package processor

import (
	"encoding/json"
	"math"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"

	"apskel-pos-be/internal/constants"
)

// fixedRNG returns the given draws in turn.
type fixedRNG struct{ draws []int64 }

func (r *fixedRNG) Int63n(n int64) (int64, error) {
	v := r.draws[0]
	r.draws = r.draws[1:]
	return v % n, nil
}

func calculate(t *testing.T, rewardType, rules string, result SessionResult, rng RewardRNG) (int64, map[string]any, error) {
	t.Helper()
	c, err := RewardCalculatorFor(rewardType)
	require.NoError(t, err)
	require.NoError(t, c.Validate(json.RawMessage(rules)), "the example rules are valid")
	return c.Calculate(json.RawMessage(rules), result, rng)
}

// The examples of docs/enakgame-prd.md §12.
func TestRewardCalculator_PRDExamples(t *testing.T) {
	t.Run("FIXED", func(t *testing.T) {
		base, _, err := calculate(t, constants.GameRewardTypeFixed, `{"amount": 5}`, SessionResult{}, nil)
		require.NoError(t, err)
		assert.EqualValues(t, 5, base)
	})

	t.Run("SCORE_BASED", func(t *testing.T) {
		rules := `{"bands": [
			{"min": 0, "max": 100, "amount": 1},
			{"min": 101, "max": 500, "amount": 5},
			{"min": 501, "max": 1000, "amount": 10},
			{"min": 1001, "amount": 20}]}`
		for score, want := range map[int64]int64{0: 1, 100: 1, 101: 5, 500: 5, 501: 10, 1000: 10, 1001: 20, 99999: 20} {
			score := score
			base, detail, err := calculate(t, constants.GameRewardTypeScoreBased, rules, SessionResult{Score: &score}, nil)
			require.NoError(t, err)
			assert.Equal(t, want, base, "score %d", score)
			assert.Equal(t, score, detail["score"])
		}
		negative := int64(-1)
		_, _, err := calculate(t, constants.GameRewardTypeScoreBased, rules, SessionResult{Score: &negative}, nil)
		assert.ErrorIs(t, err, ErrRewardResultUnusable)
		_, _, err = calculate(t, constants.GameRewardTypeScoreBased, rules, SessionResult{}, nil)
		assert.ErrorIs(t, err, ErrRewardResultUnusable, "no score")
		capped := `{"bands": [{"min": 0, "max": 10, "amount": 1}]}`
		over := int64(11)
		_, _, err = calculate(t, constants.GameRewardTypeScoreBased, capped, SessionResult{Score: &over}, nil)
		assert.ErrorIs(t, err, ErrRewardResultUnusable, "above the last band's max")
	})

	t.Run("OUTCOME_BASED", func(t *testing.T) {
		rules := `{"outcomes": {"PERFECT": 20, "GOOD": 10, "NORMAL": 5, "FAIL": 0}}`
		for outcome, want := range map[string]int64{"PERFECT": 20, "GOOD": 10, "NORMAL": 5, "FAIL": 0} {
			outcome := outcome
			base, detail, err := calculate(t, constants.GameRewardTypeOutcomeBased, rules, SessionResult{Outcome: &outcome}, nil)
			require.NoError(t, err)
			assert.Equal(t, want, base, outcome)
			assert.Equal(t, outcome, detail["outcome"])
		}
		unknown := "LEGENDARY"
		_, _, err := calculate(t, constants.GameRewardTypeOutcomeBased, rules, SessionResult{Outcome: &unknown}, nil)
		assert.ErrorIs(t, err, ErrRewardResultUnusable)
	})

