1 files changed, 173 insertions, 0 deletions
diff --git a/install.go b/install.go
new file mode 100644
index 0000000..083dd41
--- /dev/null
+++ b/install.go
@@ -0,0 +1,173 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+type agent struct {
+	Name string
+	// Home is the agent's own config directory; finding it means the agent
+	// is in use here.
+	Home string
+}
+
+func (a agent) skillsDir() string { return filepath.Join(a.Home, "skills") }
+
+func knownAgents() []agent {
+	home, _ := os.UserHomeDir()
+	env := func(key, fallback string) string {
+		if v := os.Getenv(key); v != "" {
+			return v
+		}
+		return fallback
+	}
+	xdgConfig := env("XDG_CONFIG_HOME", filepath.Join(home, ".config"))
+	return []agent{
+		{"claude", env("CLAUDE_CONFIG_DIR", filepath.Join(home, ".claude"))},
+		{"codex", env("CODEX_HOME", filepath.Join(home, ".codex"))},
+		{"opencode", filepath.Join(xdgConfig, "opencode")},
+	}
+}
+
+func agentNames() string {
+	var names []string
+	for _, a := range knownAgents() {
+		names = append(names, a.Name)
+	}
+	return strings.Join(names, ", ")
+}
+
+// targetAgents returns the agents named in the manifest, or every known agent
+// found on this machine.
+func (ws *workspace) targetAgents() ([]agent, error) {
+	known := knownAgents()
+	if len(ws.manifest.Agents) > 0 {
+		var out []agent
+		for _, n := range ws.manifest.Agents {
+			i := indexAgent(known, n)
+			if i < 0 {
+				return nil, fmt.Errorf("%s names unknown agent %q (known: %s)", ws.manifestPath, n, agentNames())
+			}
+			out = append(out, known[i])
+		}
+		return out, nil
+	}
+	var out []agent
+	for _, a := range known {
+		if fi, err := os.Stat(a.Home); err == nil && fi.IsDir() {
+			out = append(out, a)
+		}
+	}
+	if len(out) == 0 {
+		return nil, fmt.Errorf("found no agents to install into (looked for %s); set \"agents\" in %s", agentNames(), ws.manifestPath)
+	}
+	return out, nil
+}
+
+func indexAgent(agents []agent, name string) int {
+	for i, a := range agents {
+		if a.Name == name {
+			return i
+		}
+	}
+	return -1
+}
+
+type skillState int
+
+const (
+	stateMissing skillState = iota
+	stateInstalled
+	stateStale    // a link of ours to another checkout
+	stateConflict // something we did not put there
+)
+
+func (s skillState) String() string {
+	return [...]string{"missing", "installed", "outdated", "conflict"}[s]
+}
+
+func linkState(path, want string) skillState {
+	dest, err := os.Readlink(path)
+	switch {
+	case err == nil && dest == want:
+		return stateInstalled
+	case err == nil && ownedLink(dest):
+		return stateStale
+	case errors.Is(err, os.ErrNotExist):
+		return stateMissing
+	}
+	if _, statErr := os.Lstat(path); errors.Is(statErr, os.ErrNotExist) {
+		return stateMissing
+	}
+	return stateConflict
+}
+
+func ownedLink(dest string) bool {
+	return strings.HasPrefix(dest, filepath.Join(dataDir(), "checkouts")+string(filepath.Separator))
+}
+
+type change struct {
+	Agent, Skill, Action string
+}
+
+// link makes each agent's skills directory hold exactly the locked skills,
+// as symlinks into their checkouts. It leaves anything it did not create
+// alone and reports it as a conflict.
+func (ws *workspace) link(dirs map[string]string, agents []agent) ([]change, []string, error) {
+	var changes []change
+	var conflicts []string
+	for _, a := range agents {
+		dir := a.skillsDir()
+		if err := os.MkdirAll(dir, 0o755); err != nil {
+			return changes, conflicts, err
+		}
+		names := make([]string, 0, len(dirs))
+		for n := range dirs {
+			names = append(names, n)
+		}
+		sort.Strings(names)
+		for _, n := range names {
+			path, want := filepath.Join(dir, n), dirs[n]
+			switch linkState(path, want) {
+			case stateInstalled:
+				continue
+			case stateConflict:
+				conflicts = append(conflicts, path)
+				continue
+			case stateStale:
+				if err := os.Remove(path); err != nil {
+					return changes, conflicts, err
+				}
+				changes = append(changes, change{a.Name, n, "updated"})
+			default:
+				changes = append(changes, change{a.Name, n, "installed"})
+			}
+			if err := os.Symlink(want, path); err != nil {
+				return changes, conflicts, err
+			}
+		}
+
+		entries, err := os.ReadDir(dir)
+		if err != nil {
+			return changes, conflicts, err
+		}
+		for _, e := range entries {
+			if _, ok := dirs[e.Name()]; ok {
+				continue
+			}
+			path := filepath.Join(dir, e.Name())
+			if dest, err := os.Readlink(path); err == nil && ownedLink(dest) {
+				if err := os.Remove(path); err != nil {
+					return changes, conflicts, err
+				}
+				changes = append(changes, change{a.Name, e.Name(), "removed"})
+			}
+		}
+	}
+	return changes, conflicts, nil
+}