
 	m.srv.Register("BRPOP", m.cmdBrpop)
 	m.srv.Register("BRPOPLPUSH", m.cmdBrpoplpush)
 	m.srv.Register("LINDEX", m.cmdLindex)
+	m.srv.Register("LPOS", m.cmdLpos)
 	m.srv.Register("LINSERT", m.cmdLinsert)
 	m.srv.Register("LLEN", m.cmdLlen)
 	m.srv.Register("LPOP", m.cmdLpop)
@@ -165,6 +166,153 @@ func (m *Miniredis) cmdLindex(c *server.Peer, cmd string, args []string) {
 	})
 }
 
+// LPOS key element [RANK rank] [COUNT num-matches] [MAXLEN len]
+func (m *Miniredis) cmdLpos(c *server.Peer, cmd string, args []string) {
+	if !m.handleAuth(c) {
+		return
+	}
+	if m.checkPubsub(c, cmd) {
+		return
+	}
+
+	if len(args) == 1 {
+		setDirty(c)
+		c.WriteError(errWrongNumber(cmd))
+		return
+	}
+
+	// Extract options from arguments if present.
+	//
+	// Redis allows duplicate options and uses the last specified.
+	// `LPOS key term RANK 1 RANK 2` is effectively the same as
+	// `LPOS key term RANK 2`
+	if len(args)%2 == 1 {
+		setDirty(c)
+		c.WriteError(msgSyntaxError)
+		return
+	}
+	rank, count := 1, 1 // Default values
+	var maxlen int      // Default value is the list length (see below)
+	var countSpecified, maxlenSpecified bool
+	if len(args) > 2 {
+		for i := 2; i < len(args); i++ {
+			if i%2 == 0 {
+				val := args[i+1]
+				var err error
+				switch strings.ToLower(args[i]) {
+				case "rank":
+					if rank, err = strconv.Atoi(val); err != nil {
+						setDirty(c)
+						c.WriteError(msgInvalidInt)
+						return
+					}
+					if rank == 0 {
+						setDirty(c)
+						c.WriteError(msgRankIsZero)
+						return
+					}
+				case "count":
+					countSpecified = true
+					if count, err = strconv.Atoi(val); err != nil || count < 0 {
+						setDirty(c)
+						c.WriteError(msgCountIsNegative)
+						return
+					}
+				case "maxlen":
+					maxlenSpecified = true
+					if maxlen, err = strconv.Atoi(val); err != nil || maxlen < 0 {
+						setDirty(c)
+						c.WriteError(msgMaxLengthIsNegative)
+						return
+					}
+				default:
+					setDirty(c)
+					c.WriteError(msgSyntaxError)
+					return
+				}
+			}
+		}
+	}
+
+	withTx(m, c, func(c *server.Peer, ctx *connCtx) {
+		db := m.db(ctx.selectedDB)
+		key, element := args[0], args[1]
+		t, ok := db.keys[key]
+		if !ok {
+			// No such key
+			c.WriteNull()
+			return
+		}
+		if t != "list" {
+			c.WriteError(msgWrongType)
+			return
+		}
+		l := db.listKeys[key]
+
+		// RANK cannot be zero (see above).
+		// If RANK is positive search forward (left to right).
+		// If RANK is negative search backward (right to left).
+		// Iterator returns true to continue iterating.
+		iterate := func(iterator func(i int, e string) bool) {
+			comparisons := len(l)
+			// Only use max length if specified, not zero, and less than total length.
+			// When max length is specified, but is zero, this means "unlimited".
+			if maxlenSpecified && maxlen != 0 && maxlen < len(l) {
+				comparisons = maxlen
+			}
+			if rank > 0 {
+				for i := 0; i < comparisons; i++ {
+					if resume := iterator(i, l[i]); !resume {
+						return
+					}
+				}
+			} else if rank < 0 {
+				start := len(l) - 1
+				end := len(l) - comparisons
+				for i := start; i >= end; i-- {
+					if resume := iterator(i, l[i]); !resume {
+						return
+					}
+				}
+			}
+		}
+
+		var currentRank, currentCount int
+		vals := make([]int, 0, count)
+		iterate(func(i int, e string) bool {
+			if e == element {
+				currentRank++
+				// Only collect values only after surpassing the absolute value of rank.
+				if rank > 0 && currentRank < rank {
+					return true
+				}
+				if rank < 0 && currentRank < -rank {
+					return true
+				}
+				vals = append(vals, i)
+				currentCount++
+				if currentCount == count {
+					return false
+				}
+			}
+			return true
+		})
+
+		if !countSpecified && len(vals) == 0 {
+			c.WriteNull()
+			return
+		}
+		if !countSpecified && len(vals) == 1 {
+			c.WriteInt(vals[0])
+			return
+		}
+		c.WriteLen(len(vals))
+		for _, val := range vals {
+			c.WriteInt(val)
+		}
+	})
+}
+
 // LINSERT
 func (m *Miniredis) cmdLinsert(c *server.Peer, cmd string, args []string) {
 	if len(args) != 4 {