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// Copyright 2009 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 quick implements utility functions to help with black box testing.
package quick

import (
        "flag"
        "fmt"
        "math"
        "math/rand"
        "reflect"
        "strings"
)

var defaultMaxCount *int = flag.Int("quickchecks", 100, "The default number of iterations for each check")

// A Generator can generate random values of its own type.
type Generator interface {
        // Generate returns a random instance of the type on which it is a
        // method using the size as a size hint.
        Generate(rand *rand.Rand, size int) reflect.Value
}

// randFloat32 generates a random float taking the full range of a float32.
func randFloat32(rand *rand.Rand) float32 {
        f := rand.Float64() * math.MaxFloat32
        if rand.Int()&1 == 1 {
                f = -f
        }
        return float32(f)
}

// randFloat64 generates a random float taking the full range of a float64.
func randFloat64(rand *rand.Rand) float64 {
        f := rand.Float64()
        if rand.Int()&1 == 1 {
                f = -f
        }
        return f
}

// randInt64 returns a random integer taking half the range of an int64.
func randInt64(rand *rand.Rand) int64 { return rand.Int63() - 1<<62 }

// complexSize is the maximum length of arbitrary values that contain other
// values.
const complexSize = 50

// Value returns an arbitrary value of the given type.
// If the type implements the Generator interface, that will be used.
// Note: in order to create arbitrary values for structs, all the members must be public.
func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool) {
        if m, ok := reflect.Zero(t).Interface().(Generator); ok {
                return m.Generate(rand, complexSize), true
        }

        switch concrete := t; concrete.Kind() {
        case reflect.Bool:
                return reflect.ValueOf(rand.Int()&1 == 0), true
        case reflect.Float32:
                return reflect.ValueOf(randFloat32(rand)), true
        case reflect.Float64:
                return reflect.ValueOf(randFloat64(rand)), true
        case reflect.Complex64:
                return reflect.ValueOf(complex(randFloat32(rand), randFloat32(rand))), true
        case reflect.Complex128:
                return reflect.ValueOf(complex(randFloat64(rand), randFloat64(rand))), true
        case reflect.Int16:
                return reflect.ValueOf(int16(randInt64(rand))), true
        case reflect.Int32:
                return reflect.ValueOf(int32(randInt64(rand))), true
        case reflect.Int64:
                return reflect.ValueOf(randInt64(rand)), true
        case reflect.Int8:
                return reflect.ValueOf(int8(randInt64(rand))), true
        case reflect.Int:
                return reflect.ValueOf(int(randInt64(rand))), true
        case reflect.Uint16:
                return reflect.ValueOf(uint16(randInt64(rand))), true
        case reflect.Uint32:
                return reflect.ValueOf(uint32(randInt64(rand))), true
        case reflect.Uint64:
                return reflect.ValueOf(uint64(randInt64(rand))), true
        case reflect.Uint8:
                return reflect.ValueOf(uint8(randInt64(rand))), true
        case reflect.Uint:
                return reflect.ValueOf(uint(randInt64(rand))), true
        case reflect.Uintptr:
                return reflect.ValueOf(uintptr(randInt64(rand))), true
        case reflect.Map:
                numElems := rand.Intn(complexSize)
                m := reflect.MakeMap(concrete)
                for i := 0; i < numElems; i++ {
                        key, ok1 := Value(concrete.Key(), rand)
                        value, ok2 := Value(concrete.Elem(), rand)
                        if !ok1 || !ok2 {
                                return reflect.Value{}, false
                        }
                        m.SetMapIndex(key, value)
                }
                return m, true
        case reflect.Ptr:
                v, ok := Value(concrete.Elem(), rand)
                if !ok {
                        return reflect.Value{}, false
                }
                p := reflect.New(concrete.Elem())
                p.Elem().Set(v)
                return p, true
        case reflect.Slice:
                numElems := rand.Intn(complexSize)
                s := reflect.MakeSlice(concrete, numElems, numElems)
                for i := 0; i < numElems; i++ {
                        v, ok := Value(concrete.Elem(), rand)
                        if !ok {
                                return reflect.Value{}, false
                        }
                        s.Index(i).Set(v)
                }
                return s, true
        case reflect.String:
                numChars := rand.Intn(complexSize)
                codePoints := make([]rune, numChars)
                for i := 0; i < numChars; i++ {
                        codePoints[i] = rune(rand.Intn(0x10ffff))
                }
                return reflect.ValueOf(string(codePoints)), true
        case reflect.Struct:
                s := reflect.New(t).Elem()
                for i := 0; i < s.NumField(); i++ {
                        v, ok := Value(concrete.Field(i).Type, rand)
                        if !ok {
                                return reflect.Value{}, false
                        }
                        s.Field(i).Set(v)
                }
                return s, true
        default:
                return reflect.Value{}, false
        }

        return
}

// A Config structure contains options for running a test.
type Config struct {
        // MaxCount sets the maximum number of iterations. If zero,
        // MaxCountScale is used.
        MaxCount int
        // MaxCountScale is a non-negative scale factor applied to the default
        // maximum. If zero, the default is unchanged.
        MaxCountScale float64
        // If non-nil, rand is a source of random numbers. Otherwise a default
        // pseudo-random source will be used.
        Rand *rand.Rand
        // If non-nil, Values is a function which generates a slice of arbitrary
        // Values that are congruent with the arguments to the function being
        // tested. Otherwise, Values is used to generate the values.
        Values func([]reflect.Value, *rand.Rand)
}

var defaultConfig Config

// getRand returns the *rand.Rand to use for a given Config.
func (c *Config) getRand() *rand.Rand {
        if c.Rand == nil {
                return rand.New(rand.NewSource(0))
        }
        return c.Rand
}

