//! 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 panto_home = @import("panto_home.zig");
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);
    }
    const home = try panto_home.homePath(allocator, environ_map);
    defer allocator.free(home);
    return try std.fs.path.join(allocator, &.{ home, "sessions" });
}

/// 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);
}