--- /dev/null
+package version
+
+import (
+ "fmt"
+ "reflect"
+ "regexp"
+ "strings"
+)
+
+// Constraint represents a single constraint for a version, such as
+// ">= 1.0".
+type Constraint struct {
+ f constraintFunc
+ check *Version
+ original string
+}
+
+// Constraints is a slice of constraints. We make a custom type so that
+// we can add methods to it.
+type Constraints []*Constraint
+
+type constraintFunc func(v, c *Version) bool
+
+var constraintOperators map[string]constraintFunc
+
+var constraintRegexp *regexp.Regexp
+
+func init() {
+ constraintOperators = map[string]constraintFunc{
+ "": constraintEqual,
+ "=": constraintEqual,
+ "!=": constraintNotEqual,
+ ">": constraintGreaterThan,
+ "<": constraintLessThan,
+ ">=": constraintGreaterThanEqual,
+ "<=": constraintLessThanEqual,
+ "~>": constraintPessimistic,
+ }
+
+ ops := make([]string, 0, len(constraintOperators))
+ for k := range constraintOperators {
+ ops = append(ops, regexp.QuoteMeta(k))
+ }
+
+ constraintRegexp = regexp.MustCompile(fmt.Sprintf(
+ `^\s*(%s)\s*(%s)\s*$`,
+ strings.Join(ops, "|"),
+ VersionRegexpRaw))
+}
+
+// NewConstraint will parse one or more constraints from the given
+// constraint string. The string must be a comma-separated list of
+// constraints.
+func NewConstraint(v string) (Constraints, error) {
+ vs := strings.Split(v, ",")
+ result := make([]*Constraint, len(vs))
+ for i, single := range vs {
+ c, err := parseSingle(single)
+ if err != nil {
+ return nil, err
+ }
+
+ result[i] = c
+ }
+
+ return Constraints(result), nil
+}
+
+// Check tests if a version satisfies all the constraints.
+func (cs Constraints) Check(v *Version) bool {
+ for _, c := range cs {
+ if !c.Check(v) {
+ return false
+ }
+ }
+
+ return true
+}
+
+// Returns the string format of the constraints
+func (cs Constraints) String() string {
+ csStr := make([]string, len(cs))
+ for i, c := range cs {
+ csStr[i] = c.String()
+ }
+
+ return strings.Join(csStr, ",")
+}
+
+// Check tests if a constraint is validated by the given version.
+func (c *Constraint) Check(v *Version) bool {
+ return c.f(v, c.check)
+}
+
+func (c *Constraint) String() string {
+ return c.original
+}
+
+func parseSingle(v string) (*Constraint, error) {
+ matches := constraintRegexp.FindStringSubmatch(v)
+ if matches == nil {
+ return nil, fmt.Errorf("Malformed constraint: %s", v)
+ }
+
+ check, err := NewVersion(matches[2])
+ if err != nil {
+ return nil, err
+ }
+
+ return &Constraint{
+ f: constraintOperators[matches[1]],
+ check: check,
+ original: v,
+ }, nil
+}
+
+func prereleaseCheck(v, c *Version) bool {
+ switch vPre, cPre := v.Prerelease() != "", c.Prerelease() != ""; {
+ case cPre && vPre:
+ // A constraint with a pre-release can only match a pre-release version
+ // with the same base segments.
+ return reflect.DeepEqual(c.Segments64(), v.Segments64())
+
+ case !cPre && vPre:
+ // A constraint without a pre-release can only match a version without a
+ // pre-release.
+ return false
+
+ case cPre && !vPre:
+ // OK, except with the pessimistic operator
+ case !cPre && !vPre:
+ // OK
+ }
+ return true
+}
+
+//-------------------------------------------------------------------
+// Constraint functions
+//-------------------------------------------------------------------
+
+func constraintEqual(v, c *Version) bool {
+ return v.Equal(c)
+}
+
+func constraintNotEqual(v, c *Version) bool {
+ return !v.Equal(c)
+}
+
+func constraintGreaterThan(v, c *Version) bool {
+ return prereleaseCheck(v, c) && v.Compare(c) == 1
+}
+
+func constraintLessThan(v, c *Version) bool {
+ return prereleaseCheck(v, c) && v.Compare(c) == -1
+}
+
+func constraintGreaterThanEqual(v, c *Version) bool {
+ return prereleaseCheck(v, c) && v.Compare(c) >= 0
+}
+
+func constraintLessThanEqual(v, c *Version) bool {
+ return prereleaseCheck(v, c) && v.Compare(c) <= 0
+}
+
+func constraintPessimistic(v, c *Version) bool {
+ // Using a pessimistic constraint with a pre-release, restricts versions to pre-releases
+ if !prereleaseCheck(v, c) || (c.Prerelease() != "" && v.Prerelease() == "") {
+ return false
+ }
+
+ // If the version being checked is naturally less than the constraint, then there
+ // is no way for the version to be valid against the constraint
+ if v.LessThan(c) {
+ return false
+ }
+ // We'll use this more than once, so grab the length now so it's a little cleaner
+ // to write the later checks
+ cs := len(c.segments)
+
+ // If the version being checked has less specificity than the constraint, then there
+ // is no way for the version to be valid against the constraint
+ if cs > len(v.segments) {
+ return false
+ }
+
+ // Check the segments in the constraint against those in the version. If the version
+ // being checked, at any point, does not have the same values in each index of the
+ // constraints segments, then it cannot be valid against the constraint.
+ for i := 0; i < c.si-1; i++ {
+ if v.segments[i] != c.segments[i] {
+ return false
+ }
+ }
+
+ // Check the last part of the segment in the constraint. If the version segment at
+ // this index is less than the constraints segment at this index, then it cannot
+ // be valid against the constraint
+ if c.segments[cs-1] > v.segments[cs-1] {
+ return false
+ }
+
+ // If nothing has rejected the version by now, it's valid
+ return true
+}
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