// Copyright 2012 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 collate contains types for comparing and sorting Unicode strings
// according to a given collation order.  Package locale provides a high-level
// interface to collation. Users should typically use that package instead.
package collate

import (
	"exp/norm"
)

// Level identifies the collation comparison level.
// The primary level corresponds to the basic sorting of text.
// The secondary level corresponds to accents and related linguistic elements.
// The tertiary level corresponds to casing and related concepts.
// The quaternary level is derived from the other levels by the
// various algorithms for handling variable elements.
type Level int

const (
	Primary Level = iota
	Secondary
	Tertiary
	Quaternary
	Identity
)

// AlternateHandling identifies the various ways in which variables are handled.
// A rune with a primary weight lower than the variable top is considered a
// variable. 
// See http://www.unicode.org/reports/tr10/#Variable_Weighting for details.
type AlternateHandling int

const (
	// AltShifted sets variables to be ignorable for levels one through three and
	// adds a fourth level based on the values of the ignored levels.
	AltShifted AlternateHandling = iota

	// AltNonIgnorable turns off special handling of variables.
	AltNonIgnorable

	// AltBlanked sets variables and all subsequent primary ignorables to be
	// ignorable at all levels. This is identical to removing all variables
	// and subsequent primary ignorables from the input.
	AltBlanked

	// AltShiftTrimmed is a slight variant of AltShifted that is used to
	// emulate POSIX.
	AltShiftTrimmed
)

// Collator provides functionality for comparing strings for a given
// collation order.
type Collator struct {
	// See SetVariableTop.
	variableTop uint32

	// Strength sets the maximum level to use in comparison.
	Strength Level

	// Alternate specifies an alternative handling of variables.
	Alternate AlternateHandling

	// Backwards specifies the order of sorting at the secondary level.
	// This option exists predominantly to support reverse sorting of accents in French.
	Backwards bool

	// With HiraganaQuaternary enabled, Hiragana codepoints will get lower values
	// than all the other non-variable code points. Strength must be greater or
	// equal to Quaternary for this to take effect.
	HiraganaQuaternary bool

	// If CaseLevel is true, a level consisting only of case characteristics will
	// be inserted in front of the tertiary level.  To ignore accents but take
	// cases into account, set Strength to Primary and CaseLevel to true.
	CaseLevel bool

	// If Numeric is true, any sequence of decimal digits (category is Nd) is sorted
	// at a primary level with its numeric value.  For example, "A-21" < "A-123".
	Numeric bool

	f norm.Form

	t *table
}

// SetVariableTop sets all runes with primary strength less than the primary
// strength of r to be variable and thus affected by alternate handling.
func (c *Collator) SetVariableTop(r rune) {
	// TODO: implement
}

var (
	Root = Collator{}
)

// Buffer holds reusable buffers that can be used during collation.
// Reusing a Buffer for the various calls that accept it may avoid
// unnecessary memory allocations.
type Buffer struct {
	// TODO: try various parameters and techniques, such as using
	// a chan of buffers for a pool.
	ba  [4096]byte
	wa  [512]weights
	key []byte
	ce  []weights
}

func (b *Buffer) init() {
	if b.ce == nil {
		b.ce = b.wa[:0]
		b.key = b.ba[:0]
	} else {
		b.ce = b.ce[:0]
	}
}

// ResetKeys clears the buffer used for generated keys. Calling ResetKeys
// invalidates keys previously obtained from Key or KeyFromString.
func (b *Buffer) ResetKeys() {
	b.ce = b.ce[:0]
	b.key = b.key[:0]
}

// Compare returns an integer comparing the two byte slices.
// The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
func (c *Collator) Compare(buf *Buffer, a, b []byte) int {
	// TODO: implement
	return 0
}

// CompareString returns an integer comparing the two strings.
// The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
func (c *Collator) CompareString(buf *Buffer, a, b string) int {
	// TODO: implement
	return 0
}

// Key returns the collation key for str.
// Passing the buffer buf may avoid memory allocations.
// The returned slice will point to an allocation in Buffer and will retain
// valid until the next call to buf.ResetKeys().
func (c *Collator) Key(buf *Buffer, str []byte) []byte {
	// TODO: implement
	return nil
}

// KeyFromString returns the collation key for str.
// Passing the buffer buf may avoid memory allocations.
// The returned slice will point to an allocation in Buffer and will retain
// valid until the next call to buf.ResetKeys().
func (c *Collator) KeyFromString(buf *Buffer, str string) []byte {
	// TODO: implement
	return nil
}
