const std = @import("std");
const modal = @import("modal.zig");

// tutor_gen: a separate binary (NOT comptime) that parses tutor.txt and writes
// tutor_cases.zig — a file of standard Zig `test` blocks, one per practice block.
// `zig build tutor-gen` runs it (writing the file); `zig build unit-test` then
// compiles+runs those tests against modal.stepFile.
//
// Format of tutor.txt practice blocks (all directive lines start with "# "):
//   # keys: l l l i X esc        <- space-separated keystroke tokens
//   # at: 0,4                     <- optional starting cursor "row,col" (default 0,0)
//   # before                       <- the lines below are the starting buffer
//   <clean line>
//   # after                        <- the lines below are the expected buffer
//   <clean line>
// Everything not under a # before/# after is prose (ignored). A `# keys:` starts
// a new case; cases end at the next `# keys:` or a non-practice line.
//
// Keystroke tokens: each char of a token is typed in turn, EXCEPT the named
// specials `esc`, `enter`, `bs` (backspace), `left/right/up/down`, `home/end`,
// `pgup/pgdn`. `Ctrl-d`/`Ctrl-u`/`Ctrl-f`/`Ctrl-b` map to half/full page.

const Case = struct {
    keys: []const u8,
    at: ?[]const u8 = null,
    before: []const u8,
    after: []const u8,
};

fn parseCases(alloc: std.mem.Allocator, src: []const u8) ![]Case {
    var cases: std.ArrayList(Case) = .empty;
    var it = std.mem.splitScalar(u8, src, '\n');
    // accumulate the current case
    var cur_keys: ?[]const u8 = null;
    var cur_at: ?[]const u8 = null;
    var before: ?std.ArrayList(u8) = null;
    var after: ?std.ArrayList(u8) = null;
    // which section is actively collecting content (so # after stops before from
    // absorbing the after lines). `none` = neither.
    var section: enum { none, before, after } = .none;
    defer if (before) |*b| b.deinit(alloc);
    defer if (after) |*a| a.deinit(alloc);
    // NOTE: cur_keys / cur_at ownership is handled explicitly at each flush/drop
    // (moved into a case, or freed + nulled). We do NOT defer-free them here:
    // a defer would double-free a value that was moved into a case (the move
    // leaves the local pointing at the now-case-owned memory until it's nulled,
    // and a function-exit defer can't tell).

