package skillpack

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"

	mdagent "gitea.stevedudenhoeffer.com/steve/majordomo/agent"
	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
	mdskill "gitea.stevedudenhoeffer.com/steve/majordomo/skill"
)

// Resolve loads the pinned Pack for each enabled subscription from the cache. It
// is how a host turns "this agent subscribes to these packs" into activatable
// packs at run time without touching the network. A pinned digest missing from
// the cache is an error (the host should have cached it at pin/apply time).
// Disabled subscriptions are skipped.
func Resolve(ctx context.Context, cache PackCache, subs []Subscription) ([]*Pack, error) {
	out := make([]*Pack, 0, len(subs))
	for i := range subs {
		s := &subs[i]
		if !s.Enabled {
			continue
		}
		tree, err := cache.Get(ctx, s.PinnedDigest)
		if err != nil {
			return nil, fmt.Errorf("skillpack: resolving %q: %w", s.Name, err)
		}
		pack, err := LoadPack(tree)
		if err != nil {
			return nil, fmt.Errorf("skillpack: loading %q: %w", s.Name, err)
		}
		out = append(out, pack)
	}
	return out, nil
}

// Catalog renders the always-in-prompt block for a set of packs: one line per
// pack (name + description) plus how to load one. This is the whole prompt cost
// of a subscription — the bodies stay out until skill_use is called.
func Catalog(packs []*Pack) string {
	sorted := make([]*Pack, 0, len(packs))
	for _, p := range packs {
		if p != nil && p.Manifest != nil {
			sorted = append(sorted, p)
		}
	}
	if len(sorted) == 0 {
		return ""
	}
	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Manifest.Name < sorted[j].Manifest.Name })

	var b strings.Builder
	b.WriteString("You have access to skills — packaged instructions for specific tasks. ")
	b.WriteString("When a task matches one, call skill_use with its name to load its full instructions before proceeding.\n\n")
	b.WriteString("Available skills:\n")
	for _, p := range sorted {
		fmt.Fprintf(&b, "- %s: %s\n", p.Manifest.Name, p.Manifest.Description)
	}
	return strings.TrimRight(b.String(), "\n")
}

type skillUseArgs struct {
	Name string `json:"name" description:"the exact name of the skill to load, from the Available skills list"`
}

// BundleStager makes a pack's bundled files available to the current run and
// returns a short note the model can act on (e.g. where the files are and how to
// reference them). It is called LAZILY, inside the skill_use tool, so a pack's
// files are staged only when the model actually loads that pack — not for every
// subscribed pack on every run. A host implements it over its own file plumbing
// (mort saves the files to run-scoped storage and returns their file_ids). nil =
// no staging: skill_use just lists the bundled file names.
type BundleStager func(ctx context.Context, p *Pack) (string, error)

// Activate turns a set of resolved packs into a majordomo agent.Skill: its
// Instructions are the Catalog, and it contributes a single skill_use tool that
// returns a named pack's full body (progressive disclosure). Attach the result
// to an agent with agent.WithSkill. Returns nil when there are no packs, which
// agent.WithSkill tolerates (a nil skill contributes nothing).
//
// stager, if non-nil, is invoked when skill_use loads a pack with bundled files;
// its returned note is appended to the body so the model knows how to reach the
// staged scripts/references. A stager error degrades gracefully (the
// instructions still return, with a note that the files are unavailable).
func Activate(packs []*Pack, stager BundleStager) mdagent.Skill {
	byName := make(map[string]*Pack, len(packs))
	for _, p := range packs {
		if p != nil && p.Manifest != nil {
			byName[p.Manifest.Name] = p
		}
	}
	if len(byName) == 0 {
		return nil
	}

	tool := llm.DefineTool("skill_use",
		"Load the full instructions for a skill by name before doing a task it covers. Returns the skill's instructions and, if it has bundled files, how to access them.",
		func(ctx context.Context, args skillUseArgs) (any, error) {
			p, ok := byName[strings.TrimSpace(args.Name)]
			if !ok {
				return fmt.Sprintf("No skill named %q. Use one of the names from the Available skills list.", args.Name), nil
			}
			body := renderPackBody(p)
			if stager != nil && len(p.Bundled) > 0 {
				note, err := stager(ctx, p)
				switch {
				case err != nil:
					body += "\n\n(bundled files could not be staged: " + err.Error() + ")"
				case note != "":
					body += "\n\n" + note
				}
			}
			return body, nil
		})

	tb := llm.NewToolbox("skillpack", tool)
	return mdskill.New("skillpacks",
		mdskill.WithInstructions(Catalog(packs)),
		mdskill.WithToolbox(tb),
	)
}

// renderPackBody is the base skill_use payload: the pack's instructions plus, if
// it has any, a list of its bundled file names. A stager (see Activate) appends
// the concrete access note.
func renderPackBody(p *Pack) string {
	if p == nil || p.Manifest == nil {
		return "Error: invalid skill pack."
	}
	var b strings.Builder
	fmt.Fprintf(&b, "# Skill: %s\n\n%s\n", p.Manifest.Name, p.Manifest.Body)
	if len(p.Bundled) > 0 {
		b.WriteString("\nBundled files:\n")
		for _, f := range p.Bundled {
			fmt.Fprintf(&b, "- %s\n", f)
		}
	}
	return strings.TrimRight(b.String(), "\n")
}

// Stage materializes a pack's files under baseDir/<pack name>/ so a host can
// mount them (read-only is the host's concern) into a sandbox the agent's file
// tools can read. Returns the pack's staged directory.
func Stage(p *Pack, baseDir string) (string, error) {
	if p == nil || p.Manifest == nil {
		return "", errors.New("skillpack: Stage requires a non-nil pack")
	}
	dir := baseDir + "/" + p.Manifest.Name
	if err := p.Tree.WriteTo(dir); err != nil {
		return "", err
	}
	return dir, nil
}