package namedconf

import (
	"errors"
	"fmt"
	"strings"
)

// Parse parses a complete configuration (or configuration fragment). The
// file name is only used in error messages and positions. Include
// directives are returned as ordinary statements; callers that want to
// follow them must do so themselves.
func Parse(file, src string) ([]*Stmt, error) {
	p := &parser{lex: &lexer{src: src, line: 1, file: file}}
	if err := p.advance(); err != nil {
		return nil, err
	}
	stmts, err := p.stmts(false)
	if err != nil {
		return nil, err
	}
	return stmts, nil
}

type parser struct {
	lex *lexer
	tok token
}

func (p *parser) advance() error {
	t, err := p.lex.next()
	if err != nil {
		return err
	}
	p.tok = t
	return nil
}

func (p *parser) errorf(format string, args ...any) error {
	return &Error{Pos: p.tok.pos, Msg: fmt.Sprintf(format, args...)}
}

// stmts parses statements until EOF (top level) or a closing brace.
func (p *parser) stmts(inBlock bool) ([]*Stmt, error) {
	var out []*Stmt
	for {
		switch p.tok.kind {
		case tokEOF:
			if inBlock {
				return nil, p.errorf("missing '}' (unexpected end of input)")
			}
			return out, nil
		case tokRBrace:
			if !inBlock {
				return nil, p.errorf("unexpected '}'")
			}
			return out, nil
		case tokSemi:
			// Empty statement; BIND tolerates stray semicolons.
			if err := p.advance(); err != nil {
				return nil, err
			}
			continue
		}
		st, err := p.stmt()
		if err != nil {
			return nil, err
		}
		out = append(out, st)
	}
}

func (p *parser) stmt() (*Stmt, error) {
	st := &Stmt{Pos: p.tok.pos}
	for {
		switch p.tok.kind {
		case tokSemi:
			if err := p.advance(); err != nil {
				return nil, err
			}
			return st, nil
		case tokEOF:
			return nil, &Error{Pos: st.Pos, Msg: "missing ';' at end of statement"}
		case tokRBrace:
			return nil, p.errorf("missing ';' before '}'")
		case tokWord:
			st.Items = append(st.Items, Item{Value: &Value{Text: p.tok.text, Pos: p.tok.pos}})
		case tokString:
			st.Items = append(st.Items, Item{Value: &Value{Text: p.tok.text, Quoted: true, Pos: p.tok.pos}})
		case tokBang:
			st.Items = append(st.Items, Item{Bang: true})
		case tokLBrace:
			pos := p.tok.pos
			if err := p.advance(); err != nil {
				return nil, err
			}
			inner, err := p.stmts(true)
			if err != nil {
				return nil, err
			}
			st.Items = append(st.Items, Item{Block: &Block{Stmts: inner, Pos: pos}})
			// p.tok is now '}'.
		}
		if err := p.advance(); err != nil {
			return nil, err
		}
	}
}

// ParseStatement parses exactly one statement. A missing trailing
// semicolon is added.
func ParseStatement(src string) (*Stmt, error) {
	s := strings.TrimSpace(src)
	if !strings.HasSuffix(s, ";") {
		s += ";"
	}
	stmts, err := Parse("", s)
	if err != nil {
		return nil, err
	}
	if len(stmts) != 1 {
		return nil, fmt.Errorf("expected exactly one statement, found %d", len(stmts))
	}
	return stmts[0], nil
}

// ParseOptionValue parses the value part of an option (everything after
// the option name), for example `{ 10.0.0.0/8; localhost; }` for
// allow-query. It returns the statement "name value;".
func ParseOptionValue(name, value string) (*Stmt, error) {
	v := strings.TrimSpace(value)
	v = strings.TrimSuffix(v, ";")
	if strings.TrimSpace(v) == "" {
		return nil, fmt.Errorf("option %s needs a value", name)
	}
	st, err := ParseStatement(name + " " + v)
	if err != nil {
		var pe *Error
		if errors.As(err, &pe) {
			return nil, errors.New(pe.Msg)
		}
		return nil, err
	}
	if st.Keyword() != strings.ToLower(name) {
		return nil, fmt.Errorf("value for %s is malformed", name)
	}
	return st, nil
}