    while (it.next()) |raw_line| {
        // Practice-block lines in tutor.txt are indented by one leading space
        // (the tutor's prose style). Strip exactly that one space so directives
        // match AND content lines don't carry the indent into the buffer.
        var line = raw_line;
        if (line.len > 0 and line[0] == ' ') line = line[1..];
        line = std.mem.trimEnd(u8, line, "\r");
        if (std.mem.startsWith(u8, line, "# keys:")) {
            // flush previous case
            if (cur_keys != null and before != null and after != null) {
                try cases.append(alloc, .{
                    .keys = cur_keys.?,
                    .at = cur_at,
                    .before = try before.?.toOwnedSlice(alloc),
                    .after = try after.?.toOwnedSlice(alloc),
                });
                before = null;
                after = null;
            } else if (cur_keys != null) {
                // a # keys: with no before/after — drop it (incomplete): free the
                // owned keys/at so they don't leak.
                if (cur_keys) |k| alloc.free(k);
                if (cur_at) |at| alloc.free(at);
                before = null;
                after = null;
            }
            cur_keys = try alloc.dupe(u8, std.mem.trim(u8, line["# keys:".len..], " "));
            // cur_at from a prior case was either moved (flushed) or freed (drop);
            // start fresh.
            cur_at = null;
            before = null;
            after = null;
            section = .none;
            continue;
        }
        if (std.mem.startsWith(u8, line, "# at:")) {
            if (cur_at) |old| alloc.free(old);
            cur_at = try alloc.dupe(u8, std.mem.trim(u8, line["# at:".len..], " "));
            continue;
        }
        if (std.mem.startsWith(u8, line, "# before")) {
            before = .empty;
            after = null;
            section = .before;
            continue;
        }
        if (std.mem.startsWith(u8, line, "# after")) {
            after = .empty;
            section = .after;
            continue;
        }
        // any other "# ..." directive that isn't keys/at/before/after ends a case
        if (std.mem.startsWith(u8, line, "#")) {
            if (cur_keys != null and before != null and after != null and after.?.items.len > 0) {
                try cases.append(alloc, .{
                    .keys = cur_keys.?,
                    .at = cur_at,
                    .before = try before.?.toOwnedSlice(alloc),
                    .after = try after.?.toOwnedSlice(alloc),
                });
            } else {
                // incomplete: free the owned keys/at + any partial content
                if (cur_keys) |k| alloc.free(k);
                if (cur_at) |at| alloc.free(at);
                if (before) |*b| b.deinit(alloc);
                if (after) |*a| a.deinit(alloc);
            }
            cur_keys = null;
            cur_at = null;
            before = null;
            after = null;
            section = .none;
            continue;
        }
        // a blank line: if we have a complete case (keys + before + after with
        // content), flush it now — the practice block is delimited by blank lines
        // in the tutor, so prose after the blank line must NOT be absorbed.
        if (line.len == 0) {
            if (cur_keys != null and before != null and after != null and after.?.items.len > 0) {
                try cases.append(alloc, .{
                    .keys = cur_keys.?,
                    .at = cur_at,
                    .before = try before.?.toOwnedSlice(alloc),
                    .after = try after.?.toOwnedSlice(alloc),
                });
                cur_keys = null;
                before = null;
                after = null;
                section = .none;
            } else {
                section = .none; // a blank line closes the active section
            }
            continue;
        }
        // a content line: belongs to the ACTIVE section only
        if (section == .before) {
            if (before) |*b| {
                if (b.items.len > 0) try b.append(alloc, '\n');
                try b.appendSlice(alloc, line);
            }
            continue;
        }
        if (section == .after) {
            if (after) |*a| {
                if (a.items.len > 0) try a.append(alloc, '\n');
                try a.appendSlice(alloc, line);
            }
            continue;
        }
        // prose line, ignore
    }
    // flush trailing case
    if (cur_keys != null and before != null and after != null and after.?.items.len > 0) {
        try cases.append(alloc, .{
            .keys = cur_keys.?,
            .at = cur_at,
            .before = try before.?.toOwnedSlice(alloc),
            .after = try after.?.toOwnedSlice(alloc),
        });
        // ownership transferred; clear so the defers above don't double-free.
        cur_keys = null;
        cur_at = null;
        before = null;
        after = null;
    }
    return cases.toOwnedSlice(alloc);
}

// Emit a Zig string literal for `s`, escaping per Zig string syntax.
fn emitStringLiteral(out: *std.ArrayList(u8), alloc: std.mem.Allocator, s: []const u8) !void {
    try out.append(alloc, '"');
    for (s) |c| {
        switch (c) {
            '"' => try out.appendSlice(alloc, "\\\""),
            '\\' => try out.appendSlice(alloc, "\\\\"),
            '\n' => try out.appendSlice(alloc, "\\n"),
            '\r' => try out.appendSlice(alloc, "\\r"),
            '\t' => try out.appendSlice(alloc, "\\t"),
            else => {
                if (c >= 0x20 and c < 0x7f) {
                    try out.append(alloc, c);
                } else {
                    try out.print(alloc, "\\x{x:0>2}", .{c});
                }
            },
        }
    }
    try out.append(alloc, '"');
}

fn writeCases(io: std.Io, alloc: std.mem.Allocator, cases: []const Case, out_path: []const u8) !void {
    // Build the generated source in a buffer, then write it in one shot.
    var out: std.ArrayList(u8) = .empty;
    defer out.deinit(alloc);

    try out.appendSlice(alloc, "// AUTO-GENERATED by tutor_gen from tutor.txt. DO NOT EDIT.\n");
    try out.appendSlice(alloc, "// One `test` block per practice block in the tutor. Re-run: zig build tutor-gen\n");
    try out.appendSlice(alloc, "const std = @import(\"std\");\n");
    try out.appendSlice(alloc, "const modal = @import(\"modal\");\n\n");

