package ckconfig

import (
	"bytes"
	"errors"
	"fmt"
	"io"

	commandkit "gitea.maximumdirect.net/eric/CommandKit"
	configkit "gitea.maximumdirect.net/eric/ConfigKit"
)

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

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

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

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

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

type secretReferenceDTO struct {
	Name string `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
	if err := invocation.Context.Err(); err != nil {
		return configOperationFailure(err, nil, false)
	}
	if selected.scope.scope.Acquire == nil {
		return configOperationFailure(fmt.Errorf("configuration scope %q has no acquisition callback", name), nil, false)
	}
	acquired, acquireErr := selected.scope.scope.Acquire(invocation.Context, Request{
		Operation: Explain,
		Selection: plan.selection,
	}, selected.input, state)
	diagnostics := append([]commandkit.Diagnostic(nil), acquired.Diagnostics...)
	if acquireErr != nil {
		return configOperationFailure(acquireErr, diagnostics, false)
	}
	if err := invocation.Context.Err(); err != nil {
		return configOperationFailure(err, diagnostics, false)
	}
	if acquired.Value.Explanation == nil {
		return configOperationFailure(fmt.Errorf("configuration scope %q did not provide an explanation reader", name), diagnostics, false)
	}

	explanation, found := acquired.Value.Explanation.Explain(plan.path)
	if !found {
		return configOperationFailure(fmt.Errorf("configuration path %q is not known in scope %q", plan.path.String(), name), diagnostics, false)
	}
	if err := invocation.Context.Err(); err != nil {
		return configOperationFailure(err, diagnostics, false)
	}
	if plan.format != "yaml" {
		return writeNativeExplanation(invocation.Streams.Out, acquired.Value.Explanation, plan.path, diagnostics)
	}
	var report bytes.Buffer
	if err := encodeYAML(&report, makeExplanationReport(name, explanation)); err != nil {
		return configOperationFailure(err, diagnostics, false)
	}
	if err := invocation.Context.Err(); err != nil {
		return configOperationFailure(err, diagnostics, false)
	}
	if err := writeConfigReport(invocation.Streams.Out, report.Bytes()); err != nil {
		return configDeliveryFailure(err, diagnostics, true)
	}
	outcome := commandkit.Success()
	outcome.Diagnostics = diagnostics
	return outcome
}

func writeNativeExplanation(writer io.Writer, reader ExplanationReader, path configkit.Path, diagnostics []commandkit.Diagnostic) commandkit.Outcome {
	checked := &checkedWriter{writer: writer}
	renderErr := reader.WriteExplanation(checked, path)
	if checked.failure != nil {
		if renderErr == nil {
			renderErr = checked.failure
		} else {
			renderErr = errors.Join(renderErr, checked.failure)
		}
	}
	if renderErr != nil {
		outcome := configOperationFailure(renderErr, diagnostics, true)
		outcome.DeliveryError = checked.failure
		return outcome
	}
	outcome := commandkit.Success()
	outcome.Diagnostics = diagnostics
	return outcome
}

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
}