// Copyright 2011 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 template

import (
	"bytes"
	"fmt"
	"os"
	"runtime"
	"strconv"
)

// Template is the representation of a parsed template.
type Template struct {
	// TODO: At the moment, these are all internal to parsing.
	name     string
	root     *listNode
	lex      *lexer
	tokens   chan item
	token    item // token lookahead for parser
	havePeek bool
}

// next returns the next token.
func (t *Template) next() item {
	if t.havePeek {
		t.havePeek = false
	} else {
		t.token = <-t.tokens
	}
	return t.token
}

// backup backs the input stream up one token.
func (t *Template) backup() {
	t.havePeek = true
}

// peek returns but does not consume the next token.
func (t *Template) peek() item {
	if t.havePeek {
		return t.token
	}
	t.token = <-t.tokens
	t.havePeek = true
	return t.token
}

// A node is an element in the parse tree. The interface is trivial.
type node interface {
	typ() nodeType
	String() string
}

type nodeType int

func (t nodeType) typ() nodeType {
	return t
}

const (
	nodeText nodeType = iota
	nodeAction
	nodeCommand
	nodeElse
	nodeEnd
	nodeField
	nodeIdentifier
	nodeList
	nodeNumber
	nodeRange
	nodeString
)

// Nodes.

// listNode holds a sequence of nodes.
type listNode struct {
	nodeType
	nodes []node
}

func newList() *listNode {
	return &listNode{nodeType: nodeList}
}

func (l *listNode) append(n node) {
	l.nodes = append(l.nodes, n)
}

func (l *listNode) String() string {
	b := new(bytes.Buffer)
	fmt.Fprint(b, "[")
	for _, n := range l.nodes {
		fmt.Fprint(b, n)
	}
	fmt.Fprint(b, "]")
	return b.String()
}

// textNode holds plain text.
type textNode struct {
	nodeType
	text string
}

func newText(text string) *textNode {
	return &textNode{nodeType: nodeText, text: text}
}

func (t *textNode) String() string {
	return fmt.Sprintf("(text: %q)", t.text)
}

// actionNode holds an action (something bounded by metacharacters).
type actionNode struct {
	nodeType
	pipeline []*commandNode
}

func newAction() *actionNode {
	return &actionNode{nodeType: nodeAction}
}

func (a *actionNode) append(command *commandNode) {
	a.pipeline = append(a.pipeline, command)
}

func (a *actionNode) String() string {
	return fmt.Sprintf("(action: %v)", a.pipeline)
}

// commandNode holds a command (a pipeline inside an evaluating action).
type commandNode struct {
	nodeType
	args []node // identifier, string, or number
}

func newCommand() *commandNode {
	return &commandNode{nodeType: nodeCommand}
}

func (c *commandNode) append(arg node) {
	c.args = append(c.args, arg)
}

func (c *commandNode) String() string {
	return fmt.Sprintf("(command: %v)", c.args)
}

// identifierNode holds an identifier.
type identifierNode struct {
	nodeType
	ident string
}

func newIdentifier(ident string) *identifierNode {
	return &identifierNode{nodeType: nodeIdentifier, ident: ident}
}

func (i *identifierNode) String() string {
	return fmt.Sprintf("I=%s", i.ident)
}

// fieldNode holds a field (identifier starting with '.'). The period is dropped from the ident.
type fieldNode struct {
	nodeType
	ident string
}

func newField(ident string) *fieldNode {
	return &fieldNode{nodeType: nodeField, ident: ident[1:]} //drop period
}

func (f *fieldNode) String() string {
	return fmt.Sprintf("F=.%s", f.ident)
}

// numberNode holds a number, signed or unsigned, integer, floating, or imaginary.
// The value is parsed and stored under all the types that can represent the value.
// This simulates in a small amount of code the behavior of Go's ideal constants.
// TODO: booleans, complex numbers.
type numberNode struct {
	nodeType
	isInt     bool // number has an integral value
	isUint    bool // number has an unsigned integral value
	isFloat   bool // number has a floating-point value
	imaginary bool // number is imaginary
	int64          // the signed integer value
	uint64         // the unsigned integer value
	float64        // the positive floating-point value
	text      string
}

