feat: add usage key in params and improve messages

.gitignore

@@ -0,0 +1,2 @@
+*.md
+mdsh

monthly.md

@@ -1,32 +1,45 @@
 ---
-output: "reports_{{.from}}.md"
+output: "reports_{{.b}}.md"
 params:
-  from:
+  b:
     required: true
-  to:
+    usage: |
+      Required.
+      The begin time of report.
+      Examples:
+        2025
+        2025-07
+        2025-07-15
+        Jul
+  e:
     required: true
-  file:
+    usage: |
+      Required.
+      The end time of report.
+      Same format as -b
+  f:
     default: ~/.hledger.journal
+    usage: The ledger file to parse
 ---
 
-# Finance Report from {{.from}} to {{.to}}
+# Finance Report from {{.b}} to {{.e}}
 
 ## Previous status:
 
-{{ sh "hledger -f $file balancesheet -e $from" }}
+{{ sh "hledger -f $f balancesheet -e $b" }}
 
 ## Expenses:
 
 ### Expense Summary by Category
 
-{{ sh "hledger -f $file bal expenses -b $from -e $to --depth 3 --sort amount" }}
+{{ sh "hledger -f $f bal expenses -b $b -e $e --depth 3 --sort amount" }}
 
-{{ sh "hledger -f $file bal expenses -b $from -e $to --depth 2 --sort amount" }}
+{{ sh "hledger -f $f bal expenses -b $b -e $e --depth 2 --sort amount" }}
 
 ## Net Income:
 
-{{sh "hledger -f $file income -b $from -e $to --monthly"}}
+{{sh "hledger -f $f income -b $b -e $e --monthly"}}
 
 ## Ending balance:
 
-{{sh "hledger -f $file balancesheet -e $to"}}
+{{sh "hledger -f $f balancesheet -e $e"}}

params.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -10,16 +11,21 @@ func parseParams(meta TemplateMeta) (ctx TemplateContext, err error) {
 	result := make(map[string]*string)
 	fs := flag.NewFlagSet("params", flag.ExitOnError)
 	for key, spec := range meta.Params {
-		result[key] = fs.String(key, spec.Default, key)
+		result[key] = fs.String(key, spec.Default, spec.Usage)
 	}
 	fs.Parse(os.Args[2:])
 	ctx = make(TemplateContext)
+	message := ""
 	for key, spec := range meta.Params {
 		if spec.Required && *result[key] == "" {
-			err = fmt.Errorf("parameter '%s' required but not provided", key)
+			message += fmt.Sprintf("parameter '%s' required but not provided\n", key)
-			return
+			continue
 		}
 		ctx[key] = *result[key]
 	}
+	if message != "" {
+		message += fmt.Sprintf("Use 'mdsh %s --help' to see usage", os.Args[1])
+		return nil, errors.New(message)
+	}
 	return
 }

types.go

@@ -36,6 +36,7 @@ func (meta TemplateMeta) OutputFile(ctx TemplateContext) (output string, err err
 type ParamSpec struct {
 	Required bool   `yaml:"required"`
 	Default  string `yaml:"default"`
+	Usage    string `yaml:"usage"`
 }
 
 type TemplateContext map[string]string