// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package datafmt

import (
	"go/scanner"
	"go/token"
	"os"
	"strconv"
	"strings"
)

// ----------------------------------------------------------------------------
// Parsing

type parser struct {
	scanner.ErrorVector
	scanner scanner.Scanner
	file    *token.File
	pos     token.Pos   // token position
	tok     token.Token // one token look-ahead
	lit     string      // token literal

	packs map[string]string // PackageName -> ImportPath
	rules map[string]expr   // RuleName -> Expression
}

func (p *parser) next() {
	p.pos, p.tok, p.lit = p.scanner.Scan()
	switch p.tok {
	case token.CHAN, token.FUNC, token.INTERFACE, token.MAP, token.STRUCT:
		// Go keywords for composite types are type names
		// returned by reflect. Accept them as identifiers.
		p.tok = token.IDENT // p.lit is already set correctly
	}
}

func (p *parser) init(fset *token.FileSet, filename string, src []byte) {
	p.ErrorVector.Reset()
	p.file = fset.AddFile(filename, fset.Base(), len(src))
	p.scanner.Init(p.file, src, p, scanner.AllowIllegalChars) // return '@' as token.ILLEGAL w/o error message
	p.next()                                                  // initializes pos, tok, lit
	p.packs = make(map[string]string)
	p.rules = make(map[string]expr)
}

func (p *parser) error(pos token.Pos, msg string) {
	p.Error(p.file.Position(pos), msg)
}

func (p *parser) errorExpected(pos token.Pos, msg string) {
	msg = "expected " + msg
	if pos == p.pos {
		// the error happened at the current position;
		// make the error message more specific
		msg += ", found '" + p.tok.String() + "'"
		if p.tok.IsLiteral() {
			msg += " " + p.lit
		}
	}
	p.error(pos, msg)
}

func (p *parser) expect(tok token.Token) token.Pos {
	pos := p.pos
	if p.tok != tok {
		p.errorExpected(pos, "'"+tok.String()+"'")
	}
	p.next() // make progress in any case
	return pos
}

func (p *parser) parseIdentifier() string {
	name := p.lit
	p.expect(token.IDENT)
	return name
}

func (p *parser) parseTypeName() (string, bool) {
	pos := p.pos
	name, isIdent := p.parseIdentifier(), true
	if p.tok == token.PERIOD {
		// got a package name, lookup package
		if importPath, found := p.packs[name]; found {
			name = importPath
		} else {
			p.error(pos, "package not declared: "+name)
		}
		p.next()
		name, isIdent = name+"."+p.parseIdentifier(), false
	}
	return name, isIdent
}

// Parses a rule name and returns it. If the rule name is
// a package-qualified type name, the package name is resolved.
// The 2nd result value is true iff the rule name consists of a
// single identifier only (and thus could be a package name).
//
func (p *parser) parseRuleName() (string, bool) {
	name, isIdent := "", false
	switch p.tok {
	case token.IDENT:
		name, isIdent = p.parseTypeName()
	case token.DEFAULT:
		name = "default"
		p.next()
	case token.QUO:
		name = "/"
		p.next()
	default:
		p.errorExpected(p.pos, "rule name")
		p.next() // make progress in any case
	}
	return name, isIdent
}

func (p *parser) parseString() string {
	s := ""
	if p.tok == token.STRING {
		s, _ = strconv.Unquote(p.lit)
		// Unquote may fail with an error, but only if the scanner found
		// an illegal string in the first place. In this case the error
		// has already been reported.
		p.next()
		return s
	} else {
		p.expect(token.STRING)
	}
	return s
}

func (p *parser) parseLiteral() literal {
	s := []byte(p.parseString())

	// A string literal may contain %-format specifiers. To simplify
	// and speed up printing of the literal, split it into segments
	// that start with "%" possibly followed by a last segment that
	// starts with some other character.
	var list []interface{}
	i0 := 0
	for i := 0; i < len(s); i++ {
		if s[i] == '%' && i+1 < len(s) {
			// the next segment starts with a % format
			if i0 < i {
				// the current segment is not empty, split it off
				list = append(list, s[i0:i])
				i0 = i
			}
			i++ // skip %; let loop skip over char after %
		}
	}
	// the final segment may start with any character
	// (it is empty iff the string is empty)
	list = append(list, s[i0:])

