browser-ruler/ruler.go

package main

import (
	"fmt"
	"net/url"
	"os/exec"
	"regexp"

	"github.com/antonmedv/expr"
)

// MatchFunc is a signature for a function to match a URL
type MatchFunc = func(url.URL) bool

// A BrowserRule is a rule that will launch a browser, if matched
type BrowserRule struct {
	matcher MatchFunc
	command string
	args    []string
}

// IsMatched will check to see the rule matches the provied URL
func (r BrowserRule) IsMatched(dest url.URL) bool {
	return r.matcher(dest)
}

// Launch will launch the browser with the provided URL
func (r BrowserRule) Launch(dest url.URL) error {
	args := append(r.args, "--", dest.String())
	cmd := exec.Command(r.command, args...)
	return cmd.Start()
}

// MaybeLaunch will lauch the browser with the provided URL if it matches the rule
func (r BrowserRule) MaybeLaunch(dest url.URL) (bool, error) {
	if r.IsMatched(dest) {
		return true, r.Launch(dest)
	}
	return false, nil
}

func NewBrowserRule(command string, args []string, matcher MatchFunc) BrowserRule {
	return BrowserRule{
		command: command,
		args:    args,
		matcher: matcher,
	}
}

func NewBrowserRuleFromExpr(command string, args []string, matcherExpr string) BrowserRule {
	return NewBrowserRule(
		command, args, MakeMatchFunc(matcherExpr),
	)
}

func MakeMatchFunc(rule string) MatchFunc {
	return func(dest url.URL) bool {
		env := map[string]interface{}{
			// Prebuilt match functions
			"matchAny":        matchAny,
			"matchHostRegexp": matchHostRegexp,
			"matchHostname":   matchHostname,
			"matchNever":      matchNever,
			"matchRegexp":     matchRegexp,

			// Helpers for building custom matchers
			"MatchFunc": func(foundMatch bool) MatchFunc {
				return func(_ url.URL) bool {
					return foundMatch
				}
			},
			"fullUrl":  dest.String(),
			"hostname": dest.Hostname(),
			"url":      dest,
		}
		matchFuncExpr, err := expr.Eval(rule, env)
		if err != nil {
			fmt.Printf("Error evaluating rule %s: %v", rule, err)
			return false
		}

		matchFunc, ok := matchFuncExpr.(MatchFunc)
		if !ok {
			fmt.Printf("Error evaluating rule %s. Did not evaluate to a MatchFunc.", rule)
			return false
		}
		return matchFunc(dest)
	}
}

func matchHostname(hostnames ...string) MatchFunc {
	return func(dest url.URL) bool {
		for _, host := range hostnames {
			if host == dest.Hostname() {
				return true
			}
		}
		return false
	}
}

func matchHostRegexp(hostRegexp ...string) MatchFunc {
	matchers := []*regexp.Regexp{}
	for _, s := range hostRegexp {
		matchers = append(matchers, regexp.MustCompile(s))
	}
	return func(dest url.URL) bool {
		for _, matcher := range matchers {
			if matcher.MatchString(dest.Hostname()) {
				return true
			}
		}
		return false
	}
}

func matchRegexp(urlRegexp ...string) MatchFunc {
	matchers := []*regexp.Regexp{}
	for _, s := range urlRegexp {
		matchers = append(matchers, regexp.MustCompile(s))
	}
	return func(dest url.URL) bool {
		for _, matcher := range matchers {
			if matcher.MatchString(dest.String()) {
				return true
			}
		}
		return false
	}
}

func matchAny(matchFuncs ...MatchFunc) MatchFunc {
	return func(dest url.URL) bool {
		for _, f := range matchFuncs {
			if f(dest) {
				return true
			}
		}
		return false
	}
}

// Always returns true
func defaultBrowser(dest url.URL) bool {
	return true
}

// Never returns true
func matchNever(dest url.URL) bool {
	return false
}