    for (cases, 0..) |c, i| {
        // Derive a short human label from the keys for the test name. Sanitize
        // it to a valid Zig identifier fragment (spaces/specials -> '_').
        var name_buf: [128]u8 = undefined;
        const printed = std.fmt.bufPrint(&name_buf, "tutor_case_{d:0>2}_{s}", .{ i, c.keys }) catch "tutor_case";
        var san_buf: [128]u8 = undefined;
        const san_len = @min(printed.len, san_buf.len);
        for (printed[0..san_len], 0..) |ch, j| {
            san_buf[j] = switch (ch) {
                'a'...'z', 'A'...'Z', '0'...'9', '_' => ch,
                else => '_',
            };
        }
        const name_san = san_buf[0..san_len];
        try out.print(alloc, "test \"{s}\" {{\n", .{name_san});
        try out.appendSlice(alloc, "    const a = std.testing.allocator;\n");
        try out.appendSlice(alloc, "    var yank: ?[]u8 = null;\n");
        try out.appendSlice(alloc, "    defer if (yank) |y| a.free(y);\n");
        try out.appendSlice(alloc, "    var scroll: usize = 0;\n");
        try out.appendSlice(alloc, "    var st = modal.FileState{};\n");
        try out.appendSlice(alloc, "    const view = modal.View{ .rows = 200, .scroll = &scroll };\n");

        // starting content
        try out.appendSlice(alloc, "    var content: []u8 = try a.dupe(u8, ");
        try emitStringLiteral(&out, alloc, c.before);
        try out.appendSlice(alloc, ");\n");
        try out.appendSlice(alloc, "    defer a.free(content);\n");

        // starting cursor
        if (c.at) |at| {
            try out.print(alloc, "    st.cur = .{{ .row = {s}, .col = {s} }};\n", .{
                splitField(at, 0),
                splitField(at, 1),
            });
        }

        // keystrokes
        var tit = std.mem.tokenizeAny(u8, c.keys, " ");
        while (tit.next()) |tok| {
            try emitKey(&out, alloc, tok);
        }

        // assertion
        try out.appendSlice(alloc, "    try std.testing.expectEqualStrings(");
        try emitStringLiteral(&out, alloc, c.after);
        try out.appendSlice(alloc, ", content);\n");
        try out.appendSlice(alloc, "}\n\n");
    }
    try std.Io.Dir.cwd().writeFile(io, .{ .sub_path = out_path, .data = out.items });
}

// "row,col" -> the row part (idx 0) or col part (idx 1).
fn splitField(at: []const u8, idx: usize) []const u8 {
    var it = std.mem.splitScalar(u8, at, ',');
    var i: usize = 0;
    while (it.next()) |part| : (i += 1) {
        if (i == idx) return std.mem.trim(u8, part, " ");
    }
    return "0";
}

// Emit the stepFile calls for one keystroke token.
// One stepFile call, as a generated line. `key_expr` is the Zig Key payload
// expression (e.g. `.esc`, `.ch = 'x'`).
fn emitStep(out: *std.ArrayList(u8), alloc: std.mem.Allocator, key_expr: []const u8) !void {
    try out.print(alloc, "    {{ const n = try modal.stepFile(a, content, &st, view, {s}, &yank); if (n) |nn| {{ a.free(content); content = nn; }} }}\n", .{key_expr});
}

