package chain

import (
	"encoding/json"
	"fmt"
	"strings"

	"git.frostfs.info/TrueCloudLab/policy-engine/pkg/resource"
	"git.frostfs.info/TrueCloudLab/policy-engine/util"
	"golang.org/x/exp/slices"
)

// ID is the ID of rule chain.
type ID string

// MatchType is the match type for chain rules.
type MatchType uint8

const (
	// MatchTypeDenyPriority rejects the request if any `Deny` is specified.
	MatchTypeDenyPriority MatchType = 0
	// MatchTypeFirstMatch returns the first rule action matched to the request.
	MatchTypeFirstMatch MatchType = 1
)

type Chain struct {
	ID ID

	Rules []Rule

	MatchType MatchType
}

func (id ID) MarshalJSON() ([]byte, error) {
	return json.Marshal([]byte(id))
}

func (id *ID) UnmarshalJSON(data []byte) error {
	var idRaw []byte
	if err := json.Unmarshal(data, &idRaw); err != nil {
		return err
	}
	*id = ID(idRaw)
	return nil
}

func (c *Chain) Bytes() []byte {
	data, err := json.Marshal(c)
	if err != nil {
		panic(err)
	}
	return data
}

func (c *Chain) DecodeBytes(b []byte) error {
	return json.Unmarshal(b, c)
}

type Rule struct {
	Status Status
	// Actions the operation is applied to.
	Actions Actions
	// List of the resources the operation is applied to.
	Resources Resources
	// True iff individual conditions must be combined with the logical OR.
	// By default AND is used, so _each_ condition must pass.
	Any       bool
	Condition []Condition
}

type Actions struct {
	Inverted bool
	Names    []string
}

type Resources struct {
	Inverted bool
	Names    []string
}

type Condition struct {
	Op     ConditionType
	Object ObjectType
	Key    string
	Value  string
}

type ObjectType byte

const (
	ObjectResource ObjectType = iota
	ObjectRequest
)

type ConditionType byte

// TODO @fyrchik: reduce the number of conditions.
// Everything from here should be expressable, but we do not need them all.
// https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements_condition_operators.html
const (
	// String condition operators.
	CondStringEquals ConditionType = iota
	CondStringNotEquals
	CondStringEqualsIgnoreCase
	CondStringNotEqualsIgnoreCase
	CondStringLike
	CondStringNotLike
	CondStringLessThan
	CondStringLessThanEquals
	CondStringGreaterThan
	CondStringGreaterThanEquals

	// Numeric condition operators.
	CondNumericEquals
	CondNumericNotEquals
	CondNumericLessThan
	CondNumericLessThanEquals
	CondNumericGreaterThan
	CondNumericGreaterThanEquals

	CondSliceContains
)

func (c ConditionType) String() string {
	switch c {
	case CondStringEquals:
		return "StringEquals"
	case CondStringNotEquals:
		return "StringNotEquals"
	case CondStringEqualsIgnoreCase:
		return "StringEqualsIgnoreCase"
	case CondStringNotEqualsIgnoreCase:
		return "StringNotEqualsIgnoreCase"
	case CondStringLike:
		return "StringLike"
	case CondStringNotLike:
		return "StringNotLike"
	case CondStringLessThan:
		return "StringLessThan"
	case CondStringLessThanEquals:
		return "StringLessThanEquals"
	case CondStringGreaterThan:
		return "StringGreaterThan"
	case CondStringGreaterThanEquals:
		return "StringGreaterThanEquals"
	case CondNumericEquals:
		return "NumericEquals"
	case CondNumericNotEquals:
		return "NumericNotEquals"
	case CondNumericLessThan:
		return "NumericLessThan"
	case CondNumericLessThanEquals:
		return "NumericLessThanEquals"
	case CondNumericGreaterThan:
		return "NumericGreaterThan"
	case CondNumericGreaterThanEquals:
		return "NumericGreaterThanEquals"
	case CondSliceContains:
		return "SliceContains"
	default:
		return "unknown condition type"
	}
}

const condSliceContainsDelimiter = "\x00"

