/* Copyright 2016 The Bazel Authors. All rights reserved.

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 rule

import (
	"fmt"
	"log"
	"reflect"
	"sort"

	bzl "github.com/bazelbuild/buildtools/build"
)

// KeyValue represents a key-value pair. This gets converted into a
// rule attribute, i.e., a Skylark keyword argument.
type KeyValue struct {
	Key   string
	Value interface{}
}

// GlobValue represents a Bazel glob expression.
type GlobValue struct {
	Patterns []string
	Excludes []string
}

// ExprFromValue converts a value into an expression that can be written into
// a Bazel build file. The following types of values can be converted:
//
// * bools, integers, floats, strings.
// * slices, arrays (converted to lists).
// * maps (converted to select expressions; keys must be rules in
//   @io_bazel_rules_go//go/platform).
// * GlobValue (converted to glob expressions).
// * PlatformStrings (converted to a concatenation of a list and selects).
//
// Converting unsupported types will cause a panic.
func ExprFromValue(val interface{}) bzl.Expr {
	if e, ok := val.(bzl.Expr); ok {
		return e
	}

	rv := reflect.ValueOf(val)
	switch rv.Kind() {
	case reflect.Bool:
		tok := "False"
		if rv.Bool() {
			tok = "True"
		}
		return &bzl.LiteralExpr{Token: tok}

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		return &bzl.LiteralExpr{Token: fmt.Sprintf("%d", val)}

	case reflect.Float32, reflect.Float64:
		return &bzl.LiteralExpr{Token: fmt.Sprintf("%f", val)}

	case reflect.String:
		return &bzl.StringExpr{Value: val.(string)}

	case reflect.Slice, reflect.Array:
		var list []bzl.Expr
		for i := 0; i < rv.Len(); i++ {
			elem := ExprFromValue(rv.Index(i).Interface())
			list = append(list, elem)
		}
		return &bzl.ListExpr{List: list}

	case reflect.Map:
		rkeys := rv.MapKeys()
		sort.Sort(byString(rkeys))
		args := make([]bzl.Expr, len(rkeys))
		for i, rk := range rkeys {
			label := fmt.Sprintf("@io_bazel_rules_go//go/platform:%s", mapKeyString(rk))
			k := &bzl.StringExpr{Value: label}
			v := ExprFromValue(rv.MapIndex(rk).Interface())
			if l, ok := v.(*bzl.ListExpr); ok {
				l.ForceMultiLine = true
			}
			args[i] = &bzl.KeyValueExpr{Key: k, Value: v}
		}
		args = append(args, &bzl.KeyValueExpr{
			Key:   &bzl.StringExpr{Value: "//conditions:default"},
			Value: &bzl.ListExpr{},
		})
		sel := &bzl.CallExpr{
			X:    &bzl.LiteralExpr{Token: "select"},
			List: []bzl.Expr{&bzl.DictExpr{List: args, ForceMultiLine: true}},
		}
		return sel

	case reflect.Struct:
		switch val := val.(type) {
		case GlobValue:
			patternsValue := ExprFromValue(val.Patterns)
			globArgs := []bzl.Expr{patternsValue}
			if len(val.Excludes) > 0 {
				excludesValue := ExprFromValue(val.Excludes)
				globArgs = append(globArgs, &bzl.KeyValueExpr{
					Key:   &bzl.StringExpr{Value: "excludes"},
					Value: excludesValue,
				})
			}
			return &bzl.CallExpr{
				X:    &bzl.LiteralExpr{Token: "glob"},
				List: globArgs,
			}

		case PlatformStrings:
			var pieces []bzl.Expr
			if len(val.Generic) > 0 {
				pieces = append(pieces, ExprFromValue(val.Generic))
			}
			if len(val.OS) > 0 {
				pieces = append(pieces, ExprFromValue(val.OS))
			}
			if len(val.Arch) > 0 {
				pieces = append(pieces, ExprFromValue(val.Arch))
			}
			if len(val.Platform) > 0 {
				pieces = append(pieces, ExprFromValue(val.Platform))
			}
			if len(pieces) == 0 {
				return &bzl.ListExpr{}
			} else if len(pieces) == 1 {
				return pieces[0]
			} else {
				e := pieces[0]
				if list, ok := e.(*bzl.ListExpr); ok {
					list.ForceMultiLine = true
				}
				for _, piece := range pieces[1:] {
					e = &bzl.BinaryExpr{X: e, Y: piece, Op: "+"}
				}
				return e
			}
		}
	}

	log.Panicf("type not supported: %T", val)
	return nil
}

func mapKeyString(k reflect.Value) string {
	switch s := k.Interface().(type) {
	case string:
		return s
	case Platform:
		return s.String()
	default:
		log.Panicf("unexpected map key: %v", k)
		return ""
	}
}

type byString []reflect.Value

var _ sort.Interface = byString{}

func (s byString) Len() int {
	return len(s)
}

func (s byString) Less(i, j int) bool {
	return mapKeyString(s[i]) < mapKeyString(s[j])
}

func (s byString) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}