package config

import (
	"fmt"
	"regexp"
	"strings"
)

var idPattern = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9._-]*$`)

type ValidationErrors []string

func (e ValidationErrors) Error() string {
	if len(e) == 1 {
		return e[0]
	}
	return strings.Join(e, "; ")
}

func Validate(cfg Config) error {
	var errs ValidationErrors

	if len(cfg.Pipelines) == 0 {
		errs = append(errs, "pipelines is required")
	}

	pipelineIDs := make(map[string]struct{}, len(cfg.Pipelines))
	for pipelineIndex, pipeline := range cfg.Pipelines {
		pipelineContext := fmt.Sprintf("pipelines[%d]", pipelineIndex)
		if pipeline.ID == "" {
			errs = append(errs, pipelineContext+".id is required")
		} else if !idPattern.MatchString(pipeline.ID) {
			errs = append(errs, pipelineContext+".id must be a slug-like identifier")
		} else if _, exists := pipelineIDs[pipeline.ID]; exists {
			errs = append(errs, "pipeline id "+pipeline.ID+" is duplicated")
		} else {
			pipelineIDs[pipeline.ID] = struct{}{}
		}

		errs = validateBackend(errs, pipelineContext+".source", pipeline.Source.Backend, pipeline.Source.Path, pipeline.Source.URI, pipeline.Source.Endpoint, pipeline.Source.Bucket)
		errs = validateValidationPolicy(errs, pipelineContext+".validation", pipeline.Validation)
		if len(pipeline.Destinations) == 0 {
			errs = append(errs, pipelineContext+".destinations is required")
		}

		destinationIDs := make(map[string]struct{}, len(pipeline.Destinations))
		for destinationIndex, destination := range pipeline.Destinations {
			destinationContext := fmt.Sprintf("%s.destinations[%d]", pipelineContext, destinationIndex)
			if destination.ID == "" {
				errs = append(errs, destinationContext+".id is required")
			} else if !idPattern.MatchString(destination.ID) {
				errs = append(errs, destinationContext+".id must be a slug-like identifier")
			} else if _, exists := destinationIDs[destination.ID]; exists {
				errs = append(errs, "destination id "+destination.ID+" is duplicated in pipeline "+pipeline.ID)
			} else {
				destinationIDs[destination.ID] = struct{}{}
			}

			errs = validateBackend(errs, destinationContext, destination.Backend, destination.Path, destination.URI, destination.Endpoint, destination.Bucket)
			errs = validatePublishPolicy(errs, destinationContext+".publish", destination.Publish)
			errs = validateTransform(errs, destinationContext+".transform", destination.Publish, destination.Transform)
			errs = validateTransferPolicy(errs, destinationContext+".transfer", destination.Transfer)
		}
	}

	if len(errs) > 0 {
		return errs
	}
	return nil
}

func validateBackend(errs ValidationErrors, context, backend, path, uri, endpoint, bucket string) ValidationErrors {
	switch backend {
	case "":
		errs = append(errs, context+".backend is required")
	case BackendLocal:
		if path == "" {
			errs = append(errs, context+".path is required for local backend")
		}
	case BackendSSH:
		if uri == "" {
			errs = append(errs, context+".uri is required for ssh backend")
		}
		if path == "" {
			errs = append(errs, context+".path is required for ssh backend")
		}
	case BackendS3:
		if endpoint == "" {
			errs = append(errs, context+".endpoint is required for s3 backend")
		}
		if bucket == "" {
			errs = append(errs, context+".bucket is required for s3 backend")
		}
	default:
		errs = append(errs, context+".backend "+backend+" is unsupported")
	}
	return errs
}

func validateValidationPolicy(errs ValidationErrors, context string, policy ValidationPolicy) ValidationErrors {
	if policy.OnDigestMismatch != ValidationActionFail {
		errs = append(errs, context+".on_digest_mismatch must be "+ValidationActionFail)
	}
	return errs
}

func validatePublishPolicy(errs ValidationErrors, context string, policy *PublishPolicy) ValidationErrors {
	if policy == nil {
		errs = append(errs, context+" is required")
		return errs
	}
	if !policy.Source && !policy.HTML {
		errs = append(errs, context+" must enable source or html")
	}
	return errs
}

func validateTransform(errs ValidationErrors, context string, publish *PublishPolicy, transform Transform) ValidationErrors {
	publishesHTML := publish != nil && publish.HTML
	if transform.MarkdownToHTML == nil {
		if publishesHTML {
			errs = append(errs, context+".markdown_to_html is required when publish.html is true")
		}
		return errs
	}

	if publishesHTML && !transform.MarkdownToHTML.Enabled {
		errs = append(errs, context+".markdown_to_html.enabled must be true when publish.html is true")
	}
	if transform.MarkdownToHTML.Enabled && transform.MarkdownToHTML.Mode != TransformModeSidecar {
		errs = append(errs, context+".markdown_to_html.mode must be "+TransformModeSidecar)
	}
	if !transform.MarkdownToHTML.Enabled && transform.MarkdownToHTML.Mode != "" && transform.MarkdownToHTML.Mode != TransformModeSidecar {
		errs = append(errs, context+".markdown_to_html.mode must be "+TransformModeSidecar)
	}
	return errs
}

func validateTransferPolicy(errs ValidationErrors, context string, policy TransferPolicy) ValidationErrors {
	if policy.OnDestinationSame != TransferActionSkip && policy.OnDestinationSame != TransferActionFail {
		errs = append(errs, context+".on_destination_same must be skip or fail")
	}
	if policy.OnDestinationOlder != TransferActionReplace && policy.OnDestinationOlder != TransferActionFail {
		errs = append(errs, context+".on_destination_older must be replace or fail")
	}
	if policy.OnDestinationNewer != TransferActionSkip && policy.OnDestinationNewer != TransferActionFail {
		errs = append(errs, context+".on_destination_newer must be skip or fail")
	}
	if policy.OnConflict != TransferActionFail {
		errs = append(errs, context+".on_conflict must be fail")
	}
	return errs
}