func newNumber(text string) (*numberNode, os.Error) {
	n := &numberNode{nodeType: nodeNumber, text: text}
	// Imaginary constants can only be floating-point.
	if len(text) > 0 && text[len(text)-1] == 'i' {
		f, err := strconv.Atof64(text[:len(text)-1])
		if err == nil {
			n.imaginary = true
			n.isFloat = true
			n.float64 = f
			return n, nil
		}
	}
	// Do integer test first so we get 0x123 etc.
	u, err := strconv.Btoui64(text, 0) // will fail for -0; fixed below.
	if err == nil {
		n.isUint = true
		n.uint64 = u
	}
	i, err := strconv.Btoi64(text, 0)
	if err == nil {
		n.isInt = true
		n.int64 = i
		if i == 0 {
			n.isUint = true // in case of -0.
			n.uint64 = u
		}
	}
	// If an integer extraction succeeded, promote the float.
	if n.isInt {
		n.isFloat = true
		n.float64 = float64(n.int64)
	} else if n.isUint {
		n.isFloat = true
		n.float64 = float64(n.uint64)
	} else {
		f, err := strconv.Atof64(text)
		if err == nil {
			n.isFloat = true
			n.float64 = f
			// If a floating-point extraction succeeded, extract the int if needed.
			if !n.isInt && float64(int64(f)) == f {
				n.isInt = true
				n.int64 = int64(f)
			}
			if !n.isUint && float64(uint64(f)) == f {
				n.isUint = true
				n.uint64 = uint64(f)
			}
		}
	}
	if !n.isInt && !n.isUint && !n.isFloat {
		return nil, fmt.Errorf("illegal number syntax: %q", text)
	}
	return n, nil
}

func (n *numberNode) String() string {
	return fmt.Sprintf("N=%s", n.text)
}

// stringNode holds a quoted string.
type stringNode struct {
	nodeType
	text string
}

func newString(text string) *stringNode {
	return &stringNode{nodeType: nodeString, text: text}
}

func (s *stringNode) String() string {
	return fmt.Sprintf("S=%#q", s.text)
}

// endNode represents an {{end}} action. It is represented by a nil pointer.
type endNode bool

func newEnd() *endNode {
	return nil
}

func (e *endNode) typ() nodeType {
	return nodeEnd
}

func (e *endNode) String() string {
	return "{{end}}"
}

// elseNode represents an {{else}} action. It is represented by a nil pointer.
type elseNode bool

func newElse() *elseNode {
	return nil
}

func (e *elseNode) typ() nodeType {
	return nodeElse
}

func (e *elseNode) String() string {
	return "{{else}}"
}

// rangeNode represents an {{range}} action and its commands.
type rangeNode struct {
	nodeType
	field    node
	list     *listNode
	elseList *listNode
}

func newRange(field node, list *listNode) *rangeNode {
	return &rangeNode{nodeType: nodeRange, field: field, list: list}
}

func (r *rangeNode) String() string {
	if r.elseList != nil {
		return fmt.Sprintf("({{range %s}} %s {{else}} %s)", r.field, r.list, r.elseList)
	}
	return fmt.Sprintf("({{range %s}} %s)", r.field, r.list)
}

// Parsing.

// New allocates a new template with the given name.
func New(name string) *Template {
	return &Template{
		name: name,
	}
}

// errorf formats the error and terminates processing.
func (t *Template) errorf(format string, args ...interface{}) {
	format = fmt.Sprintf("template: %s:%d: %s", t.name, t.lex.lineNumber(), format)
	panic(fmt.Errorf(format, args...))
}

// error terminates processing.
func (t *Template) error(err os.Error) {
	t.errorf("%s", err)
}

// expect consumes the next token and guarantees it has the required type.
func (t *Template) expect(expected itemType, context string) item {
	token := t.next()
	if token.typ != expected {
		t.errorf("expected %s in %s; got %s", expected, context, token)
	}
	return token
}

// unexpected complains about the token and terminates processing.
func (t *Template) unexpected(token item, context string) {
	t.errorf("unexpected %s in %s", token, context)
}

