package ckconfig

import (
	"bytes"
	"fmt"
	"strings"
	"text/template"

	commandkit "go.maximumdirect.net/commandkit"
	configkit "go.maximumdirect.net/configkit"
)

type explanationReport struct {
	Scope           string                 `json:"scope" yaml:"scope"`
	Path            string                 `json:"path" yaml:"path"`
	Effective       snapshotDTO            `json:"effective" yaml:"effective"`
	Origin          explanationOriginDTO   `json:"origin" yaml:"origin"`
	History         []explanationChangeDTO `json:"history" yaml:"history"`
	SecretReference *secretReferenceDTO    `json:"secret_reference" yaml:"secret_reference"`
	Metadata        *explanationMetadata   `json:"metadata,omitempty"`
}

type explanationMetadata struct {
	Explicit *bool                   `json:"explicit,omitempty"`
	Null     *bool                   `json:"null,omitempty"`
	History  []metadataHistoryRecord `json:"history,omitempty"`
}

type metadataHistoryRecord struct {
	Path     string                 `json:"path"`
	Previous []explanationOriginDTO `json:"previous,omitempty"`
}

type pathDiscoveryReport struct {
	Scope string               `json:"scope"`
	Paths []pathDiscoveryEntry `json:"paths"`
}

type pathDiscoveryEntry struct {
	Path     string        `json:"path"`
	Present  bool          `json:"present"`
	Metadata *pathMetadata `json:"metadata,omitempty"`
}

type pathMetadata struct {
	Explicit bool `json:"explicit"`
}

var pathDiscoveryTemplate = template.Must(commandkit.ParseTextTemplate("paths", "{{range .Paths}}{{printf \"%q\" .Path}} {{if .Present}}{{if .Metadata.Explicit}}explicit{{else}}non-explicit{{end}}{{else}}historical{{end}}\n{{end}}", nil))

type snapshotDTO struct {
	Present  bool   `json:"present" yaml:"present"`
	Redacted bool   `json:"redacted" yaml:"redacted"`
	YAML     string `json:"yaml" yaml:"yaml"`
}

type explanationOriginDTO struct {
	Layer       string               `json:"layer" yaml:"layer"`
	Locations   []locationDTO        `json:"locations" yaml:"locations"`
	Operation   string               `json:"operation" yaml:"operation"`
	Inheritance []inheritanceStepDTO `json:"inheritance" yaml:"inheritance"`
}

type inheritanceStepDTO struct {
	From      string        `json:"from" yaml:"from"`
	To        string        `json:"to" yaml:"to"`
	Reference string        `json:"reference" yaml:"reference"`
	Locations []locationDTO `json:"locations" yaml:"locations"`
}

type explanationChangeDTO struct {
	Before       snapshotDTO          `json:"before" yaml:"before"`
	After        snapshotDTO          `json:"after" yaml:"after"`
	Origin       explanationOriginDTO `json:"origin" yaml:"origin"`
	Reasons      []string             `json:"reasons" yaml:"reasons"`
	Dependencies []string             `json:"dependencies" yaml:"dependencies"`
}

type secretReferenceDTO struct {
	Name string `json:"name" yaml:"name"`
}

func runConfigExplanation[I, S any](invocation commandkit.Invocation, plan *configOperationPlan[I, S], state S) commandkit.Outcome {
	selected := plan.scopes[0]
	name := selected.scope.scope.Name
	reporter := invocation.Reporter()
	if err := invocation.Context.Err(); err != nil {
		return configFailure("Configuration explanation was canceled.", commandkit.Explanation{}, err)
	}
	if selected.scope.scope.Acquire == nil {
		cause := fmt.Errorf("configuration scope %q has no acquisition callback", name)
		return configFailure(fmt.Sprintf("Unable to explain configuration scope %q.", name), commandkit.Explanation{}, cause)
	}
	acquired, acquireErr := selected.scope.scope.Acquire(invocation.Context, Request{
		Operation: Explain,
		Selection: selected.selection,
	}, selected.input, state)
	queueConfigAcquisition(reporter, acquired)
	if acquireErr != nil {
		return configFailure(fmt.Sprintf("Unable to explain configuration scope %q.", name), acquired.Explanation, acquireErr)
	}
	if err := invocation.Context.Err(); err != nil {
		return configFailure("Configuration explanation was canceled.", acquired.Explanation, err)
	}
	if plan.list {
		if acquired.Value.Metadata == nil {
			return configFailure("Configuration scope did not provide path metadata.", acquired.Explanation, fmt.Errorf("configuration scope %q declared path discovery without metadata", name))
		}
		report := pathDiscoveryReport{Scope: name, Paths: []pathDiscoveryEntry{}}
		for _, path := range acquired.Value.Metadata.HistoricalPaths() {
			if plan.under != nil && !pathWithin(path, *plan.under) {
				continue
			}
			info, present := acquired.Value.Metadata.Lookup(path)
			if !present && (!plan.historical || plan.explicit.Set) {
				continue
			}
			if present && plan.explicit.Set && info.Explicit != plan.explicit.Value {
				continue
			}
			entry := pathDiscoveryEntry{Path: path.String(), Present: present}
			if present {
				entry.Metadata = &pathMetadata{Explicit: info.Explicit}
			}
			report.Paths = append(report.Paths, entry)
		}
		_ = reporter.Report(commandkit.Report{Value: report, TextTemplate: pathDiscoveryTemplate})
		return commandkit.Success()
	}
	if acquired.Value.Explanation == nil {
		cause := fmt.Errorf("configuration scope %q did not provide an explanation reader", name)
		return configFailure("Configuration scope did not provide explanation data.", acquired.Explanation, cause)
	}

	explanation, found := acquired.Value.Explanation.Explain(plan.path)
	if !found {
		cause := fmt.Errorf("configuration path %q is not known in scope %q", plan.path.String(), name)
		return configFailure("The requested configuration path is not available.", acquired.Explanation, cause)
	}
	if err := invocation.Context.Err(); err != nil {
		return configFailure("Configuration explanation was canceled.", acquired.Explanation, err)
	}
	report := makeExplanationReport(name, explanation)
	if acquired.Value.Metadata != nil {
		metadata := &explanationMetadata{}
		if info, ok := acquired.Value.Metadata.Lookup(plan.path); ok {
			metadata.Explicit, metadata.Null = &info.Explicit, &info.Null
		}
		for _, change := range acquired.Value.Metadata.History(plan.path) {
			entry := metadataHistoryRecord{Path: change.Path.String()}
			for _, previous := range change.Previous {
				entry.Previous = append(entry.Previous, originReport(previous))
			}
			metadata.History = append(metadata.History, entry)
		}
		if metadata.Explicit != nil || len(metadata.History) > 0 {
			report.Metadata = metadata
		}
	}
	text := template.Must(commandkit.ParseTextTemplate("explanation", "{{render .}}", template.FuncMap{
		"render": func(report explanationReport) (string, error) {
			var output bytes.Buffer
			err := acquired.Value.Explanation.WriteExplanation(&output, plan.path)
			if err == nil && report.Metadata != nil && report.Metadata.Explicit != nil {
				_, err = fmt.Fprintf(&output, "Explicit: %t\nNull: %t\n", *report.Metadata.Explicit, *report.Metadata.Null)
			}
			return output.String(), err
		},
	}))
	renderErr := reporter.Report(commandkit.Report{Value: report, TextTemplate: text})
	if renderErr != nil && invocation.Context.Err() != nil {
		return configFailure("Configuration explanation was canceled.", acquired.Explanation, invocation.Context.Err())
	}
	return commandkit.Success()
}

func pathWithin(path, parent configkit.Path) bool {
	tokens := func(value string) []string {
		if value == "" {
			return nil
		}
		return strings.Split(strings.TrimPrefix(value, "/"), "/")
	}
	child, prefix := tokens(path.String()), tokens(parent.String())
	if len(prefix) > len(child) {
		return false
	}
	for index := range prefix {
		if prefix[index] != child[index] {
			return false
		}
	}
	return true
}

func makeExplanationReport(scope string, explanation configkit.Explanation) explanationReport {
	report := explanationReport{
		Scope:     scope,
		Path:      explanation.Path.String(),
		Effective: snapshotReport(explanation.Effective),
		Origin:    originReport(explanation.Origin),
		History:   make([]explanationChangeDTO, 0, len(explanation.History)),
	}
	for _, change := range explanation.History {
		entry := explanationChangeDTO{
			Before:       snapshotReport(change.Before),
			After:        snapshotReport(change.After),
			Origin:       originReport(change.Origin),
			Reasons:      append([]string{}, change.Reasons...),
			Dependencies: make([]string, 0, len(change.Dependencies)),
		}
		for _, dependency := range change.Dependencies {
			entry.Dependencies = append(entry.Dependencies, dependency.String())
		}
		report.History = append(report.History, entry)
	}
	if explanation.SecretReference != nil {
		report.SecretReference = &secretReferenceDTO{Name: explanation.SecretReference.Name}
	}
	return report
}

func snapshotReport(snapshot configkit.ValueSnapshot) snapshotDTO {
	return snapshotDTO{Present: snapshot.Present, Redacted: snapshot.Redacted, YAML: snapshot.YAML}
}

func originReport(origin configkit.Origin) explanationOriginDTO {
	report := explanationOriginDTO{
		Layer:       string(origin.Layer),
		Locations:   locationReports(origin.Locations),
		Operation:   string(origin.Operation),
		Inheritance: make([]inheritanceStepDTO, 0, len(origin.Inheritance)),
	}
	for _, step := range origin.Inheritance {
		report.Inheritance = append(report.Inheritance, inheritanceStepDTO{
			From:      step.From.String(),
			To:        step.To.String(),
			Reference: step.Reference.String(),
			Locations: locationReports(step.Locations),
		})
	}
	return report
}