package engine

import (
	"git.frostfs.info/TrueCloudLab/policy-engine/pkg/chain"
	"git.frostfs.info/TrueCloudLab/policy-engine/pkg/resource"
)

type defaultChainRouter struct {
	morph MorphRuleChainStorageReader

	local LocalOverrideStorage
}

func NewDefaultChainRouter(morph MorphRuleChainStorageReader) ChainRouter {
	return &defaultChainRouter{
		morph: morph,
	}
}

func NewDefaultChainRouterWithLocalOverrides(morph MorphRuleChainStorageReader, local LocalOverrideStorage) ChainRouter {
	return &defaultChainRouter{
		morph: morph,
		local: local,
	}
}

func (dr *defaultChainRouter) IsAllowed(name chain.Name, rt RequestTarget, r resource.Request) (status chain.Status, ruleFound bool, err error) {
	status, ruleFound, err = dr.checkLocal(name, rt, r)
	if err != nil {
		return chain.NoRuleFound, false, err
	} else if ruleFound {
		// The local overrides have the highest priority and thus
		// morph rules are not considered if a local one is found.
		return
	}

	status, ruleFound, err = dr.checkMorph(name, rt, r)
	return
}

func (dr *defaultChainRouter) checkLocal(name chain.Name, rt RequestTarget, r resource.Request) (status chain.Status, ruleFound bool, err error) {
	if dr.local == nil {
		return
	}

	var hasAllow bool
	for _, target := range rt.Targets() {
		status, ruleFound, err = dr.matchLocalOverrides(name, target, r)
		if err != nil || ruleFound && status != chain.Allow {
			return
		}
		hasAllow = hasAllow || ruleFound
	}

	if hasAllow {
		return chain.Allow, true, nil
	}
	return chain.NoRuleFound, false, nil
}

func (dr *defaultChainRouter) checkMorph(name chain.Name, rt RequestTarget, r resource.Request) (status chain.Status, ruleFound bool, err error) {
	var hasAllow bool
	for _, target := range rt.Targets() {
		status, ruleFound, err = dr.matchMorphRuleChains(name, target, r)
		if err != nil || ruleFound && status != chain.Allow {
			return
		}
		hasAllow = hasAllow || ruleFound
	}

	if hasAllow {
		return chain.Allow, true, nil
	}
	return chain.NoRuleFound, false, nil
}

func (dr *defaultChainRouter) matchLocalOverrides(name chain.Name, target Target, r resource.Request) (status chain.Status, ruleFound bool, err error) {
	localOverrides, err := dr.local.ListOverrides(name, target)
	if err != nil {
		return
	}
	status, ruleFound = dr.getStatusFromChains(localOverrides, r)
	return
}

func (dr *defaultChainRouter) matchMorphRuleChains(name chain.Name, target Target, r resource.Request) (status chain.Status, ruleFound bool, err error) {
	namespaceChains, err := dr.morph.ListMorphRuleChains(name, target)
	if err != nil {
		return chain.NoRuleFound, false, err
	}
	status, ruleFound = dr.getStatusFromChains(namespaceChains, r)
	return
}

func (dr *defaultChainRouter) getStatusFromChains(chains []*chain.Chain, r resource.Request) (chain.Status, bool) {
	var allow bool
	for _, c := range chains {
		if status, found := c.Match(r); found {
			if status != chain.Allow {
				return status, true
			}
			allow = true
		}
	}
	if allow {
		return chain.Allow, true
	}
	return chain.NoRuleFound, false
}