1 files changed, 141 insertions, 0 deletions
diff --git a/src/session_paths.zig b/src/session_paths.zig
new file mode 100644
index 0000000..162085e
--- /dev/null
+++ b/src/session_paths.zig
@@ -0,0 +1,141 @@
+//! Resolves session file locations from the environment.
+//!
+//! Layout (defaults; override base via `PANTO_SESSION_DIR`):
+//!
+//!   $XDG_DATA_HOME/panto/sessions/<encoded-cwd>/
+//!   ↳ falls back to $HOME/.local/share/panto/sessions/<encoded-cwd>/
+//!     if $XDG_DATA_HOME is unset.
+//!
+//! `<encoded-cwd>` is the working directory with leading `/` stripped and
+//! every `/` or `:` replaced by `-`, with `--` glued to both ends. This
+//! gives a flat directory name per project, easy to spot in `ls`.
+
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+
+/// Resolve the absolute sessions directory for the given cwd. Caller owns
+/// the returned slice.
+///
+/// Precedence:
+///   1. `PANTO_SESSION_DIR` (full path to the base dir, used as-is — no
+///      "panto/sessions" suffix is added)
+///   2. `XDG_DATA_HOME/panto/sessions`
+///   3. `HOME/.local/share/panto/sessions`
+///
+/// In all three cases, `<encoded-cwd>/` is appended.
+pub fn sessionDirForCwd(
+    allocator: Allocator,
+    environ_map: *const std.process.Environ.Map,
+    cwd: []const u8,
+) ![]u8 {
+    const base = try resolveSessionsBase(allocator, environ_map);
+    defer allocator.free(base);
+
+    const encoded = try encodeCwd(allocator, cwd);
+    defer allocator.free(encoded);
+
+    return try std.fs.path.join(allocator, &.{ base, encoded });
+}
+
+/// Resolve the absolute "sessions" base directory, before per-cwd grouping.
+/// Caller owns the returned slice.
+pub fn resolveSessionsBase(
+    allocator: Allocator,
+    environ_map: *const std.process.Environ.Map,
+) ![]u8 {
+    if (environ_map.get("PANTO_SESSION_DIR")) |explicit| {
+        return try allocator.dupe(u8, explicit);
+    }
+    if (environ_map.get("XDG_DATA_HOME")) |xdg| {
+        return try std.fs.path.join(allocator, &.{ xdg, "panto", "sessions" });
+    }
+    if (environ_map.get("HOME")) |home| {
+        return try std.fs.path.join(allocator, &.{ home, ".local", "share", "panto", "sessions" });
+    }
+    return error.NoHomeDirectory;
+}
+
+/// Encode a working directory into a flat directory name. Caller owns.
+///
+/// Example: `/Users/travis/Code/pantograph` → `--Users-travis-Code-pantograph--`
+pub fn encodeCwd(allocator: Allocator, cwd: []const u8) ![]u8 {
+    // Strip leading slash(es), then replace `/` and `:` with `-`.
+    var start: usize = 0;
+    while (start < cwd.len and (cwd[start] == '/' or cwd[start] == '\\')) : (start += 1) {}
+    const body = cwd[start..];
+    const out = try allocator.alloc(u8, body.len + 4); // `--` + body + `--`
+    out[0] = '-';
+    out[1] = '-';
+    for (body, 0..) |c, i| {
+        out[2 + i] = if (c == '/' or c == '\\' or c == ':') '-' else c;
+    }
+    out[out.len - 2] = '-';
+    out[out.len - 1] = '-';
+    return out;
+}
+
+// =============================================================================
+// Tests
+// =============================================================================
+
+const testing = std.testing;
+
+test "encodeCwd: replaces slashes and colons" {
+    const a = testing.allocator;
+    const got = try encodeCwd(a, "/Users/travis/Code/pantograph");
+    defer a.free(got);
+    try testing.expectEqualStrings("--Users-travis-Code-pantograph--", got);
+}
+
+test "encodeCwd: handles already-relative paths" {
+    const a = testing.allocator;
+    const got = try encodeCwd(a, "Users/travis");
+    defer a.free(got);
+    try testing.expectEqualStrings("--Users-travis--", got);
+}
+
+test "resolveSessionsBase: PANTO_SESSION_DIR wins" {
+    const a = testing.allocator;
+    var env: std.process.Environ.Map = .init(a);
+    defer env.deinit();
+    try env.put("PANTO_SESSION_DIR", "/custom/sessions");
+    try env.put("XDG_DATA_HOME", "/ignored");
+
+    const got = try resolveSessionsBase(a, &env);
+    defer a.free(got);
+    try testing.expectEqualStrings("/custom/sessions", got);
+}
+
+test "resolveSessionsBase: XDG_DATA_HOME before HOME" {
+    const a = testing.allocator;
+    var env: std.process.Environ.Map = .init(a);
+    defer env.deinit();
+    try env.put("XDG_DATA_HOME", "/x/data");
+    try env.put("HOME", "/h");
+
+    const got = try resolveSessionsBase(a, &env);
+    defer a.free(got);
+    try testing.expectEqualStrings("/x/data/panto/sessions", got);
+}
+
+test "resolveSessionsBase: falls back to HOME/.local/share" {
+    const a = testing.allocator;
+    var env: std.process.Environ.Map = .init(a);
+    defer env.deinit();
+    try env.put("HOME", "/home/user");
+
+    const got = try resolveSessionsBase(a, &env);
+    defer a.free(got);
+    try testing.expectEqualStrings("/home/user/.local/share/panto/sessions", got);
+}
+
+test "sessionDirForCwd: joins base and encoded cwd" {
+    const a = testing.allocator;
+    var env: std.process.Environ.Map = .init(a);
+    defer env.deinit();
+    try env.put("PANTO_SESSION_DIR", "/sess");
+
+    const got = try sessionDirForCwd(a, &env, "/Users/travis/Code/pantograph");
+    defer a.free(got);
+    try testing.expectEqualStrings("/sess/--Users-travis-Code-pantograph--", got);
+}