// FormCondSliceContainsValue builds value for ObjectResource or ObjectRequest property
// that can be matched by CondSliceContains condition.
func FormCondSliceContainsValue(values []string) string {
	return strings.Join(values, condSliceContainsDelimiter)
}

func (c *Condition) Match(req resource.Request) bool {
	var val string
	switch c.Object {
	case ObjectResource:
		val = req.Resource().Property(c.Key)
	case ObjectRequest:
		val = req.Property(c.Key)
	default:
		panic(fmt.Sprintf("unknown condition type: %d", c.Object))
	}

	switch c.Op {
	default:
		panic(fmt.Sprintf("unimplemented: %d", c.Op))
	case CondStringEquals:
		return val == c.Value
	case CondStringNotEquals:
		return val != c.Value
	case CondStringEqualsIgnoreCase:
		return strings.EqualFold(val, c.Value)
	case CondStringNotEqualsIgnoreCase:
		return !strings.EqualFold(val, c.Value)
	case CondStringLike:
		return util.GlobMatch(val, c.Value)
	case CondStringNotLike:
		return !util.GlobMatch(val, c.Value)
	case CondStringLessThan:
		return val < c.Value
	case CondStringLessThanEquals:
		return val <= c.Value
	case CondStringGreaterThan:
		return val > c.Value
	case CondStringGreaterThanEquals:
		return val >= c.Value
	case CondSliceContains:
		return slices.Contains(strings.Split(val, condSliceContainsDelimiter), c.Value)
	}
}

func (r *Rule) Match(req resource.Request) (status Status, matched bool) {
	found := len(r.Resources.Names) == 0
	for i := range r.Resources.Names {
		if util.GlobMatch(req.Resource().Name(), r.Resources.Names[i]) != r.Resources.Inverted {
			found = true
			break
		}
	}
	if !found {
		return NoRuleFound, false
	}
	for i := range r.Actions.Names {
		if util.GlobMatch(req.Operation(), r.Actions.Names[i]) != r.Actions.Inverted {
			return r.matchCondition(req)
		}
	}
	return NoRuleFound, false
}

func (r *Rule) matchCondition(obj resource.Request) (status Status, matched bool) {
	if r.Any {
		return r.matchAny(obj)
	}
	return r.matchAll(obj)
}

func (r *Rule) matchAny(obj resource.Request) (status Status, matched bool) {
	for i := range r.Condition {
		if r.Condition[i].Match(obj) {
			return r.Status, true
		}
	}
	return NoRuleFound, false
}

func (r *Rule) matchAll(obj resource.Request) (status Status, matched bool) {
	for i := range r.Condition {
		if !r.Condition[i].Match(obj) {
			return NoRuleFound, false
		}
	}
	return r.Status, true
}

func (c *Chain) Match(req resource.Request) (status Status, matched bool) {
	switch c.MatchType {
	case MatchTypeDenyPriority:
		return c.denyPriority(req)
	case MatchTypeFirstMatch:
		return c.firstMatch(req)
	default:
		panic(fmt.Sprintf("unknown MatchType %d", c.MatchType))
	}
}

func (c *Chain) firstMatch(req resource.Request) (status Status, matched bool) {
	for i := range c.Rules {
		status, matched := c.Rules[i].Match(req)
		if matched {
			return status, true
		}
	}
	return NoRuleFound, false
}

func (c *Chain) denyPriority(req resource.Request) (status Status, matched bool) {
	var allowFound bool
	for i := range c.Rules {
		status, matched := c.Rules[i].Match(req)
		if !matched {
			continue
		}
		if status != Allow {
			return status, true
		}
		allowFound = true
	}
	if allowFound {
		return Allow, true
	}
	return NoRuleFound, false
}