feat: add -config option for config file

Author: wakeful

README.md

@@ -9,6 +9,8 @@
 ```shell
 $ trick -h
 Usage of trick
+  -config string
+        path to config file
   -refresh int
         refresh IAM every n minutes (default 12)
   -region string
@@ -50,6 +52,37 @@ to your user PATH.
 trick -role arn::42::role-a -role arn::42::role-b -role arn::42::role-c
 ```
 
+<details>
+<summary>config file version</summary>
+
+```shell
+trick -config path/to/config.hcl
+```
+
+```hcl
+select_profile = profile.simple
+
+# -region eu-west-1 \
+# -role arn::42::role-a -role arn::42::role-b -role arn::42::role-c
+profile "simple" {
+  chain {
+    use {
+      arn = "arn::42::role-a"
+    }
+
+    use {
+      arn = "arn::42::role-b"
+    }
+
+    use {
+      arn = "arn::42::role-c"
+    }
+  }
+}
+```
+
+</details>
+
 ```mermaid
 stateDiagram
     rA: role A
@@ -68,11 +101,54 @@ stateDiagram
 > roles that matter to us.
 
 ```shell
-trick -role arn::42::role-a -role arn::42::role-b \
+trick -region eu-west-1 -refresh 12 \
+      -role arn::42::role-a -role arn::42::role-b \
       -role arn::42::role-c -role arn::42::role-d \
       -use  arn::42::role-a -use  arn::42::role-d
 ```
 
+<details>
+<summary>config file version</summary>
+
+```shell
+trick -config path/to/config.hcl
+```
+
+```hcl
+# -region eu-west-1 -refresh 12 \
+# -role arn::42::role-a -role arn::42::role-b \
+# -role arn::42::role-c -role arn::42::role-d \
+# -use  arn::42::role-a -use  arn::42::role-d
+profile "complex" {
+  region = "eu-west-1"
+
+  chain {
+    ttl = 12
+
+    use {
+      arn  = "arn::42::role-a"
+      skip = false # Defaults to false; you can skip it.
+    }
+
+    use {
+      arn  = "arn::42::role-b"
+      skip = true
+    }
+
+    use {
+      arn  = "arn::42::role-c"
+      skip = true
+    }
+
+    use {
+      arn = "arn::42::role-d"
+    }
+  }
+}
+```
+
+</details>
+
 ```mermaid
 stateDiagram
     rA: role A

main.go

@@ -12,6 +12,8 @@ import (
 	"os/signal"
 	"syscall"
 	"time"
+
+	"github.com/wakeful/trick/internal/parser"
 )
 
 const (
@@ -25,6 +27,7 @@ var version = "dev"
 
 //nolint:funlen
 func main() {
+	config := flag.String("config", "", "path to config file")
 	refresh := flag.Int64("refresh", defaultRefreshTime, "refresh IAM every n minutes")
 	region := flag.String("region", "eu-west-1", "AWS region used for IAM communication")
 	showVersion := flag.Bool("version", false, "show version")
@@ -60,6 +63,24 @@ func main() {
 		return
 	}
 
+	if *config != "" {
+		slog.Debug("loading config file", slog.String("path", *config))
+
+		cfgFile, err := parser.ParseFile(*config)
+		if err != nil {
+			slog.Error("failed to parse config file", slog.String("error", err.Error()))
+
+			return
+		}
+
+		*refresh, roleVars, useRoleVars, err = cfgFile.ToFlags()
+		if err != nil {
+			slog.Error("failed to convert config to flags", slog.String("error", err.Error()))
+
+			return
+		}
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 
 	signalCtx, stop := signal.NotifyContext(ctx, syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP)