input: KeyEncoder legacy encoding handles old keyCallback logic

src/input/KeyEncoder.zig

@@ -9,19 +9,102 @@ const std = @import("std");
 const testing = std.testing;
 
 const key = @import("key.zig");
+const function_keys = @import("function_keys.zig");
 
-key: key.Key,
-binding_mods: key.Mods,
+event: key.Event,
 
-/// Initialize
-fn init(event: key.Event) KeyEncoder {
-    const effective_mods = event.effectiveMods();
+/// The state of various modes of a terminal that impact encoding.
+cursor_key_application: bool = false,
+keypad_key_application: bool = false,
+modify_other_keys_state_2: bool = false,
+
+/// Perform legacy encoding of the key event. "Legacy" in this case
+/// is referring to the behavior of traditional terminals, plus
+/// xterm's `modifyOtherKeys`, plus Paul Evans's "fixterms" spec.
+/// These together combine the legacy protocol because they're all
+/// meant to be extensions that do not change any existing behavior
+/// and therefore safe to combine.
+fn legacy(
+    self: *const KeyEncoder,
+    buf: []u8,
+) ![]const u8 {
+    const effective_mods = self.event.effectiveMods();
     const binding_mods = effective_mods.binding();
 
-    return .{
-        .key = event.key,
-        .binding_mods = binding_mods,
-    };
+    // Legacy encoding only does press/repeat
+    if (self.event.action != .press and
+        self.event.action != .repeat) return "";
+
+    // If we match a PC style function key then that is our result.
+    if (pcStyleFunctionKey(
+        self.event.key,
+        binding_mods,
+        self.cursor_key_application,
+        self.keypad_key_application,
+        self.modify_other_keys_state_2,
+    )) |sequence| return sequence;
+
+    // If we match a control sequence, we output that directly.
+    if (ctrlSeq(self.event.key, binding_mods)) |char| {
+        // C0 sequences support alt-as-esc prefixing.
+        if (binding_mods.alt) {
+            if (buf.len < 2) return error.OutOfMemory;
+            buf[0] = 0x1B;
+            buf[1] = char;
+            return buf[0..2];
+        }
+
+        if (buf.len < 1) return error.OutOfMemory;
+        buf[0] = char;
+        return buf[0..1];
+    }
+
+    return "";
+}
+
+/// Determines whether the key should be encoded in the xterm
+/// "PC-style Function Key" syntax (roughly). This is a hardcoded
+/// table of keys and modifiers that result in a specific sequence.
+fn pcStyleFunctionKey(
+    keyval: key.Key,
+    mods: key.Mods,
+    cursor_key_application: bool,
+    keypad_key_application: bool,
+    modify_other_keys: bool, // True if state 2
+) ?[]const u8 {
+    const mods_int = mods.int();
+    for (function_keys.keys.get(keyval)) |entry| {
+        switch (entry.cursor) {
+            .any => {},
+            .normal => if (cursor_key_application) continue,
+            .application => if (!cursor_key_application) continue,
+        }
+
+        switch (entry.keypad) {
+            .any => {},
+            .normal => if (keypad_key_application) continue,
+            .application => if (!keypad_key_application) continue,
+        }
+
+        switch (entry.modify_other_keys) {
+            .any => {},
+            .set => if (modify_other_keys) continue,
+            .set_other => if (!modify_other_keys) continue,
+        }
+
+        const entry_mods_int = entry.mods.int();
+        if (entry_mods_int == 0) {
+            if (mods_int != 0 and !entry.mods_empty_is_any) continue;
+            // mods are either empty, or empty means any so we allow it.
+        } else if (entry_mods_int != mods_int) {
+            // any set mods require an exact match
+            continue;
+        }
+
+        return entry.sequence;
+    }
+
+    return null;
 }
 
 /// Returns the C0 byte for the key event if it should be used.
@@ -31,11 +114,11 @@ fn init(event: key.Event) KeyEncoder {
 /// This will return null if the key event should not be converted
 /// into a C0 byte. There are many cases for this and you should read
 /// the source code to understand them.
-fn ctrlSeq(self: *const KeyEncoder) ?u8 {
+fn ctrlSeq(keyval: key.Key, mods: key.Mods) ?u8 {
     // Remove alt from our modifiers because it does not impact whether
     // we are generating a ctrl sequence.
     const unalt_mods = unalt_mods: {
-        var unalt_mods = self.binding_mods;
+        var unalt_mods = mods;
         unalt_mods.alt = false;
         break :unalt_mods unalt_mods;
     };
@@ -49,7 +132,7 @@ fn ctrlSeq(self: *const KeyEncoder) ?u8 {
     // with 0x1F. However, not all apprt key translation will properly
     // generate the correct value so we just hardcode this based on
     // logical key.
-    return switch (self.key) {
+    return switch (keyval) {
         .space => 0,
         .slash => 0x1F,
         .zero => 0x30,
@@ -95,37 +178,73 @@ fn ctrlSeq(self: *const KeyEncoder) ?u8 {
     };
 }
 
+test "legacy: ctrl+alt+c" {
+    var buf: [128]u8 = undefined;
+    var enc: KeyEncoder = .{
+        .event = .{
+            .key = .c,
+            .mods = .{ .ctrl = true, .alt = true },
+        },
+    };
+
+    const actual = try enc.legacy(&buf);
+    try testing.expectEqualStrings("\x1b\x03", actual);
+}
+
+test "legacy: ctrl+c" {
+    var buf: [128]u8 = undefined;
+    var enc: KeyEncoder = .{
+        .event = .{
+            .key = .c,
+            .mods = .{ .ctrl = true },
+        },
+    };
+
+    const actual = try enc.legacy(&buf);
+    try testing.expectEqualStrings("\x03", actual);
+}
+
+test "legacy: ctrl+space" {
+    var buf: [128]u8 = undefined;
+    var enc: KeyEncoder = .{
+        .event = .{
+            .key = .space,
+            .mods = .{ .ctrl = true },
+        },
+    };
+
+    const actual = try enc.legacy(&buf);
+    try testing.expectEqualStrings("\x00", actual);
+}
+
+test "legacy: ctrl+shift+backspace" {
+    var buf: [128]u8 = undefined;
+    var enc: KeyEncoder = .{
+        .event = .{
+            .key = .backspace,
+            .mods = .{ .ctrl = true, .shift = true },
+        },
+    };
+
+    const actual = try enc.legacy(&buf);
+    try testing.expectEqualStrings("\x08", actual);
+}
+
 test "ctrlseq: normal ctrl c" {
-    const enc = init(.{ .key = .c, .mods = .{ .ctrl = true } });
-    const seq = enc.ctrlSeq();
+    const seq = ctrlSeq(.c, .{ .ctrl = true });
     try testing.expectEqual(@as(u8, 0x03), seq.?);
 }
 
 test "ctrlseq: alt should be allowed" {
-    const enc = init(.{ .key = .c, .mods = .{ .alt = true, .ctrl = true } });
-    const seq = enc.ctrlSeq();
+    const seq = ctrlSeq(.c, .{ .alt = true, .ctrl = true });
     try testing.expectEqual(@as(u8, 0x03), seq.?);
 }
 
 test "ctrlseq: no ctrl does nothing" {
-    const enc = init(.{ .key = .c, .mods = .{} });
-    try testing.expect(enc.ctrlSeq() == null);
+    try testing.expect(ctrlSeq(.c, .{}) == null);
 }
 
 test "ctrlseq: shift does not generate ctrl seq" {
-    {
-        const enc = init(.{
-            .key = .c,
-            .mods = .{ .shift = true },
-        });
-        try testing.expect(enc.ctrlSeq() == null);
-    }
-
-    {
-        const enc = init(.{
-            .key = .c,
-            .mods = .{ .shift = true, .ctrl = true },
-        });
-        try testing.expect(enc.ctrlSeq() == null);
-    }
+    try testing.expect(ctrlSeq(.c, .{ .shift = true }) == null);
+    try testing.expect(ctrlSeq(.c, .{ .shift = true, .ctrl = true }) == null);
 }