fn emitKey(out: *std.ArrayList(u8), alloc: std.mem.Allocator, tok: []const u8) !void {
    // named specials -> a single stepFile with that key
    if (std.mem.eql(u8, tok, "esc")) return emitStep(out, alloc, ".esc");
    if (std.mem.eql(u8, tok, "enter")) return emitStep(out, alloc, ".enter");
    if (std.mem.eql(u8, tok, "bs")) return emitStep(out, alloc, ".backspace");
    if (std.mem.eql(u8, tok, "left")) return emitStep(out, alloc, ".left");
    if (std.mem.eql(u8, tok, "right")) return emitStep(out, alloc, ".right");
    if (std.mem.eql(u8, tok, "up")) return emitStep(out, alloc, ".up");
    if (std.mem.eql(u8, tok, "down")) return emitStep(out, alloc, ".down");
    if (std.mem.eql(u8, tok, "home")) return emitStep(out, alloc, ".home");
    if (std.mem.eql(u8, tok, "end")) return emitStep(out, alloc, ".end");
    if (std.mem.eql(u8, tok, "pgdn") or std.mem.eql(u8, tok, "pagedown")) return emitStep(out, alloc, ".page_down");
    if (std.mem.eql(u8, tok, "pgup") or std.mem.eql(u8, tok, "pageup")) return emitStep(out, alloc, ".page_up");
    if (std.mem.eql(u8, tok, "Ctrl-d")) return emitStep(out, alloc, ".half_down");
    if (std.mem.eql(u8, tok, "Ctrl-u")) return emitStep(out, alloc, ".half_up");
    if (std.mem.eql(u8, tok, "Ctrl-f")) return emitStep(out, alloc, ".page_down");
    if (std.mem.eql(u8, tok, "Ctrl-b")) return emitStep(out, alloc, ".page_up");
    // otherwise: each byte of the token is a typed char (in order)
    for (tok) |c| {
        var expr_buf: [32]u8 = undefined;
        const expr = std.fmt.bufPrint(&expr_buf, ".{{ .ch = {d} }}", .{c}) catch return;
        try emitStep(out, alloc, expr);
    }
}

pub fn main(init: std.process.Init) !void {
    const io = init.io;
    const gpa = init.gpa;
    const args = try init.minimal.args.toSlice(init.arena.allocator());
    const in_path = if (args.len > 1) args[1] else "tutor.txt";
    const out_path = if (args.len > 2) args[2] else "tutor_cases.zig";

    const src = try std.Io.Dir.cwd().readFileAlloc(io, in_path, gpa, .limited(1 << 20));
    defer gpa.free(src);

    const cases = try parseCases(gpa, src);
    defer {
        for (cases) |c| {
            gpa.free(c.keys);
            if (c.at) |at| gpa.free(at);
            gpa.free(c.before);
            gpa.free(c.after);
        }
        gpa.free(cases);
    }

    try writeCases(io, gpa, cases, out_path);
    std.debug.print("tutor_gen: wrote {d} test cases to {s}\n", .{ cases.len, out_path });
}

// ---- self-test: the parser on tiny fixtures ----
test "parseCases extracts a before/after block" {
    const a = std.testing.allocator;
    const src =
        \\# keys: l l l
        \\# before
        \\abcdef
        \\# after
        \\abcdef
        \\
    ;
    const cases = try parseCases(a, src);
    defer {
        for (cases) |c| {
            a.free(c.keys);
            if (c.at) |at| a.free(at);
            a.free(c.before);
            a.free(c.after);
        }
        a.free(cases);
    }
    try std.testing.expectEqual(@as(usize, 1), cases.len);
    try std.testing.expectEqualStrings("l l l", cases[0].keys);
    try std.testing.expectEqualStrings("abcdef", cases[0].before);
    try std.testing.expectEqualStrings("abcdef", cases[0].after);
}

test "parseCases handles # at: and multiple cases" {
    const a = std.testing.allocator;
    const src =
        \\# keys: b i Z esc
        \\# at: 0,4
        \\# before
        \\foo bar
        \\# after
        \\Zfoo bar
        \\
        \\# keys: x d
        \\# before
        \\keep
        \\gone
        \\# after
        \\keep
        \\
    ;
    const cases = try parseCases(a, src);
    defer {
        for (cases) |c| {
            a.free(c.keys);
            if (c.at) |at| a.free(at);
            a.free(c.before);
            a.free(c.after);
        }
        a.free(cases);
    }
    try std.testing.expectEqual(@as(usize, 2), cases.len);
    try std.testing.expectEqualStrings("0,4", cases[0].at.?);
    try std.testing.expectEqualStrings("keep\ngone", cases[1].before);
    try std.testing.expectEqualStrings("keep", cases[1].after);
}