// Package parse provides a simple parser combinator library
package parse

// The N struct is a parser result node.
type N struct {
	// Match indicates whether the parser succeeded.
	Matched bool
	// Content contains whatever was matched by the parser.
	Content string
	// Nodes contains any result nodes by nested parsers.
	Nodes []N
}

// Parser function type
// Takes a string and returns a result and the remaining part of the string.
type P func(string) (N, string)

// A sequence of parsers. Matches when all of p match.
func Seq(p ...P) P {
	return func(s string) (N, string) {
		result := N{Matched: true, Nodes: make([]N, 0, len(p))}
		for _, parser := range p {
			n, r := parser(s)
			result.Nodes = append(result.Nodes, n)
			if !n.Matched {
				result.Matched = false
				break
			}
			result.Content = result.Content + n.Content
			s = r
		}
		return result, s
	}
}

// Matches and returns on the first match of p.
func Any(p ...P) P {
	return func(s string) (N, string) {
		result := N{Matched: false, Nodes: nil}
		for _, parser := range p {
			n, r := parser(s)
			if n.Matched {
				return n, r
			}
			result.Nodes, s = append(result.Nodes, n), r
		}
		return result, s
	}
}

// Kleene star (zero or more). Always matches.
func K(p P) P {
	return func(s string) (N, string) {
		result := N{Matched: true, Nodes: nil}
		for n, r := p(s); n.Matched; n, r = p(r) {
			result.Content = result.Content + n.Content
			result.Nodes = append(result.Nodes, n)
			s = r
		}
		return result, s
	}
}

// Returns a delegating parser whose delegate can be set on later.
// Useful for recursive definitions.
func Defer() (P, *P) {
	var deferred P
	return func(s string) (N, string) {
		return deferred(s)
	}, &deferred
}

// Returns a parser that accepts the specified number of bytes
func Accept(count int) P {
	return func(s string) (N, string) {
		if len(s) < count {
			return N{Matched: false, Content: "", Nodes: nil}, s
		}
		return N{Matched: true, Content: s[:count], Nodes: nil}, s[count:]
	}
}

package parse

import (
	"testing"
)

func TestAccept(t *testing.T) {
	// Accept(0) will always match :)
	p0 := Accept(0)
	if r, s := p0(""); !r.Matched || r.Content != "" || r.Nodes != nil || s != "" {
		t.Error("Invalid result for Accept's negative test", r)
	}
	// Test with a non-zero amount of bytes
	p := Accept(1)
	if r, s := p(""); r.Matched || r.Content != "" || r.Nodes != nil || s != "" {
		t.Error("Invalid result for Accept's negative test", r)
	}
	if r, s := p("a"); !r.Matched || r.Content != "a" || r.Nodes != nil || s != "" {
		t.Error("Invalid result for Accept's positive test", r)
	}
}

func TestK(t *testing.T) {
	p := Accept(1)
	k := K(p)
	if r, s := k("aaa"); !r.Matched || r.Content != "aaa" || r.Nodes == nil || s != "" {
		t.Error("Invalid result for K* match test", r)
	}
	if r, s := k(""); !r.Matched || r.Content != "" || r.Nodes != nil || s != "" {
		t.Error("Invalid result for K* no-match test", r)
	}
}

func TestSeq(t *testing.T) {
	p1, p2 := Accept(1), Accept(1)
	s := Seq(p1, p2)
	if r, s := s("aa"); !r.Matched || r.Content != "aa" || r.Nodes == nil || s != "" {
		t.Error("Invalid result for Seq positive test", r)
	}
	if r, s := s("a"); r.Matched || r.Content != "a" || r.Nodes == nil || s != "" {
		t.Error("Invalid result for Seq partial match test", r)
	}
	if r, s := s(""); r.Matched || r.Content != "" || r.Nodes == nil || s != "" {
		t.Error("Invalid result for Seq no-match test", r)
	}
}

func TestAny(t *testing.T) {
	p, p0 := Accept(1), Accept(0)
	a := Any(p, p0)
	if r, s := a(""); !r.Matched || r.Content != "" || r.Nodes != nil || s != "" {
		t.Error("Invalid result for Any match test", r)
	}
	if r, s := a("aa"); !r.Matched || r.Content != "a" || r.Nodes != nil || s != "a" {
		t.Error("Invalid result for Any match test", r)
	}
}