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package expr

import (

"fmt"

"github.com/antonmedv/expr/ast"

"github.com/antonmedv/expr/file"

"reflect"

"github.com/antonmedv/expr/checker"

"github.com/antonmedv/expr/compiler"

"github.com/antonmedv/expr/conf"

"github.com/antonmedv/expr/optimizer"

"github.com/antonmedv/expr/parser"

"github.com/antonmedv/expr/vm"

)

// Option for configuring config.

type Option func(c *conf.Config)

// Eval parses, compiles and runs given input.

func Eval(input string, env interface{}) (interface{}, error) {

if _, ok := env.(Option); ok {

return nil, fmt.Errorf("misused expr.Eval: second argument (env) should be passed without expr.Env")

}

tree, err := parser.Parse(input)

if err != nil {

return nil, err

}

program, err := compiler.Compile(tree, nil)

if err != nil {

return nil, err

}

output, err := vm.Run(program, env)

if err != nil {

return nil, err

}

return output, nil

}

// Env specifies expected input of env for type checks.

// If struct is passed, all fields will be treated as variables,

// as well as all fields of embedded structs and struct itself.

// If map is passed, all items will be treated as variables.

// Methods defined on this type will be available as functions.

func Env(env interface{}) Option {

return func(c *conf.Config) {

if _, ok := env.(map[string]interface{}); ok {

c.MapEnv = true

} else {

if reflect.ValueOf(env).Kind() == reflect.Map {

c.DefaultType = reflect.TypeOf(env).Elem()

}

}

c.Strict = true

c.Types = conf.CreateTypesTable(env)

c.Env = env

}

}

// AllowUndefinedVariables allows to use undefined variables inside expressions.

// This can be used with expr.Env option to partially define a few variables.

// Note what this option is only works in map environment are used, otherwise

// runtime.fetch will panic as there is no way to get missing field zero value.

func AllowUndefinedVariables() Option {

return func(c *conf.Config) {

c.Strict = false

}

}

// Operator allows to override binary operator with function.

func Operator(operator string, fn ...string) Option {

return func(c *conf.Config) {

c.Operators[operator] = append(c.Operators[operator], fn...)

}

}

// ConstExpr defines func expression as constant. If all argument to this function is constants,

// then it can be replaced by result of this func call on compile step.

func ConstExpr(fn string) Option {

return func(c *conf.Config) {

c.ConstExpr(fn)

}

}

// AsBool tells the compiler to expect boolean result.

func AsBool() Option {

return func(c *conf.Config) {

c.Expect = reflect.Bool

}

}

// AsInt64 tells the compiler to expect int64 result.

func AsInt64() Option {

return func(c *conf.Config) {

c.Expect = reflect.Int64

}

}

// AsFloat64 tells the compiler to expect float64 result.

func AsFloat64() Option {

return func(c *conf.Config) {

c.Expect = reflect.Float64

}

}

// Optimize turns optimizations on or off.

func Optimize(b bool) Option {

return func(c *conf.Config) {

c.Optimize = b

}

}

// Patch adds visitor to list of visitors what will be applied before compiling AST to bytecode.

func Patch(visitor ast.Visitor) Option {

return func(c *conf.Config) {

c.Visitors = append(c.Visitors, visitor)

}

}

// Compile parses and compiles given input expression to bytecode program.

func Compile(input string, ops ...Option) (*vm.Program, error) {

config := &conf.Config{

Operators: make(map[string][]string),

ConstExprFns: make(map[string]reflect.Value),

Optimize: true,

}

for _, op := range ops {

op(config)

}

if err := config.Check(); err != nil {

return nil, err

}

tree, err := parser.Parse(input)

if err != nil {

return nil, err

}

_, err = checker.Check(tree, config)

// If we have a patch to apply, it may fix out error and

// second type check is needed. Otherwise it is an error.

if err != nil && len(config.Visitors) == 0 {

return nil, err

}

// Patch operators before Optimize, as we may also mark it as ConstExpr.

compiler.PatchOperators(&tree.Node, config)

if len(config.Visitors) >= 0 {

for _, v := range config.Visitors {

ast.Walk(&tree.Node, v)

}

_, err = checker.Check(tree, config)

if err != nil {

return nil, err

}

}

if config.Optimize {

err = optimizer.Optimize(&tree.Node, config)

if err != nil {

if fileError, ok := err.(*file.Error); ok {

return nil, fileError.Bind(tree.Source)

}

return nil, err

}

}

program, err := compiler.Compile(tree, config)

if err != nil {

return nil, err

}

return program, nil

}

// Run evaluates given bytecode program.

func Run(program *vm.Program, env interface{}) (interface{}, error) {

return vm.Run(program, env)

}