	t.Run("PROBABILITY", func(t *testing.T) {
		// 0.1% 1000, 1% 100, 10% 10, 88.9% 0, as whole weights out of 1000.
		rules := `{"table": [{"weight": 1, "amount": 1000}, {"weight": 10, "amount": 100}, {"weight": 100, "amount": 10}, {"weight": 889, "amount": 0}]}`
		for roll, want := range map[int64]int64{0: 1000, 1: 100, 10: 100, 11: 10, 110: 10, 111: 0, 999: 0} {
			base, detail, err := calculate(t, constants.GameRewardTypeProbability, rules, SessionResult{}, &fixedRNG{draws: []int64{roll}})
			require.NoError(t, err)
			assert.Equal(t, want, base, "roll %d", roll)
			assert.Equal(t, roll, detail["roll"], "the draw is kept for audit")
			assert.EqualValues(t, 1000, detail["total_weight"])
		}
	})
}

func TestRewardCalculator_ProbabilityDistribution(t *testing.T) {
	rules := json.RawMessage(`{"table": [{"weight": 1, "amount": 1000}, {"weight": 10, "amount": 100}, {"weight": 100, "amount": 10}, {"weight": 889, "amount": 0}]}`)
	c, err := RewardCalculatorFor(constants.GameRewardTypeProbability)
	require.NoError(t, err)

	const draws = 100_000
	counts := map[int64]int{}
	for i := 0; i < draws; i++ {
		base, _, err := c.Calculate(rules, SessionResult{}, CryptoRewardRNG{})
		require.NoError(t, err)
		counts[base]++
	}
	// Within five standard deviations of the expected share: a correct table fails
	// this about once in a few million runs.
	for amount, p := range map[int64]float64{1000: 0.001, 100: 0.01, 10: 0.1, 0: 0.889} {
		got := float64(counts[amount]) / draws
		tolerance := 5 * math.Sqrt(p*(1-p)/draws)
		assert.InDelta(t, p, got, tolerance, "amount %d", amount)
	}
}

func TestRewardCalculator_RejectsInvalidRules(t *testing.T) {
	for name, tc := range map[string]struct{ rewardType, rules string }{
		"unknown type":             {"TIERED", `{}`},
		"not JSON":                 {constants.GameRewardTypeFixed, `{amount: 5}`},
		"unknown field":            {constants.GameRewardTypeFixed, `{"amount": 5, "amonut": 6}`},
		"trailing data":            {constants.GameRewardTypeFixed, `{"amount": 5} {}`},
		"FIXED without amount":     {constants.GameRewardTypeFixed, `{}`},
		"FIXED negative":           {constants.GameRewardTypeFixed, `{"amount": -1}`},
		"FIXED fraction":           {constants.GameRewardTypeFixed, `{"amount": 1.5}`},
		"no bands":                 {constants.GameRewardTypeScoreBased, `{"bands": []}`},
		"bands not from 0":         {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 1, "amount": 1}]}`},
		"bands overlap":            {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "max": 100, "amount": 1}, {"min": 100, "amount": 2}]}`},
		"bands leave a gap":        {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "max": 100, "amount": 1}, {"min": 102, "amount": 2}]}`},
		"open band not last":       {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "amount": 1}, {"min": 101, "amount": 2}]}`},
		"band max below min":       {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "max": -1, "amount": 1}]}`},
		"band out of order":        {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "max": 100, "amount": 1}, {"min": 501, "amount": 3}, {"min": 101, "max": 500, "amount": 2}]}`},
		"band without amount":      {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0}]}`},
		"band negative amount":     {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "amount": -2}]}`},
		"no outcomes":              {constants.GameRewardTypeOutcomeBased, `{"outcomes": {}}`},
		"blank outcome":            {constants.GameRewardTypeOutcomeBased, `{"outcomes": {" ": 1}}`},
		"negative outcome":         {constants.GameRewardTypeOutcomeBased, `{"outcomes": {"WIN": -1}}`},
		"empty table":              {constants.GameRewardTypeProbability, `{"table": []}`},
		"zero weight":              {constants.GameRewardTypeProbability, `{"table": [{"weight": 0, "amount": 1}, {"weight": 1, "amount": 0}]}`},
		"negative weight":          {constants.GameRewardTypeProbability, `{"table": [{"weight": -1, "amount": 1}, {"weight": 2, "amount": 0}]}`},
		"percent weight":           {constants.GameRewardTypeProbability, `{"table": [{"weight": 0.1, "amount": 1000}]}`},
		"entry without weight":     {constants.GameRewardTypeProbability, `{"table": [{"amount": 1}]}`},
		"negative probability pay": {constants.GameRewardTypeProbability, `{"table": [{"weight": 1, "amount": -1}]}`},
		"weights overflow":         {constants.GameRewardTypeProbability, `{"table": [{"weight": 9000000000000000000, "amount": 1}, {"weight": 9000000000000000000, "amount": 0}]}`},
	} {
		c, err := RewardCalculatorFor(tc.rewardType)
		if err == nil {
			err = c.Validate(json.RawMessage(tc.rules))
		}
		assert.ErrorIs(t, err, ErrInvalidRewardRules, name)
	}
}

