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dsxack · Mar 17, 2022 · 4aa5d4b · 4aa5d4b
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diff --git a/.github/images/railroad.png b/.github/images/railroad.png
diff --git a/.gitignore b/.gitignore
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+.idea
diff --git a/README.md b/README.md
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+# example-statement-parser
+
+An statement parser with participle.
+
+### Install
+
+```sh
+go get github.com/dsxack/example-statement-parser
+```
+
+### Usage example
+
+```golang
+package main
+
+import (
+	"github.com/dsxack/example-statement-parser"
+	"log"
+)
+
+func Example() {
+	stmt := parser.Statement{}
+	err := parser.Parse(`#{ ${insecure} ? "http" : "https" }://${domain}/${basepath}`, &stmt)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+```
+
+### Example of statements
+
+* `some value 5"`
+* `${some.variable}"`
+* `#{ true ? "yes" : "no" }`
+* `#{ ${insecure} ? ${var1} : ${var2} }`
+* `#{ true ? true : false }`
+* `#{ 5 ? 10 : 0 }`
+* `#{ ${cond1} or ${cond2} ? ${var1} : ${var2} }`
+* `#{ ${cond1} || ${cond2} ? ${var1} : ${var2} }`
+* `#{ ${cond1} and ${cond2} ? ${var1} : ${var2} }`
+* `#{ ${cond1} && ${cond2} ? ${var1} : ${var2} }`
+* `#{ ${foo} == "bar" ? ${var1} : ${var2} }`
+* `#{ (${cond1} or ${cond2}) and ${cond3} ? ${var1} : ${var2} }`
+* `#{ ${cond1} and (${cond2} or ${cond3}) ? ${var1} : ${var2} }`
+* `#{ ${cond1} and (${cond2} > 5 or ${cond3}) ? ${var1} : ${var2} }`
+* `#{ ${insecure} ? "http" : "https" }://${domain}/${basepath}`
+
+### Parser railway diagram
+
+![](.github/images/railroad.png)
diff --git a/ast.go b/ast.go
@@ -0,0 +1,109 @@
+package parser
+
+import (
+	"fmt"
+	"strings"
+)
+
+type Statement struct {
+	Fragments []Fragment `parser:"@@+"`
+}
+
+type Fragment struct {
+	IfStatement *IfStatement `parser:"'#{' @@ '}' "`
+	Variable    *string      `parser:"| '${' @Ident '}'"`
+	Literal     *string      `parser:"| @!(Ternary Variable)"`
+}
+
+type IfStatement struct {
+	Cond Expr `parser:"@@"`
+	Then Term `parser:"'?' @@"`
+	Else Term `parser:"':' @@"`
+}
+
+type Expr struct {
+	Left  *Cond       `parser:"( @@"`
+	Sub   *Expr       `parser:"| '(' @@ ')' )"`
+	Right []LogicExpr `parser:"@@*"`
+}
+
+type LogicExpr struct {
+	Operator LogicOperator `parser:"@LogicOperator"`
+	Cond     *Cond         `parser:"( @@"`
+	Sub      *Expr         `parser:"| '(' @@ ')' )"`
+}
+
+type Cond struct {
+	Left     Term               `parser:"@@"`
+	Operator ComparisonOperator `parser:"( @ComparisonOperator"`
+	Right    *Term              `parser:"@@ )?"`
+}
+
+type Term struct {
+	Variable *string `parser:"'${' @Ident '}'"`
+	Value    *Value  `parser:"| @@"`
+}
+
+type Value struct {
+	Number  *float64 `parser:"@Number"`
+	String  *string  `parser:"| @String"`
+	Boolean *Boolean `parser:"| @Boolean"`
+	Array   []Value  `parser:"| '[' @@ (',' @@)* ']'"`
+}
+
+type Boolean bool
+
+func (b *Boolean) Capture(s []string) error {
+	switch strings.ToUpper(s[0]) {
+	case "TRUE":
+		*b = true
+	case "FALSE":
+		*b = false
+	default:
+		return fmt.Errorf("unexpected string: %s", s[0])
+	}
+	return nil
+}
+
+type LogicOperator string
+
+const (
+	AndLogicOperator LogicOperator = "AND"
+	OrLogicOperator  LogicOperator = "OR"
+)
+
+func (operator *LogicOperator) Capture(s []string) error {
+	switch strings.ToUpper(s[0]) {
+	case "AND", "&&":
+		*operator = AndLogicOperator
+	case "OR", "||":
+		*operator = OrLogicOperator
+	default:
+		return fmt.Errorf("unexpected string: %s", s[0])
+	}
+	return nil
+}
+
+type ComparisonOperator string
+
