/*
   Copyright 2020 The Compose Specification Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package loader

import (
	"fmt"
	"strconv"
	"strings"

	"github.com/compose-spec/compose-go/v2/tree"
	"gopkg.in/yaml.v3"
)

type ResetProcessor struct {
	target       interface{}
	paths        []tree.Path
	visitedNodes map[*yaml.Node]string
}

// UnmarshalYAML implement yaml.Unmarshaler
func (p *ResetProcessor) UnmarshalYAML(value *yaml.Node) error {
	resolved, err := p.resolveReset(value, tree.NewPath())
	p.visitedNodes = nil
	if err != nil {
		return err
	}
	return resolved.Decode(p.target)
}

// resolveReset detects `!reset` tag being set on yaml nodes and record position in the yaml tree
func (p *ResetProcessor) resolveReset(node *yaml.Node, path tree.Path) (*yaml.Node, error) {
	pathStr := path.String()
	// If the path contains "<<", removing the "<<" element and merging the path
	if strings.Contains(pathStr, ".<<") {
		path = tree.NewPath(strings.Replace(pathStr, ".<<", "", 1))
	}

	// Check for cycle
	if p.visitedNodes == nil {
		p.visitedNodes = make(map[*yaml.Node]string)
	}

	// Check for cycle by seeing if the node has already been visited at this path
	if previousPath, found := p.visitedNodes[node]; found {
		// If the current node has been visited, we have a cycle if the previous path is a prefix
		if strings.HasPrefix(pathStr, previousPath) {
			return nil, fmt.Errorf("cycle detected at path: %s", pathStr)
		}
	}

	// Mark the current node as visited
	p.visitedNodes[node] = pathStr + "."

	// If the node is an alias, We need to process the alias field in order to consider the !override and !reset tags
	if node.Kind == yaml.AliasNode {
		return p.resolveReset(node.Alias, path)
	}

	if node.Tag == "!reset" {
		p.paths = append(p.paths, path)
		return nil, nil
	}
	if node.Tag == "!override" {
		p.paths = append(p.paths, path)
		return node, nil
	}
	switch node.Kind {
	case yaml.SequenceNode:
		var nodes []*yaml.Node
		for idx, v := range node.Content {
			next := path.Next(strconv.Itoa(idx))
			resolved, err := p.resolveReset(v, next)
			if err != nil {
				return nil, err
			}
			if resolved != nil {
				nodes = append(nodes, resolved)
			}
		}
		node.Content = nodes
	case yaml.MappingNode:
		var key string
		var nodes []*yaml.Node
		for idx, v := range node.Content {
			if idx%2 == 0 {
				key = v.Value
			} else {
				resolved, err := p.resolveReset(v, path.Next(key))
				if err != nil {
					return nil, err
				}
				if resolved != nil {
					nodes = append(nodes, node.Content[idx-1], resolved)
				}
			}
		}
		node.Content = nodes
	}
	return node, nil
}

// Apply finds the go attributes matching recorded paths and reset them to zero value
func (p *ResetProcessor) Apply(target any) error {
	return p.applyNullOverrides(target, tree.NewPath())
}

// applyNullOverrides set val to Zero if it matches any of the recorded paths
func (p *ResetProcessor) applyNullOverrides(target any, path tree.Path) error {
	switch v := target.(type) {
	case map[string]any:
	KEYS:
		for k, e := range v {
			next := path.Next(k)
			for _, pattern := range p.paths {
				if next.Matches(pattern) {
					delete(v, k)
					continue KEYS
				}
			}
			err := p.applyNullOverrides(e, next)
			if err != nil {
				return err
			}
		}
	case []any:
	ITER:
		for i, e := range v {
			next := path.Next(fmt.Sprintf("[%d]", i))
			for _, pattern := range p.paths {
				if next.Matches(pattern) {
					continue ITER
					// TODO(ndeloof) support removal from sequence
				}
			}
			err := p.applyNullOverrides(e, next)
			if err != nil {
				return err
			}
		}
	}
	return nil
}