package tools

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"regexp"

	"gitea.d-ma.be/mathias/gitea-mcp/internal/allowlist"
	"gitea.d-ma.be/mathias/gitea-mcp/internal/gitea"
	"gitea.d-ma.be/mathias/gitea-mcp/internal/registry"
)

var nameRe = regexp.MustCompile(`^[a-z][a-z0-9-]{1,38}[a-z0-9]$`)

var substitutionFiles = []string{
	"go.mod",
	"Taskfile.yml",
	"Dockerfile",
	".gitea/workflows/cd.yml",
	"README.md",
	".context/PROJECT.md",
}

func substitutions(owner, name string) map[string]string {
	return map[string]string{
		"__PROJECT_NAME__": name,
		"__MODULE_PATH__":  "gitea.d-ma.be/" + owner + "/" + name,
	}
}

// CreateProjectFromTemplate is the exported type so tests can reference it.
type CreateProjectFromTemplate struct {
	c             *gitea.Client
	a             *allowlist.Allowlist
	templateOwner string
	templateName  string
}

func NewCreateProjectFromTemplate(c *gitea.Client, a *allowlist.Allowlist, tmplOwner, tmplName string) *CreateProjectFromTemplate {
	return &CreateProjectFromTemplate{c: c, a: a, templateOwner: tmplOwner, templateName: tmplName}
}

func (t *CreateProjectFromTemplate) Descriptor() registry.ToolDescriptor {
	return registry.ToolDescriptor{
		Name:        "create_project_from_template",
		Description: "Create a new project repo from a template, applying placeholder substitutions to known files. Defaults to the server-configured template; pass template_name to override (e.g. template-go-agent).",
		InputSchema: json.RawMessage(`{
			"type":"object",
			"properties":{
				"owner":{"type":"string"},
				"name":{"type":"string","pattern":"^[a-z][a-z0-9-]{1,38}[a-z0-9]$"},
				"description":{"type":"string"},
				"private":{"type":"boolean"},
				"template_name":{"type":"string","description":"Template repo name to generate from. Defaults to the server-configured template."}
			},
			"required":["owner","name"]
		}`),
	}
}

type createProjectArgs struct {
	Owner        string `json:"owner"`
	Name         string `json:"name"`
	Description  string `json:"description"`
	Private      bool   `json:"private"`
	TemplateName string `json:"template_name"`
}

type createProjectResult struct {
	FullName         string   `json:"full_name"`
	HTMLURL          string   `json:"html_url"`
	CloneURL         string   `json:"clone_url"`
	DefaultBranch    string   `json:"default_branch"`
	FilesSubstituted []string `json:"files_substituted"`
	PartialFailure   string   `json:"partial_failure,omitempty"`
}

func (t *CreateProjectFromTemplate) Call(ctx context.Context, raw json.RawMessage) (json.RawMessage, error) {
	var args createProjectArgs
	if err := parseArgs(raw, &args); err != nil {
		return nil, err
	}

	// Allowlist check first.
	if err := t.a.Check(args.Owner); err != nil {
		return nil, err
	}

	// Validate name format.
	if !nameRe.MatchString(args.Name) {
		return nil, fmt.Errorf("name %q does not match pattern %s: %w", args.Name, nameRe.String(), gitea.ErrValidation)
	}

	// Resolve template: per-call override takes precedence over the
	// server-configured default. Owner stays server-configured.
	tmplName := args.TemplateName
	if tmplName == "" {
		tmplName = t.templateName
	}

	// Verify template exists and is marked as a template repo.
	tmpl, err := t.c.GetRepo(ctx, t.templateOwner, tmplName)
	if err != nil {
		return nil, fmt.Errorf("template lookup: %w", err)
	}
	if !tmpl.Template {
		return nil, fmt.Errorf("repo %s/%s is not marked as template: %w", t.templateOwner, tmplName, gitea.ErrValidation)
	}

	// Verify destination doesn't already exist.
	if _, err := t.c.GetRepo(ctx, args.Owner, args.Name); err == nil {
		return nil, fmt.Errorf("destination %s/%s already exists: %w", args.Owner, args.Name, gitea.ErrConflict)
	} else if !errors.Is(err, gitea.ErrNotFound) {
		return nil, fmt.Errorf("destination check: %w", err)
	}

	// Generate repo from template.
	newRepo, err := t.c.GenerateFromTemplate(ctx, t.templateOwner, tmplName, gitea.GenerateFromTemplateArgs{
		Owner:       args.Owner,
		Name:        args.Name,
		Description: args.Description,
		Private:     args.Private,
		GitContent:  true,
	})
	if err != nil {
		return nil, fmt.Errorf("generate: %w", err)
	}

	result := createProjectResult{
		FullName:      newRepo.FullName,
		HTMLURL:       newRepo.HTMLURL,
		CloneURL:      newRepo.CloneURL,
		DefaultBranch: newRepo.DefaultBranch,
	}

	// Substitute placeholders in known files (best-effort).
	repls := substitutions(args.Owner, args.Name)
	branch := newRepo.DefaultBranch
	for _, path := range substitutionFiles {
		if err := t.c.SubstituteFile(ctx, args.Owner, args.Name, branch, path, repls); err != nil {
			// Files that don't exist in this template are silently skipped.
			if errors.Is(err, gitea.ErrNotFound) {
				continue
			}
			// Any other error halts the substitution pass with partial_failure recorded.
			result.PartialFailure = fmt.Sprintf("%s: %v", path, err)
			break
		}
		result.FilesSubstituted = append(result.FilesSubstituted, path)
	}

	return textOK(result)
}