	// convert list into a literal
	lit := make(literal, len(list))
	for i := 0; i < len(list); i++ {
		lit[i] = list[i].([]byte)
	}

	return lit
}

func (p *parser) parseField() expr {
	var fname string
	switch p.tok {
	case token.ILLEGAL:
		if p.lit != "@" {
			return nil
		}
		fname = "@"
		p.next()
	case token.MUL:
		fname = "*"
		p.next()
	case token.IDENT:
		fname = p.parseIdentifier()
	default:
		return nil
	}

	var ruleName string
	if p.tok == token.COLON {
		p.next()
		ruleName, _ = p.parseRuleName()
	}

	return &field{fname, ruleName}
}

func (p *parser) parseOperand() (x expr) {
	switch p.tok {
	case token.STRING:
		x = p.parseLiteral()

	case token.LPAREN:
		p.next()
		x = p.parseExpression()
		if p.tok == token.SHR {
			p.next()
			x = &group{x, p.parseExpression()}
		}
		p.expect(token.RPAREN)

	case token.LBRACK:
		p.next()
		x = &option{p.parseExpression()}
		p.expect(token.RBRACK)

	case token.LBRACE:
		p.next()
		x = p.parseExpression()
		var div expr
		if p.tok == token.QUO {
			p.next()
			div = p.parseExpression()
		}
		x = &repetition{x, div}
		p.expect(token.RBRACE)

	default:
		x = p.parseField() // may be nil
	}

	return x
}

func (p *parser) parseSequence() expr {
	var list []interface{}

	for x := p.parseOperand(); x != nil; x = p.parseOperand() {
		list = append(list, x)
	}

	// no need for a sequence if list.Len() < 2
	switch len(list) {
	case 0:
		return nil
	case 1:
		return list[0].(expr)
	}

	// convert list into a sequence
	seq := make(sequence, len(list))
	for i := 0; i < len(list); i++ {
		seq[i] = list[i].(expr)
	}
	return seq
}

func (p *parser) parseExpression() expr {
	var list []interface{}

	for {
		x := p.parseSequence()
		if x != nil {
			list = append(list, x)
		}
		if p.tok != token.OR {
			break
		}
		p.next()
	}

	// no need for an alternatives if list.Len() < 2
	switch len(list) {
	case 0:
		return nil
	case 1:
		return list[0].(expr)
	}

	// convert list into a alternatives
	alt := make(alternatives, len(list))
	for i := 0; i < len(list); i++ {
		alt[i] = list[i].(expr)
	}
	return alt
}

func (p *parser) parseFormat() {
	for p.tok != token.EOF {
		pos := p.pos

		name, isIdent := p.parseRuleName()
		switch p.tok {
		case token.STRING:
			// package declaration
			importPath := p.parseString()

			// add package declaration
			if !isIdent {
				p.error(pos, "illegal package name: "+name)
			} else if _, found := p.packs[name]; !found {
				p.packs[name] = importPath
			} else {
				p.error(pos, "package already declared: "+name)
			}

		case token.ASSIGN:
			// format rule
			p.next()
			x := p.parseExpression()

			// add rule
			if _, found := p.rules[name]; !found {
				p.rules[name] = x
			} else {
				p.error(pos, "format rule already declared: "+name)
			}

		default:
			p.errorExpected(p.pos, "package declaration or format rule")
			p.next() // make progress in any case
		}

		if p.tok == token.SEMICOLON {
			p.next()
		} else {
			break
		}
	}
	p.expect(token.EOF)
}

func remap(p *parser, name string) string {
	i := strings.Index(name, ".")
	if i >= 0 {
		packageName, suffix := name[0:i], name[i:]
		// lookup package
		if importPath, found := p.packs[packageName]; found {
			name = importPath + suffix
		} else {
			var invalidPos token.Position
			p.Error(invalidPos, "package not declared: "+packageName)
		}
	}
	return name
}

// Parse parses a set of format productions from source src. Custom
// formatters may be provided via a map of formatter functions. If
// there are no errors, the result is a Format and the error is nil.
// Otherwise the format is nil and a non-empty ErrorList is returned.
//
func Parse(fset *token.FileSet, filename string, src []byte, fmap FormatterMap) (Format, os.Error) {
	// parse source
	var p parser
	p.init(fset, filename, src)
	p.parseFormat()

	// add custom formatters, if any
	for name, form := range fmap {
		name = remap(&p, name)
		if _, found := p.rules[name]; !found {
			p.rules[name] = &custom{name, form}
		} else {
			var invalidPos token.Position
			p.Error(invalidPos, "formatter already declared: "+name)
		}
	}

	return p.rules, p.GetError(scanner.NoMultiples)
}