+const (
+	EqualComparisonOperator            ComparisonOperator = "=="
+	NotEqualComparisonOperator         ComparisonOperator = "!="
+	GreaterThanComparisonOperator      ComparisonOperator = ">"
+	GreaterThanEqualComparisonOperator ComparisonOperator = ">="
+	LessThanComparisonOperator         ComparisonOperator = "<"
+	LessThanEqualComparisonOperator    ComparisonOperator = "<="
+	InComparisonOperator               ComparisonOperator = "IN"
+)
+
+func comparisonOperatorKeywords() []string {
+	return []string{
+		string(EqualComparisonOperator),
+		string(NotEqualComparisonOperator),
+		string(GreaterThanComparisonOperator),
+		string(GreaterThanEqualComparisonOperator),
+		string(LessThanComparisonOperator),
+		string(LessThanEqualComparisonOperator),
+		string(InComparisonOperator),
+	}
+}
diff --git a/go.mod b/go.mod
@@ -0,0 +1,14 @@
+module github.com/dsxack/example-statement-parser
+
+go 1.17
+
+require (
+	github.com/alecthomas/participle/v2 v2.0.0-alpha7
+	github.com/stretchr/testify v1.4.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v2 v2.2.2 // indirect
+)
diff --git a/go.sum b/go.sum
@@ -0,0 +1,16 @@
+github.com/alecthomas/participle/v2 v2.0.0-alpha7 h1:cK4vjj0VSgb3lN1nuKA5F7dw+1s1pWBe5bx7nNCnN+c=
+github.com/alecthomas/participle/v2 v2.0.0-alpha7/go.mod h1:NumScqsC42o9x+dGj8/YqsIfhrIQjFEOFovxotbBirA=
+github.com/alecthomas/repr v0.0.0-20181024024818-d37bc2a10ba1 h1:GDQdwm/gAcJcLAKQQZGOJ4knlw+7rfEQQcmwTbt4p5E=
+github.com/alecthomas/repr v0.0.0-20181024024818-d37bc2a10ba1/go.mod h1:xTS7Pm1pD1mvyM075QCDSRqH6qRLXylzS24ZTpRiSzQ=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
diff --git a/lexer.go b/lexer.go
@@ -0,0 +1,47 @@
+package parser
+
+import (
+	"github.com/alecthomas/participle/v2/lexer"
+	"strings"
+)
+
+var statementLexer = lexer.MustStateful(lexer.Rules{
+	"Root": []lexer.Rule{
+		{Name: "Ternary", Pattern: `\#\{`, Action: lexer.Push("Ternary")},
+		{Name: "Variable", Pattern: `\$\{`, Action: lexer.Push("Variable")},
+		{Name: "Literal", Pattern: `[^\$\#]+|[\$\#][^\{][^\$\#]+|[\$\#]`},
+		lexer.Include("Common"),
+	},
+	"Ternary": []lexer.Rule{
+		{Name: "TernaryThen", Pattern: `\?`},
+		{Name: "TernaryElse", Pattern: `\:`},
+		{Name: "TernaryEnd", Pattern: `}`, Action: lexer.Pop()},
+		lexer.Include("Expr"),
+		lexer.Include("Common"),
+	},
+	"Condition": []lexer.Rule{
+		{Name: "Variable", Pattern: `\$\{`, Action: lexer.Push("Variable")},
+		{Name: "ComparisonOperator", Pattern: strings.Join(comparisonOperatorKeywords(), "|")},
+		{Name: "String", Pattern: `'[^']*'|"[^"]*"`},
+		lexer.Include("Common"),
+	},
+	"Expr": []lexer.Rule{
+		{Name: "LogicOperator", Pattern: `and|or|AND|OR|&&|\|\|`},
+		{Name: "SubExpr", Pattern: `\(`, Action: lexer.Push("SubExpr")},
+		lexer.Include("Condition"),
+	},
+	"SubExpr": []lexer.Rule{
+		lexer.Include("Expr"),
+		{Name: "SubExprEnd", Pattern: `\)`, Action: lexer.Pop()},
+	},
+	"Variable": []lexer.Rule{
+		{Name: "VariableEnd", Pattern: `}`, Action: lexer.Pop()},
+		lexer.Include("Common"),
+	},
+	"Common": []lexer.Rule{
+		{Name: "whitespace", Pattern: `\s+`},
+		{Name: "Number", Pattern: `(?:\d*\.)?\d+`},
+		{Name: "Boolean", Pattern: `false|true|TRUE|FALSE"`},
+		{Name: "Ident", Pattern: `[a-zA-Z][a-zA-Z0-9_\.]*`},
+	},
+})
diff --git a/parser.go b/parser.go
@@ -0,0 +1,14 @@
+package parser
+
+import (
+	"github.com/alecthomas/participle/v2"
+)
+
+var statementParser = participle.MustBuild(&Statement{},
+	participle.Lexer(statementLexer),
+	participle.Unquote("String"),
+)
+
+func Parse(input string, stmt *Statement) error {
+	return statementParser.ParseString("", input, stmt)
+}