package config

import (
	"fmt"
	"regexp"
	"strings"

	"gitea.maximumdirect.net/eric/distributor/internal/link"
)

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

func IsSlugLikeID(value string) bool {
	return idPattern.MatchString(value)
}

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

	errs = validateHTTPServer(errs, "server.http", cfg.Server.HTTP)

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

	pipelineIDs := make(map[string]struct{}, len(cfg.Pipelines))
	uploadPipelineIDs := make(map[string]struct{})
	for pipelineIndex, pipeline := range cfg.Pipelines {
		pipelineContext := fmt.Sprintf("pipelines[%d]", pipelineIndex)
		if pipeline.ID == "" {
			errs = append(errs, pipelineContext+".id is required")
		} else if !IsSlugLikeID(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 = validateSourceBackend(errs, pipelineContext+".source", pipeline.Source)
		if pipeline.Source.Backend == BackendHTTPUpload && pipeline.ID != "" {
			uploadPipelineIDs[pipeline.ID] = struct{}{}
		}
		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 !IsSlugLikeID(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 = validateDestinationBackend(errs, destinationContext, destination)
			errs = validatePublishTransformPolicy(errs, destinationContext, destination.Publish, destination.Transform)
			errs = validatePathMapping(errs, destinationContext+".path_mapping", destination.PathMap)
			errs = validateLinks(errs, destinationContext+".links", destination.Links)
			errs = validateTransferPolicy(errs, destinationContext+".transfer", destination.Transfer)
		}
	}

	errs = validateUploadTokens(errs, cfg.UploadTokens, pipelineIDs, uploadPipelineIDs)

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

func validateHTTPServer(errs ValidationErrors, context string, server HTTPServer) ValidationErrors {
	if server.Bind == "" {
		errs = append(errs, context+".bind is required")
	}
	if server.StagingRoot == "" {
		errs = append(errs, context+".staging_root is required")
	}
	if server.MaxUploadSize == nil || *server.MaxUploadSize <= 0 {
		errs = append(errs, context+".max_upload_size must be greater than zero")
	}
	if server.QueueSize <= 0 {
		errs = append(errs, context+".queue_size must be greater than zero")
	}
	if server.MaxConcurrency <= 0 {
		errs = append(errs, context+".max_concurrency must be greater than zero")
	}
	if server.Retention == nil || *server.Retention <= 0 {
		errs = append(errs, context+".retention must be greater than zero")
	}
	return errs
}

func validateSourceBackend(errs ValidationErrors, context string, backend Backend) ValidationErrors {
	if backend.Backend == BackendHTTPUpload {
		return validateHTTPUploadSource(errs, context, backend.Upload)
	}
	return validateBackend(errs, context, backendViewFromSource(backend))
}

func validateDestinationBackend(errs ValidationErrors, context string, destination Destination) ValidationErrors {
	if destination.Backend == BackendHTTPUpload {
		errs = append(errs, context+".backend "+BackendHTTPUpload+" is only supported for sources")
		return errs
	}
	return validateBackend(errs, context, backendViewFromDestination(destination))
}

func validateHTTPUploadSource(errs ValidationErrors, context string, upload HTTPUpload) ValidationErrors {
	if upload.StagingPath == "" {
		errs = append(errs, context+".staging_path is required for http_upload backend")
	}
	if upload.MaxUploadSize == nil || *upload.MaxUploadSize <= 0 {
		errs = append(errs, context+".max_upload_size must be greater than zero")
	}
	return errs
}

func validateUploadTokens(errs ValidationErrors, tokens []UploadToken, pipelineIDs, uploadPipelineIDs map[string]struct{}) ValidationErrors {
	if len(uploadPipelineIDs) == 0 {
		if len(tokens) > 0 {
			errs = append(errs, "upload_tokens must reference configured http_upload pipelines")
		}
		return errs
	}
	if len(tokens) == 0 {
		return append(errs, "upload_tokens is required when any pipeline source backend is http_upload")
	}

	tokenIDs := make(map[string]struct{}, len(tokens))
	allowedUploadPipelineIDs := make(map[string]struct{}, len(uploadPipelineIDs))
	for tokenIndex, token := range tokens {
		context := fmt.Sprintf("upload_tokens[%d]", tokenIndex)
		if token.ID == "" {
			errs = append(errs, context+".id is required")
		} else if !IsSlugLikeID(token.ID) {
			errs = append(errs, context+".id must be a slug-like identifier")
		} else if _, exists := tokenIDs[token.ID]; exists {
			errs = append(errs, "upload token id "+token.ID+" is duplicated")
		} else {
			tokenIDs[token.ID] = struct{}{}
		}

		if token.TokenEnv == "" {
			errs = append(errs, context+".token_env is required")
		}
		if len(token.AllowPipelines) == 0 {
			errs = append(errs, context+".allow_pipelines is required")
		}

		seenAllowed := make(map[string]struct{}, len(token.AllowPipelines))
		for allowIndex, pipelineID := range token.AllowPipelines {
			allowContext := fmt.Sprintf("%s.allow_pipelines[%d]", context, allowIndex)
			if pipelineID == "" {
				errs = append(errs, allowContext+" is required")
				continue
			}
			if _, exists := seenAllowed[pipelineID]; exists {
				errs = append(errs, context+".allow_pipelines contains duplicate pipeline id "+pipelineID)
				continue
			}
			seenAllowed[pipelineID] = struct{}{}
			if _, exists := pipelineIDs[pipelineID]; !exists {
				errs = append(errs, allowContext+" references unknown pipeline "+pipelineID)
				continue
			}
			if _, exists := uploadPipelineIDs[pipelineID]; !exists {
				errs = append(errs, allowContext+" references non-http_upload pipeline "+pipelineID)
				continue
			}
			allowedUploadPipelineIDs[pipelineID] = struct{}{}
		}
	}

