Add new-email trigger

This patch sets up the trigger config section of aerc.conf.

Each trigger has its own function which is called from the place where
it is triggered. Currently only the new-email trigger is implemented.

The triggers make use of format strings. For instance, in the new-email
trigger this allows the user to select the trigger command and also the
information extracted from the command and placed into their command.

To actually execute the trigger commands the keypresses are simulated.

Further triggers can be implemented in the future.

Formatting of the command is moved to a new package.

3 files changed, 71 insertions, 0 deletions

diff --git a/config/aerc.conf.in b/config/aerc.conf.in
index 42190423..5b080e98 100644
--- a/config/aerc.conf.in
+++ b/config/aerc.conf.in
@@ -96,3 +96,14 @@ subject,~^\[PATCH=awk -f @SHAREDIR@/filters/hldiff
 #text/html=@SHAREDIR@/filters/html
 text/*=awk -f @SHAREDIR@/filters/plaintext
 #image/*=catimg -w $(tput cols) -
+
+[triggers]
+#
+# Triggers specify commands to execute when certain events occur.
+#
+# Example:
+# new-email=exec notify-send "New email from %n" "%s"<Enter>
+
+#
+# Executed when a new email arrives in the selected folder
+new-email=
diff --git a/config/config.go b/config/config.go
index 4a049fa0..f8637292 100644
--- a/config/config.go
+++ b/config/config.go
@@ -84,6 +84,11 @@ type ViewerConfig struct {
 	HeaderLayout   [][]string `ini:"-"`
 }
 
+type TriggersConfig struct {
+	NewEmail       string `ini:"new-email"`
+	ExecuteCommand func(command []string) error
+}
+
 type AercConfig struct {
 	Bindings BindingConfig
 	Compose  ComposeConfig
@@ -91,6 +96,7 @@ type AercConfig struct {
 	Accounts []AccountConfig `ini:"-"`
 	Filters  []FilterConfig  `ini:"-"`
 	Viewer   ViewerConfig    `ini:"-"`
+	Triggers TriggersConfig  `ini:"-"`
 	Ui       UIConfig
 	General  GeneralConfig
 }
@@ -278,6 +284,11 @@ func (config *AercConfig) LoadConfig(file *ini.File) error {
 			return err
 		}
 	}
+	if triggers, err := file.GetSection("triggers"); err == nil {
+		if err := triggers.MapTo(&config.Triggers); err != nil {
+			return err
+		}
+	}
 	return nil
 }
 
diff --git a/config/triggers.go b/config/triggers.go
new file mode 100644
index 00000000..d31f267b
--- /dev/null
+++ b/config/triggers.go
@@ -0,0 +1,49 @@
+package config
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/google/shlex"
+
+	"git.sr.ht/~sircmpwn/aerc/lib/format"
+	"git.sr.ht/~sircmpwn/aerc/models"
+)
+
+func (trig *TriggersConfig) ExecTrigger(triggerCmd string,
+	triggerFmt func(string) (string, error)) error {
+
+	if len(triggerCmd) == 0 {
+		return errors.New("Trigger command empty")
+	}
+	triggerCmdParts, err := shlex.Split(triggerCmd)
+	if err != nil {
+		return err
+	}
+
+	var command []string
+	for _, part := range triggerCmdParts {
+		formattedPart, err := triggerFmt(part)
+		if err != nil {
+			return err
+		}
+		command = append(command, formattedPart)
+	}
+	return trig.ExecuteCommand(command)
+}
+
+func (trig *TriggersConfig) ExecNewEmail(account *AccountConfig,
+	conf *AercConfig, msg *models.MessageInfo) {
+	err := trig.ExecTrigger(trig.NewEmail,
+		func(part string) (string, error) {
+			formatstr, args, err := format.ParseMessageFormat(part,
+				conf.Ui.TimestampFormat, account.Name, 0, msg)
+			if err != nil {
+				return "", err
+			}
+			return fmt.Sprintf(formatstr, args...), nil
+		})
+	if err != nil {
+		fmt.Printf("Error from the new-email trigger: %s\n", err)
+	}
+}