// Copyright 2020 CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package adt

import (
	"strconv"
	"strings"

	"cuelang.org/go/cue/ast"
	"cuelang.org/go/cue/errors"
	"cuelang.org/go/cue/token"
	"cuelang.org/go/internal"
)

// A Feature is an encoded form of a label which comprises a compact
// representation of an integer or string label as well as a label type.
type Feature uint32

// TODO: create labels such that list are sorted first (or last with index.)

// InvalidLabel is an encoding of an erroneous label.
const InvalidLabel Feature = 0x7 // 0xb111

// MaxIndex indicates the maximum number of unique strings that are used for
// labeles within this CUE implementation.
const MaxIndex int64 = 1<<28 - 1

// A StringIndexer coverts strings to and from an index that is unique for a
// given string.
type StringIndexer interface {
	// ToIndex returns a unique positive index for s (0 < index < 2^28-1).
	//
	// For each pair of strings s and t it must return the same index if and
	// only if s == t.
	StringToIndex(s string) (index int64)

	// ToString returns a string s for index such that ToIndex(s) == index.
	IndexToString(index int64) string
}

// SelectorString reports the shortest string representation of f when used as a
// selector.
func (f Feature) SelectorString(index StringIndexer) string {
	if f == 0 {
		return "_"
	}
	x := f.Index()
	switch f.Typ() {
	case IntLabel:
		return strconv.Itoa(int(x))
	case StringLabel:
		s := index.IndexToString(int64(x))
		if ast.IsValidIdent(s) && !internal.IsDefOrHidden(s) {
			return s
		}
		return strconv.Quote(s)
	default:
		return index.IndexToString(int64(x))
	}
}

// StringValue reports the string value of f, which must be a string label.
func (f Feature) StringValue(index StringIndexer) string {
	if !f.IsString() {
		panic("not a string label")
	}
	x := f.Index()
	return index.IndexToString(int64(x))
}

// ToValue converts a label to a value, which will be a Num for integer labels
// and a String for string labels. It panics when f is not a regular label.
func (f Feature) ToValue(ctx *OpContext) Value {
	if !f.IsRegular() {
		panic("not a regular label")
	}
	if f.IsInt() {
		return ctx.NewInt64(int64(f.Index()))
	}
	x := f.Index()
	str := ctx.IndexToString(int64(x))
	return ctx.NewString(str)
}

// StringLabel converts s to a string label.
func (c *OpContext) StringLabel(s string) Feature {
	return labelFromValue(c, &String{Str: s})
}

// MakeStringLabel creates a label for the given string.
func MakeStringLabel(r StringIndexer, s string) Feature {
	i := r.StringToIndex(s)

	// TODO: set position if it exists.
	f, err := MakeLabel(nil, i, StringLabel)
	if err != nil {
		panic("out of free string slots")
	}
	return f
}

// MakeIdentLabel creates a label for the given identifier.
func MakeIdentLabel(r StringIndexer, s string) Feature {
	i := r.StringToIndex(s)
	t := StringLabel
	switch {
	case strings.HasPrefix(s, "#_"):
		t = HiddenDefinitionLabel
	case strings.HasPrefix(s, "#"):
		t = DefinitionLabel
	case strings.HasPrefix(s, "_"):
		t = HiddenLabel
	}
	f, err := MakeLabel(nil, i, t)
	if err != nil {
		panic("out of free string slots")
	}
	return f
}

const msgGround = "invalid non-ground value %s (must be concrete %s)"

func labelFromValue(ctx *OpContext, v Value) Feature {
	var i int64
	var t FeatureType
	if isError(v) {
		return InvalidLabel
	}
	switch v.Kind() {
	case IntKind, NumKind:
		x, _ := v.(*Num)
		if x == nil {
			ctx.addErrf(IncompleteError, pos(v), msgGround, v, "int")
			return InvalidLabel
		}
		t = IntLabel
		var err error
		i, err = x.X.Int64()
		if err != nil || x.K != IntKind {
			ctx.AddErrf("invalid label %v: %v", v, err)
			return InvalidLabel
		}
		if i < 0 {
			ctx.AddErrf("invalid negative index %s", ctx.Str(x))
			return InvalidLabel
		}

	case StringKind:
		x, _ := v.(*String)
		if x == nil {
			ctx.addErrf(IncompleteError, pos(v), msgGround, v, "string")
			return InvalidLabel
		}
		t = StringLabel
		i = ctx.StringToIndex(x.Str)

	default:
		ctx.AddErrf("invalid label type %v", v.Kind())
		return InvalidLabel
	}

	// TODO: set position if it exists.
	f, err := MakeLabel(nil, i, t)
	if err != nil {
		ctx.AddErr(err)
	}
	return f
}

// MakeLabel creates a label. It reports an error if the index is out of range.
func MakeLabel(src ast.Node, index int64, f FeatureType) (Feature, errors.Error) {
	if 0 > index || index > MaxIndex {
		p := token.NoPos
		if src != nil {
			p = src.Pos()
		}
		return InvalidLabel,
			errors.Newf(p, "int label out of range (%d not >=0 and <= %d)",
				index, MaxIndex)
	}
	return Feature(index)<<indexShift | Feature(f), nil
}

// A FeatureType indicates the type of label.
type FeatureType int8

const (
	StringLabel           FeatureType = 0 // 0b000
	IntLabel              FeatureType = 1 // 0b001
	DefinitionLabel       FeatureType = 3 // 0b011
	HiddenLabel           FeatureType = 6 // 0b110
	HiddenDefinitionLabel FeatureType = 7 // 0b111

	// letLabel              FeatureType = 0b010

	fTypeMask Feature = 7 // 0b111

	indexShift = 3
)

// IsValid reports whether f is a valid label.
func (f Feature) IsValid() bool { return f != InvalidLabel }

// Typ reports the type of label.
func (f Feature) Typ() FeatureType { return FeatureType(f & fTypeMask) }

// IsRegular reports whether a label represents a data field.
func (f Feature) IsRegular() bool { return f.Typ() <= IntLabel }

// IsString reports whether a label represents a regular field.
func (f Feature) IsString() bool { return f.Typ() == StringLabel }

// IsDef reports whether the label is a definition (an identifier starting with
// # or #_.
func (f Feature) IsDef() bool {
	if f == InvalidLabel {
		// TODO(perf): do more mask trickery to avoid this branch.
		return false
	}
	return f.Typ()&DefinitionLabel == DefinitionLabel
}

// IsInt reports whether this is an integer index.
func (f Feature) IsInt() bool { return f.Typ() == IntLabel }

// IsHidden reports whether this label is hidden (an identifier starting with
// _ or #_).
func (f Feature) IsHidden() bool {
	if f == InvalidLabel {
		// TODO(perf): do more mask trickery to avoid this branch.
		return false
	}
	return f.Typ()&HiddenLabel == HiddenLabel
}

// Index reports the abstract index associated with f.
func (f Feature) Index() int { return int(f >> indexShift) }

// TODO: should let declarations be implemented as fields?
// func (f Feature) isLet() bool  { return f.typ() == letLabel }