package gsp

import (
	"fmt"
	"path/filepath"
	"strings"
)

type AIInitOptions struct {
	Agents bool
	Skill  string
	All    bool
	Force  bool
}

func InitAIUsage(root string, options AIInitOptions) (InitResult, error) {
	project, err := LoadProject(root)
	if err != nil {
		return InitResult{}, err
	}
	if project.Manifest == nil {
		return InitResult{}, fmt.Errorf("gsp.manifest not found; run gsp init first")
	}

	result := InitResult{Root: filepath.ToSlash(project.Root)}
	projectName := project.Manifest.Project
	if projectName == "" {
		projectName = filepath.Base(project.Root)
	}
	entry := "project.entry"
	if len(project.Manifest.Entry) > 0 && project.Manifest.Entry[0] != "" {
		entry = project.Manifest.Entry[0]
	}
	scan := "design"
	if len(project.Manifest.Scan) > 0 && project.Manifest.Scan[0] != "" {
		scan = project.Manifest.Scan[0]
	}

	files := []initFile{
		{
			Path: "README.md",
			Data: projectReadme(projectName, scan, entry),
		},
		{
			Path: "AI_USAGE.md",
			Data: aiUsage(project.Manifest.GSPVersion, scan),
		},
	}

	if options.All || options.Agents {
		files = append(files, initFile{
			Path: "AGENTS.md",
			Data: agentsUsage(),
		})
	}

	skill := strings.TrimSpace(options.Skill)
	if options.All && skill == "" {
		skill = "generic"
	}
	if skill != "" {
		path, data, err := skillUsage(skill)
		if err != nil {
			return InitResult{}, err
		}
		files = append(files, initFile{Path: path, Data: data})
	}

	for _, file := range files {
		path := filepath.Join(project.Root, filepath.FromSlash(file.Path))
		if err := writeInitFile(project.Root, path, []byte(file.Data), options.Force, &result); err != nil {
			return InitResult{}, err
		}
	}
	return result, nil
}

type initFile struct {
	Path string
	Data string
}

func projectReadme(projectName, scan, entry string) string {
	return fmt.Sprintf(`# %s

This is a GSP project.

- Manifest: `+"`gsp.manifest`"+`
- GSP source: `+"`%s/`"+`
- Entry GSP: `+"`%s`"+`
- AI rules: `+"`AI_USAGE.md`"+`

`, projectName, scan, entry)
}

func aiUsage(gspVersion, scan string) string {
	if gspVersion == "" {
		gspVersion = DefaultGSPVersion
	}
	return fmt.Sprintf(`# AI Usage

- Read `+"`gsp.manifest`"+` first.
- Use GSP version `+"`%s`"+`.
- Treat `+"`%s/`"+` as the default GSP source directory.
- `+"`.gsp`"+` files use YAML.
- Preserve `+"`id`"+`; do not rename it unless explicitly requested.
- `+"`id`"+` is the unique identity of a GSP unit.
- `+"`title`"+` is display text; use `+"`id`"+` when `+"`title`"+` is missing.
- `+"`links`"+` associates a GSP with paths, folders, URLs, or external addresses.
- Use only fields valid for the declared GSP version.
- `+"`with`"+` means related design context.
- `+"`refines`"+` means single-source refinement.
- Empty `+"`context`"+` means placeholder.
- Do not invent missing referenced GSPs silently.
- Use `+"`gsp validate`"+` after editing GSP files.
- Use `+"`gsp index`"+` to locate GSP units.
- Use `+"`gsp trace <id>`"+` to inspect relations.
- Use `+"`gsp flatten <id>`"+` before implementation or task splitting.
- Use `+"`gsp pack <id>`"+` when a compact AI context is needed.
- Use `+"`gsp links <id>`"+` to inspect associated files, folders, URLs, or addresses.
- Use `+"`gsp impact <id>`"+` before changing shared GSP units.
- Use `+"`gsp message validate <file>`"+` for agent communication messages.
- Use `+"`gsp stage-check --stage <stage>`"+` before stage handoff.

`, gspVersion, scan)
}

func agentsUsage() string {
	return `# Agent Instructions

Read ` + "`AI_USAGE.md`" + ` before working on this GSP project.

`
}

func skillUsage(kind string) (string, string, error) {
	switch strings.ToLower(strings.TrimSpace(kind)) {
	case "generic":
		return "skills/gsp/SKILL.md", `# GSP

Use this skill when working in a GSP project.

Read ` + "`gsp.manifest`" + `, then ` + "`AI_USAGE.md`" + `.
Use ` + "`gsp validate`" + `, ` + "`gsp index`" + `, and ` + "`gsp flatten <id>`" + ` when handling GSP files.

`, nil
	case "codex":
		return ".codex/skills/gsp/SKILL.md", `# GSP

Use this skill when working in a GSP project.

Read ` + "`gsp.manifest`" + `, then ` + "`AI_USAGE.md`" + `.
Use GSP Toolkit commands before editing, handoff, implementation, or review.

`, nil
	default:
		return "", "", fmt.Errorf("unsupported skill %q; use generic or codex", kind)
	}
}