// Parse parses the template definition string and constructs an efficient representation of the template.
func (t *Template) Parse(s string) (err os.Error) {
	t.lex, t.tokens = lex(t.name, s)
	defer func() {
		e := recover()
		if e != nil {
			if _, ok := e.(runtime.Error); ok {
				panic(e)
			}
			err = e.(os.Error)
		}
		return
	}()
	var next node
	t.root, next = t.itemList(true)
	if next != nil {
		t.errorf("unexpected %s", next)
	}
	return nil
}

// itemList:
//	textOrAction*
// Terminates at EOF and at {{end}} or {{else}}, which is returned separately.
// The toEOF flag tells whether we expect to reach EOF.
func (t *Template) itemList(toEOF bool) (list *listNode, next node) {
	list = newList()
	for t.peek().typ != itemEOF {
		n := t.textOrAction()
		switch n.typ() {
		case nodeEnd, nodeElse:
			return list, n
		}
		list.append(n)
	}
	if !toEOF {
		t.unexpected(t.next(), "input")
	}
	return list, nil
}

// textOrAction:
//	text | action
func (t *Template) textOrAction() node {
	switch token := t.next(); token.typ {
	case itemText:
		return newText(token.val)
	case itemLeftMeta:
		return t.action()
	default:
		t.unexpected(token, "input")
	}
	return nil
}

// Action:
//	control
//	command ("|" command)*
// Left meta is past. Now get actions.
func (t *Template) action() (n node) {
	action := newAction()
	switch token := t.next(); token.typ {
	case itemRange:
		return t.rangeControl()
	case itemElse:
		return t.elseControl()
	case itemEnd:
		return t.endControl()
	}
	t.backup()
Loop:
	for {
		switch token := t.next(); token.typ {
		case itemRightMeta:
			break Loop
		case itemIdentifier, itemField:
			t.backup()
			cmd, err := t.command()
			if err != nil {
				t.error(err)
			}
			action.append(cmd)
		default:
			t.unexpected(token, "command")
		}
	}
	return action
}

// Range:
//	{{range field}} itemList {{end}}
//	{{range field}} itemList {{else}} itemList {{end}}
// Range keyword is past.
func (t *Template) rangeControl() node {
	field := t.expect(itemField, "range")
	t.expect(itemRightMeta, "range")
	list, next := t.itemList(false)
	r := newRange(newField(field.val), list)
	switch next.typ() {
	case nodeEnd: //done
	case nodeElse:
		elseList, next := t.itemList(false)
		if next.typ() != nodeEnd {
			t.errorf("expected end; found %s", next)
		}
		r.elseList = elseList
	}
	return r
}

// End:
//	{{end}}
// End keyword is past.
func (t *Template) endControl() node {
	t.expect(itemRightMeta, "end")
	return newEnd()
}

// Else:
//	{{else}}
// Else keyword is past.
func (t *Template) elseControl() node {
	t.expect(itemRightMeta, "else")
	return newElse()
}

// command:
// space-separated arguments up to a pipeline character or right metacharacter.
// we consume the pipe character but leave the right meta to terminate the action.
func (t *Template) command() (*commandNode, os.Error) {
	cmd := newCommand()
Loop:
	for {
		switch token := t.next(); token.typ {
		case itemRightMeta:
			t.backup()
			break Loop
		case itemPipe:
			break Loop
		case itemError:
			return nil, os.NewError(token.val)
		case itemIdentifier:
			cmd.append(newIdentifier(token.val))
		case itemField:
			cmd.append(newField(token.val))
		case itemNumber:
			if len(cmd.args) == 0 {
				t.errorf("command cannot be %q", token.val)
			}
			number, err := newNumber(token.val)
			if err != nil {
				t.error(err)
			}
			cmd.append(number)
		case itemString, itemRawString:
			if len(cmd.args) == 0 {
				t.errorf("command cannot be %q", token.val)
			}
			s, err := strconv.Unquote(token.val)
			if err != nil {
				return nil, err
			}
			cmd.append(newString(s))
		default:
			t.unexpected(token, "command")
		}
	}
	return cmd, nil
}