/// Build-time generator: extracts the set of backticked identifiers
/// from each `docs/reference/config/*.md` reference page and emits them
/// as a Zig source file.
///
/// Exists because `@embedFile` cannot escape the package path, so
/// `src/` code has no way to read `docs/`. The alternative - reading
/// the markdown at test time via cwd - would make the doc-sync check
/// dependent on where the test binary was launched from, and a check
/// that can silently skip is a check that rots.
///
/// Only the NAME SET is extracted, never the prose. That keeps the
/// output free of string-escaping concerns and small (a few hundred
/// identifiers), and it is exactly what the consumer needs:
/// `srf_lint`'s doc-sync test asserts every field of each model appears
/// in that model's reference page.
///
/// An "identifier" here is a backtick-delimited token matching
/// `[a-z][a-z0-9_]*` - the shape of every SRF field name. Prose words
/// in backticks (`true`, `null`, `stock`) come along harmlessly; the
/// test only ever asks whether a known field name is PRESENT, never
/// whether an extracted name is a real field.
const std = @import("std");

pub fn main(init: std.process.Init) !void {
    const allocator = init.arena.allocator();
    const io = init.io;

    const args = try init.minimal.args.toSlice(allocator);
    if (args.len < 3) {
        var stderr_buf: [160]u8 = undefined;
        var stderr = std.Io.File.stderr().writer(io, &stderr_buf);
        try stderr.interface.writeAll("Usage: gen_config_docs <output.zig> <doc.md>...\n");
        try stderr.interface.flush();
        std.process.exit(1);
    }

    const out_file = try std.Io.Dir.cwd().createFile(io, args[1], .{});
    defer out_file.close(io);
    var out_buf: [4096]u8 = undefined;
    var file_writer = out_file.writer(io, &out_buf);
    const w = &file_writer.interface;

    try w.writeAll(
        \\// Auto-generated from docs/reference/config/*.md - do not edit.
        \\// Regenerate: zig build (runs build/gen_config_docs.zig)
        \\
        \\/// One reference page's backticked identifiers.
        \\pub const Doc = struct {
        \\    /// Basename, e.g. "portfolio-srf.md".
        \\    file: []const u8,
        \\    names: []const []const u8,
        \\};
        \\
        \\pub const docs = [_]Doc{
        \\
    );

    for (args[2..]) |path| {
        const body = try std.Io.Dir.cwd().readFileAlloc(io, path, allocator, .limited(4 * 1024 * 1024));
        const base = std.fs.path.basename(path);

        var names: std.ArrayList([]const u8) = .empty;
        try collectIdents(allocator, body, &names);

        try w.print("    .{{ .file = \"{s}\", .names = &.{{", .{base});
        for (names.items, 0..) |n, i| {
            if (i % 6 == 0) try w.writeAll("\n        ");
            try w.print("\"{s}\", ", .{n});
        }
        try w.writeAll("\n    } },\n");
    }

    try w.writeAll(
        \\};
        \\
        \\/// The `Doc` for `file`, or null when that page was not built in.
        \\pub fn find(file: []const u8) ?Doc {
        \\    for (docs) |d| {
        \\        if (std.mem.eql(u8, d.file, file)) return d;
        \\    }
        \\    return null;
        \\}
        \\
        \\const std = @import("std");
        \\
    );
    try w.flush();
}

/// Append every deduplicated backticked `[a-z][a-z0-9_]*` token in
/// `body` to `out`. Slices borrow from `body`.
fn collectIdents(
    allocator: std.mem.Allocator,
    body: []const u8,
    out: *std.ArrayList([]const u8),
) !void {
    var i: usize = 0;
    while (i < body.len) {
        if (body[i] != '`') {
            i += 1;
            continue;
        }
        // Skip fenced code blocks wholesale - a ```zig sample can
        // mention a field in a context the reference table does not,
        // and counting it would let a field be "documented" by an
        // example alone.
        if (std.mem.startsWith(u8, body[i..], "```")) {
            const rest = body[i + 3 ..];
            const close = std.mem.indexOf(u8, rest, "```") orelse break;
            i += 3 + close + 3;
            continue;
        }
        const rest = body[i + 1 ..];
        const close = std.mem.indexOfScalar(u8, rest, '`') orelse break;
        const raw = rest[0..close];
        i += 1 + close + 1;
        // The docs name a field both bare (`symbol`, in reference
        // tables) and on-wire (`symbol::`, `shares:num:100`, in prose
        // and examples). Cut at the first separator so both spellings
        // count as documenting the field.
        const tok = raw[0 .. std.mem.indexOfScalar(u8, raw, ':') orelse raw.len];
        if (!isIdent(tok)) continue;
        for (out.items) |seen| {
            if (std.mem.eql(u8, seen, tok)) break;
        } else {
            try out.append(allocator, tok);
        }
    }
}

fn isIdent(tok: []const u8) bool {
    if (tok.len == 0) return false;
    if (tok[0] < 'a' or tok[0] > 'z') return false;
    for (tok) |c| {
        const ok = (c >= 'a' and c <= 'z') or (c >= '0' and c <= '9') or c == '_';
        if (!ok) return false;
    }
    return true;
}