	for pipelineID := range uploadPipelineIDs {
		if _, exists := allowedUploadPipelineIDs[pipelineID]; !exists {
			errs = append(errs, "http_upload pipeline "+pipelineID+" is not allowed by any upload token")
		}
	}
	return errs
}

func validateBackend(errs ValidationErrors, context string, backend backendView) ValidationErrors {
	switch backend.Backend {
	case "":
		errs = append(errs, context+".backend is required")
	case BackendLocal:
		if backend.Path == "" {
			errs = append(errs, context+".path is required for local backend")
		}
	case BackendSSH:
		if backend.Host == "" {
			errs = append(errs, context+".host is required for ssh backend")
		}
		if backend.Path == "" {
			errs = append(errs, context+".path is required for ssh backend")
		}
		if backend.Port < 0 || backend.Port > 65535 {
			errs = append(errs, context+".port must be between 1 and 65535")
		}
		if backend.Port == 0 {
			errs = append(errs, context+".port is required for ssh backend after defaults are applied")
		}
		if backend.SSH.HostKeyPolicy != "" {
			if _, ok := NormalizeHostKeyPolicy(string(backend.SSH.HostKeyPolicy)); !ok {
				errs = append(errs, context+".host_key_policy must be strict, true, accept-new, off, or false")
			}
		}
	case BackendS3:
		if backend.Endpoint == "" {
			errs = append(errs, context+".endpoint is required for s3 backend")
		}
		if backend.Bucket == "" {
			errs = append(errs, context+".bucket is required for s3 backend")
		}
		if err := ValidateS3Prefix(backend.Prefix); err != nil {
			errs = append(errs, context+".prefix must be a clean relative slash-separated path")
		}
		if (backend.Creds.AccessKeyIDEnv == "") != (backend.Creds.SecretAccessKeyEnv == "") {
			errs = append(errs, context+".credentials.access_key_id_env and credentials.secret_access_key_env must be configured together")
		}
	default:
		errs = append(errs, context+".backend "+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 validatePublishTransformPolicy(errs ValidationErrors, context string, policy *PublishPolicy, transform Transform) ValidationErrors {
	if policy == nil {
		errs = append(errs, context+".publish is required")
		return errs
	}
	if err := ValidatePublishTransformPolicy(*policy, transform); err != nil {
		errs = append(errs, context+"."+err.Error())
	}
	return errs
}

func ValidatePublishTransformPolicy(publish PublishPolicy, transform Transform) error {
	if !publish.Source && !publish.HTML {
		return fmt.Errorf("publish must enable source or html")
	}
	if publish.HTML && transform.MarkdownToHTML == nil {
		return fmt.Errorf("transform.markdown_to_html is required when publish.html is true")
	}
	if transform.MarkdownToHTML == nil {
		return nil
	}
	mode := transform.MarkdownToHTML.Mode
	if mode == "" {
		mode = TransformModeSidecar
	}
	if mode != TransformModeSidecar && mode != TransformModeIndex {
		return fmt.Errorf("transform.markdown_to_html.mode must be %s or %s", TransformModeSidecar, TransformModeIndex)
	}
	if transform.MarkdownToHTML.Input != "" && !transform.MarkdownToHTML.Enabled {
		return fmt.Errorf("transform.markdown_to_html.input requires transform.markdown_to_html.enabled to be true")
	}
	if transform.MarkdownToHTML.Input != "" && mode != TransformModeIndex {
		return fmt.Errorf("transform.markdown_to_html.input is only valid when mode is %s", TransformModeIndex)
	}
	if transform.MarkdownToHTML.Enabled && !publish.HTML {
		return fmt.Errorf("transform.markdown_to_html.enabled requires publish.html to be true")
	}
	if publish.HTML && !transform.MarkdownToHTML.Enabled {
		return fmt.Errorf("transform.markdown_to_html.enabled must be true when publish.html is true")
	}
	return nil
}

func validatePathMapping(errs ValidationErrors, context string, mapping PathMapping) ValidationErrors {
	if mapping.Mode != PathMappingPreserveRelative && mapping.Mode != PathMappingFixed {
		errs = append(errs, context+".mode must be "+PathMappingPreserveRelative+" or "+PathMappingFixed)
	}
	return errs
}

func validateLinks(errs ValidationErrors, context string, links *Links) ValidationErrors {
	if links == nil {
		return errs
	}
	if links.BaseURL == "" {
		errs = append(errs, context+".base_url is required")
	} else if err := link.ValidateHTTPURL(links.BaseURL); err != nil {
		errs = append(errs, context+".base_url "+err.Error())
	}
	switch links.Primary {
	case LinkPrimaryAuto, LinkPrimaryHTML, LinkPrimarySource:
	default:
		errs = append(errs, context+".primary must be "+LinkPrimaryAuto+", "+LinkPrimaryHTML+", or "+LinkPrimarySource)
	}
	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 && policy.OnDestinationNewer != TransferActionReplace {
		errs = append(errs, context+".on_destination_newer must be skip, replace, or fail")
	}
	if policy.OnConflict != TransferActionFail && policy.OnConflict != TransferActionReplace {
		errs = append(errs, context+".on_conflict must be fail or replace")
	}
	return errs
}