// getMaxCount returns the maximum number of iterations to run for a given
// Config.
func (c *Config) getMaxCount() (maxCount int) {
        maxCount = c.MaxCount
        if maxCount == 0 {
                if c.MaxCountScale != 0 {
                        maxCount = int(c.MaxCountScale * float64(*defaultMaxCount))
                } else {
                        maxCount = *defaultMaxCount
                }
        }

        return
}

// A SetupError is the result of an error in the way that check is being
// used, independent of the functions being tested.
type SetupError string

func (s SetupError) Error() string { return string(s) }

// A CheckError is the result of Check finding an error.
type CheckError struct {
        Count int
        In    []interface{}
}

func (s *CheckError) Error() string {
        return fmt.Sprintf("#%d: failed on input %s", s.Count, toString(s.In))
}

// A CheckEqualError is the result CheckEqual finding an error.
type CheckEqualError struct {
        CheckError
        Out1 []interface{}
        Out2 []interface{}
}

func (s *CheckEqualError) Error() string {
        return fmt.Sprintf("#%d: failed on input %s. Output 1: %s. Output 2: %s", s.Count, toString(s.In), toString(s.Out1), toString(s.Out2))
}

// Check looks for an input to f, any function that returns bool,
// such that f returns false.  It calls f repeatedly, with arbitrary
// values for each argument.  If f returns false on a given input,
// Check returns that input as a *CheckError.
// For example:
//
//      func TestOddMultipleOfThree(t *testing.T) {
//              f := func(x int) bool {
//                      y := OddMultipleOfThree(x)
//                      return y%2 == 1 && y%3 == 0
//              }
//              if err := quick.Check(f, nil); err != nil {
//                      t.Error(err)
//              }
//      }
func Check(function interface{}, config *Config) (err error) {
        if config == nil {
                config = &defaultConfig
        }

        f, fType, ok := functionAndType(function)
        if !ok {
                err = SetupError("argument is not a function")
                return
        }

        if fType.NumOut() != 1 {
                err = SetupError("function returns more than one value.")
                return
        }
        if fType.Out(0).Kind() != reflect.Bool {
                err = SetupError("function does not return a bool")
                return
        }

        arguments := make([]reflect.Value, fType.NumIn())
        rand := config.getRand()
        maxCount := config.getMaxCount()

        for i := 0; i < maxCount; i++ {
                err = arbitraryValues(arguments, fType, config, rand)
                if err != nil {
                        return
                }

                if !f.Call(arguments)[0].Bool() {
                        err = &CheckError{i + 1, toInterfaces(arguments)}
                        return
                }
        }

        return
}

// CheckEqual looks for an input on which f and g return different results.
// It calls f and g repeatedly with arbitrary values for each argument.
// If f and g return different answers, CheckEqual returns a *CheckEqualError
// describing the input and the outputs.
func CheckEqual(f, g interface{}, config *Config) (err error) {
        if config == nil {
                config = &defaultConfig
        }

        x, xType, ok := functionAndType(f)
        if !ok {
                err = SetupError("f is not a function")
                return
        }
        y, yType, ok := functionAndType(g)
        if !ok {
                err = SetupError("g is not a function")
                return
        }

        if xType != yType {
                err = SetupError("functions have different types")
                return
        }

        arguments := make([]reflect.Value, xType.NumIn())
        rand := config.getRand()
        maxCount := config.getMaxCount()

        for i := 0; i < maxCount; i++ {
                err = arbitraryValues(arguments, xType, config, rand)
                if err != nil {
                        return
                }

                xOut := toInterfaces(x.Call(arguments))
                yOut := toInterfaces(y.Call(arguments))

                if !reflect.DeepEqual(xOut, yOut) {
                        err = &CheckEqualError{CheckError{i + 1, toInterfaces(arguments)}, xOut, yOut}
                        return
                }
        }

        return
}

// arbitraryValues writes Values to args such that args contains Values
// suitable for calling f.
func arbitraryValues(args []reflect.Value, f reflect.Type, config *Config, rand *rand.Rand) (err error) {
        if config.Values != nil {
                config.Values(args, rand)
                return
        }

        for j := 0; j < len(args); j++ {
                var ok bool
                args[j], ok = Value(f.In(j), rand)
                if !ok {
                        err = SetupError(fmt.Sprintf("cannot create arbitrary value of type %s for argument %d", f.In(j), j))
                        return
                }
        }

        return
}

func functionAndType(f interface{}) (v reflect.Value, t reflect.Type, ok bool) {
        v = reflect.ValueOf(f)
        ok = v.Kind() == reflect.Func
        if !ok {
                return
        }
        t = v.Type()
        return
}

func toInterfaces(values []reflect.Value) []interface{} {
        ret := make([]interface{}, len(values))
        for i, v := range values {
                ret[i] = v.Interface()
        }
        return ret
}

func toString(interfaces []interface{}) string {
        s := make([]string, len(interfaces))
        for i, v := range interfaces {
                s[i] = fmt.Sprintf("%#v", v)
        }
        return strings.Join(s, ", ")
}