// EG-902: the Budget Controller scales amounts, rounded down, and nothing else.
func TestRewardCalculator_Scale(t *testing.T) {
	for name, tc := range map[string]struct {
		rewardType, rules string
		multiplier        int64
		want              string
	}{
		"FIXED ×0.9":    {constants.GameRewardTypeFixed, `{"amount": 10}`, 9_000, `{"amount":9}`},
		"FIXED rounds":  {constants.GameRewardTypeFixed, `{"amount": 5}`, 9_000, `{"amount":4}`},
		"FIXED to zero": {constants.GameRewardTypeFixed, `{"amount": 1}`, 9_000, `{"amount":0}`},
		"FIXED ×1.1":    {constants.GameRewardTypeFixed, `{"amount": 10}`, 11_000, `{"amount":11}`},
		"FIXED ×1":      {constants.GameRewardTypeFixed, `{"amount": 7}`, 10_000, `{"amount":7}`},
		"SCORE_BASED":   {constants.GameRewardTypeScoreBased, `{"bands": [{"min": 0, "max": 100, "amount": 1}, {"min": 101, "amount": 20}]}`, 8_100, `{"bands":[{"min":0,"max":100,"amount":0},{"min":101,"amount":16}]}`},
		"OUTCOME_BASED": {constants.GameRewardTypeOutcomeBased, `{"outcomes": {"PERFECT": 20, "GOOD": 10, "FAIL": 0}}`, 9_000, `{"outcomes":{"FAIL":0,"GOOD":9,"PERFECT":18}}`},
		"PROBABILITY":   {constants.GameRewardTypeProbability, `{"table": [{"weight": 1, "amount": 1000}, {"weight": 999, "amount": 0}]}`, 8_500, `{"table":[{"weight":1,"amount":850},{"weight":999,"amount":0}]}`},
	} {
		c, err := RewardCalculatorFor(tc.rewardType)
		require.NoError(t, err)
		scaled, err := c.Scale(json.RawMessage(tc.rules), tc.multiplier)
		require.NoError(t, err, name)
		assert.JSONEq(t, tc.want, string(scaled), name)
		assert.NoError(t, c.Validate(scaled), "%s: scaled rules stay valid", name)
	}

	c, _ := RewardCalculatorFor(constants.GameRewardTypeFixed)
	_, err := c.Scale(json.RawMessage(`{"amount": 9223372036854775807}`), 15_000)
	assert.ErrorIs(t, err, ErrInvalidRewardRules, "overflow is refused, not wrapped")
	_, err = c.Scale(json.RawMessage(`{"amount": -1}`), 9_000)
	assert.ErrorIs(t, err, ErrInvalidRewardRules)

	v, err := scaleRewardAmount(math.MaxInt64/15_000, 15_000)
	require.NoError(t, err)
	assert.EqualValues(t, math.MaxInt64/15_000*15_000/10_000, v)
}