package discovery

import (
	"fmt"
	"sort"
	"strings"

	"github.com/m3tam3re/agent-lib/internal/lockfile"
)

// Tree abstracts a readable content tree: a git commit tree or a filesystem
// root. Paths are slash-separated and relative to the tree root.
type Tree interface {
	Walk(fn func(rel string, isDir bool) error) error
	ReadFile(rel string) ([]byte, error)
}

// Config directs Scan; zero values select the standard layout.
type Config struct {
	Root        string
	SkillsDir   string
	CommandsDir string
	AgentsDir   string
	McpDir      string
}

func FromLockfileDiscovery(d lockfile.Discovery) Config {
	r := d.Resolve()
	return Config{Root: r.Root, SkillsDir: r.SkillsDir, CommandsDir: r.CommandsDir, AgentsDir: r.AgentsDir, McpDir: r.McpDir}
}

// Item is one discovered deployable artifact.
type Item struct {
	Type        string
	UpstreamID  string
	RelPath     string
	Frontmatter *Frontmatter
	Warnings    []string
	// Skipped marks a file discovery recognized but deliberately excluded —
	// e.g. a documentation .md under agents/ or commands/ without definition
	// frontmatter. Skipped items carry warnings but must never enter a
	// selection, inventory or availability listing.
	Skipped bool
}

// Scan discovers items of all four content types under cfg. Discovery is a
// read-only scan; it never evaluates content beyond reading files.
func Scan(tree Tree, cfg Config) ([]Item, error) {
	dirs := lockfile.Discovery{
		Root: cfg.Root, SkillsDir: cfg.SkillsDir, CommandsDir: cfg.CommandsDir,
		AgentsDir: cfg.AgentsDir, McpDir: cfg.McpDir,
	}.Resolve()

	skillRoot := join(dirs.Root, dirs.SkillsDir)
	commandRoot := join(dirs.Root, dirs.CommandsDir)
	agentRoot := join(dirs.Root, dirs.AgentsDir)
	mcpRoot := join(dirs.Root, dirs.McpDir)

	dirEntries := map[string]map[string]bool{}
	fileEntries := map[string]map[string]bool{}
	for _, d := range []string{skillRoot, commandRoot, agentRoot, mcpRoot} {
		dirEntries[d] = map[string]bool{}
		fileEntries[d] = map[string]bool{}
	}
	var skillDescendants []string

	err := tree.Walk(func(rel string, isDir bool) error {
		parent, base := splitPath(rel)
		if isDir {
			if set, ok := dirEntries[parent]; ok {
				set[base] = true
			}
			if skillRoot != "" && (parent == skillRoot || strings.HasPrefix(parent, skillRoot+"/")) {
				skillDescendants = append(skillDescendants, rel)
			}
			return nil
		}
		if set, ok := fileEntries[parent]; ok {
			set[base] = true
		}
		return nil
	})
	if err != nil {
		return nil, fmt.Errorf("walking source tree: %w", err)
	}

	var items []Item
	for _, it := range scanSkills(tree, skillRoot, skillDescendants) {
		items = append(items, it)
	}
	items = append(items, scanFlatFiles(tree, fileEntries, commandRoot, lockfile.TypeCommand)...)
	items = append(items, scanFlatFiles(tree, fileEntries, agentRoot, lockfile.TypeAgent)...)
	items = append(items, scanMcpFiles(tree, fileEntries, mcpRoot)...)

	sort.Slice(items, func(i, j int) bool {
		if items[i].Type != items[j].Type {
			return typeRank(items[i].Type) < typeRank(items[j].Type)
		}
		return items[i].UpstreamID < items[j].UpstreamID
	})
	return items, nil
}

// scanSkills finds skill folders at any depth under skillRoot (flat layouts
// and category-nested layouts alike). The upstream id is the folder's base
// name; a directory that is itself a skill wins over anything nested inside
// it, and same-basename folders collide at the vendor layer.
func scanSkills(tree Tree, skillRoot string, descendants []string) []Item {
	if skillRoot == "" {
		return nil
	}
	sorted := append([]string(nil), descendants...)
	sort.Strings(sorted)
	withSkillMd := map[string]bool{}
	for _, d := range sorted {
		if _, err := tree.ReadFile(join(d, "SKILL.md")); err == nil {
			withSkillMd[d] = true
		}
	}
	var items []Item
	for _, d := range sorted {
		if !withSkillMd[d] {
			continue
		}
		nested := false
		for other := range withSkillMd {
			if other != d && strings.HasPrefix(d, other+"/") {
				nested = true
				break
			}
		}
		if nested {
			continue
		}
		data, err := tree.ReadFile(join(d, "SKILL.md"))
		if err != nil {
			continue
		}
		name := d[strings.LastIndex(d, "/")+1:]
		it := Item{Type: lockfile.TypeSkill, UpstreamID: name, RelPath: d}
		fm, warnings := ParseFrontmatter(data)
		it.Frontmatter = &fm
		for _, w := range warnings {
			it.Warnings = append(it.Warnings, fmt.Sprintf("skills/%s: %s", name, w))
		}
		items = append(items, it)
	}
	return items
}

func scanFlatFiles(tree Tree, fileEntries map[string]map[string]bool, root, typ string) []Item {
	var items []Item
	for base := range fileEntries[root] {
		if !strings.HasSuffix(base, ".md") {
			continue
		}
		id := strings.TrimSuffix(base, ".md")
		rel := join(root, base)
		data, err := tree.ReadFile(rel)
		if err != nil {
			continue
		}
		it := Item{Type: typ, UpstreamID: id, RelPath: rel}
		if !HasDefinitionFrontmatter(data) {
			it.Skipped = true
			it.Warnings = append(it.Warnings, fmt.Sprintf("%s: no %s frontmatter, skipped", rel, strings.TrimSuffix(typ, "s")))
			items = append(items, it)
			continue
		}
		fm, warnings := ParseFrontmatter(data)
		it.Frontmatter = &fm
		for _, w := range warnings {
			it.Warnings = append(it.Warnings, fmt.Sprintf("%s/%s: %s", typ, id, w))
		}
		items = append(items, it)
	}
	return items
}

func scanMcpFiles(tree Tree, fileEntries map[string]map[string]bool, root string) []Item {
	var items []Item
	for base := range fileEntries[root] {
		var id string
		switch {
		case strings.HasSuffix(base, ".yaml"):
			id = strings.TrimSuffix(base, ".yaml")
		case strings.HasSuffix(base, ".yml"):
			id = strings.TrimSuffix(base, ".yml")
		default:
			continue
		}
		items = append(items, Item{Type: lockfile.TypeMcp, UpstreamID: id, RelPath: join(root, base)})
	}
	return items
}

func typeRank(t string) int {
	for i, tt := range lockfile.Types {
		if tt == t {
			return i
		}
	}
	return len(lockfile.Types)
}

func join(parts ...string) string {
	var nonEmpty []string
	for _, p := range parts {
		if p != "" {
			nonEmpty = append(nonEmpty, p)
		}
	}
	return strings.Join(nonEmpty, "/")
}

func splitPath(rel string) (parent, base string) {
	i := strings.LastIndex(rel, "/")
	if i < 0 {
		return "", rel
	}
	return rel[:i], rel[i+1:]
}